Control of regenerative braking in an electric or hybrid vehicle

Abstract

A method controls regenerative braking for a vehicle equipped with regenerative brakes and with a separate braking apparatus. The vehicle includes at least one first wheel and at least one second wheel. The separate braking apparatus is applied to the at least one first wheel and to the at least one second wheel. The regenerative brakes are applied to the at least one first wheel only. The method includes receiving a speed value of the first wheel and a speed value of the second wheel, estimating a value of a parameter representing a slip associated with the regenerative braking as a function of the speed value of the first wheel and as a function of the speed value of the second wheel, and forming a regenerative braking setpoint value as a function of the estimated value of the parameter representing slip associated with the regenerative braking.

Claims

1. A method for controlling regenerative braking for a vehicle equipped with a first braking means and with a second braking means separate from the first braking means, the first braking means being a regenerative braking means, the vehicle comprising at least one first wheel and at least one second wheel, the second braking means being applied to said at least one first wheel and to said at least one second wheel, and the first braking means being applied to said at least one first wheel and not said at least one second wheel, the method comprising: receiving a speed value of said at least one first wheel and a speed value of said at least one second wheel; estimating a value of a parameter representing a slip associated with the regenerative braking as a function of the speed value of said at least one first wheel and as a function of the speed value of said at least one second wheel; and forming a regenerative braking setpoint value as a function of the estimated value of the parameter representing the slip associated with the regenerative braking, wherein the value of the parameter representing the slip associated with the regenerative braking for said at least one first wheel is estimated as the function of the speed value of said at least one second wheel lying on a same side of the vehicle as said at least one first wheel and not any wheels lying on a side of the vehicle opposite the same side of the vehicle.

2. The method as claimed in claim 1, further comprising: comparing the value of the parameter representing the slip associated with the regenerative braking with a slip threshold; and when the value of the parameter is greater than or equal to the slip threshold, instigating a decrease of the regenerative braking setpoint value.

3. The method as claimed in claim 2, wherein the receiving, the estimating, the comparing, and the instigating are repeated regularly.

4. The method as claimed in claim 1, wherein the estimating includes calculating a pseudo-speed value of said at least one second wheel based on the speed value at a center of said at least one second wheel according to: $w_2^{}=w_2.Math.\left(1-\frac{1}{2}{\left(\frac{{}_v}{K}\right)}^2\right)$ where w.sub.2 is the speed value at the center of said at least one second wheel, .sub.v is a value of an angle at a steering wheel, coming from a steering wheel angle sensor, and where K is a value of a demultiplication factor of a steering column.

5. A non-transitory computer readable medium storing instructions that, when executed by a processor of a computer, causes the computer to execute the method as claimed in claim 1.

6. A device for controlling regenerative braking for a vehicle equipped with a first braking means and with a second braking means separate from the first braking means, the first braking means being a regenerative braking means, the vehicle comprising at least one first wheel and at least one second wheel, the second braking means being applied to said at least one first wheel and to said at least one second wheel, and the first braking means being applied to said at least one first wheel and not said at least one second wheel, the control device comprising: reception means for receiving a speed value of said at least one first wheel and a speed value of said at least one second wheel; first processing means for estimating a value of a parameter representing a slip associated with the regenerative braking as a function of the speed value of said at least one first wheel and as a function of the speed value of said at least one second wheel; and second processing means for forming a regenerative braking setpoint value as a function of the estimated value of the parameter representing slip associated with the regenerative braking, wherein the value of the parameter representing the slip associated with the regenerative braking for said at least one first wheel is estimated as the function of the speed value of said at least one second wheel lying on a same side of the vehicle as said at least one first wheel and not any wheels lying on a side of the vehicle opposite the same side of the vehicle.

7. A motor vehicle comprising: the device as claimed in claim 6; the first braking means and the second braking means, which is separate from the first braking means; and at least one first wheel and at least one second wheel, wherein the second braking means is applied to said at least one first wheel and to said at least one second wheel, and the first braking means being applied to said at least one first wheel and not said at least one second wheel.

