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

Abstract

To provide a method for detecting a malfunction of an electromechanical braking device (3) of a braking system (2) for a motor vehicle (1), the braking device (3) including at least one controllable electric motor (9) and at least one actuator element (6) that can be displaced by the electric motor (9), the actuator element (6) having a clearance (x) in the actuation direction in the idle state of the braking device (3).SOLUTION: For a test procedure, an electric motor (9) is controlled such that an actuator element (6) is displaced only within a clearance (x), and the presence of a malfunction is ascertained according to at least one operating parameter of the electric motor (9) detected in the process.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for detecting a malfunction of an electromechanical brake device of a braking system for a motor vehicle, the brake device having at least one controllably driveable electric motor and at least one actuator element displaceable by the electric motor, the actuator element having an air gap in the actuation direction in the rest state of the brake device.

[0002] Furthermore, the invention relates to a device for operating an electromechanical braking device as described above, as well as an electromechanical braking device comprising such a device, and a braking system comprising at least one electromechanical braking device of this type. [Background technology]

[0003] The method and brake system of the aforementioned type are already known in the prior art. In conventional hydraulic brake systems, the functionality of the brake system can be checked by monitoring the hydraulic pressure in the brake system with a pressure sensor, but this is more complicated in electromechanical brake systems. If force transmission is performed purely mechanically, i.e., without a hydraulic system, the pressure sensors normally used in the brake system are no longer usable. In hydraulic brake systems, during the check process to detect a malfunction, the inlet valves leading to the hydraulic wheel brakes of the check system are closed, so that a braking moment cannot be generated in the wheel brakes due to pressure buildup, but this is not possible in electromechanical brake systems that act directly on each mechanical wheel.

[0004] Brake systems typically have an air gap that an actuator or actuator element must overcome before a braking force or braking moment can be generated. The air gap is understood to mean, in particular, the distance between the brake jaws or brake linings and the brake disc, and thus the travel that the actuator element must overcome before a braking force can be generated. The air gap is used to reduce wear of the brake system by avoiding sliding contact between the brake system, in particular between the brake jaws and the brake disc, when the brake system is at rest, in particular when the brake system is not being operated. Depending on the application, the air gap can be selected to be larger or smaller to avoid wear phenomena. Summary of the Invention

[0005] The method according to the present invention, having the features of claim 1, has the advantage that a malfunction of an electromechanical brake system can be detected even without a braking moment or braking force generation. To this end, according to the present invention, during the check process, the electric motor is controlled so that the actuator element is displaced only within the air gap, and the presence of a malfunction is determined depending on the operating parameters of the electric motor detected during the check. The operating parameters, in particular the motor current and / or motor voltage of the electric motor, are continuously monitored, and a malfunction of the brake system is determined based on the detected values. As long as the actuator element is displaced only within the air gap of the actuator element, it is ensured that no braking moment or braking force is exerted by the brake system. While the electric motor is controlled, in particular, to overcome the air gap, i.e., to move the actuator element in the actuating direction but without overcoming the air gap, at least one operating parameter of the electric motor is monitored and checked for abnormalities. In this way, a malfunction of the brake system can be detected advantageously without a braking moment being generated.

[0006] According to a preferred development of the invention, a malfunction is determined upon detecting a deviation of the operating parameters from the expected operating parameters, in particular upon detecting an unexpectedly high motor current and / or an unexpectedly high motor voltage of the electric motor. For example, if the motor current unexpectedly rises above a predetermined limit value and / or at an unexpectedly early time or after an unexpectedly short travel distance, it can be determined that the function of the brake system is impaired.

[0007] According to another embodiment of the present invention, a malfunction is preferably determined when it is detected that an operating parameter change does not occur unexpectedly, in particular when a motor current increase and / or a motor voltage increase does not occur. In this case, the brake system is checked to see whether the expected reaction is actually performed in the brake system by controlling the electric motor. For example, if it is recognized that the actuator element is not displaced despite controlling the electric motor, a malfunction is also determined.

