U.S. patent application number 11/741074 was filed with the patent office on 2007-11-15 for bicycle suspension assembly with inertia valve and external controller.
This patent application is currently assigned to Fox Factory, Inc.. Invention is credited to Robert C. Fox.
Application Number | 20070262555 11/741074 |
Document ID | / |
Family ID | 36097752 |
Filed Date | 2007-11-15 |
United States Patent
Application |
20070262555 |
Kind Code |
A1 |
Fox; Robert C. |
November 15, 2007 |
Bicycle Suspension Assembly With Inertia Valve and External
Controller
Abstract
A bicycle suspension assembly is first provided with an inertia
valve for selectively altering the compression damping rate of the
shock absorber. The bicycle suspension assembly is also provided
with at least one adjustable fluid damping circuit through which
fluid may flow during operation of the suspension assembly. The
fluid flow resistance through the adjustable fluid damping circuit
may be adjusted without requiring any disassembly of the bicycle
suspension assembly by using a movable external controller.
Inventors: |
Fox; Robert C.; (Los Gatos,
CA) |
Correspondence
Address: |
FOX FACTORY, INC.
130 HANGAR WAY
WATSONVILLE
CA
95076
US
|
Assignee: |
Fox Factory, Inc.
Watsonville
CA
|
Family ID: |
36097752 |
Appl. No.: |
11/741074 |
Filed: |
April 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11259629 |
Oct 26, 2005 |
7273137 |
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11741074 |
Apr 27, 2007 |
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10778882 |
Feb 13, 2004 |
7128192 |
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11259629 |
Oct 26, 2005 |
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10378091 |
Feb 28, 2003 |
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10778882 |
Feb 13, 2004 |
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10043079 |
Jan 9, 2002 |
6581948 |
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10378091 |
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10042767 |
Jan 9, 2002 |
6604751 |
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10378091 |
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60451303 |
Feb 28, 2003 |
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60451318 |
Feb 28, 2003 |
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60316442 |
Aug 30, 2001 |
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60329042 |
Oct 12, 2001 |
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60316442 |
Aug 30, 2001 |
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60329042 |
Oct 12, 2001 |
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Current U.S.
Class: |
280/276 |
Current CPC
Class: |
B62K 25/08 20130101;
B62K 25/286 20130101; B62K 25/04 20130101; F16F 9/504 20130101;
F16F 9/064 20130101; B62K 2025/048 20130101; F16F 9/34 20130101;
Y10T 29/494 20150115 |
Class at
Publication: |
280/276 |
International
Class: |
B62K 17/00 20060101
B62K017/00 |
Claims
1. A bicycle suspension assembly, comprising: a damper body having
a longitudinal axis and containing damping fluid; a piston coupled
to a piston rod, the piston and a portion of the piston rod movable
along the longitudinal axis of, and within, the damper body,
wherein during a compression stroke, portions of the piston rod
move further into the damper body to cause a compression fluid
flow; a reservoir including a reservoir tube having an inner
surface of the reservoir tube and a movable sealed barrier
partially defining a variable volume reservoir chamber; a
compression fluid flow circuit in fluid communication with the
damper body and the variable volume reservoir chamber for conveying
fluid flow from the damper body to the variable volume reservoir
chamber during a compression stroke; an inertia valve, positioned
within the reservoir tube, for at least partially controlling the
fluid flow resistance through the compression fluid flow circuit;
and at least one adjustable fluid damping circuit through which
fluid may flow during operation of the suspension assembly, the
fluid flow resistance through the adjustable fluid damping circuit
being adjustable without requiring any disassembly of the bicycle
suspension assembly, the adjustable fluid damping circuit
including: a) a movable external controller; b) a damping flow
controller at least partially located in a portion of the piston
rod and associated with the movable external controller; c) whereby
manipulating the movable external controller results in the damping
flow controller varying the fluid flow resistance through the
adjustable fluid damping circuit.
2. The suspension assembly of claim 1, wherein the damping flow
controller includes at least a control rod passing though at least
a portion of the piston rod.
3. The suspension assembly of claim 2, wherein the damping flow
controller includes a movable blocking element associated with at
least a portion of the control rod and for selectively blocking a
flow port of the adjustable fluid damping circuit.
4. The bicycle suspension assembly of claim 1, wherein: the piston
divides a portion of the damper body into a compression chamber and
a rebound chamber; a rebound fluid flow circuit includes at least
one flow port associated with the piston for allowing a rebound
fluid flow through the piston and from the rebound chamber to the
compression chamber during a rebound stroke; at least one fluid
flow bypass associated with the adjustable fluid damping circuit,
the at least one fluid flow bypass providing an alternative rebound
fluid flow path from the rebound chamber into the compression
chamber; and the damping flow controller at least partially
controlling the fluid flow resistance through the at least one
fluid flow bypass.
5. The bicycle suspension assembly of claim 1, wherein: the piston
divides a portion of the damper body into a compression chamber and
a rebound chamber; at least one flow port associated with the
piston for allowing a fluid flow through the piston and from one of
the compression chamber or rebound chamber to the other of the
compression chamber or rebound chamber, depending upon the
direction of the stroke of the piston rod; at least one fluid flow
bypass associated with the adjustable fluid damping circuit, the at
least one fluid flow bypass providing an alternative fluid flow
path from one of the compression chamber or rebound chambers to the
other of the compression chamber or rebound chamber; and the
damping flow controller at least partially controlling the fluid
flow resistance through the at least one fluid flow bypass.
6. A bicycle suspension assembly, comprising: a damper, the damper
comprising: a tube; a piston rod coupled to a piston in sealed,
sliding engagement with the tube, the piston and the tube defining
a compression fluid chamber and a rebound fluid chamber, wherein a
damping fluid moves from the compression chamber to the rebound
chamber during compression movement of the suspension assembly and
the piston rod occupies a successively greater portion of the tube
during the compression movement; an opening communicating with the
compression chamber; an inertia valve comprising an inertia mass,
the inertia valve having an open position wherein the inertia mass
does not block at least a portion of the opening and a flow of
damping fluid is permitted through at least a portion of the
opening, the inertia valve normally biased to a closed position
wherein the inertia mass is positioned to block more of the opening
such that the flow of damping fluid through the opening is reduced
relative to the open position of the inertia valve; a spring, the
spring configured to apply a force to the suspension assembly
tending to extend the piston rod relative to the tube; wherein the
spring and the damper cooperate, in the absence of a
terrain-induced upward acceleration of the suspension assembly
above a predetermined threshold sufficient to move the inertia
valve to the open position, to prevent significant compressive
movement of the suspension assembly in response to rider-induced
pedaling forces on the suspension assembly, and wherein the inertia
valve is movable to the open position in response to a
terrain-induced upward acceleration of the suspension assembly
above the threshold to permit significant compressive movement of
the suspension assembly; and at least one adjustable fluid damping
circuit through which fluid may flow during operation of the
suspension assembly, the fluid flow resistance through the
adjustable fluid damping circuit being adjustable without requiring
any disassembly of the bicycle suspension assembly, the adjustable
fluid damping circuit including: a) a movable external controller;
b) a damping flow controller at least partially located in a
portion of the piston rod and associated with the movable external
controller; c) whereby manipulating the movable external controller
results in the damping flow controller varying the fluid flow
resistance through the adjustable fluid damping circuit.
7. An acceleration-responsive bicycle damper, comprising: a damper
body partially defining a first chamber containing damping fluid; a
second chamber in fluid communication with the first chamber; a
compression fluid flow circuit extending from the first chamber to
the second chamber; a piston rod, coupled to a piston, having a
first end positioned within the first chamber through a sealed
opening and a second end positioned outside of the first chamber,
wherein: a) the piston divides the first chamber into two chamber
portions in fluid communication via at least one fluid flow port;
b) a translational movement of the piston rod in a direction such
that an increasing volume of the piston rod enters the first
chamber expels an amount of damping fluid from the first chamber
into the second chamber via the compression fluid flow circuit; an
acceleration-responsive inertia valve, including an inertia mass
movable in response to an upward acceleration exceeding a
threshold, at least partially controlling the fluid flow resistance
of the compression fluid flow circuit; a damping adjustment
mechanism, at least partially contained within the piston rod,
configured to enable external adjustment of a fluid flow resistance
of the at least one fluid flow port between the two chamber
portions, the adjustment mechanism comprising: a) a user-operable
adjuster element, including an external portion accessible for user
manipulation without requiring any disassembly of the damper, for
selectively setting at least a first fluid flow resistance level
and a second fluid flow resistance level of the at least one fluid
flow port; wherein the first fluid flow resistance level is greater
than the second fluid flow resistance level.
8. The acceleration-responsive bicycle damper of claim 7 wherein
the damping adjustment mechanism further comprises an adjustment
rod in communication with the user-operable adjuster element, the
adjustment rod at least partially contained within the piston
rod.
9. The acceleration-responsive bicycle damper of claim 7 wherein
the at least one fluid flow port comprises a portion of a rebound
damping fluid flow path.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to vehicle suspensions
systems. More particularly, the present invention relates to
acceleration sensitive damping arrangements suitable for use in
vehicle dampers (e.g., shock absorbers, struts, front forks).
[0003] 2. Description of the Related Art
[0004] Inertia valves are utilized in vehicle shock absorbers in an
attempt to sense instantaneous accelerations originating from a
particular portion of the vehicle, or acting in a particular
direction, and to alter the rate of damping accordingly. For
example, the inertia valve may be configured to sense vertical
accelerations originating at the sprung mass (e.g., the body of the
vehicle) or at the unsprung mass (e.g., a wheel and associated
linkage of the vehicle). Alternatively, the inertia valve may be
configured to sense lateral accelerations of the vehicle.
[0005] Despite the apparent potential, and a long history of
numerous attempts to utilize inertia valves in vehicle suspension,
commercial inertia valve shock absorbers have enjoyed only limited
success. Most attempted inertia valve shock absorbers have suffered
from unresponsive or inconsistent operation due to undesired
extraneous forces acting on the inertia valve. These extraneous
forces may result from manufacturing limitations and/or external
sources and often inhibit, or even prevent, operation of the
inertia valve.
[0006] Further, there are currently no commercially available
inertia valve shock absorbers for off-road bicycle, or mountain
bike, applications. The problems associated with the use of inertia
valves, mentioned above in relation to other vehicles, are
magnified in the environment of lightweight vehicles and the
relatively small size of mountain bike shock absorbers. Therefore,
a need exists for an inertia valve shock absorber that can be
commercially produced, and provides responsive, consistent
performance without the problems associated with prior inertia
valve designs.
SUMMARY OF THE INVENTION
[0007] A preferred embodiment is a shock absorber comprising a
first fluid chamber, a second fluid chamber and a fluid circuit
connecting the first fluid chamber and the second fluid chamber. An
inertia valve includes an inertia mass movable between a first
position and a second position. The inertia valve permits a first
rate of fluid flow through the fluid circuit in the first position
permits a second rate of fluid flow through the fluid circuit in
the second position of the inertia mass. The second rate of fluid
flow is non-equal to the first rate. A leading surface of the
inertia mass when moving in a direction from the first position to
the second position defines a leading surface area. A ratio of a
mass of the inertia mass to the leading surface area is greater
than about 130 grams per square inch.
[0008] A preferred embodiment is a shock absorber including a first
fluid chamber, a second fluid chamber and a fluid circuit
connecting the first fluid chamber and the second fluid chamber. An
inertia valve includes an inertia mass movable between a first
position and a second position. The inertia valve permits a first
rate of fluid flow through the fluid circuit in the first position
and permits a second rate of fluid flow in the second position. The
second rate of fluid flow is non-equal to the first rate. A ratio
of a mass of the inertia mass to a volume of the inertia mass is
greater than about 148 grams per cubic inch.
[0009] A preferred embodiment is a shock absorber including a first
fluid chamber, a second fluid chamber, and a fluid circuit
connecting the first fluid chamber and the second fluid chamber. An
inertia valve includes an inertia mass movable between a first
position and a second position. The inertia valve permits a first
rate of fluid flow through the fluid circuit in the first position
of the inertia mass and a second rate of fluid flow in the second
position of the inertia mass. The second rate of fluid flow is
non-equal to the first rate. At least a portion of the inertia mass
comprises tungsten.
[0010] A preferred embodiment is a shock absorber including a first
fluid chamber, a second fluid chamber, and a fluid circuit
connecting the first fluid chamber and the second fluid chamber. An
inertia valve includes an inertia mass movable between a first
position and a second position. The inertia valve permits a first
rate of fluid flow through the fluid circuit in the first position
of the inertia mass and a second rate of fluid flow through the
fluid circuit in the second position. The second rate of fluid flow
is non-equal to the first rate. The inertia mass comprises a first
portion and a second portion. The first portion is constructed from
a first material having a first density and the second portion
being constructed from a second material having a second density,
the second density being greater than the first density.
[0011] A preferred embodiment is a shock absorber including a first
fluid chamber, a second fluid chamber, and a fluid circuit
connecting the first fluid chamber and the second fluid chamber. An
inertia valve includes an inertia mass moveable between a first
position and a second position. The inertia valve permits a first
rate of fluid flow through the fluid circuit in the first position
of the inertia mass and a second rate of fluid flow in the second
position. The second rate of fluid flow is non-equal to the first
rate. The inertia mass includes a collapsible section defining at
least a portion of an external surface of the inertia mass. The
collapsible section has a first orientation when the inertia mass
is moving in a first direction from the first position to the
second position and a second orientation when the inertia mass is
moving in a second direction from the second position to the first
position. The inertia mass has a first flow resistance when the
collapsible section is in the first orientation and a second flow
resistance when the collapsible section is in the second
orientation. The second flow resistance is greater than the first
flow resistance.
[0012] A preferred embodiment is a shock absorber including a first
fluid chamber, a second fluid chamber, and a fluid circuit
connecting the first fluid chamber and the second fluid chamber. An
inertia valve includes an inertia mass moveable between a first
position and a second position. The inertia valve permits a first
rate of fluid flow through the fluid circuit in the first position
of the inertia mass and a second rate of fluid flow in the second
position. The second rate of fluid flow is non-equal to the first
rate. The inertia mass includes first and second opposing end
surfaces oriented generally normal to a direction of motion of the
inertia mass and a side wall extending between the first and second
end surfaces. The inertia mass additionally includes at least one
movable, annular skirt extending from the side wall. At least an
outer portion of the at least one skirt moves toward the side wall
when the inertia mass moves in a first direction and moves away
from the side wall when the inertia mass moves in a second
direction opposite the first direction. The at least one skirt
increases a fluid flow drag coefficient of the inertia mass when
moving in the second direction compared to the drag coefficient of
movement of the inertia mass in the first direction.
[0013] A preferred embodiment is a method of delaying an inertia
valve within a shock absorber from returning to a closed position
after an acceleration force acting on the inertia valve diminishes.
The method includes providing an inertia mass movable in a first
direction from a closed position toward an open position of the
inertia valve in response to an acceleration force above a
predetermined threshold and movable in a second direction from the
open position toward the closed position of the inertia valve when
the acceleration force is below the threshold. The method further
includes configuring the inertia mass to have a first fluid flow
drag coefficient when moving in the first direction. The method
also includes providing the inertia mass with a drag member
configured to increase the fluid flow drag coefficient when the
inertia mass moves in the second direction to delay the inertia
valve from returning to the closed position until a period of time
after the acceleration force is reduced to, and remains, below the
threshold.
[0014] A preferred embodiment is a shock absorber including a first
fluid chamber, a second fluid chamber, and a fluid circuit
connecting the first fluid chamber and the second fluid chamber. An
inertia valve includes an inertia mass and a stop. The inertia mass
is movable between a first position and a second position. The
inertia valve permits a first rate of fluid flow through the fluid
circuit in the first position of the inertia mass and a second rate
of fluid flow through the fluid circuit in the second position of
the inertia mass. The second rate of fluid flow is non-equal to the
first rate. One of the inertia mass and the stop defines a pocket
for receiving the other of the inertia mass and the stop in the
second position of the inertia mass. A first refill passage
connects the second fluid chamber and the pocket and restricts
fluid flow therethrough from the second fluid chamber to the pocket
to provide a delay in movement of the inertia mass toward the first
position. A second refill passage connects the second fluid chamber
and the pocket and a pressure actuated valve substantially prevents
fluid flow between the second fluid chamber and the pocket through
the second refill passage below a predetermined threshold pressure
differential between the second fluid chamber and the first fluid
chamber. The pressure actuated valve permits fluid flow between the
second fluid chamber and the pocket through the second refill
passage at, or above, a predetermined threshold pressure
differential between the second fluid chamber and the first fluid
chamber, thereby reducing or eliminating the delay.
[0015] A preferred embodiment is a method of delaying an inertia
valve within a shock absorber from returning to a closed position
after an acceleration force acting on the inertia valve diminishes.
The method includes providing an inertia mass movable in a first
direction from a closed position toward an open position of the
inertia valve in response to an acceleration force above a
predetermined threshold and movable in a second direction from the
open position toward the closed position of the inertia valve when
the acceleration force is below the threshold. The method further
includes providing a first delay force tending to resist movement
of the inertia mass in the second direction when a fluid pressure
differential between a first chamber and a second chamber within
the shock absorber is below a predetermined threshold. The method
also includes providing a second delay force, less than the first
delay force, when the fluid pressure differential is at, or above,
the predetermined threshold.
[0016] A preferred embodiment is a shock absorber including a first
fluid chamber, a second fluid chamber and a fluid circuit
connecting the first fluid chamber and the second fluid chamber. An
inertia valve includes an inertia mass and a moveable stop. The
inertia mass is movable between an open position and a closed
position. The moveable stop is movable between a first position and
a second position. The inertia mass is biased to move toward the
closed position at substantially a first rate. The moveable stop
and the inertia mass cooperate to define a pocket configured to
receive the other of the moveable stop and the inertia mass in the
open position of the inertia mass and the first position of the
moveable stop. The movement of the inertia mass toward the closed
position is restrained to a second rate less than the first rate.
The moveable stop moves from the first position to the second
position in response to a pressure within the second fluid chamber
being greater than a pressure within the first fluid chamber by at
least a predetermined pressure differential threshold, thereby
permitting the inertia mass to return to the closed position at
substantially the first rate.
