U.S. patent application number 09/781868 was filed with the patent office on 2002-08-15 for piston and rod assembly for air-actuated variable damping.
This patent application is currently assigned to Delphi Technologies, Inc.. Invention is credited to Jensen, Eric L., Kruckemeyer, William C., Miller, Troy Allen, Oliver, Michael L..
Application Number | 20020108825 09/781868 |
Document ID | / |
Family ID | 25124212 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020108825 |
Kind Code |
A1 |
Miller, Troy Allen ; et
al. |
August 15, 2002 |
PISTON AND ROD ASSEMBLY FOR AIR-ACTUATED VARIABLE DAMPING
Abstract
A damper includes a piston that carries a relatively compact
control valve for controlling fluid flow through the piston. The
control valve provides a variable amount of damping by regulating
damper fluid flow between the extension chamber and the compression
chamber of the damper during extension and compression strokes.
Pressure regulation across the piston is controlled through a flow
path as determined by the control valve. The damping force of the
damper varies depending upon the loading conditions of the vehicle.
The control valve is air pressure actuated to adjust the damping
force and control the flow of fluid in the flow path.
Inventors: |
Miller, Troy Allen; (Xenia,
OH) ; Oliver, Michael L.; (Xenia, OH) ;
Kruckemeyer, William C.; (Beavercreek, OH) ; Jensen,
Eric L.; (Dayton, OH) |
Correspondence
Address: |
Scott A. McBain, Esq.
Delphi Technologies Inc.
P.O. Box 5052
Mail Code 480-414-420
Troy
MI
48007-5052
US
|
Assignee: |
Delphi Technologies, Inc.
|
Family ID: |
25124212 |
Appl. No.: |
09/781868 |
Filed: |
February 12, 2001 |
Current U.S.
Class: |
188/280 ;
188/322.15; 267/64.11; 280/124.157 |
Current CPC
Class: |
B60G 2500/112 20130101;
F16F 9/512 20130101; B60G 17/08 20130101; B60G 2400/821 20130101;
B60G 2600/184 20130101; F16F 9/3482 20130101; F16F 2230/183
20130101; B60G 2400/61 20130101; F16F 9/466 20130101; F16F 9/461
20130101; F16F 9/516 20130101; B60G 17/0152 20130101 |
Class at
Publication: |
188/280 ;
267/64.11; 188/322.15; 280/124.157 |
International
Class: |
F16F 005/00; B60G
013/00; F16F 009/49 |
Claims
We claim:
1. A suspension damper comprising: a cylinder defining a cavity
being substantially filled with a fluid; a piston slidably
positioned in the cylinder separating the cavity into a compression
chamber and an extension chamber; a rod coupled to the piston and
extending through one of the chambers and exiting the cavity; a
passage through which the fluid moves between the extension chamber
and the compression chamber during sliding of the piston in the
cylinder; and an air pressure actuated control valve assembly
responsive to an air pressure input for adjustment to and between a
plurality of positions to control the movement of fluid in the
passage between the extension and compression chambers; wherein a
damping force of the suspension damper is a function of the air
pressure input.
2. The suspension damper of claim 1 wherein the passage has a first
branch and a second branch and the flow of the fluid through the
second branch is controlled by the air pressure actuated control
valve assembly.
3. The suspension member of claim 2 further comprising: a first and
a second bi-directional deflectable annular disc in the first and
second branches, respectively, to control the damping forces during
movement of the piston toward both the extension and compression
chambers.
4. The suspension member of claim 1 wherein the air pressure input
is delivered to the air pressure control valve assembly via the
rod.
5. The suspension member of claim 4 further comprising: a filter
located in the rod to filter out selected ranges of the air
pressure input.
6. The suspension member of claim 1 wherein the air pressure
actuated control valve assembly adjusts to and between open, closed
and intermediate positions to provide a variable damping force.
7. The suspension member of claim 1 wherein the air pressure
actuated control valve assembly is biased toward an open
position.
8. The suspension member of claim 1 wherein the air pressure
actuated control valve assembly further comprises a spool
valve.
9. The suspension member of claim 1 wherein the air pressure
actuated control valve assembly further comprises a pneumatically
expansible member.
10. The suspension member of claim 9 wherein the pneumatically
expansible member further comprises a bellows.
11. The suspension member of claim 1 wherein the passage is through
the piston.
12. The suspension member of claim 1 wherein the piston, the
passage, the air pressure actuated control valve assembly and a
portion of the rod are contained within the cylinder.
13. The suspension member of claim 12 wherein the air pressure
actuated control valve assembly is in the piston.
