Method and device for operating an electromechanical braking device, braking device and braking system

Abstract

The invention relates to a method for detecting a malfunction of an electromechanical braking device (3) of a braking system (2) for a motor vehicle (1), which has at least one controllable electric motor (9) and at least one actuator element (6) that can be displaced by the electric motor (9), wherein, in the rest state of the braking device (3), the actuator element (6) has a clearance (x) in the actuation direction. It is provided that, for a test procedure, the electric motor (9) is controlled in such a way that the actuator element (6) is displaced only within the clearance (x), and that the presence of a malfunction is determined as a function of at least one operating parameter of the electric motor (9) that is detected in the process.

Description

[0001] The present invention relates to a method for detecting a malfunction of an electromechanical braking device of a braking system for a motor vehicle, which has at least one controllable electric motor and at least one actuator element that can be displaced by the electric motor, wherein in the rest state of the braking device the actuator element has a clearance in the actuation direction.

[0002] Furthermore, the invention 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 to a braking system having at least one such electromechanical braking device. State of the art

[0003] Methods and braking devices of the type mentioned above are already known from the prior art. While in conventional hydraulic braking systems the functionality of the braking system can be tested by monitoring the hydraulic pressure in the braking system using a pressure sensor, this is more complicated with electromechanical braking devices. If power is transmitted purely mechanically, i.e. without hydraulics, a pressure sensor normally used in braking systems can no longer be used. While in hydraulic braking systems inlet valves on the hydraulic wheel brakes of the test system are closed during a test procedure to detect a malfunction, so that no braking torque is generated at the wheel brakes due to the pressure build-up, this is not possible with electromechanical braking devices that act directly on the respective mechanical wheel.

[0004] Braking devices typically have a clearance that the actuator or actuator element must overcome before braking force or braking torque can be generated. The clearance is defined in particular as the distance between a brake shoe or brake pad and a brake disc, and thus the travel the actuator element must travel before braking force can be generated. When the braking device is at rest, the clearance serves in particular to reduce wear on the braking device by preventing sliding contact between the braking device, particularly between the brake shoe and the brake disc, when the braking device is not actuated. Depending on the application, the clearance can be selected to be larger or smaller in order to prevent wear. Disclosure of the invention

[0005] The method according to the invention with the features of claim 1 has the advantage that a malfunction of an electromechanical braking device can be detected even without braking torque or braking force buildup. For this purpose, the invention provides that during a test process, the electric motor is controlled in such a way that the actuator element is only displaced within the release clearance, and that the presence of a malfunction is determined depending on an operating parameter of the electric motor detected in the process. In particular, a motor current and / or a motor voltage of the electric motor are continuously monitored as operating parameters, and a malfunction of the braking device is determined based on the detected values. As long as the actuator element is only displaced within its release clearance, it is ensured that no braking torque or braking force is exerted by the braking device.While the electric motor is being actuated, in particular to overcome the clearance, i.e., to move the actuator element in the actuation direction without overcoming the clearance, at least one operating parameter of the electric motor is monitored and, in particular, checked for abnormalities. This advantageously allows the malfunction of the braking device to be detected without generating a braking torque.

[0006] According to a preferred development of the invention, a malfunction of the electric motor is determined upon detection of a deviation of the operating parameter from an expected operating parameter, in particular upon detection of an unexpectedly high motor current and / or an unexpectedly high motor voltage. If, for example, the motor current rises above a predetermined limit and / or unexpectedly at a surprisingly early point in time or after a surprisingly short distance, it can be determined that the function of the braking device is impaired.

[0007] According to a further embodiment of the invention, it is preferably provided that a malfunction is determined upon detection of an unexpectedly missing operating parameter change, in particular a missing motor current increase and / or a missing motor voltage increase. In this case, the braking device is checked to determine whether the activation of the electric motor actually results in an expected reaction in the braking device. If, for example, it is detected that the actuator element is not displaced despite the activation of the electric motor, a malfunction is also determined.

