FR2958585A1 - METHOD FOR CONTROLLING A COUPLER - Google Patents

Abstract

A method of controlling a coupler (9) capable of distributing a torque between two axles (2AV, 2AR) of a motorized four-wheel drive vehicle (la, lb, lc, ld) mounted on the two axles, characterized in that the slip representing the difference in speed of the two axles (2AV, 2AR) is determined only when certain running conditions (C_roulage) are achieved during a configurable duration (MinTime), the control strategies of the coupler integrating the determined slip value .

Description

METHOD FOR CONTROLLING A COUPLER

The present invention relates, in a general manner, to four-wheel drive vehicles equipped with a system for controlling the distribution of the engine torque between a first axle and a second axle capable furthermore of controlling a mounted coupler. between the two axles. In these vehicles, the engine torque is distributed between the first axle and the second axle, the sum of the torque transmitted to the two axles being constant. The first axle is connected to a transfer shaft which is secured to the second axle by means of said coupler. Only the first axle permanently receives a torque, the second axle is more or less secured by the coupler controlled by the distribution control system. Thus, the torque level transmitted on each of the axles can be adjusted by the control system as a function, for example, of a vehicle operating mode. In a first mode of operation, the engine torque is fully transmitted to the first axle and no torque is transmitted to the second axle. In a second mode of operation, a first fixed portion of the engine torque is transmitted to the first axle and a second fixed portion of the engine torque is transmitted to the second axle. In a third mode of operation the couples transmitted to the two axles are constantly adjusted according to the driving conditions of the vehicle. In four-wheel drive vehicles can further occur a slip phenomenon. The slip corresponds to a difference in speed of rotation between the front and rear axles. Sliding can be a normal phenomenon, in the case for example of a change of speed. It may also be the consequence of a difference in rolling radius, in the case for example of a bad tire mounts or a puncture. The sliding is then permanent and it can lead to heating and / or deterioration of the coupler. Indeed, the coupler is a mechanical transmission system which may, as an exemplary embodiment, be composed of several oil-bathed discs secured to a shaft connected to the second axle and the others to the transfer shaft. In the case of normal operation, when there is a difference in speed between the transfer shaft and the shaft connected to the second axle, the discs shear the oil whose temperature increases and then expands and thickens . The pressure on the discs increases and they end up training each other. Thus, the speed difference between the two shafts decreases and the temperature of the oil and the coupler decreases. On the other hand, in the presence of a permanent slip, the discs continue to shear the oil which heats up until a possible deterioration of the coupler. Patent application JP4103433 discloses a control system of the torque distribution in a four-wheel drive vehicle. This system includes a torque distribution clutch, as well as slip detection means, vehicle speed and the difference in tire diameter of the four-wheel drive. The system makes it possible to reduce slippage by using the torque distribution clutch while taking into account, if necessary, a difference in tire diameter.

Patent application JP61275028 describes a system for increasing the maneuverability of a four-wheel drive vehicle whose wheels do not have exactly the same diameter. This system is equipped with front and rear wheel speed sensors, a front and rear wheel drive force distribution device, a subtraction system and a compensating device. It is thus possible to determine a rotation speed difference between the front and rear wheels taking into account a compensation factor relating to a difference in diameter. The ratio between the torque transmitted on the front and rear axle is then controlled from the difference in speed of rotation. These systems use a control of the distribution of the torque to reduce the slip but nothing is planned to protect the coupler effectively in the case of a permanent slip. They also do not allow to overcome slippage resulting from specific driving conditions. They do not propose a control system for the torque distribution integrated in the four-wheel drive management system which makes it possible to alert the user of the vehicle of permanent sliding of the coupler. One of the objects of the present invention is to detect a permanent slip and to discriminate it from a normal slip or slip related to specific rolling conditions. Permanent slip can be caused by improper riding, a difference in wheel diameter, a slow puncture, over or under inflation.

