WO2007138223A1

WO2007138223A1 - Device and method for controlling efforts on a vehicle comprising four driving wheels

Info

Publication number: WO2007138223A1
Application number: PCT/FR2007/051338
Authority: WO
Inventors: Xavier Claeys; Philippe Pognant-Gros; Richard Pothin
Original assignee: Renault S.A.S.
Priority date: 2006-05-31
Filing date: 2007-05-29
Publication date: 2007-12-06
Also published as: FR2901762A1; EP2021216A1; FR2901762B1

Abstract

The invention relates to a device (28) and a method for implementing the means of the device for controlling the efforts or torques of a motor vehicle comprising four driving wheels and two trains, a front train (AV) and a rear train (AR), said device being used to apply an effort or a torque suitable for the driving situation to at least one wheel of a train of the vehicle. The inventive device comprises: a means for detecting the driving situation, and a calculating means for calculating, from the means for detecting the driving situation, a longitudinal effort or a torque for driving at least one wheel of a train of the vehicle. The invention is characterised in that the calculating means comprises a means for establishing an adherence potential, a means for testing the conditions of adherence of the vehicle to the ground, and a means for controlling the longitudinal effort according to the adherence potential and the result of the test of the conditions of adherence of the vehicle to the ground.

Description

"Device and method for controlling forces on a four-wheel drive vehicle"

The invention relates to a device and a method for controlling forces or torques on a four-wheel drive motor vehicle. More particularly, the invention relates to a device and a method of saturation of the torque or the force of a vehicle train, to impose a force or a torque on at least one wheel of the vehicle adapted to its driving situation. Such a device generally comprises: a means for detecting the driving situation

and calculating means for calculating, from the driving situation detection means, a longitudinal force or a torque for driving at least one wheel of a vehicle train

The new four-wheel-drive hybrid vehicles are usually equipped with an independent mechanical power source on each train. The front end of the vehicle is driven either by a conventional power train with an explosion engine and a manual gearbox, robot or automatic, or concurrently by a combustion engine and an electric motor. The rear axle is driven by an electric motor which is an electric machine capable of operating as a generator or motor to provide torque and power to the rear wheels via a differential. The energy storage element comprises a battery for supplying or receiving energy from one of the electrical machines operating either as a motor or as a current generator. Thus, an electric machine operating as a motor is capable of providing a torque and a power required to the wheels of a given train. The heat engine associated with an electric motor in this type of hybrid vehicle makes it possible to provide additional power for road journeys, or recharge the battery with a current generator or with the electric motor when it is reversible and running as a power generator.

This type of vehicle also has a control device for distribution of forces or torques on the four-wheel drive taking into account the different driving situations.

In fact, in different driving situations, such as, for example, driving, a slippery road, an avoidance maneuver, etc. the distribution of the forces on the four wheels of the vehicle is modified in such a way as to optimize the stability of the vehicle in order to maintain it in its trajectory and to respect the will of the driver, inter alia, by the position of the accelerator and brake pedals only by the steering angle of the steering wheel.

However, respecting the stability conditions of the vehicle, it is possible to negate the effects specific to hybrid vehicles such as torque compensation during a gearshift or an electrical energy recovery phase to charge the battery. . These phases can lead to a sudden drop in torque on one of the trai ns, commonly known as "torque hole", which can momentarily disrupt the distribution of forces to the drive wheels of the vehicle. Controllers are designed to control the distribution of torques or forces on the four-wheel drive of a hybrid vehicle according to the driving situation.

An example of such a control device is the subject of document FR-2.799.41 7. This document describes and represents a control device for a four-wheel-drive hybrid vehicle that manages the distribution of vehicles. driving forces or couples according to the conditions of the driving situation. In this document, the distribution of the driving forces to the wheels is calculated according to several constraints including the will of the driver, the temperature of the electrical components, the operating state of the vehicle, and the estimation of the longitudinal forces applied to each wheel.

More specifically, the management of the distribution of the driving forces is calculated from the differences in the sliding speeds between the front and rear wheels, that is to say the difference in the speeds of the wheels taken independently.

