Suspension and damping device with two suspension-damper combinations

The present invention relates to a suspension and damping device comprising a damping cylinder and a first piston movable in this cylinder, a first and a second chamber containing hydraulic damping fluid being respectively provided on either side of the cylinder. this first piston, the latter being provided with means for regulating the passage of the fluid between the first and second chambers, the device further comprising first suspension means connected to the first piston in the vicinity of a first end of the damping cylinder.

Devices of this type are known, in which the first suspension means can be constituted by a mechanical spring (for example a helical spring) or by a pneumatic spring (of the type operating with the aid of a compressible gas contained in an air spring). enclosure correctly delimited in the vicinity of the first end of the damping cylinder).

These known devices are generally satisfactory. However, they are generally only suitable for providing the optimum response to ensure vehicle suspension and oscillation damping in only one type of terrain. Thus, a suspension and damping device tuned for a good or average road quality may give poor results in terms of suspension and damping when the vehicle is traveling over less smooth terrain such as a road or road. a paved road.

The invention aims to remedy these drawbacks by providing a device suitable for several types of stresses.

This object is achieved thanks to the fact that the device comprises a second piston movable in the damping cylinder, as well as second suspension means connected to the second piston in the vicinity of a second end of said cylinder, the second chamber being provided, d 'one side of the second piston, between the first and second pistons, while a third chamber is provided on the other side of the second piston, the latter being provided with means for regulating the passage of the fluid between the second and third chambers, the first combined formed by the first piston and the first suspension means and the second combined formed by the second piston and the second suspension means being adapted for loads in different frequency ranges.

The device according to the invention therefore comprises two combined suspension-shock absorber arranged in series; in fact, the damper part of the device behaves practically like two dampers arranged in series, the first damper comprising the first piston and the first and second chambers, while the second damper comprises the second piston and the second and third chambers. The two handsets in series complement each other and the device is ultimately able to give a satisfactory response in a wide variety of situations.

The settings are advantageously chosen so that the damping and the suspension means of the first handset generally provide responses similar to those given by the handsets conventionally used on the vehicle in question. Thus, the stiffness of the first suspension means and the braking of the first shock absorber will often correspond to current values.

In this case, one chooses rather the settings of the shock absorber and of the suspension means of the second combined so that the latter is provided with a shorter piston stroke and only provides less braked damping (more liberated). ). Thus, the stiffness and the preload of the second suspension means can then be determined so that the second piston is in a position close to its mid-stroke of the second combined, when the vehicle is in a static position. It is thus possible to choose either a higher stiffness with a lower preload, or a lower stiffness with a higher preload than those used on the first handset. The braking of the second suspension means will be markedly weaker than that of the conventional combined suspension means used on the same type of vehicle.

With such adjustments, the device according to the invention can respond satisfactorily to frequency stresses close to the resonant frequency of the suspended masses of the vehicle (of the order of 1 Hz and up to 4-5 Hz, such as those to which a vehicle traveling on an asphalt road of average or good quality is subjected by means of the first instrument panel, as well as to higher frequency stresses (of the order of 10 Hz and more, such as those to which a vehicle traveling on a paved road or lane is subjected) via the second handset.

The means for regulating the passage of the fluid between the first and second chambers are generally constituted by controlled passages which allow the liquid to pass through the piston to allow its movement in both directions inside the damping cylinder 10, these passages being dimensioned so as to provide resistance to displacement of the piston, which resistance conditions damping braking. In some situations, however, it is desirable that the piston be able to move faster. This is in particular the case on the occasion of losses of adhesion of a wheel which, after having been subjected to a strong load, cannot descend fast enough to touch the ground when it passes over a road. rut. In order to increase the grip, it would be desirable to allow an almost instantaneous release of the damper piston to ensure that in such a situation the wheel could descend very quickly and come into contact with the ground.

Such a brake release function has already been proposed in hydropneumatic shock absorbers, in which an inertial weight is used which is capable of releasing the braking of the shock absorber in sudden expansion. The operation of this system is not entirely satisfactory, insofar as the movement of the weight is not controlled, which sometimes induces too much brake release, which can continue once the wheel has recovered. contact with the ground and is therefore done to the detriment of damping. In addition, a system of this type comprises a large number of parts and its cost price is therefore very high.

To remedy these drawbacks and provide an improved brake release function, the device according to the invention advantageously furthermore comprises means for placing the first and second chamber in communication capable of being activated as a function of the position of the second piston.

