U.S. patent application number 09/768119 was filed with the patent office on 2001-10-04 for damper and valve.
Invention is credited to Caron, Gerald F., Crawley, Edward F., Lazarus, Kenneth B., Moore, Jeffrey W., Russo, Farla M., Simpson, Douglas A..
Application Number | 20010025752 09/768119 |
Document ID | / |
Family ID | 25397386 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010025752 |
Kind Code |
A1 |
Crawley, Edward F. ; et
al. |
October 4, 2001 |
Damper and valve
Abstract
A valve regulates fluid displacement in a damper assembly, for
example, displacement of hydraulic fluid in a sealed shock
absorber. The valve is placed between a portion of fluid at one
pressure and regulates the passage of fluid through an aperture or
passage to a portion of fluid at a lower pressure by a blocking
member which moves to obstruct the aperture in accordance with a
desired level of damping. The blocking member is, or is driven by,
an electroactive device, such as a bimorph actuator formed of
ferroelectric material. In one embodiment, the blocking member is a
bimorph which covers the aperture, and is flexibly displaced by
passage of pressurized fluid through the aperture. A controller
provides an electrical actuation signal to move the bimorph toward
or away from the aperture, augmenting or decreasing its closing
bias to affect both the threshold flow initiation pressure and the
rate of flow once the passage opens. Preferably the blocking member
is a flexible piezoelectric assembly, which moves across a gap to
provide a varying obstruction in the near field of fluid flow as
the fluid moves through the passage. Piezobenders, washers and
various pinned or cantilevered constructions of electroactive
elements are adapted to different passage geometries. The valve
assembly may be implemented in a plenum that attaches between
chambers of a fluid housing, and include a first passage leading to
one side, illustratively the high pressure side, of the damping
piston, and a second passage connecting to the other, e.g., low
pressure side of the piston. A piezo bender covers an elongated
opening between the first and second passages and a controller
moves the bender toward or away from the opening to reduce or
increase flow. Preferably, a position sensor connected to the
controller senses piston position, and the controller operates to
energize the bender and to obstruct the opening or to further
restrict flow if the piston position or its velocity is determined
to lie above a threshold. This extends the useful range of the
damper and may allow optimal stroke of the damper during all
conditions of use, enhancing comfort while preventing bottoming
out.
Inventors: |
Crawley, Edward F.;
(Cambridge, MA) ; Lazarus, Kenneth B.; (Concord,
MA) ; Moore, Jeffrey W.; (Arlington, MA) ;
Simpson, Douglas A.; (Cambridge, MA) ; Caron, Gerald
F.; (Andover, MA) ; Russo, Farla M.;
(Brookline, MA) |
Correspondence
Address: |
TESTA, HURWITZ & THIBEAULT, LLP
HIGH STREET TOWER
125 HIGH STREET
BOSTON
MA
02110
US
|
Family ID: |
25397386 |
Appl. No.: |
09/768119 |
Filed: |
January 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
09768119 |
Jan 23, 2001 |
|
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08890955 |
Jul 8, 1997 |
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6193029 |
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Current U.S.
Class: |
188/266.7 |
Current CPC
Class: |
F16F 9/34 20130101; F16F
9/466 20130101; F16F 9/463 20130101; F16F 2224/0283 20130101 |
Class at
Publication: |
188/266.7 |
International
Class: |
F16F 009/32 |
Claims
1. A damper for a hydraulic system of the type having a movable
displacing member that acts on a fluid assembly such that movement
of the displacing member creates a pressure to induce flow in a
passage in accordance with force on the movable displacing member,
wherein the damper comprises a flexible electroactive element
positioned to control flow in the passage and being configured with
electrodes such that application of electrical charge to the
electrodes deforms said electroactive element to control said flow
and regulate damping of the hydraulic system.
2. A damper according to claim 1, further including a controller
for applying an electrical control signal to the electrodes to
control said flow.
3. A damper according to claim 2, further including a sensor for
sensing a state of said system and producing a sensing signal, and
wherein the controller determines said electrical control signal in
response to said sensing signal.
4. A damper according to claim 3, wherein said sensor senses
pressure in said passage.
5. A damper according to claim 3, wherein said sensor determines a
function of position of said movable displacing member.
6. A damper according to claim 2, further including a battery power
source and a voltage multiplier for developing said electrical
control signal.