[0008] When carrying out the method, the electric motor is preferably driven in such a way that inertial forces, particularly those of the brake system or the electric motor, can be detected as a reaction moment. The inertial forces of the electric motor, particularly of the rotor of the electric motor, are thus utilized to test the functionality of the electric motor. The inertial forces arise, on the one hand, from the mass of the rotor of the electric motor and, on the other hand, from magnetic forces acting between the rotor and the stator and which can exert a blocking moment on the rotor. Furthermore, the inertial forces are influenced by the mass of the actuator element itself and by an optional transmission between the electric motor and the actuator element. The reaction moment resulting from the inertial forces is detected by changes in operating parameters, particularly by an increase in motor current. The detected reaction moment can thus be advantageously compared with an expected reaction moment, determined by prior calculation and / or experimentation or by a check process in another brake system of the brake system, thereby determining whether the brake system, particularly the electric motor, functions as intended.

[0009] Preferably, the electric motor is driven at a frequency or dynamics insufficient to overcome the inertial forces, thereby ensuring that the electric motor is not driven into a rotational movement that would cause the actuator element to displace so much that the air gap is overcome. The frequency or dynamics ensure that the electric motor is driven only briefly to generate a torque that is lower than the inertial forces of the brake device, thereby ensuring that the electric motor does not start to rotate.

[0010] According to an alternative embodiment of the present invention, the electric motor is preferably driven to operate in the opposite direction to the actuation direction. This ensures that the air gap cannot be overcome by the actuator element. Instead, the electric motor is driven in the opposite direction, thereby moving the actuator element, in particular, to an end position opposite the operating position. In particular, the actuator element is assigned an end stop, up to which the actuator element can be retracted at a maximum. The end stop ensures, for example, a defined initial position for the actuator element, making calibration of the actuator element possible even while the brake system or a vehicle having the brake system is in operation. By moving the actuator element toward the end stop by the electric motor, a function check of the electric motor is also ensured without the generation of a braking torque. As soon as the actuator element hits the end stop, the motor current of the electric motor rises sharply. This makes it possible to reliably determine that the actuator element has reached the end stop and that the electric motor or the braking system comprising the actuator element is functioning as intended, if the operating parameter change corresponds to an expected operating parameter change, and in particular to determine that a malfunction of the braking system exists if the expected operating parameter change does not occur.

[0011] According to another embodiment of the present invention, a parking brake is preferably applied to lock the brake system before the electric motor is activated. Corresponding parking brakes are known in the prior art. The parking brake is mechanically engaged by, for example, inserting a locking element into the power transmission in the force transmission path from the electric motor to the actuator element. The inserted locking element ensures that the brake force once generated is maintained even in the de-energized state. This allows for energy-saving parking braking. Locking the brake system before the electric motor is activated, i.e., when the brake system is at rest, allows the electric motor to be activated to move the actuator element in the actuating direction without overcoming the air gap. Rather, the force or torque provided by the electric motor acts directly against the parking brake, which prevents the actuator element from displacing. In this way, too, it is possible to compare one or more detected operating parameters of the electric motor with expected operating parameters that can be expected when controlling the parking brake, thereby making it possible to recognize a malfunction of the brake system.

[0012] Preferably, the brake system includes a plurality of electromechanical brake devices, which are preferably checked for malfunctions one after the other in time, thereby ensuring that the operation of one brake device does not affect the behavior of one of the other brake devices. Preferably, the detected operating parameters of the plurality of brake devices, each assigned to one axle of the vehicle, are compared with each other, thereby making it possible to omit a comparison with a previously detected, i.e., calculated and / or measured, reference parameter. Instead, preferably, the plausibility of the detected operating parameters of the brake devices is checked with each other.

[0013] Preferably, as operating parameters, friction, hysteresis between reciprocating movements of the actuator elements, power train clearance, stiffness of the power train and / or caliper, power train efficiency, response time, dynamics, acceleration, motor constants, at least one electrical resistance and / or the state of the power electronics of the electric motor are determined as alternatives or additions to the motor current or motor voltage and serve as the basis for a function check. This also makes it possible to determine power train errors, such as damaged power train teeth or ball ramps, which manifest themselves, for example, in oscillations in the current signal or position signal in the braking direction.

