GB2270136A - Shock absorber for vehicle suspension - Google Patents

Abstract

A shock-absorber for a vehicle suspension, in particular for a heavy vehicle of the fast armored type, comprises a body (101) including an internal central counter-rod (120) passing through the end wall (108) of a hollow rod (102) and having an end forming a piston (128) which is slidably received inside said hollow rod. The central counter-rod (120) comprises two coaxial tubes (121, 122) delimiting two independent fluid passages (123, 125) communicating respectively with the annular chamber (116) and with the chamber (117) delimited by the counter-rod piston (128) and by a separating piston (109). Throttling members (130) connected to fluid passages (123, 125) are grouped together in the end wall (103) of the body (101), and are individually adjustable from outside said body. <IMAGE>

Description

A SHOCK-ABSORBING ACTUATOR FOR A VEHICLE SUSPENSION The invention relates to a shock-absorbing actuator for a vehicle suspension, in particular for a heavy vehicle capable of travelling over difficult terrain.

Shock-absorbing actuators are already known that have firstly a body in which a hollow rod is slidably received, the hollow rod being equipped with a separating piston delimiting a pressurized gas end chamber and a hydraulic fluid chamber which communicates with a hydraulic fluid chamber inside said body, and secondly throttling members for determining shock absorption.

In general, the end wall of the hollow rod is provided with a diaphragm in the vicinity of the center of said end wall. The diaphragm serves to control the compression (or contraction) of the shock-absorbing actuator, and the end wall defines an annular expansion chamber delimited by the body and by the hollow rod, with associated valves being provided.

The throttling members are therefore integrated in the shock-absorbing actuator. As a result, the actuator must be disassembled fully if its shock-absorption characteristics are to be modified.

Moreover, under severe operating conditions, e.g. when such shock-absorbing actuators are included in suspensions of heavy vehicles, such as fast armored vehicles with six or eight driving wheels, it is necessary to provide hydraulic fluid flow-rates that are high because of the high speeds involved, so that the valves are usually both large and also complicated in structure.

The invention aims to solve those two problems, by designing a shock-absorbing actuator that does not suffer from the above-mentioned drawbacks and/or limitations.

Therefore, an object of the invention is to provide a shock-absorbing actuator of structure that facilitates adjusting the throttling members, and that makes it possible to reduce the hydraulic fluid flow-rates that occur in operation.

More particularly, the invention provides a shockabsorbing actuator for a vehicle suspension, in particular for a heavy vehicle of the fast armored type, the shockabsorbing actuator including firstly a body in which a hollow rod is slidably received, the hollow rod being equipped with a separating piston delimiting a pressurized gas end chamber and a hydraulic fluid chamber which communicates with a hydraulic fluid chamber inside said body, and secondly throttling members for determining shockabsorption, said shock-absorbing actuator being characterized in that:: the body includes an internal central counter-rod extending from the end wall of said body, through the end wall of the hollow rod in fluid-tight manner, and on to a free end forming a piston which is slidably received in fluid-tight manner inside said hollow rod; the central counter-rod comprises two coaxial tubes delimiting two independent fluid passages, namely an annular passage which communicates, via associated orifices, with the annular chamber delimited by the end wall of the hollow rod and by the counter-rod piston, and a central passage which opens out directly into the chamber delimited by the counter-rod piston and by the separating piston; and the throttling members include diaphragms and shockabsorption force limiters that are grouped together in the end wall of the body, and that are disposed therein so as to be individually adjustable from outside said body.

Preferably, the chamber inside the body communicates with the annular chamber in the hollow rod via a non-return valve provided in the end wall of the hollow rod, said valve opening naturally during compression of the shock-absorbing actuator.

Advantageously, the communication orifices establishing communication between the annular chamber in the hollow rod and the annular passage in the counter-rod are then organized as regards shape and size so as to produce predetermined end-of-stroke shock-absorption during extension of the shock-absorbing actuator. For example, the communication orifices are constituted by a set of through holes, and by an elongate slot disposed axially between said set and the counter-rod piston.

