IMPROVED METHOD FOR CONTROLLING THE TORQUE OF AN ELECTROMECHANICAL BRAKE

Abstract

The invention relates to a method for controlling the tightening torque of an electromechanical brake for a motor vehicle, the brake comprising an electric motor provided with a rotary shaft intended to drive mechanical brake-clamping means. The method comprises the following steps: - acquiring data from a wheel speed sensor (32) that takes a characteristic measurement of the speed of at least one of the wheels of the vehicle; - determining, according to the data from the wheel speed sensor (32), a deceleration indicator characteristic of the acceleration of the vehicle; - regulating the tightening torque according to the deceleration indicator.

Description

Method for controlling the tightening torque of an improved electromechanical brake

[0001] The invention relates to the field of motor vehicle braking actuators, more particularly electromechanical brakes, and methods for controlling their tightening torque.

[0002] A braking system of a motor vehicle generally comprises mechanical means for applying the brake, including in particular friction means, such as brake pads, connected to an actuator capable of moving these friction means towards the wheel of the vehicle to grip it and thus brake the vehicle by friction, or of moving them apart in order to stop braking. In the case of an electromechanical brake, the mechanical application means are controlled by an electric motor equipped with a rotating shaft which drives them.

[0003] To control the tightening torque of electromechanical vehicle brakes, it is known in the state of the art to proceed by regulating the tightening torque according to indicators based on data from sensors. These sensors are generally placed at the level of the electric motor or the actuator moving the friction means. For example, it is known to use data from a force sensor between the motor and the actuator to control the brake tightening torque command and thus attempt to obtain the desired vehicle deceleration.

[0004] However, in addition to the cost and complexity involved in setting up and operating such a force sensor, it only allows factors influencing the tightening torque dependent on the electric motor and the actuator to be taken into account. In particular, it does not allow factors related to the rest of the braking system to be taken into account, and even less so to the motor vehicle in general and its environment, such as, for example, the swelling of the brake pads under the effect of heat caused by braking, the condition of the road on which the vehicle is traveling, etc.

[0005] The invention thus aims to provide a method for controlling the tightening torque of an electromechanical brake which takes into account more parameters than those linked to the electric motor of the brake and its actuator.

[0006] To this end, the subject of the invention is a method for controlling the tightening torque of an electromechanical brake for a motor vehicle, the brake comprising an electric motor provided with a rotating shaft intended to drive mechanical brake tightening means, characterized in that it comprises the following steps: - data are acquired from a wheel speed sensor carrying out a characteristic measurement of the speed of at least one of the wheels of the vehicle, - a deceleration indicator characteristic of the acceleration of the vehicle is determined, as a function of the data from the wheel speed sensor, - the tightening torque is regulated as a function of the deceleration indicator.

[0007] By using a sensor that performs a characteristic measurement of the speed of a wheel of the vehicle, it is possible to take into account, in order to regulate the brake application torque, parameters related to the motor vehicle in general and its environment. Such a method thus makes it possible to obtain braking control that is more precise than that permitted by the control methods of the prior art. In addition, since a speed sensor is less expensive and less difficult to operate than a force sensor, the method according to the invention is less expensive to implement.

[0008] According to one embodiment of the invention, an actuator modifies friction means as a function of the tightening torque thus regulated.

[0009] According to a preferred embodiment of the invention, the wheel speed sensor is part of an anti-lock braking system or electronic trajectory control system already present in the vehicle. This makes it possible to reduce the costs of implementing the method since a system already present in most vehicles, or even in almost all new vehicles, is reused. In addition, data is used that is known to be reliable and accurate given the safety standards that an anti-lock braking system must meet.

[0010] Preferably, the tightening torque is also regulated as a function of an indicator that characterizes the position of the electric motor, called a position indicator, calculated as a function of data from a sensor measuring a parameter related to the rotation of the motor shaft, called a rotation sensor. Regulating the tightening torque of the motor as a function of its position makes it possible to further improve the precision of the control method.

[0011] According to a preferred embodiment of the invention, the tightening torque is also regulated according to data from a sensor measuring a parameter related to the intensity of the electric current supplying the electric motor, called a current sensor. Regulating the tightening torque of the motor according to its position makes it possible to further improve the precision of the control method.

[0012] According to a particular embodiment of the invention, the tightening torque is also regulated as a function of a braking instruction, the braking instruction preferably corresponding to the acquisition of a state of a brake pedal.

