GB2209375A

GB2209375A - Damper assembly

Info

Publication number: GB2209375A
Application number: GB8720828A
Authority: GB
Inventors: John Roger Plummer
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-09-04
Filing date: 1987-09-04
Publication date: 1989-05-10
Also published as: GB8720828D0

Abstract

A damper assembly for a semi-active suspension system includes a first chamber, a piston head (4) or diaphragm defining a boundary of the first chamber, a second chamber, passage means (19) providing a path of fluid communication between the first and second chambers, and a rotary valve associated with the passage means and having a valve member (16) rotatable about an axis aligned with the fluid path through the valve to vary the degree of opening of the passage means, and a motor for rotating the rotary valve member to any one of a multiplicity of positions. The invention also provides a fully active suspension system and a rapidly acting levelling system using a similar valve. <IMAGE>

Description

Damper assembly for semi-active suspension system, fully active suspension system and rapidly acting levelling system This invention relates particularly to a damper assembly for use in a semi-active suspension system.

The invention also relates to a fully active suspension system and to a rapidly acting levelling system.

A semi-active suspension system may be regarded as one having a damper whose characteristics can be altered very rapidly by a powered adjusting means as the vehicle reacts to various inputs. Such a semi-active suspension system differs from a fully active system in that only the damping characteristic of the damper is adjusted by the powered adjusting means, so that the effect can be likened to switching very rapidly between a variety of totally passive dampers of varying characteristics. In a fully active system significant external power is added and the powered adjusting means is employed to vary the volume of fluid into or out of the system from a pump or accumulator.

Much theoretical work has been done to show the performance gains in both ride and handling that can be achieved with a semi-active suspension system in a vehicle. Such a system requires a damper whose damping force can be adjusted to a value chosen from a wide range very quickly.

It is an object of the invention to provide a damper assembly suitable for use in a semi-active suspension system.

According to the invention a damper assembly for a semi-active suspension system includes a first chamber, a piston head or diaphragm defining a boundary of the first chamber, a second chamber, passage means providing a path of fluid communication between the first and second chambers, and a rotary valve associated with the passage means and having a valve member rotatable about an axis aligned with the fluid path through the valve to vary the degree of opening of the passage means, and a motor for rotating the rotary valve member to any one of a multiplicity of positions.

The provision of a rotary valve having a valve member rotatable about an axis aligned with the fluid path enables the valve to be opened or closed with a shearing action at high speed without significant displacement of the fluid and therefore with relatively little force. Thus it is possible to provide a damper with a force ratio of greater than 100:1 at normal suspension ride velocity and an ability to change from maximum to minimum damping at a rate of up to 50 cycles per second.

The second chamber may be at a location remote from the first chamber and may for example comprise a fluid reservoir. It is preferable however for the second chamber to be adjacent to the first chamber and for the piston head or diaphragm also to define a boundary of the second chamber.

The rotary valve is preferably provided in the piston head or diaphragm but may alternatively be provided externally of the cylinder.

In an embodiment of the invention described below with reference to the drawings the chamber is defined by part of a cylinder in which a piston head is slidably mounted.

The motor for rotating the rotary valve member is preferably a stepper motor. The stepper motor may be controlled by digital pulses from an electronic control unit, which may include a micro-computer, and may be capable of operating at a speed of the order of 4,000 steps per second. The software required to control the motor has been discussed in published technical literature, does not form part of the present invention and will not be discussed in this specification.

Preferably the passage means comprises a plurality of orifices symmetrically positioned about the axis of rotation of the valve member and preferably the valve member is arranged such that the degree of opening of each orifice is the same for a given rotary position of the valve member. This provides a balanced arrangement facilitating rapid operation of the valve member at low torque.

The orifices may be provided in the valve member and may extend through a cylindrical wall thereof concentric with the axis of rotation of the valve member, rotation of the valve member serving to adjust the degree of overlap between the orifices and ports in a cylindrical wall of the valve body immediately adjacent to the cylindrical wall of the valve member. The orifices preferably extend through the cylindrical waltz at an angle inclined to the radial direction such that flow of fluid through the orifices tends to rotate the valve member. A portion of the wall defining each orifice may be inclined to the radial direction in the opposite direction to the general inclination of each orifice.