[0017] A preferred embodiment is a damper including a first fluid
chamber and a second fluid chamber. A fluid circuit connects the
first fluid chamber and the second fluid chamber. An acceleration
sensor is configured to produce a control signal in response to an
acceleration force above a first predetermined threshold. The
damper also has an inertia valve including an inertia mass that at
least partially comprises a magnetic material and is movable
between a first position and a second position. The inertia valve
permits a first rate of fluid flow through the fluid circuit in the
first position of the inertia mass and a second rate of fluid flow
through the fluid circuit in the second position of the inertia
mass. The second rate of fluid flow is non-equal to the first rate.
The inertia mass moves in a direction from the first position to
the second position in response to an acceleration force above a
second predetermined threshold. An electromagnetic force generator
is capable of retaining the inertia mass in the second position. A
control system is configured to receive the control signal from the
sensor and selectively activate the electromagnetic element in
response to the control signal to retain the inertia mass in the
second position for a predetermined period of time after the
acceleration force diminishes below the first predetermined
threshold.
[0018] A preferred embodiment is a bicycle including a front wheel
defining a hub axis, a rear wheel, and a main frame. An
acceleration sensor is mounted for movement with the hub axis of
the front wheel and is configured to produce a control signal in
response to sensing an acceleration above a predetermined
threshold. A shock absorber is operably positioned between the rear
wheel and the frame. The shock absorber includes a valve
arrangement configured to receive the control signal from the
sensor and to selectively alter a damping rate of the shock
absorber in response to the control signal.
[0019] A preferred embodiment is a bicycle including a front wheel
defining a hub axis, a rear wheel, and a main frame. An
acceleration sensor is mounted for movement with the hub axis of
the front wheel and is configured to produce a control signal in
response to sensing an acceleration above a predetermined
threshold. A shock absorber is operably positioned between the
front wheel and the frame and includes a valve arrangement
configured to receive the control signal from the sensor. The valve
arrangement is configured to selectively alter a damping rate of
the shock absorber in response to the control signal.
[0020] A preferred embodiment is a method of altering a rate of
damping of a bicycle rear wheel shock absorber including sensing an
acceleration force above a predetermined threshold acting on a hub
axis of a front wheel of said bicycle. The method further includes
providing a valve assembly within said rear wheel shock absorber
configured to selectively alter a damping rate of said rear wheel
shock absorber, and altering said damping rate of said rear wheel
shock absorber in response to an acceleration force above said
predetermined threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] These and other features of the damper will now be described
with reference to drawings of preferred embodiments. The
embodiments are illustrated in the context of use on an off-road
bicycle, however, these embodiments are merely intended to
illustrate, rather than limit, the present invention. The drawings
contain the following figures:
[0022] FIG. 1 is a perspective view of a bicycle including
preferred front and rear shock absorbers;
[0023] FIG. 2 is a cross-section of the rear shock absorber of FIG.
1;
[0024] FIG. 3a is an enlarged cross-section of a main portion of
the shock absorber of FIG. 2 and FIG. 3b is an enlarged
cross-section of a reservoir of the shock absorber of FIG. 2
showing an inertia valve in a closed position;
[0025] FIG. 4a is a top plan view of the inertia mass of the shock
absorber of FIG. 2. FIG. 4b is a side cross-section view of the
inertia mass of FIG. 2 taken along line 4b-4b in FIG. 4a. FIG. 4c
is a bottom plan view of the inertia mass of FIG. 2;
[0026] FIG. 5 is an enlarged cross-section of the reservoir of the
shock absorber of FIG. 2, showing the inertia valve in an open
position;
[0027] FIG. 6 is an enlarged cross-section of the inertia valve of
the shock absorber of FIG. 2;
[0028] FIG. 7a is an enlarged view of a portion of the inertia
valve of FIG. 6. FIG. 7b is an enlarged view of a portion of an
alternative inertia valve;
[0029] FIG. 8 is a graph illustrating the relationship between
position, velocity and acceleration for a simple mass;
[0030] FIG. 9 is a schematic illustration of an inertia valve in an
off-center condition;
[0031] FIG. 10 is a schematic illustration of an inertia valve in a
second off-center condition;
[0032] FIG. 11 is a cross-section view of the inertia valve of FIG.
3b showing various zones of cross-sectional fluid flow areas;
[0033] FIG. 12 is a cross-section view of the inertia valve of FIG.
3b in an off-center condition;
[0034] FIG. 13 is an enlarged view of an adjustable return fluid
flow beneath the inertia mass;
[0035] FIG. 14 is the front shock absorber, or suspension fork, of
FIG. 1 as detached from the bicycle;
[0036] FIG. 15 is a cross-section view of the right leg of the fork
of FIG. 14, illustrating various internal components;
[0037] FIG. 16 is an enlarged cross-section of a lower portion of
the fork leg of FIG. 15, illustrating an inertia valve damping
system;
[0038] FIG. 17 is an enlarged cross-section of a base valve
assembly of the lower portion of the fork leg of FIG. 16;
[0039] FIG. 18 is a cross-section view of the lower portion of the
fork of FIG. 15, with the inertia valve in an open position;
[0040] FIG. 19 is the base valve assembly of FIG. 17, with the
inertia valve in an open position;
[0041] FIG. 20 is a cross-section view of the lower portion of the
fork of FIG. 16 illustrating rebound fluid flow;
[0042] FIG. 21 is the base valve assembly of FIG. 17 illustrating
rebound fluid flow;
[0043] FIG. 22 is a cross-section view of a lower portion of an
alternative embodiment of a suspension fork;
[0044] FIG. 23 is an enlarged view of the base valve assembly of
the fork of FIG. 22, with the inertia valve in a closed
position;
[0045] FIG. 24 is the lower portion of the fork of FIG. 22, with
the inertia valve in an open position;
[0046] FIG. 25 is the base valve assembly of FIG. 23, with the
inertia valve in an open position;
[0047] FIG. 26 is a graph of the pressure differential of fluid
acting on the left and right sides of the inertia mass versus
internal diameter of the inertia mass;
[0048] FIG. 27 is a graph of the pressure differential factor of
fluid acting on the left and right sides of the inertia mass versus
the internal diameter of the inertia mass for a radial gap between
the inertia mass and shaft of 0.002 inches; and
[0049] FIG. 28 is a graph of the pressure differential factor of
fluid acting on the left and right sides of the inertia mass versus
the internal diameter of the inertia mass for a radial gap between
the inertia mass and shaft of 0.001 inches.
[0050] FIG. 29 is an enlarged, cross-section view of an alternative
inertia valve assembly comprising an inertia mass having increased
density, in comparison to the embodiments of FIGS. 1-28, in order
to provide increased responsiveness to acceleration forces.
[0051] FIG. 30 is an enlarged view of an alternative embodiment of
an inertia mass including a plurality of drag members to increase
the fluid drag on the inertia mass when moving in one direction in
comparison with the drag on the inertia mass during movement in the
opposite direction.
[0052] FIG. 31A is a cross-section view of the inertia mass of FIG.
30 illustrating an orientation of the drag members when the inertia
mass is moving in a downward direction within a fluid-filled
reservoir chamber. FIG. 31B is a cross-section view of the inertia
mass of FIG. 30 illustrating an orientation of the drag members
when the inertia mass is moving in an upward direction within a
fluid-filled reservoir chamber.
[0053] FIG. 32 is an enlarged, cross-section view of a
pressure-responsive inertia valve assembly.
[0054] FIG. 33 is an enlarged, cross-section view of another
embodiment of a pressure-responsive inertia valve assembly.
[0055] FIG. 34 is a side elevational view of bicycle employing yet
another embodiment of an acceleration-sensitive shock absorber.
[0056] FIG. 35 is an enlarged, cross-section view of an
acceleration-sensitive valve assembly within a shock absorber of
the bicycle of FIG. 35. The inertia valve assembly of FIG. 30
includes a valve body that is at least partially controlled by an
electromagnetic system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0057] FIG. 1 illustrates an off-road bicycle, or mountain bike, 20
including a frame 22 which is comprised of a main frame portion 24
and a swing arm portion 26. The swing arm portion 26 is pivotally
attached to the main frame portion 24. The bicycle 20 includes
front and rear wheels 28, 30 connected to the main frame 24. A seat
32 is connected to the main frame 24 and provides support for a
rider of the bicycle 20.
[0058] The front wheel 28 is supported by a preferred embodiment of
a suspension fork 34 which, in turn, is secured to the main frame
24 by a handlebar assembly 36. The rear wheel 30 is connected to
the swing arm portion 26 of the frame 22. A preferred embodiment of
a rear shock 38 is operably positioned between the swing arm 26 and
the main frame 24 to provide resistance to the pivoting motion of
the swing arm 26. Thus, the illustrated bicycle 20 includes
suspension members 34, 38 between the front and rear wheels 28, 30
and the frame 22, which operate to substantially reduce wheel
impact forces from being transmitted to the rider of the bicycle
20. The rear shock absorber 38 desirably includes a fluid reservoir
44 hydraulically connected to the main shock body by a hydraulic
hose 46. Preferably, the reservoir 44 is connected to the swingarm
portion 26 of the bicycle 20 above the hub axis of the rear wheel
30.
[0059] The suspension fork 34 and the rear shock 38 preferably
include an acceleration-sensitive valve, commonly referred to as an
inertia valve, which allows the damping rate to be varied depending
upon the direction of an acceleration input. The inertia valve
permits the suspension fork 34 and rear shock 38 to distinguish
between accelerations originating at the sprung mass, or main frame
24 and rider of the bicycle 20, from accelerations originating at
the unsprung mass, or front wheel 28 and rear wheel 30, and alter
the damping rate accordingly. It is generally preferred to have a
firm damping rate when accelerations originate at the sprung mass
and a softer damping rate when the accelerations originate at the
unsprung mass. On an automobile or other four-wheel vehicle, this
helps to stabilize the body by reducing fore and aft pitching
motions during acceleration and braking, as well as by reducing
body roll during cornering.
[0060] In a similar manner, on two-wheel vehicles such as
motorcycles and bicycles, vehicle stability is improved by
reduction of fore and aft pitching motions. In addition, in the
case of bicycles and other pedal-driven vehicles, this reduces or
prevents suspension movement in response to rider-induced forces,
such as pedaling forces, while allowing the suspension to absorb
forces induced by the terrain on which the bicycle 20 is being
ridden. As will be described in detail below, the inertia valving
within the suspension fork 34 and rear shock 38 include features
which permit responsive, consistent performance and allow such
inertia valves to be manufactured in a cost effective manner.
Preferably, the inertia valve is located within the reservoir 44,
which may be rotated relative to the swingarm portion 26 of the
bicycle 20. Rotating the reservoir 44 alters the component of an
upward acceleration of the rear wheel 30 which acts along the axis
of motion of the inertia valve and thereby influences the
responsiveness of the inertia valve.
[0061] FIGS. 2-7 illustrate a preferred embodiment of the rear
shock absorber 38. A shock absorber 38 operates as both a
suspension spring and as a damper. Preferably, the spring is an air
spring arrangement, but coil springs and other suitable
arrangements may also be used. The shock 38 is primarily comprised
of an air sleeve 40, a shock body 42 and a reservoir 44. In the
illustrated embodiment, a hydraulic hose 46 physically connects the
main body of the shock 38 (air sleeve 40 and shock body 42) to the
reservoir 44. However, the reservoir 44 may also be directly
connected to the main body of the shock absorber 38, such as being
integrally connected to, or monolithically formed with, the air
sleeve 40.
[0062] The air sleeve 40 is cylindrical in shape and includes an
open end 48 and an end closed by a cap 50. The cap 50 of the air
sleeve 40 defines an eyelet 52 which is used for connection to the
main frame 24 of the bicycle 20 of FIG. 1. The open end 48 of the
air sleeve 40 slidingly receives the shock body 42.
[0063] The shock body 42 is also cylindrical in shape and includes
an open end 54 and a closed end 56. The closed end 56 defines an
eyelet 58 for connecting the shock 38 to the swing arm portion 26
of the bicycle 20 of FIG. 1. Thus, the air sleeve 40 and the shock
body 42 are configured for telescopic movement between the main
frame portion 24 and the swing arm portion 26 of the bicycle 20. If
desired, this arrangement may be reversed and the shock body 42 may
be connected to the main frame 24 while the air sleeve 40 is
connected to the swing arm 26.
[0064] A seal assembly 60 is positioned at the open end 48 of the
air sleeve 40 to provide a substantially airtight seal between the
air sleeve 40 and the shock body 42. The seal assembly 60 comprises
a body seal 62 positioned between a pair of body bearings 64. The
illustrated body seal 62 is an annular seal having a substantially
square cross-section. However, other suitable types of seals may
also be used. A wiper 66 is positioned adjacent the open end 48 of
the air sleeve 40 to remove foreign material from the outer surface
of the shock body 42 as it moves into the air sleeve 40.
[0065] A damper piston 68 is positioned in sliding engagement with
the inner surface of the shock body 42. A shock shaft 70 connects
the piston 68 to the cap 50 of the air sleeve 40. Thus, the damper
piston 68 is fixed for motion with the air sleeve 40.
[0066] A piston cap 72 is fixed to the open end 54 of the shock
body 42 and is in sliding engagement with both the shock shaft 70
and the inner surface of the air sleeve 40. The piston cap 72
supports a seal assembly 74 comprised of a seal member 76
positioned between a pair of bearings 78. The seal assembly 74 is
in a sealed, sliding engagement with the inner surface of the air
sleeve 40. A shaft seal arrangement 80 is positioned to create a
seal between the cap 72 and the shock shaft 70. The shaft seal
arrangement 80 comprises a seal member 82 and a bushing 84. The
seal member 82 is an annular seal with a substantially square
cross-section, similar to the body seal 62. The shaft seal
arrangement 80 creates a substantially airtight seal between the
cap 72 and the shock shaft 70 while allowing relative sliding
motion therebetween.
[0067] A positive air chamber 86 is defined between the closed end
50 of the air sleeve 40 in the cap 72. Air held within the positive
air chamber 86 exerts a biasing force to resist compression motion
of the shock absorber 38. Compression motion of the shock absorber
38 occurs when the closed ends 56 and 50 of the shock body 42 and
air sleeve 40 (and thus the eyelets 52, 58) move closer to one
another.
[0068] A negative air chamber 88 is defined between the cap 72 and
the seal assembly 60, which in combination with the shock body 42
closes the open end 48 of the air sleeve 40. Air trapped within the
negative air chamber 88 exerts a force which resists expansion, or
rebound, motion of the shock absorber 38. Rebound motion of the
shock absorber 38 occurs when the closed ends 56 and 50 of the
shock body 42 and air sleeve 40 (and thus the eyelets 52, 58) move
farther apart from each other. Together, the positive air chamber
86 and the negative air chamber 88 function as the suspension
spring portion of the shock absorber 38.
[0069] An air valve 90 communicates with the positive air chamber
86 to allow the air pressure therein to be adjusted. In this
manner, the spring rate of the shock absorber 38 may be easily
adjusted.
[0070] A bypass valve 92 is provided to allow the pressure between
the positive air chamber 86 and the negative air chamber 88 to be
equalized. The bypass valve 92 is configured to allow brief
communication between the positive air chamber 86 and the negative
air chamber 88 when the air sleeve seal assembly 74 passes thereby.
A bottom out bumper 94 is positioned near the closed end 50 of the
air sleeve 40 to prevent direct metal to metal contact between the
closed end 50 and the cap 72 of the shock body 42 upon full
compression of the shock absorber 38.
[0071] The shock absorber 38 also includes a damper assembly, which
is arranged to provide a resistive force to both compression and
rebound motion of the shock absorber 38. Preferably, the shock
absorber 38 provides modal response compression damping. That is,
the shock absorber 38 preferably operates at a first damping rate
until an appropriate acceleration input is sensed, then the shock
absorber 38 operates at a second damping rate for a predetermined
period thereafter, before returning the first damping rate. This is
in opposition to a system that attempts to continually respond to
instantaneous input. Such a modal system avoids the inherent delay
associated with responding separately to each input event.
[0072] The piston 68 divides the interior chamber of the shock body
42 into a compression chamber 96 and a rebound chamber 98. The
compression chamber 96 is defined between the piston 68 and the
closed end 56 of the shock body 42 and decreases in volume during
compression motion of the shock absorber 38. The rebound chamber 98
is defined between the piston 68 and the piston cap 72, which is
fixed to the open end 54 of the shock body 42. The rebound chamber
98 decreases in volume upon rebound motion of the shock absorber
38.
[0073] The piston 68 is fixed to the shock shaft 70 by a hollow
threaded fastener 100. A seal 102 is fixed for movement with the
piston 68 and creates a seal with the inner surface of the shock
body 42. The illustrated seal 102 is of an annular type having a
rectangular cross-section. However, other suitable types of seals
may also be used.
[0074] The piston 68 includes one or more axial compression
passages 104 that are covered on the rebound chamber 98 side by a
shim stack 106. As is known, the shim stack 106 is made up of one
or more flexible shims and deflects to allow flow through the
compression passages 104 during compression motion of the shock
absorber 38 but prevents flow through the compression passages 104
upon rebound motion of the shock absorber 38. Similarly, the piston
68 includes one or more rebound passages 108 extending axially
therethrough. A rebound shim stack 110 is made up of one or more
flexible shims, and deflects to allow flow through the rebound
passages 108 upon rebound motion of the shock absorber 38 while
preventing flow through the rebound passages 108 during compression
motion of the shock absorber 38.
[0075] A central passage 112 of the shock shaft 70 communicates
with the compression chamber 96 through the hollow fastener 100.
The passage 112 also communicates with the interior chamber of the
reservoir 44 through a passage 114 defined by the hydraulic hose
46. Thus, the flow of hydraulic fluid is selectively permitted
between the compression chamber 96 and the reservoir 44.
[0076] A rebound adjustment rod 116 extends from the closed end 50
of the air sleeve 40 and is positioned concentrically within the
passage 112 of the shock shaft 70. The rebound adjustment rod 116
is configured to alter the amount of fluid flow upon rebound motion
thereby altering the damping force produced. An adjustment knob 118
engages the rebound adjustment rod 116 and is accessible externally
of the shock absorber 38 to allow a user to adjust the rebound
damping rate. A ball detent mechanism 120 operates in a known
manner to provide distinct adjustment positions of the rebound
damping rate.
[0077] The reservoir 44 includes a reservoir tube 122 closed on
either end. A floating piston 124 is in sliding engagement with the
interior surface of a reservoir tube 122. A seal member 126
provides a substantially fluid-tight seal between the piston 124
and the interior surface of the reservoir tube 122. The seal member
126 is preferably an annular seal having a substantially square
cross-section. However, other suitable seals may also be used.
