METHOD FOR CONTROLLING THE PULLING TORQUE OF AN ELECTROMETAL BRAKE

Description

[0001] The invention relates to the field of motor vehicle braking actuators, more particularly electromechanical brakes, and methods for regulating 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 a rotor linked in rotation to a wheel of the vehicle to grip it and thus brake the vehicle by friction, or to move 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] Document WO 2019 / 151146 A1 describes a method for controlling the tightening torque of an electromechanical brake for a motor vehicle comprising a step of determining a reaction torque observer, which characterizes at least one reaction of the mechanical brake tightening means to the action of the electric brake motor on these mechanical tightening means, and a step of regulating the tightening torque as a function of the reaction torque observer.

[0006] The invention thus aims to provide a method for controlling the tightening torque of an electromechanical brake which is economical and which takes into account different parameters in order to regulate the tightening torque precisely.

[0007] To this end, 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 rotating shaft intended to drive mechanical means for tightening the brake, the method comprising the following steps: determination of an indicator, called reaction torque observer, which characterizes at least one reaction of the mechanical means of applying the brake to the action of the electric motor on these mechanical means of applying, as a function of a rotation speed of the rotating shaft of the electric motor and an intensity of an electrical supply current of the electric motor, and regulation of the brake applying torque as a function of the reaction torque observer.

[0008] Thus, the presence of a force sensor to measure the reaction torque of the mechanical brake application means to the action of the electric motor on them is not necessary. Indeed, the reaction torque observer makes it possible to estimate this reaction torque from parameters which are already known or measured elsewhere, namely the intensity of the electrical supply current of the electric motor and the rotational speed of the rotating shaft of the electric motor. The reaction torque observer thus makes it possible to estimate, from information relating to the electric motor (intensity of the supply current and rotational speed of the rotating shaft) information on the elements which are located downstream of this motor, namely the mechanical brake application means, without having to add a sensor.As previously stated, the reaction torque of the mechanical brake application means is dependent on external conditions, such as, for example, the swelling of the brake pads due to the heat caused by braking or the various components of the brake. By estimating this reaction torque using the reaction torque observer, it is therefore possible to regulate the brake application torque precisely in order to ensure the most precise and safest braking possible.

[0009] The brake application torque regulation consists of controlling an increase or a decrease in the application force of the mechanical brake application means as a function of the reaction torque observer. For example, if the reaction torque estimate provided by the reaction torque observer indicates that it is necessary to increase the application force to obtain a desired deceleration, an increase in the application force is controlled. If the reaction torque estimate provided by the reaction torque observer indicates that it is necessary to reduce the application force to obtain a desired deceleration, a decrease in the application force is controlled.

[0010] The process is economical since no additional sensors are required, in particular no force sensors, and allows the actual conditions of application of the mechanical brake application means to be taken into account in real time.

[0011] According to one embodiment, the reaction torque observer comprises a high-pass filter configured to reduce disturbances caused by a variation in speed of the electric motor.

[0012] Such a speed variation occurs, for example, when the engine is accelerated.

[0013] According to one embodiment, the reaction torque observer comprises a low-pass filter.

[0014] Advantageously, the reaction torque observer (OBs CR ) is estimated according to the following relationship: Obs CR = I q × K n + J n × wc × Ω m − Δ j × ω − Δ k × I q − C × wc p + wc − J n × wc × Ω m in which, I q corresponds to the intensity of the electric supply current of the electric motor, K n corresponds to the nominal torque coefficient of the motor, J n corresponds to the nominal inertia of the motor, wc corresponds to the cut-off frequency of a low-pass filter, Ω m corresponds to the rotation speed of the rotating shaft of the motor, p corresponds to the Laplace variable, Δj corresponds to the variation of the inertia value of the brake, Δk corresponds to the variation of the brake application torque value, C corresponds to the nominal friction coefficient of the brake, and ω corresponds to the acceleration of the rotation of the rotating shaft of the electric motor.

[0015] The application of this relationship makes it possible to obtain a good estimate of the reaction torque of the mechanical means of applying the brake and therefore to regulate the brake applying torque precisely.

[0016] In particular, the part ( I q × K n) of this relationship corresponds to the engine torque used to accelerate the electric motor. Its unit is Nm. This torque is therefore proportional to the intensity I q of the electric supply current of the electric motor.

[0017] The part ( J n × wc × Ω m ) of this relationship corresponds to the acceleration torque of the engine. It reflects the reaction of the engine to the torque that was used to accelerate it. Its unit is therefore also Nm

[0018] The part - (Δ j × ω - Δ k × I q ) of this relationship corresponds to the relative difference between the useful torque and the nominal torque. This difference provides information on losses of useful torque, for example in the form of friction or noise.