This solution does not take into account parameters such as the ground connection that a motor vehicle may encounter in a real driving situation. The hybrid vehicle may be destabilized. To solve this problem, the present invention proposes a device for saturation of the torque or of a force of the type described above characterized in that characterized in that the calculating means comprises:

means for establishing an adhesion potential; means for testing vehicle ground connection conditions;

a means for controlling the longitudinal force as a function of the adhesion potential and the result of the test of the conditions of the vehicle's ground connection. According to other features of the invention:

the device is applied to a hybrid four-wheel drive vehicle having a front end driven concurrently by a heat engine and / or a first electric motor powered by a storage element and a rear axle driven by at least a second electric motor and the longitudinal force drives the rear of the vehicle; the means for detecting the driving situation comprises: means for determining the driver's will from, in particular, the position of the brake and accelerator pedals, the steering angle of the vehicle;

. a means for detecting the parameters outside the vehicle falling, inter alia, at the outside temperature and comprising means for calculating a coefficient of friction of the wheels at the roadway;

. motor parameter detection means for detecting the operating speed of the vehicle engine (s); and

. means for detecting the parameters relating to the dynamics and to the ground connection of the vehicle for detecting speeds and accelerations at the four wheels as well as forces or torques at the front and rear axle;

the calculating means comprises means for calculating vertical forces at the rear axle, representing the reaction of the ground with the wheels of the rear axle projected along a vertical axis, and these forces are calculated from the sensor signals relating to the static loads of the vehicle; and lateral and longitudinal accelerations. the means for calculating the forces or torques comprises:

^* First means for checking the value of the longitudinal force transmitted to the rear axle by means of detecting the previous driving situation, which tests whether the value is positive or zero; ^* A first calculation means controlled by the first verification means and applies a method for calculating the longitudinal force to the rear axle in the case where the value of the longitudinal force is not positive;

^* A second verification means which is controlled by the first verification means which verifies whether the longitudinal force at the front axle is in a range defined by two thresholds, where the longitudinal force is positive or zero; and

^* A second calculation means which is controlled by the second checking means and which calculates a saturated longitudinal force value in the case where the longitudinal force at the front axle is in the range of thresholds, so as to satisfy the stability conditions of the vehicle as well as the driving situation;

the first calculation means, once activated by the first verification means, comprises means for calculating a longitudinal force value for the rear axle such that it respects the effort setpoint defined by the driver's will, which imposes that the sum of the forces to the two trains is equal to a total effort and which is also such that the potential for adhesion to the rear axle is never greater, in absolute value, than the adhesion potential on the front axle so as to satisfy a group of equations (2) that follows:

Fxtotale - Fxav + Fxar

- The second calculation means, once activated by the second verification means, calculates a constant saturated longitudinal force value to the rear axle so as to satisfy the stability conditions of the vehicle as well as the driving situation;

the device comprises a force distribution means which distributes the longitudinal force to the rear axle calculated by one of the calculation means in two forces: a rear longitudinal force left for the left rear wheel of the vehicle, and a right rear longitudinal force for the right rear wheel of the vehicle whose values are calculated so as to satisfy the stability conditions of the vehicle and the driving situation detected.

The invention also relates to a method for controlling the forces or torques of a four-wheel drive motor vehicle comprising two trains, a front axle and a rear axle, in order to impose an effort or a torque adapted to the driving situation at the vehicle. least one wheel of a vehicle train characterized in that it comprises:

a step for detecting a driving situation of the vehicle;

a step of estimating the forces at the front and rear trains of the vehicle from the information collected at the stage of detecting the driving situation;

a step of testing the sign of the value of the longitudinal force at the rear axle which receives the value of the force applied to the rear axle and which activates one of the following steps depending on whether the value of the longitudinal force on the train back is positive or not;

a step of checking the value of the longitudinal force to the front axle which is activated by the preceding control step if the value of the longitudinal force at the rear trai n is positive and which verifies whether the value of the the longitudinal force at the front end is included in the range delimited by two single values;

a calculation step which is activated after the verification step if the value of the longitudinal force at the front step is included in the interval delimited by the two threshold values and which calculates a value saturation of the effort longitudinal to the rear axle adapted to the driving situation and the conditions of ground connection of the hybrid vehicle;

a calculation step which is activated after the checking step if the value of the longitudinal force at the rear axle is not positive or after the verification step if the value of the longitudinal force at the front axle does not is not within the range defined by the two threshold values and which calculates a saturated value of the longitudinal force at the rear end which satisfies the equations of group (2); and

a distribution step activated after one of the preceding calculation steps and which distributes the saturated value of the longitudinal force to the rear axle in two forces: a left rear longitudinal force for the left rear wheel of the vehicle, and a longitudinal force rear right for the right rear wheel of the vehicle. Other features and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

