FR2916717A3 - Yawing moment application controlling device for motor vehicle, has front axle with wheels, where device emits setpoint towards piloting unit and control system respectively for applying brake and motor torques on wheels - Google Patents

Abstract

The device has a power unit or an engine (M) to drive front axles of a motor vehicle. The axles include inner and outer front wheels (21, 22) equipped with a braking actuator (F). The device emits a setpoint towards an actuator piloting unit in order to apply high brake torque (C-F) on one of the wheels, and emits the setpoint towards a control system so as to apply a motor torque (C-M) on the other wheel, in order to stabilize the vehicle in turn. The control system controls a motor torque distributing member.

Description

DEVICE FOR APPLYING A LACET MOMENT TO A MOTOR VEHICLE AND

  MOTOR VEHICLE EQUIPPED WITH SUCH A DEVICE

  FIELD OF THE INVENTION The present invention relates to a device controlling the application of a yaw moment to an automobile so as to stabilize it in a turn.

  Furthermore, the present invention also relates to a motor vehicle equipped with such a control device. The present invention thus relates to the field of motor vehicle construction.

  When a motor vehicle is to follow a turn, it travels a curved path along which the outer wheels must travel a greater distance than the inner wheels during the same time interval. As a result, the angular velocity of the outer wheels is greater than that of the inner wheels. A motor vehicle comprises a power train which generally drives at least the front axle. Such vehicles are said to be front-wheel drive. Sometimes the power train drives the front axle and the rear axle of the vehicle. This is called a four-wheel drive vehicle. During a sharp acceleration or deceleration in a turn, a motor vehicle can reach or even exceed its limit of adhesion on the ground. Such overtaking is further reinforced by the centrifugal force which transfers a portion of the mass of the vehicle to the outside of the turn. Thus, the outer wheels are more loaded than the inner wheels when the vehicle is running. That is why it is preferable to equip a motor vehicle with a device capable of controlling its trajectory by creating a yaw moment on this vehicle.

  For example, a motor vehicle may be equipped with an ESP 35 system (Electronic Stability Program) which uses braking forces to create a yaw moment capable of stabilizing the vehicle in a turn. this, when the vehicle is in oversteer, the ESP trajectory correction system applies a greater braking torque on the outer front wheel than on the inner front wheel.

  Conversely, when the vehicle is understeering, the ESP system applies a greater braking torque on the inner front wheel than on the outer front wheel. Moreover, the wheels that must be the least braked, may also not receive braking torque at all.

  The difference between the forces at the feet of the inner and outer wheels, thus generates the desired stabilizing yaw moment. The vehicle will therefore recover under the effect of this stabilizing yaw moment and it can then better follow its curved path.

  The principle of this curved trajectory control therefore relies solely on the use of the brakes to stabilize the vehicle. For this, the vehicle must be equipped with a control unit of the brake actuators equipping each of the wheels of the front axle. Such a control unit can indeed issue different instructions to each of the braking actuators so as to apply a greater braking torque on one or the other wheel.

  Furthermore, some motor vehicles are equipped with a distributor member distributing the engine torque to each wheel of the front axle, or to each of the four wheels of the vehicle. Such a splitter is most often controlled by a system for optimizing the vehicle efficiency in longitudinal acceleration along rectilinear paths. Thus, the control system of the engine torque distributor takes into account the driving conditions, communicated for example by on-board sensors, to accelerate one wheel more than another during a very fast regulation.

  Consequently, the vehicles of the prior art equipped with an ESP system use only the braking forces to generate a stabilizing yaw moment. These vehicles are therefore necessarily slowed in a turn. They therefore do not allow to follow a turn at constant speed while maintaining the stability of the vehicle, so following the path desired by the driver.

  The object of the present invention therefore relates to a device for controlling the application of a stabilizing yaw moment in a turn, which allows not to decrease the speed of the vehicle without leaving its curved path.

  SUMMARY OF THE INVENTION The object of the invention is therefore a device controlling the application of a yaw moment to a vehicle in a turn, able to maintain the speed and trajectory desired by the driver while maintaining the stable vehicle. .

