METHOD FOR ESTIMATING THE CLAMPING FORCE AND / OR THE TRAVEL OF AN ELECTRIC PARKING BRAKE

Abstract

A method for estimating the clamping force exerted by an electric brake on a motor vehicle and / or the stroke of a moving element of the electric brake, comprising the steps: - monitoring the electric brake environment in the motor vehicle to detect an event likely to cause a variation in voltage and / or current within the electrical system, selecting the value of at least one parameter to be used to estimate the clamping force and / or stroke, estimating the clamping force and / or stroke. [Fig. 3]

Description

Title of the invention: METHOD FOR ESTIMATING THE TIGHTENING FORCE AND / OR THE ELECTRIC PARKING BRAKE TRAVEL TECHNICAL FIELD AND PREVIOUS ART

[0001] The present invention relates to a method for estimating the clamping force and / or stroke of an electric parking brake.

[0002] A motor vehicle is equipped at each wheel with either a disc brake or a drum brake.

[0003] In addition, parking brakes are increasingly electrically activated. For example, a screw-nut system operated by an electric motor causes the brake pads to be applied against the disc in the case of a disc brake, and the brake linings against the drum in the case of a drum brake.

[0004] The clamping force exerted by the brake pads or linings and the stroke of the moving parts of the brake, for example the piston or the nut, are not measured but estimated. This estimation takes place when the parking brake has been activated in order to verify whether the braking force is sufficient.

[0005] Such an estimation eliminates the need for a force sensor, thereby simplifying the braking system. Motor activation is interrupted when the clamping force reaches a predetermined threshold value.

[0006] This mode of operation is satisfactory.

[0007] The inventors have observed, however, that the estimation of the clamping force applied by the parking brake could be inaccurate, in particular could be significantly lower than the actual value and therefore lead to a premature shutdown of the electric motor of the parking brake.

[0008] This error in the estimation results from the measurement of the current consumed by the motor. Indeed, the inventors discovered that a rapid variation in voltage and / or electrical current in the vehicle's electrical system caused an error in the estimation of at least some of the parameters involved in calculating the braking force and travel, for example the motor torque constant K and / or the electrical resistance R of the parking brake motor.

[0009] For example, a large increase in voltage in the electrical system causes an underestimation of the value of K and a large decrease in voltage generates an overestimation of the value of K.

[0010] This erroneous estimation of the parameters can lead to an erroneous estimation of the braking force and therefore cause an inappropriate control of the parking brake. For example, when the estimated clamping force exceeds the expected clamping threshold, the controller commands the electric motor to stop. Thus, the electric brake is considered sufficiently engaged when it is not.

[0011] The premature stopping of the electric motor of a parking brake results in a weaker clamping force, and therefore a less effective immobilization of the vehicle, particularly on a slope.

[0012] The variation in voltage and / or current results from external phenomena that occur simultaneously with the actuation of the parking brake. Such phenomena are, for example, the starting of the internal combustion engine or the ignition of the engine heater, Description of the invention

[0013] It is therefore an object of the present invention to offer a method for estimating the braking force exerted by a brake and / or the stroke of a moving element of the brake of at least one electric parking brake offering improved operation, and to a braking system exhibiting improved operational safety.

[0014] The stated objective is achieved by a method for estimating the braking force exerted by the brake and / or the stroke of a moving element of the brake comprising the following steps: - Selection of the value(s) of the parameter(s) used in calculating the braking force and / or the stroke, - Calculation of braking force and / or stroke from the value of the parameter(s) chosen in the previous step.

[0015] Prior to the selection step, the method according to the invention comprises: - either a step of monitoring the operation of the motor vehicle to detect the possibility of a voltage and / or current variation occurring within the vehicle's electrical system. If a voltage and / or current variation is possible, predetermined values ​​for the parameters are used; - or a step of estimating the parameters and a step of monitoring the estimated value of the parameter(s) to verify whether the estimated value is acceptable. If the estimated values ​​are acceptable, they are used in the calculation of the estimated braking force and / or travel. If the estimated values ​​are not acceptable, predetermined values ​​for these parameters are used.

