FR3053938A1 - METHOD FOR CONTROLLING A REVERSE MOTOR VEHICLE RUNNING - Google Patents

Abstract

The invention relates to a driving method of a motor vehicle comprising wheels, an electric motor coupled to the wheels and a wheel braking system, comprising the steps of: - acquisition of the speed (V1) of the motor vehicle; acquiring the position of a gear lever fitted to the motor vehicle; acquiring an acceleration instruction relating to the position of or the force exerted on an accelerator pedal fitted to the motor vehicle; and - developing an electric motor control setpoint as a function of the position of the speed lever and the acceleration instruction. According to the invention, if the acquired speed is lower than a first threshold (S1) negative and the gear lever is in the forward position, it is expected to develop a control set of the braking system based at least the acceleration instruction.

Description

Technical field to which the invention relates

The present invention relates generally to electric or hybrid motor vehicles.

It applies to any motor vehicle comprising wheels, an electric motor coupled to the wheels, a wheel braking system separate from said electric motor, a gear lever and an accelerator pedal.

It relates more particularly to a method for driving such a vehicle, comprising steps:

- acquisition of the speed of the motor vehicle, which is positive when the motor vehicle is advancing and negative when the motor vehicle is reversing,

- acquisition of the position of the gear lever,

- acquisition of an acceleration instruction relating to the position of (or the force exerted on) the accelerator pedal, and

- developing an electric motor control instruction based on the position of the gear lever and the acceleration instruction.

It also relates to a motor vehicle as mentioned above, further comprising an electronic control unit which is capable of implementing this method.

Technological background

When the motor vehicle is on a hill, it may happen that the driver wishes to let his vehicle back while taking advantage of the slope, without shifting into reverse. This is particularly the case when the vehicle is parked in a parking space from which the driver wishes to exit easily, while remaining in forward gear ("D" mode on an automatic gearbox).

In this situation, the driver's intuitive reflex is then to control the vehicle's reversing speed by means of the electric motor, using only the accelerator pedal (i.e. without using the brake pedal).

However, it has been noted that the braking torque generated by the electric motor can sometimes prove to be insufficient, not allowing the vehicle to slow down as much as the driver wishes. We understand that this situation must absolutely be avoided because it is dangerous, surprising and not intuitive for the driver.

For this, we know from document US20130197733 a strategy for detecting a reversing situation of the electric vehicle not desired by the driver, which is based on the analysis of the state of the vehicle, the position of the brake pedals and of accelerator, handbrake, and physical limitations of the electric motor. In the event that an inadvertent backing up of the electric vehicle is detected, the engine torque is then controlled to stop the vehicle before the backing up speed is too great.

This solution, although it makes it possible to prevent any accident, is binding on the driver who no longer has the option of voluntarily letting his vehicle back down the slope in the conditions he wishes.

Object of the invention

In order to overcome the aforementioned drawback of the prior art, the present invention proposes an innovative strategy for controlling the electric motor and the vehicle braking system when the latter is in the aforementioned situation, which allows the driver drive your vehicle comfortably and intuitively using the single accelerator pedal.

More particularly, a method as defined in the introduction is proposed according to the invention, in which, if the speed acquired is less than a first negative threshold and the gear lever is in the forward position, a control instruction of the braking system is developed based on the acceleration instruction.

The Applicant has found that in the aforementioned situation (when the vehicle is reversing on a hill while taking advantage of the slope), the electric motor is not able to brake the vehicle in particular if the traction battery (the one to which the electric motor) is very charged.

The explanation for this phenomenon is as follows. When the vehicle is reversing (and its speed is therefore negative), the vehicle's electric motor must operate in generator mode to brake the vehicle. In this situation, when the traction battery is charged, the braking torque that the electric motor is capable of exerting is limited by the algorithms for monitoring the traction battery. Indeed, overcharging the battery could damage it permanently. Therefore in a situation that the driver intuitively considers favorable because his traction battery is well charged, the risk of braking deficiency is actually greater than when the traction battery is discharged.

Furthermore, in generator mode, the braking torque that the electric motor is capable of exerting is inversely proportional to the speed of rotation of the engine and therefore to the speed of the vehicle's reversing. Consequently, the faster the vehicle reverses, the less its engine is able to provide the necessary braking torque.

