Method for controlling the braking of a motor vehicle with an electromechanical brake with optimized electrical power.

Abstract

Method for controlling the braking of a motor vehicle (10) in which at least one electric motor (18) for actuating an electromechanical brake (16) of a wheel (12D, 12G, 14D, 14G) of the vehicle (10) is electrically powered. The method comprises the steps in which: a) the deceleration of the vehicle (10) and the power supply to the motor are recorded, b) the instant T at which the deceleration of the vehicle reaches a predetermined value is recorded, and c) from this instant T, when the power supply to the motor reaches a predetermined threshold (Pmax), this power supply to the motor is stabilized at the value of this threshold by reducing the power supply voltage to the motor (18). Figure for the abstract: figure 1

Description

Title of the invention: Method for controlling the braking of a motor vehicle with an electromechanical brake with optimized electrical power. Technical field of the invention

[0001] The invention relates to a method for controlling the braking of a motor vehicle with an electromechanical brake with optimized electrical power. Technical background

[0002] A braking system for a vehicle, in particular an automobile, of the disc type is already known in the prior art, i.e. comprising at least two friction elements, also called friction pads, intended to cooperate by friction respectively with two opposite faces of a disc integral in rotation with a wheel of the vehicle. The tightening of the friction pads against the disc causes the vehicle to brake. When the friction pads are separated from the faces of the disc, the braking ceases.

[0003] Usually, at least one of the friction pads is urged against a corresponding face of the disc by a clamping force application member, sometimes called a piston. It is known to control the clamping force application member by hydraulic means.

[0004] More recently, it has been proposed to control the clamping force application member by electromechanical means. Indeed, the electromechanical control means have the particular advantage of being electronically controlled and thus of making it possible to define different operating modes depending on different situations.

[0005] The electromechanical means for controlling the clamping force application member usually comprise an electric actuator intended to provide a clamping force.

[0006] Thus, it is known to brake each wheel of the vehicle by means of an electromechanical brake comprising an electric motor forming an actuator intended to provide a clamping force for braking the wheel of the vehicle.

[0007] The electrical consumption of the motor of an electromechanical brake is subject in particular to the following constraints: it is necessary, on the one hand, that the electrical power of the motor is sufficient to ensure a sufficient clamping force and, on the other hand, that this electrical power does not generate excessive electrical energy consumption.

[0008] In addition to these electrical constraints, there is a constraint of limiting the masses and the volumes leading to minimizing the dimensions of the electrical components intended to power an electromechanical brake or to be integrated into this electromechanical brake.

[0009] Finally, in addition to all these constraints, there is a performance constraint of the electromechanical brake which must make it possible to achieve a predetermined objective of deceleration of the vehicle in a predetermined limited time. Thus it may be desired that a predetermined deceleration value of 1.1 g (g = 9.80665 m / s2) be reached at the latest 150 ms after activation of the electromechanical brake.

[0010] The invention aims in particular to optimize the electrical consumption of the motor of an electromechanical brake as a function of at least some of the constraints stated above. Summary of the invention

[0011] To this end, the invention relates to a method for controlling the braking of a motor vehicle of the type in which at least one electric motor for actuating an electromechanical brake of a wheel of the vehicle is electrically powered,

[0012] characterized in that it comprises the steps in which: a. the vehicle deceleration and the engine power supply are recorded, b. the instant T at which the vehicle's deceleration reaches a pre-set value is noted. determined, and c. from this instant T, when the motor supply power reaches a predetermined threshold, this motor supply power is stabilized at the value of this threshold by reducing the motor supply voltage.

[0013] Thus, first of all, steps a) and b) of this braking control method make it possible to comply with a performance constraint of the electromechanical brake making it possible to achieve a predetermined objective of deceleration of the vehicle in a predetermined limited time T. During these steps a) and b), the value of the electrical power of the motor is adapted to ensure a sufficient clamping force making it possible to achieve the predetermined objective of deceleration of the vehicle in the predetermined limited time defined between the instant of initialization of the braking and the instant T.

[0014] In step c) of the braking control method, the previous objective having been achieved, it becomes possible to stabilize the power supply to the motor at a predetermined threshold by lowering the supply voltage to the motor. This voltage drop causes a drop in the speed of the electric motor due to the proportionality factor, also called speed constant, between the voltage applied to the motor and the speed of the motor. However, this drop in the speed of the electric motor is acceptable because the predetermined objective of decelerating the vehicle in a time predetermined limit T has already been reached in step b).