8. The motor vehicle as claimed in claim 7, further comprising: an electrical actuator.

9. The motor vehicle as claimed in claim 7, wherein said at least one first wheel includes one or more rear wheels of the motor vehicle.

10. A system for controlling regenerative braking for a vehicle equipped with a first brake system and a second brake system separate from the first brake system, the first brake system being a regenerative brake system, the vehicle comprising at least one first wheel and at least one second wheel, the second brake system being applied to said at least one first wheel and to said at least one second wheel, and the first brake system being applied to said at least one first wheel and not said at least one second wheel, the system comprising: circuitry configured to receive a speed value of said at least one first wheel and a speed value of said at least one second wheel, estimate a value of a parameter representing a partial slip associated with the regenerative braking as a function of the speed value of said at least one first wheel experiencing regenerative braking and as a function of the speed value of said at least one second wheel that does not experience regenerative braking, and form a regenerative braking setpoint value as a function of the estimated value of the parameter representing the partial slip associated with the regenerative braking, wherein the estimating the value of the parameter representing the partial slip associated with the regenerative braking includes comparing a first output of the function of the speed value of said at least one first wheel experiencing regenerative braking with a second output of the function of the speed value of said at least one second wheel that does not experience regenerative braking, and wherein the value of the parameter representing the partial slip associated with the regenerative braking for said at least one first wheel is estimated as a function of the speed value of said at least one second wheel lying on a same side of the vehicle as said at least one first wheel and not any wheels lying on a side of the vehicle opposite the same side of the vehicle.

11. The system as claimed in claim 10, wherein the circuitry is configured to compare the value of the parameter representing the partial slip associated with the regenerative braking with a slip threshold, and when the value of the parameter is greater than or equal to the slip threshold, instigate a decrease of the regenerative braking setpoint value.

12. The system as claimed in claim 11, wherein the receiving, the estimating, the comparing, and the instigating of the circuitry are repeated regularly.

13. The system as claimed in claim 10, wherein the estimating includes calculating a pseudo-speed value of said at least one second wheel based on the speed value at a center of said at least one second wheel according to: $w_2^{}=w_2.Math.\left(1-\frac{1}{2}{\left(\frac{{}_v}{K}\right)}^2\right)$ where w.sub.2 is the speed value at the center of said at least one second wheel, .sub.v is a value of an angle at a steering wheel, coming from a steering wheel angle sensor, and where K is a value of a demultiplication factor of a steering column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a highly schematic view from above of an example of a vehicle according to one embodiment of the invention.

(2) FIG. 2 schematically represents an example of a control device according to one embodiment of the invention.

(3) FIG. 3 is a flowchart of an example of a method according to one embodiment of the invention.

DETAILED DESCRIPTION

(4) Referring to FIG. 1, a vehicle 1 comprises an internal combustion engine (not represented), and an electric motor 10 capable of driving the rear wheels 11.sub.RL, 11.sub.RR. The vehicle furthermore comprises front wheels 11.sub.FL and 11.sub.FR. The front wheels and the rear wheels all experience hydraulic braking. Conversely, the electrical braking as applied via the electric motor 10 is experienced only by the rear wheels 11.sub.RL, 11.sub.RR.

(5) An ESC module 12 receives measurement values of shaft rotation sensors making it possible to measure speeds at the centers of the front wheels and rear wheels. This ESC module is in communication, for example via a CAN (Controller Area Network) bus, with the electrical actuator 10.

(6) FIG. 2 shows the operation of the ESC 12 in more detail.

(7) The ESC 12 comprises a stability module 20 receiving values of rotation at the center of the front and rear wheels, as well as a braking pressure value P and a steering wheel angle value .sub.v coming from a steering wheel angle sensor of the vehicle.