[0008] When carrying out the method, it is preferably provided that the electric motor is controlled in such a way that an inertial force, in particular of the braking device or the electric motor, can be detected as a counter-torque. The inertial force of the electric motor, in particular of its rotor, is thus used to test the functionality of the electric motor. Inertial force results, on the one hand, from the mass of a rotor of the electric motor and, on the other hand, from the magnetic forces that act between the rotor and stator and can exert a braking torque on the rotor. In addition, the inertial force is influenced by the mass of the actuator element itself and by an optional gear between the electric motor and the actuator element. The counter-torque resulting from the inertial force is detected by changing the operating parameters, in particular by increasing the motor current.Thus, the detected counter-torque is advantageously compared with an expected counter-torque determined by previous calculations and / or tests or by a test procedure on another braking device of the braking system in order to determine whether the braking device, in particular the electric motor, is functioning properly.

[0009] Preferably, the electric motor is controlled at a frequency or dynamic that is insufficient to overcome the inertial force. This ensures that the electric motor is not set into rotational motion and the actuator element is not displaced so far that the clearance is overcome. Controlling at a frequency or dynamic ensures that the electric motor is only briefly controlled to generate a torque that is lower than the inertial force of the braking device, thus preventing the electric motor from rotating.

[0010] According to an alternative embodiment of the invention, the electric motor is preferably controlled to operate opposite to the actuation direction. This ensures that the clearance cannot be overcome by the actuator element. Instead, the electric motor is controlled in the opposite direction, so that the actuator element is moved, in particular, into an end position facing away from the actuation position. In particular, an end stop is assigned to the actuator element, up to which the actuator element can be retracted to its maximum extent. The end stop ensures, for example, a defined starting position for the actuator element, which enables calibration of the actuator element even during operation of the braking device or a motor vehicle having the braking device.Because the electric motor moves the actuator element toward the end stop, the electric motor's functional testing is also ensured without generating braking torque. As soon as the actuator element reaches the end stop, the electric motor's current increases suddenly. This reliably determines that, when the operating parameter change corresponds to the expected operating parameter change, the actuator element has reached the end stop and the electric motor or the braking device with the actuator element is functioning properly.

[0011] In particular, if the expected change in operating parameters does not occur, it is determined that there is a malfunction in the braking direction.

[0012] According to a further embodiment of the invention, a parking brake is preferably activated before the electric motor is activated, blocking the braking device. Corresponding parking brakes are known from the prior art. These mechanically intervene in the power flow from the electric motor to the actuator element, for example, by retracting a locking element into the transmission. The retracted locking element ensures that the braking force generated is maintained in the de-energized state. This allows for energy-saving parking braking. By blocking the braking device before the electric motor is activated, i.e., when the braking device is at rest, the electric motor can be controlled to move the actuator element in the actuation direction without overcoming the clearance.Rather, the force or torque provided by the electric motor acts directly against the parking brake, preventing the actuator element from shifting. This also allows a comparison of the recorded operating parameter(s) of the electric motor with the expected operating parameters that can be expected when the parking brake is activated, thus detecting any malfunction of the braking system.

[0013] The braking system preferably comprises a plurality of electromechanical braking devices, wherein the braking devices are preferably tested for malfunctions one after the other. This ensures that the activation of one braking device does not influence the behavior of the other braking devices. Preferably, the recorded operating parameters of braking devices, each assigned to an axle of the motor vehicle, are compared with one another. This eliminates the need for comparison with reference parameters that were previously recorded, i.e., calculated and / or measured. Instead, the recorded operating parameters of the braking devices are preferably checked against one another for plausibility.

[0014] Preferably, friction, hysteresis between the forward and reverse movement of the actuator element, gear play, gear and / or saddle stiffness, gear efficiency, response time, dynamics, acceleration, a motor constant, at least one electrical resistance, and / or the state of the electric motor's power electronics are determined as operating parameters alternatively or in addition to motor current or motor voltage and used as the basis for the functional test. This also allows for the detection of gear errors, such as a damaged gear tooth or a ball ramp, which may be reflected, for example, in a vibration in the current or position signal of the braking direction.