[0016] Thanks to the invention, the risks of significant error in estimating the braking force or stroke are substantially reduced and the immobilization safety of the vehicle is increased.

[0017] In other words, an error or risk of error in the estimation of parameters for the calculation of braking force or stroke is mitigated by using predetermined values ​​when a risk of erroneous estimation or false estimation occurs.

[0018] The present invention relates to a method for estimating the clamping force exerted by an electric brake comprising an electric motor of a motor vehicle and / or the stroke of a moving element of the electric brake comprising the following steps: - monitoring of the electric brake environment in the motor vehicle or the estimated value of at least one parameter to be used to estimate the clamping force and / or stroke, - selection of the value of at least one parameter to be used to estimate the clamping force and / or stroke, estimation of clamping force and / or stroke.

[0019] In one embodiment, the monitoring step involves monitoring an electric brake environment in the motor vehicle in order to detect an event likely to cause a variation in voltage and / or current within the electrical system.

[0020] For example, when an event likely to cause a variation in voltage and / or current within the electrical system is detected, the value of at least one parameter is a predetermined value and the estimation of the clamping force and / or torque takes place with the predetermined value of the parameter.

[0021] Advantageously, the predetermined value of the parameter is a value estimated during a previous cycle.

[0022] According to an additional feature, as soon as an event is detected that is likely to cause a variation in voltage and / or current within the electrical system, it is decided to use the predetermined value of the parameter for calculating the clamping force and / or stroke during a given period.

[0023] According to one feature, if no possibility of occurrence of a variation in voltage or current is detected, the parameters are estimated and the estimation of the clamping force and / or stroke is made using the estimated parameter values.

[0024] According to another example, the monitoring step includes calculating the estimated value of at least one parameter and verifying the acceptability of said estimated value. The verification may include comparing the estimated value with a range of values; if the estimated value is outside said range, the parameter takes a predetermined value, and the estimation of the clamping force and / or stroke can be performed with this predetermined value.

[0025] The method may include a step of counting the number of successive times in which the estimated value was considered unacceptable and in which, when the counter exceeds a certain number, an alert is sent.

[0026] According to an additional feature, at least one parameter includes the motor torque constant and the electrical resistance of the electric brake motor.

[0027] The present invention also relates to a braking system comprising at least one electric parking brake intended to apply a clamping force to a wheel of a motor vehicle, and a control unit for an electric actuator of the parking brake, said control unit being configured to estimate the clamping force of the parking brake and / or the stroke of a moving element of the brake by applying the estimation method according to the invention. BRIEF DESCRIPTION OF THE FIGURES

[0028] The following description will be better understood with the aid of the attached drawings, in which: - [Fig. 1] is a schematic representation of an example of a parking braking system to which the present invention can be applied, - [Fig.2] represents a flowchart of a method for estimating parameters involved in calculating braking force or stroke according to a first embodiment of the invention, - [Fig.3] represents a first method of controlling a parking brake according to the first embodiment of the invention, - [Fig.4] represents a second method of controlling a parking brake according to the first embodiment of the invention, - [Fig. 5] represents a flowchart of a method for estimating parameters involved in calculating braking force or stroke according to a second embodiment, - [Fig.6] represents a method of controlling a parking brake according to the second embodiment of the invention. DETAILED DESCRIPTION OF PRODUCTION METHODS

[0029] In [Fig.1], we can see a vehicle V, represented schematically, comprising a braking system S including brakes F equipping each wheel.

[0030] Service braking is provided on command by hydraulic brakes or electric brakes.

[0031] The braking system also includes a parking braking device comprising at least a first parking brake FP1 at the right rear wheel and a second parking brake FP2 at the left rear wheel.

[0032] The FP1 and FP2 parking brakes are electric parking brakes.

[0033] Generally the parking brake is integrated into the service brake.

[0034] Each electric parking brake includes an actuator equipped with an electric motor and means for converting the rotational movement of the electric motor into a translational movement applying the brake pads against the brake disc or the brake linings against the drum.

