WO1986000675A1

WO1986000675A1 - Shock absorber

Info

Publication number: WO1986000675A1
Application number: PCT/GB1985/000298
Authority: WO
Inventors: Geoffrey Hugh Williams; William Joseph Howgego
Original assignee: Handling Consultants Limited
Priority date: 1984-07-06
Filing date: 1985-07-04
Publication date: 1986-01-30
Also published as: GB8630908D0; GB2185087A; GB2185087B; EP0221064A1

Abstract

A hydraulic shock absorber comprises a cylinder (1), a piston rod (2), a fluid or fluids contained within the cylinder, a piston structure (7, 12), the piston structure incorporating fluid conducting passageways (10, 11) and means (13, 14) to regulate the passageways, the regulating means being controlled by relative displacement between the piston structure and the cylinder. If a displacement is applied to the shock-absorber which causes relative motion between the piston structure and the cylinder, fluid will be caused to pass from the side of the piston structure to the other side through passageways which offer a degree of restriction to fluid dependent on the position of the piston structure relative to the cylinder.

Description

SHOCK ABSORBER

The present invention relates to a hydraulic shock absorber.

Shock absorbers are widely used for arresting bodies in motion, for absorbing energy from impacts and generally controlling the motion of objects and equipment. A typical hydraulic shock absorber comprises a rod attached to a piston, w th the piston acting within a cylinder containing fluid. Forces acting upon the hydraulic shock absorber cause the piston to travel along the cylinder. Fluid within the cylinder is thus forced to pass from one side of the piston to the other side, during which process the energy of motion is converted to heat energy. A principal feature of shock absorbers is the manner in which fluid passes from one side of the piston to the other side. This may be through passageways in the cylinder walls or the piston. The restriction to fluid flow in the passageways,and hence the variation in energy absorption rate, may be controlled during the piston stroke,^'and may also be adjusted to cater for various operating conditions. However, many shock absorbers have only limited control features, or, if such features do exist, the resulting unit is bulky and expensive. There is, however, scope for incorporating various control features into a shock absorber that, for example, may be arranged to achieve near constant deceleration of a body acting on it whilst resulting in a compact and inexpensive unit. According to the present invention,there is provided a hydraulic shock absorber comprising a cylinder; a piston rod; a fluid or fluids contained within the cylinder; a piston structure attached to the piston rod, the piston structure incorporating fluid conducting passageways; and means to regulate said fluid conducting passageways, said regulating means being controlled by relative displacement between said piston structure and the cylinder.

If a displacement is applied to the shock absorber which causes relative motion between the piston structure and the cylinder, fluid will be caused to pass from one side of the piston structure to the other side through passageways which offer a degree of restriction to fluid flow dependent on the position of the piston structure relative to the cylinder. Said piston structure may comprise a piston with such passageways,a slidably mounted tube and at least one spring which control(s) the position of said tube relative to the piston and thereby regulate(s) the capacity of said passageways to conduct fluid. The slidably mounted tube may be ported. The piston structure may incorporate a sleeve fixed relative to the piston and acting as a bearing surface between the tube and the piston, which sleeve may be ported.

Means may be provided which compensates for variation in the internal volume of the shock absorber- due to relative movement between the piston rod and the cylinder.

Means may be provided to permit adjustment of the rate of movement of the slidably mounted tube relative to the piston, thereby providing a means of adjusting the energy absorption rate to suit a variety of operating conditions.

Means may be provided which, for a given position of the piston structure relative to the cylinder, allows the relative positions of the slidably mounted tube and the piston to be adusted. The spring(s) which control(s) the position of the slidably mounted tube relative to the piston may be arranged so that it (they) act(s) tourge the piston structure towards one end of the cylinder.

The outer surfaces of the shock absorber may be modified to facilitate the dissipation of heat to its surroundings. Associated with the piston structure may be a non-return valve comprising an annular plate and a spring, the plate and the spring co-operating with the piston structure in such a way that some of the passageways in the piston structure are closed off while relative movement between the piston structure and the cylinder in one direction occurs and are opened while such movement in the opposite direction occurs. The non-return valve may be arranged so that such movement which results in withdrawal of the rod from the cylinder requires a lesser force than such movement which results in insertion of the rod into the cylinder.

In another possible arrangement, the piston structure and associated parts are arranged so that the relative movement between the piston structure and the cylinder which results in insertion of the rod into the cylinder requires a lesser force than such movement which results in withdrawal of the rod from the cylinder. There may be in the cylinder a twin piston structure, suitably arranged, which provides a shock absorber which, in effect, is double acting.