14. A suspension damper comprising: a cylinder defining a cavity
being substantially filled with a fluid; a piston slidably
positioned in the cylinder separating the cavity into a compression
chamber and an extension chamber; a rod coupled to the piston and
extending through one of the chambers and exiting the cavity; a
passage in the piston through which the fluid moves between the
extension chamber and the compression chamber during sliding of the
piston in the cylinder, the passage having a first branch and a
second branch; an air pressure actuated control valve assembly
located in the piston and being responsive to an air pressure input
for adjustment to and between open, closed and intermediate
positions to provide a variable damping force by controlling the
movement of fluid in the second branch of the passage between the
extension and compression chambers, the air pressure input being
delivered to the air pressure actuated control valve via the rod,
the air pressure actuated control valve assembly being biased
toward an open position; wherein the air pressure actuated control
valve assembly further comprises a spool valve coupled to a
pneumatically expansible member; and a filter located in the rod to
filter out selected ranges of the air pressure input; wherein a
damping force of the suspension damper is a function of the air
pressure input.
15. The suspension member of claim 14 further comprising: a first
and a second bi-directional deflectable annular disc in the first
and second branches, respectively, to control the damping forces
during movement of the piston toward both the extension and
compression chambers.
16. A suspension damper comprising: a cylinder defining a cavity
being substantially filled with a fluid; a piston slidably
positioned in the cylinder separating the cavity into a compression
chamber and an extension chamber; a rod coupled to the piston and
extending through one of the chambers and exiting the cavity; a
passage through which the fluid moves between the extension chamber
and the compression chamber during sliding of the piston in the
cylinder; and means for controlling the movement of the fluid in
the passage between the extension and compression chambers, the
controlling means being responsive to an air pressure input;
wherein a damping force of the suspension damper is a function of
the air pressure input.
17. A suspension system for a vehicle comprising: a pneumatic
suspension sub-system selected from at least one of the following:
a vehicle air-suspension system and a vehicle air-leveling system,
the pneumatic suspension sub-system generating an air pressure
value as a function of a weight of the vehicle and a condition of
the road on which the vehicle travels; at least one damper
comprising: a) a cylinder defining a cavity being substantially
filled with a fluid; b) a piston slidably positioned in the
cylinder separating the cavity into a compression chamber and an
extension chamber; c) a rod coupled to the piston and extending
through one of the chambers and exiting the cavity; d) a passage
through which the fluid moves between the extension chamber and the
compression chamber during sliding of the piston in the cylinder;
e) an air pressure actuated control valve assembly to control the
movement of fluid in the passage between the extension and
compression chambers; wherein the damper is operably coupled to the
pneumatic suspension sub-system to receive the air pressure value
as an input to the air pressure actuated control valve assembly;
wherein a damping force of the damper is a function of the air
pressure value.
18. A method of adjusting a damping force of a vehicle suspension
damper, the method comprising the steps of: generating an air
pressure input from a pneumatic suspension sub-system selected from
at least one of the following: a vehicle air-suspension system and
a vehicle air-leveling system; transmitting the air pressure input
to the vehicle suspension damper; controlling a flow of fluid
through a passage in the vehicle suspension damper through which
the fluid may move between extension and compression chambers in
the vehicle suspension damper; wherein the damping force is a
function of the flow of fluid through the passage.
19. The method of claim 18 wherein the generating of the air
pressure input is derived from a weight of the vehicle and a
condition of the road on which the vehicle travels.
20. The method of claim 18 further comprising: filtering a portion
of the air pressure input prior to transmitting it to the vehicle
suspension damper.
21. The method of claim 18 wherein the passage further comprises a
first and a second branch and the controlling of the flow of fluid
further comprises selectively restricting the flow through only the
second branch.
22. The method of claim 18 wherein the controlling of the flow of
fluid further comprises adjusting a control valve in the vehicle
suspension damper to and between open, intermediate and closed
positions.
23. The method of claim 18 wherein the controlling of the flow of
fluid provides a variable damping force from the vehicle suspension
damper.
24. The method of claim 22 further comprising: biasing the control
valve toward the open position.