[0035] The braking system advantageously includes a control unit for an anti-lock braking system ™ABS and / or a stability control system ™ESP.

[0036] The braking system includes an electronic control unit or ECU (Electronic control unit in Anglo-Saxon terminology), incorporating software, also referred to as a microcontroller MC, for controlling the parking brakes FP1 and FP2. The parking brakes are controlled, for example, by operating a button located in the passenger compartment.

[0037] The motor vehicle includes an electrical circuit, also referred to as the on-board circuit, comprising at least one electric battery, to which various electrically consuming systems are connected. Examples of such systems include the internal combustion engine starting system, a vehicle temperature control system, and the two electric brakes FP1 and FP2.

[0038] The microcontroller includes means for calculating 2 an estimated value of the clamping force exerted by each of the electric brakes and / or the stroke of a moving element of each brake, for example the piston or a nut.

[0039] Monitoring, for example of voltage, preferably takes place continuously and periodically, for example every 5 seconds.

[0040] Thanks to this periodic monitoring, several operating modes are possible.

[0041] According to one mode of operation, if the monitoring took place before the braking action, default parameters are used for any braking action occurring in the period between two monitorings.

[0042] According to another mode of operation, if the voltage varies during a braking action and the parameters K and / or R have not been selected, the system uses previously selected parameters K and / or R for the period until the next monitoring.

[0043] According to another mode of operation, if the voltage varies during a braking action and the parameters K and / or R have been selected, the system uses these parameters K and / or R for the period until the next monitoring.

[0044] These operating modes will be detailed below.

[0045] In the description that follows, we will describe the control of the electric brake FP1 by the microcontroller, but it will be understood that the microcontroller controls both electric brakes in a similar manner.

[0046] Figure 2 shows a flowchart of an example of a process estimation of parameters involved in calculating braking force and / or stroke.

[0047] In the following description, the parameters considered are the motor torque constant K and the electrical resistance R of the motor, but the present invention applies to any other parameter estimation based on the observation of the voltage and / or current involved in the calculation of the braking force and / or stroke.

[0048] The estimation method comprises:

[0049] - The monitoring step 100 of the control unit environment in the motor vehicle to anticipate the occurrence of a variation in voltage and / or current;

[0050] - Step 200 of selecting the value of K and / or R;

[0051] - Step 300 of estimating the clamping force and / or stroke.

[0052] For the implementation of step 100, the control unit includes means for continuously monitoring the risk of a variation in the voltage AU and / or a variation in the current AI occurring within the electrical system, which would be caused by an event within the motor vehicle. For example, the monitoring means receive information from the various systems of the vehicle, for example, the starting system.

[0053] During step 200, the control unit processes the information received from the vehicle systems and decides which parameters to use.

[0054] If the control unit receives signals informing it of the activation of one or more external systems, predetermined values ​​of the parameter(s) are used.

[0055] More specifically, if the control unit receives information indicating that the voltage and / or current will change, for example, that the motor is going to start, and therefore receives a start button command, the control unit issues a command in step 300 not to estimate K and / or R or not to use the estimated values, if these have already been calculated. The control unit then issues a command to select predetermined values ​​of K and / or R, for example, the last validated values ​​of K and / or R. Alternatively, these are values ​​of K and / or R stored in memory during the manufacturing of the control unit.

[0056] When no information is available regarding the risk of a voltage variation occurring and / or current is not reported to the control unit, the control unit instructs step 400 to estimate the parameters K and / or R according to the methods provided for in the absence of a variation in voltage and / or currents based on observation of the motor's inrush current and the current reached in the phase without load, and use the estimated values ​​to calculate the estimated value of the braking force and / or stroke.

[0057] During step 500, the values ​​of the clamping force and / or stroke are calculated and are used to control the actuation of the brake.

