GB2372308A - A retractable and extendable buffer assembly - Google Patents

Abstract

A retractable and extendable buffer assembly (10) of the piston (16) and cylinder (12) type with the piston (16) serving as a force receiving member. Cylinder (12) is closed at one end by a plug (13) defining a base chamber (14). The opposite end of the piston (16b) and the inner walls of cylinder (12) define a main chamber (17) that is filled with an incompressible fluid. The end of the main chamber (17) remote from the piston (16) is closed by a plug (18) which is rigidly secured relative to the interior of cylinder (12). Plug (18) supports several components including a fluid conduit (21) defining a fluid flow path between main chamber (17) and base chamber (14). The fluid conduit (21) permits flow of the fluid when pressurised to a predetermined threshold value. The flow of fluid is controlled by control elements (11), including a fluid pump (23), a fluid reservoir (24) and a control valve (27). The control elements can also include additional control circuitry (see Fig.12).

Description

A RETRACTABLE AND EXTENDABLE BUFFER ASSEMBLY This invention relates a retractable and extendable buffer assembly. More particularly the invention relates to such an assembly configured as a coupler/buffer element intended for installation on vehicles such as but not limited to locomotives, railways carriages trams and light rail cars.

Such vehicles may be operated as individual units or, when desired, coupled into multiple vehicle trains.

It is desirable for the coupler head of eg. such a vehicle to be a dual purpose component, that provides both coupling and buffing functions.

An uncoupled coupler head protrudes from the front or rear of a car of train.

Since tram cars in particular run at street level, protruding coupler heads represent a hazard to other road users. In any event the protruding coupler heads are aerodynamically and aesthetically undesirable. Therefore there is a need for a mechanism that permits retraction or withdrawal of an unused coupler head, preferably to a location within the outer skin of the vehicle.

Solutions to this issue have been implemented using manually moved coupler heads, that are mechanically locked and operated by the driver or service personnel. Alternative designs have also been proposed operated remotely by the driver based on a concertina principle or using a secondary linear drive actuator and eg. a folding support arm. In both cases secondary mechanical locking is needed. In these designs the energy-absorbing element of the unit follows conventional design principles and has limited stroke.

This is because the space eg. under the cab of a tram car is limited. Since in the prior art retractable couplers space is needed for the retracting actuator (folding leg, concertina etc. ) the overall length of the buffer element must be correspondingly limited, thereby reducing its stroke and hence its effectiveness.

In some other designs powered movement is provided by a separate mechanism requiring extra space and increased weight.

According to the invention there is provided an extendable and retractable buffer assembly comprising an essentially closed main chamber, of variable volume, that is defined in part by a force receiving member and that contains an incompressible fluid; a fluid conduit communicating with the main chamber to permit flow of the said fluid, that is pressurised to a predetermined threshold value, from the main chamber, and including in the resulting fluid flow path an energy conversion device for providing a constant force conversion of potential energy in the said fluid to kinetic energy; a pump for pumping the said fluid, via a selectively openable, filling conduit that bypasses the energy converting device, into the main chamber, to expand the main chamber and thereby extend the force receiving member relative to the remainder of the assembly; an essentially closed, secondary, fluid containing chamber, of variable volume, that is defined in part by said force receiving member; a pressuriser for selectively pressurising the secondary chamber, the resulting pressure in the secondary chamber acting on the force receiving member to contract the main chamber and retract the force receiving member relative to the remainder of the assembly; and a drain conduit that bypasses the energy converting device and is openable during pressurising of the secondary chamber to permit flow of

fluid from the main chamber during its contraction resulting from the pressurising. The buffer assembly of the invention advantageously integrates the energy absorbing element of a coupler buffer with a linear actuator, for extending and retracting the coupler buffer, by controlling the flow of eg. hydraulic oil between different chambers of the energy absorbing device.

Consequently for a given stroke the buffer assembly of the invention is smaller, and cheaper to produce, than the prior art designs.

Significantly, the buffer assembly of the invention allows the entire stroke of the assembly to be used for energy absorption when the force receiving member is fully extended.

The buffer assembly of the invention advantageously is operable under the control of an hydraulic power supply, components of which may be located in the vehicle at a location remote from the buffer assembly. The power supply need only be operatively connected to power the buffer assembly eg. by means of fluid delivery lines (conduits).

The buffer assembly of the invention lends itself to operation under the control of a control valve such as a spool valve forming part of the hydraulic power supply. The ability to locate the control valve remotely from the buffer assembly advantageously permits the driver of eg. a tram or other vehicle incorporating the buffer assembly to extend and retract the buffer without leaving his cab, using appropriate control levers and/or buttons connected to the control valve.

This advantage may be arranged to arise in prior art designs of retractable

buffer that employ hydraulic cylinders that are separate from the energy absorbing part of the coupler. However such "separate cylinder" designs take up excessive space under the cab of the vehicle.

Further, advantageous features of the invention are defined in the claims hereof that depend from Claim 1.

