EP0941165A1

EP0941165A1 - Braking system for electric vehicle

Info

Publication number: EP0941165A1
Application number: EP97948948A
Authority: EP
Inventors: Benjamin Marrara; Jean-Charles Papazian
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 1996-11-29
Filing date: 1997-11-28
Publication date: 1999-09-15
Also published as: TW349063B; FR2756520A1; FR2756520B1; WO1998023461A1

Abstract

The invention concerns a braking system for an electric vehicle, characterised in that it consists in the following steps: detecting a raised position of the accelerator pedal (2); detecting the value of the stoplight indicator, representing the actuating or not of the brake pedal (3); measuring the moving speed of the vehicle and computing the deceleration of the vehicle on the basis of this speed; computing a first component of the braking torque value, in inverse variation to the speed of the vehicle; computing a second component, proportional to the deceleration of the vehicle, of the braking torque value; computing a braking torque value, which is a linear function of the two previous components; modifying the torque reference input value of the electric motor by this computed braking value for braking.

Description

BRAKING PROCESS FOR ELECTRIC VEHICLE

The present invention relates to electric vehicles and, more particularly in such vehicles, a method of calculating and applying an electric braking torque of the vehicle.

In electric vehicles, it is known to use braking of the electric motor when the brake pedal is applied, together or not with mechanical braking. However, this electrical braking has the drawback of being relatively imprecise; in addition, the implementation of this electric braking requires a potentiometer for measuring the position of the brake pedal.

The object of the present invention is therefore to implement, in an electric vehicle, an electric braking method which does not have the drawbacks of the solutions currently known and succinctly set out above.

This object is therefore to implement an electric braking method which in particular simulates a braking torque substantially equivalent to the engine brake, existing on a thermal vehicle and the absence of which on electric vehicles seems unnatural to the driver of such a vehicle. .

This object is achieved by introducing a braking torque on the electric motor of the vehicle, the value of which is a function of the speed of movement of the vehicle, its acceleration, actuation of the brake and accelerator pedals and activation of an anti-lock device for the wheels.

To this end, the present invention provides a braking method for an electric vehicle comprising:

- an electric motor (10) whose output shaft (19) is mechanically connected to the drive wheels (13) of the vehicle,

- a storage battery (14) for supplying the electric motor (10) with electric energy,

- an accelerator pedal (2) associated with a device (1) for measuring the position of said pedal to supply signals representative of this position,

a brake pedal (3) associated with a device for detecting (4) the start of the travel of said pedal to provide a signal representative of this start of travel,

- means for measuring (21) the speed of rotation of the driving wheels (13) or of the electric motor (10) to supply the speed of movement (V_VE) of the electric vehicle, - an anti-lock device (20) of the wheels ,

- a control device (9) of the electric motor (10) for supplying said motor with electric energy as a function of the position of the accelerator pedal (2), the brake pedal (3) and the speed of movement of the vehicle (V_VE), characterized in that said method comprises the following stages: -

- detect a raised position (POS_AC = l) of the accelerator pedal (2), - detect the value of the brake light indicator (IND_STOP), representative of whether or not the brake pedal is actuated (3),

- measure the speed of movement (V_VE) of the vehicle and calculate the deceleration (A_VE) of the vehicle from this speed (V_VE), - calculate a first component CFj (V_VE) of the value of the braking torque CF, varying in direction reverse of vehicle speed (V_VE),

- calculate a second component CF2 (A_VE), proportional to the deceleration of the vehicle, of the value of the braking torque CF, - calculate according to whether or not a signal representative of the actuation of the brake pedal is detected, a value of the braking torque CF equal to the sum CF (V_VE) + CFj (A_AE) or CF (V_VE),

- modify the torque setpoint value of the electric motor by this calculated braking value CF so as to obtain braking.

According to another characteristic of the present invention, the component CFi (A_VE) of the braking torque is of the form: - CFi (A_VE) = CFι (A_VE) = K.A_VE as long as the value of the deceleration remains greater than a first threshold (A_MINI2),

- CFi (A_VE) = CF ₂ (A_VE) = K.A_MINI2. {(A_MINI3 - A_VE) / (A_MINI3 - A_MINI2)}, as long as the value of the deceleration remains between the first threshold (A_MINI2) and a second predetermined threshold (A_MINI3). According to another characteristic of the present invention, the component CF (V_VE) of the braking torque is of the form:

- CF (V_VE) = ai + bι .V_VE as long as the speed value (V_VE) of the vehicle remains greater than a predetermined value (V_MINI).

According to another characteristic of the present invention, the coefficient K is strictly positive.

According to another characteristic of the present invention, the coefficients al and bl are strictly positive and negative respectively.

According to another characteristic of the present invention, the braking torque is zero, when at least one of the following conditions is achieved:

- detection of the activation of the anti-lock braking system,

- vehicle speed (V_VE) below a predetermined threshold (V_MINI) corresponding to a virtual stop of the vehicle,

- vehicle deceleration (A_VE) below the second threshold (A_MINI3).