7. A damper according to claim 2, wherein the controller includes a
switch assembly for providing two distinct voltages to said
electrodes to determine different damping characteristics.
8. A damper according to claim 1, wherein said passage is an
elongated passage and the flexible electroactive element is a sheet
piezobender mounted to variably occlude the passage.
9. A damper according to claim 1, wherein the movable displacing
member is a push-pull piston assembly of a vehicle suspension, and
the damper includes a plenum attached in fluid communication
between opposite sides of the piston assembly, said passage being
formed in the plenum, and wherein the flexible electroactive
element is mounted on the plenum to variably obstruct flow through
the plenum.
10. A damper according to claim 9, wherein the damper is a bicycle
or motorcycle suspension damper.
11. A damper according to claim 9, wherein the electroactive
element includes a piezoelectric bimorph having a free edge
extending over the passage.
12. A damper according to claim 9, wherein the passage includes a
slot.
13. A damper according to claim 1, wherein said flexible
electroactive element constitutes a blocking member having a bias
force or position that varies in accordance with said electrical
charge.
14. A damper according to claim 1, wherein the flexible
electroactive element is configured to be displaced by pressure of
fluid at said passage.
15. A damper according to claim 14, wherein said electrical charge
effectively varies maximum displacement of a blocking member
occurring under influence of fluid flow through the aperture to
regulate shape of a damping curve.
16. A damper according to claim 2, further comprising a sensor to
detect a function of position of the displacing member and wherein
the controller activates the electroactive element in accordance
with the detected function of position.
17. A damper according to claim 16, wherein the controller
activates the electroactive element to increase stiffness of the
hydraulic system and prevent bottoming-out.
18. A damper according to claim 2, wherein the controller switches
said control signal between a first signal level effective to
provide soft damping and a second signal level to provide hard
damping.
19. A damper in accordance with claim 1, wherein the passage and
electroactive element are effective to variably block and therefore
change flow along said passage in a first direction, while
substantially completely blocking flow in a reverse direction.
20. A damper according to claim 2, wherein the passage is located
in a piston and said electroactive element variably obstructs flow
through the piston.
21. A damper according to claim 20, wherein the electroactive
element and passage form a one way valve.
22. A damper according to claim 21, wherein the hydraulic system is
a bicycle suspension and the controller applies a control signal
effective to soften damping characteristics while preventing
bottoming out.
23. A damper according to claim 22, wherein the hydraulic system is
a bicycle suspension and the controller applies a control signal at
a rate faster than natural frequency of the suspension.
24. A damper according to claim 21, wherein the hydraulic system is
a bicycle suspension and the controller varies damping during
individual cycles of movement of said suspension.
25. A damper for a hydraulic system of the type comprising a
movable displacing member in a fluid filled assembly such that
movement of the displacing member forces fluid from a first fluid
filled chamber to a second fluid filled chamber or back as the
member moves forward or back, respectively, in the assembly,
wherein the first and second chambers communicate via an aperture,
and the damper comprises an electrically actuated blocking member
over the aperture, and means for selectively energizing the
blocking member to provide or restrict flow in one direction
through the aperture so as to achieve smoothing and comfort while
effectively preventing bottoming-out of the displacing member.
26. A bicycle shock absorber comprising a hydraulic piston assembly
which divides a closed fluid body into upper and lower chambers an
aperture forming a flow passage between said upper and lower
chambers, a flexible piezoelectric member positioned to deform by
fluid pressure and move to control flow through the passage, and
means for applying electrical energy to the piezoelectric member in
accordance with a desired damping of piston movement.
27. The bicycle shock absorber of claim 26, further comprising a
voltage multiplier circuit for raising voltage of a battery-powered
source to a raised output voltage, and wherein the means for
applying electrical energy applies the raised output voltage to the
piezoelectric member.
28. The bicycle shock absorber of claim 26, wherein said means for
applying electrical energy changes the voltage applied to the
piezoelectric member in accordance with a detected condition of
said shock absorber.
29. The bicycle shock absorber of claim 26, wherein said means for
applying the raised output applies the raised output in accordance
with a microprocessor-selected control state.
30. A damper for a hydraulic system of the type having a movable
displacing member that acts on a fluid assembly such that movement
of the displacing member creates a pressure to induce flow in a
passage in accordance with force on the movable displacing member,
wherein the damper comprises a flexible electroactive element
positioned to control flow in the passage and being opened by said
displacing pressure and configured with electrodes such that
application of electrical charge to the electrodes deforms said
electroactive element to control said flow and regulate damping of
the hydraulic system.