There now follows a description of four preferred embodiments of the invention, by way of non-limiting example, with reference being made to the accompanying drawings in which: Figure 1 is a cross sectional view of a first embodiment of retractable and extendable buffer assembly according to the invention; Figure 2 is a cross sectional view of a second embodiment of retractable and extendable buffer assembly according to the invention, including a gas spring for restoring the buffer after compression; Figure 2A shows an energy converting device, forming part of the Figure 2 arrangement, in more detail; Figure 2B shows the circuit of Figure 2A in schematic form ; Figure 3 is a cross sectional view of a third embodiment of the invention, including another kind of gas spring; Figure 3A shows one alternative arrangement that is equivalent to the gas spring of Figure 3; Figure 4 is an end elevational view of a fourth embodiment of a buffer assembly according to the invention, viewed from the free end of the buffer piston; Figure 5 is a vertically sectioned view of the assembly of Figure 4, viewed on line AK-AK ; Figure 6a is an end elevational view of the assembly of Figures 4 and 5 rotated through approximately 90'as shown; Figure 6b is a vertically sectioned view, on line Y-Y of Figure 6a, of

a central portion of the assembly ; Figure 6c shows the components of Figure 6b in more detail ; Figure 7a is an end elevational view of the Figure 4 assembly, viewed from the opposite end to that of Figure 4; Figure 7b is a vertically sectioned view on line F-F of Figure 7a; Figure 7c is an enlargement of the portion AJ circled in Figure 7b; Figure 8a is a side elevational view of the assembly of Figure 4, viewed on a different orientation; Figure 8b is a vertically sectioned view on line A-A of Figure 8a; Figure 9a is a view similar to Figure 4; Figure 9b is a vertically sectioned view on line B-B of Figure 9a, showing the region circled in Figure 5; Figure lOa is a view similar to Figure 6a; Figure 10b is a sectioned view on line D-D of Figure lOa ;

Figure 11 is an enlarged sectional view of the components of Figure 9b, viewed from a different angle ; and Figure 12 is a schematic representation of the hydraulic circuit represented by Figures 4 to 11, together with control elements not forming part of the buffer assembly per se.

Referring to the drawings there are shown four embodiments of buffer assembly each according to the invention.

Figure 1 shows a first embodiment of buffer assembly 10 together with external control elements indicated generally by reference numeral 11.

The embodiments of Figures 2 to 11, described below, are also intended for use in conjunction with control elements such as elements 11 visible in Figure 1; however, for clarity the control elements 11 are omitted from Figures 2 to 11. The connections of the control elements 11 typically will

be as illustrated in Figure 1.

As is described in more detail below, the control elements 11 may in accordance with the invention be located remotely from the buffer assembly 10, eg. in or adjacent the cab of a vehicle to which the buffer assembly 10 is secured.

Buffer assembly 10 comprises a main body constituted by elongate, hollow cylinder 12.

Cylinder 12 is closed at one end by a plug 13 defining a concave recess, referred to herein as base chamber 14, on its side facing the interior of hollow cylinder 12.

A force receiving member in the form of elongate piston 16 is slideably sealingly received in the hollow interior of cylinder 12 and protrudes from an open end 12a thereof at the opposite end of cylinder 12 to plug 13.

Piston 16 is in the embodiments shown a hollow cylinder that is closed at either end.

The end 16a of piston 16 that protrudes from cylinder 12 is adapted to receive secured thereto in a per se known manner eg. a coupler head (omitted from the drawings for clarity).

The coupler head may be of a per se known design, and in preferred embodiments is keyed to end 16a in a non-rotatable manner. Details of the manner of securing of the coupler head will be known to those skilled in the art.

The opposite end 16b of piston 16 defines, together with the interior walls of cylinder 12, a main chamber 17 that in use of the buffer assembly 10 is filled with an incompressible fluid, especially hydraulic oil.

The end of main chamber 17 remote from piston 16 is closed by a plug 18 that is rigidly secured relative to the interior of cylinder 12, by virtue of engagement of a flange 18a extending about the periphery of plug 18 that is firmly received between an end face of plug 13 and an annular shoulder 19 formed in the interior wall of cylinder 12.

Plug 18 supports several components described in more detail below, including an oil conduit 21 defining a fluid flow path between main chamber 17 and (in the Figure 1 embodiment) base chamber 14.

Conduit 21 includes in the fluid flow path an energy conversion device that may be a metering pin or constant force valve ofper se known design.

A characteristic of such an energy conversion device 22 is that it includes a normally closed valve that opens to permit fluid flow when the pressure of fluid in main chamber 17 reaches a predetermined threshold value.

A further characteristic of such a device 22 is that when the normally closed valve opens the device converts potential energy in the flowing hydraulic oil to kinetic energy and heat while exhibiting a constant. Therefore pressurisation of hydraulic oil in main chamber 17 by virtue of end 16a of piston 16 receiving eg. an impact force causes energy dissipating device 22 to permit flow of fluid from main chamber 17 into base chamber 14 via energy dissipating conduit 21, with the result that the impact energy is absorbed and dissipated in a manner that is predictable according to the characteristic of the energy dissipating device 22.

A pump 23 is operatively connected to a reservoir 24 of hydraulic oil.

An output line 26 of pump 23 feeds hydraulic oil to the assembly 10 via a per se known control valve 27 that may be eg. a spool valve.

As shown in Figure 1 control valve 27 is normally closed.

In one of the two open positions of control valve 27 line 26 is connected to supply fluid via connection 28 that constitutes part of a filling conduit that is, by virtue of operation of control valve 27, selectively openable to permit pumped filling of main chamber 17.

Connection 28 perforates the wall of cylinder 12 adjacent plug 18 so as to permit the supply therethrough of hydraulic oil under pressure.

In the vicinity of connection 28 there is an annular gap 29 between the outer wall of plug 18 and the inner wall of cylinder 12, whereby hydraulic oil supplied by pump 23 from reservoir 24 is pumped into main chamber 17 when line 26 is connected by control valve 27 to connection 28. Annular gap 29 therefore constitutes a selectively openable, filling conduit that bypasses the energy dissipating device.

Adjacent its end 12a there is rigidly secured within cylinder 12 a compression ring 31 against which the exterior of piston 16 slidingly seals. The end 31a of compression ring 31 that is remote from open end 12a of cylinder 12 defines a shoulder extending inwardly of the interior wall of cylinder 12.

Between shoulder 31a and the remainder of main chamber 17 piston 16

includes an outwardly projecting annular protrusion 32.

The annular space between shoulder 31a and protrusion 32 defines an essentially closed, secondary, fluid containing chamber of variable volume that is defined in part by the force receiving member (piston) 16.