  The device of the invention is intended to control the application of a moment of yaw to a motor vehicle corner, this vehicle comprising a powertrain, or engine, capable of driving the front axle of the vehicle. This axle comprises two driving wheels each equipped with a braking actuator. According to the invention, the device comprises a control unit of these braking actuators and is able to issue instructions to this unit for the application of a greater braking torque on one of these wheels. In addition, it is able to control the application of a motor torque on at least one of these wheels, so as to stabilize the vehicle in its turn.

  In other words, the device that is the subject of the present invention simultaneously orders the application of a different braking torque and a different engine torque on each of the driving wheels, which makes it possible to stabilize the vehicle more rapidly and more efficiently. his turn.

  Conveniently, this device may comprise a distributing member adapted to distribute the torque of the motor to each of these wheels and a control system of said distributor member, and it may be able to issue instructions to this system for the application a larger engine torque on one of the wheels, so as to stabilize said vehicle in said bend.

  In practice, this device may be able to issue instructions to the control unit for the application of a greater braking torque on the outside wheel at the turn and to the control system for the application of a higher value. large engine torque on the inner wheel at the turn, so as to straighten the vehicle in an oversteer situation.

  In a practical way also, the device may be able to issue instructions to the control unit for the application of a greater braking torque on the inner wheel at the turn and to the control system for the application of a greater engine torque on the wheel outside the turn, so as to straighten the vehicle understeer. Thus, such a device keeps the vehicle on the desired curved path 5 by the driver avoiding oversteer or understeer.

  According to one embodiment of the invention, the device may be able to transmit to the control system instructions for the application of the same engine torque on each wheel, the engine torque thus applied to the wheel adding 10 vectorially to the braking torque applied to the most braked wheel.

  In this case, the engine torque is distributed equitably between the two drive wheels of the front axle and it is superimposed on the braking torque on the most braked wheel. This therefore makes it possible to generate a significant stabilizing yaw moment on the vehicle.

  According to a particular embodiment of the invention, the device may be able to issue instructions to the control unit for the application of a braking torque exclusively on a wheel, and to the control system for the control unit. application of one engine torque exclusively on the other wheel.

  Thus, braking the inner wheel and accelerating the outer wheel minimizes the energy expended to stabilize the vehicle in the turn.

  In practice, the device may be able to transmit, depending on the driving parameters including the instantaneous speed of the vehicle, the steering angle setpoint of the steering wheel, the setpoint of depression of the brake pedal, the driving instruction of the vehicle. the accelerator pedal, instructions to the unit and to the system for application to the wheels of a braking torque and a motor copula generating on each wheel a longitudinal force and a lateral force registered in the optimal adhesion ellipse.

  Such a device therefore makes it possible to optimize the adhesion and thus the effectiveness of the stabilization of the vehicle while respecting the driver's choice of driving.

  According to a practical embodiment of the invention, the device may be able to calculate from the driving parameters the instantaneous longitudinal and lateral accelerations, the radius of curvature of the trajectory and the yaw rate of the vehicle, and in that that it is able to compare the results of this calculation with analogous quantities evaluated by on-board sensors, so as to determine the state of stability of the vehicle when cornering.

  This allows a control loop to control the curved path of the vehicle according to the driver's choice of driving.

  Furthermore, the invention relates to a motor vehicle comprising two drive wheels mounted on the front axle and each equipped with a braking actuator, a powertrain, or motor, a distributing member adapted to distribute the torque. motor, independently or not, to each of these wheels. The vehicle object of the invention further comprises a device as previously discussed. BRIEF DESCRIPTION OF THE FIGURES The manner in which the invention may be implemented and the advantages which result therefrom will also emerge from the following exemplary embodiments, given by way of indication and not by way of limitation, in support of the appended figures among which: FIG. a schematic representation of an adhesion ellipse of a tire; - Figures 2a to 2d are schematic representations of a tire and the forces it undergoes in a turn when braked; FIGS. 3a to 3d are schematic representations of a tire and the forces it undergoes in a turn when it is accelerated; Figure 4a is a schematic representation of a vehicle equipped with a device 25 of the prior art; Figure 4b is a schematic representation of a vehicle equipped with a device according to the present invention; Figure 5 is a schematic representation of the front axle of a vehicle equipped with a device according to the invention; FIG. 6 is a diagram illustrating the determination of the instructions issued by the device for regulating the stability of the vehicle; Figure 7a shows a diagram illustrating the angular drifts at the center of gravity of vehicles of the prior art and vehicles according to the invention; Figure 7b is a diagram illustrating the speed of vehicles of the prior art and vehicles according to the present invention.

