FR3049505B1 - HYDRAULIC SUSPENSION SYSTEM OF A VEHICLE - Google Patents

Abstract

Hydraulic suspension system of a vehicle running gear comprising for each wheel of this train a suspension spring (17b), a damper (1b) with cylinder and piston movable in the cylinder to delimit two chambers and interposed between the body of the the vehicle and the vehicle wheel-spindle, a compressible mechanical attack stop (7b) positioned between the cylinder and the vehicle body, or between the stub axle and the vehicle body, and a hydraulic drive abutment Piston (9b) mounted in the compression chamber, this suspension system further comprising a hydraulic expansion stop (15b) and an anti-roll bar (30) connecting the two axles of the undercarriage, switchable between a first and a second state, a stiffness of the anti-roll bar in the second state being decreased relative to the first state.

Description

The invention relates to a hydraulic suspension system for a vehicle, in particular a motor vehicle.

In a manner known per se, a hydraulic suspension system of a vehicle, in particular an automobile, comprises for each of the wheels of the vehicle a piston damper movable in its corresponding cylinder and interposed between the body and the wheel stub axle. of the vehicle. The role of this damper is to greatly limit the oscillations transmitted by the wheels to the vehicle body when the wheels encounter roughness or obstacles present on the road on which the vehicle is traveling, and to curb the cash movements in the dynamic actions like braking and turning.

[003] In order to limit and brake the piston stroke of the damper in a compression stroke also called attack stroke, the latter comprises a compressible mechanical mechanical stop, or possibly hydraulic. The role of this attack stop is also to protect the chassis of the vehicle during the appearance of strong deflections of the corresponding wheel, due to incidents or significant obstacles, such as retarders type back-d donkey.

[004] It is known in particular from FR 2995048 a hydraulic piston stop piston movable in its corresponding cylinder, and whose piston is intended to be moved by the piston of the damper when the latter approaches its end of course .

[005] However, in cases of major strokes of the piston of the damper which are mainly of an incidental nature, the comfort of the suspension is not a priority with regard to the preservation of the mechanical integrity of the vehicle. For this reason, the attack stop is usually very stiff and generates discontinuities of brutal efforts. Comfort for the occupants of the vehicle is then strongly penalized in these situations.

[006] In addition, the motor vehicles generally comprise on each wheel train an anti-roll bar having a transverse central portion forming a torsion bar, each end of which is connected to a suspension. During different suspension travel on each side of the vehicle from a roll of the body, a twist of the central portion of the anti-roll bar generates on each suspension a return force which tends to restore the positional balance between these two sides.

[007] The anti-roll bar adds on each suspension in case of roll of the body, a stiffness that adds to that of the suspension spring. The suspension is then firmer, which reduces the impression of comfort.

The present invention aims to overcome the above disadvantages of the prior art.

[009] To achieve this object, the invention relates to a hydraulic suspension system of a vehicle undercarriage, including automobile, comprising for each wheel of this train a suspension spring, a cylinder damper and movable piston in the cylinder to delimit two chambers respectively of compression and expansion and interposed between the vehicle body and the wheel-carrier of the vehicle, a compressible mechanical attack stop positioned between the cylinder and the vehicle body, or between the carrier rocket and the body of the vehicle, and a hydraulic piston thrust bearing mounted in the compression chamber, this suspension system further comprising a hydraulic expansion stop mounted in the expansion chamber of the cylinder of the corresponding damper, and an anti-roll bar connecting the two axles of the undercarriage, switchable between a first and a second state, a stiffness of the anti-rust bar read in the second state being decreased in relation to the first state.