These means of placing the first and second chamber in communication make it possible to ensure the rapid brake release function, for example used in the event of a loss of grip of a wheel. Indeed, the position of the second piston is obviously directly related to the load to which it is subjected. To ensure brake release in the event of loss of grip, it suffices to ensure that the position of the second piston corresponding to the activation of the communication means is obtained in a situation in which this second piston is unloaded and subjected to the only constraint of the weight of the wheel. It will be understood that, the first and second chambers then being placed in communication, the movement of the first piston is practically no longer braked, so that it can very quickly occupy a position of maximum stretching which allows the wheel to enter. quickly in contact with the ground. When this contact is established, the second piston is subjected to a load linked to the support of the vehicle on the ground and returns to a position in which the communication means are deactivated, so that the damping resumes normally.

Thus, the second handset makes it possible, depending on whether the communication means are more or less activated, to regulate the rebound damping of the first handset. This device is simpler than the flyweight system of the prior art, and therefore less expensive. In addition, the brake release can be automatically controlled by the greater or lesser activation of the communication means.

If one chooses to ensure that the second combination has a higher stiffness and / or a lower damping than the first, one ensures that in the event of loss of grip of a wheel to which is connected the device, the second handset is quickly and preferably triggered to relax, which allows the second piston to come to occupy its position corresponding to the activation of the communication means.

According to a first advantageous variant, the means for placing the first and second chamber in communication comprise a communication passage having a first opening situated in the first chamber and a second opening situated in the region of the second chamber, this second opening. being capable of being more or less closed by the second piston depending on the position occupied by the latter in the second chamber. In this case, the communication means of the first and second chambers are made in a simple manner and, in particular, they can be directly activated or deactivated according to the position of the second piston, by closing the second opening, without qu 'it is necessary to provide additional means of control.

According to another advantageous variant, the means for placing the first and second chambers in communication comprise a passage passing through the first piston equipped with a controlled valve and means for controlling said valve capable of being activated or deactivated as a function. of the position of the second piston.

Advantageously, to compensate for the volume of the operating rod of the mobile piston, a compensating reservoir of the type described in French Patent No. 1,055,443 or of the type known under the name of twin-tube damper is used.

Indeed, the volume of the operating rod of the piston entering the damping cylinder must correspond to the same volume of hydraulic damping liquid discharged from this same cylinder. The compensation tank is most often composed of two chambers, a hydraulic chamber filled with damping liquid and an additional chamber separated from the hydraulic chamber by, for example, a floating piston containing a pressurized gas. In addition, there may be at the inlet of the hydraulic chamber of the reservoir means for regulating the passage of fluid between the damping cylinder and the reservoir. Pressurization and the means for regulating the passage of the fluid make it possible, in principle, during the compression phase of the shock absorber, to avoid the phenomenon of cavitation in the first chamber of the damping cylinder by creating resistance to the shock. evacuation of the fluid towards the reservoir, thus facilitating the filling of the first chamber through the passages of the piston.

Despite the pressurization of this reservoir and the means for regulating the passage of the fluid from the damping cylinder to the reservoir, it may happen, during repeated and / or very violent compression shocks, that the phenomenon of cavitation appears in the first chamber. Compression is then followed by instantaneous and uncontrolled expansion (no braking) while the cavitation disappears. This unwanted rebound throws the vehicle off, which can be the cause of serious accidents.

To remedy these drawbacks and effectively combat the risks of cavitation in the damping cylinder, the device according to the invention advantageously furthermore comprises means for placing the hydraulic chamber of the compensation tank 5 in communication with the first chamber and / or the third chamber of the damping cylinder. These means of communication include a valve allowing the passage of fluid only from the compensation tank to the chamber to which it is connected. Thus, during a shock, even a very violent one, the arrival of fluid through this communication makes it possible to avoid cavitation in the chamber in question, then the closing of the valve ensures controlled operation of the expansion phase.

The combined suspension-shock absorber according to the invention therefore makes it possible to ensure an optimal response to various stresses. If the means for placing the first and second chambers 15 in communication are present, it also allows the relaxation phase to be released during a loss of wheel grip. In addition, if it is equipped with an anti-cavitation system having means for placing a hydraulic chamber of a compensation tank in communication with the first and / or the third chamber, it makes it possible to avoid the sudden return caused. by cavitation of the chamber in question.

