METHOD FOR ADJUSTING THE CLAMPING FORCE EXECUTED BY AN ELECTROMEMIC BRAKE

Description

[0001] The invention relates to the field of motor vehicle braking actuators, more particularly a method for adjusting the clamping force exerted by an electromechanical brake.

[0002] A motor vehicle's braking system generally includes mechanical means for applying the brake, notably friction elements such as brake pads, connected to an actuator capable of moving these friction elements towards the vehicle's wheel to grip it and thus brake the vehicle by friction, or of releasing them to stop braking. In the case of an electromechanical brake, the mechanical applying means are controlled by an electric motor equipped with a rotating shaft that drives them.

[0003] To change the rotational speed of a motor ω (radius), it is necessary to vary the electromotive force E. The latter is proportional to the voltage: E = K . ω = U − R . i With : K: motor constant; U: voltage; i: current; R: motor resistance

[0004] It is thus known, for example from documents WO2019131659 and DE102014203350, to modify the rotation speed of a motor ω (rad / s) by means of a voltage control of the type PWM (“Pulse width modulation” in English) or MLI (“Pulse Width Modulation”).

[0005] This involves supplying the motor with a square wave voltage. The average voltage then depends on the duty cycle T0 / T. The speed ω varies according to this average voltage.

[0006] Thus, to control an electric motor, it is necessary to determine the PWM control, i.e., a voltage control, the motor constant K, as well as the motor resistance R. Estimating the speed ω is also important to estimate the rotation angle of the DC motor, because there is no angle sensor on this type of motor.

[0007] Currently, the motor resistance is calculated during the starting current peak in a direct current (DC) motor.

[0008] However, the motor resistance value changes with temperature, and temperature changes during braking. With current methods, there is therefore a risk of overestimating or underestimating the resistance value, and consequently, either insufficient braking or increased friction, thus reducing brake lifespan.

[0009] The invention thus aims to provide a method, as defined in the attached claim 1, for adjusting the clamping force exerted by an electromechanical brake of a motor vehicle, freeing itself from the aforementioned problems.

[0010] To this end, the invention relates to a method for adjusting the clamping force exerted by an electromechanical brake of a motor vehicle, the brake comprising an electric motor equipped with a rotating shaft intended to drive mechanical brake clamping means, the electric motor being controlled by means of a PWM type voltage control, in which the rotational speed of the motor (ω) is estimated from an estimate of the resistance of the motor (R*) and an estimate of the motor constant (K*), then the clamping force is determined from the estimate of the rotational speed of the motor (ω), in which the estimate of the resistance of the motor is updated during an inactive phase (of the motor controller (ECU)) of absence of voltage control (called "idle phase" and corresponding to a phase of approach of the pads towards the disc).

[0011] By calculating the motor resistance during the motor controller's idle phase and continuously updating this estimate, a more accurate motor resistance reading can be obtained. Furthermore, this solution can be implemented with or without a specific sensor.

[0012] Finally, such a process can be used to detect anomalies in the first estimation of resistance, or even as an angle sensor.

[0013] The process may also include one or more of the following characteristics, taken alone or in combination: The motor resistance estimate is updated using a polynomial function of order n, where n is greater than or equal to 2, centered around the nominal value of the motor resistance expressed as an integer; by using only a second-degree polynomial function, the motor resistance estimate is computationally inexpensive, and therefore, this simple and quick-to-implement equation allows observation of the evolution of the motor resistance, and consequently that of the temperature, over shorter time periods (less than 1 ms); the motor resistance estimate is updated with a sampling step of less than 1 ms;the brake comprising an electric motor equipped with a rotating shaft intended to drive mechanical brake clamping means, the clamping force is determined as a function of the updated motor resistance (R[n]), and an actuator controls the mechanical brake clamping means in order to apply the clamping force thus estimated; the motor resistance (R[n]) is estimated at a given instant from a previous value of the motor resistance (R[n-1]), and using a relation describing the resistance of a solenoid in which the voltage (Vbat) is replaced by the difference (V'bat) between the voltage (Vbat) and the motor voltage (V); in the relation describing the resistance of a solenoid, the exponential function is replaced by a Taylor series of order n, n being greater than or equal to 2, centered around the nominal value of the motor resistance expressed as an integer;The resistance of the motor (R[n]) at a given instant is estimated using the following relation: ; R n = V ′ bat δ i n + i n − 1 R n − 1 i n − V ′ bat δ i n a . R n − 1 2 + b . R n − 1 − c with: ➢ R [ n ]:motor resistance at step n ➢ R [ n - 1]:motor resistance at step n-1 ➢ i [ n ]:motor intensity at step n ➢ i [ n - 1]:motor intensity at step n-1 ➢ V' beats δ = V beats δ- K * w :with Vbat, the motor supply voltage, K, the motor constant, and ω, the motor rotational speed. ➢ a :polynomial coefficient ➢ b :polynomial coefficient ➢ c :polynomial coefficient The polynomial coefficients have the following values: a = 0 , 4523 b = 0 , 291 c = 0 , 07027 The polynomial coefficients a, b, and c are integers; the polynomial coefficients have the following values: a = 3 b = 2037 c = 490979 The parameters of the motor resistance determination relationship are expressed in uint32, after applying gains to and the motor resistance in mΩ, the voltage value is expressed with a gain of 100000, the current with a gain of 100; a gain of 7000000 is added; the motor voltage is determined by multiplying the motor constant by the motor rotation speed; the motor rotation speed is estimated or measured using an on-board sensor.