The orifices may be of generally elongate cross-section having a major axis in a direction parallel to the axis of rotation of the valve member and a minor axis transverse to the axis of rotation of the valve member, and may be of simple or complex shape. The ports may be larger than the orifices so that each orifice comes into a fully overlapping relationship with the port before the centres of the orifices and ports are aligned.

Mechanical stop means may be provided for limiting rotary movement of the rotary valve member. The mechanical stop means may serve to ensure that the rotary valve member does not move into a position from which it could be retrieved only by the application of a substantially increased torque and may also serve to provide a reference position of the valve member so that the electronic control circuit and motor can position the rotary valve member accurately without the provision of a feedback signal indicating the position of the valve member.

In the case where the rotary valve is provided in the piston head or diaphragm, the motor may nonetheless be mounted externally of the chamber as in an embodiment described below with reference to the drawings but the motor may alternatively be mounted within the chamber.

The present invention also provides a semi-active suspension system including a damper assembly as defined above. The damper assembly may be combined with a steel, air, gas or oleo-pneumatic spring.

The invention may also be used in a fully active suspension system. Thus according to another aspect of the invention there is provided a fully active suspension system including a piston and cylinder assembly or the like, pumping means for adjusting the amount of fluid in the cylinder on one side of the piston, passage means provided in the path of fluid communication between the pumping means and the piston and cylinder assembly, a rotary valve having a valve member rotatable about an axis coincidental with the axis of the fluid path to vary the degree of opening of the passage means, and a motor for rotating the rotary valve member to any one of a multiplicity of positions.

The invention may also be used in a rapidly acting levelling system. Thus according to another aspect of the invention there is provided a rapidly acting levelling system including a piston and cylinder assembly or the like, pumping means for adjusting the amount of fluid in the cylinder on one side of the piston, passage means provided in the path of fluid communication between the pumping means and the piston and cylinder assembly, a rotary valve having a valve member rotatable about an axis coincidental with the axis of the fluid path to vary the degree of opening of the passage means, and a motor for rotating the rotary valve member to any one of a multiplicity of positions.

By way of example certain illustrative embodiments of the invention will now be described with reference to the accompanying drawings, of which: Fig. 1 is a sectional view of a semi-active suspension system for a vehicle in which a rotary valve is mounted concentrically within a piston and cylinder assembly, Fig. 2 is a sectional side view of a valve part of Fig. 1 to a larger scale showing the valve in an open position, Fig. 3 is a partial underneath plan of the valve part shown in Fig. 2, but showing the valve in a closed position, and Fig. 4 is a view in the direction of the arrow IV in Fig. 2.

Referring first to Fig. 1 the semi-active suspension system shown generally comprises a lower mount 1 for connection to a member which in use will move up and down, for example the wheel of a vehicle, an upper mount 2 for connection to a member which is to be cushioned against movement of the lower mount, for example a vehicle body, a cylinder 3 fixed to the lower mount 1, a piston having a piston head 4 and a tube 5 slidably mounted in the cylinder 3 and fixed to the upper mount 2, and a stepper motor 6 having an output drive shaft 7 connected via a coupling 8 and a rod 10 located within the tube 5 to a rotary valve member 16 in the piston head 4.

The cylinder 3 has a main central portion 11 the peripheral wall of which is sealingly engaged by the piston head 4 and a peripheral reservoir portion 12 which communicates with the central portion 11 via a check valve assembly 13. A shrader valve 14 is provided for experimental purposes only to pressurize with nitrogen the space over the fluid in portion 12. The arrangement provides a pressurized twin tube chamber design which gives enhanced performance.

Referring now also to Figs. 2 and 3 which show the piston head 4 in more detail, the rotary valve member 16 is fixed by a nut 17 to the end of the rod 10. The valve member 16 is of inverted cup shape having a cylindrical wall 18 in which four orifices 19 are provided spaced at 900 intervals around the axis of rotation of the valve member. The piston head 4 defines a valve body for the rotary valve member 16, the valve body having a cylindrical wall 20 which closely surrounds the wall 18 of the valve member and has four radial blind bores 21 spaced at 900 intervals around the wall and positioned so that in the position of the valve member shown in Fig. 2 the orifices 19 overlap the bores 21.