According to another advantageous characteristic, the throttling members are organized in two independent assemblies, one assembly acting during compression of the shock-absorbing actuator and the other assembly acting during extension thereof, and each assembly including a diaphragm and a shock-absorption force limiter that are individually adjustable.

In a particular embodiment, each diaphragm is implemented by a through orifice which co-operates with the conical end of a screw whose head is accessible from outside the body, and each shock-absorption force limiter is implemented by a flat valve member rated by means of a resilient washer having prestress that is adjustable from outside the body.

Advantageously, the prestress of the resilient washer is then adjustable by means of a fine adjustment system using two coaxial threads having respective pitches that are slightly different.

Preferably, a non-return valve is also associated with the throttling assembly that acts during compression of the shock-absorbing actuator, said valve being disposed downstream from the associated force limiter and closing naturally during said compression.

Finally, advantageously, the body is further equipped with a valve which enables the volume of fluid contained in the shock-absorbing actuator to be modified when the actuator is under static load, so as to cause the actuator to extend or contract.

Other characteristics and advantages of the invention will appear more clearly on reading the following description of a particular embodiment given with reference to the accompanying drawings, in which: Figure 1 is a section through a shock-absorbing actuator of the invention, with the throttling members of the actuator being represented diagrammatically; Figure 2 supplements Figure 1 with a structural view of the mechanical throttling members associated with one of the two independent assemblies (one assembly acting during compression of the shock-absorbing actuator, and the other assembly acting during extension thereof);; Figure 3 is a fragmentary view in section through the end of the central counter-rod whose outer tube has orifices which are organized to produce shock absorption at the end of the extension stroke, the orifices being more clearly visible in Figure 4 which is a view of a detail as seen looking along arrow F in Figure 3; and Figure 5 is a section on V-V in Figure 1, making it easier to discern the way in which the throttling members are organized, which members are grouped together in the end wall of the body, and are further individually adjustable from outside the body.

Figure 1 is a section through a shock-absorbing actuator 100 of the invention, with the throttling members 130 of the actuator being represented diagrammatically. A possible embodiment of the throttling members is described below with reference to Figures 2 and 5.

The shock-absorbing actuator 100 includes a body 101 and a hollow rod 102 which is slidably received therein and which is coaxial with the axis X of said body. The body 101 includes an end wall 103, a cylindrical skirt 105 inside which the hollow rod 102 is slidably received, sealing between the cylindrical skirt 107 of the hollow rod 102 and the skirt 105 of the body being provided by a dynamic sealing ring 112. A separating piston 109 is provided inside the hollow rod 102. The separating piston delimits a pressurized gas end chamber 113 (the pressurized gas generally speaking being nitrogen), the chamber being inflated via a valve 114, and the chamber being sealed by means of a sealing ring 118 carried by the separating piston 109.The end of the end wall 103 is provided with a ball coupling 104, while the end of the hollow rod 102 is in the form of a projection 110, and is also provided with a ball coupling 111. The two ball couplings 104 and 111 serve to fasten the shock-absorbing actuator which is used for the suspension of a vehicle, in particular of a heavy vehicle of the fast armored type.

In accordance with a first characteristic of the invention, a central counter-rod 120 is provided inside the body 101. The central counter-rod extends from the end wall 103 of said body, through the end wall 108 of the hollow rod 102 in fluid-tight manner, and on to a free end forming a piston 128 slidably received in fluid-tight manner in said hollow rod. In this way, the cylindrical skirt 105, the end wall 103, and the counter-rod 120 with its counter-rod piston 128 constitute a single assembly. The central counter-rod 120 comprises two coaxial tubes 121 and 122 which extend over the entire height of said central counterrod, from the end wall 103 to the counter-rod piston 128.

The two tubes 121 and 122 thus define two independent passages, one of which is an annular passage 123 which communicates via associated orifices 124 with the annular chamber 116 that is delimited by the end wall 108 of the hollow rod and by the counter-rod piston 128. The inner tube 122 is hollow so that it delimits a central passage 125 which opens out directly into the chamber 117 delimited by the counter-rod piston 128 and by the separating piston 109.