Optional and advantageous features are as follows: [0011] the stiffness of the anti-roll bar in the second state decreased with respect to the first state may be a stiffness for a low roll angle; [0012] the passage between the first state and the second state can be controlled by the driver; - The hydraulic expansion stop may comprise a floating piston disposed in the expansion chamber, surrounding a damper rod, and comprising a fluid passage between the two sides of the floating piston, the hydraulic expansion stop comprising in addition a collar integral with the rod, disposed on a first side of the floating piston facing the piston of the damper, forming a valve closing the passage of the fluid when it bears on this floating piston, and a spring disposed of the other side of the floating piston; - The system may comprise a mechanical expansion stop which is arranged to act at the same time as the hydraulic expansion stop; - The hydraulic expansion stop may comprise a floating piston disposed in the expansion chamber, surrounding a damper rod, and comprising a fluid passage between the two sides of the floating piston, the hydraulic expansion stop comprising in addition a collar integral with the rod, disposed on a first side of the floating piston facing the piston of the damper, forming a valve closing the passage of the fluid when it bears on this floating piston, and a spring disposed of the other side of the floating piston; [0016] the suspension spring may comprise a stiffness calculated to give a natural oscillation frequency of the vehicle body less than 1.2 Hz; The hydraulic attack stop may comprise a cylinder and a piston movable relative to each other, the piston and the cylinder of the hydraulic attack stop being intended to be moved relative to each other; to the other during a stroke of the damper piston when the latter reaches a first stroke in the cylinder of the damper, and the mechanical attack stop being intended to be compressed between the cylinder of the damper damper and the vehicle body when the damper piston reaches a second attacking stroke in the damper cylinder greater than the first stroke; - The hydraulic expansion stop can be arranged to act when the expansion stroke of the piston of the damper reaches a relaxation stroke of less than fifty millimeters from the vehicle reference attitude.

The invention also relates to a vehicle, including an automobile, comprising a hydraulic suspension system as described above.

The invention will be better understood, and other objects, features, details and advantages thereof will appear more clearly in the explanatory description which follows with reference to the accompanying drawings given solely by way of example illustrating a prior art and an embodiment of the invention, in which: - Figures 1A and 1B respectively represent a longitudinal sectional diagram of a damper of the prior art, and a graph illustrating the efforts delivered by the system suspension as a function of the stroke of the piston of the damper in the cylinder of the damper; - Figure 2 shows the dynamic forces applying in a turn on a vehicle seen from the front; FIG. 3 represents a graph illustrating for the damper according to the prior art, the forces delivered by the suspension system as a function of the stroke of the damper piston, in a turn by adding the effects of a bar anti-roll; FIGS. 4A and 4B respectively represent a longitudinal sectional diagram of a damper of a suspension system according to the invention when the vehicle is at a reference attitude, as well as a graph illustrating the forces delivered by the control system. suspension corresponding to the position of the piston identified in Figure 4A, the system being in a first state; FIGS. 5A and 5B respectively represent a longitudinal sectional diagram of a shock absorber of a suspension system according to the invention when the vehicle is at a reference attitude and a graph illustrating the forces delivered by the suspension system corresponding to the position of the piston marked in Figure 5A, the system being in a second state.

Referring to Figure 1A, a hydraulic suspension system of a vehicle, including automotive, will now be described.

The suspension of the vehicle comprises, for each wheel of the vehicle, a hydraulic damper 1 comprising a body 2 in the form of a cylinder and a movable piston 3 in the cylinder 2. This damper 1 is interposed between the body 6 of the vehicle and the corresponding wheel knuckle. The piston 3, integral with a first end of a rod 14 whose other end is connected to the body 6 of the vehicle, defines in the cylinder 2 two chambers 4, 5 respectively of compression and expansion, between which fluid incompressible hydraulic (oil) included in the cylinder 2, is exchanged by circulating through holes not shown piston 3 which brakes this exchange, according to the movements of the latter in the cylinder 2.

The behavior of each hydraulic damper 1 of the vehicle hydraulic suspension system can be described according to a damping law in which the force exerted by the damper 1 depends on the speed of movement of the corresponding wheel. In other words, the faster the piston 3 moves in the cylinder 2 of the damper, the higher the braking of the piston is, and the greater the force exerted by the damper 1 on the body 6 of the vehicle is important.

The hydraulic suspension system also comprises, for each wheel of the vehicle, a suspension spring 17 mounted around the damper 1 and whose ends are respectively supported against the body 6 of the vehicle via a cup 18 and against a cup 19 secured to the cylinder 2 of the damper. The suspension spring 17 is an element of constant stiffness, the behavior of which can be described by a law according to which the force exerted by the spring 17 on the body 6 of the vehicle depends on its compression and therefore on the amplitude of the deflection of the vehicle. the corresponding wheel. In other words, the more the suspension spring 17 is compressed, the greater the force exerted on the body 6 of the vehicle is important. The suspension spring 17 essentially serves to carry the body 6 of the vehicle while allowing the deflections.