The aims, aspects and characteristics of the present invention will be better understood from the description given below of an embodiment of the invention, presented by way of nonlimiting example, with reference to the accompanying drawings, wherein : FIG. 1 is a functional diagram of an electric vehicle implementing the braking method according to the invention,

FIG. 2 is a diagram which makes it possible to describe the braking method according to the invention,

FIG. 3 is a diagram showing, as a function of the vehicle speed, the values of the electric braking torque, in a first braking zone, of an electric vehicle according to the invention, and of the braking torque corresponding to " engine brake "of an equivalent engine vehicle.

An electric vehicle conventionally comprises:

an electric motor 10, the output shaft 19 of which is mechanically connected to the drive wheels 13 by a differential reduction device 12, a storage battery 14 for storing electric energy,

a device 9 for controlling the electric motor 10 for supplying said motor with electric energy supplied by the storage battery 14,

an accelerator pedal 2 associated with a device 1 for measuring the position of said pedal to supply signals representative of this position,

- a brake pedal 3 associated with a device for detecting the start of travel 4 of said pedal to provide a signal representative of this start of travel, - means 21 for measuring the speed of rotation of the driving wheels 13 or of the electric motor 10 to supply the traveling speed V_VE of the electric vehicle, a computer 15 for calculating the value Ie of the power supply current to the motor 10, the so-called reference value, which is applied to the control device 9 to enable it to carry out the switching of the battery current to the electric motor of the same type as the latter provides a torque corresponding to the set value le.

- an anti-lock device 20 for the driving wheels 13 connected by a conductor 21 to the computer 8.

The calculator includes for information:

a device 6 for digitizing the signals supplied by the devices 1 and 4 and by the speed sensor 11 on the conductors 16, 17 and 18,

a computer 8 proper, and a connecting cable 7 between the digitizing device 6 and the computer 8,

The computer 8 supplies the value of the setpoint current le on the connection cable 21.

A brake light 5 which is supplied by the battery 15 via the conductors 14 is associated with the brake pedal 3 and with the device for detecting the start of the stroke 4 of the said pedal.

The braking method according to the invention is implemented by the computer 8 from signals representative of the positions of the accelerator pedal 2, from a start of travel contact of the pedal. brake 3 activating the STOP light 5, activation of the anti-lock device 20 of the wheels, and the respective values of the speed V_VE and the instantaneous acceleration A_VE of the vehicle.

The flow diagram of this method is represented in FIG. 2 and begins with the measurement of the speed of the vehicle V_VE by an appropriate sensor 11 or by an estimation of the latter using a signal representative of the rotation of the engine. traction of the vehicle.

The acceleration A_VE of the vehicle is calculated in a manner known per se, from the information on the speed of movement V_VE of the vehicle; these values A_VE and V_VE correspond respectively to the instantaneous acceleration and speed of the vehicle.

The braking method according to the invention distinguishes four electrical braking zones of the vehicle:

- The first zone corresponds to an applied electric braking torque dependent on the vehicle speed alone; in this zone, the applied electric braking torque is preferably based on the average value of the braking torque due to the engine brake of a thermal vehicle of substantially equivalent power. The values of the parameters aj and bj are chosen accordingly. FIG. 3 shows a diagram representative of the electric braking torque (dotted curve) in this area, as well as the braking torque (solid line curve) corresponding to the "engine brake" of the vehicle equipped with a heat engine of substantially equivalent power associated with a four-speed gearbox; remember that on a vehicle with an internal combustion engine, the braking torque due to the engine brake depends on both the gear engaged and the speed of the vehicle.

- The second zone corresponds to mechanical braking for low deceleration and without skidding of the drive wheels;

the third zone corresponds to a transition between braking of low deceleration to that of strong deceleration where the electric braking is eliminated for safety reasons; the choice of the value A_MINI2 delimits the passage between the second and third zones.

- The fourth zone corresponds to a zero electric braking torque beyond a maximum deceleration threshold A_MINI3, the value of which delimits the border between the third and fourth zones.

If the anti-lock braking system is activated, which corresponds to a YES answer to the question A_BLC = 1? (diamond 31), there is no electrical braking torque to apply (rectangle 40). If the anti-lock is not actuated, the STOP not lit, which corresponds to a YES answer to the question of diamond 32, and the accelerator pedal not raised, which corresponds to a NO answer to the question of diamond 33 , then there is no electrical braking torque applied (rectangle 40). If the accelerator pedal is raised but the speed V_VE of the vehicle movement is lower than a minimum speed V_MINI (diamond 34) then there is no applied electric braking torque CF = 0. If the speed of movement of the vehicle V_VE is greater than the minimum speed V_MINI, then the answer is YES to question 34 and an electric braking torque must be calculated. Preferably, the braking torque chosen (rectangle 35) is a torque CF (V_VE) proportional to the speed V_VE of the vehicle. According to the invention, the braking torque is of the form:

CF (V_VE) = aι + bι .V_VE, the values of a ^ and b \ being chosen respectively strictly negative and positive.