31. A damper for a hydraulic suspension of a wheeled vehicle of the
type having a movable displacing member that acts on a fluid
assembly such that movement of the displacing member creates a
pressure to induce flow in a passage in accordance with force on
the movable displacing member, wherein the damper comprises a
flexible electroactive element positioned to control the flow in
the passage and a controller to change actuating voltage applied to
the electroactive element and enhance efficiency of energy
transferred to the wheels of the vehicle while effectively damping
the suspension.
Description
BACKGROUND
[0001] The present invention relates to a fluid valve, and more
particularly to a valve having different, or variable, settings for
affecting flow of a fluid. In a preferred embodiment it relates to
a fluid valve for damping a hydraulic assembly.
[0002] A number of devices in the prior art employ hydraulic or
fluidic dampers or dashpots to smooth out mechanical motion or
jitter. Vehicle shock absorbers are one example of such devices,
and substantially similar devices are used for office chairs, door
closers, and other applications. In several of these applications
the device is subject to asymmetrical impulse actuations, or
operates in a range of motion about a set point offset from its
center. For example, a vehicle shock absorber may be subject to
upward impulses in which energy is delivered in larger amounts, or
during shorter time intervals, than the gravity- and spring-driven
downward return movements.
[0003] Conceptually, a vehicle suspension generally includes a
spring and a fluid damper. The spring elastically stores and
returns the energy of up-and-down motion of a mechanical assembly
such as the hub driving the wheel to smooth the sharp impacts
caused by running over irregularities in the roadway and restore
the suspension to a neutral position, while the damper dissipates a
portion of the energy in each stroke or cycle to prevent resonant
oscillations from arising. Energy dissipation is achieved by
introducing frictional losses. This may be done by arranging that a
piston connected to the suspension displaces hydraulic fluid
through a flow impediment, e.g., one or more small orifices that
introduce turbulence, drag. viscous shear or other lossy events in
the fluid, which may for example be a liquid or a high pressure
gas.
[0004] Practical implementation of such a mechanical damper entails
considerations of the expected frequency and shape of displacement
impulses, vehicle mass, the desired range of motion of the
suspension, and the required strength and allowable weight of the
damper assembly. For automobiles, suitable shock absorbers are
achieved with piston-type assemblies located at each wheel, and
each weighing two to ten kilograms, with a piston travel of about
five to thirty centimeters. Smaller assemblies may be used on
mechanisms such as steering arms or tailgate assemblies, while even
larger ones may be necessary to accommodate heavy loads or driving
on rough roadway surfaces.
[0005] When an assembly of this type is to be used for a mountain
bicycle, weight is a primary consideration since the total vehicle
weight must be pedaled by the user. Furthermore, the vehicle
handling is strongly affected by the characteristics of the damper.
The front suspension, e.g. a telescoping fork, is the steering
mechanism, and impacts on the rear wheel may pass fairly directly
to the seat, so both the comfort and actual steering aspects of
handling are affected.
[0006] One known bicycle shock absorber employs a piston that
displaces fluid within a hydraulically full and sealed cylinder.
The piston has a number of passages extending between one side and
the other, and each passage has a flexible washer fastened over one
end to act as a one-way flap valve allowing flow in only the
forward, or only the reverse direction. The number and sizes of
these passages are configured to resist fluid displacement and thus
control movement of the piston when the bicycle is subjected to
changing terrain and impact. This construction is structurally
strong and mechanically robust. However, because of the extreme
range of conditions which a bicycle may experience, these shocks
cannot operate optimally under some combinations of diverse
conditions. When the passages are sized to resist flow of hydraulic
fluid only weakly, a smoother or "soft" ride is obtained, but a
large force will cause the shock to quickly "bottom out" and become
ineffective. On the other hand, if the passages are configured to
inhibit flow so much that the shock absorber never bottoms out
under conditions of energetic impact, then the shock absorber
provides a "hard" ride, greatly reducing comfort. It is generally
desirable to have a stiff suspension during pedaling, so that
energy of pedaling is not lost to the suspension. However, between
periods of pedaling, when there are moderate impacts, a softer ride
is needed.
[0007] Accordingly, if would be advantageous to provide a flow
valve having different characteristics suitable for controlling a
range of expected flows occurring over a wide range of driving
conditions.