[0015] The power supply to the motor being, in step c), stabilized at a predetermined threshold, the dimensions of the electrical components intended to supply the electromechanical brake or to be integrated into this electromechanical brake can be limited, which makes it possible to control the masses and volumes of these components.

[0016] Other optional characteristics of this braking control method which can be taken alone or in combination will be specified below.

[0017] The predetermined deceleration value is 1.1 g, with g = 9.80665 m / s2.

[0018] The predetermined deceleration value is reached at the latest at T=150 ms after activation of the electromechanical brake.

[0019] At least first and second electric motors for actuating respectively first and second electromechanical brakes of first and second wheels of the vehicle are electrically powered, and first and second motor power supply thresholds of different values ​​are associated with the first and second electric motors respectively.

[0020] The vehicle comprising two first wheels, called front wheels, and two second wheels, called rear wheels, the first and second engine supply power thresholds are differentiated so that the share of electrical power allocated to the front wheels is greater than the share of electrical power allocated to the rear wheels.

[0021] In this way, it is possible to provide for distributing the overall electrical power available for braking a vehicle in a differentiated manner between the wheels of the vehicle, the share of electrical power allocated to the front wheels being, for example, greater than the share of electrical power allocated to the rear wheels of the vehicle. Thus, it is possible to provide for allocating a maximum of 500 W of electrical power for each electromechanical brake on the front wheel of the vehicle and 250 W for each electromechanical brake on the rear wheel of the vehicle.

[0022] The motor supply power threshold is adjusted as a function of at least one parameter chosen from the speed of the vehicle, a braking action which precedes this adjustment of the power threshold, a temperature of an electromechanical brake component such as a brake disc or a brake pad, the trajectory of the vehicle, the front or rear position in the vehicle of the wheel associated with the electric motor actuating the electromechanical brake.

[0023] In this way, various braking strategies for a vehicle can be developed depending on various events or operating circumstances of the vehicle.

[0024] The electric motor for actuating each electromechanical brake is a direct current motor.

[0025] The electric motor for actuating each electromechanical brake is a motor alternating current, preferably of the synchronous type, provided with phases supplied by an inverter transforming direct current into alternating current, steps a) to c) of the braking control method being implemented by an electronic control unit of the inverter.

[0026] The invention also relates to an electromechanical brake, characterized in that it comprises a control unit configured to implement steps a) to c) of a braking control method as defined above.

[0027] According to an optional characteristic of this electromechanical brake, when the electric motor actuating this brake is an alternating current motor, the control unit configured to implement steps a) to c) of the braking control method is the electronic control unit of the inverter transforming a direct current into alternating current for each phase of the motor.

[0028] The invention also relates to a computer program comprising instructions which, when the program is executed by a control unit forming a computer, lead this control unit to implement steps a) to c) of a braking control method as defined above.

[0029] Thus, because the invention can be implemented by implementing computer program instructions in the electronic control unit of the inverter, it is not necessary to modify the hardware structure of the electromechanical brake to implement the method according to the invention. Brief description of the figures

[0030] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0031] [Fig-1] is a schematic view of a motor vehicle equipped with electromechanical brakes caniques according to the invention, each electromechanical brake comprising an alternating current motor provided with phases supplied by an inverter transforming a direct current into alternating current;

[0032] [Fig.2] is a schematic detail view showing an electronic control unit electronics of the power supply inverter of an electromechanical brake motor;

[0033] [Fig.3] is a graph showing curves of evolution as a function of time (on the abscissa) of quantities (on the ordinate) corresponding respectively to the electrical supply power of the motor of [Fig.2], the rotation speed of the shaft of this motor and the torque delivered by this motor. Detailed description

[0034] [Fig.l] shows a motor vehicle, designated by the general reference 10, equipped with two front wheels, respectively right 12D and left 12G, and two rear wheels respectively right 14D and left 14G.

[0035] During a braking action, each wheel 12D, 12G, 14D, 14G of the vehicle is braked by means of an electromechanical brake 16. Each electromechanical brake 16 comprises an electric motor 18 forming an actuator intended to provide a clamping force for braking the associated wheel 12D, 12G, 14D, 14G. Thus, the shaft of the motor 18 delivers a clamping torque to the corresponding wheel 12D, 12G, 14D, 14G shown diagrammatically by an arrow 19 in [Fig.l].

[0036] The actuation of the electric motor 18 forming an actuator causes the relative movement of friction pads against a disc secured to the corresponding wheel and thus the clamping of this disc between the two pads.

[0037] The vehicle 10 also comprises a power source 20 delivering a direct current into a circuit 22 for supplying various electrical components of the vehicle. The power source 18 comprises at least one battery or, preferably, two batteries allowing operation of the power source 18 in emergency mode when one of the two batteries fails.

