FR3049233B1 - HYDRAULIC SUSPENSION SYSTEM OF A VEHICLE - Google Patents

Abstract

The invention relates to a hydraulic suspension system for a motor vehicle, comprising a hydraulic attack stop (9b), the piston and the cylinder of which are displaced relative to one another by the piston of a shock absorber ( 1b) when it reaches a first stroke in attack, and a mechanical attack stop (7b) compressed between the damper cylinder and the vehicle body when it reaches a second attacking stroke in the cylinder of the damper greater than the first stroke, the suspension system comprising a hydraulic expansion stop (15b) mounted in the expansion chamber of the cylinder of the corresponding damper (1b), and a computer (32) acting on control means ( 30) of the damper (1b) which modify the level of effort generated by the displacement of the piston in the cylinder.

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.

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

[007] To achieve this object, the invention relates to a hydraulic suspension system of a vehicle undercarriage, in particular automobile, comprising for each wheel of this train a damper cylinder and piston movable in the cylinder to delimit two chambers respectively detent and compression and interposed between the vehicle body and the vehicle wheel stub axle, a compressible mechanical attack stop positioned between the cylinder and the vehicle body, or between the stub axle and the body of the vehicle. vehicle, a piston hydraulic thrust bearing mounted in the compression chamber and having a cylinder and a piston movable relative to each other, the piston and the cylinder of the hydraulic stop being intended to be moved the relative to each other during a stroke of the damper piston when the latter reaches a first attacking stroke in the damper cylinder, and the mechanical attack stop being intended to be compressed when the piston of the damper reaches a second stroke in the cylinder of the damper greater than the first stroke, the suspension system further comprising a hydraulic expansion stop mounted in the expansion chamber of the cylinder of the corresponding damper, and a computer acting on damping control means which modify the level of force generated by the displacement of the piston in the cylinder.

[008] According to another feature, the first stroke of the piston of the damper is between zero and twenty millimeters from a reference attitude of the vehicle.

[009] According to another feature, the second stroke of the piston of the damper is greater than forty millimeters, preferably fifty millimeters, from the reference attitude of the vehicle.

According to another feature, the computer comprises a number of laws predefining the level of effort generated by the displacement of the piston in the cylinder, which is limited.

According to another feature, the computer comprises a range of continuous variation of the level of force generated by the displacement of the piston in the cylinder.

According to another feature, the damper control means comprise a function which, in the absence of a signal from the computer, automatically places these means in a state giving an intermediate damping law between the level of effort the weaker and the highest one.

According to another feature, the mechanical attack abutment is elastomeric material and has an annular cross section so as to be traversed by the piston rod of the damper connected to the vehicle body.

According to another feature, the suspension system comprises for each wheel of the undercarriage at least one expansion stop mounted in the expansion chamber of the cylinder of the corresponding damper.

In another feature, the suspension system comprises for each wheel of the running gear a suspension spring mounted around the damper.

The invention also relates to a vehicle, particularly 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; - Figures 2A and 2B respectively show a longitudinal sectional diagram of a controlled damper of a suspension system according to the invention when the vehicle is at a reference attitude, and a graph illustrating the efforts delivered by the system suspension corresponding to the position of the piston marked in Figure 2A; and FIG. 3 represents a graph illustrating different stress curves for a controlled damper of the suspension system according to the invention.

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 passage, 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 this piston, 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 supported respectively 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 comparable 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.

In addition, the hydraulic attacking stops 9 and the trigger 15 are progressive effort stops that increase 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.

Each hydraulic stop of attack 9 and relaxation 15 is in turn assimilable to a damper and thus 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.

Referring to Figure 1A, the mechanical attack abutment 7 is integral with 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 integral with 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 stroke relaxation, the flange 22 forming the 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 expansion 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 races 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 attack 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 abutment 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 from 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 Figures 2A and 2B, the suspension system according to the invention will now be described.

It comprises for each wheel of the vehicle a shock absorber 1b, a suspension spring 17 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 stop 7b shorter than the mechanical attack stop 7 of the prior art, as well as an attacking 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 attack 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 a large number 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 shock absorber 1. 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 hydraulic attack abutment 9b decreases because an increasing number of through holes 13 are plugged by the piston 11b of the hydraulic abutment 9b as the cylinder 10b moves along the piston 11b of the hydraulic abutment 9b towards the wall bottom bottom 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 of between 40 and 50 mm, preferably 50 mm, the mechanical attack abutment 7b is compressed and contributes to the strengthening of the piston braking 3 of the shock absorber 1.

Note that the discontinuity of the force exerted by the suspension system during its compression, generating discomfort for the passengers of the vehicle, 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 1, 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 1 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 1 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 1 comprises a wall 2b of substantially frustoconical shape whose cross section decreases in the upper direction towards the wall 8 of the damper 1. Thus, the force exerted by the trigger stops 15b, 16b on the vehicle body increases very gradually with the stroke of the floating piston 15b: as the floating piston 15b moves to the upper end wall 8 of the cylinder 2 of the damper 1 along the frustoconical wall 2b, the slot and the annular space 23b of the floating piston 15b closes progressivem ent, effectively decreasing the cross 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.