[0013] According to a particular embodiment of the invention, the data from the wheel speed sensor are recorded over a predetermined period and a physical model of the evolution of the deceleration is constructed as a function of the evolution of the position indicator, this physical model being a function of the data from the wheel speed sensor thus recorded.

[0014] Advantageously, in the event of temporary unavailability of data from the wheel speed sensor, the tightening torque is regulated according to the data from the physical model. In this way, a certain degree of precision is maintained in the tightening torque control despite temporary unavailability of the wheel speed sensor, which the physical model can replace until it is available again.

[0015] According to another particular embodiment of the invention, the data from the wheel speed sensor are recorded over a predetermined period and filtered through a prediction filter, preferably a Kalman filter.

[0016] Advantageously, in the event of temporary unavailability of the data from the wheel speed sensor, the tightening torque is regulated according to the data from the prediction filter relating to an estimated state of the wheel speed sensor data. In this way, a certain degree of precision is maintained in the control of the tightening torque despite a temporary unavailability of the wheel speed sensor, which the estimated state of the wheel speed sensor data from the prediction filter allows to compensate for until it is available again.

[0017] Preferably, using the wheel speed sensor, it is detected whether at least one of the vehicle wheels is locked, and if at least one of the wheels is locked, the anti-lock braking system or electronic stability control system sends a torque command to the electromechanical brake. In this way, the anti-lock braking system or electronic stability control system can supplement the braking command in the event of wheel lock, thereby providing additional safety to the vehicle.

[0018] The invention also relates to a braking system capable of implementing the method according to the invention.

[0019] The invention also relates to a vehicle comprising the braking system according to the invention. Brief description of the figure

[0020] The invention will be better understood by reading the following description, given solely by way of example and with reference to the attached drawing in which:

[0021] is a diagram representing a flowchart of operation of the method for controlling the braking torque of an electromechanical brake according to a particular embodiment of the invention. Detailed description

[0022] A diagram representing a flowchart of operation of the method for controlling the braking torque of an electromechanical brake according to a particular embodiment of the invention is shown.

[0023] The electromechanical brake conventionally comprises an electric motor provided with a rotating shaft intended to drive mechanical brake application means (not shown). The electric motor is preferably a brushless electric motor. Since this is an electromechanical brake known per se, it will not be described further here.

[0024] The mechanical brake application means are controlled by a tightening torque command. In order to control the brake application torque, a deceleration command is generated, which corresponds to a desired deceleration for the motor vehicle. This deceleration command may, for example, come from a driver of the vehicle, by actuating a brake pedal P, and this command is transmitted to a deceleration request member 10. The deceleration command may also come from a computer controlling an autonomous vehicle, or a control station controlling the vehicle remotely, etc.

[0025] The desired deceleration command is converted into a raw torque tightening command using a deceleration conversion model 12, known per se, giving the tightening torque as a function of the deceleration command. Here, raw tightening command is understood to mean a tightening command which results directly from the conversion of the deceleration command from the deceleration request member, in other words which has not yet benefited from a servocontrol.

[0026] The raw tightening command thus obtained is sent to a deceleration control member 14 which, during a step of controlling the deceleration command, will obtain information from various indicators and adjust the raw tightening torque command. The raw tightening torque command will then be converted into the tightening torque to be achieved, as a function of these indicators, in particular on the basis of a control of the tightening torque command as will be seen later.

[0027] The target torque command is sent to a motor target position determining member 16, which converts the torque command into a raw target motor position command using a torque conversion model 18, known per se, giving the target motor position as a function of the target torque command.

[0028] Then, the raw target position command of the motor is sent to a motor position control member 20. The position of the motor is in parallel identified by a position indicator calculated according to the data from a rotation sensor R measuring a parameter linked to the rotation of the motor shaft.

[0029] The motor position data thus recorded are returned to the motor target position determining member 16, in order to compare the deviation between the actual motor position and the target motor position. In other words, a servo-control of the motor positioning control is achieved. Thus, the tightening torque is also regulated as a function of the indicator which characterizes the position of the electric motor.

[0030] Then, the position command of the motor 20 is sent to a motor supply intensity determination member 22, in order to adapt the motor supply current intensity command to the position of the motor.

[0031] Then, the target power supply intensity command is sent to a motor power supply current intensity control member 24. The motor power supply current intensity is in parallel identified by a current indicator calculated according to the data from a power supply current intensity sensor I.