The invention aims in particular to take into account a permanent slip, when it exists, in the control strategies of a coupler for a motorized four-wheel drive vehicle. The present invention also relates to a torque distribution control method that is able to effectively protect the coupler in the case of permanent sliding and, in particular, to preserve the coupler of a heating due to permanent sliding. Another object of the present invention is to protect the coupler without unnecessarily stopping the operation of the "four-wheel drive" mode according to a compromise between the protection of the coupler and the availability of the optimum and adjustable "four-wheel drive" mode. Another object of the invention relates to a four-wheel drive vehicle equipped with a computer and a coupler controlled so that it is protected in the case of permanent sliding. According to another aspect of the invention, there is provided a slip warning method of a coupler capable of distributing a torque between two axles of a four-wheel drive motor vehicle mounted on the two axles. According to a general characteristic of this method, the slip representing the difference in speed of the two axles is determined only when certain driving conditions are achieved for a configurable duration.

According to another embodiment, which is also preferred, a counter is incremented at each occurrence of slip detected.

According to another implementation, an alert is sent to a user of the vehicle when the counter reaches a first configurable threshold MaxCounter. According to another implementation, it raises the alert when the counter becomes less than or equal to a second parameterizable threshold Mincounter. According to yet another implementation, it raises the alert when the counter is reset to the start of the vehicle. According to another implementation, it is tested whether the average value of the slip Gmoy during said configurable duration MinTime is greater than a third threshold MinWheelSlip and if the amplitude of the variation of the slip Gmax-Gmin during said configurable duration MinTime is less than a fourth threshold MaxDeltaSlip, the counter is incremented if the two tests are checked. Thus, it is not taken into account hazards causing a significant variation in slip; only the stabilized sliding linked to a problematic mechanical dimensioning such as a difference in rolling radius between the front and rear wheels is detected.

According to one implementation, it is tested whether the average value of the slip Gmoy during said configurable duration MinTime is less than a fifth threshold equal to said third threshold minus a constant MinWheelSlip-Constant, and the counter is decremented only when the average value of the slip is less than the fifth threshold and the magnitude of the slip variation Gmax-Gmin during said configurable duration MinTime is less than a fourth threshold. Thus, the decrementation is only triggered in the case where the slip is in a stabilized phase, below the value of the second threshold. This avoids a decrement related to a particular driving situation or the presence of measurement noise. In the case of an oscillating permanent sliding, a succession of incrementation and decrementation phases is avoided which would make the detection of oscillating sliding impossible.

According to yet another aspect of the method, a counter is incremented or decremented as a function of the determined slip and any transfer of torque towards one or other of the axles is eliminated when the average value of the sliding during said duration MinTime exceeds one threshold and when said counter 36 reaches a first threshold MaxCounter. According to another object, there is provided a motorized four-wheel drive vehicle mounted on two axles comprising a transfer shaft connected to the first axle and a controlled coupler capable of transferring a part of the torque from the transfer shaft to the second axle, means for determining the respective speeds of the two axles and a torque distribution control system capable of determining a slip value representing the difference in speed between the two axles and driving the coupler. According to a general characteristic of this embodiment, the torque distribution control system is configured to inform the user by warning according to the slip alert method of a coupler of the invention. The invention will be better understood on studying the detailed description of an embodiment taken by way of nonlimiting example and illustrated by the accompanying drawings in which: Figure 1 schematically shows a motorized four-wheel drive vehicle; Figure 2 schematically shows the main elements of the control system of the operation of the vehicle; Figure 3 schematically shows the main aspects of a software implanted in the vehicle computer and allowing the protection of the coupler. In Figure 1 are schematically illustrated the main elements of a Ve motorized four-wheel drive with a permanent transmission of the engine torque on the front axle 2AV. This type of vehicle was chosen as an example. The vehicle engine may be a heat engine 3, an electric motor or a hybrid combination. Permanent transmission of the engine torque could also be exerted on the 2AR rear axle. The vehicle comprises four wheels 1a, 1b, 1c, 1d respectively mounted on a front axle 2AV and a rear axle 2AR. The vehicle also comprises a steering wheel 4 connected to a steering column 5. The vehicle further comprises a gearbox 6 transmitting the torque of the engine 3 to the front axle 2AV and to a front transfer case 7. A transfer shaft 8, driven by the transfer box 7 is connected by a coupler 9 to a rear axle transfer box 10 so as to transfer torque from the gearbox 6 to the rear axle 2AR. The vehicle also comprises a computer 11 capable in particular of controlling the coupler 9, a mode control device 12 and a control unit 13 of the engine 3 capable of controlling the operation of the engine 3 (in particular for determining the torque exerted by the engine and to estimate the gear ratio engaged). The vehicle also includes four wheel speed sensors 14a, 14b, 14c, 14d, one on each of the wheels 1a, 1b, 1c, 1d. The computer 11 is connected to each of the wheel speed sensors 14a ... 14d by connections 16a ... 16d allowing the exchange of information. The computer 11 is also connected to the mode control device 12 via a connection 16e, to the motor control unit 13 via a connection 16f and to the coupler 9 via a connection 16g. The electrical connection 16g also allows the circulation of a control current to close the controlled coupler 9. A display unit of the instrument panel 15 is also connected by a connection 16h to the computer 11 in order to display the driver of the particular vehicle the mode of operation four-wheel drive used.