  MODES FOR CARRYING OUT THE INVENTION In a known manner, the longitudinal forces FX and the transverse forces Fy that apply to the feet of a wheel, that is to say between the tire and the road, must be inscribed in FIG. As shown in FIG. 1, a longitudinal force FX, in acceleration or braking, determines the lateral force Fy by means of a projection on the adhesion ellipsoid 10. In this way, Known, the adhesion ellipse represents the envelope of the places (FX, Fy) possible for a given vertical force FZ.

  FIGS. 2a to 2d show the successive steps during which the forces are established on the wheel of a vehicle in a turn.

  First of all, the wheel or the tire 20 of the vehicle in a corner undergoes a lateral force FL without undergoing any effort in the longitudinal direction. The lateral force FL thus determines the adhesion ellipse 10 and it saturates the tire 20 to some extent. Then, as shown in FIG. 2b, a braking force FF is applied to the tire 20, which causes a deferral. load on this tire.

  As shown in FIG. 2c, this load transfer, by increasing the friction at the foot of the wheel, enlarges the tire adhesion ellipse 10. Thus, the braking force FF determines the adhesion ellipse 11.

  As illustrated in FIG. 2d, the return on the initial operating ellipse 10 of the tire 20 implies an AFL deterioration of the lateral force FL. This deterioration of the lateral force induces a yaw moment on the vehicle, in this case in a clockwise direction since the wheel 20 represents a wheel of the front axle.

  Similarly, FIGS. 3a to 3d illustrate the successive steps of the adhesion of a tire 20 undergoing an acceleration, that is to say a traction force, during a turn. Thus, FIG. 3a, similar to FIG. 2a, shows a lateral force FL applied to a tire 20.

  FIG. 3b illustrates the application of a motor torque to the wheel which generates a longitudinal force FM on the tire 20. This longitudinal force FM consequently causes the narrowing of the traction ellipse 10 of the tire 20. The ellipse of adhesion then has the dimension of the ellipse 12.

  Then, FIG. 3d illustrates the return to the initial adhesion ellipse 10 accompanied by an AFL deterioration of the lateral force FL and therefore of a moment of yaw applied to the vehicle. As in the case of Figure 2d, the yaw moment is here oriented in the direction of clockwise since the tire 20 represents a wheel of the front axle.

  The behaviors of a front axle tire shown in Figures 2a to 2d and 3a to 3d are used to straighten a vehicle deriving in a turn, such as those illustrated in Figures 4a and 4b.

  FIG. 4a illustrates a vehicle in oversteer equipped with a device of the prior art of the ESP type. The vehicle is here represented by its center of gravity G. In this case, the device makes it possible to control the application of a yaw moment to the vehicle by means of the sole braking forces.

  As explained above, the control unit of the braking actuators composing such a device applies a braking torque to the outer front wheel 22, so as to generate a longitudinal force FF at the foot of the wheel 22. Thus, the loss of lateral force AFL generates a moment of lace ML around the center of gravity G which tends to stabilize the vehicle. Likewise, the braking force FF generates a moment of yaw MF around the center of gravity G of the vehicle, which also contributes to straightening the vehicle in oversteer.

  FIG. 4b illustrates a vehicle equipped with a device according to the present invention controlling the application of a stabilizing yaw moment to the vehicle, not only by generating a braking torque on the outer front wheel 22, but also by generating a engine torque on the inner front wheel 21.

  As explained above, the control device of the invention comprises a control unit of the braking actuators so as to apply differentiated braking forces according to the wheels 21 to 24. In addition, this device comprises a system for controlling the braking actuators. distributing member which distributes the driving torque, independently or not, to each of the drive wheels, in this case the wheels 21 and 22. Such a distributor member may consist of a limited slip differential, a differential visco -coupler or else a differential clutch. Such differentials transmit the rotational movement of a motor shaft, such as the output shaft of the gearbox to two generally coaxial half-shafts which each carry a driving wheel.

