WO1993012360A1

WO1993012360A1 - A buffer

Info

Publication number: WO1993012360A1
Application number: PCT/GB1992/002313
Authority: WO
Inventors: Ronald Cecil Page; John James Bushnell; Raymond Buckingham Stephens
Original assignee: Oleo International Holdings Limited
Priority date: 1991-12-13
Filing date: 1992-12-14
Publication date: 1993-06-24
Also published as: AU3092992A; EP0615585A1; GB9126506D0

Abstract

A buffer comprises a plunger (13) slideable in a ported tube (26). A metal tubular member (46) circumferentially surrounds that part of the ported tube (26) in which all the flow resisting ports (49) are formed and is the radially inner wall of an annular space (53) filled with compressed gas. The outer wall of the annular space (53) is formed by a tubular membrane (51). The annular chamber (50) between the ported tube (26) and the metal tubular member (46) is part of the low pressure reservoir of the buffer and communicates via an annular passage (48, 48A) in the closed end (11) of the buffer with the remainder of the reservoir which is an annular chamber (54) formed between the tubular membrane (51) and the outer tubular wall (10) of the buffer. Heat generated by forcing the liquid through the flow resisting ports (49) during compression of the buffer is carried by liquid flow from the radially inner annular chamber (50) to the radially outer annular chamber (54) via the annular passage (48, 48A) and is dissipated from the radially outer annular chamber (54) through the external tubular wall (10) of the buffer.

Description

A BUFFER

DESCRIPTION

This invention relates to a buffer comprising a plunger and cylinder unit, the plunger being forced into the cylinder when a load is applied to the buffer whereby liquid is displaced from a compression chamber within the cylinder into a relatively low pressure reservoir through flow resisting means which provide dynamic resistance, there also being an enclosed body of compressed gas which provides a recoil force opposing inward movement of the plunger with respect to the cylinder by acting to urge liquid in the reservoir into the compression chamber through said flow resisting means. Such a buffer is referred to as "a buffer of the kind referred to" in the remainder of this description.

US-A-4153145 discloses a different type of buffer comprising a plunger and cylinder unit, the cylinder being formed by a ported tube, the ports of which are at axially spaced locations along the tube, and the plunger being forced into the cylinder when a load is applied to the buffer whereby liquid is displaced from a compression chamber within the cylinder into a relatively low pressure reservoir which surrounds the tube, the radially outer wall of the reservoir being formed by external structure of the buffer so that heat is dissipated from liquid in the reservoir through that external structure, resilient means being provided for providing a recoil force opposing inward movement of the plunger into the cylinder.

GB-A-864703 discloses a vehicle shock absorber comprising a piston and cylinder unit with an annular low pressure reservoir around the cylinder. There is a radially deformable annular membrane which, together with part of the external surface of the shock absorber, encloses a body of compressed gas which acts through the membrane to urge liquid in the cylinder to oppose inward movement of the plunger. Heat can be dissipated from liquid in the reservoir through the remainder of the external surface of the shock absorber. That would be insufficient for the amount of heat dissipation required for industrial uses because the heat dissipating area is small. It is also unsuitable for industrial uses because there would be a risk of deterioration of the material of the membrane and because the body of gas and the membrane which separate liquid in the reservoir from the external surface of the shock absorber have a heat insulating effect so they oppose heat dissipation.

One object of this invention is to provide a buffer of the kind referred to which is suitable for continuous use. That requires provision to be made for dissipation through a major part of the external surface of the buffer of heat generated by the frequent forcing of liquid through the flow restricting means.

