GB1582242A

GB1582242A - Resilient coupling

Info

Publication number: GB1582242A
Application number: GB2131676A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1976-05-22
Filing date: 1976-05-22
Publication date: 1981-01-07
Also published as: PL198293A1; DE2722875A1; FR2351812A1; PL116448B1; FR2351812B1

Description

(54) A RESILIENT COUPLING (71) We, DUNLOP LIMITED, a British Company of Dunlop House, Ryder Street, St. James's, London S.W.-l, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a resilient coupling, and in particular though not exclusively to a resilient coupling for interconnecting railway vehicles.

It is necessary for a railway vehicle coupling to withstand large loads particularly during buffering of the railway couplings. Such buffering Iqads can be as high as 200 tons for short periods and such loads should be absorbed and damped by the coupling to prevent excessive and dama ging forces being applied to the vehicle frame.

The coupling should also provide resilience in transmitting traction forces and the requirements -of the coupling should be met in as small a space as practicable.

According to the present invention a resilient coupling including a hydraulic damper comprising a fluid chamber and a fluid accumulator interconnected by a valve comprising a valve spool movable in response to a fluid pressure differential between the chamber and the accumulator in excess of a predetermined value from an inoperative position in which the valve is closed preventing fluid flow between the chamber and the accumulator to one of two operative positions in which the valve is open allowing fluid flow between the chamber and the'accumulator, a first operative position allowing fluid flow from the chamber to the accumulator and a second operative position allowing fluid flow from the accumulator to the chamber, and a fluid restriction orifice providing a permanent fluid connection between the chamber and the accumulator, the arrangement being such that in use the valve is normally closed and impact or traction loads causing a pressure differential between the chamber and the accumulator are damped by fluid flow through the restriction orifice until the pressure differential exceeds the predetermined value causing the valve spool to move to one of said operative positions opening the valve.

The fluid restriction orifice permits a small flow of fluid between the fluid chamber and the accumulator thus by-passing the valve means and allowing equalisation of small fluid pressure differentials between the fluid chamber and the accumulator without movement of the valve spool.

Preferably the resilient coupling further includes a spring formed from elastomeric material and arranged to act in parallel with the hydraulic damper.

The spring may be a compression spring comprising a series of blocks of elastomeric material bonded between a pair of rigid end plates, with a series of reinforcing interleaving plates positioned one each between successive blocks of elastomeric material. Stability of the spring against instability in a direction perpendicular to the compression direction of the spring may be assisted by the structure of the hydraulic damper.

In an alternative construction the compression spring may be formed from a tube of elastomeric material having a plurality of reinforcing rings or helical reinforcing coils extending around the tube. The elastomeric material may be reinforced with a woven or non-woven fabric.

To provide a compact construction the elastomeric material, whether in the form of a series of blocks or a tube, preferably is formed with an aperture defining a cavity in which at least a part of the hydraulic damper may be located.

The fluid chamber of the hydraulic damper may be defined by a tubular guide, closed at one end and in which a damper piston is slidably mounted. Where a compression spring is provided the guide tube may be located within a cavity defined by apertured elastomeric material of the compression spring, or the fluid chamber may be defined in part by apertured elastomeric material of the compression spring.

The fluid accumulator preferably comprises a deformable member which separates the fluid employed in the hydraulic damper from pressurised gas within the accumulator, the deformable member being movable to compensate for changes in the volume of the fluid chamber on compression of the spring. Alternatively, the fluid accumulator may be of a mechanical type comprising, for example, a spring-loaded piston movable within a cylinder, or it may comprise a deformable member in the form of, for example, a deformable sponge.

The valve comprises a spool type valve in which the valve spool is slidably mounted in a guide member, for example, the abovementioned damper piston. Preferably the valve spool is tubular and has one or more apertures formed in the wall thereof which move into - alignment with one or more ports formed in the guide member to permit fluid flow between the fluid chamber and the accumulator in the operative positions of the valve spool. In the inoperative position the apertures and ports are out of alignment.