This is the reason why the present invention proposes, when the vehicle is reversing on a hill taking advantage of the slope effect, to control the vehicle's reversing speed by using the brakes, even when the driver is not using the brake pedal.

Other advantageous and non-limiting characteristics of the piloting method according to the invention are as follows:

- if the speed acquired is less than the first threshold and the gear lever is in the forward position, the electric motor and the braking system are controlled in combination in the active state;

- as soon as the speed acquired becomes again above a second threshold, greater than or equal to the first threshold, and the gear lever is in the forward position, the electric motor is controlled in the active state and the braking system is controlled in the inactive state;

- if the speed acquired becomes less than a third negative threshold and less than the first threshold and the gear lever is in the forward position, the electric motor is controlled in an inactive state and the braking system is controlled in the state active;

- if the speed acquired, after having been lower than the third threshold, becomes again greater than a fourth threshold, greater than or equal to the third threshold, and the gear lever is in the forward position, the electric motor and the braking system are piloted in combination in the active state;

- if the speed acquired, after having been lower than the third threshold then greater than the fourth threshold, becomes greater than a fifth threshold, greater than or equal to the fourth threshold, and the gear lever is in the forward position, the electric motor is controlled in the active state and the braking system is controlled in the inactive state;

- if the speed acquired, after having been lower than the third threshold then greater than the fourth threshold, becomes less than a sixth threshold, less than or equal to the fourth threshold, and the gear lever is in the forward position, the electric motor is controlled in the inactive state and the braking system is controlled in the active state;

- when the electric motor and the braking system are controlled in combination in the active state, the proportion of the braking torque exerted by the electric motor compared to the braking torque exerted by the braking system varies according to the speed acquired ; and

- the control instructions for the electric motor and the braking system are drawn up so that the braking torque exerted on the wheels varies continuously.

The invention also relates to a motor vehicle comprising wheels, an electric motor coupled to the wheels, a wheel braking system, and a control unit for the electric motor and the braking system which is adapted to implement a driving method. as mentioned above.

Detailed description of an exemplary embodiment

The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be carried out.

In the accompanying drawings:

- Figure 1 is a graph illustrating the conditions for switching between different modes for calculating driving instructions for a motor vehicle;

- Figure 2 shows different blocks corresponding to algorithms for calculating the driving instructions of the motor vehicle; and

- Figures 3 to 7 are graphs illustrating the variations of parameters useful for calculating the driving instructions of the motor vehicle.

The present invention applies to any electric or hybrid motor vehicle.

Conventionally, such a vehicle comprises a chassis which is supported by wheels and which in particular supports an electric motor coupled to the drive wheels, a wheel braking system, brake and accelerator pedals, a gearbox and a computer.

We will consider here that the gearbox is automatic. It therefore includes a gear lever which can, for example, take various positions commonly referred to as “D” for forward gear (“Drive”), “R” for reverse gear, “N” for neutral position and “P »For the stop on a parking space.

It will also be considered here that the electric motor can be used in generator mode, in order to recover the kinetic energy of braking of the motor vehicle and to transform it into electric current. We will consider in the following of this presentation only the case where the engine is used in this generator mode.

To control the electric motor and the braking system, the computer includes a processor (CPU), a random access memory (RAM), a read only memory (ROM), analog-digital converters (A / D), and various interfaces of entry and exit.

Thanks to its input interfaces, the computer is adapted to receive input signals from various sensors fitted to the motor vehicle. It can thus receive, digitally:

- the speed V1 of the motor vehicle, measured for example by a speed sensor located on one of the axles of the vehicle,

- the position P, R, N or D of the gear lever, measured for example by a position sensor located on the gear lever,

- a lace acceleration instruction, which relates to the position of the accelerator pedal or to the force exerted on it (here, we will consider that this instruction is expressed as a percentage of depression of the pedal d accelerator, and

- a braking instruction, which relates to the position of the brake pedal or the force exerted on it.

The ROM stores data used in the process described below, in particular speed thresholds which will be explained in the following description. The data stored in the ROM will be described in the following description as "predetermined", in the sense that they will be determined during the design of the vehicle.