The suspension system also comprises for each wheel of the vehicle two respective mechanical 7 and hydraulic 9 drive stops respectively, as well as two mechanical and 16 hydraulic and 15 mechanical expansion stops respectively.

Each mechanical stop 7, 16 is similar to a stiffness, and therefore exerts a force on the body 6 according to the displacement of the corresponding wheel. In the same way as the suspension spring 17, the force exerted on the body 6 of the vehicle by the mechanical stops respectively of attack 7 and relaxation 16 is even greater than the deflection in attack and relaxation of the corresponding wheel is important.

Each hydraulic stop of attack 9 and relaxation 15 is in turn assimilable to a damper and therefore exerts a force on the body 6 of the vehicle according to the speed of travel of the corresponding wheel. In the same way as the hydraulic damper 1, the force exerted on the body 6 of the vehicle by the hydraulic stops respectively of attack 9 and relaxation 15 is even greater than the speed of travel of the corresponding wheel is important.

In addition, the hydraulic attacking stops 9 and trigger 15 are progressive effort stops which increases as a function of the stroke, by the progressive reduction of the fluid passages according to their stroke, which also gives an effort of as much bigger than the race is big.

Referring to Figure 1A, the mechanical attack abutment 7 is secured to one end of the cylinder 2 of the damper, and positioned axially between the end of the cylinder 2 of the damper and the body 6 of the vehicle . It also has an annular cross-section so as to be traversed by the rod 14 of the piston 3 of the damper 1. Thus, when the piston 3 exceeds a certain stroke in attack, the mechanical attack stopper 7 is compressed between end of the cylinder 2 of the damper 1 and the body 6 of the vehicle so as to strongly slow the stroke of the piston 3 in the cylinder 2 of the damper.

Preferably, the mechanical attack stop 7 is elastomer material having a very high stiffness constant, so that the force exerted by the mechanical attack stop 7 on the vehicle body 6 increases very rapidly with the deflection in attack of the wheel.

The hydraulic attack stop 9 is mounted in the compression chamber 4 of the cylinder 2 of the damper 1. The hydraulic attack stop 9 comprises a piston 11 secured to the lower bottom wall 12 of the cylinder 2 of the damper, and a cylinder 10 to be moved along the piston 11 of the attack abutment 9 by the piston 3 of the damper 1 when it reaches the vicinity of the end of stroke attack. The cylinder 10 of the hydraulic abutment 7 forms a compression chamber 20 filled with hydraulic fluid, which is likely to escape from this chamber 20 by leaks around the piston 11 of the hydraulic abutment 9 when the piston 3 of the damper moves the cylinder 10 of the hydraulic attack stop 9 towards the lower bottom wall 12 of the damper. Thus, the piston 3 of the damper 1 arriving near its end stroke attack is very quickly braked.

In addition, the hydraulic abutment 9 comprises a return spring 21 surrounding the piston 11 of the hydraulic abutment 9 and whose ends are supported axially respectively against the lower bottom wall 12 of the cylinder 2 of the damper, and the annular end edge flanking the cylinder 10 of the hydraulic stop 9 orifice. In this way, the return spring 21 allows the cylinder 10 of the hydraulic attack stop 9 to return to the rest position , the piston 11 emerging from this cylinder, when the piston 3 of the damper 1 moves away from the cylinder 10 of the hydraulic stop 9.

The hydraulic expansion stop 15 is in turn a floating piston surrounding the rod 14 of the damper 1 so as to maintain an annular space 23 between the rod 14 and the inner edge of the floating piston through which the hydraulic fluid is likely to circulate. The hydraulic expansion stop 15 is positioned in the expansion chamber 5 of the cylinder 2 of the damper, axially between the upper end wall 8 of the cylinder 2 of the damper through which the rod 14 of the damper and a collar 22 forming a valve secured to the rod 14 of the damper. The mechanical expansion stop 16 is in turn a high stiffness spring positioned in the expansion chamber 5 and whose ends are axially respectively bearing against the floating piston 15 and the upper end wall 8 of the cylinder 2 of the shock absorber 1.