[0014] The invention also relates to a braking system , as defined in attached claim 15, arranged to implement the method according to the invention.

[0015] According to the invention, the braking system may include an electric braking motor, and a controller capable of implementing the method according to the invention.

[0016] According to an example, the nominal resistance of the motor is 0.34 Ω and the inductance of the motor is 0.000117 H, and the controller has a sampling time (t) of 100ms.

[0017] The controller can be a 16-bit or 32-bit controller.

[0018] The invention also relates to a vehicle including the braking system according to the invention. Brief description of the figures

[0019] 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: [Fig. 1]the figure 1 is an example of a result illustrating the estimation of motor resistance, motor voltage, and motor current as a function of time; [Fig. 2] figure 2 is a magnification of the figure 1 around 0.0688s; [Fig. 3] figure 3is a diagram representing a flowchart of the operation of the method for adjusting the clamping force exerted by an electromechanical brake of a motor vehicle, according to a particular embodiment of the invention; [Fig. 4] figure 4 is a diagram representing a flowchart of operation of the method of adjusting the clamping force exerted by an electromechanical brake of a motor vehicle, according to a second particular embodiment of the invention. Detailed description

[0020] We represented at figures 3 and 4 diagrams representing a flowchart of operation of the method of adjusting the clamping force (F*) exerted by an electromechanical brake (B) of a motor vehicle, according to two particular embodiments of the invention.

[0021] The electromechanical brake (B) typically comprises an electric motor with a rotating shaft designed to drive mechanical brake-locking means (not shown). The electric motor is preferably a direct current (DC) motor. As this type of electromechanical brake is well-known, it will not be described further here.

[0022] The electric motor is controlled by means of a voltage control of the PWM type (for Pulse Width Modulation).

[0023] According to the invention, the process comprises the following steps: We estimate the resistance of the motor R*; we estimate the motor constant K*; we estimate the rotational speed of the motor ω* from the estimates of resistance R* and motor constant K*; then we determine the clamping force F* from the estimate of the rotational speed of the motor ω*.

[0024] On the figures 3 and 4 : The first two steps are noted: "Estim: R*, K*"; the third step is noted: "Estim: ω*"; the fourth step is noted: "Estim: F*".

[0025] The clamping force F* is determined continuously, and to obtain an accurate and reliable value of this clamping force, the estimate of the motor resistance is continuously updated.

[0026] To do this, we update the motor resistance estimate during an inactive phase ("idle phase") of the motor controller (ECU), that is, during the phase of no voltage control (OFF phase of the PWM type voltage control).

[0027] The "Idle" phase corresponds to the phase where the brake pads approach the disc. For example... figure 1This phase is visible on the left. Thus, we are at the maximum available voltage without voltage control. This last characteristic allows us to improve the estimation of the motor resistance R* and the motor constant K*.

[0028] To do this, and advantageously, the motor resistance estimate is updated using a polynomial function of order n, n being greater than or equal to 2, centered around the nominal value of the motor resistance expressed as an integer.

[0029] Thus, the calculation time for the update is very fast, and allows for an update of the engine resistance estimate during the idle phase of the engine controller (ECU) even when this idle phase is on the order of one millisecond.

[0030] The term "continuous" refers to a calculation and update with a sampling step of less than 1ms.

[0031] Thus, the clamping force F* is continuously determined from the updated motor resistance value (R[n]). Then, an actuator controls the mechanical brake clamping means to apply the clamping force thus determined.