The four-wheel drive vehicle can, in fact, operate in three different types of operating mode. In a first mode of operation, the gearbox 6 drives the front axle 2AV, the coupler 9 is open and does not transfer any torque to the rear axle transfer box 10. This mode is called "4x2" mode, only the two wheels la and lb of the front axle being driven. In a second mode of operation, the gearbox 6 drives the front axle 2AV and the transfer shaft 8 drives the coupler 9 which is kept completely closed. The coupler 9 therefore drives the rear axle transfer box 10 so that a maximum portion of the engine torque is transferred to the rear axle 2AR. This mode is called "four wheel drive all terrain". In a third mode of operation, the gearbox 6 drives the front axle 2AV and the transfer shaft 8 drives the coupler 9 which is driven by the current of the computer 11 so as to be more or less closed depending on the torque requested by each axle. Thus a variable portion of the engine torque is transferred to the rear axle 2AR. This mode is called "automatic four-wheel drive".

The various operating modes depend on the state of the coupler 9. The closing of the controlled coupler 9 is controlled by the computer 11 via the connection 16g. Thus, the level of torque transmitted from the transfer shaft 8 to the transfer box of the rear axle 10 is controlled by the computer 11. For this purpose, the computer 11 receives information concerning: - the operation of the engine 3 by the motor control unit 13 via the link 16f; the will of the driver of the vehicle by the mode control device 12 which can be actuated by the driver. This information is transmitted to the computer 11 via the link 16e; and - the speed of rotation of the four wheels la ... ld determined by the four wheel speed sensors 14a ... 14d. This information is transmitted to the computer 11 via the four links 16a ... 16d.

Based on all this information, the computer 11 is able to choose the appropriate operating mode. The computer 11 is also capable of communicating to the driver of the vehicle information concerning the active mode of operation via the display unit of the control panel 15 and the link 16h.

In the case where the selected mode is the automatic mode, the computer 11 is able to determine the appropriate clamping to be applied to the coupler 9. The links 16a ... 16g to which reference has been made can, by way of exemplary embodiment. , be branches of a bus type CAN (Controller Area Network according to an Anglo-Saxon term well known to those skilled in the art). According to the invention, the computer 11 can further transmit according to the received information, a control signal to completely open the coupler 9 so as to avoid heating and or excessive wear of the coupler 9 in case of permanent slip. In Figure 2, are schematically illustrated the main elements of the control system of the operation of the vehicle. The elements already illustrated in FIG. 1 bear the same references. FIG. 2 shows the computer 11 connected by the connection 16g to the coupler 9 and the mode control device 12 connected to the computer 11; The connection bus 16 makes it possible to ensure the links between the computer 11, the control unit 13 of the engine 3 and the rest of the control and control elements of the vehicle represented in the form of a single block 20. among these members, for example, an ABS braking system and an AYC (Active Yaw Control) trajectory control system according to an Anglo-Saxon term well known to those skilled in the art). The computer 11 can receive from the block 20, information relating to the driving conditions: - information relating to the braking of the vehicle: ABS braking system, parking brake, brake pedal. - information relating to the operation of the AYC trajectory control system. The computer 11 can then for example send an opening control signal to the coupler via the electrical connection 16g as a function of the driving conditions, the will of the driver and the state of the coupler. FIG. 3 schematically illustrates in the form of a block the subfunctions of an opening decision software of the coupler 9. The program can be integrated in the computer 11.