Preferably the cross-sectional area of the fluid flow path between the chamber and the accumulator with the valve spool in the second operative position exceeds that with the valve spool in the first inoperative position so as to allow rapid equalisation of fluid pressures in the accumulator and fluid chamber under rebound conditions. The increase in crosssectional area of the fluid flow path may be achieved by ensuring the number of aligned apertures and ports with the valve spool in the second operative position exceeds that with the valve spool in the first operative position.

The guide member may have a fluid passage which communicates with the or each port and which is disposed so that fluid pressure forces acting on the valve spool are substantially balanced in a plane perpendicular to the length of the valve spool thereby ensuring fluid pressure forces do not significantly urge the valve spool against the guide member in which it is slidably mounted to restrain relatively free sliding movement of the valve spool.

Preferably the guide member has a plurality of fluid passages, each comprising an axially extending bore and each bore communicates with at least one port. Conveniently the apertures and ports are constructed and arranged so that fluid flows through some of the passages with the valve spool in the first and second operative positions and through the remaining passages with the valve spool in the second operative position only.

Preferably each of the passages through which fluid flows in both operative positions has an associated restriction to fluid flow through the passage provided by means of a fured orifice arranged in series with the associated port(s) and spaced therefrom so as to define an intermediate fluid chamber within at least a part of the fluid passage. The pressure difference acting across an aligned aperture during flow or fluid through the passage between the fluid chamber and the accumulator is thus reduced compared with that which would act if the fixed orifice was not provided.

To effect movement of the slidable valve control tube under the action of a difference in fluid pressure between the chamber and the accumulator, the valve spool may be provided with a plug exposed on opposite faces to the fluid pressures in the chamber and the accumulator. The plug may seal across the bore of the valve spool but more preferably the plug has a through bore defining the fluid restriction orifice which provides the permanent fluid connection between the chamber and the accumulator. In constructions where the plug permits a direct flow between the chamber and the accumulator the plug may be profiled such that the cross-sectional area of the direct fluid flow path between the chamber and the accumulator depends on the position of the valve spool, and the profiling may be such that there results distinctly different damping characteristics between impact and rebound movements.

Faces of the plug exposed respectively to the fluid in the chamber and the accumulator may be of equal area in a plane perpendicular to the direction of movement of the spool, or may be of different areas so that the forces acting on the spool are a fraction or multiple of the difference.

Movement of the valve spool relative to the guide member may be linear or it may be angular in which case fluid flow through the valve spool will be in a substantially radial direction.

Two embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a longitudinal sectional view of a coupling in accordance with the present invention on the line XX of Figure 2; Figure 2 is a plan view of the coupling shown in Figure 1 part-sectioned along the line W of Figure 1 to show the valve means; Figures 3 to 5 respectively are cross-sectional views on the lines AA, BB and CC of Figure 1, and Figure 6 is a longitudinal sectional view of part of another coupling in accordance with the present invention.

The coupling illustrated with reference to Figure 1 comprises three compression spring sections 30 each formed from a plurality of discs 4 of rubber arranged side-by-side to form a tubular spring section, metal discs 31 being disposed one each between successive rubber discs. Each spring section 30 is located between a pair of end plates 32, and the rubber-metal interfaces of each spring unit 30 are united by bonding. The end plates of the assembly of the three spring units 30 abut annular shoulders 33 formed one on a flange portion 34 of a hydraulic damper guide tube 2 and one on a fluid accumulator housing 1 of a hydraulic damper body 35.

The damper body 35 comprises in addition to the accumulator housing 1 a damper piston 36 slidably mounted in the guide tube 2 and fitted with a circumferentially extending seal 15 which provides fluid sealing between the piston 36 and guide tube 2. The guide tube 2 is closed at one end by the flange portion 34 and thus a fluid chamber 37 is defined by the space within the guide tube between the flange portion of the tube and the end of the damper piston 36.