[0078] The floating piston 124 divides the interior chamber of the
reservoir tube 122 into a reservoir chamber 128 and a gas chamber
130. The reservoir chamber 128 portion of the reservoir tube is
closed by an end cap 132. The end cap 132 additionally receives the
end of the hydraulic hose 46 and supports a hollow reservoir shaft
134. The central passage 136 of the reservoir shaft 134 is in fluid
communication with the passages 114 and 112 and, ultimately, the
compression chamber 96.
[0079] The reservoir shaft 134 supports an inertia valve assembly
138 and a blowoff valve assembly 140. Each of the inertia valve
assembly 138 and the blowoff valve assembly 140 allows selective
communication between the compression chamber 96, via the passages
112, 114, 136, and the reservoir chamber 128.
[0080] The gas chamber 130 end of the reservoir tube 122 is closed
by a cap 142 which includes a valve assembly 144 for allowing gas,
such as nitrogen, for example, to be added or removed from the gas
chamber 130. The pressurized gas within the gas chamber 130 causes
the floating piston 124 to exert a pressure on the hydraulic fluid
within the reservoir chamber 128. This arrangement prevents air
from being drawn into the hydraulic fluid and assists in refilling
fluid into the compression chamber 96 during rebound motion of the
shock absorber 38.
[0081] With reference to FIG. 3b, the blowoff valve assembly 140 is
supported by the reservoir shaft 134 and positioned above the
inertia valve assembly 138. The reservoir shaft 134 reduces in
diameter to define a shoulder portion 154. An annular washer 156 is
supported by the shoulder 154 and the blowoff valve assembly 140 is
supported by the washer 156. The washer 156 also prevents direct
contact between the inertia mass 150 and the blowoff valve assembly
140.
[0082] The blowoff valve assembly 140 is primarily comprised of a
cylindrical base 158 and the blowoff cap 160. The base 158 is
sealed to the reservoir shaft 134 by a shaft seal 162. The
illustrated seal 162 is an O-ring, however other suitable seals may
also be used. The upper end of the base 158 is open and includes a
counterbore which defines a shoulder 164. The blowoff cap 160 is
supported by the shoulder 164 and is sealed to the inner surface of
the base 158 by a cap seal 166. The cap seal 166 is preferably an
O-ring, however other suitable seals may also be used. A threaded
fastener 168 fixes the blowoff cap 160 and base 158 to the
reservoir shaft 134.
[0083] The blowoff cap 160 and base 158 define a blowoff chamber
170 therebetween. A plurality of radial fluid flow passages 172 are
defined by the reservoir shaft 134 to allow fluid communication
between the blowoff chamber 170 and the shaft passage 136.
[0084] The blowoff cap 160 includes one or more axial blowoff
passages 174 and one or more axial refill passages 176. A blowoff
shim stack 178 is positioned above the blowoff cap 160 and covers
the blowoff passages 174. The blowoff shim stack 178 is secured in
place by the threaded fastener 168. The individual shims of the
shim stack 178 are capable of deflecting about the central axis of
the fastener 168 to selectively open the blowoff passages 174 and
allow fluid communication between the blowoff chamber 170 and the
reservoir chamber 128. The blowoff shim stack 178 is preferably
configured to open in response to pressures within the blowoff
chamber above a minimum threshold, such as approximately 800 psi,
for example.
[0085] A refill shim stack 180 is positioned between the blowoff
cap 160 and the reservoir shaft 134 and covers the refill ports
176. The refill shim stack 180 is configured to prevent fluid from
flowing from the blowoff chamber 170 through ports 176 to the
reservoir 128 while offering little resistance to flow from the
reservoir 128 into the blowoff chamber 170.
[0086] The inertia valve assembly 138 includes a plurality of
radially extending, generally cylindrical valve passages 148,
connecting the passage 136 to the reservoir chamber 128. The
inertia valve assembly 138 also includes a valve body, or inertia
mass 150, and a spring 152. The spring 152 biases the inertia mass
150 into an upward, or closed, position wherein the inertia mass
150 covers the mouths of the valve passages 148 to substantially
prevent fluid flow from the passage 136 to the reservoir chamber
128. The inertia mass 150 is also movable into a downward, or open,
position against the biasing force of the spring 152. In the open
position, the inertia mass 150 uncovers at least some of the valve
passages 148 to allow fluid to flow therethrough.
[0087] The end cap 132, which closes the lower end of the reservoir
tube 122, defines a cylindrical pocket, or socket, 182 which
receives the inertia mass 150 in its lowermost or open position.
The lowermost portion of the pocket 182 reduces in diameter to form
a shoulder 184. The shoulder 184 operates as the lowermost stop
surface, which defines the open position of the inertia mass 150,
as illustrated in FIG. 5.
[0088] The inertia mass 150 includes a check plate 190 which allows
fluid to be quickly displaced from the pocket 182 as the inertia
mass 150 moves downward into the pocket 182. The inertia mass 150
has a plurality of axial passages 188 extending therethrough. The
check plate 190 rests on several projections, or standoff feet, 192
(FIG. 6) slightly above the upper surface of the inertia mass 150
and substantially covers the passages 188. A series of stop
projections 193, similar to the standoff feet, are formed or
installed in the upper, necked portion of the inertia mass 150 to
limit upward motion of the check plate 190.
[0089] With reference to FIG. 4a, a top plan view of the inertia
mass 150 is shown. The axial passages 188 are preferably
kidney-shaped, to allow the passages 188 to occupy a large portion
of the transverse cross-sectional area of the inertia mass 150.
Desirably, the ratio of the passage 188 cross-sectional area to the
inertia mass 150 cross-sectional area is greater than approximately
0.3. Preferably, the ratio of the passage 188 cross-sectional area
to the inertia mass 150 cross-sectional area is greater than
approximately 0.5, and more preferably greater than approximately
0.7.
[0090] The large area of the passages 188 provides a low-resistance
flow path for hydraulic fluid exiting the pocket 182. As a result,
the flow rate of the fluid exiting the pocket 182 is high, and the
inertia mass is able to move rapidly into the open position. In
addition, the amount of fluid which must be displaced by the
inertia mass 188 for it to move into the open position is reduced.
Advantageously, such an arrangement allows the inertia mass 150 to
respond rapidly to acceleration forces.
[0091] When the check plate 190 is resting against the standoff
feet 192 on the upper surface of the inertia mass 150 it provides
restricted fluid flow through the passages 188. The check plate 190
also has an open position in which it moves upward relative to the
inertia mass 150 until it contacts the stop projections 193. When
the check plate 190 is open, fluid is able to flow from the pocket
182 through the passages 188 and into the reservoir 128, with
desirably low resistance.
[0092] The inertia mass 150 also includes a third series of
projections, or standoff feet, 194. The standoff feet 194 are
comprised of one or more projections located on the uppermost
surface of the upper neck portion of the inertia mass 150. The
standoff feet 194 on the upper surface of the neck portion of the
inertia mass 150 contact the washer 156 when the inertia mass 150
is in its uppermost or closed position. A fourth set of
projections, or standoff feet, 195 are positioned on the lower
surface of the inertia mass 150 (FIG. 4c) and contact the shoulder
184 when the inertia mass 150 is in its lower or open position.
[0093] In each set of stop projections, or standoff feet, 192-195,
preferably between three to five individual projections are
disposed radially about the inertia mass 150. However, other
suitable numbers of feet may also be used. Desirably, the surface
area of the stop projections, or standoff feet, 192-195 is
relatively small. A small surface area of the standoff feet 194,
195 lowers the resistance to movement of the inertia mass 150 by
reducing the overall surface contact area between the inertia mass
150 and the washer 156 or shoulder 184, respectively. The small
surface area of the standoff feet 192 and stop projections 193
lower the resistance to movement of the check plate 190 relative to
the inertia mass 150. Desirably, the projections 192-195 have
dimensions of less than approximately 0.025''.times.0.025''.
Preferably, the projections 192-195 have dimensions of less than
approximately 0.020''.times.0.020'' and, more preferably, the
projections 192-195 have dimensions of less than approximately
0.015''.times.0.015''.
[0094] When utilized with an inertia mass 150 having a mass
(weight) of approximately 0.5 ounces, the preferred projections
192-195 provide a desirable ratio of the mass (weight) of the
inertia valve mass 150 to the contact surface area of the
projections 192-195. Due to the vacuum effect between two surfaces,
a force of approximately 14.7 lbs/in.sup.2 (i.e., atmospheric
pressure) is created when attempting to separate the inertia mass
150 from either the washer 156 or shoulder 184, respectively. By
lowering the contact surface area between the inertia mass 150 and
either the washer 156 or shoulder 184, the vacuum force tending to
resist separation of the contact surfaces is desirably reduced.
[0095] Preferably, the contact surface area is small in comparison
with the mass (weight) of the inertia mass 150 because the
magnitude of the acceleration force acting on the inertia mass 150
is proportional to it's mass (weight). Accordingly, a large ratio
of the mass (weight) of the inertia valve mass 150 to the contact
surface area of the projections 192-195 is desired. For example,
for a set of three (3) standoff feet 194, 195 with dimensions of
approximately 0.025''.times.0.025'', the ratio is at least
approximately 17 lbs/in.sup.2. A more desirable ratio is at least
approximately 25 lbs/in.sup.2. Preferably, the ratio is at least 50
lbs/in.sup.2 and more preferably is at least 75 lbs/in.sup.2. These
ratios are desirable for an inertia mass utilized in the context of
an off-road bicycle rear shock absorber and other ratios may be
desirable for other applications and/or vehicles. Generally,
however, higher ratios increase the sensitivity of the inertia mass
150 (i.e., allow the inertia mass 150 to be very responsive to
acceleration forces). For example, with a ratio of 50 lbs/in.sup.2
the sensitivity of the inertia mass 150 is about +/-1/3 G.
Likewise, for a ratio of 147 lbs/in.sup.2 the sensitivity of the
inertia mass 150 is about +/- 1/10 G.
[0096] As illustrated in FIG. 6, the outside diameter of the lower
portion of the inertia mass 150 is slightly smaller than the
diameter of the pocket 182. Therefore, an annular clearance space
is defined between them when the inertia mass 150 is positioned
within the pocket 182. The clearance C restricts the rate with
which fluid may pass to fill the pocket below the inertia mass 150,
to influence the rate at which the inertia mass 150 may exit the
pocket 182. Thus, in the illustrated shock absorber 38, a fluid
suction force is applied to the inertia mass 150 within the pocket
182 to delay the inertia mass 150 from returning to the closed
position.
[0097] The interior surface of the inertia mass 150 includes an
increased diameter central portion 195 which, together with the
shaft 134, defines an annular recess 196. The annular recess 196 is
preferably located adjacent to one or more of the ports 148 when
the inertia mass 150 is in its closed position. Thus, fluid exiting
from the shaft passage 136 through the passages 148 enters the
annular recess 196 when the inertia mass 150 is its closed
position.
[0098] The interior surface of the inertia mass 150 decreases in
diameter both above and below the central portion 195 to create an
upper intermediate portion 197 and a lower intermediate portion
199. The upper intermediate portion 197 and lower intermediate
portion 199, together with the shaft 134, define an upper annular
clearance 198 (FIG. 7a) and a lower annular clearance 200,
respectively. An upper lip 201 (FIG. 7a) is positioned above, and
is of smaller diameter than, the upper intermediate portion 197. A
step 205 (FIG. 7a) is defined by the transition between the upper
intermediate portion 197 and the upper lip 201. Similarly, a lower
lip 203 is positioned below, and has a smaller diameter than, the
lower intermediate portion 199. A step 205 is defined by the
transition between the lower intermediate portion 199 and the lower
lip 203. The upper lip 201 and the lower lip 203, together with the
shaft 134, define an upper exit clearance 202 (FIG. 7a) and a lower
exit clearance 204.
[0099] With reference to FIG. 7a, the upper lip 201 preferably
includes a labyrinth seal arrangement 206. As is known, a labyrinth
seal comprises a series of annular grooves formed into a sealing
surface. Preferably, the lower lip 203 also includes a labyrinth
seal arrangement substantially similar to the labyrinth seal 206 of
the upper lip 201.
[0100] Advantageously, the labyrinth seal arrangement 206 reduces
fluid flow (bleed flow) between the reservoir shaft 134 and the
upper lip 201 when the inertia mass 150 is in a closed position.
Excessive bleed flow is undesired because it reduces the damping
rate when the inertia valve 138 is closed. By utilizing a labyrinth
seal 206, the clearance between the inertia mass 150 and the shaft
134 may be increased, without permitting excessive bleed flow. The
increased clearance is particularly beneficial to prevent foreign
matter from becoming trapped between the inertia mass 150 and shaft
134 and thereby inhibiting operation of the inertia valve 138.
Thus, reliability of the shock absorber 38 is increased, while the
need for routine maintenance, such as changing of the hydraulic
fluid, is decreased.
[0101] With reference to FIG. 7b, an alternative inertia mass 150
is illustrated. The upper intermediate portion 197 of the inner
surface of the inertia mass 150 of FIG. 7b is inclined with respect
to the outer surface of the shaft 134, rather than being
substantially parallel to the outer surface of the shaft 134 as in
the inertia mass of FIG. 7a. Thus, in the inertia mass 150 of FIG.
7b, the step 205 is effectively defined by the entire upper
intermediate portion 197. The inertia mass 150 configuration of
FIG. 7b theoretically provides approximately one-half the
self-centering force of the inertia mass 150 of FIG. 7a. In
addition, other suitable configurations of the inner surface of the
inertia mass 150 may be utilized to provide a suitable
self-centering force, as will be apparent to one of skill in the
art based on the disclosure herein. For example, the inclined
surface may begin in an intermediate point of the upper
intermediate portion 197. Alternatively, the step 205 may be
chamfered, rather than orthogonal.
[0102] With reference to FIGS. 1-7, the operation of the shock
absorber 38 will now be described in detail. As described
previously, the shock absorber 38 is operably mounted between the
main frame 24 and the swing arm portion 26 of the bicycle 20 and is
capable of both compression and rebound motion. Preferably, the
shock body 42 portion of the shock absorber 38 is connected to the
swing arm portion 26 and the air sleeve 40 is connected to the main
frame 24. The reservoir 44 is desirably connected to the swing arm
portion 26 of the bicycle 20 preferably near the rear axle, and
preferably approximately vertical as shown in FIG. 1.
[0103] When the rear wheel 30 of the bicycle 20 encounters a bump
the swing arm portion 26 articulates with respect to the main frame
24, tending to compress the shock absorber 38. If the acceleration
imparted along the longitudinal axis of the reservoir 44 is below a
predetermined threshold, the inertia mass 150 will remain in its
closed position, held by the biasing force of the spring 152, as
illustrated in FIG. 3b.
[0104] For the piston 68 to move relative to the shock body 42
(i.e., compression motion of the shock absorber 38) a volume of
fluid equal to the displaced volume of the shock shaft 70 must be
transferred into the reservoir 128. With the inertia mass 150
closing the passages 148 and the blowoff valve 140 remaining in a
closed position, fluid flow into the reservoir 128 is substantially
impeded and the shock absorber 38 remains substantially rigid.
[0105] If the compressive force exerted on the rear wheel 30, and
thus the shock absorber 38, attains a level sufficient to raise the
fluid pressure within the blowoff chamber 170 above a predetermined
threshold, such as 800 psi for example, the blowoff shims 178 open
to allow fluid to flow from the blowoff chamber 170 through the
blowoff ports 174 and into the reservoir 128. As an example, if the
diameter of the shock shaft 70 is 5/8'' (Area=0.31 square inches)
and the predetermined blow-off threshold is 800 psi, then a
compressive force at the shaft of at least 248 pounds is required
to overcome the blowoff threshold and commence compression of the
shock absorber. This required force, of course, is in addition to
the forces required, as is known in the art, to overcome the basic
spring force and the compression damping forces generated at the
piston 68 of the shock absorber. In this situation, compression of
the shock absorber is allowed against the spring force produced by
the combination of the positive and negative air chambers 86, 88.
The damping rate is determined by the flow through the compression
ports 104 of the piston 68 against the biasing force of the
compression shim stack 106. When the pressure within the blowoff
chamber 170 falls below the predetermined threshold, the blowoff
shim stack 178 closes the blowoff ports 174 and the shock absorber
38 again becomes substantially rigid, assuming the inertia mass 150
remains in the closed position.
[0106] If the upward acceleration imposed along the longitudinal
axis of the reservoir 44 (i.e., the axis of travel of the inertia
mass 150) exceeds the predetermined minimum threshold, the inertia
mass 150, which tends to remain at rest, will overcome the biasing
force of the spring 152 as the reservoir 44 moves upward relative
to the inertia mass 150. If the upward distance of travel of the
reservoir 44 is sufficient, the inertia mass will move into the
pocket 182. With the inertia mass 150 in the open position, fluid
is able to be displaced from the compression chamber 96 through the
passages 112, 114 and the shaft passage 136, through the passages
148 and into the reservoir 128. Thus, the shock 38 is able to
compress with the compression damping force again being determined
by flow through the compression ports 104 of the piston 68.
[0107] The predetermined minimum threshold for the inertia mass 150
to overcome the biasing force of the spring 152 is determined
primarily by the mass of the inertia mass 150, the spring rate of
the spring 152 and the preload on the spring 152. Desirably, the
mass of the inertia mass is approximately 0.5 ounces. However, for
other applications, such as the front suspension fork 34 or
vehicles other than off-road bicycles, the desired mass of the
inertia mass 150 may vary.
[0108] The spring rate of the spring 152 and the preload on the
spring 152 are preferably selected such that the spring 152 biases
the inertia mass 150 into a closed position when no upward
acceleration is imposed along the longitudinal axis of the
reservoir 44. However, in response to such an acceleration force
the inertia mass 150 will desirably overcome the biasing force of
the spring 152 upon experiencing an acceleration which is between
0.1 and 3 times the force of gravity (G's). Preferably, the inertia
mass 150 will overcome the biasing force of the spring 152 upon
experiencing an acceleration which is between 0.25 and 1.5 G's and
more preferably upon experiencing an acceleration which is between
0.4 and 0.7 G's. For certain riding conditions or other
applications, such as the front suspension fork 34, or other
applications besides off-road bicycles, however, the predetermined
threshold may be varied from the values recited above.
[0109] The check plate 190 resting on the standoff feet 193 of the
inertia mass 150 allows fluid to be easily displaced upward from
the pocket 182 and thus allows the inertia mass 150 to move into
the pocket 182 with little resistance. This permits the inertia
mass 150 to be very responsive to acceleration inputs. As the
inertia mass 150 moves into the pocket 182, fluid within the pocket
182 flows through the passages 188 and lifts the check plate 190
against the stop projections 193.