In the illustrated example, a first processing block 31 receives variables relating to the operation of the vehicle as input. The processing block 31 notably receives: variables labeled ACF. They are related to the condition of the driving assistants and braking. The ACF variables may be transmitted by one or more brake management and driver assistance programs located for example in the computer 11. Among the ACF variables, there may be: a binary variable signaling the use of the ABS (Anti Blocking System); a binary variable signaling the use of the AYC trajectory control; a binary variable signaling the use of traction control (ASR Accelaration Slip Regulation according to an Anglo-Saxon term well known to those skilled in the art); a binary variable signaling the use of the regulation of the motor inertia torque (MSR MotorSchleppmomentRegler according to a German term well known to those skilled in the art); and a variable indicating the use of braking by the driver, whether by the pedal or by the parking brake (hand brake).

From the ACF variables, the processing block 31 determines whether at the same time no driving assistant (AYC, MSR, ASR), no braking assistance system (ABS) and no braking is active. If this is the case, it returns to a detection block 32 the binary value ACF OK with the value 1.

The processing unit 31 also receives variables V, G, Cm relating respectively to the speed of the vehicle, the slip between the two axles and the torque supplied by the engine to the two axles. The variables V and G are provided by the four wheel speed sensors 14a, 14b, 14c, 14d while the variable Cm is supplied by the control unit 13 of the engine 3. More precisely, the speed V of the vehicle Ve is estimated from the average speeds provided by the two rear wheel speed sensors 14c and 14d. The slip between the two axles is estimated from the difference between two speeds of rotation, that of the front axle 2AV and that of the rear axle 2AR. The speed of rotation of the front axle may, as an exemplary embodiment, be determined by averaging the speeds provided by the two front wheel sensors 14a, 14b. Similarly, the rotational speed of the rear axle can be determined by averaging the speeds provided by the two rear wheel sensors 14c and 14d. Finally, the engine torque Cm is estimated by the control unit 13 of the engine 3. The control unit 13 also returns an estimate of the gear ratio engaged. From the variables V and G, the processing block 31 calculates the slip expressed as a percentage with respect to the vehicle speed% G, it then transmits this value to a calculation block 33. From the variable Cm and from the estimation of the gear ratio engaged, the processing block 31 determines the torque exerted by the engine on the front axle Cm_AV, it then transmits this value to the detection block 32.

The processing block 31 also receives DISP variables relating to the availability and the validity of the input information, they are used for the detection of sensor faults or input information. Among the variables DISP, there are, for example, the following variables: a binary state variable of the determination of the motor torque; a bit state variable of the detection of the commitment of a speed; a binary state variable of the detection of the position of the accelerator pedal; a binary state variable of the detection of the ABS; a binary state variable of the detection of the trajectory control (AYC); - a binary state variable of the traction control detection (ASR); a binary state variable of the detection of the control of the motor inertia torque (MSR). The processing block 31 also determines whether the speed sensors 14a, 14b, 14c, 14d are in working order and whether the information they transmit is in working order. From these variables and information, processing block 31 determines whether all sensors are working and all required variables are available and valid. If necessary, it transmits to an activation block 35 a binary value, DISP_OK, relating to the availability of information. The detection block 32 receives, in addition to the variables transmitted by the processing block 31, ACF_OK and Cm_AV, variables V, POS and BV. The variable V corresponds to the variable V at the input of processing block 31. The variable POS is a decimal variable whose value expresses the position of the accelerator pedal. This information is, for example, provided by the control unit 13 of the engine 3. The variable BV is a binary variable which takes the value 1 if the gear ratio is indeed engaged in the gearbox 6. This information is, for example, provided by the control unit 13 of the engine 3. From the received variables, the detection block 32 is configured to detect whether the rolling conditions for calculating a permanent slip are satisfied. If the conditions are not satisfied then the calculation block 33 is not activated. This makes it possible to perform slip detection only when the driving conditions are satisfied. Thus, for the detection of permanent slip, normal slips are not taken into account due to particular circumstances such as: the passage of a gear ratio, the driving during a turn, the braking, the operation of a driving assistant, lifting the foot of the accelerator pedal, the vehicle in full acceleration.