The damper unit accumulator housing 1 has a flexible diaphragm 6 of rubber secured thereto at spaced positions by means of an end plate 5 and retaining cap 8. The diaphragm, which may be reinforced, acts as a flexible boundary between an annular cavity 38 which is filled with pressurised gas (typically at a pressure between 15 and 50 psi) through valve means 17, and a central hydraulic fluid cavity 39 which communicates with the fluid chamber 37 via valve means (to be described in detail later) provided in the damper piston 36. A plug valve (not shown) is provided in the end plate 5 to permit filling of the cavity 39 with hydraulic fluid.

The resilient coupling is mounted in the frame of a vehicle (not shown) within a rectangular section aperture shown by outline reference 40 and lies between traction and impact stops 41,42 (Figure 2) respectively.

These stops are spaced so as partly to precompress the spring, the degree of pre-compression determining the minimum traction or buffering load which will cause further compression of the coupling outside the rubber blocks 4 and interleaving plates 31. They are each screw-threaded at one end to a coupler mount 46 and provided with heads 16 to bear against the damper body 35. A coupler pin 45 held by the mount 46 enables traction loads applied to the pin to be transmitted to the damper body 35. The tie rods 43 pass through apertures in the flange portion 34 of the guide tube 2 so that said flange portion may slide freely relative to the tie rods.

The coupler pin mount 46 comprises a pair of semi-circular-shaped surfaces 48 against which the ends of the pin 45 are urged under the action of two compression springs 49 disposed one each between an end of the pin 45 and a flanged spacer 50 supported by the flange portion 34 of the guide tube 2.

A compression plate 52 is provided against the guide tube 2, and that surface of the compression plate facing the pin 45 is suitably curved to conform to the curved outer surface of a conventional coupler arm (not shown) fitted around the pin 45 between the pin and compression plate 52; thus impact forces are transmitted directly from the coupler arm to the compression plate 52 which then urges the guide tube 2 in a direction towards the impact stops 42.

The valve means provided in the damper piston 36 comprises a spool type valve comprising a tubular valve spool 7 to slidably mounted in a bore provided centrally in the damper piston 36, the bore extending parallel with the axial direction of the guide tube 2. A pair of opposed precompressed helical compression springs 18, seated each at one of their ends on respective shoulders provided in the bore of the piston 36 and at their other ends on respective shoulder surfaces of a protruding band portion 14 formed externally on the spool 7, resiliently bias the spool 7 towards a predetermined datum or inoperative position relative to the piston 36 in which the valve, means is closed. The valve spool 7 is partly closed at its end furthest from the accumulator by a plug 10. The plug is formed with a stem portior 53 which extends from the main part of the plug in a direction away from the accumulator to pass through an aperture 54 formed centrally in a cover plate 55 secured to the end of the damper piston 36. The stem portion 53 is of tubular form and has a bore defining a fluid restriction orifice 56. The orifice 56 provides a permanent fluid connection between the chamber and the accumulator and permits a restricted flow of fluid to equalise pressure differentials between the chamber on the accumulator up to a predetermined minimum without movement of the valve spool 7. Vent passages 57 allow fluid to flow through the plug between the spool 7 and a chamber 58 defined by the space between the plug and the cover plate 55 to ensure equalisation of pres sures within the spool and cavity 58.

Rotation of the valve spool 7 relative to the damper body 35 is restrained by a key 19 secured relative to the valve spool and engaging a slot which extends through the cap 8.

The piston 36 is drilled to form four fluid passages 59a, 59b (see Figures 1 and 2) uni formly disposed in a circumferential direction around the piston, each passage comprising an axially-extending bore which communicates at one end with the chamber 37 and at the other end with the valve spool via a radially extending port. Two of the passages 59a are shown in Figure 1 and another two 59b are shown in the inset sectional view of Figure 2.

The cover plate 55 is formed with two apertures 60 of smaller diameter than the axially extending bores of the passages 59a so as to present a restriction to the flow of fluid between the fluid chamber 37 and passages 59a and two apertures 61 (see Figure 2) of diameter identical to the axially-extending bores of the passages 59b so as to allow substantially unrestricted flow of fluid from the damper chamber 37 to the passages 59b.