FIG. 1 is a diagram of the vehicle comprising a device for controlling the saturation of the forces according to the invention; FIG. 2 is a flowchart of the method for controlling the saturation of the forces according to the invention;

FIG. 3 is a block diagram of the device for controlling the saturation of the forces according to a particular embodiment of the invention; FIG. 4 is a block diagram of part of the device for controlling the saturation of the forces according to the invention. In the following description, we will use the longitudinal, vertical and transverse (or lateral) terminology and the indices x, y and z with reference to the trihedron L, V, T shown in FIG. 1. In the following description, identical, similar or similar elements will be designated by the same reference numerals.

A hybrid vehicle, shown in a particular embodiment of the invention in Figure 1, comprises a heat engine 20, mechanically coupled to the drive wheels of a front train AV of the vehicle.

Each front and rear rear axle of the vehicle has two left and right G drive wheels.

The vehicle also comprises two electric machines 22 and 24 that can operate as a motor or a current generator and each driving a train of the hybrid vehicle. The front electric machine 22 drives concurrently with the heat engine 20 the vehicle's front axle while the rear electric machine 24 drives the rear axle AR to propel the vehicle in four-wheel drive mode.

The energy storage element 26 comprises a battery and control elements so as to respect safety conditions and to avoid excessive charging or discharging of the battery. The storage element 26 is connected to the electrical machines 22 and 24 via controllers 30 and 32, and supplies the front 22 and rear 24 electrical machines with energy.

The heat engine 20 thus makes it possible to drive the vehicle in the case where the state of charge of the storage element 26 supplying the front electric motor 22 is weak, or to recharge the battery 26 by making one of the machines work. front 22 or rear 24 electric in current generator mode.

According to a not shown variant of the invention, the vehicle more simply comprises a heat engine driving only the front end of the vehicle and an electric motor driving the rear axle of the vehicle.

A device 28 for controlling the saturation of the forces or torques of the drive wheels according to the invention is arranged in the vehicle. I l makes it possible to vary the saturation of the force or the torque applied to the rear axle AR of the vehicle so as to compensate for any falls in torque to the wheels of the vehicle that may occur for example when changing gear.

The device 28 for controlling the saturation of the forces is connected to front and rear differentials 14 and 14 respectively to record information on trains before and after

AR, including the speed of each wheel and the forces, noted Fav and Far, applied to each AV and AR train of the vehicle. The front 12 and rear 14 differentials also comprise means for distributing the drive and braking torques imposed by the device for controlling the saturation of the forces 28 and in particular for the rear axle AR.

The device for controlling the saturation of the forces 28 is also connected to the front 22 and rear 24 and thermal 20 electric motors of the vehicle to record information on their respective operating conditions.

A particular embodiment of the device 28 for controlling the saturation of the forces of the invention is shown more precisely in FIG.

It includes a block 34 for detecting the driving situation to collect operating parameters of the vehicle and external parameters. The driving situation comes under different parameters, in particular:

- parameters on the will of the driver: amount of support on the brake and accelerator pedals, steering angle of the steering wheel, ...;

- parameters outside the vehicle: the adhesion of the wheels to the road surface (coefficient of friction), the outside temperature, ...;

- parameters on the running mode: detection of engines in operation and engine speed, engine torques ....

- vehicle dynamics and ground-link parameters: longitudinal and lateral acceleration and four-wheel speeds, vehicle acceleration and overall speed, yaw rate, effort or overall driving torque, effort or torque to front and rear AR trains.

The block for detecting the driving situation 34 comprises a driver setpoint detection block 40 which comprises means for detecting the parameters reflecting the driver's will.

The parameters relating to the will of the driver are detected by means of sensors (not shown) capable of raising inter alia the amount of pressure on the accelerator and brake pedals, reflected by the position of the pedals, and a sensor of angle to raise the steering angle of the alpha steering wheel.

The block for detecting the driving situation 34 also comprises a detection unit 42 of parameters outside the vehicle.

The information relating to the state of the roadway is detected by means of sensors (not shown) able to raise the outside temperature, to evaluate the adhesion of the wheels of the vehicle to the road by estimating at regular intervals of time for example a coefficient of friction of the tires on the roadway.