If necessary, the detection block 32 transmits to the calculation block 33 a variable C_roulage equal to 1. In order for the detection block 32 to transmit a variable C_roulage, all the conditions below must be respected: - the variable ACF_OK is equal at 1, this prevents the calculation of permanent slip occurs in the case where the vehicle is braking or while a driving assistant or braking is active. the variable V is greater than a first threshold, which makes it possible to prevent the calculation of permanent slip from occurring in the case where the vehicle is in a turn. the variable Pos is greater than a second threshold: this makes it possible to avoid the calculation of permanent slip if the driver's foot lifts intervene. - The variable BV is equal to 1: this prevents the calculation of permanent slip occurs while the vehicle is changing speed. the variable Cm_AV is less than a third threshold: this makes it possible to prevent the calculation of permanent slip from occurring while the vehicle is in full acceleration. The three thresholds to which reference is made are configurable. This makes it possible to adapt the conditions for the detection of a permanent slip according to the driving of the driver or of the rolling ground. For example, the minimum speed from which slip detection is provided can be escalated in the case of sporty driving.

The activation block 35 receives, in addition to the variable DISP_OK, a security variable Sec and a commissioning variable ON. The variable Sec is binary, it is 1 if no fault from other computers or programs is detected. The variable ON is also binary it is 1 if the permanent slip alert function is activated. On the basis of this information, the activation block 35 returns to the calculation block 33 an activation variable State 35. This variable is equal to 1 if the variables DISP_OK, Sec and ON have the value 1. As an option, the block of Activation 35 may receive a value from the mode controller 12. Where appropriate, it returns a state value equal to 1 only when the automatic four-wheel drive mode is selected by the driver of the vehicle. The calculation block 33 receives, in addition to the variables C_roulage,% G and state 35, a variable V. The variable V corresponds to the speed V at the input of the processing block 31. From the variable% G and the speed V , the calculation block 33 calculates speed variables Vmin, Vmax, Vmoy and slip Gmin, Gmax, Gmoy of the vehicle. The values Gmin, Gmax, Gmoy respectively correspond to the minimum, maximum and average slip value during a configurable duration MinTime. The values Vmin, Vmax, Vmoy correspond to the minimum, maximum and average vehicle speeds during the MinTime time, respectively. These calculations are performed by the calculation block 33 only when the binary values C_roulage and state 35 are equal to 1.

The calculation block 33 also calculates a binary value Fav relating to the fulfillment of the required conditions. The value of Fav goes to 1 if the rolling conditions C_roulage are checked during the MinTime time. The calculation block 33 also calculates a binary value State 33 on 2 bits corresponding to the state on a flow diagram of the sub-function of the calculation block 33. The subfunction of the block 33 can indeed be represented in the form of a 4-state diagram: - state -1 corresponds to the default state of block 33. - state 0 corresponds to an initialization state. The speed and slip variables to be calculated are initialized to 0. - State 1 is active as soon as the binary variable C_roulage goes to 1, and is inactive as soon as it returns to O. As long as C_roulage remains equal to 1 , velocity and slip variables are calculated. - State 2 is active if the value C_roulage is equal 1 for a configurable minimum duration, the binary variable Fav then changes from 0 to 1. It is at the moment of activation of this state 2 that are sent the speed and slip variables as well as the variable Fav towards a counting block 34. The counting block 34 filters these variables to control if necessary the triggering of a permanent slip alert via the binary variable Alert. When the Alert variable goes to 1, the permanent slip alert is triggered. It is this alert which triggers the opening of the controlled coupler 9 by the computer 11 via the connection 16g. More specifically, the counting block 34 performs both the permanent slip detection, the counting of the occurrences of permanent slip, and the generation of the alert. For this, the counting block 34 cooperates with a counter 36. The counter 36 is controlled by the counting block 34 to be incremented (plus) at each occurrence of permanent slip detected. When counter 36 reaches a configurable threshold MaxCounter, the value of the variable Alert goes to 1.