The valve spool 7 has two apertures 62 at dia metrically opposite positions which move into alignment with the radial ports of the passages 59a when the spool is displaced towards the accumulator under the action of greater fluid pressure inthe fluid chamber than the accumu lator causing a pressure differential in excess of the predetermined minimum. A shoulder 12 on the spool abuts the retaining cap 8 when the apertures and ports are fully aligned. The spool has a further two apertures 63, again at dia metrically opposite positions and at a position axially spaced along the length of the spool from the apertures 62, which move into alignment with the radial ports of the passages 59a under the action of greater fluid pressure in the accumulator than the fluid chamber causing a pressure differential in excess of the predetermined minimum. A shoulder 13 on the spool abuts a shoulder 11 formed at one end of the damper piston spring recess when the apertures and ports are fully aligned. In addition the valve spool has two apertures 64, again at diametrically opposite positions and at an axial position along the length of the spool corresponding to the axial position of the apertures 63, which move into alignment with the radial ports of the passages 59b when the apertures 63 move into alignment with the ports of the passages 59a. The passages 59b thus acts as bypass passages to allow ready flow of hydraulic fluid in one direction only from the accumulator back to the chamber 37 thus allowing rapid equalisation of fluid pressure subsequent to compression of the coupling. The spool is formed also with vent holes 65 which allow for ready equalisation of pressures between the bore of the spool and the recesses formed in the damper pistion 36 for location of the compression springs 18.

In operation of the coupling under traction or buffering loads greater than the precompression loading of the spring sections 30 between the impact and traction stops 42, 41 the volume of the fluid chamber 37 is decreased either by traction loads acting via the tie rods 43 to urge the damper unit 35 towards the traction stops 41 or by buffering forces acting on'the compression plate 52 to urge the guide tube 2 in a direction towards the impact stops 42..The resulting increase in pressure of fluid in the chamber 37 generates a force related to the difference between the fluid pressures in the chamber and the accumulator acting on the exposed cross-sectional area of the stem portion 53 of the plug 10 in the fluid chamber 37. For pressure differentials in excess of the predetermined minimum the spool 7 moves in a direct tion towards the accumulator to bring the apertures 62 progressively into alignment with the radial ports of the passages 59a thereby opening the valve means and allowing pressurised fluid to flow through orifices 60, passages 59a, spool apertures 62, along the bore of the spool and into the accumulator. The degree of opening of the valve means depends on the position of the spool which in turn depends on the pressure differential.

By passing fluid through spaced apertures 62 and orifices 60 the fluid pressure in each passage 59a is intermediate that in the accumulator and that in the chamber 37 and the velocity of fluid flow therethrough is thus reduced compared with the flow velocity which would result if the orifices 60 were not provided. In consequence of the relatively reduced fluid flow velocity heat generated in the fluid during transfer is less and wear on the valve means is reduced. A further advantage of having intermediate pressures in the passages 59a is that the magnitude of unbalance forces is less than in a similar construction having fluid in the passages 59a at a pressure substantially similar to that in the chamber 37.

In operating under traction or buffering conditions the compression spring sections 30 also play an important part. Under initial loading the hydraulic damper unit has a high load carrying capacity reducing with velocity, whilst the three spring sections have a low initial load carrying capacity increasing with deflection and thus acting in combination the spring and damper give a good and substantially uniform rate of energy absorption.

Under rebound conditions, i.e. when the traction or buffering forces acting on the coupling are relatively quickly reduced, the fluid pressure in the accumulator is greater than that in the fluid chamber 37. The fluid pressure differential forces acting on the plug 10 then urge the valve spool 7 to move in a direction towards the fluid chamber 37 to bring the apertures 63 and 64 progressively into alignmen with the radial ports of the passages 59a and 59b respectively. Four passages thus interconnect the accumulator and fluid chamber 37 to permit a relatively speedy equalisation of fluid pressures. Under the above described dynamic operating conditions of the valve the vent passages 57 in the plug 10 and vent holes 65 in the valve spool respectively allow speedy flow of fluid into the cavity 58 and spring recesses to give speedy equalisation of pressure and avoidance of undue damping to movement of the valve spool.