[0008] It would be further advantageous to provide a flow valve
with variable flow control or regulation characteristics which
change to match existing conditions.
SUMMARY OF THE INVENTION
[0009] This is achieved in accordance with the present invention by
providing a valve to regulate fluid displacement, for example of
hydraulic fluid in a sealed shock absorber, wherein the valve is
placed between a portion of the fluid at one pressure and controls
fluid flow as the fluid is driven along a passage to a portion of
fluid at a lower pressure. An aperture constitutes or communicates
with the passage, and a blocking member is moved to obstruct the
aperture in accordance with a desired level of damping. An
electroactive device, such as an actuator formed of ferroelectric
material, is actuated to position the blocking member.
[0010] In one embodiment, the blocking member is a bimorph which
covers the aperture. The bimorph is deflected by passage of fluid
through the aperture, and a controller provides an electrical
activation signal to drive the bimorph toward or away from the
aperture, augmenting or decreasing its closing bias. This affects
both the threshold flow initiation pressure and the degree of flow
permitted once the passage is opened. In other embodiments the
aperture or passage may be a slot-like channel, with the blocking
member positioned in the slot like a flap or reed. Actuation of the
member bends it into the stream to affect flow. In other
embodiments the passage may feed to a groove formed in a plate
surface, and the blocking member covers the groove. Preferably the
blocking member is a flexible piezoelectric assembly, which moves
across a gap to provide a varying obstruction in the near field of
fluid flow as the fluid moves through the passage. Piezobenders,
washers and various pinned or cantilevered constructions adapt to
different passage geometries.
[0011] In a presently preferred embodiment, a plenum attaches to a
damper housing, and includes a first passage leading to one side,
illustratively the top or high pressure side, of the damping
piston, and a second passage connecting to the other, e.g., bottom
or return pressure side of the piston. A piezo bender covers an
elongated opening between the first and second passages and a
controller moves the bender toward or away from the opening to
reduce or increase flow along the first passage into the second
passage. A position sensor connected to the controller senses
piston position, and the controller operates to energize the bender
and to obstruct the opening or further restrict flow if the piston
position or velocity is determined to lie above a threshold. This
extends the useful range of the damper and may allow optimal stroke
of the damper during all conditions of use, enhancing comfort while
preventing bottoming out and unnecessary loss of rider energy.
Other passages with fixed one-way valves in each direction may be
provided to tailor the general damping characteristics of the
damper.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other features of the invention will be understood
from the description herein, together with illustrative drawings,
wherein:
[0013] FIG. 1 shows a partly schematic cross-sectional view of a
first embodiment of the invention;
[0014] FIG. 1A shows a similar view of a second embodiment;
[0015] FIG. 1B shows prior art fixed damper elements which may be
used in the embodiment of FIG. 1A;
[0016] FIGS. 2 and 2A show exploded views of a third embodiment of
the present invention implemented in a shock absorber;
[0017] FIGS. 3 and 3A illustrate details of a fourth embodiment of
the invention;
[0018] FIGS. 4 and 4A illustrate details of a further embodiment of
the invention; and
[0019] FIGS. 5A-5I illustrate further embodiments.
DETAILED DESCRIPTION
[0020] FIG. 1 shows a basic embodiment of the invention wherein a
system or device includes a body of fluid F at a first pressure
that is driven through a passage 20 and controlled by a deformable
flow restrictor 26 responsive to electrical control signals from a
controller 28. In this embodiment, the deformable flow restrictor
26 is a plate-like member, cantilevered across the passage 20 to
block the opening with a varying degree of obstruction. For
example, the plate 26 may be an encapsulated piezoelectric sheet,
e.g., a two-layer piezo bender made in accordance with the
teachings of commonly-owned published International Patent
application WO95/20827, and clamped over the passage in the manner
of a valve as described, for example, in commonly owned U.S. patent
application Ser. No. 08/760,607 filed Dec. 4, 1996. Each of those
documents is incorporated herein by reference for their
descriptions of methods of fabricating such piezoelectric plate
devices. As relevant here, the plate 26 is mounted to exert a
downward (as illustrated) force over the passage 20, for example in
the range of 0.1 to 1.0 pounds, and to be pushed open and deflected
along the direction of arrow "A" by the fluid pressure. The
controller 28 applies a voltage across the plate to cause it to
bend toward or away from the opening. For example a voltage of
fifty to two hundred volts may be applied, with the polarity
selected to augment or diminish the closing bias of the plate over
the passage.
