Method and device for operating electromechanical brake device, brake device and brake system

Abstract

The invention relates to a method and a device for operating an electromechanical brake device, a brake device and a brake system. The invention relates to an electromechanical brake device (3) for a motor vehicle, comprising at least one actuatable electric motor (9) and at least one actuating element (6) which can be displaced by the electric motor (9), the actuating element (6) having a ventilation gap (x) in the actuating direction in the idle state of the brake device (3). According to the invention, for the checking process, the electric motor (9) is actuated in such a way that the actuating element (6) is displaced only within the ventilation gap (x), and the presence of an error function is ascertained on the basis of at least one operating parameter of the electric motor (9) detected in the process.

Description

Technical Field

[0001] The invention relates to a method for detecting a malfunction of an electromechanical brake device of a brake system of a motor vehicle, the electromechanical brake device having at least one controllable electric motor and at least one actuating element displaceable by the electric motor, wherein, in the idle state of the brake device, the actuating element has a ventilation gap in the actuating direction.

[0002] The invention further relates to a device for operating an electromechanical braking device as described above, as well as to an electromechanical braking device having such a device and a brake system having at least one such electromechanical braking device. Background Art

[0003] Methods and braking devices of the type described above are already known from the prior art. While conventional hydraulic brake systems can monitor the hydraulic pressure in the brake system using pressure sensors to check the function of the brake system, this is more complex with electromechanical brake systems. If the force transmission is entirely mechanical—that is, without a hydraulic system—then the pressure sensors typically used in brake systems are no longer usable. While in hydraulic brake systems, during the test process, the inlet valves to the hydraulic wheel brakes of the test system are closed to detect malfunction, thereby preventing the wheel brakes from generating a braking torque due to the pressure buildup, this is not possible with electromechanical brake systems that act directly on the corresponding mechanical wheels.

[0004] Braking devices typically have a clearance gap that an actuator or actuating element must bridge before a braking force or braking torque can be generated. The clearance gap is to be understood as the distance between the brake pad or brake lining and the brake disc, and therefore the distance that the actuating element must bridge before a braking force can be generated. In the idle state of the braking device, the clearance gap serves in particular to reduce wear on the braking device by avoiding frictional contact between the braking device, in particular the brake pad, and the brake disc when the braking device is not actuated. Depending on the application, the clearance gap can be selected to be larger or smaller to prevent wear. Summary of the Invention

[0005] An advantage of the method according to the invention is that a malfunction of the electromechanical brake device can be detected even when there is no braking torque or braking force increase. To this end, according to the invention, the electric motor is controlled during the check process so that the actuating element is displaced only within the ventilation gap, and the presence of a malfunction is determined based on the operating parameters of the electric motor detected in this process. In particular, the motor current and / or motor voltage of the electric motor are continuously monitored as operating parameters, and a malfunction of the brake device is determined based on the detected values. As long as the actuating element is displaced only within its ventilation gap, it is ensured that the brake device does not apply a braking torque or braking force. Although the electric motor is controlled, in particular to eliminate the ventilation gap and thus to move the actuating element in the actuation direction, without eliminating the ventilation gap, at least one operating parameter of the electric motor is controlled and, in particular, checked for anomalies. This advantageously allows a malfunction of the brake device to be detected without generating a braking torque.

[0006] According to a preferred embodiment of the present invention, a malfunction is detected when a deviation of operating parameters from expected operating parameters is detected, in particular when an unexpectedly high motor current and / or an unexpectedly high motor voltage of the electric motor is detected. For example, if the motor current unexpectedly rises above a predefined limit value and / or rises at an unexpectedly early time or after an unexpectedly short distance, then an impairment of the function of the braking device should be determined.

[0007] According to another embodiment of the present invention, a malfunction is preferably determined when an unexpected absence of a change in an operating parameter is detected, in particular when a motor current increase and / or a motor voltage increase is absent. In this case, the brake device is checked to see whether the desired reaction in the brake device is fully achieved by actuating the electric motor. A malfunction is also determined if, for example, it is detected that the actuating element is not displaced despite actuation of the electric motor.