In the case of slow changes in the forces acting on the coupling pressure equalisation between the fluid chamber 37 and the accumulator is effected by the flow of fluid directly through the fluid restriction orifice 56 in the plug so that small frequent movements of the valve spool and consequential wear are avoided.

Under static conditions the fluid pressures in the accumulator and the fluid chamber are substantially equal irrespective of the loads being carried by the coupling and thus high pressures exist in the coupling only under dynamic conditions. There is therefore no significant problem caused by possible fluid leakage as compared with hitherto used constructions where fluid is continuously at a high pressure whenever high loads are being carried by the coupling.

In another embodiment of the invention illustrated in Figure 6, a coupling is constructed substantially as described in respect of the preceding embodiment except that the valve mechanism is of a modified construction.

In this modified construction only one helical compression spring is used to resiliently bias the spool 71 to the datum or inoperative position. Two flanged sleeves 70 are slidably mounted on the valve spool 71 and a helical compression spring 72 extends between flanges of the two sleeves to urge the sleeves apart.

Separation of the sleeves in an axial direction is limited by the sleeve flanges abutting shoulders 73 formed on the damper piston 74. Two annular bands 75 are secured to the outer surface of the spool 71 and are spaced-apart in the direction of the length of the spool by a distance equal to the spacing of the shoulders 73.

Under the action of fluid pressure differential forces on the plug 10 sufficient to cause axial movement of the valve spool 71, one of the fixed bands 75 abuts one of the slidable shouldered sleeves 70 causing axial compression of the spring 72 and the spool slides within the other shouldered sleeve which is restrained from axial movement by abutment with a piston shoulder 73.

This valve construction is further modified over the construction described in respect of the preceding embodiment of the invention insofar as the damper piston 74 has one passage 78 through which fluid flows in both operative positions. The passage 78 comprises an axially extending bore which communicates at one end with the fluid chamber and at the other end with the spool 71 via two radially extending ports 77. The spool 71 has two apertures 76 at positions axially spaced along the length of the spool by a distance corresponding to the axial spacing of the ports 77. The apertures 76 move progressively into alignment with the ports 77 when the spool is displaced towards the accumulator under the action of greater fluid pressure in the fluid chamber than in the accumulator thus allowing a relatively greater flow of fluid through the passage 78 as compared with either of the passages 59a. When the spool is displaced towards the fluid chamber under the action of greater fluid pressure in the accumulator than in the fluid chamber, an aperture 79 in the spool 71 moves into alignment with one of the ports 77 and one of the two apertures 76 moves into alignment with the other port 77 to permit the flow of fluid through the axially extending bore of the passage 78. Simultaneously an aperture 80 in the valve spool moves into alignment with a radial port which communicates with an axially extending by-pass passage 81 and permits additional flow of fluid from the accumulator into the fluid chamber.

WHAT WE CLAIM IS: 1. A resilient coupling including a hydraulic damper comprising a fluid chamber and a fluid accumulator interconnected by a valve comprising a valve spool movable in response to a fluid pressure differential between the chamber and the accumulator in excess of a predetermined value from an inoperative position in which the valve is closed preventing fluid flow between the chamber and the accumulator to one of two operative positions in which the valve is open allowing fluid flow between the chamber and the accumulator, a first operative position allowing fluid flow from the chamber to the accumulator and a second operative position allowing fluid flow from the accumulator to the chamber, and a fluid restriction orifice providing a permanent fluid connection between the chamber and the accumulator, the arrangement being such that in use the valve is normally closed and impact or traction loads causing a pressure differential between the chamber and the accumulator are damped by fluid flow through the restriction orifice until the pressure differential exceeds the predetermined value causing the valve spool to move to one of said operative positions opening the valve.

2. A resilient coupling according to Claim 1 wherein a spring is provided to act in parallel with the hydraulic damper to resist compression of the coupling.