[0015] Preferably, the method is performed at regular intervals and / or after each activation of the braking system. In particular, the method is performed when a driving situation is suitable, such as when dynamic, heavy braking is required. In this case, however, the driving is only performed when the activation of the respective braking device cannot negatively impact the driving operation of the motor vehicle and, in particular, is not noticeable to the vehicle's occupants.

[0016] The device according to the invention with the features of claim 10 is characterized in that it comprises a control unit specifically designed to carry out the method according to the invention. This results in the advantages already mentioned above.

[0017] The braking device according to the invention with the features of claim 11 is characterized by the device according to the invention. This results in the advantages already mentioned above.

[0018] The braking system according to the invention with the features of claim 12 is characterized in that it comprises several of the above-mentioned braking devices, each of which is assigned a device according to the invention or which together are assigned a common device according to the invention. This results in the advantages already mentioned above.

[0019] Further advantages and preferred features and combinations of features emerge in particular from the above description and from the claims. The invention will be explained in more detail below with reference to the drawings. Fig. 1 in a motor vehicle with an advantageous braking system in a simplified plan view, Fig. 2 a braking device of the braking system in a schematic representation and Fig. 3 a flow chart to explain the advantageous method for operating the braking system.

[0020] Fig. 1 shows a simplified representation of a motor vehicle 1 with an advantageous braking system 2. The braking system 2 has a braking device 3 for each wheel of the motor vehicle 1, wherein the braking devices 3 are operated by a common control unit 4. The control unit 4 controls the braking devices 3, in particular as a function of a braking request specified by a driver of the motor vehicle or a braking request from an autonomous driving system of the motor vehicle 1, in order to decelerate the motor vehicle 1 in accordance with the braking request. In this case, the braking devices 3 are designed as electromechanical braking devices 3.

[0021] Fig. 2 shows a schematic representation of an exemplary embodiment of one of the braking devices 3. Each of the electromechanical braking devices 3 has an actuator 5 and an actuator element 6 that can be displaced by the actuator 5. The actuator element 6 is designed in this case as a pressure piston that is connected to a brake shoe 7 or brake pad of a brake caliper 8 having two brake shoes 7. A brake disc 9 is guided between the brake shoes 7 and is connected in a rotationally fixed manner to the wheel of the motor vehicle 1 assigned to it. If the brake shoe 7 is displaced against the brake disc 9 by the actuator element 6, the brake disc 9 is clamped between the two brake shoes, thereby generating a braking torque on the brake disc that acts on the assigned wheel and thereby decelerates the motor vehicle 1.

[0022] According to the present embodiment, the actuator 5 has a controllable electric motor 9, which is connected to the actuator element 6 for its displacement by an advantageous gear 10. The actuator element 6 is mounted in a longitudinally displaceable manner. The gear 10 is designed in particular to convert a rotational movement of a rotor of the electric motor 9 into the translational movement of the actuator element 6.

[0023] In order to check the functionality of the braking devices 3, the following and with reference to Fig. 3 described procedures are carried out. Fig. Figure 3 shows a flow chart in which the essential process steps are presented in a simplified manner.

[0024] In a first step S1, the motor vehicle is put into operation and the braking system 2 is activated. In a subsequent query S2, a check is carried out to determine whether the current operating situation of the motor vehicle 1 allows the test procedure to be carried out safely. In particular, it is checked whether carrying out the test procedure has an impact on the vehicle's behavior or not. The test procedure is only released if carrying out the test procedure does not negatively affect the operating behavior of the motor vehicle 1. In addition, a check is carried out to determine when the test procedure was last carried out, whether a specified time period has elapsed since the last test procedure was carried out, and whether a new test procedure is necessary. Optionally, a check is carried out to determine whether dynamic braking is occurring due to a brake torque request.If this is the case, the test procedure can also be carried out without the test process affecting the driving operation or being noticeable to a driver of motor vehicle 1.