[0008] When carrying out the method, it is preferably provided that the electric motor is controlled so that the inertia force, in particular the inertia force of the brake device or the electric motor, can be detected as a counter-torque. Therefore, the inertia force of the electric motor, in particular its rotor, is used to test the functional effect of the electric motor. Here, the inertia force is generated on the one hand by the mass of the rotor of the electric motor, and on the other hand by the magnetic force acting between the rotor and the stator and which can apply a restraining torque to the rotor. In addition, the inertia force is affected by the mass of the actuating element itself and the optional transmission device between the electric motor and the actuating element. The counter-torque generated by the inertia force is detected by a change in operating parameters, in particular by an increase in the motor current. Therefore, the detected counter-torque is advantageously compared with the expected counter-torque obtained on another brake device of the brake system by previous calculations and / or tests or by a check process in order to determine whether the brake device, in particular the electric motor, is operating normally.

[0009] The electric motor is preferably actuated with a frequency or dynamics that are insufficient to eliminate the inertial forces. This ensures that the electric motor is not in rotation and that the actuating element is not displaced in such a way as to eliminate the ventilation gap. The actuation with frequency or dynamics ensures that the electric motor is only briefly actuated to generate a torque that is, however, lower than the inertial forces of the braking device, thereby preventing the motor from starting.

[0010] According to an alternative embodiment of the present invention, the electric motor is preferably controlled to operate in the opposite direction of the actuation. This ensures that the ventilation gap cannot be eliminated by the actuating element. Instead, the electric motor is controlled in the opposite direction, thereby moving the actuating element, in particular, into an end position facing away from the operating position. In particular, the actuating element is assigned an end stop, toward which it can be pulled as far as possible. The end stop ensures, for example, a defined initial position of the actuating element, thereby enabling calibration of the actuating element even during operation of the braking device or a motor vehicle equipped with the braking device. Since the actuating element is moved in the direction of the end stop by the electric motor, a functional check of the electric motor is also possible without generating a braking torque. If the actuating element hits the end stop, the motor current of the electric motor suddenly increases. This ensures that the actuating element reaches the end stop when the operating parameter change corresponds to the expected operating parameter change, and that the electric motor or the braking device equipped with the actuating element is operating normally. In particular, if the expected operating parameter change disappears, a malfunction of the braking device is detected.

[0011] According to another embodiment of the present invention, the parking brake is preferably activated before the electric motor is operated, which blocks the braking device. Corresponding parking brakes are known from the prior art. These parking brakes mechanically interfere with the force flow from the electric motor to the actuating element, during which the parking brake, for example, moves a locking element into the transmission. The moved-in locking element ensures that the braking force generated once is maintained in the no-current state. This allows for energy-saving parking braking. By blocking the braking device before operating the electric motor, that is, when the braking device is in the idle state, the electric motor can be operated to move the actuating element in the actuating direction without eliminating the ventilation gap. Instead, the force or torque provided by the electric motor acts directly on the parking brake, which prevents the actuating element from being displaced. Therefore, in this case, it is also possible to compare one or more detected operating parameters of the electric motor with the expected operating parameters expected when operating the parking brake in order to identify malfunctions of the braking device.

[0012] Preferably, the braking system comprises a plurality of electromechanical braking devices, wherein the braking devices are preferably each checked for malfunction in temporal succession. This ensures that activation of a braking device does not affect the behavior of one of the other braking devices. Preferably, the detected operating parameters of the braking devices respectively assigned to an axle of the motor vehicle are compared with one another. This makes it possible to dispense with a comparison with previously detected (i.e., calculated and / or measured) reference parameters. Instead, the detected operating parameters of the braking devices are preferably checked against one another for plausibility.

[0013] Alternatively or in addition to the motor current or motor voltage, friction, hysteresis between forward and reverse movement of the actuating element, gear play and / or caliper stiffness of the transmission, transmission efficiency, response time, dynamics, acceleration, motor constant, at least one resistance, and / or the state of the power electronics of the electric motor are preferably determined as operating parameters and serve as the basis for the functional check. Thus, for example, transmission faults, such as damaged gear teeth or ball ramps, which manifest themselves, for example, as oscillations in the current or position signals of the brake device, can also be determined.