[0014] Preferably, the method is performed at regular intervals and / or each time after the start of operation of the brake system. In particular, the method is performed when the driving conditions are suitable for this, for example when strong dynamic braking is required. In this case, the driving is performed only when the activation of the respective brake device cannot have a negative effect on the driving operation of the vehicle, in particular when it is not noticeable to the vehicle occupants.

[0015] The device according to the invention with the features of claim 10 is characterized in that it comprises a control device specially designed for carrying out the method according to the invention, resulting in the advantages already mentioned above.

[0016] A braking device according to the invention with the features of claim 11 is characterized by the device according to the invention described above. The advantages already mentioned above result.

[0017] A braking system according to the invention with the features of claim 12 is characterized in that it comprises a plurality of braking devices as described above, each of which is assigned an inventive device or which are all assigned a common inventive device, thereby resulting in the advantages already mentioned above.

[0018] Further advantages and preferred features and feature combinations can be seen in particular from the preceding description and the claims.The invention will now be explained in more detail with reference to the drawings. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a simplified plan view of a motor vehicle having an advantageous braking system; [Figure 2] 1 is a schematic diagram of a brake device of a brake system. [Figure 3] 1 is a flow chart illustrating an advantageous method of operating a braking system. DETAILED DESCRIPTION OF THE INVENTION

[0020] 1 shows, in a simplified diagram, a motor vehicle 1 with an advantageous brake system 2. For each wheel of the motor vehicle 1, the brake system 2 comprises one brake device 3, which are operated by a common control device 4. The control device 4 controls the brake devices 3, in particular, in response to a braking request set by the motor vehicle driver or a braking request of an autonomous driving system of the motor vehicle 1, in order to decelerate the motor vehicle 1 in accordance with this braking request. In this case, the brake devices 3 are configured as electromechanical brake devices 3.

[0021] 2 shows, in a schematic diagram, an exemplary embodiment of one of the braking devices 3. Each electromechanical braking device 3 comprises an actuator 5 and an actuator element 6 displaceable by the actuator 5. The actuator element 6 is here configured as a pressure piston, which is connected to one of the brake jaws 7 of a brake caliper 8 having two brake jaws 7 or to a brake lining. A brake disc 9 is guided between the brake jaws 7 and is connected to the wheel of the motor vehicle 1 assigned to it in a non-rotatable manner. When the brake jaws 7 are pressed towards the brake disc 9 by the actuator element 6, the brake disc 9 is clamped between the brake jaws, which generates a braking moment on the brake disc that acts on the assigned wheel and thereby slows down the motor vehicle 1.

[0022] According to the present embodiment, the actuator 5 comprises a controllably driven electric motor 9 which is connected to the actuator element 6 by means of an advantageous transmission 10 in order to displace the latter. The actuator element 6 is held so as to be displaceable, in particular longitudinally slidably. The transmission 10 is in particular designed to convert the rotational movement of the rotor of the electric motor 9 into a translational movement of the actuator element 6.

[0023] To check the functionality of the braking device 3, the method described below and with reference to Figure 3 is carried out, which for this purpose shows a flow chart in which the main method steps are shown in a simplified manner.

[0024] In a first step S1, the vehicle is started, and the brake system 2 is accordingly activated. In a subsequent query S2, it is checked whether the current driving situation of the vehicle 1 allows the check process to be carried out reliably. For this purpose, it is checked, in particular, whether carrying out the check process will have an effect on the vehicle behavior. The check process is only permitted if carrying out the check process will not have a negative effect on the driving behavior of the vehicle 1. Furthermore, it is checked when the check process was last carried out, or whether a predetermined time has passed since the last check process was carried out, and whether a new check process is necessary. Optionally, it is checked whether a dynamic braking process due to a braking moment request is present. If this is the case, the check method can also be carried out without the check process having an effect on driving or being perceptible by the driver of the vehicle 1.

[0025] If the conditions necessary for the execution of the check process are met (j), the check process is started in the next step S3 by driving the electric motor 9 so as to generate a torque that does not overcome the air gap of the actuator element 6.