[0025] If the conditions necessary for performing the test procedure are met (j), the test procedure is started in the next step S3. For this purpose, the electric motor 9 is controlled to generate a torque without, however, overcoming the clearance of the actuator element 6.

[0026] At rest, brake shoe 7 is spaced apart from brake disc 9. This distance x is referred to as the clearance. Only when the clearance is overcome and brake shoe 7 touches brake disc 9 can a braking torque or braking force be generated. The clearance serves, in particular, to ensure that no friction occurs between brake disc 9 and brake shoe 7 or brake pad during driving when there is no braking demand. The advantageous control of the electric motor in step S3 ensures that no braking torque or braking force is generated during the test process that could impair driving operation.

[0027] In the subsequent step S4, operating parameters, in particular of the electric motor, are monitored and evaluated in response to its control.

[0028] In the subsequent step S5, it is determined, depending on at least one of the determined operating parameters, whether the braking device 3 is functioning properly or whether a malfunction is present. For this purpose, for example, the selected operating parameter is compared with a comparison value or reference value that was calculated and / or measured or determined. Optionally, the selected operating parameter is compared with an equivalent operating parameter of another of the braking directions 3 to check whether one of the two braking devices 3 is malfunctioning.

[0029] If it is determined in step S5 that no malfunction (y), the process is restarted or repeated with step S2. However, if it is determined that a malfunction exists (n), an error warning is generated and output in the subsequent step S6. For example, the driver is notified that one of the braking devices 3 is malfunctioning. Optionally, an emergency operation mode is set up for the faulty braking device 3.

[0030] The described method has the advantage that a functional test is possible even without the presence of a pressure or force sensor, and without generating a braking force on one of the vehicle's wheels. To control the electric motor 9 without overcoming the clearance, one of the variants described below is implemented: According to a first variant, the motor inertia of the electric mode 9 is utilized. Dynamic control and / or control of the motor frequency ensures that the motor inertia is not overcome, thus preventing displacement of the actuator element 6. The motor inertia results in particular from the mass of the rotor of the electric motor 9 to be rotated, as well as from any magnetic forces acting in the electric motor 9, and optionally from the mass of the gear 10 to be driven and the actuator element 6 itself.

[0031] In a further variant, the actuator element 6 is moved by the electric motor 9 in the direction opposite to the actuation direction, toward an end stop 11, which prevents further displacement of the actuator element 6, in particular of the brake shoe 7. This also reliably prevents the clearance from being overcome, while still reliably testing the functionality of the electric motor 9 and the braking device 3 as a whole.

[0032] According to a third variant, the actuator 5, in particular the transmission 10, is assigned a parking brake 12, which engages mechanically or positively with the transmission 10 upon each activation in order to lock it. In this case, the parking brake 12 is activated before the electric motor 9 is activated, so that the transmission 10 is locked. If the electric motor 9 is subsequently activated, the actuator element 6 is prevented from overcoming the clearance. Instead, the electric motor 9 works against the locking of the parking brake 12.

[0033] Should it nevertheless be necessary to press a brake pad 7 or the brake shoe against the brake disc 9 during the test procedure, this is achieved by applying only very light pressure or with little braking torque.

[0034] Preferably, the malfunction is not detected due to a deviation of an actual sensor value from a desired sensor value, but rather due to a parameter deviation, which is identified, in particular, based on a model. For this purpose, for example, the selected operating parameter of the respective braking device 3 is compared with the same operating parameter of another of the braking devices 3 in order to check whether the braking devices operate the same or differently and to detect whether a malfunction is present. To prevent the testing processes of the braking devices 3 from influencing each other, they are performed sequentially, in particular slightly offset from one another in time.

[0035] Due to the signals typically already present in the braking system 2 relating to the operating current, an operating voltage, a motor position, which manifests itself, for example, as the rotor rotation angle, and possibly a motor temperature, the following operating parameters of the electric motor 9 are preferably taken into account during fault diagnosis: friction, hysteresis between forward and reverse travel, gear play, gear and saddle stiffness, gear efficiency, response time, time constant, dynamics, motor acceleration, motor constant, electrical resistances, and / or the condition of the power electronics, in particular a bridge circuit of the power electronics. In addition, gear errors, such as tooth damage, a ball ramp, or the like, are determined depending on vibrations in the current or position signal of the electric motor 10.