25. A method of adjusting a damping force of a vehicle suspension
damper, the method comprising the steps of: generating an air
pressure input from a pneumatic suspension sub-system selected from
at least one of the following: a vehicle air-suspension system and
a vehicle air-leveling system, the air pressure input being derived
from a weight of the vehicle and a condition of the road on which
the vehicle travels.; filtering a portion of the air pressure
input; transmitting the air pressure input to the vehicle
suspension damper; controlling a flow of fluid through a passage in
the vehicle suspension damper through which the fluid may move
between extension and compression chambers in the vehicle
suspension damper, the passage further comprising a first and a
second branch and the controlling of the flow of fluid further
comprising selectively restricting the flow through only the second
branch by adjusting a control valve in the vehicle suspension
damper to and between open, intermediate and closed positions;
biasing the control valve toward the open position; wherein the
damping force is a function of the flow of fluid through the
passage.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to a valved damper and more
particularly, to a damper that is pneumatically controlled to
provide variable damping forces.
[0002] Conventional vehicle suspension dampers typically consist of
direct double-acting telescopic hydraulic passive dampers. They are
generally described as either shock absorbers or struts. A primary
purpose of shock absorbers is to dampen oscillations of the vehicle
suspension spring. This is accomplished by converting kinetic
energy in the form of motion between sprung and unsprung masses of
a vehicle into heat and then dissipating the heat. Struts also
serve this capacity and in addition, support reaction and side-load
forces on the suspension.
[0003] Typical dampers are hydraulic devices using oil as the fluid
medium for converting motion into heat. As the damper is cycled, a
piston is forced to move in extension and compression directions
through the oil that is contained within a cylinder tube. This
creates pressure within a portion of the cylinder tube and a
consequent pressure drop across the piston. During an extension
stroke, high pressure is created in the extension chamber of the
cylinder tube above the piston, forcing oil to flow through the
valving of the piston. During a compression stroke, high pressure
is created in the compression chamber of the cylinder tube below
the piston, forcing oil to flow back through the piston's
valving.
[0004] As oil is forced to flow through the orifices in the piston
a pressure drop is effected and the oil is heated. In this way, the
damper dissipates energy stored by the vehicle's suspension
springs. The extent to which the oil is heated and consequently,
the amount of energy dissipated is controlled by the size of the
orifices in the piston and the amount of flow forced through the
piston valving.
[0005] Damping force is a common measurement of the performance of
a damper. It is used to quantify the amount of spring control
provided by a damper. Passive dampers are tuned to provide selected
vehicle performance characteristics. Because passive dampers
provide a set damping characteristic they are generally somewhat of
a compromise in providing optimum damping performance over a wide
range of operating conditions.
[0006] The concept of dampers with an electrically controlled
damping force has been developed in the art wherein an algorithm is
used to provide a control mechanism as a means of varying the
damping force provided by a damper. One example is shown in U.S.
Pat. No. 5,690,195 hereby incorporated by reference. Electrical
control is typically achieved by varying the valving orifices in
response to various sensors which are used to detect vehicle
operating conditions. Such dampers adjust the damping force in
response to the control mechanism so that various performance
characteristics can be provided by an individual damper. An
electrically controllable orifice however, provides less than ideal
levels of control at low flow rates.
[0007] Electrically controlled hydraulic dampers for vehicle
suspensions have, in principle, been known in the art for some
time. However, their actual widespread application and use have
been tempered because of the expense of such a system.
SUMMARY OF THE INVENTION
[0008] This invention solves the above-described and other problems
associated with known systems by providing a damper with variable
damping fluid flow control in a preferred monotube design. This is
accomplished through variable state pressure regulation in a valved
damper piston. A damper in accordance with a preferred embodiment
of this invention includes a cylinder slidably carrying a piston
which separates the cylinder into extension and compression
chambers. The piston carries a control valve for controlling fluid
flow through the piston. The control valve provides a variable
amount of damping force by regulating damper fluid flow between the
extension chamber and the compression chamber of the damper during
extension and compression strokes. Pressure regulation across the
piston is controlled through a primary and a secondary flow path in
which the flow through the secondary flow path or branch is
determined by the control valve. The primary flow path or branch
remains open.
[0009] A first bi-directional, deflectable, single annular disc
passive damping valve mechanism is positioned in the primary flow
path of the piston between the extension and compression chambers.
The first passive damping valve provides pressure regulation across
the piston for both extension and compression strokes during all
operation of the damper. A second bi-directional, deflectable,
single annular disc passive damping valve mechanism is positioned
in the secondary flow path of the piston between the extension and
compression chambers. The second passive damping valve selectively
provides pressure regulation across the piston in parallel with the
first passive damping valve during both extension and compression
strokes.
[0010] The control valve includes a movable element responsive to a
control mechanism. The flow passage through the piston include a
secondary flow path or second branch that communicates through
ports in the control valve, and flow therethrough is alternately
interrupted, completely or partially, or permitted as determined by
the control mechanism or valve. When flow through the second branch
is permitted by the control valve, the flow passage through the
piston extends through the first passive valve and the control
valve and through the second branch that includes the second
passive valve in a parallel arrangement with the first passive
valve. When flow through the second branch is interrupted by the
control valve, the flow passage through the piston extends only
through the first branch which includes the first passive valve
individually.