If the STOP is on, the method according to the invention provides for three possible cases according to the value of the acceleration A_VE of the vehicle with respect to two values A_MINI2 and A_MINI3 which correspond respectively to predetermined maximum and minimum deceleration thresholds.

When the deceleration A_VE is greater than the maximum threshold A_MINI2 (diamond 36), the computer calculates (rectangle 37) a value of the braking torque which is the sum of a braking torque linearly dependent on the speed CF (V_VE) and d ' a braking torque CFj (A_VE) proportional to the deceleration A_VE of the vehicle. According to the invention, this first braking torque is the form:

CF i (A_VE) = K. A VE with K strictly positive. When the deceleration A_VE of the vehicle is less than A_MINI2 but greater than A_MINI3 (diamond 38), the computer calculates a second braking torque CF equal to the sum of an electric braking torque depending on the speed CF (V_VE) and d ' a second braking torque depending on the deceleration CF2 (A_VE). According to the invention, this second braking torque is the form:

CF2 (A_VE) = K.A_MINI2. {(A_MINI3-A_VE) / (A_MINI3 - A_MINI2)}

This formulation makes it possible to obtain continuity in the value of the braking torque between the second and third deceleration zones.

The rectangle 41 indicates the value of the setpoint torque which is applied and which is the sum of the setpoint of the torque Ce in the absence of implementation of the method according to the invention and of the value CF calculated according to said method.

The braking method according to the invention therefore has the advantage of introducing an electric braking torque varying continuously as a function of the deceleration; moreover, it allows the driver to rediscover the familiar feeling of the engine brake; it only requires the use of a limit switch, less expensive than a potentiometer, for the brake and accelerator pedals; the cost of the vehicle is reduced accordingly and its reliability increased. The braking process also has full compatibility with the anti-lock devices existing on electric vehicles.

Of course, the invention is in no way limited to the embodiments described and illustrated which have been given only by way of example.

On the contrary, the invention includes all the technical equivalents of the means described as well as their combinations if these are carried out according to the spirit.

Claims

1) Method of braking an electric vehicle comprising:

means for measuring (21) the speed of rotation of the driving wheels (13) or of the electric motor (10) to supply the speed of movement (V_VE) of the electric vehicle,

- an anti-lock device (20) for the wheels,

- a control device (9) of the electric motor (10) for supplying said motor with electric energy as a function of the position of the accelerator pedal (2), the brake pedal (3) and the speed of movement of the vehicle (V_VE), characterized in that said method comprises the following steps:

- detect a raised position (POS_AC = l) of the accelerator pedal (2), - detect the value of the brake light indicator (IND_STOP), representative of the actuation or not of the brake pedal (3) , - measure the speed of movement (V_VE) of the vehicle and calculate the deceleration (A_VE) of the vehicle from this speed (V_VE),

- calculate a first component CFι (V_VE) of the value of the braking torque CF, varying in opposite direction to the speed of the vehicle (V_VE),

- calculate a second component CF2 (A_VE), proportional to the deceleration of the vehicle, of the value of the braking torque CF,

- calculate, depending on whether or not a signal representative of the actuation of the brake pedal is detected, a value of the braking torque CF equal to the sum CF (V_VE) + CFj (A_AE) or CF (V_VE),

2) Braking method according to claim 1, characterized in that the component CFj (A_VE) of the braking torque is of the form:

- CFi (A_VE) = CFι (A_VE) = K.A_VE as long as the deceleration value remains above a first threshold (A_MINI2), - CFi (A_VE) = CF2 (A_VE) = K.A_MINI2. {(A_MINI3 - A_VE) / (A_MINI3 - A_MINI2)}, as long as the value of the deceleration remains between the first threshold (A_MINI2) and a second predetermined threshold (A_MINI3).

3) Braking method according to claim 1, characterized in that the component CF (V_VE) of the braking torque is of the form: - CF (V_VE) = ai + bι .V_VE as long as the speed value (V_VE) of the vehicle remains greater than a predetermined value (V_MINI).

4) Braking method according to claim 2, characterized in that the coefficient K is strictly positive.

5) A braking method according to claim 3, characterized in that the coefficients al and bl are respectively strictly positive and negative.

6) Braking method according to any one of the preceding claims, characterized in that the braking torque is zero, when at least one of the following conditions is achieved:

- detection of the activation of the anti-lock brakes, - vehicle speed (V_VE) below a predetermined threshold (V_MINI) corresponding to a virtual stop of the vehicle,

- vehicle deceleration (A_VE) below the second threshold (A MINI3).