[0032] In one example implementation, the motor resistance (R[n]) at a given instant is estimated from a previous value of the motor resistance (R[n-1]), using a relationship describing the resistance of a solenoid in which the voltage (Vbat) is replaced by the difference (V'bat) between the voltage (Vbat) and the motor voltage (U). Thus, the function for updating the motor resistance is written as: R n = V ′ bat δ i n + i n − 1 R n − 1 i n − V bat ′ δ i n e − t L R n − 1

[0033] To obtain a polynomial function of order n, we replace, in preferred mode, the exponential function of the relation describing the resistance of a solenoid with a Taylor series of order n, where n is greater than or equal to 2, centered around the nominal value of the motor resistance expressed as an integer. Thus, the function used to update the motor resistance is written: R n = V ′ bat δ i n + i n − 1 R n − 1 i n − V ′ bat δ i n a . R n − 1 2 + b . R n − 1 − c with : R [ n ]: motor resistance at step n R [ n - 1]: motor resistance at step n-1 i [ n ]: motor intensity at step n i [ n - 1]: motor intensity at step n-1 V' beats δ = v bat δ- K * w :with Vbat, the motor's supply voltage, K , the constant engine, and w , the engine's rotational speed. t : no sampling L motor inductance a:polynomial coefficient b:polynomial coefficient c:polynomial coefficient

[0034] To further reduce the update calculation time, the parameters of the motor resistance determination equation are expressed as integers of the type "uint32", rather than as floating-point numbers. Therefore, a, b, and c are preferably integers. To achieve this, the motor resistance is expressed in mΩ, and a gain of 100000 is applied to the voltage value, a factor of 100 to the current, and a factor of 1000 to the time step. Thus, for a motor with a nominal resistance of 0.34 Ω and an inductance of 0.000117 H, and for a controller with a sampling step (t) of 100 µs, the exponential function of the equation describing the resistance of a solenoid is centered around 340 mΩ instead of 0.34 Ω. The exponential function is then written as follows: e − t ∗ 1000 L R n − 1 = 5 , 5868 e − 6 R 2 + 2 , 91 e − 4 R − 0 , 07014

[0035] According to a preferred embodiment, a gain of 7000000 is added, in order to obtain integer polynomial coefficients: a = 3 b = 2037 c = 490979

[0036] There figure 1 is an example of a result illustrating the estimation of motor resistance R*, motor voltage U, and motor current i as a function of time T.

[0037] On the figure 1 The x-axis represents time (T) in seconds, and the y-axis represents, on the right, the motor current (i) in amperes and the voltage (U) in volts, and on the left, the estimated motor resistance (R*) in ohms. The thick solid curve corresponds to the evolution of the motor current i. The dashed curve corresponds to the evolution of the motor voltage U. The thin solid curve corresponds to the evolution of the estimated resistance R*.

[0038] We observe a precise and continuous estimation of the resistance, starting from the phase of no voltage command (inactive phase of the engine controller (ECU)). The evolution of the estimation during this phase is more visible on the figure 2 which represents a magnification of the figure 1 around 0.0688s.

[0039] We now describe a first mode of implementation in reference to the figure 3According to this embodiment, no sensor is required to estimate the clamping force F*. Indeed, the two known parameters are the voltage U and the current i of the motor. Then, the motor resistance (R*) is estimated from the motor current i and the motor voltage U (which can be estimated (U*) from the estimated motor constant K*). Next, the motor speed ω is estimated (ω*) from the estimated motor resistance R*, the voltage U, and the motor current i. Finally, the clamping force F* is estimated from this speed ω*. The motor voltage (U) can be determined by multiplying the estimated motor constant (K*) by the estimated motor speed (ω*).

[0040] We now describe a second embodiment in reference to the figure 4According to this embodiment, an onboard speed sensor is used. The known parameters are the rotational speed ω, the voltage U, and the motor current i. In this embodiment, the clamping force F* is estimated from the estimated motor resistance R*, which is derived from the three known parameters (rotational speed ω, voltage U, and motor current i). The resistance R* is estimated from two known parameters, the current i and the motor speed ω, and one estimated parameter, the motor voltage (U*). The latter is estimated during a verification step of the rotational speed estimate ω* from U (see the lower section on the...). figure 4 , referenced: "Chk ω* : U*").

[0041] The invention also relates to a braking system capable of implementing the process according to the invention.

[0042] The system includes an electric braking motor, and a controller capable of implementing the process according to the invention.

[0043] According to one embodiment, the nominal resistance of the motor is 0.34 Ω and the inductance of the motor is 0.000117 H, and the controller has a sampling time (t) of 100ms.

[0044] According to one embodiment, the braking system includes a 16-bit or 32-bit controller.