An annular chamber 106 is delimited by the cylindrical skirt 105 of the body 101, by the outer tube 122 of the counterrod 120, by the end wall 103 of the body 101, and by the end wall 108 of the hollow rod 102. Chamber 106 in the body 101, together with annular chamber 116 and chamber 117 in the hollow rod 102, are hydraulic fluid chambers, with the hydraulic fluid passing through the passages 123 and 125 in the central counter-rod 120 when the hollow rod 102 and the body 101 are moving relative to each other. The shock absorbing actuator is filled with hydraulic fluid via a filling valve 115.

The chamber 106 inside the body 101 also communicates with the annular chamber 116 in the hollow rod 102 via a non-return valve 126 which is provided in the end wall 108 of the hollow rod. The non-return valve opens naturally during compression of the shock-absorbing actuator that causes the actuator to contract. The non-return valve 126 is preferably implemented in the form of a single flat metal valve member which provides sealing by metal-metal contact, and which is actuated solely by the force of the hydraulic fluids present, without an associated return spring being provided.

In accordance with another characteristic of the invention, throttling members for determining shock absorption are provided. Said members are referenced 130 and they include diaphragms and shock-absorption force limiters that are grouped together in the end wall 103 of the body 101, and that are disposed therein so as to be individually adjustable from outside said body.

In this way, unlike conventional structures, the structure of the invention provides access from outside the body of the shock-absorbing actuator to the adjustment members that are associated with the throttling members, thereby enabling the various throttling characteristics to be adjusted individually both for compression of the shockabsorbing actuator and for expansion thereof, without it being necessary for the shock-absorbing actuator to be completely disassembled.

In a preferred embodiment, the throttling members 130 are organized in two independent assemblies 131 and 132, one assembly (131) acting during compression of the shockabsorbing actuator 100 and the other assembly (132) acting during extension thereof. In Figure 1, two circles drawn using dot-dash lines diagrammatically represent the two independent assemblies 131 and 132, the way said assemblies operate also being shown so that the operating principle of the shock-absorbing actuator of the invention can be better understood.

Assembly 131 is constituted by a pipe 131.1 opening out via an orifice 04 into the chamber 106 in the actuator body 101, which pipe leads both to a diaphragm 131.2 and also to a shock-absorption force limiter 131.3. The diaphragm and the force limiter are connected to a pipe 131.4 that opens out via an orifice 03 into the central passage 125 in the counter-rod 120. A non-return valve 131.5 is also associated with the throttling assembly 131 that acts during compression of the shock-absorbing actuator, which valve is disposed downstream from the force limiter 131.3 and closes naturally during said compression. The diaphragm 131.2 and the shock-absorption force limiter 131.3 are adjustable so that it is possible to modify the shock-absorption characteristics that apply during compression of the shockabsorbing actuator.

Similarly, assembly 132, which acts during extension (i.e. expansion) of the shock-absorbing actuator 100, comprises a pipe 132.1 opening out via an orifice 02 into the annular passage 123 in the counter-rod 120, which pipe leads both to a diaphragm 132.2 and also to a shockabsorption force limiter 132.3. The diaphragm and the force limiter are connected to a pipe 132.4 that opens out via an orifice O1 directly into the chamber 106 inside the body 101. As with the other assembly, the diaphragm and the shock-absorption force limiter of assembly 132 are also designed so that they can be adjusted, thereby making it possible to modify the shock-absorption characteristics that apply during expansion of the shock-absorbing actuator.

An embodiment of the structural members performing the above mentioned functions of diaphragm and of pressure limiter is described below with reference to Figures 2 and 5. Before that description, a description is given of the overall operation of the shock-absorbing actuator 100 on compression (i.e. on contraction), and then on extension (i.e. on expansion).

During compression of the shock-absorbing actuator 100, the hollow rod 102 penetrates into the body 101, and the greater portion of the hydraulic fluid in chamber 106 passes via non-return valve 126 into annular chamber 116. The remaining portion of the fluid, which portion corresponds to the cross-sectional area determined by the thickness of the cylindrical skirt 107 of the hollow rod, passes via orifice 04, and then via diaphragm 131.2, downstream from which the fluid passes via orifice 03 into the central passage 125 of the counter-rod 120. It should be noted that, in this situation, non-return valve 131.5 is closed.