[0014] The method is preferably performed at regular time intervals and / or after each commissioning of the brake system. In particular, the method is performed when the driving situation is suitable for this purpose, for example, when significant dynamic braking is required. However, in this case, driving is only performed if actuation of the corresponding braking device does not negatively affect the driving behavior of the motor vehicle and is, in particular, not noticeable to the vehicle's occupants.

[0015] The device according to the invention is characterized in that it has a control unit which is specially designed for carrying out the method according to the invention. The advantages already mentioned above result.

[0016] The braking device according to the invention is characterized by the device according to the invention. The advantages already mentioned above result.

[0017] The braking system according to the invention is characterized in that it comprises a plurality of the above-mentioned braking devices, each of which is assigned a device according to the invention or a common device according to the invention is jointly assigned to the braking devices, resulting in the advantages already mentioned above. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further advantages and preferred features and feature combinations are particularly apparent from the preceding description. The invention will now be explained in detail with reference to the accompanying drawings.

[0019] Figure 1 A motor vehicle with an advantageous brake system is shown in a simplified top view.

[0020] Figure 2 The braking system is schematically shown, and

[0021] Figure 3 A flow chart is shown for explaining an advantageous method for operating a brake system. DETAILED DESCRIPTION

[0022] Figure 1 A simplified diagram shows a motor vehicle 1 having an advantageous braking system 2. Braking system 2 has a braking device 3 for each wheel of motor vehicle 1, wherein braking devices 3 are operated by a common control unit 4. Control unit 4 actuates braking devices 3, in particular in response to a braking request predefined by the driver of the motor vehicle or a braking request from an automated driving system of motor vehicle 1, in order to decelerate motor vehicle 1 in accordance with the braking request. In this case, braking devices 3 are designed as electromechanical braking devices 3.

[0023] Figure 2 The schematic diagram shows an exemplary embodiment of one of the brake devices 3. Each electromechanical brake device 3 has an actuator 5 and an actuating element 6 that can be displaced by the actuator 5. In this case, the actuating element 6 is designed as a pressure piston, which is connected to a brake pad 7 or brake lining of a brake caliper 8 having two brake pads 7. A brake disk 9 is guided between the brake pads 7 and is connected in a rotationally fixed manner to the wheel of the motor vehicle 1 assigned to the brake disk. If the brake pad 7 is moved toward the brake disk 9 by the actuating element 6, the brake disk 9 is clamped between the two brake pads, thereby generating a braking torque on the brake disk, which acts on the assigned wheel and thus decelerates the motor vehicle 1.

[0024] According to the present embodiment, the actuator 5 comprises a controllable electric motor 9, which is connected to the actuating element 6 via an advantageous transmission 10 for displacement thereof. The actuating element 6 is held in a longitudinally displaceable and displaceable manner. The transmission 10 is designed, in particular, to convert the rotational movement of the rotor of the electric motor 9 into a translational movement of the actuating element 6.

[0025] To check the function of the brake device 3, the following is performed and reference is made to Figure 3 Described method. Figure 3 For this purpose, a flow chart is shown in which the essential method steps are illustrated in a simplified manner.

[0026] In a first step S1, the motor vehicle is put into operation and the brake system 2 is activated. In a subsequent query S2, a check is performed to determine whether the current operating conditions of the motor vehicle 1 allow the inspection process to be carried out safely. In particular, a check is performed to determine whether the execution of the inspection process will affect the vehicle's behavior. The inspection process is only initiated if the execution of the inspection process will not negatively affect the operating behavior of the motor vehicle 1. Furthermore, a check is performed to determine when the inspection process was last carried out or whether a predetermined duration has elapsed since the last inspection process was carried out, and whether a new inspection process is required. Optionally, a check is performed to determine whether a dynamic braking process is occurring due to a braking torque requirement. If this is the case, the inspection method can also be carried out without the inspection process affecting driving operation or being perceptible to the driver of the motor vehicle 1.