According to this invention there is provided a buffer of the kind referred to wherein the cylinder comprises a ported tube, the ports of which are formed at axially spaced locations along the tube and collectively comprise said flow resisting mean, the number of ports in direct communication with the compression chamber reducing as the plunger moves into the cylinder the reservoir comprises an annular chamber which circumferentially surrounds the tube and the body of compressed gas is enclosed within an annular enclosure which also surround the ported tube and which comprises an annular radially deformable membrane, in which a part of the reservoir is bounded by structure which forms an external surface of the buffer which is arranged so that liquid displaced from the compression chamber through the flow restricting means is directed to said part of the reservoir so that heat can be dissipated from that liquid through said structure which forms an external surface of the buffer, wherein said annular enclosure is spaced from said structure which forms an external surface of the buffer and is within said reservoir, being between said part which is bounded by structure which forms an external surface of the buffer and another part which is formed between it and the outside of the ported tube, and passage means wholly contained within the structure of said buffer provide communication between said part of the reservoir which is bounded by said structure which forms an external surface of the buffer and the other part between the ported tube and said annular enclosure.

Preferably the enclosure comprises a tubular member of substantially rigid gas impervious material and said radially deformable membrane, the tubular member being between the ported tube and the radially deformable membrane and the gas being enclosed within a space between the tubular member and the radially deformable membrane. Conveniently the plunger has a piston head which slides within the bore of the ported tube and which is formed by a ring which is mounted on an axially inner end portion of the plunger for limited axial displacement relative to the remainder of the plunger, there being passage means through said inner end portion of the plunger extending between an orifice at the inner end of the plunger and an opening which is closed by the ring when the latter is at the end of its limited axial displacement further from said inner end of the plunger and which is opened by displacement of the ring relative to the remainder of the plunger towards said inner end of the plunger, the diameter of the remainder of the plunger between said ring and the outer end of the plunger being less than the inside diameter of the ported tube so that an annular space is formed therebetween.

One embodiment of this invention is described now by way of example with reference to the accompanying drawing which is a longitudinal section of the buffer in a transverse plane through the longitudinal axis of the buffer, the buffer being shown in full lines in its contracted condition, the form of the radially deformable membrane when the buffer is extended being shown in. chain-dotted lines.

The drawing shows the buffer comprises a plunger and cylinder unit. The major part of the external surface of the buffer is formed by a tube 10 which is closed at one end by an end plate 11 and which has a radially outer end ring 12 fitted to its other end which is the end of the buffer through which the plunger 13 extends. A radially inner end ring 14 is spigotted into the outer end ring 12 and is fixed therein by a locking ring 15 which is screwed into the outer end ring 12 and into which the axially outer end of the inner ring 14 is spigotted. The bore of the inner ring 14 is doubly-rebated at its axially inner end to form two shoulders 16 and 17. The larger diameter shoulder 17 is surrounded by a cylindrical wall 18 which has a circumferential protruberance 19 formed in its radially outer surface adjacent its brim

21 . A conduit 22 extends through the inner ring 14 to a mouth 23 in the brim 21, there being an inflation valve 24 screwed into the end of the conduit

22 at the outer end of the ring 14.

The end plate 11 has a central cylindrical boss 25. The outside diameter of the boss 25 is greater than the inside diameter of the inner end ring 14. The boss

25 is spigotted into one end of a ported tube 26 which is spigotted at its other end into the rebate that forms the inner one 16 of the two shoulders 16 and 17. A tubular spacer 27 is spigotted into the ported tube

26 at its end which, in turn, is spigotted into the inner end ring 14. The ported tube 26 has a number of ports 49 of flow restricting dimensions at varying axially-spaced locations, and a larger diameter hole 49A which allows relatively unrestricted return flow into the tube 26.

The major part 28 of the plunger 13 slides within the inner end ring 14 from which it projects. Sealing rings 29 and 31 each mounted in a respective one of two annular grooves 32 and 33 in the radially inner wall of the inner end ring 14 provide dynamic sealing to oppose escape of liquid from within the cylinder between the major plunger part 28 and the inner end ring 14 and to minimise the amount of liquid that is transferred out of the cylinder as a film on the surface of the major plunger part 28. A buffer plate

34 is mounted on the outer end of the plunger 13.