[0045] The invention also relates to a vehicle , as defined in attached claim 19, comprising the braking system according to the invention. List of references

[0046] B: Brake T: Time i: Motor current U: Motor voltage U*: Estimated motor voltage R*: Estimated motor resistance K*: Motor constant ω: Motor speed ω*: Estimated motor speed F*: Estimated clamping force

[0047] References related to the estimation formula: R [ n ] : motor resistance at step n R [ n - 1] : motor resistance at step n-1 i [ n ] : motor intensity at step n i [ n - 1] : motor intensity at step n-1 V' beats δ = V beats δ- K * w : with Vbat, the motor's supply voltage, K , the constant engine, and w , the engine's rotational speed. t : no sampling L motor inductance a :polynomial coefficient b:polynomial coefficient c:polynomial coefficient

Claims

1. Method for adjusting the clamping force (F*) exerted by an electromechanical brake (B) of a motor vehicle, the brake (B) comprising an electric motor provided with a rotating shaft which is intended to drive mechanical brake-application means, the electric motor being controlled by means of a PWM-type voltage control, in which the rotational speed of the motor (ω) is estimated from an estimate of the motor resistance (R*) and an estimate of the motor constant (K*), and then the clamping force (F*) is determined from the estimate of the rotational speed of the motor (ω), characterised in that the estimate of the motor resistance (R*) is updated during an idle phase of the motor controller with no voltage control.

2. Method according to the preceding claim, in which the estimate of the motor resistance (R*) is updated using a polynomial function of order n, n being greater than or equal to 2, centred around the nominal value of the motor resistance (R*) expressed as an integer.

3. Method according to one of the preceding claims, in which the estimate of the motor resistance (R*) is updated according to a sampling interval less than 1 ms.

4. Method according to one of the preceding claims, in which, the brake (B) comprising an electric motor provided with a rotating shaft which is intended to drive mechanical brake application means, the clamping force (F*) is determined according to the updated motor resistance (R[n]), and an actuator controls the mechanical brake application means to apply the clamping force (F*) so estimated.

5. Method according to one of the preceding claims, in which the motor resistance (R[n]) is estimated at a given time from a previous value of the motor resistance (R[n-1]), and using a relation describing the resistance of a solenoid in which the voltage (Vbat) is replaced by the difference (V'bat) between the voltage (Vbat) and the motor voltage (U).

6. Method according to the preceding claim, in which a relation is used describing the resistance of a solenoid in which the exponential function is replaced by a Taylor series of order n, n being greater than or equal to 2, centred around the nominal value of the motor resistance expressed as an integer.

7. Method according to the preceding claim, in which the motor resistance (R[n]) is estimated at a given time using the following relation: R n = V ′ bat δ i n + i n − 1 R n − 1 i n − V ′ bat δ i n a . R n − 1 2 + b . R n − 1 − c where: ➢ R[n]: motor resistance at interval n ➢ R[n - 1]: motor resistance at interval n-1 ➢ i[n]: motor current at interval n ➢ i[n - 1]: motor current at interval n-1 ➢ V'batδ = Vbatδ - K * w: where Vbat is the motor supply voltage, K is the motor constant, and w is the rotational speed of the motor. ➢ a:polynomial coefficient ➢ b: polynomial coefficient ➢ c: polynomial coefficient8. Method according to the preceding claim, in which: a = 0.4523 b = 0.291 c = 0.070279. Method according to claim 7, wherein a, b and c are integers.

10. Method according to the preceding claim, in which: a = 3 b = 2037 c = 49097911. Method according to the preceding claim, in which the parameters of the relation for determining the motor resistance are expressed in uint32, after expressing the motor resistance in mΩ, the voltage value is expressed with a gain of 100000 and the current is expressed with a gain of 100.

12. Method according to the preceding claim, in which a gain of 7000000 is added.

13. Method according to one of claims 5 to 10, in which the motor voltage (U*) is determined by multiplying the motor constant (K*) by the rotational speed of the motor (ω*).

14. Method according to the preceding claim, in which the rotational speed of the motor (ω*) is estimated or measured using an onboard sensor.

15. Braking system configured to implement the method according to any one of claims 1 to 14.

16. Braking system according to the preceding claim, comprising a braking electric motor, and a controller adapted to implement the method according to any one of claims 1 to 14.

17. Braking system according to the preceding claim, in which the nominal resistance of the motor is 0.34 Ω and the inductance of the motor is 0.000117 H, and in which the controller has a sampling time (t) of 100 ms.

18. Braking system according to the preceding claim, in which the controller is a 16-bit or 32-bit controller.

19. Vehicle comprising the braking system according to one of claims 15 to 18.