The invention will be well understood and its advantages will appear better on reading the following detailed description of embodiments shown by way of non-limiting examples. The description refers to the accompanying drawings in which:

- Figure 1 is an axial sectional view of a device according to the invention,

- Figures 2, 3, 4 and 5 are views similar to Figure 1 showing four variants of the device,

- Figures 6 and 7 show details of two variants, in view 30 along arrow VI of Figure 2, and

- Figure 8 shows a detail of a variant, in view along arrow VIII of Figure 2.

Figure 1 shows a suspension and damping device 10 comprising a damping cylinder 12 and a first piston 14 movable therein. This piston slides in the calibrated interior 16 of the cylinder and divides the interior of the latter into a first chamber 18 and a second chamber 20 which are filled with a suitable hydraulic damping fluid, generally hydraulic oil. When the device is subjected to high loads, that is to say when the damper operates in compression, the piston 14 moves in the direction of the arrow F1 and penetrates further inside the cylinder 12, from so that the volume of the second chamber 20 is reduced while that of the first chamber 18 increases. The opposite phenomenon, with a displacement in the direction opposite to the arrow F1, occurs when the trigger is released.

Damping is achieved by the fact that the piston 14 is provided with means for regulating the passage of fluid between the first and second chambers 18 and 20 which generate resistive forces slowing down the movement of the piston in one or the other. meaning. These means comprise, on the one hand, at least a first restriction 22, located in a first passage equipped with a non-return valve 24 and, on the other hand, at least a second restriction 26, also located in a second passage. equipped with a non-return valve 28. The non-return valve 24 allows the opening of the passage in which the restriction 22 is located only during a movement of the piston 14 in the direction of the arrow F1, so that the restriction 22 is used during a stress. in compression. On the other hand, the valve 28 opens the passage in which the restriction 26 is located only during a movement in the direction opposite to the arrow F1, so that this restriction 26 is used during a relaxation bias. The restrictions 22 and 26 can be fixed passage and / or variable passage, adjustable or not. In practice, two series each comprising several passages equipped with valves and restrictions are provided in the piston to respectively create the resistive forces in one and the other direction.

The device shown in Figure 1 comprises a second piston 30, also movable in the damping cylinder 12. The aforementioned second chamber 20 is formed between the first and second pistons, while a third chamber 32 is formed on the other side. second piston side 30. The latter is provided with means for regulating the passage of the fluid between the second chamber 20 and the third chamber 32, these means comprising, for example, sets of restrictions and valves 22 ', 24', 26 'and 28', respectively similar to those who equip the first piston.

The device also comprises means for placing the first chamber 18 and the second chamber 20 in communication which comprise a communication passage 34 having a first opening 36 located in the region of the first chamber 18 and a second opening 38 located in the second chamber region 20. As seen in Figure 1, the communication passage 34 is advantageously formed in an annular space delimited between an internal wall element 40 of the cylinder 12 and an external wall element 42 of this cylinder. Pistons 14 and 30 slide sealingly along inner wall member 40.

The second opening 38 is made in a part of the cylinder which is in the path of the second piston in its displacement movement. This opening is therefore likely to be more or less closed by the axial cylindrical wall of the second piston depending on the position occupied by the latter in the second chamber. In the expansion phase of the piston 30, when the volume of the chamber 20 is practically maximum, the opening 38 is actually located in this chamber. On the other hand, in the compression phase, the volume of the chamber 20 is reduced and the opening 38 is no longer located in this chamber but opposite the axial wall of the piston 30. The indication that the opening 38 is located in the region of the second chamber 20 means that it opens into this chamber at least in a position (in particular a relaxation position) of the piston 30, which acts as a slide relative to this opening.

The device comprises first and second suspension means 44 and 45 which are respectively connected to the first piston 14 and to the second piston 30 and which, in the example shown, each comprise a mechanical spring, respectively 46 and 47.

The first chamber 18 is closed, on the side opposite to the piston 14, by leaktight sealing means 70. This is for example a stopper fixed in a leaktight manner to the wall of the cylinder 12 and comprising a central bore 72 in the chamber. which slides a rod 15 connected to the piston 14 by suitable means. Of course, the sliding of the rod takes place in a sealed manner, the sealing being ensured by a seal 73 located in the bore 72. At its end opposite to the piston 14, the rod 15 carries a stopper plate 54. The spring 46 is disposed between the closure plug 70 and this stopper plate 54.