[0032] The motor position data thus recorded are returned to the motor supply current intensity determination member 22, in order to compare the difference between the actual supply current intensity and the target supply current intensity. In other words, a servo-control of the motor supply current intensity control is carried out. Thus, the tightening torque is also regulated according to the data from the sensor I measuring a parameter linked to the intensity of the electric current supplying the electric motor.

[0033] Preferably, the motor position control member 20, the motor power supply intensity determination member 22 and the motor power supply current intensity control member 24 are controlled by a suitable control law such as for example field-oriented control 25, in six steps or in sliding mode (SMC for sliding mode control).

[0034] The power supply intensity and motor position commands thus controlled are sent to a member for calculating the stroke of a braking actuator 26 which moves friction means of the wheel W according to these commands. This member for calculating the stroke of an actuator 26 then sends the result of the calculation of the stroke of the actuator to a member for calculating the tightening torque 28 to be achieved.

[0035] The result of the calculation of the tightening torque to be achieved is sent to a motor deceleration calculation member 30, which calculates, based on the result of the calculation of the tightening torque to be achieved, a deceleration which corresponds to the deceleration of the motor vehicle taking into account only the calculation of the tightening torque to be achieved resulting from the action of the electromechanical brake motor. It is called “motor deceleration” because it only takes into account the parameters linked to the electromechanical brake motor, without taking into account a priori other factors such as for example the influence of heat on the brake pads, or the environment in which the vehicle is moving, such as for example the state of the road surface.

[0036] The result of the engine deceleration calculation is sent to the deceleration control member 14, in order to compare the difference between the engine deceleration thus calculated and the desired deceleration command. In other words, a control of the deceleration command is carried out based on the engine deceleration calculation.

[0037] The friction means naturally influence the wheel speed. In this regard, during a wheel speed data collection step, data are obtained from a wheel speed sensor 32 (“wheel speed sensor” in English terminology) carrying out a characteristic measurement of the speed of at least one of the vehicle’s wheels.

[0038] In the embodiment shown in the, in order to take advantage of equipment already present in the vehicle, the wheel speed sensor 32 is part of an anti-lock braking system or electronic trajectory control system, such as those known under the brand name ABS from the German "Antiblockiersystem" or ESP from the English "Electronic Stability Program", already present in the motor vehicle. The collection of wheel speed data is done for example at regular time intervals and is sent periodically to the deceleration control member 14 as will be seen later.

[0039] With the aid of the wheel speed sensor 32, it is detected, for example via a lock detection device 36, whether at least one of the vehicle wheels is locked. If at least one of the wheels locks, the anti-lock braking system 38 sends a torque command to the electromechanical brake. This function is in the preferred embodiment of the invention performed by the ABS system already present in the motor vehicle. In this way, the anti-lock braking system 38 can supplement the braking command in the event of wheel lock, which provides additional safety for the vehicle.

[0040] If no wheel lock is detected, during a deceleration calculation step, a deceleration indicator characteristic of the acceleration of the vehicle is obtained based on the data from the wheel speed sensor 32. This wheel deceleration indicator is calculated using a wheel deceleration calculator 34. This indicator is referred to as “wheel deceleration” because it takes into account parameters influencing the speed of the wheel, and therefore factors such as, for example, the influence of heat on the brake pads or the environment in which the vehicle is moving, such as, for example, the condition of the road surface.

[0041] The value of this deceleration indicator is then transmitted to the deceleration control member 14, in order to compare the difference between the engine deceleration thus calculated and the desired deceleration command. In other words, a control of the deceleration command to be achieved is carried out based on the calculation of the wheel deceleration.

[0042] Furthermore, in the preferred embodiment shown in the, data from the wheel speed sensor is recorded for a predetermined period and filtered through a prediction filter 40. Prediction filter 40 is preferably a Kalman filter.

[0043] Thus, in the event of temporary unavailability of the data from the wheel speed sensor 32, the tightening torque is regulated as a function of the data from the prediction filter 40 relating to an estimated state of the data from the wheel speed sensor 32. In this way, a certain degree of precision is maintained in the control of the tightening torque despite a temporary unavailability of the wheel speed sensor, which the estimated state of the data from the wheel speed sensor 32 from the prediction filter makes it possible to compensate for until it is available again.