In the embodiment shown secondary chamber 33 is filled with an incompressible fluid such as hydraulic oil supplied from reservoir 24 in a manner described below.

A connection 34 perforates the wall of cylinder 12 to communicate with secondary chamber 33.

A fluid supply line 36 is connectable by means of control valve 27 to receive hydraulic oil pumped by pump 23 from reservoir 24, as signified by the centre position of control valve 27 shown in Figure 1.

Reservoir 24, pump 23, output line 16, control valve 27, fluid supply line 26 and connection 34 therefore constitute a pressuriser for selectively pressurising the secondary chamber 33.

In the centre position of control valve 27 the output line 26 of pump 23 is connected via line 36 to connection 34. This pressurises secondary chamber 33 by increasing the volume of hydraulic oil therein. This tends to retract piston 16, relative to the remainder of assembly 10 from the extended position shown.

During such retraction hydraulic oil is expelled from main chamber 17 via annular gap 29 to connection 28. Connection 28 is in the centre position of control valve 17 connected directly to reservoir 24, whereby the excess

hydraulic oil expelled from main chamber 17 is accommodated.

As shown by the represented by the left hand position of control valve 27 in Figure 1, when output line 26 is connected to supply hydraulic oil via connection 28 the volume of hydraulic oil in main chamber 17 increases.

This tends to force piston 16 to extend relative to the remainder of assembly 10.

During this process secondary chamber 33 contracts. The porting of valve 27 therefore is as shown, ie. line 36 (and hence secondary chamber 33) is connected directly to reservoir 24.

It will be evident from the foregoing description that piston 16 may be controlledly extended and retracted relative to the remainder of assembly 10, by virtue of setting of control valve 27. In a practical embodiment of the apparatus of the invention control valve 27 would be operated eg. by a control lever or other per se known device (such as an electrical relay) located in the cab of the vehicle to which the assembly 10 is secured in use.

It is thus possible for the driver of such a vehicle remotely to effect extension and retraction of the piston 16, and hence of a coupler head secured to end 16a.

When the piston 16 achieves its maximum extension, control valve 27 is set to the right hand (normally closed) position shown in Figure 1. At this time both connection 34 and connection 28 are closed, whereby piston 16 is locked in position by the volumes of intercompressible hydraulic oil in main chamber 17 and secondary chamber 33.

If at such a time piston 16 experiences an external compressive force (as

may occur during coupling or as a result of an unintended impact) the pressure of the oil in main chamber 17 rises. Once the pressure of oil in main chamber 17 reaches the threshold pressure of the energy conversion device 22 the valve therein opens and the hydraulic oil passes into base chamber 14, while its energy is converted initially to kinetic energy and heat, and finally to heat alone in a per se known manner. Consequently the compressive force acting on piston 16 is absorbed.

Base chamber 14 is directly connected at all times to reservoir 24 by base chamber drain line 37, whereby excess oil from main chamber 17 passing into base chamber 14, during such externally forced compression of the assembly 10, is accommodated.

During the forced compression of piston 16, secondary chamber 33 expands. To prevent the formation of voids in the hydraulic oil in secondary chamber 33 during such expansion, a one way connection from base chamber drain line 37 across control valve 27 to connection 34 via line 36 may be provided, as shown by dotted line 38 in Figure 1.

Line 38 therefore constitutes a replenishment conduit communicating between the base chamber 14 and the secondary chamber 33.

Replenishment conduit 38 may include eg. a one way check valve, whereby to ensure that hydraulic oil in secondary chamber 33 does not drain to reservoir 24 when control valve 27 is in its normally closed position. The check valve also prevents the extension of piston 16 when it is subjected to an external force.

An advantage of the arrangement of Figure 1 is that the piston 16 is fully retractable and extendable, yet when it is extended the full stoke of the piston 16 is available for absorption of compressive forces. This compares

with prior art arrangements in which the piston is shortened in order to provide space for a retracting mechanism such as four bar chain or locking leg.

Control valve 27 may also be set to its neutral (normally closed, right hand) position when piston 16 is partially stroked. Thus the piston 16 may be locked in position at any location between its fully stroked and fully destroked extremities.

One may summarise the states of the assembly 10 of Figure 1, according to the following table.

State reference Description si Retracting under the operation of the hydraulic pump S2 Extending under the operation of the hydraulic pump S3 external compressive force S4 Fully retracted pump disconnected S5 Fully extended pump disconnected S6 Partially stroked, pump disconnected Table 1 Referring now to Figure 2 there is shown a second embodiment of buffer assembly 110 according to the invention.

Assembly 110 is a modified version of assembly 10 of Figure 1.

As previously noted the control elements 11 of Figure 1, that would normally be present in the Figure 2 embodiment are omitted for clarity.

Buffer assembly 110 includes a hollow cylinder 112 that is similar to cylinder 12 of Figure 1.

Cylinder 112 is open at one end 112a and closed by a plug 113 at the opposite end. Plug 118 is similar to plug 18 of Figure 1 in that it is secured within the interior of hollow cylinder 112, adjacent and spaced from plug 113.

However, instead of defining a base chamber between plugs 118 and 113, in the Figure 2 embodiment base chamber 114 is defined forwardly of plug 118. This is achieved by the presence of further, elongate circular section member 139 that is secured protruding from plug 118 towards the open end 112a of cylinder 112.

Circular section member 139 is concentric with cylinder 112 and plugs 118 and 113.

Further circular section member 139 has a hollow interior that defines base chamber 114 (that is described in more detail below).

The diameter of member 139 is less than the interior diameter of cylinder 112, whereby an annular chamber is defined between member 139 and the interior wall of cylinder 112.

In the embodiment of Figure 2 the force receiving member is in the form of a hollow plunger 116. Plunger 116 is open at one end 116b and is slidingly sealingly receivable within the annular gap between member 139 and cylinder 112.