[0110] Once the inertia mass 150 is in its open position within the
pocket 182, as illustrated in FIG. 5, the spring 152 exerts a
biasing force on the inertia mass 150 tending to move it from the
pocket 182. Fluid pressure above the inertia mass 150 causes the
check plate 190 to engage the standoff feet 192 located on the
upper surface of the inertia mass 150 restricting flow through the
ports 188. The height of the standoff feet 192 which the check
plate 190 rests on is typically 0.003'' to 0.008'' above the exit
surface of the passages 188 to provide an adequate level of flow
restriction upon upward movement of the inertia mass 150. Fluid may
be substantially prevented from flowing through the passages 188
and into the pocket 182, except for a small amount of bleed flow
between the checkplate 190 and the upper surface of the inertia
mass 150. However, the height of the standoff feet 192 may be
altered to influence the flow rate of the bleed flow and thereby
influence the timer feature of the inertia mass 150, as will be
described below.
[0111] Fluid also enters the pocket 182 through the annular
clearance, or primary fluid flow path, C (FIG. 6) between the
interior surface, or valve seat, of the pocket 182 and the exterior
surface of the inertia mass 150. Thus, the size of the clearance C
also influences the rate at which fluid may enter the pocket 182
thereby allowing the inertia mass 150 to move upward out of the
pocket 182.
[0112] Advantageously, with such a construction, once the inertia
mass 150 is moved into an open position within the pocket 182, it
remains open for a predetermined period of time in which it takes
fluid to refill the pocket behind the inertia mass 150 through the
clearance C. This is referred to as the "timer feature" of the
inertia valve assembly 138. Importantly, this period of time can be
independent of fluid flow direction within the shock absorber 38.
Thus, the shock absorber 38 may obtain the benefits of a reduced
compression damping rate throughout a series of compression and
rebound cycles, referred to above as "modal response." Desirably,
the inertia mass 150 remains in an open position for a period
between approximately 0.05 and 5 seconds, assuming no subsequent
activating accelerations are encountered. Preferably, the inertia
mass 150 remains in an open position for a period between about 0.1
and 2.5 seconds and more preferably for a period between about 0.2
and 1.5 seconds, again, assuming no subsequent accelerations are
encountered which would tend to open the inertia mass 150, thus
lengthening or resetting the timer period. The above values are
desirable for a rear shock absorber 38 for an off-road bicycle 20.
The recited values may vary in other applications, however, such as
when adapted for use in the front suspension fork 34 or for use in
other vehicles or non-vehicular applications.
[0113] In order to fully appreciate the advantages of the modal
response inertia valve assembly 138 of the present shock absorber
38, it is necessary to understand the operation of a bicycle having
an acceleration-sensitive damping system utilizing an inertia
valve. With reference to FIG. 8, the relationship between vertical
position P, vertical velocity V and vertical acceleration A, over
time T, for a simple mass traversing two sinusoidally-shaped bumps
is illustrated. FIG. 8 is based on a mass that travels horizontally
at a constant velocity, while tracking vertically with the terrain
contour. This physical model, somewhat simplified for clarity,
correctly represents the essential arrangement utilized in
inertia-valve shock absorbers wherein the inertial element is
shaft-mounted and spring-biased within the unsprung mass.
[0114] The primary simplification inherent in this model, and in
this analysis, is that the flexibility of an actual bicycle tire is
ignored. The tire is assumed to be inflexible in its interaction
with the terrain, offering no compliance. An actual tire, of
course, will provide some compliance, which in turn produces some
degree of influence on the position, velocity, and acceleration of
the unsprung mass. The actual degree of influence in a given
situation will depend on many variables, including the actual
vehicle speed and the specific bump geometry, as well as the
compliance parameters of the particular tire. However, the
simplified analysis discussed here is a good first approximation
which clearly illustrates the key operative physics principles,
while avoiding these complications. The basic validity of this
simplified analysis can be demonstrated by a sophisticated computer
motion analysis that incorporates the effects of tire compliance
and several other complicating factors.
[0115] Relating FIG. 8 to the situation of a bicycle, the heavy
solid line indicating position P represents both the trail surface
and, assuming the wheel of the bicycle is rigid and remains in
contact with the trail surface, the motion of any point on the
unsprung portion of the bicycle, such as the hub axis of the front
or rear wheel, for example. The lines representing velocity V and
acceleration A thus correspond to the vertical velocity and
acceleration of the hub axis. In FIG. 8, the trail surface (solid
line indicating position P) includes a first bump B1 and a second
bump B2. In this example, as shown, each bump is preceded by a
short section of smooth (flat) terrain.
[0116] As the wheel begins to traverse the first bump B1, the
acceleration A of the hub axis H rises sharply to a maximum value
and, accordingly, the velocity V of the hub axis H increases.
Mathematically, of course, the acceleration as shown is calculated
as the second derivative of the sinusoidal bump curve, and the
velocity as the first derivative. At a point P1, approximately
halfway up the first bump B1, the second derivative (acceleration
A) becomes negative (changes direction) and the velocity begins to
decrease from a maximum value. At a point P2, corresponding with
the peak of the bump B1, the acceleration A is at a minimum value
(i.e., large negative value) and the velocity V is at zero. At a
point P3, corresponding with the mid-point of the downside of the
first bump B1, the acceleration A has again changed direction and
the velocity V is at a minimum value (i.e., large negative value).
At a point P4, corresponding with the end of the first bump B1, the
acceleration A has risen again to a momentary maximum value and the
velocity V is zero. The second bump B2 is assumed to be
sinusoidally-shaped like the first bump B1, but, as shown, to have
somewhat greater amplitude. Thus, the relationship between position
P, velocity V and acceleration A are substantially identical to
those of the first bump B1.
[0117] When a simple inertia valve is utilized in the suspension
system of a bicycle and the acceleration A reaches a threshold
value, the inertia mass overcomes the biasing force of the spring
and begins moving relatively downward on the center shaft, which
moves upward. Once the shaft has moved upward relative to the
inertia mass a sufficient distance, the inertia valve passages are
uncovered and a reduced compression damping rate is achieved.
Although a compression inertia valve is discussed in this example,
the same principles may be applied to an inertia valve which
operates during rebound.
[0118] Before the inertia valve passages are open, the shock
absorber operates at its initial, firm damping rate. This results
in an undesirably firm damping rate, creating a "damping spike",
over the initial portion of the bump B1. The damping spike
continues until the shaft has moved upward relative to the inertia
mass a sufficient distance to open the valve passages. The amount
of movement of the shaft relative to the inertia mass necessary to
uncover the passages is determined primarily by the size of the
passages and the position of the uppermost surface of the inertia
mass relative to the passages when the mass is in its fully closed
position. This distance is referred to as the spike distance
S.sub.D. The amount of time necessary for the inertia passages to
be opened and to reduce the damping rate is dependent upon the
shape of the bump and the spike distance S.sub.D. and is referred
to as the spike time S.sub.T. The reduction of the damping rate is
at least partially dependent upon the size of the passages and,
therefore, it is difficult to reduce the spike time S.sub.T without
reducing the spike distance S.sub.D which necessarily affects the
achievable lowered damping rate.
[0119] The inertia mass begins to close (i.e., move relatively
upward) when the acceleration acting upon it either ceases, changes
direction, or becomes too small to overcome the biasing force of
the spring. As shown graphically in FIG. 8, the acceleration A
becomes zero at point P1, or at approximately the mid-point of the
bump B1. Accordingly, a simple inertia valve begins to close at, or
before, the middle of the bump BI. Therefore, utilizing a simple
inertia valve tends to return the shock absorber to its initial,
undesirably firm damping rate after only about one-half of the
up-portion of bump B1 has been traversed. The operating sequence of
the inertia valve is similar for the second bump B2 and each bump
thereafter.
[0120] In actual practice, the specific point on a bump where a
simple inertia valve will close will vary depending on bump
configuration, vehicle speed, inertia valve size and geometry,
spring bias force, compliance of the tire and other factors. Thus,
it should be understood that the extent of mid-bump "spiking"
produced by "premature closing" of a simple inertia valve will be
greater for some bumps and situations than for others.
[0121] It is desirable to extend the amount of time the inertia
valve stays open so that the reduced damping rate can be utilized
beyond the first half of the up-portion of the bump. More complex
inertia valve arrangements utilize the fluid flow during
compression or rebound motion to hydraulically support the inertia
valve in an open position once acceleration has ceased or
diminished below the level necessary for the inertia valve to
remain open from acceleration forces alone. However, these types of
inertia valve arrangements are dependent upon fluid flow and allow
the inertia valve to close when, or slightly before, the
compression or rebound motion ceases. A shock absorber using this
type of inertia valve in the compression circuit could experience a
reduced damping rate from after the initial spike until compression
motion ceases at, or near, the peak P2 of the bump B1. This would
represent an improvement over the simple inertia valve shock
absorber described previously. However, the flow dependent inertia
valve necessarily reacts to specific terrain conditions. That is,
the inertia mass responds to each individual surface condition and
generally must be reactivated upon encountering each bump that the
bicycle traverses. Therefore, this type of shock absorber
experiences an undesirably high damping rate "spike" as each new
bump is encountered.
[0122] In contrast, the inertia valve arrangement 138 of the
present shock absorber 38 is a modal response type. That is, the
inertia valve 138 differentiates rough terrain conditions from
smooth terrain conditions and alters the damping rate accordingly.
During smooth terrain conditions, the inertia valve 138 remains in
a closed position and the damping rate is desirably firm, thereby
inhibiting suspension motion due to the movement of the rider of
the bicycle 20. When the first bump B1 is encountered, the inertia
valve 138 opens to advantageously lower the damping rate so that
the bump may be absorbed by the shock absorber 38. The timer
feature retains the inertia valve 138 in an open position for a
predetermined period of time thereby allowing the shock absorber 38
to maintain the lowered damping rate for the entire bump (not just
the first half of the up-portion), and to furthermore absorb the
second bump B2 and subsequent bumps possibly without incurring any
additional "spikes." Thus, in the preferred embodiment of the
present shock absorber 38, the timer feature is configured to delay
the inertia mass 150 from closing until a period of time after
completion of both the compression stroke and rebound stroke and,
preferably, until after the beginning of the second compression
stroke resulting from an adjacent bump. As discussed above, the
timer period may be adjustable by altering the rate at which fluid
may refill the timer pocket 182.
[0123] Once the shock absorber 38 has been compressed, either by
fluid flow through the blowoff valve 140 or the inertia valve 138,
the spring force generated by the combination of the positive air
chamber 86 and the negative air chamber 88 tend to bias the shock
body 42 away from the air sleeve 40. In order for the shock
absorber 38 to rebound, a volume of fluid equal to the displaced
volume of the shock shaft 70 must be drawn from the reservoir 128
and into the compression chamber 96. Fluid flow is allowed in this
direction through the refill ports 176 in the blowoff valve 140
against a desirably light resistance offered by the refill shim
stack 180. Gas pressure within the gas chamber 130 exerting a force
on the floating piston 124 may assist in this refill flow. Thus,
the rebound damping rate is determined primarily by fluid flow
through the rebound passages 108 against the biasing force of the
rebound shim stack 110.
[0124] With reference to FIGS. 3b and 5, the fluid flow path during
compression or rebound motion of the shock absorber 38, with the
inertia mass 150 in either of an open or closed position, is above
and away from the inertia mass 150 itself Advantageously, such an
arrangement substantially isolates fluid flow from coming into
contact with the inertia mass 150, thereby inhibiting undesired
movement of the inertia mass due to drag forces resulting from
fluid flow. Thus, the inertia mass 150 advantageously responds to
acceleration inputs and is substantially unaffected by the movement
of hydraulic fluid during compression or rebound of the shock
absorber 38.
[0125] The present shock absorber 38 includes an inertia valve 138
comprising a self-centering valve body, or inertia mass 150. In
order to fully appreciate the advantages of the self-centering
inertia mass 150 of the present inertia valve assembly 138, it is
necessary to describe the conditions which have prevented prior
inertia valve designs from operating reliably, with acceptable
sensitivity, and for a reasonable cost.
[0126] Each of FIGS. 9 and 10 schematically illustrate an
off-center condition of the inertia mass 150 relative to the shaft
134. The off-center condition of the inertia mass 150 may cause it
to contact the shaft 134 causing friction, which tends to impede
motion of the inertia mass 150 on the shaft 134. Due to the
relatively small mass of the inertia mass 150 and the desirability
of having the inertia mass 150 respond to small accelerations, any
friction between the inertia mass 150 and the shaft 134 seriously
impairs the performance of the inertia valve 138 and may render it
entirely inoperable. Each of the off-center conditions illustrated
in FIGS. 8 and 9 may result from typical manufacturing processes.
However, modifying the manufacturing process to avoid these
conditions often results in a prohibitively high manufacturing
cost.
[0127] FIG. 9 illustrates an inertia valve arrangement in which the
inertia valve passages 148 are of slightly different diameter. Such
a condition is often an unavoidable result of the typical
manufacturing process of drilling in a radial direction through a
tubular piece of material. Such a process may result in an entry
diameter N created by the drilling tool being slightly larger than
the exit diameter X created by the drilling tool. The resulting
difference in area between the passages 148 causes the fluid
pressure within the shaft passage 136 to exert an unequal force
between the entry passage 148 having an entry diameter N and the
exit passage 148 having an exit diameter X.
[0128] For example, a difference between the entry diameter N and
the exit diameter X of only two thousandths of an inch (0.090''
exit diameter versus 0.092'' entry diameter) at a fluid pressure of
800 psi, results in a force differential of approximately 0.2
pounds, or 3.6 ounces, between the passages 148. The inertia mass
150 itself may weigh only about one half of an ounce (0.5 oz.).
Such a force differential will push the inertia mass 150 off-center
and reduce the responsiveness of the inertia mass 150, if not
prevent it from moving entirely.
[0129] FIG. 10 illustrates an off-center condition of the inertia
mass 150 caused by the inertia valve passages 148 being positioned
off-center relative to the shaft 134. A center axis AC of the
inertia valve passages 148 is offset from the desired diametrical
axis AD of the shaft 134 by a distance O. Therefore, the force
resulting from fluid pressure within the shaft passage 136 does not
act precisely on a diametrical axis AD of the inertia mass 150,
resulting in the inertia mass 150 being pushed off-center with
respect to, and likely contacting, the shaft 134. The offset
condition of the center axis AC of the passages 148 is the result
of inherent manufacturing imperfections and cannot easily be
entirely avoided, at least without raising the cost of
manufacturing to an unfeasible level.
[0130] Furthermore, even if manufacturing costs were not of concern
and the passages 148 could be made with identical diameters and be
positioned exactly along the diametrical axis AD of the shaft 134,
additional forces may tend to push the inertia mass 150 off-center.
For example, if the reservoir 44 experiences an acceleration which
is not exactly aligned with the axis of travel of the inertia mass
150 (such as braking or forward acceleration), the transverse
component of the acceleration would create a force tending to move
the inertia mass 150 off-center and against the shaft 134. If the
transverse component of the acceleration is large enough, the
resulting frictional force between the inertia mass 150 and the
reservoir shaft 134 will inhibit, or prevent, movement of the
inertia mass 150. Accordingly, it is highly desirable to compensate
for factors which tend to push the inertia mass 150 off-center in
order to ensure responsive action of the inertia valve 138. This is
especially important in off-road bicycle applications, where it is
desirable for the inertia valve assembly 138 to respond to
relatively small accelerations and the mass of the inertia mass 150
is also relatively small.
[0131] As described above, the inertia valve assembly 138
preferably includes a self-centering inertia mass 150. With
reference to FIG. 11, the inertia mass 150 of FIG. 5 is shown
without the fluid flow lines to more clearly depict the
cross-sectional shape of its interior surface. The inertia mass 150
has a minimum internal diameter "D" while the shaft 134 has a
constant external diameter "d," which is smaller than the internal
diameter D. The difference between the shaft diameter d and the
inertia valve diameter D is desirably small. Otherwise, as
described above, the bleed flow between the shaft 134 and the
inertia mass 150 undesirably reduces the damping rate which may be
achieved when the inertia mass 150 is in a closed position.
Accordingly, for the rear shock 38 the difference between the shaft
diameter d and the inertia mass diameter D is desirably less than
0.01 inches. Preferably, difference between the shaft diameter d
and the inertia mass diameter D is less than 0.004 inches and more
preferably is approximately 0.002 inches. For the front suspension
fork 34, the difference between the shaft diameter d and the
inertia mass diameter D is desirably less than 0.02 inches.
Preferably, difference between the shaft diameter d and the inertia
mass diameter D is less than 0.008 inches and more preferably is
approximately 0.004 inches. The recited values may vary in other
applications, however, such as when adapted for vehicles other than
off-road bicycles or non-vehicular applications.
[0132] The preferred differences between the shaft diameter d and
the inertia mass diameter D recited above assume that a labyrinth
seal arrangement 206 (FIG. 7) is provided at the upper and lower
portions of the internal surface of the inertia mass 150, as
described above. However, the bleed rate may be influenced by
factors other than the difference between the shaft diameter d and
the inertia mass diameter D. Accordingly, driven by a pressure
differential of 400 psi, the bleed rate between the inertia mass
150 and the shaft 134, for an off-road bicycle shock with a shaft
diameter of 5/8 inches, is desirably less than 1.0 cubic
inches/sec. Preferably, the bleed rate between the inertia mass 150
and the shaft 134 is less than 0.5 cubic inches/sec and more
preferably is less than 0.3 cubic inches/sec. However, for
applications other than off-road bicycle shock absorbers, the
preferred bleed rates may vary.
[0133] As described, an annular recess 196 is defined between the
interior surface of the inertia mass 150 and the shaft 134. The
annular recess 196 is preferably located in approximately the
center of the inertia mass 150. The annular recess 196 is referred
to as zone 1 (Z.sub.1) in the following description of the fluid
flow between the shaft 134 and the self-centering inertia mass 150.