[0026] In the rest state, the brake jaws 7 are spaced apart from the brake disc 9. This distance x is referred to as the air gap. Only when the air gap is overcome and the brake jaws 7 come into contact with the brake disc 9 can a braking moment or force be generated. The air gap is used, in particular, to prevent friction from occurring between the brake disc 9 and the brake jaws 7 or brake linings when no braking demand is present during driving. The advantageous drive control of the electric motor in step S3 ensures that no braking moment or force is generated during the check process that could adversely affect driving.

[0027] In the following step S4, the operating parameters, in particular the operating parameters of the electric motor, are monitored and evaluated with respect to their response to the drive control.

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

[0029] If step S5 determines that there is no malfunction (j), the method starts anew or repeats with step S2. However, if it determines that there is a malfunction (n), an error warning is generated and output in the following step S6, e.g., to indicate to the driver that one of the braking devices 3 is malfunctioning. Optionally, an emergency run is set for the braking device 3 with the error.

[0030] The described method has the advantage that a function check is possible even without the presence of a pressure or force sensor and without a braking force being generated at one of the wheels of the vehicle. For the control of the electric motor 9 without overcoming an air gap, in particular one of the variants described below is implemented.

[0031] According to a first variant, the motor inertia of the electric motor 9 is utilized. By dynamic drive control and / or drive control of the motor frequency, it is achieved that the motor inertia is not overcome, thereby preventing displacement of the actuator element 6. The motor inertia arises in particular from the mass of the rotor of the electric motor 9 that is about to start turning, and possibly from magnetic forces acting within the electric motor 9, and optionally from the mass of the gear train 10 to be driven and of the actuator element 6 itself.

[0032] In another variant, the actuator element 6 is moved by the electric motor 9 against the actuation direction towards an end stop 11 which prevents further displacement of the actuator element 6, in particular the brake jaw 7. This again reliably prevents the air gap from being overcome, but nevertheless reliably checks the functionality of the electric motor 9 and the brake device 3 as a whole.

[0033] According to a third variant, a parking brake 12 is assigned to the actuator 5, in particular to the transmission 10, which engages mechanically or positively in the transmission 10 each time it is activated to lock the transmission 10. The parking brake 12 is then activated before the electric motor 9 is actuated, thereby locking the transmission 10. When the electric motor 9 is subsequently actuated, the actuator element 6 is prevented from overcoming the air gap. Instead, the electric motor 9 works against the locking of the parking brake 12.

[0034] If pressing of the brake lining 7 or brake jaws against the brake disc 9 is nevertheless necessary during the check process, it is achieved that this is carried out only lightly or with only slight pressure or with only a slight braking moment.

[0035] Preferably, a malfunction is not recognized based on a deviation of a sensor actual value from a sensor target value, but on a parameter deviation that is identified, in particular, based on a model. For this purpose, for example, selected operating parameters of each brake system 3 are compared with the same operating parameters of other brake systems 3 of the plurality of brake systems 3 to check whether these brake systems are operating in the same or different ways and to recognize whether a malfunction exists. In order to prevent the check processes of the plurality of brake systems 3 from influencing each other, these check processes are carried out, in particular, one after the other, in particular slightly offset in time from one another.

[0036] Based on signals typically present in the brake system 2 anyway, such as operating current, operating voltage, motor position, e.g., as the rotor rotation angle, and possibly motor temperature, the following operating parameters of the electric motor 9 are preferably taken into account during error diagnosis: friction, hysteresis between strokes, power train clearance, stiffness of the power train and caliper, power train efficiency, response time, time constant, dynamics, motor acceleration, motor constants, electrical resistance and / or the state of the power electronics, in particular the bridge circuit of the power electronics. Furthermore, power train errors, such as tooth damage, ball ramps or the like, can be determined as a function of oscillations in the current or position signals of the electric motor 10.

[0037] The check process is carried out in particular whenever the driving situation is particularly suitable for this, for example, during dynamic heavy braking with a corresponding braking torque demand. In this case, the check is carried out during braking. During this check, the air gap x must, however, be overcome. In this case, however, an additional or separate check process can be omitted.