A detection block 44 of the rolling mode parameters comprises means for knowing the speed at which the various engines fitted to the vehicle operate, for example based on the data of the controllers 30 and 32 of the front and rear electric machines 24. and on the speed of the engine 20.

The detection block 44 of the rolling mode parameters makes it possible to evaluate from the engine data whether the vehicle is in the acceleration, deceleration or running phase with a load, for example, if it starts the rise of a coast, etc.

The vehicle dynamic and ground link parameters are recorded by an estimating block 48 of wheel forces and a vehicle speed estimation block 46.

The speed estimation and acceleration block 46 comprises speed and acceleration sensors (not shown) to record the speed w of each wheel at regular time intervals, longitudinal and lateral accelerations at each wheel, and the speed and the acceleration, lateral and longitudinal, overall of the vehicle.

The information recorded by the speed and acceleration estimation block 46 is used by the effort estimation unit 46 to calculate the forces Fav and Far, respectively, for the front and rear rear trains AR.

The estimating block 48 of the forces comprises means for measuring or estimating the forces applied to each wheel, longitudinal forces Fxav, Fxar and vertical Fzav, Fzar respectively of the front and rear axles AR, which are the orthogonal projection on an axis longitudinal and a vertical axis a total effort, Ftotale, requested by the driver, through the detection of the position of the pedals.

The estimation block 48 comprises means for estimating from the total force, Ftotal, imposed by the driver and longitudinal and lateral accelerations of each wheel of the vehicle taken up by suitable sensors of the block 46:

- the longitudinal forces to the trains before AV and AR respectively noted Fxav and Fxar;

- and the vertical forces to the trains before AV and AR respectively noted Fzav and Fzar.

All the data of the block 34 for detecting the driving situation are transmitted to a block 52 for calculating the longitudinal forces Fxar applied to the rear wheels of the vehicle. The calculation block 52 comprises means for calculating, from the driving situation, wheel forces and the speed of each wheel, a value adapted to the longitudinal force Fxar sat applied to the rear axle AR.

The value calculated by the calculation block 52 is then transmitted to a distribution unit 54 of the forces to the wheels, which distributes to the left rear wheels G and right D, through the rear differential 14, the longitudinal force Fxar sat at AR rear axle so as to respect the stability conditions of the vehicle according to the driving situation. Calculation block 52 is shown in greater detail in FIG. 4. Calculation block 52 comprises a plurality of means each executing a particular function.

A first means is a first verification sub-block 60 which receives the values of the longitudinal forces Fxar to the wheels of the rear axle AR measured or estimated by the estimation block 46. The first verification sub-block 60 comprises means for testing the sign of the values of the longitudinal forces at the two rear wheels.

If the longitudinal forces to the two rear wheels, Fxar, are not positive, a first calculation means activated.

The first calculation means is a first sub-block of calculation 68 which receives the data coming from the detection block of the driving situation 34 and the activation instruction coming from the block 60. The first sub-block of calculation 68 makes it possible to calculate the longitudinal forces of the AR Fxar sat. The value of Fxar sat is such that it satisfies two criteria:

- the first criterion is that the value of the longitudinal force Fxar sat must respect the fact that the sum of the longitudinal forces on the front and rear rear trains AR does not exceed a longitudinal stress, Fxtotale, imposed by the driver, in order to respect the instructions of the driver;

the second criterion is that a potential of adhesion Mu of the rear axle AR, defined as being the ratio of the longitudinal force on the vertical force on the rear axle AR is never greater (in absolute value) than a potential of adhesion Mu on the front axle AV so as to respect the stability of the vehicle.

The first calculation sub-block 68 therefore comprises means for determining a longitudinal force value Fxar_sat at the rear axle AR from the total torque setpoint requested by the driver so as to satisfy the group of equations (2). next: txtotal - t xav + t xar

where Mu represents the adhesion potential defined above. The longitudinal longitudinal force value Fxar_sat is then transmitted to the distribution block Left / Right 54 which distributes the force to the left wheel G and right D of the rear axle AR according to the driving situation. For example, if the vehicle approaches a right turn, the amount of braking on the outer wheels, the left wheels G, is greater than the inner wheels, the right wheels D, in the case of a sub-turning vehicle.

