Suspension device and automotive vehicle fitted with such device

0001SUSPENSION DEVICE AND MOTOR VEHICLE EQUIPPED WITH SUCH A DEVICE FIELD OF THE INVENTION

0002The present invention relates to a suspension device for a vehicle comprising suspension actuators, sensors measuring the vertical force of the ground exerted on the wheels of the vehicle as well as the control means of these suspension actuators so as to increase these vertical downward forces. depending on the needs.

0003Furthermore, the present invention relates to a method for controlling the suspension actuators of a vehicle, as well as a vehicle equipped with such a device.

PRIOR TECHNICAL STATE

0005In known manner, a suspension device fitted to a vehicle must fulfill a comfort function for the occupants of this vehicle as well as a safety function consisting in maintaining the stability of the vehicle when it is moving. The comfort of the passengers in the vehicle depends on the ability of the suspension device to filter out shocks and vibrations due to irregularities on the road. Current vehicles generally implement three levels of screening for these irregularities.

0006First of all, it is possible to filter these vibrations directly between the ground and the wheel, that is to say at the level of the tires. Insofar as the tire is a member which transmits the guiding forces from the vehicle to the road, it is also it which transmits the vertical excitations of the shocks and the vibrations due to the road.

0007The second level of filtering is carried out between the wheels and the chassis of the vehicle. To treat the forces exerted or undergone by the chassis of the vehicle in the vertical direction, this chassis is suspended above the wheels by means of a suspension device. The elements carried by this suspension are conventionally called "suspended masses". Such a device therefore makes it possible to filter vibrations and jolts due to road irregularities. In the longitudinal direction and in the lateral direction, the filtering of the forces and the vibrations is ensured by the trains or half-trains connecting the wheels to their rotating drive member. The half-trains are thus designed to control the plane of the wheels and they contribute significantly to the stability of the vehicle and to the comfort of these occupants.

0008In addition, there is a third level of filtering of road irregularities which occurs between the chassis and the body of the occupants of the vehicle. In fact, the seats of a vehicle are provided to minimize the transmission of chassis vibrations for the occupants. This level of filtering is not directly related to the object of the present invention.

0009In addition to the comfort of the vehicle occupants, a suspension device plays a key role in the stability, and therefore the safety, of the vehicle it equips. In fact, it contributes to the handling of the vehicle, in particular when the latter is subjected to significant acceleration, braking or cornering by its driver. For this, the suspension device comprises suspension actuators capable of exerting on each of the wheels the moments and the forces making it possible to avoid detachment of the wheels and to ensure their tracking as close as possible to the profile of the road.

0010In addition, the suspension system of a vehicle makes it possible to dampen jolts, percussions and other bounces of wheels by damping the vibrations generated by the profile of the road. In particular, when the vehicle is traveling on a degraded road surface, on a paved road or on projecting obstacles such as potholes or speed bumps, the suspension actuators have the function of keeping the vehicle tires in contact with the road. In terms of safety, this makes it possible in particular to limit the braking distance of the vehicle to a stop.

0011There are different methods of controlling the suspension device of a vehicle as a function of the profile of the road, the driving conditions and / or the requests expressed by the driver in terms of braking, acceleration or cornering. In all cases, these various methods aim to improve the stability of the vehicle and the comfort of these occupants by controlling the variations in the vertical forces exerted on each wheel or tire.

0012The vehicles of the prior art are equipped with suspension devices using different measures and information to perform the comfort functions, that is to say to filter the vibrations generated by road irregularities, and safety, it that is, essentially to keep the wheels in contact with the road. These measurements and this information in fact represent driving variables and driving requests evaluated by sensors fitted to the vehicle.

0013Among the driving variables used by current suspension devices, mention may be made of the speed of the vehicle, its lateral acceleration, its longitudinal acceleration, the vertical travel height of each wheel and the speed of this vertical travel. Among the driving requests, we can cite the angle of the steering wheel chosen by the driver, the pressure he exerts on the brake and accelerator pedals. Other variables can also be evaluated to inform the suspension device and allow it to calculate the instructions it must send to the suspension actuators to perform its functions. Thus, the suspension device can be informed of the intensity of the current flowing in such or such suspension actuator or braking actuator.

