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

Abstract

A method for controlling the braking of a motor vehicle (10) in which at least one electric motor (18) is electrically powered to actuate an electromechanical brake (16) on a wheel (12D, 12G, 14D, 14G) of the vehicle (10). The method comprises the steps in which: a) the deceleration of the vehicle (10) and the power supplied to the motor are recorded, b) the time T at which the deceleration of the vehicle reaches a predetermined value is recorded, and c) from this time T, when the power supplied to the motor reaches a predetermined threshold (Pmax), this power supplied to the motor is stabilized at the value of this threshold by decreasing the 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 disc-type braking system for vehicles, particularly automobiles, is already known in the art. This system comprises at least two friction elements, also called friction pads, designed to cooperate by friction with two opposite faces of a disc that is fixed to a rotating wheel of the vehicle. The friction pads pressing against the disc causes the vehicle to brake. When the friction pads are pulled away from the faces of the disc, the braking ceases.

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

[0004] More recently, it has been proposed to control the clamping force application element by electromechanical means. Indeed, electromechanical control means have the particular advantage of being electronically controlled and thus allowing different operating modes to be defined according to different situations.

[0005] The electromechanical control means of the clamping force application member usually include 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: on the one hand, the electrical power of the motor must be sufficient to ensure a sufficient clamping force and, on the other hand, this electrical power must not generate an excessive consumption of electrical energy.

[0008] In addition to these electrical constraints, there is a constraint limiting the masses and the volumes leading to minimizing the dimensions of 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 for the electromechanical brake, which must enable the vehicle to reach a predetermined deceleration target within a predetermined time limit. Thus, it may be desirable that a predetermined deceleration value of 1.1 g (g = 9.80665 m / s²) be reached no later than 150 ms after the activation of the electromechanical brake.

[0010] The invention aims in particular to optimize the electrical consumption of the motor of an electromechanical brake according to 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 is electrically powered to actuate an electromechanical brake on a wheel of the vehicle,

[0012] characterized in that it comprises the steps in which: a. The vehicle's deceleration and the engine's power supply are recorded. b. We record the instant T at which the vehicle's deceleration reaches a pre-defined value 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 lowering the motor supply voltage.

[0013] Thus, firstly, steps a) and b) of this braking control method make it possible to comply with a performance constraint of the electromechanical brake allowing to reach 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 allowing to reach the predetermined objective of deceleration of the vehicle in the predetermined limited time defined between the instant of initialization of braking and the instant T.

[0014] In step c) of the braking control method, once the previous objective has been achieved, it becomes possible to stabilize the motor's power supply at a predetermined threshold by lowering the motor's supply voltage. This voltage reduction causes a decrease in the electric motor's speed due to the proportionality factor, also called the speed constant, between the voltage applied to the motor and the motor's speed. However, this decrease in the electric motor's speed is acceptable because the predetermined objective of decelerating the vehicle within a certain time limited predetermined T has already been reached in step b).

[0015] Since the motor supply power is stabilized at a predetermined threshold in step c), 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 features of this braking control method which can be taken alone or in combination will be specified below.

[0017] The predetermined value of deceleration 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 are electrically powered to actuate first and second electromechanical brakes of first and second wheels of the vehicle respectively, and first and second electric motors are associated respectively with first and second motor power thresholds of different values.

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

[0021] In this way, the total electrical power available for braking a vehicle can be distributed differently between the vehicle's wheels, with the proportion of electrical power allocated to the front wheels being, for example, greater than the proportion allocated to the rear wheels. Thus, a maximum of 500 W of electrical power can be allocated to each electromechanical front wheel brake and 250 W to each electromechanical rear wheel brake.