The distribution block 54 thus calculates a longitudinal force value for the right rear wheel, Fxar_sat_D, and a longitudinal force value for the left rear wheel Fxar_sat_G, values which depend on the driving situation.

If the longitudinal forces at the rear axle AR, Fxar, are positive, a second verification means is activated. The second means is a control sub-block 62 which comprises means for checking whether the value of the longitudinal force Fxav to the front axle AV is in a range of the lowest values delimited by two threshold values, SeuiM and Seuil2. These threshold values correspond to the values of longitudinal force Fxav AV front train the lowest in absolute value, values below which trai n rear AR is considered to be not subjected to any effort or torque.

The interval of the lowest values corresponds to very small values (absolute) of longitudinal force Fxav, a phenomenon which is generally referred to as a "torque hole" where the forces (or torques) on the front axle AV drop sharply when example of a change of report.

In the case where the value of Fxav is in this range of the lowest values, the second verification means 62 controls a second calculation means which comprises means for calculating a saturated longitudinal force Fxar sat to the rear wheels whose value varies depending on the driving situation.

The second calculation means is a second calculation sub-block 66 which then calculates a saturated longitudinal force value for the rear axle wheels AV, Fxar sat taking into account the will of the driver and the driving situation explained above.

This saturated longitudinal force calculation technique makes it possible, depending on the driving situation, to authorize or not the compensation of a torque hole or the recovery of energy, by making the rear electric motor 24 work in current generating mode. to recharge the energy storage element 26, in the case where there would be no or very little longitudinal force, Fxav, applied to the front axle AV, where the value of the longitudinal force Fxav to the front axle AV is in the range of the lowest values.

The longitudinal longitudinal force value Fxar_sat is then transmitted to the distribution block Left / Right 54 which distributes the force to the left wheel G and right D of the rear axle AR according to the driving situation. The distribution block 54 calculates a saturated value of longitudinal force for the right wheel, Fxar_sat_D, and a saturated value of longitudinal force for the left wheel Fxar sat G dependent on the driving situation.

In the case where the value of Fxav is not within this range, the second verification means 62 controls the first calculation sub-block 68, described above, which calculates a longitudinal longitudinal force velocity Fxar_sat which satisfies the group of equations 2. The value of longitudinal force Fxar sat thus calculated is then distributed as a function of the driving situation by the distribution block 54.

FIG. 2 shows a flowchart of the control method of the invention, especially when this method is implemented as software in a calculator in the hybrid vehicle.

After a start step that can be started by the driver's maneuver, a step S1 is executed, which implements the means of the driving condition detection unit 34 to record the various parameters, in particular on the driving situation. , the condition of the roadway and the operating speed of the engines.

Once the information has been collected during the step S1, the method proceeds to a step S2, which implements the estimation block means 48 to estimate the applied forces Fav to the front and rear wheels of the rear axle AR. . We can decompose the Fav and Far forces along two longitudinal and vertical axes to obtain longitudinal forces, Fxav and Fxar, and vertical, Fzav and Fzar.

The signals corresponding to the longitudinal forces before Fxav and rear Fxar can be estimated from measuring the loads applied to the front and rear rear axle AR and the overall speed of the vehicle. It is possible to estimate the signals of the vertical forces

Fzav and Fzar of the front and rear rear axle from the lateral and longitudinal acceleration of the vehicle by accelerating sensors (not shown) provided for this purpose.

The signals Fav and Far thus calculated or estimated are then transmitted to a control step S3 of the value of the longitudinal force Fxar to the rear axle AR and which implements the means of the first verification sub-block 60.

The control step S3 executes a command that tests the sign of the value of the longitudinal force Fxar to the rear axle AR. If the value of the longitudinal force Fxar to the rear axle AR is positive, the method proceeds to a step S5 of verification of the value of the longitudinal force Fxav to the front axle AV which implements the means of the control sub-block 62.

The verification step S5 checks whether the value of the longitudinal force Fxav AV forward train is in a range of the lowest values of Fxav, delimited by two threshold values, SeuiM and Seuil2.

If the value of Fxav is within this range of the lowest values of Fxav, the method of the invention proceeds to a calculation step S6 implementing the means of the first sub-block of calculation 66.

Step S6 executes a command which makes it possible to calculate a saturated value of the longitudinal force Fxar_sat to the train AR which takes into account the force Fav applied to the train AV and the various parameters of the vehicle which reflect the driving situation, the condition of the roadway and the driver's will.