0014Thus, all of this information and measurements collected by the suspension device allow it to estimate the vertical force exerted on each wheel in order to determine the instructions to be issued to the suspension actuators.

0015However, several difficulties are likely to distort the estimate of these vertical forces and, therefore, to limit the effectiveness of the vehicle suspension.

0016First of all, when the vehicle is traveling in quasi-stationary regime, the estimate of the vertical forces is based on an estimate of the mass of the vehicle, of the location of its center of gravity and of its longitudinal and lateral accelerations. However, the mass of the vehicle can vary depending on the number of passengers and / or the payload transported, so that the location of the center of gravity can also vary depending on the distribution of its mass, while the signals representing the accelerations may be noisy.

0017In addition, a vehicle with four wheels is a degree one hyperstatic mechanism. The information and measurements previously listed are therefore insufficient to precisely determine the vertical force exerted on each wheel of the vehicle. The suspension device must then know precisely the stiffness and the damping coefficients specific to each sub-assembly of front-rear-right-left suspension. However, these quantities depend on the position of each wheel, the elements of the suspension having a parasitic stiffness, therefore the interdependent contributions of the actuators and the passive elements of the suspension device.

0018On the other hand, the vertical forces obviously vary depending on the dynamic stresses exerted on the chassis and on the wheels. When the vehicle is traveling at a speed which is not almost stationary, it is therefore necessary to take account of the transient movements of the chassis and the inertias which it has locally, which can prove to be difficult.

0019Similarly, when the wheel undergoes a vertical clearance generated by road obstacles, the energy of such deflections is absorbed by the elements of the chassis such as tires, articulation components (ball joints, cardan joints), shock absorbers, etc. . However, this energy absorption prevents precise knowledge of the intensity of the vertical forces exerted on each of the vehicle wheels.

0020Consequently, the suspension devices of the prior art are not really able to assess such vertical forces. Consequently, these suspension devices cannot optimally regulate the suspension actuators which make it possible to distribute the vertical forces on each wheel in order to ensure the comfort and the stability of the vehicle.

0021The object of the present invention therefore relates to a suspension device for a motor vehicle whose evaluation of the vertical forces on the wheels is not approximate or disturbed.

STATEMENT OF THE INVENTION

0023The present invention relates to a suspension device for a motor vehicle capable of achieving effective regulation of the vertical forces exerted on the wheels of the vehicle in order to keep each wheel in contact with the road.

0024The present invention firstly relates to a suspension device for a motor vehicle, which comprises suspension actuators acting individually on the wheels of the vehicle. This vehicle has physical parameters and is equipped with sensors capable of evaluating driving variables and driving requests. According to the invention, this device comprises sensors able to measure the vertical force of the ground exerted on each of the wheels, as well as control means for, as a function of these parameters, variables and / or requests, calculate and issue instructions towards at least one of these suspension actuators, so as to increase the vertical force of the ground exerted on one of the wheels.

0025In other words, the suspension device which is the subject of the present is able to accurately measure the vertical forces on the wheels of the vehicle and to regulate the suspension actuators accordingly to keep these wheels in contact with the road.

0026In practice, each of these sensors can be constituted by strain gauges housed in a bearing of one of these wheels.

0027These sensors then indirectly measure the vertical forces on each wheel, since a strain gauge generally measures an elongation via the variation of the electric current flowing through it. Such force sensors represent a minimum space requirement and they are positioned at places where the vertical forces to be measured are actually exerted.

0028According to a practical embodiment of the invention, these means can calculate and issue instructions to at least one of the suspension actuators acting on the inner rear wheel at a turn followed by the vehicle.

0029Such a device makes it possible to avoid detachment of the inner rear wheel when the vehicle approaches a turn in difficult driving conditions.

0030In practice, each of the suspension actuators can act on at least one of the wheels by means of the front and rear half-shafts on which these wheels are mounted.