An inner end portion 35 of the plunger 13 has a smaller outside diameter than the major plunger part 28. It is spigotted into an annular piston head 36 which is a sliding fit within the" ported tube 26. A circlip 37, which is retained in an annular groove 38 formed in the radially outer surface of the smaller diameter plunger part 35, is spaced from a step 39 between the smaller diameter axially inner end portion

35 of the plunger 13 and the major plunger part 28 by a distance which is a little greater than the axial length of the annular piston head 36. The arrangement . is such that limited axial movement of the annular piston head 36 relative to the inner end portion 35 of the plunger 13 is possible whereas the inner end portion 35 locates the annular piston head 36 against relative radial movement. A partially radial and partially axial passage 41 provides communication between an annular recess 42 which is formed in the radially outer surface of the inner end portion 35 of the plunger 13 adjacent the step 39, and an orifice 43 which is formed at the centre of the axially inner end of the inner end portion 35 of the plunger 13. A piston ring seal 44, which is carried by the annular piston head 36 in an annular groove 45 formed in its radially outer surface engages the radially inner surface of the ported tube 26.

A tubular member 46 formed of a relatively thin metal has one end spigotted into the bore of the cylindrical wall 18 and a larger diameter end which is spigotted into an annular groove 47 which is formed in the axially inner face of the end plate 11 around the cylindrical boss 25. The radially outer wall of the annular groove 47 has an outwardly sloping frusto-conical portion 47A leading to its brim. Two or more holes 48 are drilled at circumferentially spaced locations in the axially inner face of the inner end plate 11 with their centres on a pitch circle having a diameter greater than the outside diameter of the annular groove 47. The diameter of each hole 48 is sufficient for part of that hole 48 to be in the base of the annular groove 47. That part of each hole 48 which is disposed radially outwardly with respect to the annular groove 47 is a projection of a respective arcuate recess 48A in the radially outer wall of the annular groove 47. The holes 48 and the recesses 48A allow free communication between the interior of the tubular member 46 and the area surrounding that tubular member 46, around the larger diameter end of that tubular member 46.

The tubular member 46 surrounds the ported tube 26 from which it is spaced so as to form an annular chamber 50 with which each port 49 of the ported tube 26 communicates and which thereby forms part of the low pressure reservoir of the buffer. The major part of the tubular member 46 has a diameter which is greater than the diameter of the smaller end part that is spigotted into the cylindrical wall 18 but which is smaller than the diameter of the larger diameter end part that is spigotted into the annular groove 47 in the end plate 11.

A tubular membrane 51 of radially deformable gas impermeable material, such as an elastomeric material, is clamped at one end around the larger diameter end portion of the tubular member 46 and at its other end around the outer surface of the cylindrical wall 18. It is so clamped at either end by a respective clamping ring 52. The tubular metal member 46 and the annular membrane 51, together with the brim 21 of the cylindrical wall 18, enclose an annular space 53 with which the conduit 22 communicates. This space 53 is filled with compressed gas introduced by the inflation valve 24 through the conduit 22. Another annular chamber 54 is bounded primarily by the interior of the tube 10 and the exterior of the tubular membrane 51, and extends between the end plate 11 and the end rings 12 and 14. That annular chamber 54, being in communication via the arcuate recesses 48A and the holes 48 with the annular chamber 50 between the ported tube 26 and the tubular member 46, forms the remainder of the reservoir space and thereby is a part of the reservoir which is bounded by structure, namely the tube 10, which forms an external surface of the buffer.

When the buffer is charged for use, the reservoir comprising the annular chambers 50 and 54 is filled with liquid as is the cylinder space within the ported tube 26,-the buffer plunger 13 being at the end of its travel that is furthest from the end wall 11 and in which the annular piston head 36 is adjacent to the sleeve bearing 27. The part 55 of the cylinder space between the buffer plunger 13 and the end wall 11 is known as the compression chamber.

As the system is substantially unloaded, the radially deformable membrane 51 is extended radially by the action of the compressed gas within it and it adopts the position which is shown in chain-dotted lines in the drawing.