Likewise, the chamber 32 is closed by a plug 70 'having a bore 72' in which the rod 31 of the piston 30 slides with sealing 5 thanks to the seal 73 '. The spring 47 is disposed between the plug 70 'and the stop plate 54'.

The stop plates 54 and 54 'can be respectively fixed to the frame and to a wheel of a vehicle. Figure 1 shows the device when subjected to an average load, for example due to the weight of the vehicle when it is stationary. The two pistons then occupy intermediate positions and, if a greater load is exerted, the volumes of the chambers 18 and 32 may increase while that of the chamber 20 decreases, while in the event of expansion, the volumes of the chambers 18 and 32 may decrease while that of chamber 20 increases. The opening 38 of the annular communication passage 34 is arranged so as to be masked by the piston 30 under medium load conditions and to open into the chamber 20 at lower loads.

In fact, for medium loads, the volume of the chamber 20 20 is delimited just above this opening 38. The axial height H of the piston 30 is determined such that the opening 38 remains hidden by this same piston. when the latter occupies its position of maximum compression. In other words, the opening 38 cannot communicate with the fluid contained in the third chamber 32, even when the piston 30 is at the end of its compression stroke. On the other hand, the opening 38 is located in the vicinity of the upper end of the piston 30 when the latter occupies its intermediate position conditioned by average loads.

Thus, if the wheel equipped with the device loses grip with the ground, the piston 30 is triggered to relax, that is to say it is moved in the direction tending to exit from the cylinder 12. On this occasion , the opening 38 is gradually released and the fluid can freely communicate between the chambers 18 and 20, which makes it possible to accelerate the relaxation of the piston 14 so that the wheel quickly regains contact with the ground. This accelerated relaxation 35 continues until a sufficient load is found to compress the spring 47 and urge the piston 30 in the opposite direction ίο to the arrow F1 to close the opening 38. The spring 47 is a spring. compression. The valve 24 'and the restriction 22' can be adjusted so as to slow down only slightly the movement of the piston 30 during the expansion, which makes it possible to ensure that the latter quickly releases the opening 38.

Advantageously, as can be seen in Figures 6 and 7, the opening 38 can extend over a determined portion of the stroke of the piston 30, which makes it possible to ensure that the means for placing the chambers in communication 18 and 20 are more or less open depending on the position of the piston. Thus, according to Figure 6, this opening has the form of a vertical slot 138, Figure 6 showing a position of the piston 30 in which the latter masks approximately two thirds of this opening. Figure 7 shows another variant in which the opening comprises a plurality of orifices 238 stepped relative to each other, that is to say that they are located at different horizontal levels.

These arrangements make it possible to design the means for placing the first and second chamber in communication as an auxiliary system of the means for regulating the passage of the fluid between the first and second chambers situated on either side of the piston 14. It is in fact possible to choose that, for an average load position of the piston 30, only a part of the opening 38 (for example the lower part of the slot 138 or the orifice 238 which is the lowest) is closed by this piston. Under these conditions, the damping of the piston 14, both in compression and in expansion, is reduced since the fluid does not only pass through the controlled passages of the restrictions 22 or 26, but also through the communication passage 34. On the other hand, in the event of a high load, the piston 30 can completely hide the opening 38 (it blocks the entire window 138 or all the orifices 238) so that maximum damping of the displacement of the piston 14 is obtained. since the fluid can only pass through the restrictions 22 or 26 between the first and second chambers.

To avoid cavitation phenomena in the enclosure 12, a reservoir chamber 180, of the type described in French Patent No. 1,055,443, is provided in the variant of Figure 1. It comprises an enclosure 181 containing hydraulic fluid, connected to the chamber 20 by a pipe 182 which comprises a section 183 extending through the rod 31 and the piston 30. The connection between the conduit 182 and the enclosure 181 comprises a valve 184 allowing the passage of the fluid from the enclosure 181 to the chamber 20. When the volume of the chamber 20 decreases, the excess fluid can return to the chamber. enclosure 181 by a restriction 185. In a manner known per se, the pressure is maintained in the enclosure 181 by virtue of a floating piston 186 which separates it from an upper enclosure 187 containing gas such as nitrogen.