When the piston 3 of the hydraulic damper 1 moves in the vicinity of its end of travel in expansion, the flange 22 forming valve moves the floating piston 15 towards the upper end wall 8 of the cylinder 2 of the 1. The floating piston 15 moving simultaneously compresses the mechanical expansion stop 16. In addition, the flange 22 forming a valve, in contact with the floating piston 15, closes the space 23 between the inner edge of the piston 15 and the rod 14 which reduces the section allowing the passage of the fluid from the top of the floating piston towards the bottom, thus increasing the resistance of the hydraulic expansion stop to the displacement towards the upper end wall 8 of the cylinder 2 of the damper 1. Thus, the piston 3 of the hydraulic damper 1 arriving near its end of stroke is very quickly braked by the two stops of relaxation 15, 16.

Referring to the graph of Figure 1 B, the arrangement of the attacking stops 7, 9 and trigger 15, 16 depending on the stroke of the piston 3 of the damper 1 in the cylinder 2 of the damper 1 will be described.

The vertical scale represents the stroke in millimeters of the piston 3 of the damper in the cylinder 2 of the damper 1 during deflections of the vehicle wheel. The horizontal scale is a visual scale representing the force exerted by each element of the hydraulic suspension at a wheel as a function of the stroke of the piston 3 in the cylinder 2 of the corresponding damper 1. The zero stroke (zero millimeters) corresponds to the position of the piston 3 of the damper 1 in the cylinder when the suspension of the vehicle does not undergo any other effort than that exerted by the mass of the vehicle. The vehicle is then at the reference base AR.

The negative races of the piston 3 of the damper in the cylinder 2 correspond to deflections in attack of the wheel, that is to say that the suspension tends to compress and the body 6 of the vehicle to move closer to the road compared to the reference base AR. Conversely, the positive strokes of the piston 3 of the shock absorber 1 in the cylinder 2 correspond to displacements in relaxation of the wheel, that is to say that the suspension tends to relax and the body 6 of the vehicle to move away from the road relative to the reference base AR.

It is considered that strokes in attack or relaxation of the piston 3 of the damper 1 between -15 mm and 15 mm from the reference base AR correspond to low energy DLE deflections which represent the solicitations the most frequent, encountered on roads of good quality.

It is considered that races in piston stroke 3 of the damper 1 between -15 mm and -50 mm from the reference base AR, and strokes piston 3 of the damper 1 between 15 mm and 50 mm from the reference base AR, correspond to medium energy DME deflections which represent also frequent solicitations. These stresses are encountered on slightly degraded roads, where when the wheels cross small obstacles, such as small speed bumps.

Finally, it is considered that races in piston stroke 3 of the damper 1 beyond -50 mm from the reference base AR, up to the maximum of -80 mm, and races in piston expansion 3 of the shock absorber 1 greater than 50 mm from the reference attitude AR, up to a maximum of 110 mm, correspond to high energy DHE deflections which represent infrequent solicitations. These stresses are encountered especially when the wheels cross a major hurdle-type retarder in the back of a donkey, or a relatively deep pothole.

For more convenience in the following description, we will discuss the races in attack or relaxation of the piston 3 of the damper 1 in absolute value.

Referring to the graph of Figure 1 B, the mechanical attack stop 7 is compressed as soon as the stroke of the piston 3 of the damper 1 exceeds an attack stroke of about 10 mm. Thus, the mechanical attack stop 7 intervenes quickly to slow the stroke of the piston 3 of the damper 1 to the beginning of the medium energy deflections DME. Beyond an attack stroke of the piston 3 of the damper 1 of 50 mm, that is to say for high energy deflections DHE, the piston 3 of the hydraulic damper 1 causes the displacement of the cylinder 10 of the hydraulic attack stop 9 along its corresponding piston 11, to quickly brake the piston 3 of the damper 1 in its cylinder 2 corresponding by adding a braking force dependent on the speed to the braking force of the mechanical stop 7. This protects the body 6 of the vehicle against end-of-stroke shocks that could destroy elements.