A load is applied to the buffer in the form of an impact on the buffer plate 34. As a result the buffer plunger 13 is forced into the cylinder. Such movement of the plunger 13 into the cylinder displaces liquid from the compression chamber 55 through the ports 49 into the reservoir. Such displacement of liquid is resisted by the ports 49 due to their flow restricting dimensions. Hence the ports 49 provide dynamic resistance to inward movement of the plunger 13. It will be understood that the number of ports 49 that communicate with the compression chamber 55 at any one instant reduces as the plunger 13 moves into the cylinder so that the dynamic resistance is increased. Liquid forced through the ports 49 first enters the annular chamber 50 formed between the ported tube 26 and the tubular member 46 around it. That liquid is forced from that annular chamber 50 into the annular chamber 54 through the holes 48 and the arcuate recesses 48A and is thereby directed to a part of the reservoir from which heat dissipation from the liquid to the surrounding atmosphere is possible through the structure of the buffer. Forcing liquid into the annular chamber 54 causes radial contraction of the tubular membrane 51 thereby increasing the pressure of the gas enclosed within the annular space 53. It will be understood that the compressed gas within the annular space 53 tends to oppose entry of additional liquid into the annular chamber 54 and thus tends to oppose displacement of liquid from the compression chamber 55. Also the compressed gas in the annular space 53 provides a recoil force since it will expand, causing the tubular membrane 51 to expand radially. and thereby displace liquid from the annular chamber 54 through the arcuate recesses 48A and the holes '48 into the annular chamber 50 between the tubular member 46 and the ported tube 26 and back through the return hole 49A into the interior of the ported tube 26 when the load is removed from the buffer plunger 13. Liquid that re-enters the interior of the ported tube 26 between the spacer 27 and the annular piston head 36 initially will urge the piston head 36 against the circlip 37, thereby uncovering an opening formed by the annular recess 42 and thus obtaining passage to the compression chamber 55 and causing movement of the plunger 13 out of the cylinder, to uncover ports 49 and allow further flow of liquid into the compression chamber 55.

Claims

1. A buffer comprising a plunger and cylinder unit, the cylinder comprising a ported tube, the ports of which are formed at axially spaced locations along the tube, the plunger being forced into the cylinder when a load is applied to the buffer whereby liquid is displaced through said ports which collectively comprise flow resisting means which provide dynamic resistance, from a compression chamber within the cylinder into a relatively low pressure reservoir which comprises an annular chamber which circumferentially surrounds the tube, the number of ports in direct communication with said pressure chamber reducing as the plunger moves into the cylinder, there being a body of compressed gas enclosed within an annular enclosure which also surrounds the ported tube and which comprises an annular radially deformable membrane arranged to provide a recoil force opposing inward movement of the plunger with respect to the cylinder by acting to urge liquid in the reservoir into the compression chamber through said flow resisting means, wherein a part of the reservoir is bounded by structure which forms an external surface of the buffer which is arranged so that liquid displaced from the compression chamber through the flow resisting means is directed to said part of the reservoir so that heat can be dissipated from that liquid through said structure which forms an external surface of the buffer, characterised in that said annular enclosure is spaced from said structure which forms an external surface of the buffer and is within said reservoir, being between said part which is bounded by said structure which forms an external surface of the buffer and another part which is formed between it and the outside of the ported tube, and passage means wholly contained within the structure of said buffer provide coπaπunication between said part of the reservoir which is bounded by said structure which forms an external surface of the buffer and the other part between the ported tube and said annular enclosure.

2. A buffer according to claim 1, wherein the enclosure comprises a tubular member of substantially rigid gas impervious material and said radially deformable membrane, the tubular member being between the ported tube and the radially deformable membrane and the gas being enclosed within a space between the tubular member and the radially deformable membrane.

3. A buffer according to claim 1 or claim 2, wherein the plunger has a piston head which slides within the bore of the ported tube and which is formed by a ring which is mounted on an axially inner end portion of the plunger for limited axial displacement relative to the remainder of the plunger, there being passage means through said inner end portion of the plunger extending between an orifice at the inner end of the plunger and an opening which is closed by the ring when the latter is at the end of its limited axial ' displacement further from said inner end of the plunger and which is opened by displacement of the ring relative to the remainder of the plunger towards said inner end of the plunger, the diameter of the remainder of the plunger between said ring and the outer end of the plunger being less than the inside diameter of the ported tube so that an annular space is formed therebetween.