The portion of the aforesaid annular gap between end 116b of plunger 116 and a shoulder defined by plug 113 constitutes an annular main chamber 117 whose operation is described in more detail below.

The end 116a of plunger 116 remote from end 116b lies on. tie exterior of the assembly 110. As in the Figure 1 embodiment the end 116a as secured thereto eg. a coupler head of per se known design (not shown in Figure 2).

The wall of plunger 116 is thickened in the vicinity of end 116b, so as to seal slidingly against both the interior wall of cylinder 112 and the exterior wall of member 139.

At the open end 112a of cylinder 112 an annular flange 112b seals slidingly against the exterior of plunger 116, which at locations remote from end 116b is of lesser diameter than the diameter of thickened portion 116b.

Consequently there is defined between end 116b and flange 112b an annular, secondary chamber 133 of variable volume.

Plug 118 has passing therethrough an energy dissipating conduit 121 that is normally closed by an energy dissipating device 122 that is functionally similar to energy dissipating device 22 of Figure 1.

The outlet of energy dissipating conduit 121 opens into the hollow interior of further circular section member 139, whereby base chamber 114 is defined within the interior of the said member 139.

A sealingly slideable separator member 141 plugs the cylindrical interior of member 139 and is slideable therein.

The portion 142 of the interior of member 139 on the side of separator member 141 remote from plug 118 is filled with a compressible gas. Portion 142 therefore defines a gas spring chamber whose function is to restore plunger 116 to its fully stroked position following externally forced

compression.

Separator member 141 defines a base chamber 114 of variable volume into which the energy dissipating conduit 121 permits flow of fluid when the pressure of the hydraulic oil in main chamber 117 reaches a predetermined threshold value (as described below).

Connection 134, that is functionally the same as connection 34 of Figure 1, perforates the wall of cylinder 112 in the vicinity of annular, secondary chamber 133. Connection 134 is in use of the assembly 110 secured to line 36 of the control element 11.

Connection 128, that is functionally the same as connection 28 of Figure 1, perforates the wall of cylinder 112 at the end of main chamber 117 adjacent plug 118.

There is no need in the Figure 2 embodiment for line 37 connecting base chamber 114 to tank, because of the variable volume of base chamber 114 that is able to accommodate excess fluid from main chamber 117 during forced retraction of plunger 116 as described below.

Considering now the states of operation defined in Table 1, in use the

assembly 110 of Figure 2 behaves in the following manner.

Si Oil flows from the pump 23 (not visible in Figure 2) via connection 134 to annular secondary chamber 133. With connections 128 and 128A open to tank by virtue of setting of control valve 27 to the right hand position shown in Figure 2A and the conventional operation of pilot operation check valves

125 and 125A that are in series with connections 128 and 128A, the gas spring chamber 142 exerts a pressure on the hydraulic oil in base chamber 114. This causes oil to flow from chamber 114 via a conduit 120 to port 128A and thence to reservoir 24. As pressure builds in secondary chamber 133 the plunger 16 retracts, reducing the volume of main chamber 117. The

excess oil is discharged from main chamber 117 to the reservoir 24, via connection 128 and valve 27.

S2 Oil flowing from pump 23 via the paths represented by the left hand position of valve 27 pilot operated check valve 125 and via connection 128 into main chamber 117 causes the plunger 116 to extend expelling oil from secondary chamber 133. Once the plunger 116 reaches its position of maximum extension, the oil pressure increases to that of the gas pressure in chamber 142 and oil is pumped, into base chamber 114. As chamber 114 fills the separator member 141 moves to the left in Figure 2, compressing the gas in chamber 142. When the separator member reaches its correct setting its movement ceases. This point is determined by the pressure, quantity and nature of the gas in chamber 142 and may be realised using a timer started by a signal from a limit switch (not sown but of per se known design), situated at the full extension position of plunger 116. The correct volume would be function of the timed interval and the pump output.

Alternatively a metering chamber 130 and associated limited switch 135 with a moving piston may be inserted between pilot operated check valve 125A and valve 27 as shown schematically in Figure 2B. Figure 2B also shows a simple restriction 140 and parallel connected one way valve 150 whose function is to ensure filling of metering chamber 130 before connecting line 128 to drain 24 (that is the same as the Figure 2A drain and

is omitted from Figure 2B for clarity). Consequently the performance of the gas spring defined by chamber 142 may be tuned by the choice and filling pressure of the gas. Connections 128 and 128A are then isolated by control valve 27 and pilot operated check valves 125 and 125A.

S3 Compression of the plunger 116 raises the oil pressure in chamber 117.

Once this pressure reaches the threshold pressure of device 122, oil flows in a controlled, energy converting manner as aforesaid into chamber 114 across the pressure controlling valve forming part of device 122. An increase in the quantity of oil in chamber 114 causes the separator member 141 to move, compressing the gas within chamber 142. The annular volume increase in chamber 133 is made up by oil supply from reservoir 24

via valve 27.

S4 When plunger 116 is fully retracted the gas pressure in chamber 142 generates a force on separator member 141. If the assembly 110 is discharged (fully retracted through action SI) this force is balanced mechanically by contact between the separator member 141 and the valve forming part of device 122. The plunger 116 when subject to no external forces would therefore remain immobile. If on the other hand the assembly 10 has not been discharged it behaves as described below in relation to conditions S5 and S6 of Table 1.

S5 and S6 (see also S4) Gas pressure in chamber 142 is transferred to oil pressure in base chamber

114 by means of separator member 141. Chamber 117 is pressurised by oil in chamber 114, via the non-return valve 160 incorporated into device 122, maintaining or restoring the plunger at the fully extended position shown.