The saturated value of the longitudinal force Fxar_sat to the rear axle is transmitted to a distribution step S8, implementing the means of the distribution block 54, to distribute this force to the right rear wheels D and left G depending on the situation of conduct.

Once the calculation step S8 has been executed, the method returns to the beginning of the program to execute step S1 again.

If, during step S5, the value of Fxav is not within this range of the lowest values of Fxav, the method of the invention proceeds to another calculation step S7 implementing the means of the second subset. calculation block 68.

The calculation step S7 executes commands for determining a longitudinal force value Fxar_sat at the rear axle AR as it satisfies the two following criteria: the first criterion is that the value of the longitudinal force

Fxar sat must respect the fact that the sum of the longitudinal forces on the front and rear traps does not exceed not a guideline of longitudinal force, Fxtotale, imposed by the driver.

- the second criterion is that a potential of adhesion of the rear axle AR, defined as being the ratio of the longitudinal force on the vertical force on the rear axle AR is never superior (in absolute value) to a potential of adhesion of the front axle AV.

The calculation step S7 therefore calculates a longitudinal force to the saturated rear axle AR Fxar sat which solves the group of equations 2.

The saturated value of the longitudinal force Fxar_sat to the rear axle AR thus calculated is transmitted to a distribution step S8, implementing the means of the distribution block

54, to distribute this force to the right rear wheels D and left G depending on the driving situation.

If, during step S3, the value of the force Fav to the forward train AV is not positive, the method goes directly to the calculation step S7 to calculate a saturated value of the longitudinal force Fxar sat at AR rear axle as previously described.

Claims

REVEN DICATIONS

1. Device (28) for controlling the forces or torques of a four-wheel drive motor vehicle comprising two trains, a front axle (AV) and a rear axle (AR), to impose a force (Fxar_sat) or a torque adapted to the driving situation at least one wheel of a vehicle train which comprises:

means (34) for detecting the driving situation

and calculating means (52) for calculating, from the driving situation detection means (34), a longitudinal force (Fxar_sat) or a torque for driving at least one wheel of a vehicle train characterized by characterized in that the calculating means (52) comprises: - means for establishing an adhesion potential (Mu),

means for testing vehicle ground link conditions, and

a longitudinal force control means (Fxar_sat) as a function of the adhesion potential and the result of the test of the conditions of connection to the ground of the vehicle.

2. Device (28) according to claim 1, characterized in that it is applied to a four-wheel drive hybrid vehicle a front train (AV) is driven concurrently by a heat engine (20) and / or a first engine electric motor (22) powered by a storage element (26) and a rear axle (AR) driven by at least a second electric motor (24) and in that the longitudinal force (Fxart_sat) drives the rear axle (AR) of the vehicle .

3. Device (28) according to claim 2, characterized in that the means for detecting the driving situation (34) comprises: means (40) for determining the driver's will from, in particular, the position of the brake and accelerator pedals, the steering angle of the vehicle (alpha), etc .;

means (42) for detecting the parameters outside the vehicle, including, inter alia, the outside temperature and comprising means for calculating a coefficient of friction of the wheels with the roadway;

- means (44) for detecting the engine parameters to detect the operating speed of the vehicle engine or engines;

means (46, 48) for detecting the parameters relating to the dynamics and to the ground connection (46, 48) of the vehicle for detecting four-wheel speeds (w) and accelerations as well as forces (Fav, Far); or couples with the front (AV) and rear (AR) trains.

4. Device (28) according to claim 2, characterized in that the calculating means (52) comprises means for calculating vertical forces (Fzar) rear axle (AR), representing the ground reaction to the wheels of the rear axle (AR) projected along a vertical axis, and in that these forces (Fzar) are calculated from the sensor signals relating to the static loads of the vehicle and the lateral and longitudinal accelerations.