Referring again to the graph of Figure 1 B, when the expansion stroke of the piston 3 of the damper 1 exceeds a value of about 70 mm the floating piston 15 of the hydraulic expansion stop is moved and simultaneously compresses the spring constituting the mechanical expansion stop 16 when the expansion stroke of the piston 3 of the damper 1 exceeds a value of about 70 mm, to quickly brake the piston 3 of the damper 1 in its corresponding cylinder 2 by the combined effect of the two trigger stops.

Referring to Figure 2, the vehicle taking a turn to the right, its inertia generates on this vehicle an outward force F1 depending on the speed of the vehicle and the radius of curvature of the turn. We then have a support on the ground of the wheels of the vehicle, which is more important on the outer wheels F2 compared to that F3 applying on the inner wheels. The vehicle body tilts lowering towards the outside of the turn.

The anti-roll bar of the front or rear axle then sees a greater compression of the suspension on the outside of the turn, and less important on the other side, it then generates on each side a return force on the suspension, having a certain stiffness which will be added to that of the suspension spring 17.

Referring to Figure 3, we superimposed on the force given by the stiffness of the suspension spring 17, the force applied by the anti-roll bar 30 in the case of a turn on the same train of the vehicle having an average height which is the reference base AR. The force of the anti-roll bar 30 is zero for the central point 36 disposed on the reference base AR, the two suspensions being at this average height.

We have for an attack stroke from the reference base AR, a force given by the anti-roll bar 30 represented by an upper triangle, adding to that given by the suspension spring 17 which is compressed, to obtain for example at height 32 a total effort 34 higher. This higher effort gives an uncomfortable situation, especially in the case of deformations of the road which are then strongly felt.

On the contrary, for a relaxation stroke from the reference attitude AR, there is a negative force given by the anti-roll bar 30 represented by a lower triangle, retreating to that given by the spring of suspension 17 which is relaxed. A total cumulative stiffness of the suspension spring 17 and the anti-roll bar 30 is obtained which is significantly higher.

Referring to Figures 4A, 4B, 5A and 5B, the suspension system according to the invention will now be described.

It comprises for each wheel of the vehicle a damper 1b, a suspension spring 17b and two stops mechanical respectively 16 mechanical and hydraulic 15 as described above.

The hydraulic suspension system according to the invention also comprises for each wheel of the vehicle a mechanical attack abutment 7b shorter than the mechanical attack abutment 7 of the prior art, as well as an attack abutment hydraulic 9b whose cylinder 10b has an amplitude of displacement along the corresponding piston 11b between its end stroke and its limit stroke end of between 40 and 60 mm. This displacement amplitude is greater than the displacement amplitude of the cylinder 10 of the hydraulic attack stop 9 of the prior art, which is of the order of 30 mm.

In addition, the structure of the cylinder 10b of the hydraulic attack stop 9b is different, since the cylinder 10b comprises in its wall a plurality of through radial holes 13, and allowing the entry or exit of the hydraulic fluid of the compression chamber 4 of the cylinder 2 of the damper 1b when the piston 11b and the cylinder 10b of the hydraulic abutment 9b move relative to each other. Thus, as the cylinder 10b of the hydraulic attack stop 9b moves along the corresponding piston 11b towards the bottom bottom wall 12 of the cylinder 2 of the damper 1b, an increasing number of through holes 13 are blocked by the piston 11b of the hydraulic thrust bearing 9b, thus decreasing the overall cross section of the through holes 13 so that the braking force exerted by the hydraulic thrust bearing 9b on the body 6 of the vehicle increases for a moving speed of the cylinder 10b constant.

The arrangement of the mechanical attack abutments 7b and hydraulic 9b as a function of the strokes of the piston 3 of the damper 1b is also different compared to that of the prior art.