[0011] The invention includes a hydraulic damper that uses
pneumatic control of the control valve to vary damping levels. Air
pressure from an air-suspension or air-leveling system of the
vehicle is vented in a presently preferred embodiment of this
invention to a bellows or air-pressure actuated control valve
located in the piston. The bellows or control valve compresses in
response to higher pressure from the air-suspension or air-leveling
system. The compression of the bellows control valve controls the
position of a spool valve and as the spool valve is closed, one of
two parallel flow paths through the piston is closed. Each flow
path has its own valving. When only one of the flow paths is open,
a higher damping force is generated. As a result, a continuously
variable damper provides varied damping force according to the
vehicle payload and operating conditions.
[0012] The pneumatic control of the damper uses the air pressure of
the vehicle's air-suspension or air-leveling systems to control the
position of the spool valve. The air pressure input to the control
valve varies according to the overall vehicle weight as well as the
road conditions. As the damper is stroked due to road input, the
pressure varies. Higher frequency pressure oscillations resulting
from road input are filtered with an orifice mounted inside a
hollow piston rod in an attempt to limit damper variation to only
static vehicle weight. The resulting air pressure is used as an
input to the bellows or air-actuated control valve. A higher
vehicle payload will result in higher pressure surrounding the
bellows resulting in contraction of the bellows. As the bellows
contracts or compresses, the secondary flow path is blocked by the
spool valve. A higher pressure surrounding the bellows will result
in the bottom face of the bellows lifting and the spool valve and
thereby shutting off the secondary flow path. The pneumatic system
is isolated from the piston hydraulic system with seals that are
held in place with a seal plate, seal retainer and piston
adapter.
[0013] The air pressure input must first overcome a preload force
before the bellows will move or compress. As a result, low
pressures will not cause a change in the bellows and the spool
valve will remain open. The control valve is biased by a spring
into an open position. Both the primary and secondary valves are
then open which generate damping forces optimized for normal
driving conditions when the vehicle is not heavily loaded. In the
case of a pressure supply failure, the vehicle still operates
optimally when it is not heavily loaded. When the vehicle is
heavily loaded, the air pressure reaching the bellows is also
higher thereby causing the bellows to compress, the spool valve to
move toward the closed position and the overall damping forces to
be higher. At intermediate payloads, the spool valve will only be
partially moved and the secondary flow path is partially blocked
resulting in intermediate damping forces. As a result, the damper
is continuously variable over the given pressure range. Changing
the characteristics of the bellows, the spool spring, bellows
compression preload or the orifice insert will tune the performance
of the damper.
[0014] Advantages of the present invention include internal
packaging of the control valve in the piston which utilizes less
space than externally packaged designs that carry the control valve
outside the cylinder tube or designs that carry components of the
control valve within the piston rod. Additionally, the damper of
this invention reduces the total number of parts and can be easily
included in common air-leveling systems. Moreover, the invention is
adaptable to vehicles with other pressurized air systems (i.e., air
brakes). The invention provides continuously variable control
without the need for electronic control systems or electrical
connections.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The objectives and features of the invention will become
more readily apparent from the following detailed description taken
in conjunction with the accompanying drawings in which:
[0016] FIG. 1 is a fragmentary cross sectional view of a presently
preferred embodiment of a damper according to this invention with a
control valve in a closed position;
[0017] FIG. 2 is a view of the piston assembly of FIG. 1 with the
control valve in an open position;
[0018] FIG. 3 is a schematic block diagram of the operation of the
damper of FIG. 1; and
[0019] FIG. 4 is a graph including a range of pressure conditions
showing damping force graphed on the abscissa and velocity graphed
on the ordinate for the damper of FIG. 1.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT
[0020] Referring to the drawings, illustrated in FIGS. 1 and 2 is
an alternating state pressure regulation valved monotube suspension
damper embodied as a shock absorber 10 according to a presently
preferred embodiment of this invention. The vehicle suspension
damper or shock absorber 10 includes a single tube designated as
cylinder 12. Cylinder 12 has a closed lower end (not illustrated),
and an upper end closed by a rod guide (not illustrated), in a
conventional manner defining cylindrical cavity 16. Cavity 16 is
divided into an extension chamber 18 and a compression chamber 20
by a piston assembly 22. Piston assembly 22 is sealingly disposed
in cylinder 12 for slidable axial movement therein.