The upper annular clearance 198, above the annular recess 196, is
referred to as zone 2 (Z.sub.2) and the upper exit clearance 202 is
referred to as zone 3 (Z.sub.3). One half of the difference between
the diameter of the upper annular clearance 198 and the diameter D
at the upper exit clearance 202 defines a distance B, which is
equivalent to the size of the step 205. The size B of the step 205
(referred to as a "Bernoulli Step" in FIGS. 26, 27 and 28) may be
precisely manufactured by a computer controlled lathe operation,
for example. Other suitable methods for creating a precisely sized
step 205 may also be used. Thus, in the illustrated arrangement,
the outer surface of the shaft 134 defines a first surface and the
interior surface of the inertia mass 150 defines a second surface
which faces the first surface. Preferably, a first annular passage
is defined by the upper annular clearance 198 and the upper exit
clearance 202. A first portion of the first annular passage is
defined by the upper exit clearance 202 and a second portion of the
first annular passage is defined by the upper annular clearance
198. Thus, in the illustrated embodiment, the first and second
portions define first and second cross-sectional flow areas of the
first annular passage. Preferably, a second annular passage is
defined by the lower annular clearance 200 and the lower exit
clearance 204. A first portion of the second annular passage is
defined by the lower exit clearance 204 and a second portion of the
second annular passage is defined by the lower annular clearance
200. Thus, in the illustrated embodiment, the first and second
portions of the second annular passage also define first and second
cross-sectional flow areas of the second annular passage.
[0134] Zone 1 Z.sub.1 has a larger cross-sectional fluid flow area
than zone 2 Z.sub.2 which, in turn, has a larger cross-sectional
flow area than zone 3 Z.sub.3. The cross-sectional area
differential between the zones Z.sub.1, Z.sub.2, Z.sub.3 causes the
fluid within each zone Z.sub.1, Z.sub.2, Z.sub.3 to vary in
velocity, which causes a self-centering force to be exerted on the
inertia mass 150 when it becomes off-center, as will be described
below. Although the zones Z.sub.1, Z.sub.2, Z.sub.3 are annular,
the discussion below, for simplicity, is in the context of a
two-dimensional structure having left and right sides. Accordingly,
the zones Z.sub.1, Z.sub.2, Z.sub.3 of the example will vary in
cross-sectional distance, rather than in cross-sectional area.
Although the example is simplified, it correctly describes the
general self-centering action of the inertia mass 150.
[0135] A rough approximation of the centering force developed by
the self-centering inertia mass 150 can be estimated using
Bernoulli's equation. This is a rough approximation only since
Bernoulli's equation assumes perfect frictionless flow, which is
not valid for real fluids. However, this is a useful starting point
for understanding the general principles involved, and for
estimating the forces that occur. Bernoulli's equation expresses
the law of conservation of energy for the flow of an incompressible
fluid. In estimating the centering force of the inertia mass 150,
the potential energy height) portion of Bernoulli's equation is not
significant and may be ignored. Thus, for any two arbitrary points
on a fluid streamline, Bernoulli's equation reduces to:
P.sub.1+(.rho./2g)(V.sub.1).sup.2=P.sub.2+(.rho./2g)(V.sub.2).sup.2
where:
[0136] P.sub.1--fluid pressure (psi) at point 1
[0137] P.sub.2=fluid pressure (psi) at point 2
[0138] V.sub.1=fluid velocity (in/sec) at point 1
[0139] V.sub.2=fluid velocity (in/sec) at point 2
[0140] .rho.=fluid density
[0141] g=gravity constant
[0142] Using the values of 0.03125 lb/in.sup.3 for fluid density
.rho. of typical hydraulic fluid and 386 in/sec.sup.2 for gravity
constant g, the equation becomes:
P.sub.1+(4.05.times.10.sup.-5)(V.sub.1).sup.2=P.sub.2+(4.05.times.10.sup.-
-5)(V.sub.2).sup.2
[0143] For a simple example, assume that the fluid pressure P.sub.1
in zone 1 is 400 psi, due to an external force tending to compress
the shock absorber 38 and the fluid velocity V.sub.1 is zero due to
relatively little fluid exiting from zone 1. Also, for simplicity,
assume that the floating piston 124 is absent or is not exerting a
significant pressure on the fluid within the reservoir chamber 128.
Accordingly, the fluid pressure P.sub.3 in zone 3 Z.sub.3 is 0 psi.
Insert these values into Bernoulli's equation to find the velocity
in zone 3:
400+(4.05.times.10.sup.-5)(0).sup.2=0+(4.05.times.10.sup.-5)(V.sub.3).sup-
.2 V.sub.3=3,142 in/sec
[0144] Therefore, as a first approximation (accurate to the degree
that the assumptions Bernoulli's equation are based upon are valid
here) the velocity V.sub.3 of fluid exiting zone 3 is 3,142 in/sec.
Assuming the validity of assumptions inherent in Bernoulli's
equation here, this value is true for all exit points of zone 3
Z.sub.3 regardless of their dimensions. Further, based on flow
continuity, the change in velocity of the fluid between zone 2
Z.sub.2 and zone 3 Z.sub.3 is proportional to the change in the
clearance, or gap G, between zone 2 Z.sub.2 and zone 3 Z.sub.3. The
gap G is the cross-sectional distance between the outer surface of
the shaft 134 and the relevant inner surface of the inertia mass
150.
[0145] The relationship between the change in the size of the gap G
and the change in velocity allows solving of the velocity in zone 2
Z.sub.2 for both the right and left sides. Assuming that D is 0.379
inches, d is 0.375 inches and B is 0.001 inches, then the gaps on
both the right and left sides, with the inertia mass 150 centered
are: GAP Zone 2=B+(D-d)/2=0.003 GAP Zone 3=(D-d)/2=0.002
[0146] Then, based on flow continuity, fluid velocity in Zone 2 is
calculated as follows: V.sub.3[Gap Zone 3/Gap Zone 2]=V.sub.2=2,094
in/sec
[0147] Therefore, the fluid velocity V.sub.2 in zone 2 Z.sub.2 for
each of the right and left side is 2,094 in/sec. Using Bernoulli's
equation to find the pressure P.sub.2 in zone two gives:
400+(4.05.times.10.sup.-5)(0).sup.2=(P.sub.2)+(4.05.times.10.sup.-5)(2,09-
4).sup.2 P.sub.2=222 psi
[0148] Assuming that, for a particular inertia valve, the area in
zone 2 Z.sub.2 that the fluid pressure acts upon for each of the
right and left side is 0.0375 in.sup.2, then the force F at both
the left and right sides of the inertia mass 150 can be calculated
as: F=222 psi(0.0375 in.sup.2)=8.3 lbs.
[0149] The force F acting on the inertia mass 150 in the above
example is equal for the right and left side due to the velocity
V.sub.2 in zone 2 Z.sub.2 being the same for each side. The
velocity V.sub.2 is the same because the ratio of gap 3 G.sub.3 to
gap 2 G.sub.2 between the right side and the left side is equal due
to the inertia mass 150 being centered relative to the shaft
134.
[0150] With reference to FIG. 12, however, if the inertia mass 150
becomes off center relative to the shaft 134 by a distance x, for
example 0.001 inches to the left, the ratio of gap 3 G.sub.3 to gap
2 G.sub.2 is different between the right and left sides. This
results in the velocity V.sub.2 being different between the right
and left sides and, as a result, a force differential between the
right side and left side is produced. These calculations are
substantially similar to the previous calculations and are provided
below (for an off-center condition 0.001 inches to the left:
V.sub.3=3,142 in/sec Left Side: GAP Zone
3(G.sub.3L)=(D-d)/2+x=0.003 GAP Zone 2(G.sub.2L)=B+(D-d)/2+x=0.004
V.sub.3[Gap Zone 3/Gap Zone 2]=V.sub.2=2,356.5 in/sec P.sub.2=175
psi F=(175)(0.0375)=6.55 lbs. Right Side: GAP Zone
3(G.sub.3R)=(D-d)/2-x=0.001 GAP Zone 2(G.sub.2R)=B+(D-d)/2-x=0.002
V.sub.3[Gap Zone 3/Gap Zone 2]=V.sub.2=1571 in/sec P.sub.2=300 psi
F=(300)(0.0375)=11.25 lbs. F.sub.right-F.sub.left=4.7 lbs. pushing
right
[0151] As shown, a force differential of as much as 4.7 lbs,
depending on the degree of validity of the Bernoulli assumption,
pushes the inertia mass 150 to the right to correct for the
off-center condition. As noted above, preferably the lower portion
of the inertia mass 150 also includes a step 205 creating a lower
zone 2 and zone 3 (FIG. 12). Accordingly, a centering force acts on
the lower portion of the inertia mass 150 when it is off-center
from the shaft 134. Therefore, in the example above, a force of as
much as 4.7 lbs also acts on the lower portion of the inertia mass
150, resulting in a total centering force of as much as 9.4 lbs
acting to center the inertia mass 150 relative to the shaft
134.
[0152] For a typical off-road bicycle application, with the
inertial mass centered, the ratio of the velocity in zone 2 V.sub.2
to the velocity in zone 3 V.sub.3 (i.e., V.sub.2/V.sub.3) is
desirably between 0.9 and 0.2. Preferably, the ratio of the
velocity in zone 2 V.sub.2 to the velocity in zone 3 V.sub.3 is
desirably between 0.8 and 0.35 and more preferably the ratio of the
velocity in zone 2 V.sub.2 to the velocity in zone 3 V.sub.3 is
desirably between 0.75 and 0.5.
[0153] The ratio of the gap G between the shaft 134 and the inertia
mass 150 in zone 3 Z.sub.3 and in zone 2. Z.sub.2 (i.e.,
G.sub.3/G.sub.2), as demonstrated by the calculations above,
influences the magnitude of the self-centering force produced by
the inertia mass 150. The ratio (G.sub.3/G.sub.2) is desirably less
than one. If the ratio (G.sub.3/G 2) is equal to one, then by
definition there is no step 205 between zone 2 Z.sub.2 and zone 3
Z.sub.3.
[0154] Based on flow continuity from Zone 2 to Zone 3, the ratio of
the velocity V.sub.2 in Zone 2 to the velocity V.sub.3 in Zone 3
(V.sub.2N.sub.3) is equal to the ratio of the Gap G.sub.3 at Zone 3
to the Gap G.sub.2 at Zone 2 (G.sub.3/G.sub.2). In other words,
based on flow continuity it follows that:
(G.sub.3/G.sub.2)=(V.sub.2/V.sub.3).
[0155] Thus, for a typical off-road bicycle application with the
inertia mass centered, the ratio of the gap at Zone 3 to the gap at
Zone 2 is desirable between 0.90 and 0.20. Preferably the ratio of
the gap at Zone 3 to the gap at Zone 2 is desirably between 0.80
and 0.35 and more preferably the ratio of the gap at Zone 3 to the
gap at Zone 2 is desirably between 0.75 and 0.50.
[0156] Advantageously, the self-centering inertia mass 150 is able
to compensate for force differentials due to the manufacturing
variations in the passage 148 size and position as well as
transverse accelerations, all of which tend to push the inertia
mass 150 off-center. This allows reliable, sensitive operation of
the inertia valve assembly 140 while also permitting cost-effective
manufacturing methods to be employed without compromising
performance.
[0157] Although a fluid pressure in zone 1 Z.sub.1 of 400 psi was
used in the above example, the actual pressure may vary depending
on the force exerted on the shock assembly 38. The upper pressure
limit in zone 1 Z.sub.1 is typically determined by the
predetermined blow off pressure of the blow off valve 140.
Desirably, for an off-road bicycle rear shock with a shaft diameter
of 5/8 inches, the predetermined blow off pressure is approximately
400 psi. Preferably, the predetermined blow off pressure within
zone 1 Z.sub.1 is approximately 600 psi and more preferably is
approximately 800 psi. These predetermined blow off pressures are
provided in the context of an off-road bicycle rear shock
application and may vary for other applications or vehicle
types.
[0158] FIG. 13 illustrates an alternative arrangement for
controlling the refill rate, or timer function, of fluid flow into
the pocket 182 as the inertia mass 150 moves in an upward direction
away from its closed position. The end cap 132 includes a channel
208 communicating with an orifice 209 connecting the reservoir
chamber 128 and the pocket 182. The orifice 209 permits fluid to
flow between the reservoir chamber 128 and the pocket 182 in
addition to the fluid flow through the clearance C and bleed flow
between the check plate 190 and inertia mass 150. The size of the
orifice 209 may be varied to influence the overall rate of fluid
flow into the pocket 182.
[0159] FIG. 13 also illustrates an adjustable pocket refill
arrangement 210. The adjustable refill arrangement 210 allows
external adjustment of the refill rate of fluid flow into the
pocket 182. The adjustable refill arrangement includes an inlet
channel 212 connecting the reservoir chamber 128 to a valve seat
chamber 213. An outlet channel 214 connects the valve seat chamber
213 to the pocket 182.
[0160] A needle 215 is positioned within the valve seat chamber 213
and includes a tapered end portion 216, which extends into the
outlet channel 214 to restrict the flow of fluid therethrough.
External threads of the needle 215 engage internal threads of the
end cap 132 to allow the needle 215 to move relative to the outlet
channel 216. The needle 215 includes a seal 217, preferably an
O-ring, which creates a fluid tight seal between the needle 215 and
the end cap 132. The exposed end of the needle 215 includes a
hex-shaped cavity 218 for receiving a hex key to allow the needle
215 to be rotated. The exposed end of the needle 215 may
alternatively include other suitable arrangements that permit the
needle 215 to be rotated by a suitable tool, or by hand. For
example, an adjustment knob may be connected to the needle 215 to
allow a user to easily rotate the needle without the use of
tools.
[0161] Rotation of the needle 215 results in corresponding
translation of the needle 215 with respect to the end cap 132 (due
to the threaded connection therebetween) and adjusts the position
of the tapered end 216 relative to the outlet channel 214. If the
needle 215 is moved inward, the tapered end 216 blocks a larger
portion of the outlet channel 214 and slows the fluid flow rate
into the pocket 182. If the needle 215 is moved outward, the
tapered end 216 reduces its blockage of the outlet channel 214 and
speeds the fluid flow rate into the pocket 182. This permits user
adjustment of the refill rate of the pocket 182 and, accordingly,
adjustment of the period of time the inertia mass 150 is held in an
open position. Advantageously, the adjustable refill arrangement
210 allows a user to alter the period of time the inertia valve 138
is open and thus, the period of lowered compression damping once
the inertia valve 138 is opened.
[0162] FIG. 14 illustrates the suspension fork 34 detached from the
bicycle 20 of FIG. 1. The suspension fork 34 includes right and
left legs 220, 222, as referenced by a person in a riding position
on the bicycle 20. The right leg 220 includes a right upper tube
224 telescoping received in a right lower tube 226. Similarly, the
left leg 222 includes a left upper tube 228 telescopingly received
in a left lower tube 230. A crown 232 connects the right upper tube
224 to the left upper tube 228 thereby connecting the right leg 220
to the left leg 222 of the suspension fork 34. In addition, the
crown 232 supports a steerer tube 234, which passes through, and is
rotatably supported by the frame 22 of the bicycle 20. The steerer
tube 234 provides a means for connection of the handlebar assembly
36 to the suspension fork 34, as illustrated in FIG. 1.
[0163] Each of the right lower tube 226 and the left lower tube 230
includes a dropout 236 for connecting the front wheel 28 to the
fork 34. An arch 238 connects the right lower tube 226 and the left
lower tube 230 to provide strength and minimize twisting of the
tubes 226, 230. Preferably, the right lower tube 226, left lower
tube 230, and the arch 238 are formed as a unitary piece, however,
the tubes 226, 230 and the arch 238 may be separate pieces and
connected by a suitable fastening method.
[0164] The suspension fork 34 also includes a pair of rim brake
bosses 240 to which a standard rim brake assembly may be mounted.
In addition, the fork 34 may include a pair of disc brake bosses
(not shown) to which a disc brake may be mounted. Of course, the
suspension fork 34 may include only one or the other of the rim
brake bosses 240 and disc brake bosses, depending on the type of
brake systems desired.
[0165] FIG. 15 is a cross-section view of the right leg 220 of the
suspension fork 34 having the front portion cutaway to illustrate
the internal components of a damping assembly 244 of the fork 34.
Preferably, the left leg 222 of the suspension fork 34 houses any
of a known suitable suspension spring assembly. For example, an air
spring or coil spring arrangement may be used. In addition, a
portion of the suspension spring assembly may be housed within the
right fork leg 220 along with the damper assembly 244.
[0166] As described previously, the upper tube 224 is capable of
telescopic motion relative to the lower tube 226. The fork leg 220
includes an upper bushing 246 and a lower bushing 248 positioned
between the upper tube 224 and the lower tube 226. The bushings
246, 248 inhibit wear of the upper tube 224 and the lower tube 226
by preventing direct contact between the tubes 224, 226.
Preferably, the bushings 246, 248 are affixed to the lower tube 226
and are made from a self-lubricating and wear-resistant material,
as is known in the art. However, the bushings 246, 248 may be
similarly affixed to the upper tube 224. Preferably, the bushings
246, 248 include grooves (not shown) that allow a small amount of
hydraulic fluid to pass between the bushings 246, 248 and the upper
fork tube 224 to permit lubrication of the bushing 246 and seal,
described below.
[0167] The lower tube 226 has a closed lower end and an open upper
end. The upper tube 224 is received into the lower tube 226 through
its open upper end. A seal 250 is provided at the location where
the upper 224 enters the open end of the lower tube 226 and is
preferably supported by the lower tube 226 and in sealing
engagement with the upper tube 224 to substantially prevent oil
from exiting, or a foreign material from entering the fork leg
220.
[0168] The damping assembly 244 is operable to provide a damping
force in both compression and a rebound direction to slow both
compression and rebound motion of the fork 34. The damper assembly
244 is preferably an open bath, cartridge-type damper assembly
having a cartridge tube 252 fixed with respect to the closed end of
the lower tube 226 and extending vertically upward. A damper shaft
254 extends vertically downward from a closed upper end of the
upper tube 224 and supports a piston 258. Thus, the piston 258 is
fixed for movement with the upper tube 224 while the cartridge tube
252 is fixed for movement with the lower tube 226.
[0169] The piston 258 is positioned within the cartridge tube 252
and is in telescoping engagement with the inner surface of the
cartridge tube 252. A cartridge tube cap 260 closes the upper end
of the cartridge tube 252 and is sealing engagement with the damper
shaft 254. Thus, the cartridge tube 252 defines a substantially
sealed internal chamber which contains the piston 258.
[0170] The piston 258 divides the internal chamber of the cartridge
tube 252 into a variable volume rebound chamber 262 and a variable
volume compression chamber 264. The rebound chamber 262 is
positioned above the piston 258 and the compression chamber 264 is
positioned below the piston 258. A reservoir 266 is defined between
the outer surface of the cartridge tube 252 and the inner surfaces
of the upper and lower tubes 224, 226. A base valve assembly 268 is
operably positioned between the compression chamber 264 and the
reservoir 266 and allows selective communication therebetween.