The valve in device 122 maintains pressure in oil chamber 117 at not less than the pressure in chamber 114. The pressure in chamber 114 exerts a force on plunger 16 extending plunger 16 to its maximum travel where further movement is restrained mechanically, eg. by end stops.

Referring now to Figure 3 there is shown in vertically sectioned view a third embodiment of assembly 10 according to the invention.

The Figure 3 embodiment is in effect a hybrid of the embodiments of Figures 1 and 2, in that there is defined a cylindrical main chamber having received therein a piston encircled by an annular secondary chamber.

A plug permits fluid communication between the main chamber and a base chamber defined within the hollow cylinder. Hollow cylinder additionally communicates with a variable volume hollow chamber defined by a rubber bag sealingly secured on the exterior of the cylinder.

In Figure 3 the construction and operation of the following components is the same as their counterparts in Figure 1. Consequently they will not be described further in relation to Figure 3: Control elements 11 Cylinder 12 Plug 13 Piston (force receiving member) 16 Main chamber 17 Plug 18 Shoulder 19

Energy dissipating conduit 21 Energy dissipating device 22 Annular gap 29 Compression ring 31 Annular protrusion 32 Secondary chamber 33 Connection 34 Connection 28 Base chamber 14 of Figure 1 is in Figure 3 modified in that it comprises two parts 214a and 214b.

Portion 214a of base chamber 214 is a fixed volume chamber similar to chamber of Figure 1 defined at one end by a recess in plug 13 and at the other end by the face of plug 18 remote from main chamber 17.

Base chamber portion 214a communicates with a variable volume portion 214b of the base chamber via a base chamber conduit 247.

Conduit 247 perforates the wall of cylinder 12 in the vicinity of base chamber 214a.

Conduit 247 opens into the variable volume portion 214b of an accumulator 214b forming part of base chamber 214, and defined by a flexible, resiliently deformable (eg. rubber) tubular bag 246 that is open at either end and sealed onto the exterior of the hollow cylinder 12.

An alternative design of accumulator 214b is the spring biassed piston and cylinder assembly shown connected in place of bag 246, in Figure 3A. The spring biassing shown in Figure 3A may of course be provided by any

suitable means such as the wire compression spring shown ; a gas spring or a bladder.

It will thus be apparent that the assembly 10 of Figure 3 includes a resilient deformable base chamber portion 214b lying outside the hollow cylinder 12, the conduit 21 permitting fluid communication between the main chamber 17 and the said resiliently deformable base chamber 14b via the energy converting device 22.

If desired at least one further chamber may be disposed externally of tube 246, in pressurising contact therewith.

The further chamber may contain a pressurisable fluid whereby fluid pressure in the further chamber acts on the exterior of tubular bag 246, tending to contract it. A per se known means, such as a pump, may be used to pressurise the fluid in the further chamber. By this means a gas charge may be used to augment the pressure effect of the resiliently deformable tension in the tubular bag 246.

Operation of the embodiment of Figure 3 is similar to operation of the Figure 2 embodiment, with the tension in the tubular bag material substituting for the effect of the gas spring chamber 142, augmented as necessary by gas pressure in any further chamber as described hereinabove acting on the exterior of tubular bag 246 or separate hydraulic accumulator shown in Figure 3A.

Referring now to Figures 4 to 12 there is shown in detail a further embodiment of the invention.

In Figures 4 to 12 the buffer assembly 310 operates on the same principles

as the embodiment of Figure 1. However, the main chamber 317 (equivalent to chamber 17 of Figure 1) is defined within the hollow interior of plunger 316. Also the energy dissipating conduit and associated energy dissipating device are located at the end of the assembly 310 adjacent the plunger 316. As a result it has proved possible to relocate all the fluid connections to the end 312b of cylinder 312 remote from plunger 316. This allows all the connection ports to be located conveniently close to one another, thereby permitting easy installation and removal of the assembly 310.

Assembly 310 of Figures 4 to 12 additionally includes various refinements that improve operation of the device in use.

Referring to Figures 4 to 12, a buffer assembly 310 according to the invention comprises a main body defined as a hollow, rigid cylinder 312.

Cylinder 312 is open at one end 312a and closed by a plug 313 at its opposite end 312b.

Plug 313 rigidly supports a manifold 351 rigidly secured in end 312b of cylinder 312 eg. by means of sets screws 352 passing through plug 313 and threadedly received in manifold block 351.

Plug 313 is eg. a press fit in the end of tube 312, as best shown eg. in Figure lOb.

Manifold block 351 secured to plug 313 includes a plurality of longitudinally through going apertures that receive a plurality of set screws securing to manifold block 351 a cylinder internal sub-assembly described in more detail below.

As best shown in Figure lOb the further set screws 353 are obscured from exterior view by plug 313.

The cylinder internal sub-assembly includes a hollow, secondary cylinder 354 that extends from manifold block 351 for most of the length of cylinder 312 towards end 312a. Secondary cylinder 354 defines the major part of secondary chamber 333 described in more detail below.

Secondary cylinder 354 is concentric with cylinder 312.

The cylinder internal sub-assembly also includes, generally concentric with and lying inside secondary cylinder 354, an oil exhaust tube 356 defining the major part of the base chamber 314 of the embodiment of Figures 4 to 12.

Plug 318, that supports conduit 321 and energy converting device 322, is secured on the end of secondary cylinder 354 proximate end 312a of cylinder 312.

In this embodiment of the invention the force receiving member is in the form of hollow cylindrical plunger 316 having a free end 316a lying externally of the remainder of the assembly 310.

As in the other embodiments of the invention, free end 316a is capable of receiving secured thereto a coupler head of per se known design, secured by per se known means.

The end 316b of plunger 316 remote from free end 316a terminates within cylinder 312 and is sealingly secured to an annular compression ring 331

the inner diameter of which is sealingly slidingly engaged about the outer diameter of secondary cylinder 354, in the elongate annular space between plug 318 and manifold block 351.