0031Such suspension actuators are therefore capable of generating a vertical force on each of the wheels of the vehicle, namely at the front, at the rear, to the right and to the left.

0032According to an advantageous embodiment of the invention, the suspension actuators may comprise at least one anti-roll bar associated with a rotary actuator capable of applying a torque to each of the half-shafts.

0033Such a suspension actuator generates an anti-roll torque, which implies the realization of a vertical downward force on one and / or the other of the wheels mounted on these half-shafts.

0034According to another advantageous embodiment of the invention, the suspension actuators can comprise at least one linear actuator capable of exerting a force on each of the half-shafts.

0035Such a suspension actuator can therefore exert a vertical force on each of the wheels by means of the corresponding half-shaft.

0036According to an alternative embodiment of the invention, the suspension actuators can comprise at least one controlled suspension.

0037In practice :

0038- the physical parameters can include the wheelbase, the front and rear tracks, the mass of the vehicle, the stiffness of the suspension actuators; - the rolling variables can include the longitudinal and lateral accelerations, the roll angle, the height on the ground of the front and rear roll centers, the vertical distance separating the roll axis from the center of inertia of the suspended masses, longitudinal distances separating the front wheels and the rear wheels respectively from the center of inertia, the travel and the vertical travel speed of each wheel;

0039- driving requests include the steering wheel angle, the pressure exerted on the brake pedal, the pressure exerted on the accelerator pedal.

0040Thus, knowledge of all these physical parameters, rolling variable and driving request makes it possible to completely determine the hyperstatic system of degree one represented by the vehicle suspended above four wheels.

0041On the other hand, the present invention relates to a motor vehicle equipped with a device according to the invention. BRIEF DESCRIPTION OF THE FIGURES

0042The manner in which the invention can be implemented and the advantages which ensue therefrom will also emerge from the following exemplary embodiments, given by way of non-limiting example, in support of the appended figures among which:

0043FIG. 1 is a three-dimensional schematic representation illustrating the parameters and the variables to be taken into account for establishing the balance of the forces exerted on the components of a vehicle according to the present invention. FIG. 2a represents a flowchart illustrating the regulation of a suspension device according to the invention.

0044FIG. 2b represents a flowchart illustrating the regulation of a suspension device which is the subject of the present invention.

0045FIG. 3 is a comparative diagram illustrating the measurement of the vertical force exerted on the inner rear wheel as a function of the position of a vehicle in a turn, the curve in solid lines corresponds to a vehicle according to the present invention, while that the curve in dotted lines corresponds to a vehicle of the prior art.

MODES FOR CARRYING OUT THE INVENTION

0047FIG. 1 illustrates all the forces, forces and moments which are exerted on the chassis of the vehicle, that is to say between the wheels and the chassis via the suspension actuators. In addition, Figure 1 illustrates the forces due to the accelerations exerted on the vehicle at its center of gravity. FIG. 1 also shows the geometrical parameters which make up the physical parameters characteristic of the vehicle, as well as the driving variables which characterize the instantaneous conditions under which the vehicle is traveling.

0048In general, the notation of the parameters represented in FIG. 1 makes it possible to distinguish the quantities of the same kind according to their location on the chassis.

0049Indeed, the first numerical index affixed to a quantity characterizes the longitudinal location of this quantity, that is to say its position at the front or at the rear of the vehicle. Index 1 therefore represents the front of the vehicle, while index 2 represents the rear of the vehicle. In addition, the second numerical index possibly appended to a quantity of FIG. 1 represents the lateral or transverse location of this quantity on the chassis.

0050Thus, index 1 designates the left side, while index 2 designates the right side. Consequently, the vertical forces F ^ - exerted by each of the wheels on the chassis are noted respectively F_Λ1, F ^₂, F_22I and F₂₂₂TO designate the forces at the front right, front left, rear right and rear left wheels of the vehicle. The indices are also used to differentiate the other quantities represented in figure 1.