[0021] FIG. 1A illustrates generally these basic elements of the
flow controller in a damper in accordance with the present
invention. As shown schematically in cross section, a piston 2 is
displaced within a housing H filled with fluid F, dividing it into
two chambers C.sub.1 and C.sub.2. The piston seals against walls of
the chambers, and the housing is hydraulically full, so movement of
the piston in the direction of one chamber forces fluid to the
other chamber, for which purpose a fluid return assembly 10
including a return passage 12 is provided. Thus motion of the
piston along the direction of the axis of its shaft 4 shifts the
relative sizes of the chambers C.sub.1, C.sub.2 and moves fluid
therebetween through the assembly 10. More generally, the
displacing body or source of fluid-driving pressure may reside
entirely separate from the assembly 10, and be connected by a
conduit. For the illustrated structure, in a practical
implementation, the other end of the piston shaft may connect, as
is well understood, to the structure or assembly which is to be
damped, for example to a wheel axle or front fork of a bicycle. As
shown schematically, fluid communication between the two sides of
the piston is effected by passage indicated generally by 12, which
communicates with a space 12a enclosing a bypass opening 20 leading
from chamber C1, via a blocking member 26 positioned over the
opening 20. Fluid pressure drives the member 26 upward, opening the
aperture 20. The resistance to flow presented by the aperture 20,
blocking member 26, and passage 12, together, serves to limit the
rate of fluid displacement, hence the rate and the amount which
piston 2 may travel, when the piston is subjected to an impulse.
Furthermore, as illustrated, the blocking member 26 is suspended
over aperture 20, so that when the piston 2 moves downward to
increase fluid pressure in chamber C2, force on member 26 drives it
closed, in the manner of a reed or flap. The valve therefore
operates unidirectionally to allow flow only from C1 to C2.
[0022] Other mechanisms known in the art and not illustrated in
FIG. 1 may be provided to allow damped flow from C2 to C1, and
further mechanisms of reverse orientation to provide additional
damped flow passages from C1 to C2 may be provided, so that
hydraulic assembly operates as a basic bidirectional damping
assembly. Such other mechanisms may include fixed one-way openings
running directly through the piston head with valved endings to
allow flow in one or both directions, as is known. Such fixed,
one-way flow restriction passages are shown in a piston 2' in FIG.
1B. One passage u opens directly through the piston head and has a
flexible washer w positioned beneath it to flex open when upward
pressure on the piston raises the pressure in the upper chamber and
drives fluid downwardly. A second, illustratively larger, through
passage d has a flexible washer over its top end, and provides a
generally softer restriction or larger flow allowing damped flow
during downward motion of the piston. Additional prior art fixed
damping passages of this type may be provided in the piston 2 of
FIG. 1A.
[0023] Returning to FIG. 1A, the blocking member 26 is suspended
with a fixed mounting portion 26a fastened to the housing, and
positioned to have a free end 26b covering the aperture 20. Control
leads 28a extend from the blocking member to a control unit, not
shown, which provides electrical control signals to regulate the
member 26 and control its damping characteristics as described in
more detail below. In this embodiment, the member 26 is a
cantilevered sheet, such as a piezobender or other electrically
actuated bimorph, and actuation of the bimorph increases or
decreases the force with which it biases the aperture 20 closed,
and correspondingly decreases or increases its displacement,
respectively, away from the opening when it is driven open under
the influence of fluid pressure exiting the aperture.
[0024] In the prior art construction of FIG. 1B, the piston 2'
moves bidirectionally within a cylindrical housing to displace
fluid, and a plurality of passages are formed directly through the
piston head to control the rate of displacement. Generally a first
set of passages includes several of the passages u open to the
upper face of the piston, which have their lower ends obstructed by
a flexible washer or a flap w, so that when pressure above the
piston exceeds the pressure below by a certain amount, fluid may
deflect the washer and pass through the passages. A second set
includes several of the apertures denoted d, which are
illustratively of larger size or may have a more easily displaced
flex flap or washer w, to allow flow in the reverse direction when
the piston is pushed downwardly by the return spring.