[0038] All of the electromechanical brakes are controlled by a centralized domain control unit 24, this domain being able to group together, for example, the braking and active safety functions of the vehicle.

[0039] The centralized domain control unit 24 is connected to each of the electromechanical brakes 16 by redundant digital circuits for safety reasons, namely a primary digital circuit 26 and a secondary digital circuit 28. It will be noted that a conventional communication gateway 30 is interposed between each electromechanical brake 16 and the centralized domain control unit 24. Each communication gateway 30 is therefore connected by the primary 26 and secondary 28 digital circuits, on the one hand, to the centralized domain control unit 24 and, on the other hand, to a corresponding electromechanical brake 16.

[0040] It will be noted that the vehicle 10 comprises, for each wheel 12D, 12G, 14D, 14G, a speed sensor 32 delivering to the electromechanical brake 16 associated with the wheel information allowing the measurement of the speed of the wheel. This information is transmitted to the electromechanical brake 16 for example via an analog circuit 34.

[0041] In the example described, the electric motor 18 of each electromechanical brake 16 is an alternating current motor, preferably of the synchronous type, provided with three phases supplied by an inverter unit 36 ​​transforming the direct current delivered by the energy source 20 into alternating current.

[0042] The inverter unit 36 ​​is shown in more detail in [Fig. 2]. In this [Fig. 2], it can be seen that the unit 36 ​​comprises an inverter 38 and an electronic control unit 40 for the inverter 38. The inverter 38 is provided with transistors 42 forming inter electronic circuit breakers. The output of the inverter 38 supplies, for example via an intermediate transistor device 44, the three phases of the motor 18.

[0043] Preferably, the unit 36 ​​includes a transistor safety device 46 for deactivating the power supply to the inverter 38 in certain undesired operating circumstances.

[0044] The inverter 38 and the safety device 46, connected together in series, are connected to the energy source 20 by the circuit 22.

[0045] The electronic control unit 40 of the inverter 38 comprises a microcontroller 48 provided with a memory 50. Thus, because it comprises the microcontroller 48, the control unit 40 forms a computer making it possible to execute computer program instructions recorded in the memory 50 of the microcontroller 48.

[0046] The electronic control unit 40 of the inverter 38 also comprises a pilot unit 52 receiving, as input, signals 54 with modulated duty cycle, also called PWM signals in accordance with the English acronym for Pulse Width Modulation, emitted by the microcontroller 48. The pilot unit 52 sends, as output, pilot signals 56 to the inverter 38.

[0047] For each electromechanical brake 16, a computer program has been recorded in the memory 50 of the microcontroller 48, comprising instructions which, when the program is executed by the electronic control unit 40 of the inverter 38, cause this control unit 40 to implement the steps of a braking control method for the vehicle 10.

[0048] The electronic control unit 40 of the inverter 38 therefore forms a control unit of the electromechanical brake 16 configured to implement the steps of the braking control method of the vehicle 10 which will be described below with particular reference to [Fig.3].

[0049] Thus, because the invention can be implemented by implementing computer program instructions in the memory 50 of the microcontroller 48, it is not necessary to modify the hardware structure of the electromechanical brake 16 to implement the method according to the invention.

[0050] In [Fig. 3], the curve of the rotation speed V of the shaft of the electric motor 18 as a function of time is shown in a continuous line, the curve of the torque C delivered by this motor 18 as a function of time is shown in a single-dash line, and the curve of the electrical power P of this motor 18 as a function of time is shown in a double-dash line.

[0051] According to the braking control method of the vehicle 10, at a time t = 0, the electric motor 18 of the electromechanical brake 16 of each of the four wheels 12D, 12G, 14D, 14G of the vehicle is electrically powered.

[0052] It will be noted that the control method could, where appropriate, only apply to a limited number of wheels of the vehicle, for example only to the front wheels 12D, 12G.

[0053] In the following, it will be considered that at least one electric motor 18 for actuating an electromechanical brake 16 of a wheel 12D, 12G, 14D, 14G of the vehicle is electrically powered. The electrical power supply of the motor 18 is carried out by means of the direct current, supplied by the energy source 20, converted into alternating current by the inverter 38.

[0054] While the motor 18 is electrically powered, the deceleration of the vehicle 10 and the electrical power supply of this motor 18 are recorded. The deceleration of the vehicle 10 is calculated by the microcontroller 48 from the information delivered by the speed sensor 32 to the electromechanical brake 16.