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

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

[0024] The electric motor for actuation of 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, equipped 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 feature of this electromechanical brake, when the electric motor actuating this brake is an AC motor, the control unit configured to implement steps a) to c) of the braking control method is the electronic control unit of the inverter converting a direct current into an 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 computer-forming control unit, cause that 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 material 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 upon reading the following description, given solely by way of example and made with reference to the accompanying drawings in which:

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

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

[0033] [Fig.3] is a graph showing curves of evolution as a function of time (on the x-axis) of quantities (on the y-axis) 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] Figure 1 shows a motor vehicle, designated by the general reference numeral 10, equipped with two front wheels respectively right 12D and left 12G and two rear wheels respectively right 14D and left 14G.

[0035] During braking, 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, schematically represented by an arrow 19 in [Fig. 1].

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

[0037] The vehicle 10 also includes a power source 20 delivering direct current to a circuit 22 supplying power to various electrical components of the vehicle. The power source 18 includes at least one battery, or preferably two batteries, enabling the power source 18 to operate in backup mode when one of the two batteries fails.

[0038] The entire electromechanical brake system is controlled by a centralized control unit of domain 24, this domain being able to group, 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 should 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 digital circuits 26 and secondary digital circuits 28, on the one hand, to the centralized domain control unit 24 and, on the other hand, to a corresponding electromechanical brake 16.

[0040] It should be noted that the vehicle 10 includes, for each wheel 12D, 12G, 14D, 14G, a speed sensor 32 which provides the electromechanical brake 16 associated with the wheel with information enabling the measurement of the wheel's speed. 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, equipped 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 [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 equipped with transistors 42 forming inter electronic switches. 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 transistorized safety device 46 allowing the inverter 38 to be switched off under certain undesired operating conditions.

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

[0045] The electronic control unit 40 of the inverter 38 includes a microcontroller 48 equipped with a memory 50. Thus, because it includes the microcontroller 48, the control unit 40 forms a computer capable of executing computer program instructions stored in the memory 50 of the microcontroller 48.

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

[0047] For each electromechanical brake 16, a computer program comprising instructions has been recorded in the memory 50 of the microcontroller 48, which, when executed by the electronic control unit 40 of the inverter 38, leads 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 thus forms an electromechanical brake control unit 16 configured to implement the steps of the vehicle braking control process 10 which will be described below with reference in particular 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 material structure of the electromechanical brake 16 to implement the method according to the invention.

[0050] On [Fig.3], the curve of the rotational speed V of the shaft of the electric motor 18 is represented as a function of time in a solid line, the curve of the torque C delivered by this motor 18 as a function of time in a dashed line, and the curve of the power P of the electrical supply of this motor 18 as a function of time in a dashed line with two dashes.

[0051] According to the vehicle braking control method 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 should 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 what follows, it will be assumed that at least one electric motor 18 actuates an electromechanical brake 16 of a wheel 12D, 12G, 14D, 14G of the vehicle. The motor 18 is powered by direct current supplied by the power source 20, which is converted into alternating current by the inverter 38.

[0054] While the motor 18 is being electrically powered, the deceleration of the vehicle 10 and the electrical power supply to 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], during the energizing time of the electric motor 18, a first period PI between t=0 and t=tl is observed, corresponding to the compensation of the play between the pads and the disc. During this period PI, the rotational speed V of the motor 18 rapidly reaches a plateau of maximum value, and the power P supplied to the motor 18, as well as the torque C delivered by this motor 18, remain at plateaus of minimum values.

[0056] In [Fig. 3], a second period P2 between t=0 and t=T is also observed during the energization time of the electric motor 18. This period includes, in particular, the period PL. T is the instant at which the vehicle's deceleration 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 no later than T=150 ms after the activation of the electromechanical brake, i.e., after t=0.

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

[0058] In order to stabilize the supply power of the motor 18 at a predetermined threshold, time T is recorded and, from that time T onwards, when the supply power P of the motor 18 reaches a predetermined threshold Pmax, this supply power P of the motor 18 is stabilized at the value of this threshold by lowering the supply voltage of the motor 18. This voltage reduction 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 The power supply of motor 18 can be fixed, for example, so as to provide a maximum power of 1500 W for a braking operation.