[0036] The test procedure is always performed when a driving situation is particularly suitable, for example, when dynamically strong braking occurs due to a corresponding braking torque demand. In this case, a test is performed during braking, during which the clearance x must be overcome. In this case, however, an additional or separate test procedure can be omitted.

[0037] However, the present method actively controls the electric motor 9 in a state of the braking system 2 in which a braking request is not present, so that the operating behavior of the motor vehicle 1 cannot be impaired by the test process.

[0038] Preferably, the test procedure is performed when the motor vehicle 1 is put into operation or when the braking devices 3 have not been used for a specified period of time. A combination of the test procedures, one during braking and one outside of braking, is also conceivable. It is also conceivable to add the test procedure to a normal brake application, i.e., when a braking request is present, by adding a sine wave to the target values ​​during the release process of the braking devices 3, i.e., when the actuator element 6 is moved counter to the actuation direction, and monitoring the response in the operating parameters.

[0039] A sudden drift of an operating parameter on one of the braking devices indicates a malfunction. Slow or smaller deviations, on the other hand, are more likely to indicate signs of wear and are therefore preferentially compensated for in the control system.

Claims

[1] Method for detecting a malfunction of an electromechanical braking device (3) of a braking system (2) for a motor vehicle (1), which has at least one controllable electric motor (9) and at least one actuator element (6) displaceable by the electric motor (9), wherein in the rest state of the braking device (3) the actuator element (6) has a clearance (x) in the actuation direction, characterized by that for a test process the electric motor (9) is controlled in such a way that the actuator element (6) is only displaced within the clearance (x), and that the presence of a malfunction is determined as a function of at least one operating parameter of the electric motor (9) detected in the process. [2] Method according to claim 1, characterized by that when a deviation of the operating parameter from an expected operating parameter of the electric motor (9) is detected, a malfunction is determined. [3] Method according to one of the preceding claims, characterized by that if an unexpectedly missing change in operating parameters is detected, a malfunction is determined. [4] Method according to one of the preceding claims, characterized by that the electric motor (9) is controlled in such a way that an inertial force can be detected as a counter-torque. [5] Method according to one of the preceding claims, characterized by that the electric motor (9) is controlled with a frequency or dynamics that is not sufficient to overcome the inertial force. [6] Method according to one of the preceding claims, characterized by that the electric motor (9) is controlled to operate opposite to the actuation direction. [7] Method according to one of the preceding claims, characterized by that before the electric motor (9) is activated, a parking brake () is activated which blocks the braking device (3). [8] Method according to one of the preceding claims, characterized by that the braking system (2) has a plurality of electromechanical braking devices (3), wherein the braking devices (3) are each checked for malfunction one after the other. [9] Method according to one of the preceding claims, characterized by that it is carried out at regular intervals and / or after each commissioning of the braking system (2). [10] Device for operating an electromechanical braking device (3) of a braking system (2) for a motor vehicle (1), which has at least one controllable electric motor (9) and at least one actuator element (6) displaceable by the electric motor (9), wherein in the rest state of the braking device (3) the actuator element (6) has a clearance (x) in the actuation direction, characterized bya control device () which is specially adapted to carry out a method according to one of claims 1 to 9 when used as intended. [11] Electromechanical braking device (3) for a braking system (2) of a motor vehicle (1), which has at least one controllable electric motor (9) and at least one actuator element (6) which can be displaced by the electric motor (9), wherein in the rest state of the braking device (3) the actuator element (6) has a clearance (x) in the actuation direction, characterized by a device according to claim 10. [12] Braking system (2) for a motor vehicle, comprising a plurality of electromechanical braking devices (3) according to claim 11, wherein the braking devices (3) are each assigned a device according to claim 10 or together a common device according to claim 10.

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