To avoid even better the phenomena of cavitation in the enclosure 12 which could be created during a very rapid depression due to a sudden impact, a communication is provided between the enclosure 181 of the reservoir 180 and the first chamber 18 of the cylinder 12 This communication is effected by a pipe 188, a section 189 of which extends into the plug 70 so as to open into the chamber 18. On this section is arranged a non-return valve 79 preventing the circulation of the fluid from the chamber 18 to the reservoir 180. This valve 79 may or may not be of the type calibrated at the opening for a pressure, for example, of the. order of that existing in the reservoir 180. Thus, during the compression phase, the valve 79 will allow passage only from the moment when the pressure difference between the reservoir 180 and the chamber 18 is sufficient. As a result, the compression phase is not disturbed and the expansion phase is free from cavitation.

The variant of Figure 2 differs from that of Figure 1 in that the first and second suspension means 144 and 145 each comprise a pneumatic spring, respectively 146 and 147.

More precisely, the spring 146 comprises a so-called suspension cylinder 148 capable of sliding on the damping cylinder 12 and having for this purpose a diameter greater than that of the latter. The end 148a of this cylinder is closed on the wall of the cylinder 12 by means 150 ensuring the seal while allowing the relative sliding of the two cylinders. The other end 148b of the cylinder 148 is closed by sealing means 154. The rod 15 of the first piston 14 is connected to these closure means 154, so that this piston and the cylinder 148 are integral in displacement. On the side opposite to the piston 14, the first chamber 18 is closed by closure means 156 located in the vicinity of the end of the cylinder 12. These closure means comprise a central bore 157 in which the rod 15 of the piston 14 slides. Sealing means are arranged in the bore 157 to cooperate with the rod. The enclosure 160 delimited by the wall of the cylinder 148, the closure means 154, the sealing means 150 and the closure means 156, contains pressurized suspension gas. The stiffness of the pneumatic spring 144 is a function of the volume of gas contained in the enclosure 160 and of its initial pressure.

As regards the second suspension means, the rod 31 of the second piston 30 is connected to a plate 80. The cylinder 12 is extended beyond the plug 170 '(which closes the chamber 32 on the side opposite the piston 30) by a tube 82 forming a suspension cylinder. The piston plate 80 is capable of sliding in a sealed manner inside the tube 82, sealing means 84 being provided for this purpose. The space delimited by the plug 170 ', the plate 80 and the interior of the tube 82 constitutes a chamber 86 which can be filled with gas under pressure.

This variant also differs from that of Figure 1 in that the connection of the reservoir 180 is no longer made to the second chamber 20 but to the third chamber 32. In fact, in the case of a very free adjustment of the means 22 'and 26' for regulating the passage of the fluid between the second chamber 20 and the third chamber 32, these passages can also be used for the small circulation of the fluid from the enclosure 12 towards the reservoir 180 necessary to compensate for the relatively small volume of the rods 15 and 31 in motion.

More precisely, the reservoir 180 is connected to the chamber 32 by a conduit 282 which comprises a section 283 extending through the plug 170 'so as to open into the chamber 32.

In addition, in this second version, the tight sliding of the end 148a on the wall of the cylinder 12 no longer makes it possible to connect the enclosure 181 of the reservoir 180 to the first chamber 18 in the same way as that used in the first version. (Figure 1). In this case, the connection is made by a conduit 288 which, starting from the enclosure 181, opens into a passage 135 near the lower end of the enclosure 12, for example through the plug 170 '. The communication passage 135 can be formed in an annular space coaxial and external to the passage 34 of Figure 1. It may however advantageously be formed by one or more sections of an annular space similar to that of Figure 1. More precisely, as seen in figure 8, the wall 40 can define an annular passage having several sectors 134 and 135. The sectors 134 are isolated from the sectors 135 and serve for the communication of the first and second chambers 18 and 20 like the passage 34 of FIG. 1, while the sectors 135 are used for the communication between the conduit 288 and the first chamber 18. The distribution and the number of sectors 134 and 135 of FIG. 8 are given by way of non-limiting example.

FIG. 3 shows another variant which differs from that of FIG. 1 by the means making it possible to avoid cavitation in the enclosure 12. These means use a twin-tube for the body of the damper part of the device. More precisely, the enclosure 12 comprises an external cylindrical wall 250 and an internal cylindrical wall 252 between which is formed an annular chamber 254 forming a reservoir for hydraulic fluid. The stopper 270 which closes the enclosure 12 on the side of the second suspension means 45 is provided with a bore 272 in which the rod 231 of the piston 30 slides in a sealed manner, thanks to a seal 273.

In this bore 272 is formed a communication chamber 274. The rod 231 of the piston 30 has a bore 276 which communicates with a bore 278 of the piston 30 and with the chamber 274 (this bore 276 has for example a T-shape). The chamber 274 has an axial height h at least equal to the stroke of the piston 30, so that the bore 276 can communicate with it regardless of the position of the piston 30.