[0027] If the conditions required for carrying out the checking process are met (yes), the checking process is started in the next step S3 . To this end, the electric motor 9 is actuated to generate a torque, but without eliminating the ventilation clearance of the actuating element 6 .

[0028] In the idle state, the brake pad 7 is spaced apart from the brake disc 9. This distance x is called the air gap. A braking torque or braking force can only be generated when the air gap is closed and the brake pad 7 contacts the brake disc 9. The air gap ensures, in particular, that no friction occurs between the brake disc 9 and the brake pad 7 or brake lining during driving operation, when no braking is required. The advantageous control of the electric motor in step S3 ensures that no braking torque or braking force is generated during the test that could impair driving operation.

[0029] In a next step S4 , operating parameters, in particular operating parameters of the electric motor, are monitored and evaluated in response to the activation of the electric motor.

[0030] In the next step S5, based on at least one of the determined operating parameters, it is determined whether the brake device 3 is operating normally or whether a malfunction exists. To this end, for example, the selected operating parameter is compared with a calculated and / or measured or determined comparison value or reference value. Optionally, the selected operating parameter is compared with equivalent operating parameters of other brake devices in the brake device 3 to check whether one of the two brake devices 3 is malfunctioning.

[0031] If it is determined in step S5 that there is no malfunction (yes), the method restarts or repeats with step S2. However, if it is determined that there is a malfunction (no), an error warning is generated and output in the following step S6. For example, this indicates to the driver that one of the brake devices 3 is malfunctioning. Optionally, an emergency operation is provided for the malfunctioning brake device 3.

[0032] The advantage of the method is that a functional check can be performed without a pressure or force sensor and without generating a braking force on one of the vehicle's wheels. In order to control the electric motor 9 without eliminating the ventilation gap, one of the following variants is implemented in particular:

[0033] According to a first variant, the motor inertia of the electric motor 9 is utilized. By controlling the motor frequency and / or the dynamics, the motor inertia is not eliminated and thus prevents displacement of the actuating element 6. The motor inertia is generated, in particular, by the mass of the rotor to be driven of the electric motor 9 and optionally by magnetic forces acting in the electric motor 9, and optionally by the mass of the transmission 10 to be driven and the actuating element 6 itself.

[0034] In another variant, the actuating element 6 is moved by the electric motor 9 in the direction opposite to the actuating direction in the direction of the end stop 11, which prevents further displacement of the actuating element 6, in particular of the brake shoe 7. This also safely prevents the ventilation gap from being eliminated, and the overall functioning of the electric motor 9 and the brake device 3 can still be checked safely.

[0035] According to a third variant, a parking brake 12 is assigned to the actuator 5, in particular the transmission 10. Upon activation, the parking brake engages mechanically or form-lockingly in the transmission 10 to block the transmission. Parking brake 12 is activated before the electric motor 9 is actuated, thereby blocking the transmission 10. If the electric motor 9 is subsequently actuated, the actuating element 6 is prevented from closing the ventilation gap. Instead, the electric motor 9 operates to prevent the parking brake 12 from locking.

[0036] If during the testing process it should still be necessary to press the brake lining 7 or the brake shoe against the brake disk 9 , it is realized that this can be achieved only very easily or with a low pressure or a low braking torque.

[0037] Preferably, a malfunction is detected not due to a deviation between an actual sensor value and a target sensor value, but rather due to a parameter deviation, which is particularly identified based on a model. For this purpose, for example, selected operating parameters of the respective brake device 3 are compared with the same operating parameters of other brake devices in the brake device 3 to check whether the brake devices are operating identically or differently and to detect whether a malfunction is present. In order to prevent the checking processes of the brake devices 3 from influencing each other, these checking processes are particularly performed sequentially, particularly with a slight temporal offset.

[0038] Due to the signals typically present in brake system 2, which are related to operating current, operating voltage, motor position (e.g., as a rotor rotation angle), and possibly motor temperature, the following operating parameters of electric motor 9 are preferably considered in the fault diagnosis: friction, hysteresis between forward and reverse travel, gear play and caliper stiffness of the transmission, transmission efficiency, response time, time constant, dynamics, motor acceleration, motor constant, resistance, and / or the state of the power electronics, in particular the bridge circuit of the power electronics. Furthermore, transmission faults, such as tooth damage, ball slope, etc., are detected based on oscillations in the current or position signals of electric motor 10.