The read only memory also stores a computer application, consisting of computer programs comprising instructions whose execution by the processor allows the implementation by the computer of the method described below.

The read-only memory stores in particular a computer program which makes it possible to calculate, in a manner well known to those skilled in the art:

a conventional command setpoint Cmot_class of the electric motor, which is in practice a setpoint of engine torque determined as a function of the lace acceleration instruction, and

- a classic Cfrein_class control instruction for the braking system, which is in practice a hydraulic braking instruction determined according to the braking instruction.

Since the manner of determining these two instructions is well known to those skilled in the art, this computer program will not be described here.

Finally, thanks to its output interfaces, the controller is adapted to transmit these output signals to the various organs of the vehicle, in particular to the electric motor and to the braking system.

The present invention proposes to correct the two aforementioned piloting instructions in the case where the vehicle reverses on a hill while taking advantage of the slope of this hill.

Indeed, in this case, the use of the accelerator pedal alone to brake the vehicle and then make it go up the slope may not be sufficient.

The present invention therefore proposes to use the braking system in combination with the electric motor in order to reduce the speed of recoil of the motor vehicle when it reverses on the hill and the driver uses only the accelerator pedal.

More specifically, according to a particularly advantageous characteristic of the invention, if the speed V1 of the vehicle is less than a first negative threshold S1 (which means that the vehicle is reversing) and the gear lever is in position "D", it It is planned to develop control instructions Cmot, C brake for the electric motor and the braking system according to the acceleration instruction îacc.

In the following description, we will always consider that the gear lever is in position "D". The invention will in fact not apply in the case where the gear lever is in the R, N or P position.

To fully understand the invention in its entirety, we can first of all refer to FIG. 1 which illustrates that the computer can operate according to one or the other of four modes in order to calculate the control instructions Cmot, Cfrein electric motor and braking system.

Mode "0" is the mode which is most often encountered and which corresponds to the case where the vehicle is traveling in forward or is stopped or backing up at a reduced speed (greater than the first threshold S1, of which it is recalled that it is negative).

In this mode 0, only the control setpoint Cmot of the electric motor varies depending on the position of the accelerator pedal (the braking system is said to be in the inactive state).

Mode "1" corresponds to the case where the vehicle is traveling in reverse and accelerates until reaching a speed lower than the first threshold S1.

In this mode 1, the control instructions Cmot, C brake of the electric motor and of the braking system are both calculated as a function of the position of the accelerator pedal. Thus, the electric motor and the brakes are used in combination to slow down the motor vehicle (it is said that they are both active).

The computer is designed to exit from this mode 1 in two cases.

The first case is that where the vehicle slowing down, the speed V1 of the vehicle becomes greater than a second threshold S2 (which can be chosen greater than or equal to the first threshold S1). In this case, the computer returns to mode 0.

The second case is that where the vehicle accelerating, the speed V1 becomes less than a third threshold S3 (negative and less than the first threshold S1). In this case, the computer goes into a "2" mode.

In this mode 2, the control setpoint Cmot of the electric motor is chosen to be equal to zero. In other words, only the brakes are used to slow down the motor vehicle (the electric motor is said to be in the inactive state).

The computer is designed to exit from this mode 2 when the vehicle reversing speed decreases, so that the vehicle speed V1 becomes greater than a fourth threshold S4 (which must be chosen greater than or equal to the third threshold S3). In this case, the computer goes into mode "3".

In this mode 3, the control instructions Cmot, C brake of the electric motor and of the braking system are both calculated as a function of the position of the accelerator pedal. Thus, the electric motor and the brakes are used in combination to slow down the motor vehicle (it is said that they are both active).

The computer is designed to exit from this mode 3 in two cases.

The first case is that where the vehicle recoil speed continues to decrease, so that the speed V1 becomes greater than a fifth threshold S5 (which must be chosen greater than or equal to the fourth threshold S4). In this case, the computer returns to mode 0.

The second case is that where the vehicle recoil speed increases, so that the vehicle speed V1 becomes less than a sixth threshold S6 (which is chosen to be less than or equal to the fourth threshold S4). In this case, the computer returns to mode 2.