The reservoir chamber 254 is capable of communicating with the communication chamber 274 by a pipe 280 made in the plug 270, on which a valve 284 allows the passage of the fluid only in the direction going towards the chamber 274 so that, through the 'Intermediate bores 276 and 278, the chamber 20 can be filled when its volume increases. Restriction 285 is also placed on line 280 to allow a controlled return of fluid to chamber 254 as the volume of chamber 20 decreases. The pressure is therefore maintained in the chambers.

However, to simplify the machining of the establishment of the fluid communication from chamber 20 to reservoir 254, one can use the solution of the variant shown in Figure 2, which consists in passing the fluid through the means for regulating the piston 30 (if they are sufficiently released). It suffices for this to remove the conduit 278, the chamber 274 and to open the valve 284 and the restriction 285 directly into the chamber 32.

It will be noted that the means for placing the chambers 18 and 20 in communication may be similar to those in FIG. 1. However, to simplify the machining, the passage between these chambers may be made by a pipe 234 attached to the chamber 254 on the wall 252.

It is also possible to make the first chamber 18 and the enclosure 254 communicate in the same way as in FIG. 2. Thus, an opening can be made in the lower part of a passage similar to the passage 135 of FIG. 2.

However, to simplify the machining, the passage between the enclosure 254 and the chamber 18 can be made by a pipe 235 attached to the chamber 254 on the wall 252. This pipe has a lower opening 58 which puts it in communication with the 'enclosure 254. The communication of this pipe 235 to the chamber 18 is similar to that of Figure 2, for the passage 135.

Whatever variant is chosen, the passage for placing the chambers 18 and 20 in communication could also be made by using an external pipe, or even a flexible pipe, connected to an opening, similar to the opening 38, extended in the wall. of the enclosure 12 to allow it to communicate with the chamber 20, and connected to the chamber 18 by any means such as an opening made in the wall of this chamber or a bore, formed in the rod of the piston 14 and opening into the chamber 18. This remark is just as valid with regard to the realization of the passage for placing the chambers 18 and 254 in communication.

The variant of Figure 4 differs from that of Figure 1 by the means for placing the chambers 18 and 20 in communication and by the fact that the first suspension means 144 are similar to those of Figure 2. In this variant, the communication of the enclosure 181 of the reservoir 180 to the chamber 18 of the enclosure 12 is not shown. It can, however, be installed in the same way as on the variant of the

Figure 2. The unchanged elements, respectively compared to Figures 1 and 2, are assigned the same references as in these figures.

In FIG. 4, the means for placing the chambers 18 and 20 in communication comprise a passage 334 which passes through the first piston 314 and which is equipped with a controlled valve 338. The control means of this valve can be activated. or deactivated depending on the position of the second piston 30. Thus, the piston 30 can cause the opening of the valve 338 to release the circulation of the fluid between the chambers 18 and 20 through the passage 334.

More precisely, in the example shown, the control means of the valve 338 comprise an electromechanical actuator 340, housed in the piston 314 and connected to an actuator 342 by a control circuit 344 passing through the rod 315 of the piston 314. In the example shown, the member 342 is a contactor which, when requested by the underside of the piston 30, closes the circuit 344 in order to supply the actuator 340 so that it opens the valve. 338. The contactor 342 is installed in the plug 370 and protrudes into the chamber 32 beyond the upper face of this plug. Other actuators such as a photoelectric cell located on the wall of the chamber 32, or the like, can be envisaged. By choosing a suitable actuator and circuit, it is possible to ensure that the valve 338 is more or less open depending on the position of the piston 30.

Another more compact version consists in placing the electromechanical actuator 340 outside the handset. The action on the control valve 338 being effected by an operating rod which passes through the rod 315 of the piston 314. Instead of the operating rod, it is also possible to use a hydraulic circuit passing through the rod 315. Yet another version consists in also placing the control valve 338 outside the handset and in providing a bypass of the oil circuit starting from the chamber 20 through an orifice in the piston 314, passing inside the rod. 315, passing through the valve 338, passing again inside the rod 315 (a double circulation system, coaxial or not, is practiced in the rod 315) to open into the chamber 18.

Of course, the means of communication illustrated by the variant of Figure 4 can be used in the device according to the invention, by choosing, for the suspension means, mechanical or pneumatic springs and with all types of systems for prevent cavitation.