[0019] The part ( wc p + wc ) of this relationship corresponds to a low-pass filter and makes it possible to reduce disturbances caused by variations in the speed of the motor, for example during acceleration of the latter or during a control step.

[0020] The part - ( J n × wc × Ω m ) of this relationship corresponds, as indicated previously, to the acceleration torque of the engine.

[0021] In one embodiment, the method further comprises a step of determining an indicator, called a tightening torque disturbance observer, which characterizes at least one disturbance likely to disturb the determination of the reaction torque observer, as a function of the rotation speed of the rotating shaft of the electric motor and the intensity of the electrical supply current of the electric motor, the step of regulating the tightening torque of the brake being further carried out as a function of the tightening torque disturbance observer.

[0022] This makes it possible to reduce the noise that interferes with the determination of the reaction torque observer so that the reaction torque estimation is more accurate and therefore the regulation of the brake application torque is also more accurate.

[0023] According to one embodiment, the torque disturbance observer includes a low-pass filter configured to reduce high-frequency disturbances.

[0024] Advantageously, the tightening torque disturbance observer (Obs CS ) is estimated according to the following relationship: Obs CS = I q × K n + J n × wc × Ω m × wc p + wc + J n × wc × Ω m in which, I q corresponds to the intensity of the electric supply current of the electric motor, K n corresponds to the nominal torque coefficient of the motor, J n corresponds to the nominal inertia of the motor, wc corresponds to the cut-off frequency of a low-pass filter, Ω m corresponds to the rotation speed of the rotating shaft of the motor, and p corresponds to the Laplace variable.

[0025] Applying this relationship allows for a good estimate of a disturbance that may disturb the determination of the reaction torque observer and therefore reduces noise and provides a more accurate estimate of the brake reaction torque.

[0026] As before, the portion ( I q × K n ) of this relationship corresponds to the engine torque used to accelerate the electric motor. Its unit is Nm. This torque is therefore proportional to the intensity I q of the electric supply current of the electric motor.

[0027] The portion ( J n × wc × Ω m ) of this relationship corresponds to the acceleration torque of the engine. It reflects the reaction of the engine to the torque that was used to accelerate it. Its unit is therefore also Nm

[0028] The portion ( wc p + wc ) of this relationship corresponds to a low-pass filter which makes it possible to reduce high-frequency disturbances.

[0029] In one embodiment, the electric motor is included in an irreversible type geared motor assembly.

[0030] The implementation of an irreversible geared motor allows the brake to be used, in addition to its service brake function, as a parking brake. The implementation of an irreversible geared motor allows the maintenance of a constant braking torque without electrical consumption, for example when stopping the vehicle at a red light or when the vehicle is descending a slope.

[0031] Advantageously, the motor being a three-phase motor, the method comprises a step of transforming three currents of the three-phase motor into a direct current of zero intensity and a quadratic current, the intensity of the electrical supply current of the electric motor used for the determination of the reaction torque observer and / or the tightening torque disturbance observer corresponding to the intensity of the quadratic current of the electric motor.

[0032] The intensity of the quadratic current is proportional to the motor force. The use of this quadratic current therefore makes it easy to characterize this force.

[0033] The invention also relates to an electromechanical brake for a motor vehicle comprising means for implementing the method described above.

[0034] The invention further relates to a motor vehicle comprising at least one electromechanical brake as described above. Brief description of the figures

[0035] 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: [ Fig. 1 ] there [ Fig. 1 ] is a diagram representing a flowchart of operation of the method for controlling the tightening torque of an electromechanical brake according to an embodiment of the invention. [ Fig.2 ] there [ Fig.2 ] is a graph representing a first control simulation of a tightening torque and an estimation of the tightening torque obtained by the method according to an embodiment of the invention. [ Fig.3 ] there [ Fig.3] is a graph representing a second control simulation of a tightening torque and a tightening torque estimate obtained by the method according to an embodiment of the invention. [ Fig.4 ] there [ Fig.4 ] is an exploded perspective view of an electromechanical brake according to one embodiment of the invention. Detailed description

[0036] It has been represented on the [ Fig. 1 ] a diagram representing a flowchart of operation of the method for controlling the tightening torque of an electromechanical brake 1 according to an embodiment of the invention.

[0037] The electromechanical brake 1 conventionally comprises an electric motor 2 provided with a rotating shaft intended to drive mechanical means for applying the brake 3. Advantageously, the electromechanical brake 1 according to the invention comprises a mechanical speed reducer 11 increasing the output torque. The electric motor 2 is preferably a brushless electric motor. The electromechanical brake 1 also comprises an electronic control unit 10 allowing the implementation of the method described below. As this is an electromechanical brake 1 known per se and shown in [ Fig.4 ], it will not be described further here.