  The vehicle illustrated in FIG. 4b is in an oversteer situation. A sensor on board the vehicle regularly evaluates the drift angle and the yaw rate of the vehicle and transmits this value to the device object of the present invention. This device then sends instructions to the brake control unit and to the control system of the distributor so as to apply ML, MF, and MM lace moments respectively induced by the lateral force loss AFL, the FF braking force and the traction force of the FM engine. The braking force FF is applied to the outer front wheel 22, while the motor force FM is applied to the inner front wheel 21. Thus, the vehicle G will rotate clockwise around its front wheel. center of gravity G to stabilize in the turn.

  Conversely, in the case where the vehicle G is understeer, the device of the present invention is able to issue the instructions to the control unit and to the control system to straighten the vehicle in the vehicle. 'other way. FIG. 5 illustrates a front axle formed of two coaxial half-shafts, each carrying a drive wheel 21 and 22. In addition, each half-shaft carries a disk-shaped brake member F through which the torque is applied. corresponding CF braking. As the vehicle G is equipped with a differential distributor, the engine torque CM can be equally distributed between the two drive wheels 21,22. The accelerated wheel 21 thus receives half of the engine torque and the braked wheel 22 receives the same value of engine torque, namely CM / 2. For the braked wheel 22, the motor torque portion CM / 2 is added vectorially to the braking torque CF, this vectorial addition being represented by the descending vertical arrow to the right of the wheel 22. Therefore, the difference between the efforts thus created at the wheels 21, 22 generates a yaw moment on the vehicle G, which stabilizes the latter.

  According to the invention, the yaw moment control device calculates the instructions it sends to the brake control unit F and to the engine torque control system from the driving parameters chosen by the driver. In known manner, these driving parameters include the instantaneous speed of the vehicle V, the steering wheel angle setpoint a, the brake pedal depressing instruction PF and the depression instruction of the accelerator pedal PM. For this, the device regularly records in a memory calculator 61 the values of these parameters communicated by appropriate sensors. This calculator can also process other parameters.

  From these driving parameters, the computer 61 determines the instantaneous longitudinal acceleration setpoint yxc, the instantaneous lateral acceleration setpoint yy, as well as the yaw rate setpoint yr 'deduced from the radius of curvature of the trajectory.

  These intermediate instructions are transmitted to a comparator 62 incorporated in the device. The comparator 62 also receives quantities evaluated by on-board sensors, namely the actual yer yer speed and the actual lateral acceleration y y. By comparing these measured values with the calculated readings, the comparator determines the requests to be sent to the braking actuators and the motor torque splitter. These requests CFZ1_CFZ4 and CM are therefore executed by actuators 63 of the vehicle, thus producing as much longitudinal and lateral forces FX ,, as necessary for the stabilization of the vehicle. Therefore, the device of the present invention can assist the driver in his turn respecting as much as possible his driving choices. In particular, the vehicle equipped with such a device sees its speed slightly reduced along its curved path.

  Figures 7a and 7b show comparative readings of the drift at the center of gravity and the speed V of vehicles equipped with devices according to the prior art and devices according to the invention. As shown in Figure 7a, the first two curves, taken in the order of the legend, show such a small drift angle, since it is limited to plus or minus 6. These first two curves, denoted F + M, illustrate the performance of a device according to the present invention.

  The third curve, denoted F, shows the drift measured for a vehicle equipped with an ESP type device, that is to say applying a stabilizing yaw moment only from braking. As shown in Figure 7a, the drift reaches a maximum of -13 at time T = 4 s. In addition, the device driving the vehicle along the curve F, takes about 2.5 seconds to bring the vehicle back on its trajectory. On the contrary, the device object of the present invention allows only short drifts, that is to say of the order of one second.

  The device that is the subject of the present invention therefore makes it possible to regulate the stability of a vehicle in a turn that is more efficient than the devices of the prior art.

  Moreover, the fourth and fifth curves, denoted M, OF and OF-0M correspond to trajectories of vehicles which are not equipped with stabilization device. We then note a very important drift since the oversteer reaches at least 90.