FIG. 5 will now be described, which differs from FIG. 1 in that the variant which it represents comprises first improved pneumatic suspension means 444. The elements unchanged, respectively compared to Figures 1 and 2, are assigned the same references as in these figures.

More precisely, the device comprises a so-called suspension cylinder 448, which has a diameter greater than that of the damping cylinder 12 and is capable of sliding on the latter. A first end 448a of the suspension cylinder 448 (its lower end in FIG. 5) is closed on the wall of the damping cylinder 12 by tight sealing means 450 which provide the seal while allowing the relative sliding of these. two cylinders. To facilitate this sliding, a guide 452 can also be provided between the two cylinders.

At its second end 448b, the cylinder 448 is closed by sealing means 454 such as a tight stopper. The first piston 14 has a rod 15 which is integral with the suspension cylinder 448. For example, this rod, which is suitably attached to the first piston 14, is also attached to the closure means 454. The rod therefore makes it possible to make it integral the displacement of cylinder 448 and that of piston 14.

A plug 470 is arranged in the damping cylinder 12 so as to close the first chamber 18 on the side opposite the first piston 14. In Figure 5, this chamber is therefore delimited by the upper face of the piston 14, by the internal wall. of the cylinder 12 and by the underside of the stopper 470. The latter is provided with a bore 472 in which the rod 15 of the piston 14 can slide. A sealing means (not shown) is provided to ensure the seal between the plug 470 and the rod 15.

A separation piston 456 is arranged in the damping cylinder 12 so as to create a compensation chamber 481. In FIG. 5, this chamber is therefore delimited by the face of the stopper 470 opposite to the chamber 18, by the internal wall. of the cylinder 12 and by the separator piston 456. The latter is a floating piston which is capable of sliding inside the damping cylinder 12 and floats on the fluid contained in the chamber 481. This piston 456 is provided with a bore 457 in which the rod 15 of the piston 14 can slide. Sealing means (not shown) are provided to ensure the seal between the piston 456 and the rod 15 and between said piston 456. and the inner wall of the damping cylinder 12.

An enclosure 460 is defined between the separation piston 456 and the closure means 454 of the second end of the suspension cylinder. More precisely, this enclosure 460 is closed by the closure means 454, by the cylindrical wall of the cylinder 448, by the sealing means 450 between the cylinders 12 and 448, and by the separation piston 456. It contains a gas. suspension, generally a compressible gas such as nitrogen.

In Figure 5, the compensation chamber 481 acts in exactly the same way as the enclosure 181 of Figure 1. The auxiliary reservoir is in fact integrated into the handset using the suspension means (here an air spring) of the first. combined, as a pressurizing force. In this case, the non-return valve 184 and the restriction 185 of Figures 1 and 2 are replaced by a non-return valve 484 and a restriction 485 respectively similar to these first but arranged this time in the stopper 470 ', so as to make the chamber 32 and the chamber 481 communicate through the passage 135 and the communication hole 475 made in the plug 470.

In this case, the passage 135 is no longer used to communicate the chamber of the auxiliary tank and the chamber 18 (as is the case in Figure 2), but to communicate the chamber 32 and the chamber 481 of the auxiliary tank. integrated. Despite this difference in circulation, the means of communication of the chambers 18 and 20 (passing through the passage 134) and the passage 135 are in all respects in accordance with the embodiment shown in Figures 2 and 8. The non-return valve 79 is housed in the plug 470 and allows the passage of the fluid from the chamber 481 to the chamber 18.

In Figure 5, the communication allowing the circulation of fluid from the enclosure 12 to the auxiliary reservoir (the chamber 481) is carried out in the same way as in Figure 2, that is to say that the chamber 481 is connected to the third chamber 32 by a passage provided with a restriction (485). As a variant of Figure 5, one can however imagine a design similar to that of Figure 3 by connecting the second chamber 20 to the chamber 481, by means similar to the bores 276, 278 and to the chamber 274, and by driving with a restriction.

By moving relative to the damping cylinder 12, the suspension cylinder 448 acts as an air spring whose stiffness is a function of the pressure of the gas contained in the chamber 460. The separator piston 456 can move to compensate the volume of the rods 15 and 31 entering the enclosure 12 during a compressive stress, this separator piston then rising in the enclosure 460 to reduce its volume in proportion.