The hollow, cylindrical interior of plunger 316 defines the main chamber 317 of the embodiment of Figures 4 to 12. Main chamber 317 is therefore filled with an incompressible fluid such as hydraulic oil. Plug 318 and the components associated therewith control the flow of hydraulic oil into and out of chamber 317 during operation of the device.

Plug 318 includes at its end remote from chamber 317 a shoulder 357 (Figure 6b).

Axially spaced from shoulder 357 an annular end wall 358 defines a further shoulder. The shoulders 357,358 define in the space between them an annular chamber 333a that forms part of the secondary chamber 333 that is also defined as an annular column by the members 354 and 356.

Annular chamber 333a communicates with the end of secondary chamber 333 adjacent plug 318, by means of conduit 359 passing through plug 318.

Chambers 317 and 321 are separated from one another by a closing plug that adjacent main chamber 317 includes formed therein a through-going bore 361 having seated therein valve 362.

Once valve 362 is open chamber 317 contracts under the influence of the external compressive force, forcing hydraulic oil to pass via the conduit 363 and the energy converting device 322 (that may in preferred embodiments by a measuring pin or constant force valve of per se known design) into base chamber 314 defined as the central oil exhaust tube forming part of the

cylinder internal sub-assembly.

Operation of the constant force valve (energy conversion device) 322 is best illustrated by Figure 6C.

This device 322 is basically a direct, differential-area relief valve, with features to provide a wide flow range without a significant pressure increase at high flow rates.

The device 322 includes a large chamber gas spring 321 to provide a flat spring rate, so that when the valve 322 needs to open wide, the pressure needed to open it is not significantly different to when the valve is only "cracked".

The control pressure is taken via conduit 363 from an area of relatively low oil velocity, remote from the very high velocities near the seal of valve 322.

Therefore, the valve opening is not affected by the variation in pressure normally experienced when oil is accelerated to high velocity.

Valve Function 1. The oil in chamber 317 is pressurised by an external force on plunger 316.

2. When this pressure, which acts on a control chamber 376 encircling valve member 322, via a pilot hole 375, reaches the design value, the valve opens sufficiently to prevent any further increase in pressure.

3. The pressure in chamber 317 accelerates the oil through the orifice thus created at the valve seat, giving the oil kinetic energy.

4. This kinetic energy becomes heat energy through the"internal friction" (viscosity) and turbulent and laminar flow through the pipes

etc., back to the reservoir. If the kinetic energy has not been fully dissipated, the oil will swirl around the reservoir 24 until it has.

5. The oil reaches the valve seat via conduit 363.

The energy converting device 322 includes a valve that controls the resistive force by controlling the flow of oil through an orifice or a combination of orifices. To suit a wide variety of operating conditions (in particular variations in velocity) the area of the orifice is adjusted by various mechanism by means of applied force and other variable parameters such as stroke. The valve shown in the figures generates a near-constant resistive force will applied load and velocity of impact. There is no flow across the valve unless a predetermined force is achieved.

Other forms of energy converting device are possible, including but not limited to a metering pin orifice with or without a multiplying valve.

As is best shown in Figure 6b, oil from main chamber 317 passes to base chamber 314 via a conduit 363 and bypasses a parallel connected pilot operated check valve 364 that is normally closed.

The pilot conduit of check valve 364 is in fluid communication with chamber 333, whereby pressure in secondary chamber 333 pilots check valve 364.

When pilot operated check valve 364 is open, hydraulic oil may flow via conduit 363 into chamber 314, bypassing the energy converting device 322, thereby permitting controlled retraction of piston 316.

Base chamber 314 is vented to the reservoir 24 of the control elements 11 (not visible in Figures 3 to 12) via base chamber drain conduit 337 (Figure

8b) that passes through manifold block 351 and terminates in a port 337a extending through to the exterior of plug 313.

In a manner similar to that of filling line 28 of Figure 1, filling line 328 (Figure 7b) is capable of supplying pump hydraulic oil into the interior of main chamber 317.

Filling line 328 terminates on the exterior of plug 313 in a filling port 328a that in use of the apparatus is connectable via the control valve to the output line 26 of an hydraulic pump 23. Pump 23 may be located at any convenient position on the vehicle to which the buffer/coupler assembly 310 is installed.

Filling line 328 is in the embodiment of Figures 4 to 12 constituted as a pipe extending off centre within secondary cylinder 354 and parallel thereto.

Filling line 328 is connected selectively to supply hydraulic oil to main chamber 317 via bypass conduit 363. Operatively interposed between the end of filling line 328 and bypass conduit 363 is one way check valve 366, which ensures that hydraulic oil does not pass from main chamber 317 into filling line 328.

As is evident from the nature of the cylinder internal sub-assembly, and the fact that secondary cylinder 354 and oil exhaust tube 356 are fixed relative to manifold 351 (that is in turn secured relative to plug 313), base chamber 314 is of fixed volume.

Port 337a is vented direct to reservoir 24.

Replenishment conduit 338 interconnects base chamber 314 and secondary

chamber portion 333a, via one way check valve 367.

As a result, during forced retraction of plunger 316, base chamber 314 replenishes secondary chamber portion 333a as the latter expands as compression ring 331 is pushed by plunger 316 away from plug 318.

Consequently the occurrence of voids in secondary chamber portion 333a is minimised. The presence of a one way check valve ensures that oil cannot pass from secondary chamber 333a back into base chamber 314.

When plunger 316 extends the volume of secondary chamber portion 333a decreases.

Pressure in secondary chamber 333 is controlled via pilot operated check valve 368 (Figure 11) that is spring biased to seat in a closed position.

A flow conduit at the centre of valve 368 terminates in connector portion 334 on the exterior of manifold block 351.