The present invention will now be described, by way of example, with reference to the accompanying drawings,in which Figures 1, 2 and 3 are longitudinal sections through examples of shock absorbers according to the present invention.

In the drawings, identical or like items are given the same reference numerals in the different figures.

Referring first to Figure 1, a hydraulic shock absorber comprises a cylinder 1, a piston rod 2, screwed-in end caps 3 and 4, with end cap seals 5, and a rod seal 6. A hollow piston 7, open at one end, is attached to the piston rod 2 by means of a screw thread 8, which mates with a thread cut in the piston 7, and is secured by means of a lock nut 9. The piston 7 has in it a number of holes 10, drilled through the length of piston 7 parallel to the centre line axis of the cylinder 1 and disposed concentrically around the axis of piston 7. There are other holes 11 in piston 7 drilled radially and disposed of along a helical line around the piston. Each hole 11 intersects with a corresponding hole 10.

A tube 12 slides within piston 7 and is held in position axially by springs 13 and 14. Spring 13 is located axially between piston 7 and tube 12. Spring

14 is located axially between tube 12 and end cap 4, with a number of washers 23 (only one shown) held between spring 14 and end cap 4.

A plate 15 and spring 16 in co-operation with piston 7 and tube 12 act as a non-return valve. The plate 15 is able to move axially relative to the piston 7 whilst being spring-loaded towards the piston 7 by the action of spring 16. There is an annular gap between the outer circumference of plate 15 and the bore of cylinder 1.

A closed cellular foam structure 17 is contained radially between cylinder 1 and a collar 18 and is held axially between end cap 3 and collar 18.

If a displacement is applied which causes movement of piston rod 2 in the direction indicated by arrow 21, piston 7 will move in the same direction, thereby compressing springs 13 and 14 and causing fluid to flow from one side of the piston to the other side along passageways, as indicated by arrow 19. The compression of the springs will cause tube 12 to move axially relative to piston 7 and some of the holes will be covered. As the piston continues to move in the direction of arrow 21, further holes 11 will be covered, thus progressively restricting the flow of fluid through the passageways formed by holes 10 and 11. Whilst piston 7 is moving in direction 21, plate

15 will be held against piston 7 by a hydrostatic force and spring 16, thus closing off the holes 10 on that side of the piston. The closed cellular foam structure 17 will be compressed as the rod occupies volume and displaces fluid within the cylinder. When the driving force is- removed, springs 13 and

14 will act to move the piston and the rod in the direction indicated by arrow 22. Plate 15 will, due to hydrodynamic force, be held away from the piston 7 in position 15a_, thus allowing flow of fluid from one side of piston 7 to the other side along passageways, as indicated by arrows 20. This is a less restricted flow path than that indicated by arrow 19, so the piston 7 and rod 2 will move relatively freely in the direction indicated by arrow 22. The springs 13 and 14 will extend as the piston 7 moves in the direction indicated by arrow 22, causing the tube 12 to move relative to piston 7 and to uncover holes 11. Closed cellular foam structure 17 will expand as the rod 2 moves out of the cylinder 1, thus preventing aeration of the fluid. During operation of the shock absorber, there may be leakage between the adjacent surfaces of the piston 7 and cylinder 1. This, together with fluid that reaches the cylinder walls via holes_?will lubricate the piston/cylinder interface. To accomodate different operating requirements, it may be desirable to vary the rate at which tube 12 moves axially relative to piston 7, thus altering the rate at which holes 11 are covered as the piston 7 moves axially relative to cylinder 1. The axial position of tube 12 is determined by the relative stiffnesses of springs 13 and 14, so adjustment can be achieved by replacing spring 14 by another spring with the required stiffness.

The initial position of tube 12 relative to piston 7 can be adjusted by inserting the required number of washers 23 between the spring 14 and end cap 4. Referring to Figure 2, a hydraulic shock absorber comprises a cylinder 1, a piston rod 2, screwed-in end caps 3 and 4, with end cap seals 5, and a rod seal 6. A hollow piston 7, open at one end_;is attached to the rod by means of a screw thread 8, which mates with a thread cut in the piston 7, and is secured by means of a lock nut 9. The piston 7 has in it a number of holes 10, drilled through the length of piston 7 parallel to the centre line axis of the cylinder 1 and disposed concentrically around the axis of piston 7. There is a groove 11 in the bore of piston 7 which intersects,, with holes 10.

There is a sleeve 24 within piston 7, the sleeve 24 being fixed in position relative to piston 7. The sleeve 24 may be a push fit in piston 7, but other means of fixing are possible. There is a slot 25 in sleeve 24, which slot forms an oblique port which communicates with groove 11.