[0038] The mechanical means for applying the brake 3 are controlled by a tightening torque command 4. In order to control the tightening torque of the brake 1, a deceleration command is generated, which corresponds to a desired deceleration for the motor vehicle equipped with this brake 1. This deceleration command may, for example, come from a driver of the vehicle, by actuating a brake pedal, and this command is transmitted to a deceleration request member. The deceleration command may also come from a computer controlling an autonomous vehicle, or a control station controlling the vehicle remotely.

[0039] The desired deceleration command is converted into a raw tightening command using a deceleration conversion model, known per se, giving the tightening torque as a function of the deceleration command.

[0040] The raw tightening command 4 thus obtained is sent to a deceleration control member 5 which, during a step of controlling the deceleration command, will obtain information from various indicators and adjust the raw tightening torque command. In the case of the present invention, these indicators are in particular a reaction torque observer and a brake tightening torque disturbance observer which will be detailed below. The raw tightening torque command 4 is converted into the tightening torque to be achieved, according to these indicators.

[0041] The tightening torque command to be achieved is transmitted to the motor 2 and is in particular converted into a command for the intensity of the electric current supplying the motor 2 and into a target rotation speed of the rotary shaft of the electric motor 2. In the present embodiment, the conversion of the tightening torque command to be achieved into a power supply current intensity of the electric motor 2 to be achieved and into a target rotation speed of the rotary shaft of the electric motor 2 is controlled by the deceleration control member 5 by a suitable control law such as for example field-oriented control.

[0042] The motor 2 then causes the movement of an actuator of the mechanical brake application means 3 which is a function of the intensity of the electrical supply current of the motor 2 and the rotational speed of the rotary shaft of the motor 2 (and therefore of the application torque command) so that the mechanical brake application means 3 operate a braking of a wheel of the vehicle with which they are associated. During braking, the actual braking torque is different from the application torque which has been commanded, in particular because of the influence of environmental factors, such as the temperature or the state of the road. According to the invention, the application torque of the brake is regulated by means of an indicator, called a reaction torque observer, which characterizes at least one reaction of the mechanical brake application means 3 to the action of the electric motor 2 on these mechanical brake application means 3.The use of this observer makes it possible to estimate the reaction torque of the mechanical braking means without needing to use a force sensor.

[0043] The reaction torque observer (Obs CR ) 6 is estimated as a function of the rotational speed 7 of the rotating shaft of the motor and the intensity 8 of the electrical supply current of the electric motor 2. This speed 7 and this intensity 8 are either measured or estimated according to known techniques which will not be detailed here. In the present case, the motor 2 is a three-phase motor. The method comprises a step of transforming the three currents of the three-phase motor into a direct current of zero intensity and a quadratic current, the intensity of the electrical supply current of the electric motor used for the determination of the reaction torque observer 6 corresponding to the intensity of the quadratic current 8 of the electric motor 2.

[0044] In the present embodiment, the reaction torque observer (Obs CR ) 6 is estimated according to the following relationship: Obs CR = I q × K n + J n × wc × Ω m − Δ j × ω − Δ k × I q − C × wc p + wc − J n × wc × Ω m in which, I q corresponds to the intensity 8 of the quadratic current of the electric supply of the electric motor 2, K n corresponds to the nominal torque coefficient of the motor 2, J n corresponds to the nominal inertia of the motor 2, wc corresponds to the cut-off frequency of a low-pass filter, Ω m corresponds to the rotation speed 7 of the rotating shaft of the motor 2, p corresponds to the Laplace variable, Δj corresponds to the variation of the inertia value of the brake, Δk corresponds to the variation of the brake tightening torque value, C corresponds to the nominal friction coefficient of the brake, and ω corresponds to the acceleration of the rotation of the rotating shaft of the electric motor.

[0045] Furthermore, in order to reduce noise, the method further comprises a step of determining an indicator, called tightening torque disturbance observer 9, which characterizes at least one disturbance likely to disturb the determination of the reaction torque observer 6, as a function of the rotation speed 7 of the rotating shaft of the electric motor 2 and the intensity 8 of the electrical supply current 6 of the electric motor 2.

[0046] The brake torque disturbance observer (Obs CS ) 9 is estimated according to the following relationship: Obs CS = I q × K n + J n × wc × Ω m × wc p + wc + J n × wc × Ω m in which, I q corresponds to the intensity 8 of the quadratic current of the electric motor supply, K n corresponds to the nominal torque coefficient of the motor, J n corresponds to the nominal inertia of the motor, wc corresponds to the cut-off frequency of a low-pass filter, Ω m corresponds to the rotation speed 7 of the rotating shaft of the motor, and p corresponds to the Laplace variable.