In these four modes, the control setpoints Cmot, Cfrein of the electric motor and of the braking system are developed so that the braking torque exerted in combination by the electric motor and by the braking system on the wheels varies continuously, especially when switching from one to the other of the modes.

Furthermore, here, in modes 1 and 3, provision is made to vary the proportion of the braking torque exerted by the electric motor relative to the braking torque exerted by the braking system, as a function of the speed V1 acquired. In this way, it will be possible to progressively move from a conventional preparation of the driving instructions to an improved preparation in which the electric motor and the brakes are used in combination to slow the vehicle backing down.

All speed thresholds are predetermined. In the embodiment described here, it will be considered that:

- the thresholds S1 and S2 are equal (they will be referenced S1),

- the thresholds S4 and 86 are equal (they will be referenced S4),

the threshold 83 is equal to the difference between the first threshold S1 and a predetermined difference, according to the formula: S3 = S1 -Δ813,

- threshold 85 is equal to the sum of fourth threshold 84 and another predetermined difference, according to the formula: S5 = S4 + Δ814.

We can now explain in detail the manner in which the invention can be implemented, considering Figure 2.

In this figure, five blocks B1, B2, B3, B4 and B5 have been represented, which correspond to five algorithms which allow the computer to determine the control instructions Cfrein, Omet of the electric motor and of the braking system.

To the left of each block are the input parameters. The output parameters are shown to the right of each block. Above each block are represented the conditional parameters, that is to say the parameters which allow the computer to know whether or not to implement the corresponding algorithm.

These five algorithms together form a computer program that includes 5 inputs (referenced by * in Figure 2) and two outputs (referenced by #).

The five inputs are the speed V1 of the motor vehicle, the PRND position of the gear lever, the lace acceleration instruction, the classic control instruction Cmot_class of the electric motor, and the classic control instruction Cfrein_class of the braking system.

The two outputs are the Cfrein, Cmot control instructions for the electric motor and the braking system.

The first block B1 has the function of determining in which mode (0, 1, 2 or 3 in FIG. 1) the computer must be placed to calculate the control instructions Cfrein, Cmot of the electric motor and of the braking system.

As input, this first block B1 uses the speed V1 of the motor vehicle and the position PRND of the gear lever.

At the output, this first block B1 produces a signal indicating the mode M1 (0,

1,2 or 3) in which the computer must be placed.

The value assigned to mode M1 is chosen as follows.

At the time step considered (t), the value 1 is assigned to mode M1 if the following conditions are met:

- the position of the gear lever is "D",

- the mode M1 was equal to 0 or 1 at the previous time step (t-1), and

- the speed V1 satisfies the following relation:

S1-AS13 <V1 <S1.

The value 2 is assigned to mode M1 if the following conditions are met:

- the position of the gear lever is "D",

- the mode M1 was equal to 0 or 1 at the previous time step (t-1), and

- the speed V1 satisfies the following relation:

V1 <Sf -Δ813.

The value 2 is also assigned to mode M1 if the following conditions are met:

- the position of the gear lever is "D",

- the mode M1 was equal to 2 at the previous time step (t-1), and

- the speed V1 satisfies the following relation:

V1 <S4.

The value 3 is assigned to mode M1 if the following conditions are met:

- the position of the gear lever is "D",

- the mode M1 was equal to 2 or 3 at the previous time step (t-1), and

- the speed V1 satisfies the following relation:

S4 <V1 <S4 + AS14.

Otherwise, the value 0 is assigned to mode M1.

The second block B2 has the function of determining the steering instruction which should be applied to the braking system if only the latter was used to brake the motor vehicle.

As input, this second block B2 uses the speed V1 of the motor vehicle, the mode M1, and the lace acceleration instruction.

At the output, this second block B2 produces a signal Cfrein_seul.

If the mode M1 is equal to 0, this block B2 remains inactive, so that this algorithm will not be implemented.

Otherwise, the signal Cfrein_seul is obtained by means of the following equation:

Cfrein_seul = min [Cfrein_max, Cfrein_acc Coef_frein_vit].

In this equation, the parameter Cfrein_max, which is expressed in Nm, is predetermined. It represents the maximum braking torque that the braking system can exert.