The incrementation (plus) occurs when the variable Fav is equal to 1, the amplitude of the slip variation (Gmax-Gmin) during a MinTime duration is less than another configurable threshold (MaxDeltaSlip) and that during the MinTime time the average Gmoy slip is greater than a configurable MinWheelSlip threshold value. The counter can also be decremented (minus) when the variable Fav is equal to 1, the amplitude of the slip variation (Gmax-Gmin) is less than MaxDeltaSlip during the MinTime duration and the average slip is less than a threshold equal to said second threshold minus a constant MinWheelSlip- Constant. The constant (Constant) can advantageously be chosen with a value relating to the hysteresis (WheelSlipHyst). The permanent slip alert is raised when the Alert variable goes to 0. This variable goes to 0 when the counter 36 goes to a value less than or equal to a configurable threshold MinCounter. This passage can take place after a sufficient number of successive decrements or when the counter 36 undergoes a forced reset by a particular event related to the use of the vehicle. One can make sure to reset the counter 36 at each start (or alternatively at each stop) of the vehicle, so that the user is not interrupted from the start by an alert message on the dashboard following the passage the Alert variable at 1 or the coupler is not forced into an open state at each startup. Indeed, the user was able to perform an intervention to correct (tire changing, puncture repair etc ...) permanent slip before restarting it. For this purpose, the counting block 34 receives as input (or directly the counter 36 with which it cooperates), an Ignit variable passing to 1 when the vehicle start event is detected. The presence of such a permanent slip alert provides a detection system that is both robust and responsive, and provides information to the user with a reduced degree of intrusion. The ability to adjust the counter size, the slip averaging time, the maximum allowed slip value and the hysteresis - all parameterizable - allow a very precise focus of the warning strategy of the while ensuring high durability and coupler protection.

The block 37 for estimating an offset value estimates a permanent slip value over time, in order to carry out a correction of the slip value used in the control strategies of the coupler.

The block 37 for estimating an offset value receives, on a first input, a variable representing the average slip Gmoy during the configurable duration MinTime as calculated by the calculation block 33.

The block 37 also receives on a second input, the variable D taking the value of the output of a logical OR gate whose inputs are respectively a variable Rev_Calc representing the waking state of the computer and the variable Fav emitted by the block The operations for estimating the offset value are conditioned by the value taken by this variable D so that the operations performed by the block 37 are performed when the variable D takes the value 1. The block 37 comprises in in addition to storage means forming a buffer whose size is parameterizable according to the value taken by a variable T_B. The buffer memory receives average slip values Gmoy, since the variable D is equal to 1, and the amplitude of the variation between two immediately consecutive values of average slip Gmoy is less than a parameterizable threshold (MaxDeltaGmoySlip).

When the number of values stored in the buffer reaches a configurable threshold MaxCounterGmoySlip, then an arithmetic mean of these stored average Gmoy slip values is computed. The result of this calculation is then sent on the output G_Offset to communicate the offset value of the permanent slip. Advantageously, one can not directly report the result of the calculation on the output GOffset, and limit the variations between the current value present on the GOffset output and the new calculated value. In the case where the difference between the new calculated value and the current value is greater than a configurable threshold MaxGOffsetVar, then the value applied on the output GOffset is equal to the current value plus the threshold value MaxGOffsetVar. In the case where the difference between the new calculated value and the current value is less than a configurable threshold MaxGOffsetVar then the value applied to the output GOffset is equal to the new calculated value. This results in a filtering of the offset values of the permanent slip G_Offset, making it possible to limit the changes in vehicle behavior produced and / or any jolts at the coupler (due to disturbances of the coupler control loops). In addition, the smoothing makes it possible to increase the parameterizable threshold MaxCounterGmoySlip of the stored values, without however increasing the variations of the values applied on the output G_Offset.