[0021] Securely connected to piston assembly 22 is piston rod 24
which extends through the extension chamber 18 of the cylinder tube
12 exiting the cavity 16 through the rod guide. The upper end of
the piston rod 24 is adapted for connection to the sprung mass
(body), of the motor vehicle (not illustrated), in a conventional
manner. A similar means of attachment is provided at the lower end
(not illustrated), of cylinder 12 for connection to the unsprung
mass (wheel assembly), of the vehicle in a conventional manner.
Relative movement between the sprung and unsprung masses of the
vehicle, to which shock absorber 10 is connectable, produces
relative axial sliding movement of the piston assembly 22 within
the cylinder 12.
[0022] The piston assembly 22 includes a control valve assembly 26
that is carried on the bottom of the rod 24 and is connected
therewith by mating threads. A piston cup 28 is mounted on the
control valve assembly 26 and is fixed thereon by a threaded nut
30. The piston cup 28 includes a seal ring 32 made of low friction
material. Seal ring 32 sealingly bears against the cylinder 12
providing fluid separation between the compression chamber 20 and
the extension chamber 18.
[0023] The piston cup 28 spans between the control valve assembly
26 and the cylinder 12 opening at its top to the extension chamber
18 within the rim 34. Piston cup 28 is provided with a plurality of
openings 36 which open the interior of the piston cup 28 to the
compression chamber 20. Therefore, a flow passage 38 is provided
through the piston assembly 22 between the compression chamber 20
and the extension chamber 18. The flow passage 38, and more
specifically a first or primary branch 40 thereof, is normally
closed by the first or primary valve assembly 42. A second or
secondary branch 44 of the flow passage 38 extends through a spool
valve 48 of the control valve assembly 26 and the second valve
assembly 46 in parallel to the branch 40.
[0024] More specifically, a valve plate 50 is positioned on the
control valve partially within the piston cup 28 and supports the
primary valve 42 in the form of a bi-directional, deflectable,
single annular valve disc 42a. A second bi-directional,
deflectable, single annular valve disc 46a is supported by the
piston cup 28. The spool valve 48 is carried within the control
valve assembly 26 in central bore 52 and operates to selectively
provide the flow path 44 between the openings 54 and 56 through the
control valve assembly 26. Accordingly, during compression or
extension travel of the piston assembly 22 within the cylinder 12
fluid flow between the extension chamber 18 and the compression
chamber 20 can be through either of two branches 40 and 44 through
the flow passage 38 across the piston assembly 22.
[0025] When the spool valve 48 is in the open position as shown in
FIG. 2, fluid flow travels through the primary valve assembly 42,
deflecting the disc 42a if pressure differentials dictate, and
through the spool valve 48 and secondary valve assembly 46
deflecting disc 46a providing one level of damping typically for
lighter vehicle loading conditions. This effects a first pressure
drop for fluid travel across the piston assembly 22 providing a
first degree of pressure regulation for a first state of operation
of the shock absorber 10. When the spool valve 48 is moved to its
closed position (see FIG. 1), fluid flow between the extension
chamber 18 and the compression chamber 20 travels solely through
primary valve assembly 42 deflecting disc 42a providing another
level of damping typically for heavy vehicle loading. This effects
a second pressure drop for fluid travel across the piston assembly
22 providing a second degree of pressure regulation for a second
state of operation of the shock absorber 10.
[0026] For more specificity, additional reference is directed to
FIG. 2, along with FIG. 1. The control valve assembly 26 includes
housing 58 and substantially cylindrical body 60. The second flow
path of branch 44 is effected through the control valve assembly 26
between the openings 54 provided in the side of cylindrical body 60
and the opening 56 provided in the end of cylindrical body 60 at
the bottom of piston assembly 22. The spool valve 48 is active
during operation of the shock absorber 10, in-that, it is
selectively positioned so that an open, intermediate or closed flow
path 44 is provided between the openings 54 and 56.
[0027] The piston cup 28 is received on the cylindrical body 60 of
the control valve assembly 26 and fixed thereon by the nut 30
thereby additionally carrying the various passive valving
components of the piston assembly 22. Valve assemblies 42 and 46 of
the piston assembly 22 are passive, in-that they respond only by
deflection upon the presence of fluid pressure differentials at
various stages across the piston assembly 22.
[0028] The juncture between the cylindrical body 60 and the housing
58 of the control valve assembly 26 includes an annular shoulder
62. A plurality of radially extending openings 54 are formed
through the cylindrical body 60 at the annular shoulder 62
intersecting the central bore 52. The spool valve assembly 48 opens
and closes the openings 54 to the central bore 52.