Advantageously, the damper of FIG. 1A, or of FIG. 2 discussed
below, may incorporate a piston of this prior art construction. In
that case, the apertures may be made smaller or more obstructed
than usual, to provide a generally harder of stiffer ride. The
piezo-controlled aperture 20 (FIG. 1A) then functions as an
addition flow path, or bypass valve, which allows the shock
absorber to have significantly more extended range, and either an
automated or user-set electric selection of its range or
characteristics.
[0025] In FIG. 1A, the housing H and piston 2 are shown in a
generally vertical orientation, resulting in upper and lower
chambers, and the return or bypass assembly is located lateral to
the principal chambers. Since the housing and bypass are
hydraulically full, actual physical orientation of the assembly is
substantially irrelevant to its structure and operation, and it
will be understood that the damping assembly may reside
horizontally, or obliquely, such as, for example, when connected
between cross-members of an articulated frame or suspension.
However, to provide a uniform vocabulary for referring to the
opposed chambers, these will be referred to simply as "upper" and
"lower" chambers, and these terms will be used to describe the
corresponding portions of the housing and passages from the
chambers. However despite the non-directionality of the damper in
this sense, one asymmetry that is generally present in the
preferred applications, is that the valve assembly preferably
operates to affect the flow of displaced fluid in one direction,
and may be operated to further restrict flow when the piston
displacement is driven toward its end of travel in the housing.
This condition especially arises, in the case of a vehicle shock
absorber, along the direction experiencing roadway impact impulses,
rather than the direction of spring return motion that generally
occurs after some damping of the initial impulse, and is subjected
to lower maximum forces exerted over potentially longer time
intervals. However, even in that context, as noted above the
invention contemplates that the bypass assembly of the invention
may include a further valve mechanism, or more than one such
mechanism, to dampen either one or both directions of displacement.
Such operation will be more readily understood from the detailed
discussion below.
[0026] FIG. 2 shows an exploded perspective view of a damper valve
100 of the present invention incorporated in a bicycle shock
absorber. The valve includes a controlled return assembly 110 which
is mounted to a fluid displacing assembly 140. The fluid displacing
assembly has the overall structure of a bidirectionally movable
hydraulic piston/cylinder assembly, including a piston 142 mounted
on a shaft 144 and reciprocable within a fluid housing 145. An end
cap 146 secures the piston/shaft to the housing 145 and seals about
the shaft, and the piston itself divides the housing into upper and
lower chambers. A lateral surface region 110a of the housing 145 is
configured for sealing attachment to the valve 110, and has a
surface 111 with passages 111a, 111b opening to the interior of the
fluid housing. The passages 111a extend from the surface 111 to the
interior of the housing 145 above the piston 142, while the
passages 111b enter at a level generally lower than the normal
position of the piston. Thus fluid will be driven from the cylinder
through the passages 111a or 111b depending on whether the piston
142 moves upward or downward.
[0027] In this embodiment, the valve assembly 110 sealingly fits
over the surface 111 and is clamped down with a gasket 110b to
maintain the assembly sealed. An electrical controller 140 connects
to the valve 110 and provides control signals to affect its
operation, described further below. Within the assembly 110, shown
in greater detail in FIG. 2A, an aperture plate 130 separates the
passages 111a extending to the first chamber from those extending
to the second chamber, and a piezoelectric member varies flow
characteristics through the aperture to alter and preferably
dynamically control the damping achieved by the assembly.
[0028] As shown in FIG. 2A, the valve assembly 110 includes a lower
aperture plate 130 having an aperture 132 therein and the blocking
member 134 having a flexible conductor or lead in 134a, such as a
ribbon connector, extending therefrom to the controller 140 to
electrically actuate the member 134 and control its blocking force
or position over the aperture 132. The lower aperture plate 130 has
an area smaller than the total surface 111, and is fitted against
that surface with a gasket 110b (FIG. 2) so as to entirely cover
the first set of passages 111a without covering the passages 111b.
Fluid exiting the passages 111a must therefore pass through the
aperture 132 to reach the passages 111b. Above the blocking member
134, which is shown as a cantilevered piezoelectric bending sheet,
a cover plate 136 encloses the second side of the aperture plate,
and assures that fluid exiting aperture 132 is forced through
passages 111b. A seal ring 136a fits around the conductor ribbon
134a of the piezoelectric actuating member, to provide a seal where
the conductor exits the housing of the valve assembly 110, and a
clamp plate 136b compresses the seal over the electrical passage.
The flexible conductor is attached to the controller 140 (FIG. 2).