The shock-absorption force limiter 131.3, which forms a pressure limiter, opens only if the throttling pressure exceeds the associated opening threshold, which is adjustable. In any event, the delivered volume passes via the central passage 125 towards chamber 117 in the hollow rod 102. This compression motion imparts thrust to the separating piston 109, and, as a result, compresses the volume of gas confined in chamber 113.

It can be easily understood that this structure makes it possible for the fluid flow-rates that are to be controlled to be low. This is made possible by means of the small difference in cross-sectional area between chambers 106 and 116 (thickness of the skirt 107), and, as a result, it is possible to avoid the high dynamic flow-rates that occur in conventional structures in suspensions associated with heavy vehicles. By having low fluid flow-rates, it is also possible to use pressure limiter systems of simple structure, and, as a result the reliability of the throttling system is improved.

During extension of the shock-absorbing actuator 100, the hollow rod 102 moves out of the body 101. Non-return valve 126 is then closed, so that the fluid contained in annular chamber 116 is forced to pass through the orifices 124 provided in the end portion of the counter-rod 120, in the vicinity of the counter-rod piston 128. Said fluid then flows through the annular passage 123 towards the end wall 103 which includes the throttling elements. The fluid thus passes via orifice 02, then via diaphragm 132.2, and returns into the chamber 106 in the body 101 via orifice 01. The forcelimiter forming the pressure limiter 132.3 opens if the throttling pressure exceeds the associated opening threshold, which is also adjustable. Therefore, the volume of fluid in annular chamber 116 passes into chamber 106 in the body 101 after throttling.The volume needed to compensate for the volume of fluid associated with the displacement of the rod end wall is supplied by chamber 117 in the hollow rod 102 via the central passage 125 in the counter-rod 120: non-return valve 131.5, which is closed on compression, opens automatically under the effect of the hydraulic forces, thereby allowing fluid to pass into chamber 106 via orifice 04. This makes it possible to avoid any cavitation in chamber 106 in the body 101, and thus to control operation well even under difficult operating conditions, in particular when expansion is suddenly followed by compression. Furthermore, the rod 102 moving out of the body causes the volume of gas contained in chamber 113 to expand, and therefore the associated piston 109 to be displaced.The extension stroke of the rod is also limited by internal mechanical abutments, in this case constituted by a projecting or thickened portion referenced 121.1 on the outer tube of the counter-rod 120: such an abutment system is not designed to absorb much energy, but it can withstand the moving mass if the associated wheel is no longer in contact with the ground. Similarly, internal mechanical abutments may be provided for the compression stroke, which abutments are capable of withstanding the associated static load if the shock-absorbing actuator is not under pressure.

It is also advantageous for the orifices 124 to be organized, both as regards shape and size, so as to produce predetermined end-of-stroke shock-absorption during extension of the shock-absorbing actuator 100. An advantageous embodiment of such orifices is shown in Figures 3 and 4, with the end of the central counter-rod 120 being shown in part.

Figure 3 shows piston rings 119, preferably made of bronze, for providing sealing between the hollow rod 102, and firstly the counter-rod piston 128 and secondly the outer tube 121 of the counter-rod, the projecting portion 121.1 on said outer tube constituting a mechanical abutment limiting the extension stroke of the hollow rod by cooperating with a milled abutment collar 108.1 projecting from the end wall 108 of the hollow rod (the position shown corresponds exactly to the expansion abutment). Figure 3 and the detail shown in Figure 4 (which is a view looking along arrow F) show a through hole 124.1 followed by an elongate slot 124.2 disposed axially between the through hole and the counter-rod piston 128.In this way, a set of a plurality of through holes 124.1 may be provided distributed angularly on a circle having a plane that is perpendicular to the axis of the actuator, followed by an elongate slot 124.2 for providing end-of-stroke shockabsorption when the piston ring 119 of the end wall 108 goes beyond the through holes 124.1, with the fluid then passing solely via the elongate slot 124.2, with a through section that decreases as the hollow rod 102 moves out of the body.