[0055] Referring to [Fig. 3], we observe, during the duration of power supply of the electric motor 18, a first period PI between t=0 and t=tl corresponding to the compensation of the play between the pads and the disk. During this period PI, we observe that the speed V of rotation of the motor 18 quickly reaches a maximum value level and that the power P of electrical supply of the motor 18 as well as the torque C delivered by this motor 18 remain at minimum value levels.

[0056] In [Fig. 3], during the duration of power supply of the electric motor 18, a second period P2 between t=0 and t=T is also observed, including in particular the period PL T is the instant at which the deceleration of the vehicle reaches a predetermined value. Preferably, the predetermined deceleration value is 1.1 g, with g = 9.80665 m / s2. Also preferably, the predetermined deceleration value is reached at the latest at T=150 ms after activation of the electromechanical brake, i.e. after t=0.

[0057] During this second period P2, between t = t1 and t = T, it is observed that the rotational speed V of the motor 18, the power supply P of the motor 18, and the torque C delivered by this motor 18 increase in a substantially linear manner. During periods P1 and P2, the value of the power supply P of the motor is adapted to ensure a sufficient clamping force to achieve the predetermined deceleration objective of the vehicle 10 within the predetermined limited time defined between the instant t = 0 of braking initialization and the instant T.

[0058] In order to stabilize the power supply of the motor 18 at a predetermined threshold, the instant T is noted and, from this instant T, when the power P supplying the motor 18 reaches a predetermined threshold Pmax, this power P supplying the motor 18 is stabilized at the value of this threshold by lowering the supply voltage of the motor 18. This voltage drop is controlled by the electronic control unit 40 of the inverter 38, in particular by the program instructions implemented in the memory 50. The predetermined threshold Pmax of motor supply power 18 may be set, for example, to provide a maximum power of 1500 W for a braking operation.

[0059] Thus, in [Fig.3], we observe a third period P3 between t=0 and t=tx, including in particular the periods PI and P2, which can correspond to the duration of power supply to the electric motor 18 to carry out the braking operation.

[0060] In this third period P3, at time t=t2 after time T, the power P supplying the motor 18 reaches the predetermined threshold Pmax. Between t=T and t=t2, it is observed that the rotation speed V of the motor 18, the power P supplying the motor 18 and the torque C delivered by this motor 18 continue to increase in a substantially linear manner. However, after time t=t2, the supply voltage of the motor 18 is lowered as can be visually deduced from the curve representing the rotation speed V of the motor 18. Indeed, there is a proportionality factor (speed constant) between the voltage applied to the phases of the motor 18 and the speed of this motor 18.

[0061] Thus, between t=t2 and t=tx, it is observed in [Fig.3], on the one hand, that the power P supplying the motor is stabilized at the predetermined threshold Pmax and, on the other hand, that the speed V of rotation of the motor 18 and therefore the voltage applied to the phases of the motor 18 decrease substantially linearly so as to allow the stabilization of the power supplying the motor at the threshold Pmax. Of course, between t=t2 and t=tx, an increase in the intensity of the current applied to the phases of the motor 18 remains permitted in order to allow a constant power P supplying the motor 18 to be maintained.

[0062] Furthermore, between t=t2 and t=tx, it is observed that the torque C delivered by the motor 18 continues to increase substantially linearly, but in a lesser proportion than between the times t=0 and t=t2. This evolution of the torque C remains satisfactory, however, because the objective of a predetermined deceleration value, preferably 1.1g, to be reached in a limited time, preferably T=150 ms after the activation of the electromechanical brake 16, has been fulfilled at the end of the period P2 which preceded t=t2.

[0063] Where appropriate, it is possible to provide elaborate braking strategies by adjusting the power threshold Pmax for supplying the motor 18 as a function of a parameter chosen from the speed of the vehicle 10, a braking action which precedes this adjustment of the power threshold Pmax, a temperature of a component of the electromechanical brake such as the brake disc or at least one of the brake pads, the trajectory of the vehicle 10, the front or rear position in the vehicle 10 of the wheel associated with the electric motor 18.

[0064] Thus, it is possible to provide for distributing the overall electrical power available for braking the vehicle 10 in a differentiated manner between the wheels 12D, 12G, 14D, 14G.

[0065] In this case, it can be decided to electrically supply at least the first and second electric motors 18 for actuating respectively first and second electromechanical brakes 16 of first and second wheels and these first and second electric motors 18 are associated respectively with first Pmaxl and second Pmax2 motor supply power thresholds of different values.