Indeed, when the piston 3 of the hydraulic damper 1b exceeds an attacking stroke CA1 between 0 and 20 mm, preferably 10 mm, the latter causes the displacement of the cylinder 10b of the hydraulic attack stop 9b the along its corresponding piston 11b. For low and medium energy deflections, the overall section of many of the holes 13 passing through the cylinder 10b of the hydraulic thrust bearing 9b is sufficiently high to provide gentle braking of the piston 3 of the damper 1b. For DHE higher energy deflections in which the damper piston 3 1b is approaching its end of attack stroke, the overall section of a smaller number of holes 13 through the cylinder 10b of the attack abutment 9b hydraulic decreases because an increasing number of through holes 13 are plugged by the piston 11b of the hydraulic thrust bearing 9b as the cylinder 10b moves along the piston 11b of the hydraulic thrust bearing 9b in the direction of the lower bottom wall 12 of the cylinder 2 of the damper 1b: this ensures a stronger braking of the piston 3 of the damper 1b in order to protect the body 6 and the chassis of the vehicle.

In addition, as soon as the piston 3 of the damper 1b exceeds an attack stroke CA2 between 40 and 50 mm, preferably 50 mm, the mechanical attack stop 7b is compressed and participates in strengthening the piston braking 3 of the shock absorber 1b.

It will be noted that the discontinuity of the force exerted by the suspension system during its compression, generating discomfort for the vehicle passengers, is greatly reduced thanks to the hydraulic attack stop 9b, whose cylinder 10b has an elongated displacement amplitude, which acts before the mechanical attack stop 7b. In addition, the force exerted by the hydraulic attack stop 9b depending both on the speed and the displacement amplitude of the piston 3 of the shock absorber 1b in its cylinder 2, the braking of the piston 3 of the The shock absorber is progressively adapted to the amplitude and the speed of its travel in the cylinder 2, in particular for the medium energy DME deflections, which also has a positive effect on the comfort of the passengers.

Finally, the hydraulic attack stop 9b dissipates the energy without accumulating it, thus avoiding any stimulus effect during low and medium energy deflections.

The hydraulic suspension system according to the invention also comprises for each wheel of the vehicle a mechanical expansion stop 16b longer than the mechanical expansion stop 16 of the prior art. Therefore, the floating piston of the hydraulic expansion stopper 15b according to the invention has an amplitude of displacement around the rod 14 of the damper 1b, between its rest position and its end-of-travel relaxation position, between for example between 40 and 80 mm. This displacement amplitude is greater than the displacement amplitude of the floating piston of the hydraulic expansion stopper 15 of the prior art, which is of the order of 20 to 30 mm. In addition, the extension of the displacement amplitude of the hydraulic expansion stop 15b makes it possible to reduce the stiffness of the spring of the mechanical expansion stop 16b, so that it contributes little to the braking of the piston 3 of the shock absorber 1b in relaxation.

In addition, the floating piston 15b of the hydraulic expansion stop is formed by an annular ring radially split over its entire thickness and intended to slide along the rod 14 of the damper 1b so as to maintain an annular space. 23b between the rod 14 and the inner edge of the floating piston 15b, while the upper part of the expansion chamber 5 of the cylinder 2 of the damper 1b comprises a wall 2b of substantially frustoconical shape whose cross section decreases in the upper direction towards the wall 8 of the damper 1b. Thus, the force exerted by the detent stops 15b, 16b on the vehicle body increases very gradually with the stroke of the floating piston 15b: as the floating piston 15b moves towards the upper end wall 8 of the cylinder 2 of the damper 1b along the frustoconical wall 2b, the slot and the annular space 23b of the floating piston 15b closes gradually, thereby decreasing the passage section of the hydraulic fluid. This therefore ensures a variable damping according to the stroke of the floating piston 15b, significantly improving control of the vertical movements of the vehicle body, and thus the comfort of the vehicle.

In addition, the suspension system comprises a suspension spring 17b having a decreased stiffness relative to the suspension spring 17 shown in Figures 1A and 1B. The decreased stiffness is represented by the straight line 42 which is less inclined than the straight line of the preceding suspension spring 17 (FIG. 1), while passing through the same central point 36 disposed on the reference base AR, corresponding to a force of identical suspension spring to balance the mass of the vehicle that has not changed.