Thus, the valve forms a bolt-on assembly over a shock absorber to
provide electrically controlled and variable damping of the fluid
flow between chambers of the shock absorber. It will be understood
that since the blocking member 134 is suspended on the outflow side
of aperture 132, it will allow passage of high pressure fluid from
the upper to the lower chamber, but will be urged more tightly in
contact with the aperture by the reverse pressure gradient and
therefore block return flow from the lower to the upper chamber.
Thus, it serves to variably damp motion of the shock absorber in
one direction, allowing a stiffer or softer motion. Such actuation
alone would, of course, result in the shock absorber moving in one
direction and locking up at the end of its travel. Thus, it is
understood that further passages for return of fluid are
provided.
[0029] The return passages may be of similar operation, or may be
fixed passages of conventional type, in which case only the damping
in one direction is electrically varied. In the prior art as noted
above, communication between chambers is accomplished by having two
sets of one-way apertures, for example, flap-covered valves or flow
restrictor passages in the piston head itself as shown in FIG. 1B.
Each set of apertures allows a restricted damped fluid flow from
one side to the other, and the number and areas of the apertures,
as well as the restrictions provided by the flap covers, are
selected to assure that the energy required to move the piston in
each of the two directions is appropriate for the desired level of
damping. These prior art damping passages each have fixed flow
characteristics set by their mechanical structures. By contrast,
the blocking member 134 and aperture 132 provide an electrically
varied damping bypass, whose characteristics are changed by the
controller by application of different electrical signals. The
bypass may thus soften the fixed stiffness provided by the prior
art construction. The exact size or degree of restriction applied
to the aperture 132 will vary depending on measured or intended
conditions, and is controlled by the controller 130.
[0030] The controller 130 may operate as a simple electrical switch
which applies one of several, illustratively three different
control signals across the control member 110 to switch it between
different biased positions over the aperture. These may include a
zero-voltage or mechanically-biased state, and two states to drive
on or the other piezo element of the bimorph bender to enhance or
decrease the blocking force. In accordance with this aspect of the
invention, the blocking member 134 is preferably mechanically
mounted to bear against the aperture 132 in its neutral or
electrically unactuated state, so that it serves as a plate
cantilevered over the opening. The member 134 is a preferably a
piezoelectric bimorph constructed as shown, for example, in
commonly-owned U.S. patent application Ser. No. 08/188,145 filed on
Sep. 10, 1996, or is otherwise built to achieve a stiff member that
develops a high actuation force in a short time, and to reside in
the fluid and resist cracking and electrode failure. Thus, when a
voltage of one polarity and magnitude, illustratively between about
ten and several hundred volts, is applied to the blocking member
134, it deflects and bends toward the aperture, increasing its bias
force. When the controller applies a different signal, the blocking
member 134 moves away or is urged in the opposite sense, decreasing
its bias force and allowing the passage 132 to open more easily, at
lower pressures, and to open wider, thus permitting greater amounts
of fluid through per unit time. The aperture may have a relatively
small area, between several square millimeters and about one square
centimeter, so despite the relatively high pressures which may
arise, the piezo actuation forces are sufficient to significantly
resist opening of the valve and substantially alter the flow
through the aperture once it has opened. This is because when the
stiff but flexible piezo plate is pushed aside by the fluid
pressure, the blocking member moves in the near field of fluid flow
to still exert frictional drag on the moving fluid. At the
relatively small gaps involved, and with flow interacting with the
larger areas of the actuator sheet, fluid control forces are
significant. Furthermore, the closing force is substantial,
typically between about 0.1 and 1.0 pounds.
[0031] Preferably, the controller is powered by a simple and light
weight dry cell battery, such as a nine volt battery of small size,
which may further be a rechargeable cell. Voltage doubler circuits
of solid state construction are preferably provided, and may be
arranged in series as a charge ladder to increase the voltage to
suitably high level, so that the piezo elements can be quickly
switched between charge states and actuated in a relatively small
time interval. For piezoelectric elements about ten to sixty mils
thick, an actuation voltage of about two hundred to six hundred
volts is used, and the response time of the actuator is shorter
than the natural frequency of the vehicle suspension.