A tube 12 slides within sleeve 24 and is held in position axially by springs 13 and 14. Spring 13 is located axially between piston 7 and tube 12. Spring 14 is located axially between tube 12 and end cap 4, with a number of washers 23 (only one shown) held between spring 14 and end cap 4. A plate 15 and spring 16 in co-operation with piston 7 and tube 12 act as a non-return valve. The plate 15 is able to move axially relative to the piston 7 whilst being spring-loaded towards the piston 7 by the action of spring 16. There is an annular gap between the outer circumference of plate 15 and the bore of cylinder 1.

A closed cellular foam structure 17 is contained radially between cylinder 1 and a collar 18 and is held axially between end cap 3 and collar 18. If a displacement is applied which causes movement of piston rod 2 in the direction indicated by arrow 21, piston 7 will move in the same direction, thereby compressing springs 13 and 14 and causing fluid to flow from one side of the piston to the other side along passageways, as indicated by arrow 19. The compression of the springs will cause tube 12 to move axially relative to sleeve 24 and part of the slot 25 will be covered. As the piston continues to move in the direction of arrow 21, slot 25 will be further- covered, thus progressively restricting the flow of fluid through the passageways formed by holes 10, groove 11 and slot 25. Whilst piston 7 is moving in direction 21, plate 15 will be held against piston 7 by a hydrostatic force and spring 16, thus closing off the holes 10 on that side of the piston. The closed cellular foam structure 17 will be compressed as the rod occupies volume and displaces fluid within the cylinder.

When the driving force is removed, springs 13 and 14 will act to move the piston and the rod in the direction indicated by arrow 22. Plate 15 will, due to hydrodynamic force, be held away from the piston 7 in position 15a_, thus allowing flow of fluid from one side of piston 7 to the other side along passageways, as indicated by arrows 20. This is a less restricted flow path than that indicated by arrow 19, so the piston 7 and rod 2 will move relatively freely in the direction indicated by arrow 22. The springs 13 and 14 will extend as the piston 7 moves in the direction indicated by arrow 22, causing the tube 12 to move relative to sleeve 24 and uncover slot 25. Closed cellular foam structure 17 will expand as the rod 2 movesout of the cylinder 1, thus preventing aeration of the fluid.

During operation of the shock absorber, there may be leakage of fluid between the adjacent surfaces of the piston 7 and cylinder 1. This will act to lubricate the piston/cylinder interface.

To accommodate different operating requirements, it may be desirable to vary the rate at which tube 12 moves axially relative to sleeve 24, thus altering the rate at which slot 25 is covered as the piston 7 moves axially relative to cylinder 1. The axial position of tube 12 is determined by the relative stiffnesses of springs 13 and 14, so adjustment can be achieved by replacing spring 14 by another spring with the required stiffness.

Alternatively, different operating conditions may be accommodated by replacing sleeve 24 by another sleeve with a different slot configuration.

By making use of a variety of sleeves with varying slot configurations, shock absorbers which cater for a range of operating conditions can be constructed from otherwise identical components. The initial position of tube 12 relative to sleeve 24 can be adjusted by inserting the required number of washers 23 between the spring 14 and end cap 4.

Referring to Figure 3, a^' hydraulic shock absorber comprises a cylinder 1, a piston rod 2, an end cap 3 retained by a clip 27, a welded-in cap 4, an end cap seal 5, a rod seal 6 and a rod wiper ring 26. A hollow piston 7, open at one end, is attached to the rod by means of a screw thread 8, which mates with a thread cut in the piston 7, and is secured by means of a locking pin 9. The piston 7 has in it a number of holes 10, drilled through the length of piston 7 parallel to the centre line axis of the cylinder 1 and disposed concentrically around the axis of piston 7. There are other holes 25 in a tube 12, drilled radially and disposed along a helical line around the tube 12. There is an annular chamber 11 in piston 7 which communicates with holes 10 and 25.

The tube 12 slides within piston 7 and is held in position axially by springs 13 and 14. Spring 13 is located axially between piston 7 and tube 12. Spring 14 is located axially between a spring carrier 24, which co-operates wi h tube 12, and end cap 4, wi h a number of washers 23 (only one shown) held between spring 14 and end cap 4.

A plate 15 and spring 16 in co-operation with piston 7 and spring carrier 24-act as a non-return valve. The plate 15 is able to move axially relative to the piston 7 whilst being spring-loaded towards the piston 7 by the action of spring 16. There is an annular gap between the outer circumference of plate 15 and the bore of cylinder 1.