Advantageously, the decreased stiffness of the suspension spring 17b gives a vertical natural oscillation frequency of the vehicle body which is less than 1.2 Hz, while the values usually allowed are between 1.2 and 1.4 Hz. In particular one can choose a natural oscillation frequency between 1 and 1.1 Hz, which gives great flexibility to the suspension.

Improved suspension comfort is obtained by combining the elements of the hydraulic suspension system of the invention. Indeed, there is a suspension spring 17b having a higher flexibility, which will give for the low energy DLE movements slower movements of the body and having a greater amplitude. There is therefore a reduction in suspension forces for the low energy DLE deflections, and a better absorption of the small irregularities of the road.

We then for more important road irregularities with deflections in medium energy DME attack, an early entry into action of the hydraulic attack stop 9b which brakes quickly and gradually the movements of the body 6, while the reduced stiffness of the suspension spring 17b tend to lessen these movements. This replaces a portion of the forces previously generated by the stiffness of the suspension spring 17, by efforts generated by the damping of the hydraulic attack stop 9b which depend on the speed of movement, and therefore the energy of the solicitation.

According to a first supplement of the invention, the damping level of the shock absorber 1b is reduced in attack and relaxation, below that usually used for the same type of vehicle, represented in FIG. width of the reduced effort. In particular for the medium energy DME deflections in attack, the decrease in the damping level of the shock absorber 1b corresponds substantially on average to this stroke, to the value of the additional damping given by the hydraulic thrust bearing 9b, in order to preserve the control of the cash movements 6 for this type of movements.

We then for the low energy DLE deflections an additional drop of the suspension forces that increases comfort. Beyond for the medium-energy DME and high energy DHE deflections, this reduced damping is compensated by the action of the hydraulic attack stop 9b, which is progressive and depends on the speed.

The system according to the invention comprises a switching means 100 allowing, at the choice of the driver or following an automated logic to switch the anti-roll bar 30 between two states A and B.

Referring to FIG. 4A and FIG. 4B relating to a vehicle turning, according to a first state of the anti-roll bar of the system of the invention, noted A, the stiffness of the anti-roll bar is maintained. -dévers 30 at the level usually used for the same type of vehicle or according to the prior art. This is a mode of behavior of the vehicle typed "sport", which can be triggered by the driver.

Referring to FIG. 5A and FIG. 5B relating to a vehicle in a turn, according to a second state of the anti-roll bar of the system of the invention, noted B, the stiffness of the anti-roll bar is reduced. -does 30, for low angles of roll, below that usually used for the same type of vehicle, giving a force shown in this figure by a surface 30 having a reduced width at low DLE travel values or average displacement value DME compared to what is shown in Figure 3 and Figure 4A.

On the other hand, at the high values of roll angles or clearance distance DHE, it has a width similar to that shown in FIG. 3 and FIG. 4A, and has a high stiffness at the entrance of the strong DHE travel values. This is a mode of behavior of the "comfort" vehicle, which can be triggered by the driver.

With the decrease of the stiffness of the suspension spring 17b and the stiffness of the anti-roll bar, a corner and a higher roll speed are obtained in turns, but which are in this case partly compensated for on the side. outside the turn by the effect of the hydraulic attack stop 9b which acts quickly thanks to its elongated stroke. It is thus compensated for the average energy attack stroke DME substantially between the first attack stroke CA1 and the second attack stroke CA2, the stiffness decrease of the anti-roll bar by the effort developed dynamically by the damping of the hydraulic attack stop 9b, giving a total effort which stabilizes the vehicle when cornering at a level equivalent to that applied to vehicles of the same category.

With the invention is added comfort in a straight line thanks to the stiffness of the anti-roll bar 30 decreased in the B state, reducing the forces transmitted to the body 6 in the case where the stresses on the wheels of the left and right side of the axle are not equal.

The configuration as described is not limited to the embodiment described above and shown in the figures. It has been given only as a non-limiting example. Multiple modifications can be made without departing from the scope of the invention. In particular, the invention is not limited to a single hydraulic thrust bearing configuration 9b. One could for example imagine a hydraulic attack stop 9b whose cylinder 10b is integral with the inner walls of the compression chamber 4 of the damper 1b and whose piston 11b is intended to be moved in its corresponding cylinder 10b by the piston 3 of the shock absorber 1b. Of course, any type of hydraulic drive stop 9b known and adapted to be housed in the compression chamber 4 of a damper 1b may be considered. It is also possible to implement for each wheel of the vehicle a suspension spring 17b or a mechanical attack abutment 7b offset outside the hydraulic damper 1b, mounted in parallel with the hydraulic damper 1b between the wheel knuckle and the body 6 of the vehicle.