[0058] During step 200, when a command is issued not to estimate K and / or R or not to use the estimated values, it is decided not to estimate K and / or R for a given period, for example 5 seconds, and to use the predetermined values ​​of K and / or R. For example, if the parking brake is activated again during this period, the clamping force and / or stroke are calculated directly using the predetermined values ​​of K and / or R. If the parking brake is activated after the end of this period, K and / or R are estimated conventionally, and the clamping force and / or stroke are calculated using these estimated values.

[0059] In [Fig.3], we can see an example of the operation of the braking system representing the variation of the start signal D, the variation of the voltage U and the brake control signal B as a function of time t.

[0060] When the engine ignition signal changes from 0 to 1 at time t0, for a given time period T, 5s in the example shown, the values ​​of K and R are fixed. As an example, K is fixed at 0.0141 Nm / A and R is fixed at 0.58 Q.

[0061] A voltage variation AU appears just after the instant tO.

[0062] The signal not to estimate the values ​​of K and / or R goes to 1.

[0063] If the parking brake is activated at a time tl in the period T, the calculation of the clamping force and / or stroke is carried out with the fixed values ​​of K and / or R.

[0064] When period T is over and the start signal remains at 0, normal operation resumes.

[0065] Figure 4 shows another example of the operation of the braking system according to the invention, in which the engine ignition signal changes from 0 to 1 at time t2 and causes a change in the current i. The period T1, during which the values ​​K and / or R are fixed, starts at t2. The parking brake is activated at t3 during period T1 and is activated at t4 after the end of T1. The brake is deactivated at t5 and is deactivated at t6. In this case, predetermined values ​​of K and / or R are preferably used during period T1. In this example, the predetermined values ​​of K and / or R are used between t2 and t4.

[0066] The flowchart in [Fig.5] represents another embodiment of the estimation method according to the invention.

[0067] The process comprises:

[0068] - step 100' of calculating the estimated value of K Kest and / or the estimated value of R Rest;

[0069] - step 200' of monitoring the value of Kest and / or Rest in order to verify that the values ​​are acceptable, and the choice of K and / or R values ​​to be used. If the Kest and / or Rest values ​​are acceptable, they are used to calculate the clamping force and / or stroke, otherwise predetermined K and / or R values ​​are used to determine Kest and / or Rest;

[0070] - step 300' or 400' of calculating the estimate of the clamping force and / or the race ;

[0071] During step 200', it is checked, for example, whether Kest is within the interval [Kmin; Kmax]. If so, the process proceeds to step 300', during which Kest is used. Conversely, if Kest is outside the interval [Kmin; Kmax], the process proceeds to step 400', and a predetermined value of K is used.

[0072] For example, if Kest < Kmin, we set K = Kmin fixed > Kmin. If Kest > Kmax, K = Fixed Kmax < Kmax.

[0073] Similarly, Rest is calculated and then it is checked whether Rest is within the interval [Rmin; Rmax]. If Rest is indeed within the interval, the Rest value is used for calculating the clamping force and / or stroke; otherwise, the value of R for the calculations is fixed. For example, if Rest < Rmin, R is fixed as Rmin > Rmin. If Rest > Rmax, R is fixed as Rmax < Rmax.

[0074] For example, Kmax = 0.0205 Nm / A and Kmin = 0.089 Nm / A, and Rmax = 1.65 Q and Rmin = 0.28 Q.

[0075] During step 300', the Kest and / or Rest value is used, or during step 400', the predetermined value of K or R is used to calculate the clamping force and / or stroke.

[0076] Very advantageously, a counter C is added to count the number of successive times when the value Kest could not be used in the calculation of the clamping force and / or stroke, in order to detect a possible malfunction in the estimation of K.

[0077] In [Fig.6], an example of the operation of the braking system can be seen according to the embodiment of [Fig.5].

[0078] When the brake is actuation at t7, the Kestl and Restl values ​​are estimated and verified and are considered acceptable and usable. The counter C remains at 0. The brake is deactivated at t8 and reactivated at t9; the Kest2 and Rest2 values ​​are estimated and verified, but they are not considered acceptable and usable, and the counter changes to 1.