Each of the bores 21 communicates with a respective passageway 22 which extends approximately axially and has an open end at the upper surface of the piston head.

A seal 24 prevents fluid passing between the piston head and the central portion 11 of the cylinder 3 and a seal 25 prevents fluid passing between the piston head and the rod 10 which rotates the valve member 16.

A blow-off plate 26 is provided around the piston head and biased downwardly by a compression spring 27 to the position shown in Fig. 2 in which the plate closes off openings in the piston head 4. In normal operation the openings remain closed but in the event of fluid pressure below the piston head reaching an unacceptably high level the plate 26 is lifted upwardly against the bias of the spring 27 to allow fluid to pass through the piston head 4 via the openings. Such an arrangement is known per se and will not be described further. The blow-off plate does not obstruct the open ends of the passageways 22 in any position.

Referring now also to Fig. 4, it will be seen that the blind bores 21 are of circular cross-section while the orifices 19 in the valve member are of generally elongate shape having a height approximately equal to the diameter of the bores 21 and a much smaller width. Midway along that side of each orifice 19 which projects furthest across the bore 21 there is a small transverse extension 30 to the orifice. As shown in Fig. 3 the side walls 31 of the orifices 19 are generally parallel to one another but are inclined to the radial direction. Also one side wall of each orifice (the one that projects less far across the bore 21) has an innermost portion 32 which is inclined to the radial direction in the opposite direction to the general inclination of the side walls.

The stepper motor 6 is in this particular example of the invention a 5-phase motor and is controlled by digital pulses from a drive card and micro-computer, operates at a rate typically of 4,000 steps per second, and has 100 stable positions.

Mechanical stop means (not shown in the drawings) are provided to limit the rotation of the valve member.

One stop prevents opening of the valve member beyond the position shown in Fig. 4 and the other stop prevents movement in the opposite direction beyond the position shown in Fig. 3. That other stop also provides a rest position for the valve member when the system is not in operation and which the stepper motor 6 and its electronic control unit can employ as a datum in order to position the valve member accurately during operation.

During operation, as the wheel of the vehicle is subjected to upwardly directed shocks, the lower mount 1 applies large upward forces to the cylinder 3 and the resilient mounting for the wheel provides a reaction force to maintain the wheel on the ground thereby applying sizeable downward forces to the cylinder 3. As will be appreciated the downward forces will be less severe than the largest upward forces. The damping effect is provided primarily by the passage of fluid in the assembly from one side of the piston head to the other through the orifices 19 in the rotary valve member 16, the blind bores 21 and the passageways 22, the position of the valve member determining the impedance to the fluid flow. The motor continuously adjusts the position of the rotary valve member 16 via the rod 10 and thereby adjusts the damping of the damper provided by the piston and cylinder assembly. Rotation of the rotary valve member 16 moves the valve member transverse to the direction of fluid flow through the orifices 19 and thus has a shearing effect on the fluid but does not lead to significant displacement of the fluid. Thus the valve member 16 can be rotated rapidly using less than 12 watts of power and the damping force of the damper can be adjusted as it responds to a shock in order to provide a damper having whatever characteristic is on that particular occasion required. High damping may be provided to control resonance and to modify tyre to road forces and modify handling. On the other hand low damping is required to reduce the forces transmitted from the wheel to the vehicle body and thus provide a better ride.

When the valve member is approaching the closed position and only narrow passageways remain through the orifices 19 into the bores 21, there can be substantial closing force on the rotary valve member, as a result of the Bernoulli Force, caused by fluid flow through the restricted passageways; this is particularly so when fluid is flowing at its fastest when the greatest force is applied to the lower mount 1, namely during the application of an upward shock force to the mount when fluid is flowing upwardly from below the piston head through first the orifices 19 and then through the blind bores 21 and the passageways 22.The general inclination of the orifices 19 to the radial direction leads to the fluid exerting a force on the valve member 16 tending to rotate the valve member and, when the fluid is flowing upwardly, this force acts to rotate the valve member in the opening direction thereby counterbalancing the closing force arising from the Bernoulli Force. The transverse extensions 30 to the orifices 19 also prevent sudden absolute closing of the orifices.