The Cfrein_acc and Coef_frein_vit parameters are obtained in the following way.

First of all, the parameter Cfrein_acc, it is calculated using the following relationships:

* If the lace acceleration instruction is greater than or equal to a predetermined threshold Sacc, then:

Cfrein_acc = Cfrein_laccmax + ((Cfrein_Sacc-Cfrein_laccmax) (lacc100)) / ((Sacc-100)) • Otherwise:

Cfrein_acc = Cfrein_ Sacc + ((Cfrein_laccmin-Cfrein_ Sacc) (lace-Sacc)) / (Sacc)

In these two equations, the parameters used are defined as follows:

- Sacc is an adjustment parameter which is expressed as a percentage and which represents the threshold for depressing the accelerator pedal above which the braking torque control is changed.

- Cfrein_laccmax is a positive adjustment parameter which is expressed as a percentage and which represents the braking torque setpoint corresponding to maximum depressing of the accelerator pedal.

- Cfrein_Sacc is a positive or zero adjustment parameter which is expressed in Nm and which represents the braking torque setpoint corresponding to depressing the accelerator pedal equal to the Sacc threshold.

- Cfreinjaccmin is a positive or zero adjustment parameter which is expressed in Nm and which represents the braking torque setpoint corresponding to a zero depressing of the accelerator pedal.

FIG. 3 illustrates the adjustment parameters mentioned. It is observed that beyond the depressing threshold of the accelerator pedal Sacc, the derivative of the braking torque setpoint as a function of depressing the pedal increases. This allows you to quickly ascend the slope when the driver presses "hard" on the accelerator pedal.

Now being the Coef_frein_vit parameter, it increases the "reactivity" of the braking in response to pressing the accelerator pedal when the vehicle's reversing speed becomes very high.

This Coef_frein_vit parameter is obtained according to the following equation: Coef_frein_vit = min [Coef_max, max (1, Coef_frein_vit_non_sat)], with

Coef_frein_vit_non_sat = 1 + ((Coefjnax-1) (V1-Svit_ 1)) / (Svit_coef_max-Svit_ 1 day

In this equation, the parameters used are defined as follows:

- Coef_max is a setting parameter greater than or equal to 1 which represents the maximum value that the Coef_frein_vit signal can reach.

- Svit_1 is a negative adjustment parameter which is expressed in km / h and which represents the reversing speed threshold below which the Coef_frein_vit signal begins to increase.

- Svit_coef_max is a negative setting parameter which is expressed in km / h and which represents the reversing speed for which the signal Coef_frein_vit reaches its maximum value Coef_max. For recoil speed values below this threshold, the Coef_frein_vit signal no longer increases and remains equal to the Coef_max value.

FIG. 4 illustrates the variations of the adjustment parameter Coef_frein_vit as a function of the speed V1 of the vehicle, as well as the aforementioned adjustment parameters. It is observed that the Coef_frein_vit adjustment parameter makes it possible to increase the "reactivity" of braking in response to a press on the accelerator pedal when the vehicle reversing speed is high.

The third block B3 has the function of determining the instructions according to which the electric motor and the braking system should be controlled if the mode M1 was equal to 1.

At the input, this third block B3 uses the speed V1 of the motor vehicle, the mode M1, the conventional command setpoint Cmot_class of the electric motor, and the signal Cfrein_seul.

At the output, this third block B3 produces two signals:

the setpoint in mode 1 of driving Cmot_1 of the electric motor, which is a setpoint of engine torque, expressed in Nm, to be exerted at the wheels of the vehicle, and

- the setpoint in mode 1 of driving Cfrein_1 of the braking system, which is a setpoint of the hydraulic brake torque, expressed in Nm, to be exerted at the wheels of the vehicle.

As long as the mode M1 is different from 1, this third block B3 remains inactive.

Otherwise, the setpoints sought are obtained using the following equations:

Cmot_1 = (1-a) Ctot_1 Cfreir> _1 = a- Ctot_1

In these two equations, the parameter Ctot_1 used is obtained by means of the following equation:

Ctot_1 = (1-a) Cmot_class R1 η1 + a Cfrein_seul, with:

- R1 which corresponds to the gear ratio of the gearbox or the reduction gear,

- η 1 which corresponds to the efficiency of the gearbox or the reduction gear, and

- has a setting parameter here obtained by means of the following equation:

a (t) = max [0; min (1; (S1 - V1) / AS13)]

In FIG. 5, the variations of this adjustment parameter a have been illustrated as a function of the speed V1 of the vehicle.