A closed cellular foam structure 17 is contained radially between cylinder 1 and a collar 18 and is held axially between end cap 3 and collar 18, the latter being a press fit in end cap 3 in contrast to Figures 1 and 2 where it is a screw fitting.

Bronze filled polytetrafluorethylene tapes are used as the bearing surfaces between the piston 7 and cylinder 1 and between spring carrier 24 and cylinder 1. There is also such bearing tape between rod 2 and collar 18.

If a displacement is applied which causes movement of piston rod 2 in the direction indicated by arrow 21, piston 7 will move in the same direction, thereby compressing springs 13 and 14 and causing fluid to flow from one side of the piston to the other side along passageways, as indicated by arrow 19. The compression of the springs will cause tube 12 to move axially relative to piston 7 and some of the holes 25 will be covered. As the piston continues to move in the direction of arrow 21, further holes 25 will be covered, thus progressively restricting the flow of fluid through the passageways formed by holes 10, chamber 11 and holes 25. Whilst piston 7 is moving in direction 21, plate 15 will be held against piston 7 by a hydrostatic force and spring 16, thus closing off the chamber 11 on that face of the piston. The closed cellular foam 17 structure will be compressed as the rod occupies volume and displaces fluid within the cylinder.

When the driving force is removed, springs 13 and 14 will act to move the piston and the rod in the direction indicated by arrow 22. Plate 15 will, due to hydrodynamic force, be held away from the piston 7 in position 15a , hus allowing flow of fluid from one side of piston 7 to other side along passageways, as indicated by arrows 20. This is a less restricted flow path than that indicated by arrow 19, so the piston 7 and rod 2 will move relatively freely in the direction indicated by arrow 22. The springs 13 and 14 will extend as the piston 7 moves in the direction indicated by arrow 22,causing the tube 12 to move relative to piston 7 and uncover holes 25. Closed cellular foam structure 17 will expand as the rod 2 moves out of the cylinder l.thus preventing aeration of the fluid.

During operation of the shock absorber, there may be leakage between the adjacent surfaces of the piston 7 and cylinder 1 which will lubricate the piston/cylinder interface.

To accommodate different operating requirements* it may be desirable to vary the rate at which tube 12 moves axially relative to piston 7_?thus altering the rate at which holes 25 are covered as the piston 7 moves axially relative to cylinder 1. The axial position of tube 12 is determined by the relative stiffnesses of springs 13 and 14 so adjustment can be achieved by replacing spring 14 by another spring with the required stiffness.

The initial position of tube 12 relative to piston 7 can be adjusted by inserting the requried number of washers 23 between the spring 14 and end cap 4. Instead of holes 25 according to Figure 3, a slot or slots according to Figure 2 may be used in the Figure 3 embodiment.

Claims

1. A hydraulic shock absorber comprising a cylinder; a piston rod; a fluid or fluids contained within the cylinder; a piston structure attached to the

5 piston rod, the piston structure incorporating fluid conducting passageways; and means to regulate said fluid conducting passageways, said regulating means being controlled by relative displacement between said piston structure and the cylinder.

10 2. A shock absorber according to claim 1, wherein the cylinder has cylinder end caps and there is provided means for sealing interfaces between the cylinder, the end caps and the piston rod.

3. A shock absorber according to claim 1 or 2,

15 wherein the piston structure comprises a piston with such passageways, a slidably mounted tube and at least one spring which control(s) the position of the tube relative to the piston and thereby regulate(s) the capacity of the passageways to conduct fluid.

20 4. A shock absorber according to any preceding claim, which includes means which compensates for variation in the internal volume of the shock absorber due to relative movement between the piston rod and the cylinder. 25 5. A shock absorber according to any preceding claim, in which a non-return valve is associated with the piston structure, the non-return valve comprising an annular plate and a spring, the plate and the spring co-operating with the piston structure in such a way

30 that some of the passageways in the piston structure are closed off while relative movement between the piston structure and the cylinder in one direction occurs and are opened while such movement in the opposite direction occurs.

35 6. A shock absorber according to claim 3 or any of claims 4 to 6 as dependent on claim 3, including means which, for a given position of the piston structure relative to the cylinder, allows the relative positions of the slidably mounted tube and the piston to be adjusted.

7. A shock absorber according to claim 3 or any of claims 4 to 7 as dependent on claim 3, wherein the slidably mounted tube is ported.

8. A shock absorber according to claim 3 or any of claims 4 to 7 as dependent on claim 3, wherein the piston structure incorporates a sleeve fixed relative to the piston and acting as a bearing surface between the slidably mounted tube and the piston.

9. A shock absorber according to claim 8, wherein the sleeve is ported.