[0029] A valve plate 50 is positioned over the cylindrical body 60
receiving the annular shoulder 62 within counterbore 64 and bearing
against the housing 58. An annular groove 66 is formed in the valve
plate 50. A number of openings 68 extend through the valve plate 50
providing a passage between the openings 54 and the annular groove
66. Therefore, when the spool control valve 48 is open, the
secondary branch 44 of passage 38 is open through the central bore
52 , openings 54 and openings 68 to the annular groove 66.
[0030] Valve assembly 46 includes the valve disc 46a that is
received over the cylindrical body 60 of control valve assembly 26
against the valve plate 50. The valve disc 46a includes an inner
circumference 70 that is spaced away from the cylindrical body 60.
A center disc 72 is received over the cylindrical body 60 within
the inner circumference 70. The center disc 72 includes a plurality
of arms (not shown) that extend radially outward and operate to
maintain the valve disc 46a in an operable position.
[0031] A support disc 74 is positioned over the cylindrical body 60
adjacent the valve disc 46a and center disc 72. The support disc 74
includes a number of notches (not shown) formed around its outer
perimeter. The arms (not shown) remaining between each pair of
these adjacent notches provide a bearing surface for the inner
periphery 70 of the valve disc 46a. The outer periphery 76 of the
valve disc 46a bears against an annular rib 78 of the valve plate
50. The annular groove 66 spans radially across a portion of the
center disc 72 and the valve disc 46a. The valve disc 46a as
positioned by the center disc 72 on the cylindrical body 60, is
biased between the arms at the outer periphery of the support disc
74 and the annular rib 78 of the valve plate 50.
[0032] An annular stop plate 80 is positioned over the cylindrical
body 60 of control valve assembly 26 engaging the secondary valve
assembly 46 and maintaining the components thereof in axial
position. The stop plate 80 includes an angled annular wall 82. The
annular wall 82 provides a stop for valve disc 46a when it is
deflected. The annular wall 82 is oriented such that when the valve
disc 46a is fully deflected during extension travel of the shock
absorber 10, with its inner circumference 70 supported on the
support disc 74, the valve disc 46a is positioned against the
annular wall 82.
[0033] The primary passive valve assembly 42 including support disc
84, center disc 86 and valve disc 42a is received over the
cylindrical body 60 of control valve 26 adjacent the stop plate 80.
The support disc 84 includes a plurality of arms (not shown) like
the arms of support disc 74. The center disc 86 includes a
plurality of arms (not shown) like the arms of center disc 72. The
valve disc 42a is supported at its inner circumference 88 by the
support disc 84 and at its outer periphery 90 by annular ledge 92
of piston cup 28. The valve disc 42a normally closes off the
openings 36 through the piston cup 28. When the valve disc 42a is
fully deflected during compression travel of the shock absorber 10,
with its inner circumference 88 supported on support disc 86 , the
valve disc 42a is positioned flat against the angled annular wall
94 of stop plate 80.
[0034] A main spacer 96 is positioned against valve disc 42a
bearing against the annular leg 98 of piston cup 28 with the nut 30
applying a fixed bias to the annular leg 98 maintaining the piston
cup 28, the first and second valve assemblies 42, 46 and the valve
plate 50 in position on the cylindrical extension 60 of control
valve assembly 26. This applies a preload to the valve discs 46a
and 42a in a predetermined manner to selectively effect the damping
performance produced by their deflecting characteristics.
[0035] The control valve assembly 26 includes the cylindrical body
60 and housing 58. The valve spool 48 is received within the valve
cylinder body 60 and coacts therewith to provide a means of opening
and closing the secondary branch 44. The valve spool 48 includes a
series of openings 104 registering with the openings 54 in the
cylindrical body 60 to provide the second branch 44 passageway
through the valve spool 48. When the valve spool 48 is in an open
position (FIG. 2), the openings 104 and 54 register with each
other. Depending upon the position of the valve spool 48,
intermediate or partially opened positions may be provided when the
openings 104 and 54 are only partially in register.
[0036] To close the spool valve 48, the openings 104 are placed out
of registry with the openings 54, blocking off fluid flow through
the second branch 44 of the control valve 26 by movement of the
valve spool 48 rearwardly.
[0037] The present embodiment describes a normally open spool valve
48. When preferable, a closed valve 48 is provided by simply moving
the axial location of the openings 104 out of registry with the
openings 54. The spool valve 48 is biased toward the open position
by a spring 108. The end 110 of the valve spool 48 is also open and
receives the spring 108 that is engaged with snap ring 112 at
piston assembly 22 at open end 102 and biases the valve spool 48
into the open position. The opening through the end 110 provides
fluid balancing on opposed sides of the valve spool 48 to preempt
the formation of opposing fluid forces across the valve spool
48.