More generally, by determining the shape and the dimensions of the elongate slot 124.2, it is possible to adjust the shock-absorption force so as to satisfy the required operating conditions. In a variant, a single aperture may be provided, with a portion of the aperture being progressively masked as the shock-absorbing actuator expands.

Figure 2 shows a more structural view of the mechanical throttling members associated with one of the two independent throttling assemblies (132 in this example).

The structure of the other assembly 131 may be analogous, ignoring size.

In this example, the diaphragm 132.2 is implemented by an orifice 136 with which the conical end 142 of a screw 140 co-operates. In this way, the through section of the orifice can be adjusted by adjusting the extent to which the screw 140 is engaged therein merely by acting on the head of the screw. The screw may be locked in the desired position by means of a nut. To this end, the head 141 of the screw 140 is accessible from the outside of the body 101 at the end wall 103 thereof, and the associated locking nut 141.1 can be seen. Through holes 137 (between two successive chambers 135 and 138) are also provided associated with a pressure-limiting device enabling the shock-absorption force to be limited.A flat valve member 133 is shown, which valve member is rated by a resilient washer 134, the prestress of which is adjustable from outside the body 101, e.g. by means of a system described below with reference to Figure 5. When the throttling pressure is less than the pressure-limiting threshold corresponding to the characteristic of the resilient washer 134, the hydraulic fluid passes solely via the calibrated orifice 136. As soon as the throttling pressure exceeds the pressure-limiting threshold, the resilient washer 134 is deformed and the valve member 133 opens so as to increase the throttling section. In practice, the characteristic of the resilient washer 134 is chosen as a function of the shape and of the desired amount of pressure-limiting. After throttling, the fluid in chamber 138 flows into chamber 106 in the body 101 via orifice 01.

The section given in Figure 5 shows an advantageous embodiment for the means for adjusting the prestress of the resilient washer 134 of each throttling assembly.

In this example, two fine adjustment systems 150 are provided, each system being associated with a respective throttling assembly 131 or 132. The two systems are of identical structure, but they may be of different sizes.

Each adjustment system 150 includes a washer 158 which is accessible from the outside of the body by means of an associated recess 160, and which screws into the end wall 103 of the body via a thread 151. The washer 158 is associated with a second washer 152, in this example via a fastening screw 153. One end 154 of the second washer has its outside thread 155 penetrating into associated tapping in a part 156 which is axially movable, which is prevented from rotating by a peg 157, and which carries the deformable washer 134.

By means of an appropriate choice for the pitches of the two coaxial threads 151 and 155, with pitches that differ slightly, it is possible to obtain very small relative displacement of the part 156 for a given pivot angle of the washers 158 and 152, thereby providing particularly fine adjustment of the prestress of the resilient washer 134. By way of example, a value of 1 mm may be chosen for the pitch of thread 151, and a value of 0.8 mm may be chosen for the pitch of thread 155, thereby providing displacement of the part 156 of 0.2 mm for one screw turn. The two above-mentioned screws 140 respectively associated with each assembly 131 and 132 can also be seen.

The head 141 of each screw is accessible from outside the body, by means of an associated recess 161 provided in the end wall 103 thereof.

Figure 1 also shows a valve 127 which is provided to make it possible to modify the volume of fluid contained in the shock-absorbing actuator 100 when the actuator is under static load. The actuator can thus be caused to extend or contract, i.e. the vehicle carried by the suspension can be lowered or raised. The valve 127 may communicate either with the central passage 125 in the counter-rod 120 as shown in this example, or, in a variant, with the chamber 106 in the body 101. The extension stroke may be chosen to be equal to the extent of penetration under static load, in which case, the hollow rod 102 and the counter-rod 120 abut against each other internally. The capacity of the contraction stroke is then defined by the clearance under static load between the counter-rod piston 128 and the separating piston 129.