[0066] More particularly, one can decide for example to differentiate the powers of so that the share of electric power allocated to the front wheels 12D, 12G is greater than the share of electric power allocated to the rear wheels 14D, 14G. Thus, it is possible to allocate, for a braking action, a maximum electric power of 500 W for each electromechanical brake 16 of the front wheel 12D, 12G and a maximum electric power of 250 W for each electromechanical brake 16 of the rear wheel 14D, 14G.

[0067] The invention is not limited to the embodiment presented and other embodiments lization will be clearly apparent to those skilled in the art. Thus, according to another embodiment, the invention is implemented with an electromechanical brake whose actuator motor is of the direct current type.

[0068]

[0069] List of references 10: motor vehicle 12D: right front wheels 12G: left front wheel 14D: right rear wheel 14G: left rear wheel 16: electromechanical brake 18: electric motor 20: energy source 22: electrical organ power supply circuit 24: centralized domain control unit 26: primary digital circuit 28: secondary digital circuit 30: communication gateway 32: speed sensor 34: analog circuit 36: inverter unit 38: inverter 40: inverter electronic control unit 42: transistors 44: intermediate transistor device 46: safety device 48: microcontroller 50: memory 52: pilot unit 54: duty cycle modulated signals 56: pilot signals C: torque delivered by a motor P: motor electrical supply power Pmax: predetermined power threshold Pmaxl: first motor supply power threshold Pmax2: second motor supply power threshold V: motor shaft rotation speed

Claims

Claims

1. Method for controlling the braking of a motor vehicle (10) of the type in which at least one electric motor (18) for actuating an electromechanical brake (16) of a wheel (12D, 12G, 14D, 14G) of the vehicle (10) is electrically powered, characterized in that it comprises the steps in which: a. the deceleration of the vehicle (10) and the power (P) supplied to the motor are recorded, b. the instant T at which the deceleration of the vehicle (10) reaches a predetermined value is recorded, and c. from this instant T, when the power (P) supplied to the motor (18) reaches a predetermined threshold (Pmax), this power (P) supplied to the motor is stabilized at the value of this threshold by lowering the supply voltage of the motor (18).

2. A braking control method according to claim 1, wherein the predetermined deceleration value is 1.1 g, with g = 9.80665 m /

3. sz. Braking control method according to claim 1 or 2, wherein the predetermined deceleration value is reached at the latest at T=150 ms after activation of the electromechanical brake (16).

4. Braking control method according to any one of claims 1 to 3, in which at least first and second electric motors (18) for actuating respectively first and second electromechanical brakes (16) of first and second wheels (12D, 12G, 14D, 14G) of the vehicle (10) are electrically powered, and in which first (Pmaxl, Pmax2) and second motor (18) power supply thresholds of different values ​​are associated with the first and second electric motors (18) respectively.

5. Braking control method according to claim 4, in which, the vehicle (10) comprising two first wheels, called front wheels (12D, 12G), and two second wheels, called rear wheels (14D, 14G), the first (Pmaxl) and second (Pmax2) engine supply power thresholds are differentiated so that the share of electrical power allocated to the front wheels (12D, 12G) is greater than the share of electric power allocated to the rear wheels (14D, 14G).

6. A braking control method according to any one of claims 1 to 5, wherein the power supply threshold (Pmax) of the engine (18) is adjusted as a function of at least one parameter chosen from the vehicle speed (10), a braking action that precedes this adjustment of the power supply threshold, the temperature of a component of the electro-mechanical brake (16) such as a brake disc or a brake pad, the vehicle trajectory (10), the front or rear position in the vehicle (10) of the wheel (12D, 12G, 14D, 14G) associated with the electric motor (18) for operating the electro-mechanical brake (16).

7. A braking control method according to any one of claims 1 to 6, wherein the electric motor (18) for operating each electro-mechanical brake (16) is a direct current motor.

8. A braking control method according to any one of claims 1 to 6, wherein the electric motor (18) for actuating each electromechanical brake (16) is an alternating current motor, preferably of the synchronous type, provided with phases supplied by an inverter (38) transforming a direct current into alternating current, and wherein steps a) to c) are implemented by an electronic control unit (40) of the inverter (38).

9. Electromechanical brake, characterized in that it comprises a control unit (36, 40) configured to implement steps a) to c) of a method according to any one of claims 1 to 8.

10. Electromechanical brake according to claim 9, for implementing the method according to claim 8, wherein the control unit configured to implement steps a) to c) is the electronic control unit (40) of the inverter.

11. A computer program comprising instructions which, when the program is executed by a computer control unit (36, 40), cause the computer control unit (36, 40) to implement steps a) to c) of a method according to any one of claims 1 to 8.

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