[0038] The valve spool 48 is adjusted to and between the open,
intermediate and closed positions pneumatically by an air pressure
input generated in an air suspension or air leveling system 116 of
the vehicle. Air pressure from the air suspension or air leveling
system 116 of the vehicle is supplied to the end of the piston rod
24. This air pressure input to the suspension damper or shock
absorber 10 is a function of the overall vehicle weight 118 as well
as the road input or operating conditions 120 for the vehicle. The
piston rod 24 is hollow and includes a generally cylindrical bore
or channel 122 through which the air pressure input is delivered to
a central chamber 124 within a piston adapter 126. A bellows or
other expansible member 128 is located within the chamber 124 and
is responsive to the air pressure input delivered thereto through
the bore 122 in the piston rod 24. The piston rod 24 includes an
orifice insert 130 seated within a sleeve 132 to filter or
segregate out higher frequency pressure oscillations resulting
typically from road input 120. As a result, the air pressure input
received by the bellows 128 is primarily a static pressure
resulting from changes in the vehicle weight 118. The higher the
vehicle's payload, the higher pressure input value is experienced
by the bellows 128. This results in a higher pressure surrounding
the bellows 128 in the chamber 124. The greater the air pressure
input in the chamber 124 surrounding the bellows 128 will result in
contraction of the bellows 128.
[0039] The bellows 128 is coupled to a T-shaped push rod 134 which
projects from the piston adapter 126 through a seal retainer 136
into contact with the spool valve 48. The spool valve is held
against the push rod 134 by the spool spring 108 which his retained
within the valve support cylinder body 60 by the snap ring 112.
[0040] The spool spring 108 biases the spool valve 48 and push rod
134 against the bellows 128. Therefore, as the bellows 128
compresses in response to higher air pressure input values, the
push rod 134 face contacting the bellows 128 lifts and the spool
valve 48 moves thereby shutting off the secondary branch 44 of the
flow passage 38. The pneumatic portion of the air damper or shock
absorber 10 is isolated from the hydraulic components with seals
138, 140 that are held in place against the seal plate 142, seal
retainer 136 and piston adapter 126.
[0041] The air pressure input initially must overcome a bias or
preload force of the spring 108 before the bellows 128 will move
the spool valve 48. Thus, low air pressure input values will not
cause a change in the bellows 128 and the spool valve 48 remains
open. Both the primary and secondary branches 40, 44 are then open
providing parallel hydraulic fluid flow paths. When spool valve 48
is open, damping forces are optimized for normal driving conditions
when the vehicle is not heavily loaded. Therefore, in the case of a
pressure supply failure, the vehicle will still drive optimally
when it is not heavily loaded. This is a result of the spool valve
48 being biased toward the open position.
[0042] When the vehicle is heavily loaded, the air pressure input
reaching the bellows 128 is also higher thereby causing the bellows
128 to compress, the spool valve 48 to move toward the closed
position and the overall damping forces to be higher as shown in
FIG. 4. At intermediate payloads, the spool valve 48 will be
partially moved toward the closed position and the secondary branch
44 of the flow path 38 is partially blocked resulting in
intermediate damping forces. As a result, the damper 10 is
continuously variable over a given pressure range as shown in FIG.
4. The performance of the system can be tuned by changing the
valving, bellows, spool spring, bellows compression preload or the
orifice insert as desired.
[0043] Referring to FIG. 3, the operation of the hydraulic and
pneumatic portions of the damper 10 according to a presently
preferred embodiment of this invention is shown schematically.
Vehicle weight 118 and road input 120 variables are determined by
the air suspension or air leveling system 116 of the vehicle. The
resulting dynamic pressure is then delivered to the orifice 130 in
the rod 24 which then filters the higher frequency air input values
as desired. The static pressure input is then transmitted through
the piston rod 24 to the bellows 128 which adjusts a position of
the spool valve 48 to and between the open, intermediate and closed
positions. Depending upon the position of the spool valve 48, the
hydraulic fluid may flow through the passage 38 in the primary or
first branch 44 and the second branch provided that the spool valve
48 is at least partially opened.