The output G_Offset only takes values representative of the slip offset G_Offset only when the output activation variable SActivate takes the value 1. This is particularly useful in the case of fault finding, but also when one wishes inhibit the function.

In addition, when a vehicle stop event (engine included) is detected, for example by setting the Ignit variable to a value of 0, the offset value of the permanent slip is stored in a non-volatile memory accessed by the calculator 11. Thus, the saved offset value is immediately resumed and applied to the output G_Offset the next time the vehicle is started, well before the vehicle moves and the block 37 calculates a new value. This improves the overall responsiveness of the system, especially when the filtering of the variation of the offset value is operational.

The invention as described allows efficient coupler protection without consuming a lot of memory resources or generating unnecessary 4x4 operation interruptions. The invention for detecting permanent slip can also be applied to the revelation of a problem that creates such a permanent slip. Thus, it is possible to detect tire wear, improper inflation pressure, or excessive load of the vehicle. The values of the thresholds which trigger favorable driving conditions are parameterizable, it is therefore possible to privilege the non-interruption of the four-wheel drive mode on the protection of the coupler or to do the opposite. For example, one can in the calculation block 33 lower the minimum speed or increase the configurable time MinTime to promote the protection of the coupler. It is thus possible to adjust the compromise protection of the coupler / availability of the four-wheel drive mode.

In addition according to the invention, a dual objective of information and protection of the coupler is achieved. Indeed, on the one hand the user can be warned of the presence of abnormal slip by an alert signal on the one hand, to encourage him to remedy the problem detected and on the other hand, when the Abnormal slip remains in a range of values that does not affect the reliability of the coupler in the short term, to take into account this abnormal slip tolerable "in order to correct the control strategies of the coupler.

Claims (8)

REVENDICATIONS1. A method of controlling a coupler (9) capable of distributing a torque between two axles (2AV, 2AR) of a motorized four-wheel drive vehicle (la, lb, lc, ld) mounted on the two axles, characterized in that the slip representing the difference in speed of the two axles (2AV, 2AR) is determined only when certain rolling conditions (C-rolling) are achieved for a configurable duration (MinTime), and in that the control strategies of the coupler integrate the slip value determined. 2. A method of controlling a coupler according to the preceding claim characterized in that the slip value taken into account in the control strategies of the coupler is a mean Gmoy of the values of the slip during the parameterizable time (MinTime). 3. A method of controlling a coupler according to the preceding claim, characterized in that the average slip values Gmoy are stored in a parameterizable buffer. 4. A method of controlling a coupler according to the preceding claim, characterized in that the storage is performed only if the amplitude of the variation between two immediately consecutive values of average slip Gmoy is less than a parameterizable threshold (MaxDeltaGmoySlip) . 5. A method of controlling a coupler according to the preceding claim, characterized in that an arithmetic average of the average slip values Gmoy stored is calculated when the number of values stored in the buffer reaches a configurable threshold MaxCounterGmoySlip, this average representing the offset value of the permanent slip 6. A method of controlling a coupler according to the preceding claim, characterized in that a filtering of the offset values of the permanent slip by limiting the difference between two successive values to a threshold value MaxGOffsetVar. 7. The method of controlling a coupler for a vehicle according to claim 1 wherein a counter (36) is incremented or decremented according to the determined slip and in that it suppresses any transfer of torque to one or the other. other axles when the average value of the slip during said duration (MinTime) exceeds a threshold and when said counter (36) reaches a first threshold (MaxCounter). 8. Motor vehicle (Ve) with four driving wheels (la, lb, lc, ld) mounted on two axles (2AV, 2AR) comprising a transfer shaft (8) connected to the first axle and a controlled coupler (9) capable of transferring a part of the torque from the transfer shaft (8) to the second axle, means for determining the respective speeds of the two axles and a torque distribution control system (11) capable of determining a slip value representing the difference in speed between the two axles and to control the coupler, characterized in that the torque distribution control system (11) is configured to take into account a permanent sliding between the axles (2AV, 2AR) according to a control method of the coupler (9) according to one of the preceding claims.