The operation of the separator piston is itself known from French patent n ° 1 185 526. However, the fact of providing the plug 470, the passage 135 (which makes it possible to communicate the second or the third chamber with the hydraulic chamber 481 of the compensation tank), the valves 79 and 484, as well as the restriction 485, makes it possible to '' avoid cavitation phenomena which, with the system of French patent n ° 1 185 526, exist in the chamber located under the piston 14 in the event of loss of grip and traction on the combined under the effect of the weight of the wheel.

The pressure of the gas inside the enclosure 460, which is exerted on the upper face of the separator piston 456, initially creates a force which corresponds to the static force admissible by the air spring 444 and the first means. damping comprising the piston 14 and the chambers 18 and 20. To initially adjust the desired static force, the chamber 460 can be partially filled with a hydraulic fluid which, of course, is incompressible. The quantity of fluid present in this chamber will be used to adjust the volume of gas remaining in the chamber 460 at the end of the stroke of the piston 14. By suitably choosing this volume and the pressure of the gas at the origin, the range of stiffness of the gas is determined. air spring.

Whatever variant is chosen, to allow a reaction of the device to various types of stresses, the first and second combined respectively formed by the first shock absorber and the first suspension means and by the second shock absorber and the second suspension means, are regulated differently.

To do this, whether they are mechanical or pneumatic, it will advantageously be chosen to provide the springs of the first and second suspension means with different stiffnesses, so as to enable them to respond to different stresses.

The first handset is preferably adjusted so that it can respond to requests at medium and low frequencies (of the order of 1 to 4 or 5 Hz). The initial volume of the chambers 18 and 20, under normal load, and therefore the maximum stroke of the first piston are chosen accordingly. On the other hand, we will rather adjust the second handset so that it is able to respond to high frequency requests (of the order of 10Hz and more). To do this, we will choose to ensure that the maximum stroke of the second piston inside the chambers 20 and 32 is much lower than that of the piston 14, and we will provide the spring of the second suspension means with a stiffness and a preload ensuring that this second piston is in a position of the order of the mid-stroke of the second combined, when the vehicle is in a static position, that is to say subjected to the single load of its weight. It is thus possible to choose either a higher stiffness with a lower preload, or a lower stiffness with a higher preload than those used on the first handset.

Note that these settings are given by way of non-limiting example. Other settings can be imagined to respond to very specific demands. For example, when the means for placing the first and second chambers in communication are present and when the piston of the second handset is used to regulate the passage of fluid between these chambers (for example in the manner indicated with reference to FIGS. 6 and 7), it may be advantageous to provide the spring of the second handset with relatively high stiffness. Likewise, it may be advantageous to adjust the second handset so that it is able to respond to low frequency requests.

Depending on the case, it is possible to choose to have the regulation carried out over the entire stroke of the first piston, the stiffness of the spring of the second combined being then chosen, relative to that of the spring of the first combined, so that the end of stroke of the two pistons occurs for the same maximum load of the first and second piston. It is also possible to choose that the regulation takes place only over part of the stroke of the first piston, in which case the stiffnesses of the two springs will be chosen such that the end of stroke of the second piston corresponds to a load giving a depression d 'a fraction of the stroke of the other.

It is possible to choose that the brake release function due to the placing in communication of the first and second chambers is clearly predominant in relation to the suspension and damping functions provided by the second handset. In this case, the second suspension means oppose a very low resistance of the second piston, the stroke of which is moreover also low. In this case, it is even possible to use a compression spring located in the chamber 32 which controls the descent of the second piston (and thereby the brake release) so as to allow the brake release only in the case of strong stretching stresses.

It is known that the advantage of pneumatic springs lies in the fact that their stiffness is not constant but increases with the stress of the gas in compression, so that the suspension becomes increasingly hard as the load increases. For this reason, an air spring is advantageously chosen for the first suspension means.

On the other hand, when it is desired that the second module be capable of responding to high frequency stresses, the spring of the second suspension means is preferably chosen in the form of a mechanical spring. Indeed, it is known that the compressible gases commonly used in pneumatic springs become less and less compressible when the frequency of the stresses to which they are subjected increases, so that in the extreme, in the case of very high frequencies, the spring effect is practically canceled.

It should be noted that the mechanical spring can be a spiral spring such as the spring 46 of Figure 1, it can also be another spring such as a Belleville washer or the like, a metal spring or made of any suitable material such as elastomer.

Depending on the range of frequencies to which you want the second module to be able to respond, an air spring may still be suitable.