[0044] For this, in the embodiment illustrated in 1, the data from the wheel speed sensor 32 filtered by the prediction filter 40 are sent directly to the deceleration control member 14, which detects if no new data from the wheel speed sensor 32 is available after a predetermined period of time. In this case, it is the data relating to the estimated state of the data from the wheel speed sensor 32 from the prediction filter 40 which are sent to the wheel deceleration computer 34. The wheel deceleration computer 34 then sends the deceleration indicator that it has calculated to the deceleration control member 14.

[0045] In an alternative embodiment, the data from the wheel speed sensor 32 are recorded over a predetermined period and a physical model of the evolution of the deceleration is constructed as a function of the evolution of the position indicator, this physical model being a function of the data from the wheel speed sensor 32 thus recorded. This model is in particular an abacus.

[0046] Thus, in the event of temporary unavailability of the data from the wheel speed sensor, the tightening torque is regulated according to the data from the physical model. In this way, a certain degree of precision is maintained in the control of the tightening torque despite a temporary unavailability of the wheel speed sensor 32, which the physical model allows to replace until it is available again. In other words, in this second embodiment, the physical model fulfills a function similar to that of the prediction filter.

[0047] According to an embodiment not illustrated in the, the tightening torque is also regulated as a function of a braking instruction, the braking instruction corresponding to the acquisition of a state of the brake pedal P.

[0048] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. It is notably possible to use a force sensor between the motor and the actuator to control the braking torque control. List of references

[0049] 10: Deceleration request organ12: Deceleration conversion model

[0050] 14: deceleration control member16: motor target position determination member18: tightening torque conversion model20: motor position control member22: motor supply current intensity determination member24: motor supply current intensity control member25: oriented flux control26: braking means actuator stroke calculation member28: tightening torque calculation member30: motor deceleration calculation member32: wheel speed sensor34: wheel deceleration calculator36: lock detection device38: wheel anti-lock braking system

[0051] P: brake pedalI: motor supply current intensity sensorR: motor rotation sensorW: motor vehicle wheel

Claims

Method for controlling the tightening torque of an electromechanical brake for a motor vehicle, the brake comprising an electric motor equipped with a rotating shaft intended to drive mechanical means for tightening the brake, characterized in that it comprises the following steps: - data is acquired from a wheel speed sensor (32) performing a characteristic measurement of the speed of at least one of the wheels of the vehicle, - a deceleration indicator characteristic of the acceleration of the vehicle is determined based on the data from the wheel speed sensor (32), - the tightening torque is regulated based on the deceleration indicator. Control method according to claim 1, in which an actuator modifies friction means as a function of the tightening torque thus regulated. Control method according to claim 1 or 2, wherein the wheel speed sensor (32) is part of an anti-lock braking system (38) or electronic trajectory control system already present in the vehicle. Control method according to any one of the preceding claims, wherein the tightening torque is also regulated as a function of an indicator which characterizes the position of the electric motor, called position indicator, calculated as a function of data from a sensor which measures a parameter related to the rotation of the motor shaft, called rotation sensor (R). Control method according to any one of the preceding claims, wherein the tightening torque is also regulated according to data from a sensor measuring a parameter related to the intensity of the electric current supplying the electric motor, called current sensor (I). Control method according to any one of the preceding claims, wherein the tightening torque is also regulated as a function of a braking command, the braking command preferably corresponding to the acquisition of a state of a brake pedal (P). Control method according to claim 4, in which data from the wheel speed sensor (32) are recorded during a predetermined period and a physical model of the evolution of the deceleration is constructed as a function of the evolution of the position indicator, this physical model being a function of the data from the wheel speed sensor (32) thus recorded. Control method according to claim 7, wherein, in the event of temporary unavailability of data from the wheel speed sensor (32), the tightening torque is regulated according to data from the physical model. Control method according to any one of claims 1 to 6, wherein the data from the wheel speed sensor (32) are recorded for a predetermined period and filtered through a prediction filter (40), preferably a Kalman filter. Control method according to claim 9, wherein, in the event of temporary unavailability of data from the wheel speed sensor (32), the tightening torque is regulated according to data from the prediction filter (40) relating to an estimated state of the data from the wheel speed sensor (32). Control method according to claim 3, wherein, using the wheel speed sensor (32), it is detected whether at least one of the vehicle's wheels is locked, and in the event of a lock of at least one of the wheels, the anti-lock braking system (38) or electronic trajectory control sends a command to tighten the electromechanical brake. Braking system capable of implementing the method according to any one of claims 1 to 11. Vehicle comprising the braking system according to claim 12.