It is this parameter which will manage the proportion between the braking torque exerted by the electric motor and that exerted by the braking system (in mode 1).

Because this adjustment parameter a is equal to 0 when the speed V1 is equal to the threshold S1, the transition between mode 0 and mode 1 will be made continuously.

Because this adjustment parameter a is equal to 1 when the speed V1 is equal to the difference between the threshold S1 and the difference AS13, the transition between mode 1 and mode 2 will also be made continuously.

Between these two speed thresholds (S1 and S1-AS13), the component of the braking torque exerted by the electric motor relative to that exerted by the braking system will therefore vary in an affine manner, as a function of the speed V1 of the vehicle.

The function of the fourth block B4 is to determine the instructions according to which the electric motor and the braking system should be controlled if the mode M1 was equal to 3.

At the input, this fourth block B4 uses the speed V1 of the motor vehicle, the mode M1, the conventional command setpoint Cmot_class of the electric motor and the signal Cfrein_seul.

At the output, this fourth block B4 produces two signals:

the setpoint in mode 3 of driving Cmot_3 of the electric motor, which is a setpoint of engine torque, expressed in Nm, to be exerted at the wheels of the vehicle, and

- the setpoint in mode 3 of driving Cfrein_3 of the braking system, which is a setpoint of the hydraulic brake torque, expressed in Nm, to be exerted at the wheels of the vehicle.

As long as the mode M1 is different from 3, this fourth block B4 remains inactive.

Otherwise, the setpoints sought are obtained using the following equations:

Cmot_3 = (1-β) Ctot_3 Cfrein_3 = β Ctot_3

In these two equations, the parameter Ctot_3 used is obtained by means of the following equation:

Ctot_3 = (1-β) Cmot_class R1 η1 + β Cfrein_seul

The parameter β a setting parameter obtained here by means of the following equation:

β (ί) = max [0; min (1; 1 + (S4-V1) / AS14)]

In FIG. 6, the variations of this adjustment parameter β have been illustrated as a function of the speed V1 of the vehicle. It is this parameter which will therefore manage the proportion between the braking torque exerted by the electric motor and that exerted by the braking system in mode 3.

Because this adjustment parameter β is equal to 1 when the speed V1 is equal to the threshold S4, the transition between mode 2 and mode 3 will be made continuously.

Because this adjustment parameter β is equal to 0 when the speed V1 is equal to the sum of the threshold S4 and the difference AS14, the transition between mode 0 and mode 3 will be made continuously.

Between these two speed thresholds (S4 and S4 + AS14), the component of the braking torque exerted by the electric motor with respect to that exerted by the braking system will therefore vary in a refined manner, depending on the speed V1 of the vehicle.

The function of the fifth block B5 is to determine the control setpoints Cfrein, Cmot for the electric motor and the braking system.

As input, this fifth block B5 uses:

- M1 mode,

- the classic control setpoint Cmot_class of the electric motor,

- the classic Cfrein_class control setpoint for the braking system,

- the signal Cfrein_seul,

- the setpoint in mode 1 of control Cmot_1 of the electric motor,

- the setpoint in mode 1 of control Cfrein_1 of the braking system,

- the setpoint in mode 3 of control Cmot_3 of the electric motor, and

- the setpoint in mode 3 of control Cfrein_3 of the braking system.

At the output, this fifth block B5 produces the two control instructions Cfrein, Cmot.

The braking control command Cfrein for the braking system is obtained by means of the following equation:

Cfrein = Cfrein_class + Cfrein_M1

Otherwise formulated, the braking system control setpoint is obtained by summing the "classic" braking torque setpoint (from the interpretation of the position of the brake pedal) and a signal Cfrein_M1.

This signal is defined as follows:

Cfrein_M1 = Cfrein_seul if the mode M1 is equal to 2,

Cfrein_M1 = Cfrein_1 if the mode M1 is equal to 1,

Cfrein_M1 = Cfrein_3 if the mode M1 is equal to 3,

Cfrein_M1 = 0 if the M1 mode is equal to 0.