[0171] FIG. 16 is an enlarged cross section of the damping assembly
244. As described above, a cartridge tube cap 260 closes the upper
end of the cartridge tube 252. An outer seal 270 creates a seal
between the cartridge tube cap 260 and the cartridge tube 252 while
an inner seal 272 creates a seal between the cartridge tube cap 260
and the damper shaft 254. Accordingly, extension and retraction of
the damper shaft 254 with respect to the cartridge tube 252 is
permitted while maintaining the rebound chamber 262 in a
substantially sealed condition.
[0172] The cartridge cap 260 includes a one-way refill valve 274
which, during inward motion of the damper shaft 254 with respect to
the cartridge tube 252, allows fluid flow from the reservoir 266
into the rebound chamber 262. The refill valve 274 comprises one or
more axial passages 276 through the cap 260 which are closed at
their lower end by refill shim stack 278. Thus, the shim stack 278
allows fluid flow from the reservoir 266 to the rebound chamber 262
with a relatively small amount of resistance. When the fluid
pressure in the rebound chamber 262 is greater than the fluid
pressure in the reservoir 266, such as during retraction of the
damper shaft 254, the refill shim stack 278 engages the lower
surface of the cartridge tube cap 260 to substantially seal the
refill passages 276 and prevent fluid from flowing
therethrough.
[0173] The piston 258 is fixed to the end of the damper shaft 254
by a threaded fastener 280. The piston includes an outer seal 282
which engages the inner surface of the cartridge tube 252 to
provide a sealing engagement between the piston 258 and the inner
surface of the cartridge tube 252. Thus, fluid flow around the
piston is substantially eliminated.
[0174] The piston 258 includes a one-way rebound valve assembly 284
which permits fluid flow from the rebound chamber 262 to the
compression chamber 264 while preventing flow from the compression
chamber 264 to the rebound chamber 262. The rebound valve assembly
284 comprises one or more axial passages 286 through the piston 258
closed at their lower end by a rebound shim stack 288. Fluid is
able to flow from the rebound chamber 262 through the passages 286
and into the compression chamber 264 against the resistance offered
by the shim stack 288. When the pressure is greater in the
compression chamber 264 than in the rebound chamber 262, the shim
stack 288 engages the lower surface of the piston 258 to
substantially seal the passages 286 and prevent the flow of fluid
therethrough.
[0175] In the illustrated embodiment, the cartridge tube 252 is
split into an upper portion 290 and a lower portion 292, which are
each threadably engaged with a connector 294 to form the cartridge
tube 252. Optionally, a one-piece cartridge tube may be employed. A
base member 296 is fixed to the closed end of the lower tube 226
and supports the cartridge 252. The lower portion 292 of the
cartridge tube 252 is threadably engaged with the base member
296.
[0176] FIG. 17 is an enlarged cross-sectional view of the base
valve assembly 268. The base valve assembly 268 is housed within
the lower portion 292 of the cartridge tube 252 and is supported by
a shaft 298 which extends in an upward direction from the base
member 296. The entire base valve assembly 268 is secured onto the
shaft 298 by a bolt 300 which threadably engages the upper end of
the shaft 298.
[0177] The base valve assembly 268 includes a compression valve
302, a blowoff valve 304, and an inertia valve 306. The compression
valve 302 is positioned on the upper portion of the shaft 298. The
blowoff valve 304 is positioned below the compression valve 302 and
spaced therefrom. The compression valve 302 and the blowoff valve
304 define a blowoff chamber 308 therebetween. A plurality of
passages 310 connect the blowoff chamber 308 to a central passage
312 of the base valve shaft 298.
[0178] A snap ring 314, which is held in an annular recess of the
shaft 298, supports the compression valve 302. A washer 316
positioned underneath the bolt 300 holds the compression valve 302
onto the shaft 298. The compression valve 302 includes a
compression piston 318 sealingly engaged with the inner surface of
the lower portion 292 of the cartridge tube 252 by a seal 320. The
compression piston 318 is spaced from both the snap ring 314 and
the washer 316 by a pair of spacers 322, 324 respectively.
[0179] The compression piston 318 includes one or more compression
passages 326 covered by a compression shim stack 328. The
compression shim stack 328 is secured to the lower surface of the
compression piston 318 by the lower spacer 322. The compression
shim stack 328 deflects about the lower spacer 322 to selectively
open the compression passages 326. The compression shim stack 328
seals against the lower surface of the compression piston 318 to
prevent unrestricted compression flow past the compression shim
stack 328.
[0180] As illustrated in FIGS. 20 and 21, which show fluid flows
during the rebound stroke, the compression piston 318 also includes
one or more refill passages 330 extending axially through the
compression piston 318. The refill passages 330 are covered at the
upper surface of the compression piston 318 by a refill shim stack
332. The refill shim stack 332 is held against the upper surface of
the compression piston 318 by the upper spacer 324 and deflects to
open the refill passages 330. Thus, the refill shims 332 prevent
fluid flow through the refill passages from the compression chamber
264 to the blowoff chamber 308, but permit fluid flow from the
blowoff chamber 308 through the refill passages 330 and into the
compression chamber 264 against the slight resistance offered by
the refill shim stack 332.
[0181] As illustrated in FIG. 17, the blowoff valve 304 is
positioned between a lower snap ring 334 and an upper snap ring
336. A separator plate 338 is supported by the lower snap ring 334
and is sealingly engaged with the inner surface of the lower
portion 292 of the cartridge tube 252 by a seal 340. A lower spacer
342 spaces the blowoff piston 344 in an upward direction from the
separator plate 338. The blowoff piston 344 is also sealingly
engaged with the inner surface of the lower portion 292 of the
cartridge tube 252 by a seal 346. An upper spacer 348 spaces the
blowoff piston 344 from the upper snap ring 336. A separator
chamber 350 is defined between the blowoff piston 344 and the
separator plate 338.
[0182] As illustrated in FIGS. 20 and 21, the blowoff piston 344
includes one or more blowoff passages 352 covered on the lower
surface of the blowoff piston 344 by a blowoff shim stack 354. The
blowoff shim stack 354 is positioned between the blowoff piston 344
and the lower spacer 342 to allow fluid flow from the blowoff
chamber 308 into the separator chamber 350 at pressures above a
predetermined threshold. The blowoff shim stack 354 seals passages
352 to prevent unrestricted (without blowoff) compression fluid
flow from the blowoff chamber 308 to the separator chamber 350.
[0183] The blowoff piston 344 also includes one or more refill
passages 356 covered at the upper surface of the blowoff piston 344
by a refill shim stack 358. The refill shim stack 358 is held
against the upper surface of the blowoff piston 344 by the upper
spacer 348 to seal the refill passages 356 and prevent fluid flow
from the blowoff chamber 308 into the separator chamber 350.
However, the refill shims deflect about the upper spacer 348 to
allow fluid flow from the separator chamber 350 into the blowoff
chamber 308 through the refill passages 356 with relatively little
resistance. One or more passages 360 are formed within the lower
portion 292 of the cartridge tube 252 at a height between the
separator plate 338 and the blowoff piston 344 to allow fluid
communication between the separator chamber 350 and the reservoir
266.
[0184] Preferably, the inertia valve 306 is substantially identical
to the inertia valve previously described in relation to the shock
absorber 38. The inertia valve 306 includes an inertia mass 362
movable between a closed position, where the inertia mass 362
closes two or more passages 364, and an open position, where the
inertia mass 362 uncovers the two or more passages 364. The
uppermost or closed position of the inertia mass 362 is defined by
the snap ring 334, which supports the separator plate 338.
[0185] The inertia mass 362 is biased into its closed position by a
spring 366. The lowermost or open position of the inertia mass 362
is defined when the lower surface of the inertia mass 362 engages
the lower interior surface of a pocket 368, defined by the base
member 296. The inertia mass 362 includes one or more axial
passages 370 covered at the upper surface of the inertia mass 362
by a check plate 372 which is movable between a substantially
closed position against the standoff feet 394 at the upper surface
of the inertia mass 362 and an open position against the stop
projections 392 on the upper, necked portion of the inertia mass
362.
[0186] The check plate 372 moves into an open position when the
inertia mass 362 moves downward in relation to the base valve shaft
298 to allow fluid to flow from the pocket 368 into an inertia
valve chamber 376 above the inertia mass 362 through the passages
370. The check plate 372 moves into a substantially closed position
upon upward movement of the inertia mass 362 relative to the base
valve shaft 298 to restrict fluid flow through the passages 370.
One or more passages 378 are defined by the lower portion 292 of
the cartridge tube 252 to allow fluid communication between the
inertia valve chamber 376 and the reservoir 266.
[0187] An annular clearance C is defined between the inertia mass
362 and the pocket 368 when the inertia mass 362 is in its open
position. In a similar manner to the inertia valve described in
relation to the shock absorber 38, the clearance C restricts fluid
flow from the inertia valve chamber 376 into the pocket 368. The
inertia valve 306 preferably includes other features described in
relation to the inertia valve of the shock absorber 38. For
example, the inertia mass 362 preferably includes a plurality of
standoff feet 394 at the locations discussed above in relation to
the inertia mass of the shock absorber 38. Additionally, the
inertia mass 362 includes an annular recess 380 aligned with the
passages 364 when the inertia mass 362 is in its closed position.
The inertia mass 362 also includes a step preferably on each end of
the interior surface of the inertia mass 362 which is sliding
engagement with the base valve shaft 298, as described above. As
shown, the inertia mass 362 also includes a labyrinth seal
arrangement substantially as described above.
[0188] When the front wheel 28 of the bicycle 20 of FIG. 1
encounters a bump, a force is exerted on the fork 34, which tends
to compress the fork legs 224, 226 in relation to each other. If
the upward acceleration of the lower fork tube 226 along its
longitudinal axis (i.e., the axis of travel of the inertia mass
362) is below a predetermined threshold, the inertia mass 362
remains in its closed position. Pressure within the compression
chamber 264 causes fluid to flow through the compression passages
326 and into the blowoff chamber 308. If the pressure within the
blowoff chamber 308 is below a predetermined threshold, the blowoff
shims 354 remain closed and the suspension fork 34 remains
substantially rigid.
[0189] If the pressure within the blowoff chamber 308 exceeds the
predetermined threshold, the blowoff shim stack 354 deflects away
from the blowoff piston 344 to allow fluid to flow through the
blowoff passage 352 into the separator chamber 350 and into the
reservoir through the passages 360, as illustrated in FIG. 17.
Thus, the fork 34 is able to compress with the compression damping
rate being determined primarily by the shim stack 354 of the
blowoff piston 344.
[0190] As the upper fork leg 224 moves downward with respect to the
lower fork leg 226, and thus the piston 258 and damper shaft 254
move downward with respect to the cartridge 252, fluid is drawn
into the rebound chamber 262 through the refill valve 274, as
illustrated in FIG. 16.
[0191] When the upward acceleration of the lower fork leg 226
exceeds a predetermined threshold, the inertia mass 362 tends to
stay at rest and overcomes the biasing force of the spring 366 to
open the passages 364. Thus, fluid flow is permitted from the
central passage 312 of the base valve shaft 298 into the inertia
chamber 376 through the passages 364 and from the inertia chamber
376 into the reservoir 266 through the passages 378, as illustrated
in FIGS. 18 and 19. Accordingly, at pressures lower than the
predetermined blowoff pressure, when the inertia mass 362 is open
(down) fluid is permitted to flow from the compression chamber 264
to the reservoir 266 and the suspension fork 244 is able to
compress.
[0192] Upon rebound motion of the suspension fork 34, the refill
valve 274 closes and the fluid within the rebound chamber 262 is
forced through the rebound passages 286 of the piston 258 against
the resistive force of the rebound shim stack 288, as illustrated
in FIG. 20. A volume of fluid equal to the displaced volume of the
damper shaft 254 is drawn into the compression chamber 264 from the
reservoir chamber 266 via the passages 356 and 330 against the
slight resistance offered by the refill shims 358 and 332, as
illustrated in FIG. 21.
[0193] FIGS. 22-25 illustrate an alternative embodiment of the
suspension fork 34. The embodiment of FIGS. 22-25 operates in a
substantially similar manner as the suspension fork 34 described in
relation to FIGS. 14-21 with the exception that the embodiment of
FIGS. 22-25 allows flow through a compression valve 382 in the
piston 258 during compression motion. This is known as a
shaft-displacement type damper, because a volume of fluid equal to
the displaced volume of the shaft 254 is displaced to the reservoir
266 during compression motion of the fork 34. For reference, this
compares with the previously-described embodiment where the
displaced fluid volume equals the displaced volume of the full
diameter of the piston 258. Flow through the piston 258 into the
rebound chamber during compression eliminates the need for refill
passages in the cartridge cap, and thus a solid cap 260 is
utilized.
[0194] The compression valve 382 is a one-way valve, similar in
construction to the one-way valves described above. The compression
valve 382 comprises one or more valve passages 384 formed axially
in the piston 258 and a shim stack 386 closing the valve passages
384. As is known, the shim stack 386 may comprise one or more
shims. The shims may be combined to provide a desired spring rate
of the shim stack 386. The shim stack 386 is deflected to allow
fluid flow between the compression chamber 264 and the rebound
chamber 262 during compression of the suspension fork 34.
Preferably, shim stack 386 is significantly "softer" than shim
stack 328 in the base valve assembly 268, in order to ensure
sufficient pressure for upward flow through piston 258 into rebound
chamber 262 during compression strokes.
[0195] The operation of the suspension fork 34 of FIGS. 22-25 is
substantially similar to the operation of the suspension fork 34
described in relation to FIGS. 14-21. However, during compression
motion of the fork 34 of FIGS. 22-25, fluid flows from the
compression chamber 264 to the rebound chamber 262. This results in
less fluid being displaced into the reservoir 266 than in the
previous embodiment. As will be appreciated by one of skill in the
art, FIGS. 22 and 23 illustrate compression fluid flow when the
blow off valve 304 is open. FIGS. 24 and 25 illustrate compression
fluid flow when the inertia valve 306 is open.
[0196] As will be appreciated by one of ordinary skill, the
illustrated suspension fork and rear shock absorber arrangements
advantageously minimize unintended movement of the inertia mass 150
due to normal compression and rebound fluid flow. With particular
reference to FIG. 3b, compression fluid flow (illustrated by the
arrow in FIG. 3b) through the blow off valve 140 of the rear shock
absorber 38 occurs through the passage 136 of the reservoir shaft
134 as it passes the inertia mass 150. Accordingly, fluid moving
with any substantial velocity does not directly contact the inertia
mass 150, thereby avoiding undesired movement of the inertia mass
150 due to forces from such a flow. Similarly, compression fluid
flow through the passages 148 when the inertia mass 150 is in an
open position (FIG. 5) and refill fluid flow upon rebound of the
shock absorber 38 are similarly insulated from the inertia mass
150. With reference to FIGS. 17, 19 and 21, the inertia mass 150 is
also insulated from contact with moving fluid in the suspension
fork 34. FIGS. 23 and 25 illustrate similar flow paths for the
second embodiment of the suspension fork 34.
[0197] FIG. 26 is a graph illustrating the influence of a change in
the internal diameter D of a specific inertia mass 150 on the
pressure differential between the right and left side when the
inertia mass 150 is off-center by a distance x of 0.001 inches. As
described above in relation to FIGS. 11 and 12, the reservoir shaft
134, which defines an axis of motion for the inertia mass 150, has
a diameter referred to by the reference character "d." The
reference character "B" refers to the size of the step 205, or the
difference in the radial dimensions of the inner surface of the
inertia mass 150 between zone 2 Z.sub.2 and zone 3 Z.sub.3. For the
purposes of illustration in the graph of FIG. 26, the diameter d of
the shaft 134 is given a value of 0.375 inches. The step size B is
given a value of 0.001 inches.
[0198] In the graph of FIG. 26, the value of the minimum internal
diameter of the inertia mass 150 (i.e., the diameter at zone 3
Z.sub.3) is varied and the corresponding pressure differential
between the left and right sides is illustrated by the line 388,
given the constants d, B and x. As described above, the
self-centering force is proportional to the pressure differential
produced by the design of zones 1, 2 and 3 of the self-centering
inertia mass 150. Thus, as the pressure differential increases, so
does the ability of the inertia mass 150 to center itself with
respect to the shaft 134. As illustrated, the value of the pressure
differential between the left and right sides varies greatly with
relatively small changes in the internal diameter D of the inertia
mass 150. The pressure differential is at its maximum value on the
graph when the difference between the inertia valve diameter D and
the shaft diameter d is small. The pressure differential diminishes
as the difference between the inertia valve diameter D and the
shaft diameter d increases.
[0199] For example, when the inertia valve diameter D is equal to
0.400 inches, the pressure differential is equal to approximately 8
psi. With the inertia valve diameter D equal to 0.400 inches and
the shaft diameter d equal to 0.375 inches, the total gap at zone 3
G.sub.3 for both the left and right sides is equal to 0.025 inches
(0.400-0.375), when the inertia mass 150 is centered. Accordingly,
each gap at zone 3 for the left and right side, G.sub.3L and
G.sub.3R, is equal to 0.0125 inches (0.025/2), when the inertia
mass 150 is centered (FIG. 11).
[0200] The pressure differential has substantially increased at a
point when the inertia valve diameter D is equal to 0.385. At this
point, the resulting pressure differential is approximately 38 psi.
Following the calculation above, each gap at zone 3 for the left
and right side, G.sub.3L and G.sub.3R, is equal to 0.005 inches,
with a centered inertia mass 150.
[0201] The pressure differential has again substantially increased,
to approximately 78 psi, at a point when the inertia valve diameter
D is equal to 0.381 inches. When the inertia diameter D is equal to
0.381 inches, each gap at zone 3 for the left and right side,
G.sub.3L and G.sub.3R, is equal to 0.003 inches, assuming the
inertia mass 150 is centered about the shaft 134. At a point when
the inertia valve diameter D is equal to 0.379, the pressure
differential has increased significantly to approximately 125 psi.
At this point, the gap at zone 3 for the left and right side,
G.sub.3L and G.sub.3R, is 0.002 inches.
[0202] The illustrated pressure differential reaches a maximum when
the inertia valve diameter D is equal to 0.377 inches. At this
value of D, the pressure differential is approximately 180 psi and
each gap at zone 3 for the left and right side, G.sub.3L and
G.sub.3R, is equal to 0.001 inches, again assuming a centered
inertia mass 150 and the values of d, B and x as given above.