[0032] The controller in a further embodiment may receive a signal
from a position sensor which detects the proximity of the piston to
the top of the cylinder. Such a position sensor 125 is shown in
FIG. 2. This may be implemented in one embodiment by forming the
housing of non-magnetic material and providing ferritic or magnetic
material in the piston head, and providing the sensor 125 as a
magneto-resistive element located in the housing to detect in a
continuous manner the distance to the piston head. In accordance
with this aspect of the invention, the controller monitors the
signal received from the position sensor, and determines the
position of the piston in the chamber and/or the velocity or
direction of piston movement. As noted above, in general a hard
(stiff) or soft ride may be provided by actuating the member 26
with driving signals towards or away from the opening 20. The
controller preferably monitors piston position to determine when
substantial movement occurs. Normally a stiff (blocked) position is
used for pedaling, switching to a softer damping position for road
impacts. As piston position approaches the end-of-travel, the
controller may again switch to further obstruct the opening. Thus,
as the piston continues to move upward, the controller then
increases the actuating signals to increase the blocking force
applied by the member 134. This further restricts flow through the
aperture and assures that the piston does not bottom out against
the top of the chamber. However, when the piston is moving upward
but has not approached the top of the chamber, the controller may
apply a lesser signal, or no signal at all, or a reverse polarity
signal, to allow less obstructed flow through the bypass and
produce a relatively soft damping effect and smoother ride during
the early stages of piston travel. The shock absorber therefore
performs with greater comfort than it would if the suspension were
fixedly made stiff enough for maximum pedaling efficiency, or soft
enough for general purpose damping. Further, it may assure the
piston does not mechanically contact the top or bottom of the
cylinder.
[0033] The invention also contemplates constructions wherein the
controller incorporates more complex detection mechanisms or
software signal processing to determine piston speed, for example
by computing the difference between successive positions, or piston
acceleration, to recognize the severity of an impact before the
piston has traveled too far, and to respond by increasing the
damping during strong or abrupt piston strokes. Other sensors, such
as a pressure sensor may alternatively be provided from which the
controller determines the appropriate direction and magnitude of
its blocking member control signal. In general velocity-indicated
signals are derived by a simple processor-implemented differencing
of the basic position or pressure values sensed by an
indicator.
[0034] The invention further contemplates constructions wherein the
passages between upper and lower chambers run through the piston
head, and piezoelectric control members are mounted on the piston
itself to variably restrict these flow passages. FIGS. 3A, 3B and
4A, 4B illustrate such embodiments. In each of these
configurations, a piston has multiple passages extending through
its heads, and the electroactive flow restrictor 26 is mounted,
preferably concentrically on the shaft, and is deformed or actuated
to vary the damping achieved by the passages. Electrical leads may
be run through the shaft, or otherwise provided for energizing the
piezo portions PZ. A support plate 26a may be used to limit travel
and further define the aperture restriction geometry. The passages
need not be cylindrical holes, but may be openings or passages of
any shape adapted to be effectively obstructed by an electroactive
sheet elements. Such shapes may include, for example, a slot-like
passage of rectangular cross section, in which a bimorph sheet or
actuator deforms to bend into the flow stream and obstruct the
passage. Other passages or openings, and actuator shapes are also
contemplated, and may be adapted to the particular range of
pressures and rates of flow which are expected in use.
[0035] Thus, rather than a cantilevered sheet or plate having an
end extending over a opening, a number of mechanical systems
including pinned-pinned, clamped-pinned, clamped-sliding and other
actuator mountings are envisaged for effectively obstructing flow
through a passage, or through an orifice or aperture. Several such
configurations are shown in FIGS. 5A-5I.
[0036] These FIGURES illustrate piezobenders in various mechanical
configurations adapted for the damper of the present invention. The
embodiment of FIG. 5A represents a cantilevered piezobender as
shown in the earlier FIGURES, while FIG. 5B shows an embodiment
pinned at both ends. Such a configuration achieves a higher
blocking force at the nozzle or aperture. A pre-curved blocking
element (FIG. 5E) may be employed to provide greater displacement,
or faster overall response, while FIGS. 5F and 5G show obstructors
in the flow passage itself. The electroactive element may also be
positioned to move an obstructing body 27, as shown in FIG. 5I.
[0037] In addition to their specific actuation characteristics, one
of these configurations may be selected to fit a particular housing
or mechanical structure in which the flow damper is to be
housed.
[0038] This completes the description of the basic embodiments and
configurations of the present invention. The invention being thus
disclosed and described, variations and modifications thereof will
occur to those skilled in the art and all such variations and
modifications are considered to be within the scope of the
invention as defined in the claims appended hereto.
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