[0044] During a compression stroke of the piston assembly 22 when
the spool valve 48 is in an open position, fluid flow is permitted
through opening 56 in the bottom of cylindrical extension 60 of
control valve assembly 26. Fluid passes through the spool control
valve 48 and the openings 54 and 68 to the annular groove 66. This
defines part of the branch 44 of the flow passage 38 through the
piston assembly 22. In the annular groove 66, the fluid applies
pressure to the valve disc 46a which, in relation to the pressure
applied thereto, deflects at its outer periphery 76 with the inner
circumference 70 remaining supported on the support disc 74.
[0045] Deflection of the valve disc 46a opens a flow passage
between the outer periphery 76 thereof, and annular leg 78 of valve
plate 50, permitting fluid flow through the piston assembly 22 from
the compression chamber 20 to the extension chamber 18 and vice
versa. The valve disc 46a effects a pressure drop as the fluid
flows through the piston assembly 22 which results in a damping
effect for the travel of piston assembly 22 within cylinder 12.
[0046] During compression travel of the piston assembly 22 fluid
pressure is also applied to the valve disc 42a. The valve disc 46a
is designed to deflect under lower loading and therefore, the valve
disc 42a remains substantially undeflected under low load
conditions. However, since the valve discs 46a and 42a are arranged
in parallel in the flow passage 38 with the spool control valve 48
open, a sufficiently high pressure differential across the piston
assembly 22 will cause both valve discs 42a and 46a to open.
[0047] The damping effect produced during compression by the
passive valves, with spool control valve 48 opening branch 44 of
fluid passage 38, is shown in FIG. 4. The curves demonstrate the
performance of the piston assembly 22 showing the damping force
produced for a given velocity of travel through cylinder 12. The
valve disc 46a is designed such that the damping effect it produces
is evident when the spool control valve 48 is closed under higher
payloads.
[0048] When the spool control valve 48 is closed, the flow path
through the branch 44 of the flow passage 38 through the piston
assembly 22 is closed. Therefore, during compression and extension
strokes of the piston assembly 22 within the cylinder 12, fluid
must flow through the branch 40. During a compression stroke of the
piston assembly 22, when the spool control valve 48 is closed, a
fluid pressure effected in compression chamber 20 is communicated
through the piston 22.
[0049] Within the piston assembly 22, the fluid is open to the
extension chamber 18. Therefore, fluid is permitted to flow from
the compression chamber 20 to the extension chamber 18 through the
branch 40 of flow passage 38 deflecting the valve disc 42a. This
results in a pressure drop for fluid flow through the passage 38
across the piston assembly 22 and is graphed in FIG. 4 for
compression and rebound travel by the curves. The performance
curves demonstrate that for a given velocity of the piston assembly
22 a significantly greater force is developed during the damping or
rebound operation of the shock absorber 10 as compared to the
performance demonstrated by the compression curve.
[0050] During an extension stroke of the piston assembly 22 within
the cylinder 12 with the spool control valve 48 closed, a pressure
increase effected in extension chamber 18 is applied to the valve
disc 42a and fluid flow travels through branch 40 of flow passage
38.
[0051] During extension of the shock absorber 10, as fluid flows
through the branch 40 of passage 38 through the piston assembly 22
deflecting valve disc 42a, a pressure drop occurs which effects the
damping performance graphed by the curves in FIG. 4. As is
demonstrated by FIG. 4, the developed damping force resulting from
a given velocity for the travel of piston assembly 22 within the
cylinder 12 is significantly greater for the curves which graph the
single valve disc 42a then for the curves which graph the parallel
combination of an open or partially open spool control valve 48 and
valve disc 46.
[0052] Through means of the foregoing structure a compact manner of
regulating pressure by controlling the pressure drop as fluid flows
from one side of the piston assembly 22 to the other is provided.
The pressure drop is modified by a pneumatic input signal
communicated to the control valve assembly 26, moving it between
open, intermediate and closed positions. This selectively varies
the relative damping force effected by the piston assembly 22,
between the body and wheel of a vehicle to which the shock absorber
10 is assembled. Since the control valve assembly 26 is carried
with the piston assembly 22 instead of within the rod 24, the rod
diameter can remain relatively small for a damper with an internal
valve. The relatively small rod size minimizes the amount of
volumetric compensation required for fluid displacement resulting
in reduced overall size requirements of the piston assembly 22
within the shock absorber 10. This tends to maximize the
applications within which the shock absorber 10 can be utilized.
The flow path 38 through the piston assembly 22, remains relatively
direct for all variable states of the pressure regulation.
[0053] From the above disclosure of the general principles of the
present invention and the preceding detailed description of at
least one preferred embodiment, those skilled in the art will
readily comprehend the various modifications to which this
invention is susceptible. Therefore, we desire to be limited only
by the scope of the following claims and equivalents thereof.
* * * * *