Although the gap at zone 3 G.sub.3 may be reduced further,
resulting in theoretically greater self-centering forces, a gap in
zone 3 G.sub.3 of at least 0.001 inches is preferred to allow the
inertia mass 150 to move freely on the shaft 134. A gap G.sub.3
below this value may allow particulate matter within the damping
fluid to become trapped between the inertia mass 150 and shaft 134,
thereby inhibiting or preventing movement of the inertia mass
150.
[0203] FIG. 27 is a graph illustrating the relationship between the
size B of the "Bernoulli step" 205 and the resulting pressure
differential percentage. A pressure differential of 0% indicates no
pressure differential, and thus no self-centering force, is present
(i.e., the pressure on the right and left sides of the inertia mass
150 are equal), while a pressure differential of 100% indicates a
maximum pressure differential, and self-centering force, is present
(i.e., zero pressure on one side of the inertia mass 150). The
graph is based on a gap at zone 3 G.sub.3 of 0.002 inches, with the
inertia mass 150 centered. In other words, the inertia mass
diameter D minus the shaft diameter d is equal to 0.004 inches,
which results in a gap on each of the right and left sides,
G.sub.3R and G.sub.3L, of 0.002 inches.
[0204] The graph includes individual lines 390, 392, 394 and 396
representing different off-center values of the inertia valve. The
values are given in terms of the percentage of the total gap
G.sub.3 (0.002'' in FIG. 27) that the inertia mass 150 is
off-center. For example, an off-center amount of 25% means that the
center axis of the inertia mass 150 is offset 0.0005 inches to
either the left or right from the center axis of the shaft 134.
Similarly, an off-center amount of 50% means that the center axis
of the inertia mass 150 is offset 0.001 inches from the center axis
of the shaft 134. Line 390 represents an off-center amount of 25%,
line 392 represents an off-center amount of 50%, line 394
represents an off-center amount of 75%, and line 396 represents an
off-center amount of 99%.
[0205] The largest step size B illustrated on the graph of FIG. 27
is 0.008 inches. A step 205 of a larger size B may be provided,
however, as indicated by the graphs, theoretical self-centering
effects have diminished significantly at this point. Accordingly,
the step size is desirably less than 0.008 inches, at least for
off-road bicycle applications based on these theoretical
calculations. The ratio between the gap at zone 3 G.sub.3 and the
gap at zone 2 G.sub.2 (i.e., G.sub.3/G.sub.2) in this situation is
1/5, for a centered inertia mass 150 and a gap at zone 3 G.sub.3 of
0.002 inches.
[0206] With continued reference to FIG. 27, lines 390-396
illustrate that the pressure differential has increased at a point
when the step size B is equal to 0.006 inches in comparison to the
pressure differential at a step size B of 0.008 inches. At this
point, the ratio between the gap at zone 3 G.sub.3 and the gap at
zone 2 G.sub.2 (i.e., G.sub.3/G.sub.2), for a centered inertia mass
150, is 1/4. As a result, the self-centering effect is more
substantial for ratios which are greater than 1/4. The pressure
differential again increases at a point when the step size B is
equal to 0.004 inches. At this point, the ratio between the gap at
zone 3 G.sub.3 and the gap at zone 2 G.sub.2 (i.e.,
G.sub.3/G.sub.2), for a centered inertia mass 150, is 1/3. As a
result, the self-centering force for ratios above self-centering
force 1/3 is increased over the self-centering force obtained with
a larger step size B.
[0207] For at least a portion of the lines 390-396, the pressure
differential again increases for step sizes B less than 0.003. At
this point, the ratio of the gap at zone 3 G.sub.3 to the gap at
zone 2 G.sub.2 (i.e., G.sub.3/G.sub.2), for a centered inertia mass
150, is . Accordingly, the self-centering effect is more
substantial for ratios which are greater than . Furthermore, at
least a portion of the lines 390-396 illustrate an increase in the
pressure differential at a point when the step size B is equal to
0.002 inches. At this point, the ratio of the gap at zone 3 G.sub.3
to the gap at zone 2 G.sub.2 (i.e., G.sub.3/G.sub.2), for a
centered inertia mass 150, is 1/2. As a result, the self-centering
effect is more substantial for ratios which are greater than
1/2.
[0208] The graph of FIG. 27 illustrates a general trend that, up to
a point, the pressure differential percentage (and self-centering
force) increases as the step size B is reduced, especially for
large off-center amounts. However, practical considerations also
prevent the size B of the step 205 from becoming too small. For
example, extremely small step sizes may be difficult to
manufacture, or in the very least, difficult to manufacture for a
reasonable cost. Accordingly, the size B of the step 205 (i.e.,
G.sub.2-G.sub.3) is desirably greater than, or equal to, 0.0001
inches. Preferably, the size B of the step 205 is greater than or
equal to 0.001 inches. Additionally, for the practical concerns
described above, the effectiveness of the self-centering inertia
mass 150, at least theoretically, declines as the step sizes B
become too large. Accordingly, the size B of the step 205 is
preferably less than 0.002 inches. However, as mentioned above, the
graph of FIG. 27 is based on theoretical calculations using
Bemoulli's equation, which assumes perfect fluid flow. For actual
fluid flows, a much larger step size B may be desirable. For
example, in actual applications, a step size B of 0.02 inches, 0.03
inches, or even up to 0.05 inches is believed to provide a
beneficial self-centering effect. The effectiveness of larger step
sizes B in actual applications is primarily a result of boundary
layers of slow-moving, or non-moving fluid adjacent the inertia
mass 150 and shaft 134 surfaces resulting in a lower actual flow
rate than theoretically calculated using Bernoulli's equation.
[0209] FIG. 28 is a graph, similar to the graph of FIG. 27,
illustrating the relationship between the size B of the step 205
and the resulting pressure differential percentage, except that the
gap G.sub.3 is 0.001 inches when the inertia valve 150 is centered.
That is, the inertia mass diameter D minus the shaft diameter d is
equal to 0.002 inches, which results in a gap on each of the right
and left sides, G.sub.3R and G.sub.3L, of 0.001 inches.
[0210] The graph includes individual lines representing inertia
mass 150 off-center values of 25%, 50%, 75% and 99%. Line 400
represents an off-center amount of 25%, line 402 represents an
off-center amount of 50%, line 404 represents an off-center amount
of 75%, and line 406 represents an off-center amount of 99%.
[0211] The largest step size B illustrated on the graph of FIG. 28
is 0.008 inches. The ratio between the gap at zone 3 G.sub.3 and
the gap at zone 2 G.sub.2 (i.e., G.sub.3/G.sub.2) in this situation
is 1/9, for a centered inertia mass 150 and a gap at zone 3 G.sub.3
of 0.001 inches. A step size B of greater than 0.008 inches is
possible however, as discussed above, at least for off-road bicycle
applications, the step size B is preferably less than 0.008 inches
based on theoretical calculations.
[0212] For at least a portion of the illustrated off-center
amounts, the pressure differential increases at a point when the
step size B is equal to 0.003 inches. At this point, the ratio
between the gap at zone 3 G.sub.3 and the gap at zone 2 G.sub.2
(i.e., G.sub.3/G.sub.2), for a centered inertia mass 150, is 1/4.
As a result, the centering effect is more substantial for ratios
which are greater than 1/4. The lines 400-406 illustrate that the
pressure differential again increases at a point when the step size
B is equal to 0.002 inches. At this point, the ratio between the
gap at zone 3 G.sub.3 and the gap at zone 2 G.sub.2 (i.e.,
G.sub.3/G.sub.2), for a centered inertia mass 150, is 1/3. As a
result, the self-centering effect is greater for ratios above
1/3.
[0213] The pressure differential again increases for step sizes B
less than 0.0015. At this point, the ratio of the gap at zone 3
G.sub.3 to the gap at zone 2 G.sub.2 (i.e., G.sub.3/G.sub.2), for a
centered inertia mass 150, is . Accordingly, the centering effect
is more substantial for ratios which are greater than . Further,
the pressure differential increases at a point when the step size B
is equal to 0.001 inches. At this point, the ratio of the gap at
zone 3 G.sub.3 to the gap at zone 2 G.sub.2 (i.e.,
G.sub.3/G.sub.2), for a centered inertia mass 150, is 1/2. As a
result, the centering effect is more substantial for ratios which
are greater than 1/2.
[0214] The design parameters of the self-centering inertia mass 150
described above, including the size of the gaps G in the different
zones (Z.sub.1, Z.sub.2, Z.sub.3) and the size B of the step 205,
for example, as well as other considerations, such as the length of
time the inertia mass 150 stays open in response to an activating
acceleration force, the spring rate of the biasing spring and the
mass of the inertia mass 150, for example, may each be varied to
achieve a large number of possible combinations. More than one
combination may produce suitable overall performance for a given
application. In a common off-road bicycle application, the
combination desirably provides a self-centering force of between 0
and 800 lbs. for an off-center amount of 25%. Preferably, a
self-centering force of between 0 and 40 lbs. is produced and more
preferably, a self-centering force of between 0 and 5 lbs. is
produced for an off-center value of 25%. Desirably, the combination
provides a self-centering force of at least 0.25 ounces for an
off-center amount of 25%. Preferably, a self-centering force of at
least 0.5 ounces is produced and more preferably, a self-centering
force of at least 1 ounce is produced for an off-center value of
25%. Most preferably a self-centering force of at least 2 ounces is
produced for an off-center value of 25%. The above values are
desirable for a rear shock absorber 38 for an off-road bicycle 20.
The recited values may vary in other applications, such as when
adapted for use in the front suspension fork 34 or for use in other
vehicles or non-vehicular applications.
[0215] FIG. 29 illustrates an inertia valve assembly 410, which is
similar to the inertia valve assembly 138 of FIG. 3B. The inertia
valve assembly 410 of FIG. 29 may be incorporated in a shock
absorber, such as the shock absorber 38 of the bicycle 20
illustrated in FIG. 1. The inertia valve assembly 410 desirably
includes an inertia mass 412, which has an increased density in
comparison to the inertia mass 150 of FIG. 3B. As a result, the
inertia mass 412 is more responsive to an acceleration force of a
given magnitude. Preferably, the inertia valve assembly 410
operates in a substantially similar manner to the inertia valve
arrangement 138 described above and, therefore, the inertia valve
assembly 410 and associated shock absorber are described in limited
detail.
[0216] Preferably, the inertia valve assembly 410 is disposed
within a reservoir tube 414 and is operable to selectively permit
fluid flow between a first fluid chamber 416 and a second fluid
chamber 418. In a preferred embodiment, the first fluid chamber 416
comprises a compression chamber of the shock absorber and the
second fluid chamber 418 comprises a reservoir chamber of the shock
absorber. Preferably, the inertia mass 412 is supported for axial
movement on an axis A.sub.c, which is defined by a shaft 420. The
inertia mass 412 is biased in an upward direction (with respect to
the orientation of the tube 414 illustrated in FIG. 29) against an
upper stop, defined by snap ring 422, by a biasing member, such as
coil spring 424. In this position, the inertia mass 412 closes
openings 434 in the shaft 420 to define a closed position of the
inertia valve assembly 410.
[0217] A base 426 is coupled to a lower end of the reservoir tube
414 and, preferably, includes a cavity 428, which defines a pocket
430 below the inertia mass 412. The pocket 430 is sized and shaped
to receive at least a lower portion of the inertia mass 412. A
bottom surface of the cavity 432 functions as a lower stop for the
inertia mass 412. As described in detail above, preferably, the
inertia mass 412 is responsive to an appropriate acceleration force
input above a predetermined threshold. Upon being subjected to such
an acceleration force, the inertia mass 412 moves downwardly
relative to the shaft 420, against the biasing force of the spring
424, and into the pocket 430. In this position, the inertia mass
412 uncovers openings 434 to permit fluid flow from the first fluid
chamber 416 to the second fluid chamber 418 and define an open
position of the inertia valve assembly 410.
[0218] The inertia valve assembly 410 also includes a refill valve
assembly 436, which preferably is configured to at least partially
control a flow of fluid between the reservoir chamber 418 and the
pocket 430. In the illustrated embodiment, the valve assembly 436
includes a plurality of hooks 438 (only one shown) extending in an
upward direction from the base 426. Preferably, the hooks 438 are
disposed around the periphery of the cavity 428 adjacent an inner
surface of the reservoir tube 414. In a preferred arrangement, four
such hooks 438 are equally spaced around a periphery of the cavity
428.
[0219] The hooks 438 define an upper stop surface 440 and an upper
surface of the base 426 defines a corresponding lower stop surface
442. A check plate 444 is retained for movement between the upper
stop surface 438 and the lower stop surface 442. Preferably, the
check plate 444 is substantially annular in shape with an inner
diameter which is slightly larger than an outer diameter of an
adjacent portion of the inertia mass 412, such that a clearance
distance C is defined therebetween.
[0220] In a preferred arrangement, the check plate 444 is
configured to restrict a flow of fluid from the reservoir chamber
418 into the pocket 430 at a first level and permit fluid flow from
the pocket 430 to the reservoir 418 at a second level, which
preferably is greater than the first level. In operation, when the
inertia mass 412 is moving downward relative to the shaft 420, such
as due to an appropriate acceleration force, the movement of fluid
out of the pocket 430 lifts the check plate 444 in an upward
direction against the upper stop surface 440, as illustrated in
phantom. Accordingly, a large amount of fluid is permitted to be
displaced from the pocket 430 to the reservoir chamber 418, as
illustrated by the phantom flow line 445.
[0221] Conversely, when the inertia mass 412 is moving from a lower
most position, within the pocket 430, toward the upper stop 422,
fluid within the reservoir 418 attempts to fill the pocket 430
thereby urging the check plate 444 against the lower stop surface
442, as illustrated by the solid line position of the check plate
444. In the lower position of the check plate 444, fluid is
restricted to entering the pocket 430 by passing through the
clearance distance C between an inner surface of the check plate
444 and an outer surface of the inertia mass 412, as illustrated by
the solid flow line 446. Preferably, with such an arrangement, the
flow into the pocket 430 is restricted to a rate that is lower than
the rate in which fluid may exit the pocket 430. Accordingly, the
inertia mass 412 may move quickly in a downward direction into the
pocket 430, while movement in an upward direction is slowed to
delay the closing of the inertia valve 410 in order to extend the
reduced-damping mode of the shock absorber, as described in detail
above.
[0222] Desirably, the inertia mass 412 is configured to have a
relatively high density, and thus a high mass for a given volume,
so that the inertia mass 412 moves more easily through the damping
fluid within the chambers 418 and 430 to increase the
responsiveness of the inertia valve 410 to acceleration force
inputs. Preferably, the inertia mass 412 includes a first section,
comprising a first material, and a second section, comprising a
second material having a greater density than the first material.
Desirably, the second material has a density greater than about 10
g/cm.sup.3 and, preferably, greater than about 15 g/cm.sup.3. More
preferably, the second material has a density of about 19
g/cm.sup.3. In the illustrated arrangement, the inertia mass 412
comprises a body portion 450, which defines an annular cavity 452
filled with a high density material 454, so as to increase the
overall mass of the inertia mass 412 without increasing the volume
that it occupies. A presently preferred high density material 454
is tungsten, preferably in a powdered form.
[0223] In addition, the ratio of the mass of the inertia mass 412
to the surface area of a lowermost surface 456 of the inertia mass
412, normal to the axis A.sub.C, is also increased in comparison to
the previously described inertia mass constructions. The surface
456 may be defined as a leading surface of the inertia mass 412
when the inertia mass 412 is moving in a downward direction (i.e.,
toward the open position). Accordingly, the leading surface area
includes a surface 456a of standoff feet 455, which is generally
parallel with the surface 456 and perpendicular to the axis A.sub.C
of the shaft 420. Due to the increased mass to volume, and mass to
leading surface area ratios, the inertia mass 412 more easily
displaces fluid from the pocket 430 to move more quickly toward the
open position in response to suitable acceleration force
inputs.
[0224] In a preferred arrangement, a threaded cap 458 closes an
open, upper end of the cavity 452 to retain the tungsten 454 within
the cavity. A peripheral edge of the cap 458 includes external
threads 460, which mate with internal threads 462 of the cavity
452. Thus, the cavity 452 may be filled with tungsten 454, or
another high density material, and closed with the threaded cap
458.
[0225] The embodiment illustrated in FIG. 29 is preferred at least
because the main body portion 450 of the inertia mass 412 may be
made from a relatively dense, yet readily processable material,
such as brass for example, while permitting a material with even
higher density, such as tungsten powder, to be held within the
cavity 452 without the need for it to be formed or otherwise
processed. Alternatively, the entire inertia mass 412 may be made
from a material having higher density than brass, such as solid
tungsten for example. In a preferred embodiment, the cavity 452,
and thus the tungsten powder 454 or other high density material,
occupies a significant portion of the total volume of the inertia
mass 412. For example, desirably the high density material occupies
at least one-third volume of the inertia mass 412. Preferably, the
high density material occupies at least one-half and, more
preferably, at least two-thirds of the volume of the inertia mass
412. However, other ratios between the material comprising the main
body 450 and the material within the cavity 452 may also be
used.
[0226] An inertia mass configured substantially as described above
provides advantages mass to surface area, or mass to volume, ratios
so that the inertia mass is very responsive to acceleration force
inputs. The tables below illustrate the change in mass to surface
area and mass to volume ratios for a constant volume inertia mass
and a constant mass inertia mass, respectively, having varying
relative volumes of brass and tungsten. In generating the tables,
the annular inertia mass was assumed to have a length of 0.875
inches, an inner diameter of 0.375 inches and, for the constant
volume inertia mass, an outer diameter of one (1) inch. For the
constant mass inertia mass, the outer diameter (and, thus, the
leading surface area) varies. The density of brass was assumed to
be 8.5539 g/cm.sup.3 and the density of tungsten was assumed to be
19.3 g/cm.sup.3. The constant volume inertia mass was assumed to
have a volume of 9.685 cm.sup.3 and the constant mass inertia mass
was assumed to have a mass of 83 grams. The ratios are provided in
grams/cubic inch for mass to volume and grams/square inch for mass
to surface area. TABLE-US-00001 TABLE 1 Constant Volume % Tungsten
0 10 20 30 40 50 60 70 80 90 100 Mass 83 93 104 114 124 135 145 156
166 177 187 Mass/Vol. 140 158 175 193 211 228 246 263 281 299 316
Mass/Surf. Area 123 138 154 169 184 200 215 231 246 262 277
[0227] TABLE-US-00002 TABLE 2 Constant Mass % Tungsten 0 10 20 30
40 50 60 70 80 90 100 Volume 9.7 9.2 8.6 8.1 7.5 7.0 6.5 5.9 5.4
4.8 4.3 Mass/Vol. 140 148 158 168 180 194 210 230 253 281 316
Mass/Surf. Area 123 130 138 147 158 170 184 201 221 246 277
[0228] FIGS. 30, 31A and 31B illustrate an alternative inertia mass
470, which preferably is configured to provide increased flow
resistance, or drag, when moving in a first direction compared to
the flow resistance when moving in a second, or opposite direction.