[0038] In this way, however, active drive control of the electric motor 9 is carried out in a state of the brake system 2 in which no braking demand is currently present, so that the driving behavior of the vehicle 1 is not adversely affected by the check process. Preferably, for this purpose, the check process is carried out when the vehicle 1 starts to operate or when the brake device 3 has not been used for a predetermined period of time. A combination of check processes, one for braking cases and another for non-braking cases, is also possible. It is also possible to add a check process to normal braking, i.e., when a braking demand is present, in which a sine wave is applied to a target value and the reaction of the driving parameters is monitored during the release process of the brake device 3, i.e., when the actuator element 6 is moved in the opposite direction to the actuation direction.

[0039] A sudden drift in the operating parameters of one of the braking systems indicates a malfunction, whereas a slow or relatively small deviation, on the other hand, indicates rather a wear phenomenon and is therefore preferably compensated for in the drive control. [Explanation of symbols]

[0040] 1. Automobiles 2. Brake system 3 Brake device 4. Control device 5 Actuators 6 Actuator Elements 7 Brake Jaw 8 Brake calipers 9 Brake discs, electric motors 10 Transmission Mechanism 11 End stopper 12 Parking brake S1 Step S2 Step S3 Step S4 Step S5 Step S6 Step x-spacing

Claims

1. A method for detecting a malfunction of an electromechanical braking device (3) of a braking system (2) for a motor vehicle (1), comprising: The braking device (3) comprises at least one electric motor (9) that can be driven and controlled, and at least one actuator element (6) that can be displaced by the electric motor (9), In the rest state of the braking device (3), the actuator element (6) has an air gap (x) in the actuation direction. In the method, For the check process, the electric motor (9) is driven and controlled so that the actuator element (6) is displaced only within the air gap (x); and determining the presence of a malfunction as a function of at least one operating parameter of the electric motor (9) detected during the process; 10. A method for detecting a malfunction of an electromechanical brake device of a braking system for a motor vehicle, comprising:

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

3. 3. The method of claim 1 or 2, characterized in that a malfunction is determined upon detecting that an operating parameter change does not occur unexpectedly.

4. 4. The method according to claim 1, wherein the electric motor (9) is driven and controlled in such a way that the inertial force is detectable as a reaction moment.

5. 5. A method according to any one of claims 1 to 4, characterized in that the electric motor (9) is driven with a frequency or dynamics that is insufficient to overcome the inertial forces.

6. 6. A method according to any one of claims 1 to 5, characterized in that the electric motor (9) is driven and controlled to work in the direction opposite to the direction of actuation.

7. 7. A method according to any one of claims 1 to 6, characterized in that before controlling the drive of the electric motor (9), a parking brake () is activated, which locks the braking device (3).

8. 8. The method according to claim 1, wherein the braking system (2) comprises a plurality of electromechanical braking devices (3), the braking devices (3) being checked for malfunctions one after the other in time.

9. 9. The method according to any one of claims 1 to 8, characterized in that the method is carried out at regular intervals and / or each time after the braking system (2) is put into operation.

10. A device for operating an electromechanical brake device (3) of a braking system (2) for a motor vehicle (1), comprising: The braking device (3) comprises at least one electric motor (9) that can be driven and controlled, and at least one actuator element (6) that can be displaced by the electric motor (9), In the rest state of the braking device (3), the actuator element (6) has an air gap (x) in the actuation direction. In the apparatus, a control device ( ) specially adapted to carry out the method according to any one of claims 1 to 9 in intended use; 1. A device for operating an electromechanical brake device of a braking system for a motor vehicle, comprising:

11. An electromechanical braking device (3) for a braking system (2) of a motor vehicle (1), comprising: At least one electric motor (9) that can be driven and controlled; at least one actuator element (6) displaceable by said electric motor (9); Equipped with In the rest state of the braking device (3), the actuator element (6) has an air gap (x) in the actuation direction. In the braking device (3), 11. The device of claim 10 , 1. An electromechanical braking device for a braking system of a motor vehicle, comprising:

12. A braking system (2) for a motor vehicle, comprising: A plurality of electromechanical braking devices (3) according to claim 11, the braking devices (3) are each assigned a device according to claim 10 or are collectively assigned a common device according to claim 10; Brake systems for automobiles.

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