  FIG. 7b illustrates a comparative survey of the speeds V of stabilized or unstable cornering vehicles. The curves are presented in the same order as the legend of Figure 7a. The curves F + M show that the device of the present invention makes it possible to stabilize the vehicle in the turn by slightly decreasing its speed V. Thus, after 6 s, the vehicle still has a speed of about 70 km / h while a vehicle equipped with an ESP type device (curve F) sees its speed drop to around 60 km / h at T = 6 s. The other two curves marked M, OF and OF-0M correspond to unstabilized vehicles that do not exit the turn, so that their speed is reduced to 0 after 6 s.

  It can thus be seen that the control device which is the subject of the invention is more efficient than the devices of the prior art for stabilizing a vehicle in a situation of oversteer.

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

Claims (9)

  1. A device for controlling the application of a yaw moment to a motor vehicle (G) while turning, said vehicle (G) comprising a power unit, or motor, (M) capable of driving the front axle (21). -22) of said vehicle (G), said axle (21-22) comprising two drive wheels (21, 22) each equipped with a braking actuator (F), characterized in that it comprises a control unit of said actuators braking device (F), in that it is able to issue instructions to said unit for the application of a larger braking torque (CF) on one of said wheels and in that it is adapted to controlling the application of a driving torque (CM) on at least one of said wheels, so as to stabilize said vehicle (G) in said bend.   2. Device for controlling the application of a yaw moment to a motor vehicle (G) in a bend, said vehicle (G) comprising a powertrain, or engine, (M) capable of driving the front axle (21). -22) of said vehicle (G), said axle (21-22) comprising two drive wheels (21, 22) each equipped with a braking actuator (F), characterized in that it comprises a distributing member adapted to distribute the engine torque (M) to each of said wheels (21-22), as well as a control system of said distributor, and in that it is able to issue instructions to said system for the application of a greater driving torque (CM) on one of the wheels, so as to stabilize said vehicle (G) in said bend.   3. Device according to claim 1, characterized in that it is able to issue instructions to said unit for the application of a greater braking torque (CF) on the outer wheel (22) to said turn and to said system for applying a greater engine torque (CM) on the inner wheel (21) to said turn, so as to straighten said vehicle (G) in oversteer.   4. Device according to one of the preceding claims, characterized in that it is able to issue instructions to said unit for the application of a larger braking torque (CF) on the inner wheel (21) audit turn and to said system for the application of a greater engine torque (CM) on the outer wheel (22) in said turn, so as to straighten said vehicle (G) under understeer. 11   5. Device according to one of claims 2 or 3, characterized in that it is able to transmit to said system setpoints for the application of the same motor torque (CM / 2) on each wheel (21, 22 ), said motor torque (CM / 2) thus applied to the wheel vectorally adding to the braking torque (CF) applied to the most braked wheel (22).   6. Device according to one of the preceding claims, characterized in that it is able to issue instructions to said unit for the application of a braking torque (CF) exclusively on a wheel and to said system for the application of a motor torque (CM) exclusively on the other wheel.   7. Device according to one of the preceding claims, characterized in that it is able to emit, depending on the driving parameters including the instantaneous speed of the vehicle (V), the steering angle of the steering wheel (a), the the brake pedal depressing instruction (PF), the accelerator pedal depression instruction (PM), the instructions to said unit and to said system for application to the wheels of a braking torque ( CF21-CF24) and a motor copula (CM) generating on each wheel (21-24) a longitudinal force and a lateral force (F,; i) inscribed in the optimum adhesion ellipse.   8. Device according to claim 4, characterized in that it is able to calculate from said driving parameters (a, V, PF, PM) the longitudinal accelerations (y,) and lateral instantaneous (yy,), the radius of curvature of the trajectory and the yaw rate (yl'c) of said vehicle (G), and in that it is able to compare the results of this calculation with analogous quantities (yx, yy, yl ') evaluated by on-board sensors, so as to determine the stability state of the vehicle (G) while cornering.   9. A motor vehicle (G) comprising two driving wheels (21, 22) mounted on the front axle (21-22) and each equipped with a braking actuator (F), a power train or a motor ( M), a distributing member adapted to distribute the engine torque (CM) to each of said wheels (21, 22), characterized in that it further comprises a device according to one of the preceding claims.