[0059] Thus, on [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 supplying 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 supplied to motor 18 reaches the predetermined threshold Pmax. Between t=T and t=t2, the rotational speed V of motor 18, the power P supplied to motor 18, and the torque C delivered by motor 18 continue to increase in a substantially linear fashion. However, after time t=t2, the supply voltage of motor 18 decreases, as can be visually deduced from the curve representing the rotational speed V of motor 18. Indeed, there is a proportionality factor (speed constant) between the voltage applied to the phases of motor 18 and the speed of motor 18.

[0061] Thus, between t=t2 and t=tx, we observe in [Fig. 3], firstly, that the motor supply power P is stabilized at the predetermined threshold Pmax and, secondly, that the rotational speed V of motor 18, and therefore the voltage applied to the phases of motor 18, decreases substantially linearly so as to allow the stabilization of the motor supply power at the threshold Pmax. Of course, between t=t2 and t=tx, an increase in the current applied to the phases of motor 18 is still permitted in order to maintain a constant motor supply power P.

[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 to a lesser extent than between 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 within a limited time, preferably T=150 ms after the activation of the electromechanical brake 16, was fulfilled at the end of the period P2 which preceded t=t2.

[0063] Where appropriate, elaborate braking strategies can be provided by adjusting the power threshold Pmax of motor supply 18 as a function of a parameter chosen from among the speed of the vehicle 10, a braking action which precedes this adjustment of the power threshold Pmax, a temperature of an electromechanical brake component 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 plan to distribute 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 is possible to decide to electrically supply at least the first and second electric motors 18 respectively actuation of first and second electromechanical brakes 16 of first and second wheels and associated with these first and second electric motors 18 respectively first Pmaxl and second Pmax2 motor supply power thresholds of different values.

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

[0067] The invention is not limited to the embodiment shown and other embodiments The implications will be clear to a person 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 wheel 12G: front left wheel 14D: Right rear wheel 14G: Left rear wheel 16: Electromechanical brake 18: electric motor 20: energy source 22: Electrical component 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: Modulated duty cycle signals 56: Pilot signals C: torque delivered by a motor P: Motor electrical supply power Pmax: predetermined power threshold Pmaxl: first threshold of motor supply power Pmax2: second motor supply power threshold V: motor shaft rotation speed

Claims

Demands

1. A method for controlling the braking of a motor vehicle (10) of the type in which at least one electric motor (18) is electrically powered to actuate an electromechanical brake (16) of a wheel (12D, 12G, 14D, 14G) of the vehicle (10), 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 time T at which the deceleration of the vehicle (10) reaches a predetermined value is recorded, and c. from this time 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. A braking control method according to any one of claims 1 to 3, wherein at least first and second electric motors (18) are electrically powered to actuate first and second electromechanical brakes (16) of first and second wheels (12D, 12G, 14D, 14G) of the vehicle (10), respectively, and wherein first and second electric motors (18) are associated with first (Pmax1, Pmax2) and second motor supply power thresholds (18) of different values.

5. A braking control method according to claim 4, wherein the vehicle (10) comprises two first wheels, referred to as front wheels (12D, 12G), and two second wheels, referred to as rear wheels (14D, 14G), the first (Pmax1) and second (Pmax2) motor supply power thresholds are differentiated such that the proportion of electrical power allocated to the front wheels (12D, 12G) is greater than the share of electrical 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 threshold (Pmax) for supplying the motor (18) is set according to at least one parameter chosen from the speed of the vehicle (10), a braking action which precedes this setting of the power threshold, a temperature of an electromechanical brake component (16) such as a brake disc or brake pad, the trajectory of the vehicle (10), the front or rear position in the vehicle (10) of the wheel (12D, 12G, 14D, 14G) associated with the electric motor (18) for actuating the electromechanical brake (16).

7. 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 a DC 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 AC motor, preferably of the synchronous type, having phases supplied by an inverter (38) converting direct current into alternating current, and wherein steps a) to c) are implemented by an electronic control unit (40) for 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 inverter control unit (40).

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

Images