0051Among the anti-roll couples illustrated in FIG. 1, a distinction is made between "passive" anti-roll couples C_M. θ and Ck₂-G of “active” anti-roll couples C_ati and C_a2. Indeed, the “passive” anti-roll couples C_M.Θ and c ^ .θ are due to the inertias of the suspension springs and the front and rear axles which are modeled by their angular stiffnesses denoted C_M and Ck₂. On the other hand, the “active” anti-roll couples C_ati and C_a2 are due to anti-roll suspension actuators which are associated with motor components, such as a rotary actuator or a linear actuator, so that the values ​​of these "active" torques can be controlled C_ati and C_a2.

0052The physical parameters characterizing the vehicle are noted: m: mass of the vehicle

0053Vi: front track

0054V₂: rear track

0055E: wheelbase C_M : angular stiffness modeling the front suspension actuators

0056Ck₂ : angular stiffness modeling the rear suspension actuators

0057In this figure, the driving variables are noted as follows:

0058G: center of inertia of suspended masses A_r : vehicle roll axis h₀ : vertical distance separating the center of inertia G from the roll axis A_r γ_x : longitudinal acceleration γ_y : lateral acceleration θ: roll angle hi: height on the ground of the roll center before h₂ : height on the ground of the rear roll center

0059Li: longitudinal distance separating the front axle from the center of inertia G

0060L₂ : longitudinal distance between the rear axle and the center of inertia G

0061VS_ati: torque delivered by the actuator before C_a2 : torque delivered by the rear actuator

0062FIG. 1 therefore makes it possible to establish a balance sheet of the forces exerted on the chassis of the vehicle and, therefore, to determine the intensity of the variable forces by writing the equilibrium equations. In Figure 1, the forces F are shown_XJ, F_Yi and F_Zi exerted by the chassis on the front axle in reaction to the forces Fχi, F_Yi and F_Zthat this train exerts on the chassis. We did the same for the rear axle (with index 2).

0063Thus, the equilibrium equations of the front axle are written:

0064<img file="WO2008071663A1_D0001.tif" />

0065Similarly, the equilibrium equations of the rear axle of the vehicle are written:

0066<img file="WO2008071663A1_D0002.tif" />

0067[VIII] - ^ F₂₂I + hi (Fχ2i + Fx₂₂) + C_a2 + c_k2θ = - ^ F₂₂₂

0068The equilibrium equations of the chassis of the vehicle body are written:

0069<img file="WO2008071663A1_D0003.tif" />

0070[XII] LiF₂₁+ mγχho = L₂F₂₂

0071[XIII] L₁Fx₁+ mγ_xho.θ = L₂F_X2 [XIV] C_al + C_a2 + (c_kl+ c_k2) θ = rngho.θ + mγ_xho

0072From equation [XIV], we deduce the roll angle:

0073[XV] θ = mγ_xho - (C_al + C_a2) / (vs_kl + c_k2 - mgho)

0074Then, by replacing in equations [IX], [X] and [XI] the forces F by their expressions from equilibrium equations of the front and rear trains ([I] to [VIII]), then by subtracting two from two the intermediate equations obtained, we arrive at the expressions of the vertical forces F_zij- following: r_vΛ,_τπ I₂ 1 1 1 Ji₁L₂ 1 Jφ Ji₀

0075[XVI] F_{zl l}=^ⁱⁱ-g - - C_al - - vs_klθ - - -T ^{my '(} 2 V [^¹*** <img file="WO2008071663A1_D0004.tif" />

0076[XVIII] - (I₊MID_not,, <img file="WO2008071663A1_D0005.tif" /> [X, X] _Fz22= i_{mg +} ± c,₂ - J- C₁₂Θ₊-L M. m ,, - (I - £) £ - *

0077IE V₁ V₂ V₂ E 2 V₂ E

0078Now, equations [XVI] to [XIX] make it possible to precisely determine the vertical forces F_ZÎJ- exerted by each wheel on the chassis regulating the values ​​of the “active” anti-roll torques C_ati and C_at2 while measuring in real time the rolling variables contained in equations [XVI] to [XIX], such as the longitudinal and lateral accelerations or the roll angle. The vehicle which is the subject of the invention is in fact equipped with sensors capable of evaluating such driving variables and / or driving requests.