3. A resilient coupling according to Claim 2 wherein the spring is a compression spring comprising a series of blocks of elastomeric bonded between a pair of rigid end plates, with a series of reinforcing interleaving plates positioned one each between successive blocks of elastomeric material.

4. A resilient coupling according to Claim 1 or Claim 2 wherein the spring is a compression spring comprising a tube of elastomeric material having a plurality of reinforcing rings or helical reinforcing coils extending around the tube.

5. A resilient coupling according to any one of Claims 2 to 4 wherein the spring defines a cavity in which at least a part of the hydraulic damper is located.

6. A resilient coupling according to any one of the preceding claims wherein the hydraulic damper comprises a tubular guide which has a damper piston slidably mounted therein.

7. A resilient coupling according to Claim 6 in combination with Claim 5 wherein the tubular guide and damper piston are located within the cavity defined by the spring.

8. A resilient coupling according to any one of Claims 2 to 5 wherein the fluid chamber is defined in part by apertured elastomeric material of the spring.

9. A resilient coupling according to any one of the preceding claims wherein the fluid accumulator comprises a deformable member which separates fluid in the fluid chamber from gas in the accumulator.

10. A resilient coupling according to any one of the preceding claims wherein the fluid accumulator comprises a spring-loaded piston.

11. A resilient coupling according to any one of the preceding claims wherein the valve spool is slidably mounted in a guide member.

12. A resilient coupling according to Claim 11 wherein the valve spool is tubular and has one or more apertures formed in the wall thereof for alignment with one or more ports in the guide member to permit fluid flow between the fluid chamber and the accumulator in the operative positions of the valve spool.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of the two sleeves to urge the sleeves apart. Separation of the sleeves in an axial direction is limited by the sleeve flanges abutting shoulders 73 formed on the damper piston 74. Two annular bands 75 are secured to the outer surface of the spool 71 and are spaced-apart in the direction of the length of the spool by a distance equal to the spacing of the shoulders 73. Under the action of fluid pressure differential forces on the plug 10 sufficient to cause axial movement of the valve spool 71, one of the fixed bands 75 abuts one of the slidable shouldered sleeves 70 causing axial compression of the spring 72 and the spool slides within the other shouldered sleeve which is restrained from axial movement by abutment with a piston shoulder 73. This valve construction is further modified over the construction described in respect of the preceding embodiment of the invention insofar as the damper piston 74 has one passage 78 through which fluid flows in both operative positions. The passage 78 comprises an axially extending bore which communicates at one end with the fluid chamber and at the other end with the spool 71 via two radially extending ports 77. The spool 71 has two apertures 76 at positions axially spaced along the length of the spool by a distance corresponding to the axial spacing of the ports 77. The apertures 76 move progressively into alignment with the ports 77 when the spool is displaced towards the accumulator under the action of greater fluid pressure in the fluid chamber than in the accumulator thus allowing a relatively greater flow of fluid through the passage 78 as compared with either of the passages 59a. When the spool is displaced towards the fluid chamber under the action of greater fluid pressure in the accumulator than in the fluid chamber, an aperture 79 in the spool 71 moves into alignment with one of the ports 77 and one of the two apertures 76 moves into alignment with the other port 77 to permit the flow of fluid through the axially extending bore of the passage 78. Simultaneously an aperture 80 in the valve spool moves into alignment with a radial port which communicates with an axially extending by-pass passage 81 and permits additional flow of fluid from the accumulator into the fluid chamber. WHAT WE CLAIM IS:

1. A resilient coupling including a hydraulic damper comprising a fluid chamber and a fluid accumulator interconnected by a valve comprising a valve spool movable in response to a fluid pressure differential between the chamber and the accumulator in excess of a predetermined value from an inoperative position in which the valve is closed preventing fluid flow between the chamber and the accumulator to one of two operative positions in which the valve is open allowing fluid flow between the chamber and the accumulator, a first operative position allowing fluid flow from the chamber to the accumulator and a second operative position allowing fluid flow from the accumulator to the chamber, and a fluid restriction orifice providing a permanent fluid connection between the chamber and the accumulator, the arrangement being such that in use the valve is normally closed and impact or traction loads causing a pressure differential between the chamber and the accumulator are damped by fluid flow through the restriction orifice until the pressure differential exceeds the predetermined value causing the valve spool to move to one of said operative positions opening the valve.