In a preferred arrangement, the inertia mass 470 includes one or
more collapsible drag members 472, which are configured to assume a
first orientation when the inertia mass 470 is moving in a first
direction and a second orientation when the inertia mass 470 is
moving in the opposite direction.
[0229] As in the inertia valve assemblies described above, the
inertia mass 470 is supported for axial movement on a shaft 474
within a reservoir chamber 476. In the illustrated embodiment, the
inertia mass 470 includes a body portion 478, the outer surface of
which defines a pair of annular grooves 480. The annular grooves
support the drag members 472, which are also annular in shape. In a
preferred arrangement, the drag members 472 are constructed from a
flexible material, such as rubber or plastic, and extend upwardly
and outwardly from the outer surface of the body portion 478 of the
inertia mass. In addition, the drag members 472 may curve in an
upward direction from an inner diameter to an outer diameter of the
drag member 472. Accordingly, a peripheral edge portion of each
drag member 472 tends to be collapsible in an upward direction
relative to the inner edge portion of the drag member 472.
[0230] In operation, when the inertia mass 470 is moving in a
downward direction relative to the shaft 474, or toward an open
position, fluid flow illustrated by the arrows 482 in FIG. 31A
exerts an upward force on the drag members tending to collapse the
drag members radially inward. Accordingly, a leading surface area
of the inertia mass 470 is reduced and the fluid 482 flows past the
drag members 472 with, preferably, little interruption. Thus,
preferably, the drag members 472 exert little resistive force
against the downward movement of the inertia mass 470 toward the
open position.
[0231] Conversely, when the inertia mass 470 is moving in an upward
direction relative to the shaft 474, toward the closed position,
fluid 484 flowing beside the inertia mass 470 tends to open the
drag members 472 into their relaxed, or radially extended,
orientation, as illustrated in FIG. 31B. Thus, preferably, the drag
members 472 cause turbulent flow of the fluid adjacent the body
portion 478. Such flow significantly increases the resistance to
fluid 484 flowing past the inertia mass 470 and, thereby, slows the
movement of the inertia mass 470 toward the closed position. Thus,
the drag members 472 provide a delay, or timer function, to the
inertia mass 470, in a manner similar to the timer arrangements
described above.
[0232] The drag members 472 may be used in addition, or in the
alternative, to other delay producing devices, such as the valve
436 of FIG. 29 or the clearance passage C illustrated in FIG. 6.
Furthermore, although two drag members 472 are provided in the
illustrated inertia valve assembly 470, a greater or lesser number
of drag members 472 may also be used. In addition, although the
drag members 472 are illustrated as annular members extending
outwardly from a side wall of the inertia mass 470, other
constructions are also possible. For example, collapsible drag
members may be disposed above or below the main body 478 of the
inertia mass 470 and be configured in a similar manner to achieve
the same, or similar, effect.
[0233] FIG. 32 illustrates an alternative inertia valve assembly
490 in which the delay in closing of the inertia mass 492 is
influenced by a pressure differential between the pressure of the
fluid within the reservoir chamber 494 and the pressure of the
fluid within the passage 526. During a rebound stroke of the shock
absorber, as fluid exits the reservoir chamber 494, flowing
downward (relative to the orientation shown in FIG. 32) through the
central shaft 496, a pressure drop occurs. For a given flow rate,
the magnitude of the pressure drop is influenced by the diameter of
the flow passage in the shaft 496. A smaller flow passage diameter
creates a larger pressure drop top to bottom.
[0234] Similar to the previous embodiments, the inertia mass 492 is
supported by a shaft 496 for axial movement about an axis A.sub.c.
The inertia mass 492 is positioned within the reservoir chamber 494
defined by a reservoir tube 498. A base 500 is connected to a lower
end of the reservoir tube 498 and defines a recess 502 which, in
turn, defines a pocket 504 for receiving at least a lower portion
of the inertia mass 492 when the inertia mass 492 is in the open
position. Thus, a bottom surface of the recess 502 functions as a
lower stop for the inertia mass 492. The inertia mass 492 is biased
against an upper stop, defined by snap ring 506, by a biasing
member, such as coil spring 508.
[0235] Preferably, the base 500 defines a first passage 510 that
connects the reservoir chamber 494 and the pocket 504. Desirably,
the base 500 also defines a second passage 512 that connects the
reservoir chamber 494 and the pocket 504. A pressure actuated valve
arrangement 514 selectively permits fluid communication through the
second passage 512 when the pressure in the reservoir chamber is
above a predetermined threshold. The valve assembly 514 includes a
valve body 516 biased into a closed position by a biasing member,
such as coil spring 518. In the closed position, an enlarged
diameter upper portion 517 of the valve body is arranged to block
the second passage 512 to substantially prevent fluid flow
therethrough.
[0236] Preferably, an upper stop for the valve body 516 is defined
by a snap ring 520 and a lower stop is defined by a lower end of a
valve seat 521, which receives the upper portion 517 of the valve
body 516. Desirably, the valve body 516 includes an elongated lower
end, or shaft portion 522, which functions as a guide for the coil
spring 518. In addition, preferably a seal member 528 creates a
seal between the valve body 516 and the base 500 to inhibit fluid
from passing therebetween. Thus, the valve body 516 is normally
biased into a closed position by the force of the biasing member
518. If the pressure differential between the reservoir chamber 494
and the passage 526 exceeds a predetermined threshold, the valve
body 516 moves toward the open position, against the biasing force
of the spring 518. In the illustrated arrangement, the
predetermined threshold is determined primarily by the surface area
of the upper end surface of the valve body 516 and the spring
constant of the biasing member 518,
[0237] As described above, when the inertia mass 492 moves into its
open position, refilling of the pocket 504 is restricted to fluid
flow between an outer surface of the inertia mass 492 and an inner
surface of the cavity 502. In addition, fluid may refill the pocket
504 by flowing through the passage 510, if provided. Thus, the
inertia mass 492 is delayed from moving toward its open position
due to the restriction of the fluid from entering the pocket 504.
However, in the embodiment of FIG. 32, if the pressure differential
between the reservoir chamber 494 and the passage 526 exceeds a
predetermined threshold, the pressure actuated valve assembly 514
opens to permit fluid flow into the pocket 504 through the second
passage 512. Preferably, the second passage 512 is configured to
permit a greater rate of flow into the pocket 504 in comparison to
fluid flow through the clearance between the inertia mass 492 and
the cavity 502 and fluid flow through the passage 510 (if
provided). Accordingly, when the pressure actuated valve assembly
514 opens, the inertia mass 492 may return to its closed position
more quickly.
[0238] FIG. 33 illustrates an alternative embodiment of a pressure
activated inertia valve assembly 530. In the embodiment of FIG. 33,
an inertia mass 532 is configured for axial movement on a shaft 534
about an axis A.sub.c. Preferably, the inertia mass 532 is disposed
within a reservoir chamber 536 defined at least partially by a
reservoir tube 538 and a base 540. A passage 542 extends through
the base 540 and shaft 534 and is in fluid communication with the
reservoir chamber 536 through openings 544. Desirably, the passage
542 receives fluid from a compression chamber (not shown) of the
shock absorber, as will be appreciated by one of skill in the art.
Thus, the inertia mass 532 selectively permits fluid communication
between the passage 542 and the reservoir chamber 536.
[0239] In the embodiment of FIG. 33, a slide member 546 is
interposed between the base 540 and the inertia mass 532. The slide
546 includes a recess 548 that defines a pocket 550 for receiving
the inertia mass 532. The inertia mass 532 is biased into an
uppermost, or closed, position (against stop 552) by a biasing
member, such as coil spring 554. The spring 554 is supported
relative to the shaft 534 by a lower stop, defined by snap ring
556. The snap ring 556 also defines an uppermost position of the
slide 546. The slide 546 is also axially moveably relative to the
shaft 534 and is biased into its uppermost position by a biasing
member, such as coil spring 558.
[0240] The base 540 defines a cavity 560, which receives a lower
end of the slide 546 in a sealed arrangement. One of a lower
surface 562 of the cavity 560 or an upper surface 564 of the base
540 function as a stop to define a lowermost position of the slide
546. In addition, preferably one or more passages 566 permit fluid
communication between the passage 542 and a pocket 568 defined by
the cavity 560. Preferably, the pocket 568 is substantially sealed,
with the exception of the passages 566, such that fluid within the
pocket 568 is at substantially the same pressure as fluid within
the passage 542 (and, thus, the compression chamber of the shock
absorber).
[0241] In operation, the inertia mass 532, upon receiving an
appropriate acceleration force, moves in a downward direction
relative to the shaft 534 and into the pocket 550. Once in the
pocket 550, the inertia mass 532 is delayed in moving in an upward
direction due to the restriction of fluid being permitted to refill
the pocket 550. Thus, the inertia mass 532, when positioned within
the pocket 550, moves toward the closed position at a delayed rate.
In the illustrated embodiment, fluid may pass from the reservoir
chamber 536 into the pocket 550 through a clearance distance C
between an outer diameter of the inertia mass 532 and an inner
diameter of the cavity 548.
[0242] When a difference in fluid pressure between the reservoir
chamber 536 and the passage 542 (and, thus, the pressure within the
compression chamber of the shock absorber) exceeds a predetermined
threshold, the slide 546 moves downward relative to the shaft 534
and into the pocket 568. In the illustrated embodiment, preferably,
the predetermined threshold is determined primarily by a surface
area of an end surface 569 the slide 546, which is perpendicular to
the center axis A.sub.C of the shaft 534 and disposed within the
pocket 568, along with the spring rate of the biasing member
558,
[0243] Thus, with the inertia mass 532 in its open position, the
slide 546 moves in a downward direction away from the inertia mass
532. When the slide 546 moves downwardly a sufficient distance, the
inertia mass 532 is no longer present within the pocket 550 and
fluid may refill the pocket 550 at a relatively high rate. Thus,
the inertia mass 532 is no longer restricted from moving in an
upward direction due to the restriction of fluid moving into the
pocket 550 and, as a result, the biasing member 554 returns the
inertia mass 532 to its closed position at a normal rate,
determined primarily by the weight of the inertia mass 532 and the
spring rate of the spring 554. Accordingly, with such an
arrangement, when the inertia mass 532 is in the open position and
the pressure within the reservoir chamber 536 exceeds the pressure
within the passage 542 by a predetermined threshold, the inertia
mass 532 is permitted to return to the closed position without
significant delay.
[0244] FIGS. 34 and 35 illustrate a bicycle that employs yet
another alternative embodiment of an acceleration sensitive shock
absorber. The bicycle 580 includes a main frame portion 582, an
articulating frame portion 584, a front wheel 586, and a rear wheel
588. Preferably, a front suspension assembly 590 is operably
positioned between the front wheel 586 and the main frame 582 and a
rear suspension assembly, or shock absorber 592, is operably
positioned between the rear wheel 588 and the main frame 582.
Preferably, the articulating frame portion 584 carries the rear
wheel 588 and the shock absorber 592 is connected to the
articulating frame portion 584 to resist movement of the rear wheel
588 in an upward direction. Preferably, the shock absorber 592 is
positioned on one lateral side of the rear wheel 588 and,
desirably, on the left-hand side of the rear wheel 588.
[0245] With reference to FIG. 35, desirably, the shock absorber 592
includes a reservoir chamber 594 at least partially defined by a
reservoir tube 596 and a base 598. Preferably, an acceleration
sensitive valve assembly 600 is disposed within the reservoir
chamber 594. The valve assembly 600 preferably includes a valve
body 602 biased into an uppermost, or open position, by a biasing
member, such as coil spring 604. The valve body 602 is supported
for axial movement along an axis A.sub.c, which is defined by a
shaft 606. An uppermost position of the valve body 602 preferably
is determined by a snap ring 608. In the illustrated embodiment,
the uppermost position defines a closed position of the valve
600.
[0246] The base 598 preferably includes a cavity 610 that defines a
pocket 612 in which the valve body 602 enters in its lowermost
position. In a preferred arrangement, when the valve body 602 is in
its lowermost position, fluid flow is permitted through openings
613 of the shaft 606. A bottom surface 614 of the cavity 610
defines a lower stop for the valve body 602. Preferably, as
described above, a valve assembly 616 is provided to permit
relatively free flow of fluid from the pocket 612 to the reservoir
chamber 594 while permitting restricted flow of fluid from the
reservoir chamber 594 into the pocket 612.
[0247] Desirably, the valve assembly 600 includes a system for
sensing acceleration force inputs and for moving the valve body 602
to an open position and/or retaining the valve body 602 in an open
position. In the illustrated embodiment, preferably an
electromagnetic system 618 is provided. The system 618 preferably
includes an electromagnetic force generator 620 within the base 598
and positioned below the valve body 602. A control assembly 622 is
operably connected to the electromagnetic force generator 620.
Preferably, the valve body 602 includes a lower portion 624, which
is constructed from a magnetic material. The electromagnetic force
generator 620 desirably is configured to selectively apply an
attractive force to the magnetic portion 624 of the valve body 602.
Thus, the valve body 602 may be moved toward, or retained in, an
open position by the electromagnetic force generator 620.
[0248] With reference to FIG. 34, preferably, a sensor 626 is
positioned on the front suspension assembly 590 for movement with a
hub axis AH of the front wheel 586. In addition, or in the
alternative, a sensor 628 may be secured to the articulating frame
portion 584 for movement with a hub axis A.sub.H of the rear wheel
588. Preferably, each of the sensors 626 and 628 are configured to
sense substantially vertical acceleration force inputs to the front
or rear wheels 586, 588, respectively.
[0249] The sensors 626, 628 are configured to communicate with the
control assembly 622 to provide a control signal indicative of the
acceleration forces acting on the front or rear wheels 586, 588. In
a preferred embodiment, the sensors 626, 628 produce an electronic
signal to communicate with the control assembly 622. In such an
embodiment, the sensors 626, 628 may communication with the control
assembly 622 through a hardwired system or, preferably, over a
wireless communication system. Furthermore, other suitable types of
sensors and methods of communication between the sensors 626, 628
and the control assembly 622 may also be used, such as hydraulic or
mechanical systems, for example. Thus, the control signal may
include changes in hydraulic pressure, or movement of a mechanical
linkage, for example. Other suitable systems apparent to one of
skill in the art may also be used.
[0250] The control assembly 622 preferably includes a processor and
a memory for storing a control algorithm, or protocol. The control
assembly 622 uses the control signal provided by the sensors 626,
628 along with the control algorithm to determine whether to
activate the electromagnetic force generator 620. Thus, when an
appropriate acceleration force input is detected, the control
assembly 622 may activate the electromagnetic force generator 620
to move the valve body 602 from its closed position into an open
position and, if desirable, retain the valve body 602 in an open
position for a period of time, or a delay period.
[0251] Desirably, the control assembly 622 includes an adjustment
mechanism, to permit adjustment of the delay period in which the
valve body 602 is held in an open position and/or the acceleration
force threshold above which the valve assembly 600 is opened.
Preferably, the control assembly 622 includes a first adjustment
knob 630, to permit adjustment of the delay period, and a second
adjustment knob 632, to permit adjustment of the acceleration force
threshold.
[0252] The valve body 602 may be fully controlled by the
electromagnetic force generator 620 or may be configured to be
self-responsive to acceleration force inputs due to the inertia of
the valve body 602. Furthermore, the valve 616 may be provided to
determine a delay period of the valve body 602 or the
electromagnetic force generator 620 may be relied on to provide the
delay in the valve body 602 from returning to the closed position.
In addition, a combination of inertia forces and electromagnetic
forces may be utilized to open the valve body 602 and a combination
of fluid restriction, or fluid suction, forces and electromagnetic
forces may be utilized to provide the valve body 602 with a delay
period in moving from an open position to a closed position.
[0253] Advantageously, by positioning the sensor 626 to sense
acceleration force inputs of the front wheel 586, the valve body
602 in the rear shock absorber 592 may be moved into its open
position before the object (e.g., such as a bump, rock or other
irregularity in the trail surface) which caused the acceleration
force is encountered by the rear wheel 588. Thus, there is no delay
in the altered rate of damping of the rear shock absorber 592 due
to the valve body 602 having to move from its closed position to
its open position upon encountering the bump, or other obstacle,
because the bump has been "anticipated" by the sensor 626
positioned to detect acceleration of the front wheel 586.
[0254] As described above, preferably, the valve body 602 remains
in an open position, or is delayed from returning to its closed
position, so that the rear wheel 588 may absorb a series of bumps
and the valve assembly 600 does not have to reactivate upon
encountering each individual bump. Advantageously, by permitting
the delay to be controlled by the adjustment mechanism 630, a rider
can tune the shock absorber 592 to suit anticipated trail
conditions by providing a relatively short or a relatively long
delay time. In addition, the acceleration threshold may also be
adjusted such the size of bump necessary to open the valve assembly
may be varied.
[0255] Furthermore, the front suspension assembly 590 may also be
configured to include an acceleration sensitive valve assembly,
similar to the valve assembly 600. In addition, the various
features illustrated in FIGS. 1-35 may be used in combination with
one another to provide a desired result, as may be determined by
one of skill in the art.
[0256] Although the present invention has been explained in the
context of several preferred embodiments, minor modifications and
rearrangements of the illustrated embodiments may be made without
departing from the scope of the invention. For example, but without
limitation, although the preferred embodiments described an inertia
valve damper for altering the rate of compression damping, the
principles taught may also be utilized in damper embodiments for
altering rebound damping, or for responding to lateral acceleration
forces, rather than vertical acceleration forces. In addition,
although the preferred embodiments were described in the context of
an off-road bicycle application, the present damper may be modified
for use in a variety of vehicles, or in non-vehicular applications
where dampers may be utilized. Furthermore, the self-centering and
timer features of the inertia valve assembly may be applied to
other types of valves, which may be actuated by acceleration forces
or by means other than acceleration forces. Accordingly, the scope
of the present invention is to be defined only by the appended
claims.
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