[0047] Once the reaction torque observer 6, which makes it possible to estimate the reaction torque of the mechanical brake application means 3, and the application torque disturbance observer 9 have been determined, by the above relationships, this information is transmitted to the deceleration control member 5 in order to regulate the application torque of the brake, for example by ordering an increase or a decrease in the application command to the electric motor 2.

[0048] As shown by the figures 2 And 3, the application of these relationships makes it possible to obtain a good estimate of the reaction torque of the mechanical means for applying the brake 3 by taking into account possible noises, thanks to the tightening torque disturbance observer, and therefore to regulate the brake tightening torque precisely. These figures represent a simulation of the estimation of the reaction torque of the mechanical means for applying the brake 3 using the method presented above. The target tightening torque command is represented by a solid line and the estimation obtained with the method presented above is represented by a dotted line. It is observed that the method makes it possible to faithfully estimate the reaction torque, which shows that the method works.

[0049] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. In particular, in other embodiments, other relationships than those indicated in the present example are used for the reaction torque observer and / or the brake tightening torque disturbance observer. List of references

[0050] 1: electromechanical brake 2: electric motor 3: mechanical means of applying the brake 4: gross application control 5: deceleration control device 6: reaction torque observer 7: rotation speed of the motor rotating shaft 8: intensity of the motor electrical supply current 9: tightening torque disturbance observer 10: electronic control unit 11: mechanical reducer

Claims

1. A Method for controlling the clamping torque of an electromechanical brake (1) for a motor vehicle, the brake comprising an electric motor (2) equipped with a rotating shaft intended to drive mechanical brake clamping means (3), characterised in that it comprises the following steps: - determination of an indicator, called reaction torque observer (6), which characterises at least one reaction of the mechanical brake clamping means (3) to the action of the electric motor (2) on these mechanical clamping means (3), as a function of a speed of rotation (7) of the rotating shaft of the electric motor (2) and of an intensity (8) of an electrical supply current to the electric motor (2), - determination of an indicator, called clamping torque disturbance observer (9), which characterises at least one disturbance which may disturb the determination of the reaction torque observer (6), as a function of the speed of rotation (7) of the rotating shaft of the electric motor (2) and of the intensity (8) of the electrical supply current to the electric motor (2), and - regulation of the brake clamping torque as a function of the reaction torque observer and of the clamping torque disturbance observer.

2. The method according to claim 1, wherein the reaction torque observer (6) comprises a high-pass filter configured to reduce disturbances caused by a variation in speed of the electric motor (2).

3. The method according to claim 1, wherein the reaction torque observer (6) (ObsCR) is estimated according to the following relationship: Obs CR = I q × K n + J n × wc × Ω m − Δ j × ω − Δ k × I q − C × wc p + wc − J n × wc × Ω m in which, Iq corresponds to the intensity (8) of the electrical current supplied to the electric motor (2), Kn corresponds to the nominal torque coefficient of the motor (2), Jn corresponds to the nominal inertia of the motor (2), wc corresponds to the cut-off frequency of a low-pass filter, Ωm corresponds to the speed of rotation (7) of the rotating shaft of the motor (2), p corresponds to the Laplace variable, Δj corresponds to the variation of the inertia value of the brake (1), Δk corresponds to the variation of the value of the clamping torque of the brake (1), C corresponds to the nominal coefficient of friction of the brake (1), and ω corresponds to the acceleration of the rotation of the rotating shaft of the electric motor (2).

4. The method according to any one of the preceding claims, wherein the clamping torque disturbance observer (9) comprises a low-pass filter configured to reduce highfrequency disturbances.

5. The method according to claim 4, wherein the clamping torque disturbance observer (9) (ObsCS) is estimated according to the following relationship: Obs CS = I q × K n + J n × wc × Ω m × wc p + wc + J n × wc × Ω m in which, Iq corresponds to the intensity (8) of the electrical current supplied to the electric motor (2), Kn corresponds to the nominal torque coefficient of the motor (2), Jn corresponds to the nominal inertia of the motor (2), wc corresponds to the cut-off frequency of the low-pass filter, Ωm corresponds to the speed of rotation (7) of the motor (2), and p corresponds to the Laplace variable.

6. The method according to any one of the preceding claims, in which the electric motor (2) is included in a gearmotor assembly of the irreversible type.

7. The method according to any one of the preceding claims, wherein, the motor (2) being a three-phase motor, the method comprises a step of transforming three currents of the three-phase motor into a direct current of zero intensity and a quadratic current, the intensity (8) of the electric current supplied to the electric motor used for determining the reaction torque observer (6) and / or the clamping torque disturbance observer (9) corresponding to the intensity of the quadratic current of the electric motor (2).

8. An electromechanical brake (1) for a motor vehicle comprising means for implementing the method according to any one of claims 1 to 7.

9. Motor vehicle comprising at least one electromechanical brake (1) according to claim 8.