[0039] A check process is always performed, in particular, when the driving situation is suitable for this purpose, for example, when braking is performed with significant dynamics due to the corresponding braking torque requirement. In this case, the check is performed during braking operation, but the ventilation gap x must be closed. However, in this case, an additional or separate check process can be omitted.

[0040] However, the present method allows active control of the electric motor 9 in the state of the brake system 2 in which no braking request is present, so that the operating behavior of the motor vehicle 1 cannot be influenced by the test process. For this purpose, the test process is preferably performed during commissioning of the motor vehicle 1 or when the brake system 3 has not been used for a predetermined period of time. Combinations of test processes during and outside of braking situations are also conceivable. It is also conceivable to add a test process during normal braking operation, i.e., during a braking request, in which a sinusoidal wave is added to the target value during the release process of the brake system 3, i.e., when the actuating element 6 moves opposite to the actuation direction, and the response in the operating parameter is monitored.

[0041] A sudden drift in an operating parameter on one of the brake devices indicates a malfunction. In contrast, slow or small deviations are more likely to indicate wear phenomena and are therefore preferably compensated for during operation.

Claims

1. A method for detecting a malfunction of an electromechanical brake device (3) of a brake system (2) of a motor vehicle (1), the electromechanical brake device having at least one controllable electric motor (9) and at least one actuating element (6) displaceable by the electric motor (9), wherein: In the idle state of the braking device (3), the actuating element (6) has a ventilation gap (x) in the actuating direction, characterized in that, for the inspection process, the electric motor (9) is controlled so that the actuating element (6) is displaced only within the ventilation gap (x), and the presence of a faulty function is determined based on at least one operating parameter of the electric motor (9) detected in this process.

2. The method according to claim 1, characterized in that When a deviation of operating parameters of the electric motor (9) from expected operating parameters is detected, a malfunction is determined.

3. The method according to any one of the preceding claims, characterized in that In the event of a detected unexpected absence of a change in an operating parameter, a malfunction is determined.

4. The method according to any one of the preceding claims, characterized in that The electric motor (9) is controlled in such a way that the inertial force can be detected as a counter torque.

5. The method according to any one of the preceding claims, characterized in that The electric motor (9) is operated with a frequency or dynamics insufficient to cancel the inertial forces.

6. The method according to any one of the preceding claims, characterized in that The electric motor (9) is controlled to work in the opposite direction to the actuation direction.

7. The method according to any one of the preceding claims, characterized in that Before the electric motor (9) is actuated, a parking brake is activated, which blocks the braking device (3).

8. The method according to any one of the preceding claims, characterized in that The brake system (2) has a plurality of electromechanical brake devices (3), wherein the brake devices (3) are each checked for malfunction in chronological order.

9. The method according to any one of the preceding claims, characterized in that The method is carried out at regular time intervals and / or after each commissioning of the brake system (2).

10. A device for operating an electromechanical brake device (3) of a brake system (2) of a motor vehicle (1), the electromechanical brake device having at least one controllable electric motor (9) and at least one actuating element (6) displaceable by the electric motor (9), wherein: In the idle state of the braking device (3), the actuating element (6) has a ventilation gap (x) in the actuating direction, and is characterized by a control unit that is specially designed to carry out the method according to any one of claims 1 to 9 in normal use.

11. An electromechanical brake device (3) for a brake system (2) of a motor vehicle (1), comprising at least one controllable electric motor (9) and at least one actuating element (6) displaceable by the electric motor (9), wherein: In the idle state of the brake device (3), the actuating element (6) has a ventilation gap (x) in the actuating direction, characterized by an apparatus according to claim 10.

12. A brake system (2) for a motor vehicle, comprising a plurality of electromechanical brake devices (3) according to claim 11, wherein: A device according to claim 10 is respectively assigned to the braking devices (3), or a common device according to claim 10 is jointly assigned to the braking devices (3).

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