0079The suspension device of the present invention therefore makes it possible to control the anti-roll suspension actuators located on the front and rear axles so as to distribute the vertical forces of the ground exerted on each wheel. Indeed, insofar as these anti-roll suspension actuators are capable of generating an anti-roll torque, they are capable of inducing a vertical load transfer on one or the other of the wheels of the vehicle. You can also vary the front or rear anti-roll stiffness Cki Ck2 to modulate the F_z , as these are parameters specific to the chassis.

0080As the suspension device which is the subject of the present invention is equipped with sensors measuring the vertical force of the ground exerted on each wheel of the vehicle, it is possible to install regulation loops. According to the invention, each wheel of the vehicle can thus comprise a sensor constituted by strain gauges housed in one of the bearings of this wheel. In general, the strain gauge allows indirect measurement of the force by elongating elastically. However, such an extension varies the electrical resistance of the gauge. We can therefore know the force by circulating a current through the gauge.

0081Consequently, a suspension device in accordance with the present invention makes it possible to establish a regulation loop so as to precisely reach the values ​​of the vertical forces F_ZÎJ- desired. Thus, when it is desired to increase the vertical force of the ground on one or more wheel (s), in order to maintain the comfort and / or the stability of the vehicle for driving variables and given driving requests. FIG. 2a illustrates such a regulation loop in which the vertical forces F are determined beforehand_ZÎJ- desired, then we measure the vertical forces Fzi_j real and we regulate the “active” anti-roll torques C_ati and C_Ά2 in order to minimize the difference ΔF_Z= F_ZÎJ- desired - F_ZÎJ- real.

0082According to a particular embodiment of the invention, the suspension device makes it possible to maintain the rear inner wheel at the turn approached by the vehicle in contact with the ground, that is to say to avoid detachment of this wheel. Indeed, as explained above, the detachment of the inner rear wheel considerably degrades the stability and handling of the vehicle as well as its stopping distance.

0083FIG. 2b thus illustrates a regulation loop making it possible to guarantee a vertical force of the ground F_22D minimum, therefore to guarantee contact between the inner rear wheel and the ground. For this, when the suspension device measures a lateral acceleration γ_y important, which means that the vehicle is in a relatively restrictive turn. A suspension device computer according to the invention then determines the downward vertical force F_22D minimum desired, then regulates the active anti-roll torques C_ati and C_at2 to minimize the deviation ΔF_Z2 between the downward vertical force F_Z2_j desired and the vertical force of the soil F_Z2_j real.

0084Thus, a vehicle according to the invention is therefore equipped with a suspension device according to the invention which makes it possible to avoid the gradual detachment of the inner rear wheel, as illustrated in the diagram in FIG. 3. The sensors can thus observe the load shedding of the inner rear wheel at the turn, as represented between the instants t_v and t_D.

0085This figure shows the vertical force of the ground F_Z2j- exercised on the rear wheel inside the turn as a function of time. Until time t_v which represents the start of the vehicle turning, the vertical force of the ground exerted on the inner rear wheel F_Z2j- is relatively large and goes through a maximum value F_Zmax.

0086In the turn, the increase in γ_y continuously decreases the vertical force F_Z2j- exerted on the rear wheel inside the bend, which is represented in the diagram in FIG. 3 by the slope presented by the curves.

0087In the case of a vehicle of the prior art (dotted lines), the suspension device of which is not capable of measuring or influencing the vertical force of the ground exerted on the interior rear wheel, this wheel takes off from the pavement from time t_v where the vertical force of the ground F_Z2_j becomes zero.

0088On the contrary, the solid line curve representing the behavior of a vehicle in accordance with the present invention shows that the vertical force of the ground F_Z2j- exerted on the rear wheel inside the turn has a minimum threshold F_Zmin, so that this wheel does not take off from the road. Thus, the safety and comfort of the passengers are preserved by the suspension device which is the subject of the present invention.

0089Other embodiments are possible without departing from the scope of the present invention.