The end of valve 368 remote from plug 313 communicates directly with secondary chamber 333, whereby on pressure in connector port 334 exceeding the biasing force on the valve 368, the valve 368 opens to permit flow of hydraulic oil under pressure into chamber 333 that in turn causes controlled retraction of the piston 316. Pressure in chamber 333 which acts on pilot piston of valve 364 opens a conduit between 317 and 314, which in turn causes controlled retraction of piston 316.

Pressure of hydraulic oil at connector 334 is controlled in turn by control valve 27 forming part of the hydraulic control circuit.

Valve 368 is also in the embodiment shown openable under pilot operation

from pressure in filling line 328. Consequently when the oil pressure in filling line 328 exceeds the pilot bias of valve 368, as a result of the vehicle operator selecting controlled extension of piston 316, valve 368 opens to permit expulsion of hydraulic oil from secondary chamber 333 as the latter decreases in volume as a result of pressurised oil in line 328 flowing through valve 366 (Figure 7C) and entering chamber 317, via a conduit similar to conduit 363, in turn causing compression ring 331 attached to plunger 316 to move closer to shoulder 357.

The arrangement of Figures 4 to 12 omits the gas spring present in Figures 2 and 3. Therefore there is no automatic restoring force for re-extending the piston 316 following an impact.

Instead such re-extension following compression can be achieved either by maintaining the pump 23 permanently in circuit with the control valve 27 set to extend (in which case the pump would be balanced by means of a pressure control valve); or by an electrical limit switch that would sense that the device had stroked, and then shift the control valve 27 to the extension position.

The arrangement of Figures 4 to 11 is shown schematically in Figure 12.

Figure 12 shows two additional components, namely a manually operable pump 369 connected in series with gear pump 23; and a two position hand control valve connected in series with the three position, solenoid actuated, spring centred control valve 27.

Hand pump 369 is intended to permit extension and retraction of plunger 316 in the event of failure of the gear pump 323 eg. because of a power supply failure.

The two position hand control valve 371 provides operator control (eg. by means of a cab mounted lever 371a) of the direction of powered movement (ie. retracting or extending) of the plunger 316. The main purpose of valve 371 is, as stated, to give direction control for manual eg. hand pump operation in the event of power failure.

The presence of hand control valve 371 allows location of the main control valve remotely from the operator cab, whereby the control valve 27 may be automatically operated without the need for intervention by the driver.

Operation of the embodiment of Figures 4 to 12 is a follows: In order to extend plunger 16, control valve 27 adjusts to provide pumped oil flow via filling line 328 and one way check valve 366, to fill main chamber 317. During this time base chamber drain 337 is connected via port 337a to reservoir 24.

As the volume of oil in main chamber 317 increases the plunger 316 moves outwardly whereby the overall length of the assembly 310 increases.

During this process the volume of secondary chamber 333 decreases as noted hereinabove. Oil displaced from secondary chamber 333 by such contraction returns to reservoir 24 via secondary chamber 333 and valve 368, that is as noted above piloted by the pressure in filling line 328.

A mechanical stop limits the extension of plunger 316 at the end of this procedure. Engagement of the limit stops may be sensed eg. by a limit switch that may be of per se known design.

In order to retract plunger 316 relative to the remainder of the assembly 310, control valve 27 shifts to the left hand position vis : - in Figure 12 so that the pressure and volume of oil in secondary chamb ( 33, and hence in secondary chamber portion 333a, increase as oil flows through valve 368.

The rise in pressure in chamber 333 pilots valve 364 to permit oil to flow from main chamber 317 via bypass line 363 into base chamber 314. The increase in oil volume in secondary chamber 333 acting on compression ring 331 draws piston 316 rearwardly while oil flows from oil main chamber 317 into base chamber 314 via valve 364 and thence to reservoir 24 via port 337.

Retracting movement of the plunger 316 is limited by mechanical stops.

Attainment of the limit position may be sensed eg. by limit switches.

Compression of the buffer by an external force that creates a force in valve 362 sufficient to overcome its bias causes oil to flow from the main chamber 317 to base chamber 314 via conduit 321 and energy converting device 322. The large pressure drop across energy converting device 322 converts energy in the oil in the aforesaid manner.

A proportion of the oil in base chamber 314 passes through valve 367 to replenish the oil in secondary chamber 333 and thereby prevents the formation of voids therein.

It will thus be seen that all the embodiments of the invention permit controlled extension and retraction of the force receiving member 16,116, 216,316 whilst still making available the full stroke of the assembly 10, 110,210, 310 for energy absorption and dissipation.

Furthermore the device as a whole is compact since virtually all its components are contained within the envelope defined by the external cylinder 312. There is no need for external actuators and frameworks.

As noted the assembly of the invention may be configured in a number of ways that may, at the option of the designer, include or omit a gas spring for restoring the plunger or piston to its extended position following impact compression.

Claims (22)