[0079] The brake is deactivated at 110 and is reactivated at tl 1, the values ​​Kest3 and Rest3 are estimated and checked, they are not acceptable and usable, the counter goes to 2. If the values ​​Kest3 and Rest3 had been acceptable and usable, the counter would have gone back to 0. At tl2 the brake is deactivated.

[0080] With counter C at 2, an error message can then be sent to the control unit. Preferably, the error message is not sent as soon as the counter reaches 1, as it is assumed that Kest may become unusable, particularly in the event of a voltage variation. However, the probability of the K estimation being incorrect twice in succession is low. It will be understood that the counter may be expected to reach three before an error signal is emitted.

[0081] A similar counter can be implemented for R.

[0082] Thanks to the invention, the determination of the clamping force and / or torque is more reliable, and consequently the operation of the parking brake is made even safer. The risks of overestimating or underestimating the clamping force and therefore of insufficient brake application are reduced. References

[0083] V: vehicle S: braking system F: brakes FP1: First parking brake FP2: Second parking brake 2: Calculation methods C: counter B: brake control signal D: start signal K: motor torque constant R: electrical resistance Kest, Kestl, Kest2, Kest3: estimated values ​​of K Rest, Restl, Rest2, Rest3: estimated values ​​R 100: Control unit environment monitoring step 100': step of calculating the estimated value of K Kest and / or the estimated value of R Rest; 200: Step to select the value of K and / or R. 200': Step to monitor the value of Kest and / or Rest. 300: Step to estimate the clamping force and / or stroke. 400: Step to estimate the parameters K and / or R. 300', 400': step to calculate the estimated clamping force and / or stroke; 500': step to calculate the values ​​of the clamping force and / or stroke.

Claims

Demands

1. Method for estimating the clamping force exerted by an electric brake comprising an electric motor of a motor vehicle and / or the stroke of a moving element of the electric brake comprising the steps: - monitoring an environment of the electric brake in the motor vehicle or the estimated value of at least one parameter to be used to estimate the clamping force and / or stroke, - selection of the value of at least one parameter to be used to estimate the clamping force and / or stroke, - estimation of the clamping force and / or stroke.

2. Estimation method according to claim 1, wherein the monitoring step comprises monitoring an electric brake environment in the motor vehicle in order to detect an event likely to cause a variation in voltage and / or current within the electrical system.

3. Estimation method according to claim 2 wherein, when an event likely to cause a variation in voltage and / or current within the electrical system is detected, the value of at least one parameter is a predetermined value and the estimation of the clamping force and / or torque takes place with the predetermined value of the parameter.

4. Estimation method according to claim 3, wherein the predetermined value of the parameter is a value estimated during a previous cycle.

5. Estimation method according to claim 2, 3 or 4 wherein, upon detection of an event likely to cause a variation in voltage and / or current within the electrical system, it is decided to use the predetermined value of the parameter for the calculation of the clamping force and / or stroke during a given period.

6. Estimation method according to claim 2 or 3, wherein if no possibility of occurrence of a variation in voltage or current is detected, the parameters are estimated and the estimation of the clamping force and / or stroke is made using the estimated parameter values.

7. Estimation method according to claim 1, wherein the monitoring step comprises calculating the estimated value of at least one parameter and verifying the acceptability of said estimated value.

8. Estimation method according to claim 7, wherein the verification includes comparing the estimated value with a range of values, if the estimated value is outside said range the parameter takes a predetermined value, and the estimation of the clamping force and / or stroke is carried out with this predetermined value.

9. Estimation method according to claim 7 or 8, comprising a step of counting the number of successive times during which the estimated value was considered unacceptable and in which, when the counter exceeds a certain number, an alert is sent.

10. Estimation method according to any one of the preceding claims, wherein at least one parameter comprises the motor torque constant (K) and the electrical resistance (R) of the electric brake motor.

11. Braking system comprising at least one electric parking brake for applying a clamping force to a wheel of a motor vehicle, and a control unit for an electric parking brake actuator, said control unit being configured to estimate the clamping force of the parking brake and / or the stroke of a moving element of the brake by applying the estimation method according to any one of claims 1 to 10.

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