When fluid is flowing downwardly through the piston head the rotary force arising from the general inclination of the orifices and the Bernoulli Force both act in the closing direction but these forces will not be so great as the fluid flow will not be so rapid in this direction. Also the oppositely inclined portions 32 on the innermost part of the orifices reduce the size of this force.

It will be noted that even in the fully open position of the Valve the orifices 19 do not reach the centres of the blind bores 21 and the mechanical stop ensures that an overcentre position is never reached.

The description above is concerned exclusively with an example of a semi-active suspension system embodying the invention. The invention may also be applied to a fully active suspension system embodying the invention and to a rapidly acting levelling system. In either of these cases the flow of fluid into a piston and cylinder assembly is controlled by a rotary valve and motor such as that described above but in this case the rotary valve would not usually be provided on the piston head.

Claims

What we claim is:

1. A damper assembly for a semi-active suspension system including a first chamber, a piston head or diaphragm defining a boundary of the first chamber, a second chamber, passage means providing a path of fluid communication between the first and second chambers, and a rotary valve associated with the passage means and having a valve member rotatable about an axis aligned with the fluid path through the valve to vary the degree of opening of the passage means, and a motor for rotating the rotary valve member to any one of a multiplicity of positions.

2. A damper assembly according to claim 1 in which the second chamber is adjacent to the first chamber and the piston head or diaphragm defines a boundary of the second chamber.

3. A damper assembly according to claim 2 in which the rotary valve is provided in the piston head or diaphragm.

4. A damper assembly according to any preceding claim in which the first chamber is defined by part of a cylinder in which a piston head is slidably mounted.

5. A damper assembly according to any preceding claim in which the motor for rotating the rotary valve member is a stepper motor.

6. A damper assembly according to claim 5 in which the stepper motor is controlled by digital pulses from an electronic control unit.

7. A damper assembly according to any preceding claim in which the passage means comprises a plurality of orifices symmetrically positioned about the axis of rotation of the valve member.

8. A damper assembly according to claim 7 in which the valve member is arranged such that the degree of opening of each orifice is the same for a given rotary position of the valve member.

9. A damper assembly according to claim 7 or 8 in which the orifices are provided in the valve member and extend through a cylindrical wall thereof concentric with the axis of rotation of the valve member, rotation of the valve member serving to adjust the degree of overlap between the orifices and ports in a cylindrical wall of the valve body immediately adjacent to the cylindrical wall of the valve member.

10. A damper assembly according to claim 9 in which the orifices extend through the cylindrical wall at an angle inclined to the radial direction such that flow of fluid through the orifices tends to rotate the valve member.

11. A damper assembly according to claim 10 in which a portion of the wall defining each orifice is inclined to the radial direction in the opposite direction to the general inclination of each orifice.

12. A damper assembly according to any of claims 9 to 11 in which the orifices are of generally elongate cross-section having a major axis in a direction parallel to the axis of rotation of the valve member and a minor axis transverse to the axis of rotation of the valve member.

13. A damper assembly according to any of claims 9 to 12 in which the ports are larger than the orifices so that each orifice comes into a fully overlapping relationship with the port before the centres of the orifices and ports are aligned.

14. A damper assembly according to any preceding claim in which mechanical stop means are provided for limiting rotary movement of the rotary valve member.

15. A semi-active suspension system including a damper assembly as claimed in any preceding claim.

16. A semi-active suspension system substantially as herein described with reference to and as illustrated by the accompanying drawings.

17. A fully active suspension system including a piston and cylinder assembly or the like, pumping means for adjusting the amount of fluid in the cylinder on one side of the piston, passage means provided in the path of fluid communication between the pumping means and the piston and cylinder assembly, a rotary valve having a valve member rotatable about an axis coincidental with the axis of the fluid path to vary the degree of opening of the passage means, and a motor for rotating the rotary valve member to any one of a multiplicity of positions.

18. A rapidly acting levelling system including a piston and cylinder assembly or the like, pumping means for adjusting the amount of fluid in the cylinder on one side of the piston, passage means provided in the path of fluid communication between the pumping means and the piston and cylinder assembly, a rotary valve having a valve member rotatable about an axis coincidental with the axis of the fluid path to vary the degree of opening of the passage means, and a motor for rotating the rotary valve member to any one of a multiplicity of positions.