13. A resilient coupling according to Claim

12 wherein the cross-sectional area of the fluid flow path between the chamber and the accumulator with the valve spool in the second operative position exceeds that with the valve spool in the first operative position.

14. A resilient coupling according to Claim 12 or Claim 13 wherein the number of aligned apertures and ports with the valve spool in'the second operative position exceeds that with the valve spool in the first operative position.

15. A resilient coupling according to any one of Claims 12 to 14 wherein the guide member has a pair of fluid passages each comprising an axially extending bore and each bore com-, municates with at least one port.

16. A resilient coupling according to Claim 15 wherein the apertures and ports are constructed and arranged so that apertures and ports align with one another to allow fluid flow through both passages in the first and second operative positions.

17. A resilient coupling according to Claim 15 or Claim 16 wherein each of said passages has an associated fluid restriction orifice.

18. A resilient coupling according to any one of Claims 15, 16 or 17 wherein the guide member has a second pair of fluid passages, each comprising an axially extending bore and each bore communicates with at least one port.

19. A resilient coupling according to Claim 18 wherein the apertures and ports are constructed and arranged so that apertures and ports align with one another to allow fluid flow through said second pair of passages in the second operative position only.

20. A resilient coupling according to Claim 15 wherein the apertures and ports are constructed and arranged so that apertures and ports align with one another to allow fluid flow through one of said passages in the first and second operative positions and through the other of said passages in the second operative position only.

21. A resilient coupling according to Claim 20 wherein said one passage has an associated fluid restriction orifice.

22. A resilient coupling according to any one of Claims 15 to 21 wherein the passages are uniformly spaced in a circumferential direction around the guide member so that fluid pressure forces acting on the valve spool are substantially balanced in a plane perpendicular to the length of the valve spool.

23. A resilient coupling according to any one of Claims 15 to 22 wherein the passages communicate with the fluid chamber.

24. A resilient coupling according to any one of Claims 11 to 23 in combination with Claim 6 wherein the guide member comprises the damper piston.

25. A resilient coupling according to any one of Claims 11 to 24 wherein the valve spool is provided with a plug exposed on opposite faces to the fluid pressures in the fluid chamber and the accumulator.

26. A resilient coupling according to Claim 25 wherein the plug has a through bore defining the fluid restriction orifice providing the permanent fluid connection between the fluid chamber and the accumulator.

27. A resilient coupling according to Claim 26 wherein the plug is profiled such that the cross-sectional area of the direct fluid flow path between the fluid chamber and the accumulator depends on the position of the valve spool.

28. A resilient coupling according to Claim 27 wherein the profiling results in different damping charactertistics for impact and rebound movements of the coupling.

29. A resilient coupling according to any one of the preceding claims whereby the valve spool is resiliently biassed to a predetermined inoperative or datum position.

30. A resilient coupling according to Claim 29 wherein said inoperative or datum position is intermediate said first and second operative positions.

31. A resilient coupling according to Claim 30 wherein the valve spool has a stop against opposite surfaces of which a pair of compression springs act normally to bias the valve spool towards the predetermined datum or inoperative position.

32. A resilient coupling according to Claim 30 wherein the valve spool has a pair of spaced end stops between which a pair of abutment members are slidably mounted on the control member to abut ends of a compression spring which serves normally to bias the valve spool towards the predetermined datum of inoperative position.

33. A resilient coupling according to any one of Claims 2 to 32 wherein the hydraulic damper assists in providing stability to the spring

34. A resilient coupling constructed and arranged substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.

35. A resilient coupling constructed and arranged substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings as modified by Figure 6 of the accompanying drawings.