The damper 1b further comprises control means 30 which modify the level of force generated by the displacement of the piston 3 in the cylinder 2, according to programmed damping laws, acting by an electrical connection connected to a calculator 32. The variable level of effort of the displacement of the piston 3 in the cylinder 2 is indicated in FIG. 2B by a variable width of the rectangular zone representing the force of the damper 1b.

According to a certain amount of information received on the operation of the vehicle, such as its speed or the steering of the front wheels indicating a turn, the computer 32 sends a signal to the control means 30, in particular a current of variable intensity, to change the fluid passages on each side of the piston 3 of the damper 1b in order to vary in real time the level of effort and thus the damping of the oscillations of the suspension. One can also provide a control maneuvered by the driver to choose different modes, such as a comfort mode and a sport mode.

The computer 32 may comprise a limited number of damping laws, in particular only two predefined laws controlled by a current or a lack of current, which represents a very simple system, or a continuous range of variation of the level of current. 'amortization.

Referring to Figure 3, the horizontal axis represents the displacement velocity V of the piston 3 in the cylinder 2, expressed in meters per second, the vertical axis represents the force expressed in daN on this piston. There are different damping laws 34 for variable currents applied in the control means 30, presented for a current increment of 0.1 A, which range from a very low damping of between -75 and +150 daN for a current of 0.4 A at a high damping of between -600 and + 650daN for a current of 1.6A.

In the case of a lack of current in the control means 30, for example following a failure of the computer 32, these control means are provided to automatically enter a state giving an average damping law 40 which allows to continue the journey with a compromise between comfort and safety which is sufficient.

Improved suspension comfort is obtained by combining the elements of the hydraulic suspension system of the invention. Indeed, a low or very low level of effort of the shock absorber 1b is provided for the low-energy DLE deflections, which do not reach the attack stroke CA1 acting on the hydraulic attack stop 9b in order to obtain movements of the body 6 slower and having a greater amplitude. There is therefore a reduction in suspension forces for low energy deflections, and better absorption of small irregularities of the road.

It is then expected for more important road irregularities with deflections in medium energy DME attack, a gradual increase in the level of the efforts of the damper 1b which are added to the efforts delivered by the attacking abutment hydraulic 9b, also having a progressive action according to the deflections and according to the speed.

Finally, it is provided for significant road irregularities with DHE high energy drive deflections, a significant level of the efforts of the damper, which are added to both the forces delivered by the hydraulic attack abutment. 9b and by the mechanical attack stop 7b.

Note that the hydraulic suspension system according to the invention comprises existing techniques arranged in a new combination, it can be easily developed and manufactured with reduced costs, using existing production technologies.

The configuration as described is not limited to the embodiment described above and shown in Figures 2A, 2B. 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 damper 1. Of course, any type of hydraulic attack stopper 9b known and adapted to be housed in the compression chamber 4 of a damper 1b may be considered. One could also imagine for each wheel of the vehicle a suspension spring 17 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 shock absorber (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 piston hydraulic thrust bearing (9b) mounted in the compression chamber (4) and comprising a cylinder (10b) and a piston (11b) movable relative to each other, characterized in that the suspension system further comprises a compressible mechanical abutment stop (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, the piston (11b) and the cylinder (10b) of the hydraulic abutment (9b) being intended to be displaced by with respect to one another during a stroke of the piston (3) of the shock absorber (1b) when the latter reaches a first stroke (CA1) in the cylinder (2) of the damper (1b), 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 damper cylinder, and in that the suspension system comprises a hydraulic expansion stop ( 15b) mounted in the expansion chamber (5) of the cylinder (2) of the corresponding damper (1) and a computer (32) acting on control means (30) of the damper (1b) which modify the level of force generated by the displacement of the piston (3) in the cylinder (2). 2. Suspension system according to claim 1, 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 an expansion stroke (CD ) less than fifty millimeters from the reference attitude (AR) of the vehicle. 3. suspension system according to claim 1 or 2, characterized in that it comprises a mechanical expansion stop (16b) which is arranged to act simultaneously with the hydraulic expansion stop (15b). 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), comprising a passage 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 (16b) disposed on the other side of the floating piston. 5. Suspension system according to any one of claims 1 to 4, characterized in that the computer (32) comprises a number of laws predefining the level of effort generated by the movement of the piston (3) in the cylinder (2). ), which is limited. 6. Suspension system according to any one of claims 1 to 4, characterized in that the computer (32) comprises a continuous variation range of the level of effort generated by the displacement of the piston (3) in the cylinder (2). ). 7. Suspension system according to claim 5 or 6, characterized in that the control means (30) of the damper (1b) comprise a function which in the absence of a signal from the computer (32) automatically sets these means. in a state giving an intermediate damping law (40) between the lowest level of effort (36) and the highest level of effort (38). 8. Suspension system according to any one of claims 1 to 7, characterized in that the second stroke (CA2) in the cylinder of the damper is greater than the first stroke (CA1). 9. Suspension system according to any one of claims 1 to 8, characterized in that it comprises for each wheel of the running gear a suspension spring (17) mounted around the damper (1b). 10. Vehicle, especially automobile, comprising a hydraulic suspension system according to any one of claims 1 to 9.