A protective tube may also be disposed on the actuator body, with the top end of the tube covering the hollow rod so as to constitute a protective screen protecting the rod against external soiling or possible impacts. Such a tube is not shown in the figures.

Finally, it should be noted that, since the annular chamber 116 controlling the expansion is disposed inside the hollow rod, the dynamic sealing ring 112 is situated on the inside diameter of the skirt 105. Therefore, for a given outside size, the sealing ring 112 is on the largest possible diameter, and as a result the static pressures are as small as possible, thereby improving the endurance of the sealing ring.

A shock-absorbing actuator is thus provided having a structure that makes it possible both to facilitate adjustment operations for adjusting the throttling members, which operations can be performed in situ without the shockabsorbing actuator having to be disassembled, and also to reduce the hydraulic fluid flow-rates that occur in operation.

The invention is not limited to the above-described embodiment, but on the contrary it covers any variant that reproduces above-mentioned characteristics with equivalent means.

Claims (11)

1. A shock-absorbing actuator for a vehicle suspension, the shock-absorbing actuator including a body in which a hollow rod is slidably received, the hollow rod being equipped with a separating piston delimiting a pressurized gas end chamber and a hydraulic fluid chamber which communicates with a hydraulic fluid chamber inside said body, and throttling members for determining shockabsorption, wherein the body includes an internal central counter-rod extending from the end wall of said body, through the end wall of the hollow rod in fluid-tight manner, and on to a free end forming a piston which is slidably received in fluid-tight manner inside said hollow rod; the central counter-rod comprising two coaxial tubes delimiting two independent fluid passages, namely an annular passage which communicates, via associated orifices, with the annular chamber delimited by the end wall of the hollow rod and by the counter-rod piston, and a central passage which opens out directly into the chamber delimited by the counter-rod piston and by the separating piston; and wherein the throttling members include diaphragms and shock-absorption force limiters that are grouped together in the end wall of the body, and are disposed therein so as to be individually adjustable from outside said body.

2. A shock-absorbing actuator according to Claim 1, wherein the chamber inside the body communicates with the annular chamber in the hollow rod via a non-return valve provided in the end wall of the hollow rod, said valve opening naturally during compression of said shockabsorbing actuator.

3. A shock-absorbing actuator according to Claim 1 or 2, wherein the communication orifices establishing communication between the annular chamber in the hollow rod and the annular passage in the counter-rod are organized as regards shape and size so as to produce predetermined end-of-stroke shock-absorption during extension of said shock-absorbing actuator.

4. A shock-absorbing actuator according to Claim 3, wherein the communication orifices are constituted by a set of through holes, and wherein an elongate slot is disposed axially between said set and the counter-rod piston.

5. A shock-absorbing actuator according to any one of Claims 1 to 4, wherein the throttling members are organized in two independent assemblies, one assembly acting during compression of said shock-absorbing actuator and the other assembly acting during extension thereof, and each assembly includes a diaphragm and a shockabsorption force limiter that are individually adjustable.

6. A shock-absorbing actuator according to Claim 5, wherein each diaphragm is implemented by a through orifice which co-operates with the conical end of a screw whose head is accessible from outside the body, and each shockabsorption force limiter is implemented by a flat valve member rated by means of a resilient washer having prestress that is adjustable from outside the body.

7. A shock-absorbing actuator according to Claim 6, wherein the prestress of the resilient washer is adjustable by means of a fine adjustment system using two coaxial threads having respective pitches that are slightly different.

8. A shock-absorbing actuator according to any one of Claims 5 to 7, wherein a non-return valve is associated with the throttling assembly that acts during compression of said shock-absorbing actuator, said valve being disposed downstream from the associated force limiter and closing naturally during said compression.

9. A shock-absorbing actuator according to any one of Claims 1 to 8, wherein the body is further equipped with a valve which enables the volume of fluid contained in said shock-absorbing actuator to be modified when the actuator is under static load, so as to cause the actuator to extend or contract.

lo. A shock-absorbing actuator as claimed in any one of Claims 1 to 9, which is for a heavy vehicle of the fast armoured type.

11. A shock-absorbing actuator substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.