(8) This module 20 makes it possible to generate a flag value IS and two values of parameters representing the slips associated with the electrical braking of the left and right rear wheels, respectively g.sub.L and g.sub.R.

(9) A calculation module 21 for calculating the driver setpoint C.sub.g makes it possible, on the basis of signals which are not represented and include in particular a stop contactor signal and a master cylinder pressure signal, to generate the overall setpoint value C.sub.g corresponding to an estimate of the driver's intention to brake. This type of calculation module is known per se and will not be described in further detail.

(10) A braking management (torque manager) module receives the flag signal value IS, the parameter values g.sub.L, g.sub.R representing the slips associated with the electrical braking, and the overall braking setpoint value C.sub.g, and generates an electrical braking setpoint C.sub.el as a function, in particular, of these received values.

(11) For example, when the flag IS is at 1, the electrical braking is deactivated, that is to say the setpoint C.sub.el is zero.

(12) When the values g.sub.L, g.sub.R are less than a threshold, the electrical braking setpoint value C.sub.el is selected to be proportional to the overall braking setpoint value C.sub.g, for example equal to 10 or 20% of this value.

(13) The supplementary electrical braking setpoint value C.sub.el is sent to the electrical machine referenced 10 in FIG. 1.

(14) FIG. 3 is a flowchart schematically illustrating an example of a method carried out by the ESC module.

(15) The method includes a step 30 of receiving the rotational speed values of the wheels and the steering wheel angle value.

(16) During a step 31, values of the slip parameters g.sub.L, g.sub.R associated with the regenerative braking for the left and right rear wheels, respectively, are calculated by applying the formulae below:

(17) $g_L={\mathrm{Rw}}_{\mathrm{RL}}-{\mathrm{Rw}}_{\mathrm{FL}}\left(1-\frac{1}{2}{\left(\frac{{}_v}{K}\right)}^2\right),\mathrm{and}$$g_R={\mathrm{Rw}}_{\mathrm{RR}}-{\mathrm{Rw}}_{\mathrm{FR}}\left(1-\frac{1}{2}{\left(\frac{{}_v}{K}\right)}^2\right)$
in which
R is the radius of the wheels, which is assumed to be identical from one wheel to another,
w.sub.RL is the angular rotational speed at the center of the left rear wheel,
w.sub.FL is the angular rotational speed at the center of the left front wheel,
w.sub.RR is the angular rotational speed at the center of the right rear wheel,
w.sub.FR is the angular rotational speed at the center of the right front wheel,
.sub.v is the value of the angle at the steering wheel, received in step 30, and
K is a value of a demultiplication factor of the steering column.

(18) Then, during a test step 32, these values g.sub.L, g.sub.R are compared with a threshold THR.

(19) In this example, the test is positive if one of the values is greater than the threshold THR.

(20) In this case, the electrical braking setpoint value C.sub.el is reduced, for example decremented by 10%, during a step 33.

(21) Then, after a waiting step 34, these various steps 31, 32, 33 are repeated. Such a closed loop thus makes it possible to slave the electrical setpoint value so that the slip associated with the electrical braking remains below the threshold THR.

(22) The loop may furthermore comprise a step (not represented) of transmitting electrical braking setpoint value C.sub.el to the electrical actuator, so that a braking force corresponding to this setpoint value is applied to the rear wheels.

(23) This threshold THR may be selected so that the slip remains in a grip range in which the grip, that is to say the ratio between the drag force and the weight, varies linearly with the slip. Expressed another way, the vehicle is kept in this grip range.

(24) Returning to FIG. 2, if this regulation carried out on the basis of the slip values g.sub.L, g.sub.R associated with the electrical braking proves insufficient, the stability indicator module 20 will form a flag IS with a value equal to 1, which deactivates the regenerative braking.

(25) In the embodiment represented, the vehicle is a rear-wheel drive vehicle, that is to say the electrical braking is applied to the rear wheels. It is clear that the method could be adapted to the case of a front-wheel drive vehicle.