1. CLAIMS 1. An extendable and retractable buffer assembly comprising an essentially closed main chamber, of variable volume, that is defined in part by a force receiving member and that contains a substantially incompressible fluid; a conduit communicating with the main chamber to permit flow of said fluid, when pressurised to a predetermined threshold value, from the main chamber, and including in the resulting fluid flow path an energy converting device for controlledly converting energy in the said flowing fluid; a pump for pumping the said fluid, via a selectively openable, filling conduit that bypasses the energy converting device, into the main chamber, to expand the main chamber and thereby extend the force receiving member relative to the remainder of the assembly; an essentially closed, secondary, fluid containing chamber, of variable volume, that is defined in part by said force receiving member; a pressuriser for selectively pressurising the secondary chamber, the resulting pressure in the secondary chamber acting on the force receiving member to contract the main chamber and retract the force receiving member relative to the remainder of the assembly; and a drain conduit that bypasses the energy converting device and is openable during pressurising of the secondary chamber to permit flow of fluid from the main chamber during its contraction resulting from the pressurising.
2. 2. A buffer assembly according to Claim 1 wherein the secondary chamber contains further substantially incompressible fluid; and the pressuriser operates by increasing the amount of said incompressible fluid in the secondary chamber.
3. 3. A buffer assembly according to Claim 1 or Claim 2 including a base chamber, the end of the energy converting device remote from the main chamber communicating with the said base chamber whereby fluid flowing via the said device enters the base chamber.
4. 4. A buffer assembly according to Claim 2 and Claim 3 including a replenishment conduit communicating between the base chamber and the secondary chamber, the replenishment conduit including a selectively operable valve that opens during expansion of the secondary chamber to permit flow of the said fluid from the base chamber to occupy the increased volume of the secondary chamber.
5. 5. A buffer assembly according to Claim 3 or Claim 4 including a reservoir for the incompressible fluid and a reservoir conduit communicating between the base chamber and the reservoir to permit flow of the incompressible fluid from the base chamber to the reservoir.
6. 6. A buffer assembly according to any preceding claim wherein the main chamber is defined in part by a hollow cylinder having sealingly slideably inserted therein a piston, the end of the piston remote from the main chamber lying at the exterior of the assembly and supporting a buffer head and/or a coupler.
7. 7. A buffer assembly according to Claim 6 wherein the secondary chamber is substantially closed and is an annulus encircling the piston within the hollow cylinder whereby fluid pressure in the secondary chamber acts between the hollow cylinder and the piston to cause sliding retraction of the piston relative to the cylinder.
8. 8. A buffer assembly according to Claim 6 or Claim 7 when dependent from Claim 3, wherein the energy converting device includes a plug closing the cross section of the interior of the hollow cylinder to define a fixed end of the main chamber having the said energy converting device extending therethrough, the base chamber being of fixed volume and being defined by: (i) a side of the plug remote from the main chamber; and (ii) a portion of the interior of the hollow cylinder remote from the main chamber.
9. 9. A buffer assembly according to any of Claims 1 to 5 wherein the main chamber is defined by: (i) a hollow cylinder that is closed at one end and open at an opposite end; (ii) a further circular section member fixed within the hollow cylinder so as to protrude from the said closed end of the hollow cylinder towards the said open end, thereby defining an annular main chamber within the hollow cylinder; and (iii) a hollow, cylindrical plunger that is open at one end and slidingly sealingly engageable in the annular main chamber with the further cylindrical member slidingly sealingly received into the open end of the plunger, the end of the plunger remote from the main chamber lying at the exterior of the assembly and defining a buffer head and/or a coupler.
10. 10. A buffer assembly according to Claim 9 wherein the secondary chamber is substantially closed and is an annulus encircling the further cylindrical member within the plunger, whereby fluid pressure in the secondary chamber acts between the further cylindrical member and the plunger to cause sliding retraction of the plunger relative to the cylinder.
11. 11. A buffer assembly according to Claim 9 or Claim 10 when dependent

    from Claim 3, wherein the further cylindrical member includes a further hollow, essentially closed, resiliently deformable interior defining a variable volume base chamber, the energy converting device permitting fluid flow via the said device into the said base chamber.
12. 12. An assembly according to Claim 11 wherein the further cylindrical member includes sealingly slideably located therein a separator member that moveably divides the said further hollow interior into two chambers, the base chamber being defined between the energy converting device and the separator member; and the portion of the further hollow interior remote from the base chamber containing a compressible gas and defining a gas spring for restoring the base chamber to its initial volume following its expansion.
13. 13. A buffer assembly according to Claim 6 or Claim 7 when dependent from Claim 3, wherein the energy converting device includes a plug closing the cross section of the interior of the hollow cylinder to define a fixed, substantially closed end of the main chamber having the said device extending therethrough ; the assembly including a resiliently deformable base chamber lying outside the hollow cylinder, the energy converting device permitting fluid communication between the main chamber and the said resiliently deformable base chamber via the said device.
14. 14. A buffer assembly according to Claim 13 wherein the resiliently deformable base chamber includes a tube of resiliently deformable material sealed at either end onto the exterior of the hollow cylinder, a fluid flow port interconnecting the energy converting device and the interior of the resiliently deformable tube.
15. 15. A buffer assembly according to Claim 14 including a further chamber lying externally of and defined on at least one side by the resiliently deformable tube, the further chamber containing a pressurisable fluid whereby fluid pressure in the further chamber acts on the exterior of the resiliently deformable tube, tending to contract it.
16. 16. A buffer assembly according to any preceding claim, wherein the filling conduit includes a one way check valve preventing emptying of the main chamber via the filling conduit.
17. 17. A buffer assembly according to any preceding claim including a pilot valve for selectively opening the drain conduit, the pilot valve being piloted by pressure in the secondary chamber reaching a predetermined threshold value whereby the drain conduit opens to permit draining of fluid from the main chamber while the secondary chamber retracts the force receiving member.
18. 18. A buffer assembly according to Claim 4 or any claim dependent therefrom wherein the selectively openable valve is a one way check valve that permits fluid flow from the drain conduit to the secondary chamber and prevents fluid flow from the secondary chamber to the drain conduit.
19. 19. A buffer assembly according to any preceding claim including a secondary drain conduit permitting outflow of fluid from the secondary chamber, the secondary drain conduit including a pilot operated valve that permits said outflow while incompressible fluid flows into the main chamber via the filling conduit.
20. 20. A buffer assembly according to Claim 19 wherein the pilot operated valve is piloted by pressure in the filling conduit.
21. 21. A buffer assembly according to any preceding claim wherein the force receiving member has secured to its exterior a coupler head.
22. 22. A buffer assembly generally as herein described, with reference to and/or as illustrated in the accompanying drawings.