5. Device (28) according to claim 4, characterized in that the calculating means (52) efforts or couples comprises:

a first means for verifying (60) the value of the longitudinal force (Fxar) at the rear axle (AR) transmitted by the preceding driving situation detection means (34), which tests whether this value is positive or nothing;

a first calculation means (68), controlled by the first verification means (60) and which applies a calculation method to calculate the longitudinal force (Fxar_sat) to the rear axle (AR) in the case where the value of the longitudinal force (Fxar) is not positive;

a second verification means (62) which is controlled by the first verification means (60) and which checks whether the longitudinal force (Fxav) at the front axle (AV) is within an interval delimited by two thresholds, (SeuiM , Threshold2) in the case where the longitudinal force (Fxar) is positive or zero; )

a second calculation means (66) which is controlled by the second verification means (62) and which calculates a saturated longitudinal force value (Fxar_sat) in the case where the longitudinal force (Fxav) to the front axle (AV ) is within the threshold range, (Threshold, Threshold2) so as to satisfy the stability conditions of the vehicle as well as the driving situation.

6. Device (28) according to claim 5, characterized in that the first calculation means (68), once activated by the first verification means (60), comprises means for calculating a longitudinal force value to the train rear (Fxar_sat) as it respects the command of effort defined by the will of the driver, which requires that the sum of the efforts to the two trains (AV) and (AR) is equal to a total effort (Fxtotale) and which is also such that the potential of adhesion (Mu) to the rear axle (AR), is never superior, in absolute value, to the potential of adhesion (Mu) on the front axle (AV) so as to satisfy a group of equations (2) which follows:

Fxtotale - Fxav + Fxar)

7. Device (28) according to claim 5, characterized in that the second calculation means (66), once activated by the second verification means (62), calculates a constant saturated value of longitudinal force (Fxar_sat) at Rear axle (AR) from in order to satisfy the stability conditions of the vehicle as well as the driving situation.

8. Device (28) according to any one of claims 1 to 7, characterized in that it comprises a means (54) of distribution of forces which distributes the longitudinal force (Fxar_sat) to the rear axle (AR) calculated by one of the calculating means (66) or (68) in two forces: a left rear longitudinal force (Fxar_sat_G) for the left rear wheel of the vehicle, and a right rear longitudinal force (Fxar_sat_D) for the right rear wheel of the vehicle whose values are calculated to satisfy the stability conditions of the vehicle and the detected driving situation.

9. A method for controlling the forces or torques of a four-wheel drive motor vehicle comprising two trains, a front axle (AV) and a rear axle (AR), to impose a force (Fxar_sat) or a torque adapted to the driving situation at least one wheel of a vehicle train characterized in that it comprises:

a step (S1) for detecting a driving situation of the vehicle

a step (S2) for estimating the forces (Fav), (Far) to the front (AV) and rear (AR) trains of the vehicle from the information collected in the (S1) stage of detecting the driving situation; a step (S3) for testing the sign of the value of the longitudinal force (Fxar) to the rear axle (AR) which receives the value of the force (Fxar) applied to the rear axle (AR) and which activates the one of the following steps (S5) or (S7) depending on whether the value of the longitudinal force (Fxar) to the rear axle (AR) is positive or not. a step (S5) for checking the value of the longitudinal force (Fxav) at the front axle (AV) which is activated by the preceding control step (S3) if the value of the longitudinal force (Fxar) to the rear axle (AR) is positive and which checks whether the value of the longitudinal force (Fxav) to the front axle (AV) is within an interval delimited by two threshold values, (SeuiM, Threshold2); a calculation step (S6) which is activated after the verification step (S5) if the value of the longitudinal force (Fxav) at the front axle (AV) is within the range delimited by the two threshold values ( SeuiM, Threshold2) and which calculates a saturated value of (Fxar_sat) the longitudinal force to the rear axle (AR) adapted to the driving situation and the grounding conditions of the hybrid vehicle;

- a calculation step (S7) which is activated after the control step (S3) if the value of the longitudinal force (Fxar) to the rear axle (AR) is not positive or after the step (S5) of verification if the value of the longitudinal force (Fxav) to the front axle (AV) is not included in the interval delimited by the two threshold values (SeuiM, Threshold2) and which calculates a saturated value of (Fxar_sat) l longitudinal force to the rear axle (AR) which satisfies the equations of the group (2) - a distribution step (S8) activated after one of the preceding calculation steps (S6) or (S7) and which distributes the saturated value of the longitudinal force (Fxar_sat) to the rear axle (AR) in two forces: a left rear longitudinal force (Fxar_sat_G) for the left rear wheel of the vehicle, and a right rear longitudinal force (Fxar_sat_D) for the right rear wheel of the vehicle.