The electric motor control setpoint Cmot is defined as follows:

Cmot = 0 if the mode M1 is equal to 2,

Cmot = Cmot_1 / (R1 - / 77) if the M1 mode is equal to 1,

Cmot = Cmot_3 / (R1 η1) if the mode M1 is equal to 3,

Cmot = Cmot_class if the M1 mode is equal to 0

Thus defined, the two instructions allow, when the vehicle is reversing on a hill taking advantage of the slope, to control the braking and then the acceleration towards the front of the vehicle, smoothly.

The invention is not limited to the embodiment described.

Thus, in the case where the gear lever can take other forward positions, for example positions marked "1" or "2", it could be provided that the invention applies in the same way as the lever either in position "D", "1" or "2".

Claims (10)

1. Method for driving a motor vehicle comprising wheels, an electric motor coupled to the wheels and a wheel braking system separate from said electric motor, comprising steps: - acquisition of the position (PRND) of a gear lever fitted to the motor vehicle, - acquisition of the speed (V1) of the motor vehicle, which is positive when the motor vehicle is advancing and negative when the motor vehicle is reversing, - acquisition of an acceleration instruction (lace) relating to the position of or the force exerted on an accelerator pedal fitted to the motor vehicle, and - development of a control instruction (Cmot) of the electric motor as a function of the position (PRND) of the gear lever and of the acceleration instruction (lace), characterized in that, if the speed (V1 ) acquired is less than a first negative threshold (S1) and the gear lever is in the forward position (PRND), provision is made to draw up a control instruction (Cfrein) for the braking system as a function of at least the acceleration instruction (lace). 2. A control method according to the preceding claim, in which, if the speed (V1) acquired is lower than the first threshold (S1) and the gear lever is in the forward position (PRND), the electric motor and the system brakes are controlled in combination in the active state. 3. A control method according to the preceding claim, in which, as soon as the speed (V1) acquired again becomes greater than a second threshold (S2), greater than or equal to the first threshold (S1), and when the gear lever is in position (PRND) forwards, the electric motor is controlled in the active state and the braking system is controlled in the inactive state. 4. Control method according to one of the preceding claims, in which, if the acquired speed (V1) becomes less than a third negative threshold (S3) and less than the first threshold (S1) and the gear lever is in position (PRND) forwards, the electric motor is controlled in an inactive state and the braking system is controlled in the active state. 5. A control method according to the preceding claim, in which, if the speed (V1) acquired, after having been less than the third threshold (S3), becomes again greater than a fourth threshold (S4), greater than or equal to the third threshold (S3 ), and the gear lever is in the forward (PRND) position, the electric motor and the braking system are controlled in combination in the active state. 6. A control method according to the preceding claim, in which, if the speed (V1) acquired, after having been less than the third threshold (S3) and then greater than the fourth threshold (S4), becomes greater than a fifth threshold (S5), greater than or equal to the fourth threshold (S4), and the gear lever is in the forward (PRND) position, the electric motor is controlled in the active state and the braking system is controlled in the inactive state. 7. Control method according to one of claims 5 and 6, wherein, if the speed (V1) acquired, after having been less than the third threshold (S3) then greater than the fourth threshold (S4), becomes less than a sixth threshold (S6), less than or equal to the fourth threshold (S4), and the gear lever is in the forward gear position (PRND), the electric motor is controlled in the inactive state and the braking system is controlled at l active state. 8. Control method according to one of claims 2 and 5, wherein, when the electric motor and the braking system are controlled in combination in the active state, the proportion of the braking torque exerted by the electric motor relative the braking torque exerted by the braking system varies according to the speed (V1) acquired. 9. A driving method according to claim 1, in which the driving instructions (Cmot, Cfrein) of the electric motor and of the braking system are developed so that the braking torque exerted on the wheels varies continuously. . 10. Motor vehicle comprising wheels, an electric motor coupled to the wheels, and a wheel braking system, characterized in that it comprises a control unit for the electric motor and the braking system which is adapted to implement a piloting method according to one of the preceding claims. 1/3