Claims (10)

1. A system for hydraulically suspending a vehicle running gear, in particular an automobile, comprising for each wheel of this train a suspension spring (17b), a damper (1b) with a cylinder (2) and a piston (3) movable in the cylinder to delimit two chambers (4, 5) respectively of compression and expansion and interposed between the body (6) of the vehicle and the wheel-carrier of the vehicle, a compressible mechanical attack abutment (7b) positioned between the cylinder (2) and the body (6) of the vehicle, or between the stub axle and the body (6) of the vehicle, and a piston hydraulic thrust bearing (9b) mounted in the compression chamber (4), this suspension system being characterized in that it further comprises a hydraulic expansion stop (15b) mounted in the expansion chamber (5) of the cylinder (2) of the corresponding damper (1b), and an anti-rotation bar cant (30) connecting the two axles of the undercarriage, switchable between a and a second state (A, B), a stiffness of the anti-roll bar in the second state (B) being decreased relative to the first state (A). 2. Hydraulic suspension system according to claim 1, characterized in that the stiffness of the anti-roll bar in the second state (B) decreased relative to the first state (A) is a stiffness for low roll angle. 3. Hydraulic suspension system according to claim 1 or claim 2, characterized in that the passage between the first state (A) and the second state (B) is controlled by the driver. 4. Suspension system according to claim 3, characterized in that the hydraulic expansion stop comprises a floating piston disposed in the expansion chamber (5), surrounding a rod (14) of the damper (1b), and comprising a passage of the fluid (23) between the two sides of this floating piston, this hydraulic expansion stop further comprising a flange (22) integral with the rod (14), disposed on a first side of the floating piston facing the piston ( 3) of the damper (1b), forming a valve closing the passage of the fluid (23) when it bears on this floating piston, and a spring disposed on the other side of the floating piston. 5. Suspension system according to one of claims 1 to 4, characterized in that it comprises a mechanical expansion stop (16b) which is arranged to act simultaneously with the hydraulic expansion stop (15b). 6. Suspension system according to claim 5, characterized in that the hydraulic expansion stop comprises a floating piston disposed in the expansion chamber (5), surrounding a rod (14) of the damper (1b), and comprising a passage of the fluid (23) between the two sides of this floating piston, this hydraulic expansion stop further comprising a flange (22) integral with the rod (14), disposed on a first side of the floating piston facing the piston ( 3) of the damper (1b), forming a valve closing the passage of the fluid (23) when it bears on this floating piston, and a spring disposed on the other side of the floating piston. 7. Suspension system according to any one of claims 1 to 6, characterized in that the suspension spring (17b) has a stiffness calculated to give a natural oscillation frequency of the body (6) of the vehicle less than 1 , 2 Hz. 8. Suspension system according to any one of claims 1 to 7, characterized in that the hydraulic stop (9b) comprises a cylinder (10b) and a piston (11b) movable relative to the other, the piston (11b) and the cylinder (10b) of the hydraulic thrust bearing (9b) being intended to be displaced relative to each other during a stroke of the piston (3) of the damper (1b) when the latter reaches a first stroke (CA1) in the cylinder (2) of the damper (1b), and the mechanical attack stop (7b) being intended to be compressed between the cylinder (2) ) of the damper and the body (6) of the vehicle when the piston (3) of the damper reaches a second stroke (CA2) in the cylinder of the damper greater than the first stroke (CA1). 9. suspension system according to one of claims 1 to 8, characterized in that the hydraulic expansion stop (15b) is arranged to act when the expansion stroke of the piston (3) of the damper (1b) reaches a a clearing stroke of less than fifty millimeters from the vehicle's reference attitude (AR). 10. Vehicle, especially automobile, comprising a hydraulic suspension system according to any one of claims 1 to 9.