Method for operating an electromechanical parking brake and control device for a parking brake, parking brake and motor vehicle

Abstract

A method for operating an electromechanical parking brake (17) of a motor vehicle (10), wherein a control device (24) of the parking brake (17) on at least one friction brake (12) of the motor vehicle (10) moves at least one brake element (15) of the friction brake (12) relative to a friction unit (14) of the friction brake (12) independently of a brake pressure (P) of a hydraulic service brake (16) of the motor vehicle (10) by means of an electrical drive unit (22) of the parking brake (17), wherein during a journey of the motor vehicle (10) a respective distance (21) between the at least one brake element (15) on the one hand and the friction unit (14) on the other hand is changed by the actuation of the drive unit (22) depending on at least one brake actuation signal (27, 29, 30) of the service brake (16), characterized in that in the event that the brake actuation signal (27, 29,30) signals the start of an actuation or predictively an impending actuation of the service brake (16), by controlling the drive unit (22) the distance (21) is set to a predetermined distance value, so that by means of the parking brake (17) before or at the start of a braking process to be effected by the hydraulic service brake (16) a clearance (21) is reduced.

Description

[0001] The invention relates to a method for operating an electromechanical parking brake (EPB) of a motor vehicle. Another name for such a parking brake is electromechanical parking brake. A control device of the parking brake controls an electric drive unit of the parking brake at at least one friction brake of the motor vehicle, thereby moving a brake element of the friction brake relative to a friction unit of the friction brake. The invention also includes the control device and a parking brake with the control device.

[0002] The invention relates to a friction brake, which is particularly designed as a caliper brake. In a caliper brake, the braking effect is achieved by pressing brake pads against a brake disc. The term "brake element" mentioned above refers to a brake pad, and the term "friction unit" mentioned above refers to the brake disc.

[0003] A parking brake with a drum brake is known, for example, from WO 2006 / 013174 A1. This parking brake is also used to prevent the vehicle from rolling on an incline when starting off, until sufficient drive torque is available via a clutch.

[0004] To enable a driver to brake a motor vehicle while driving, a hydraulic service brake may be provided. This brake hydraulically actuates the respective friction brakes at the vehicle's wheels, pressing at least one brake element of the friction brake against the friction unit. This is achieved, for example, by a brake piston that is actuated by hydraulic brake pressure, thereby acting on at least one brake element.

[0005] The hydraulic service brake is intended solely for braking the vehicle while driving and, in its unactuated state, maintains a gap between at least one brake element and the friction unit, namely the so-called air gap, which is greater than zero. Therefore, when the vehicle is parked to allow the driver to exit, a parking brake must also be provided. This parking brake permanently engages the friction brake located at at least one wheel of the vehicle, even without actuation of the hydraulic service brake, i.e., it presses the brake element against the friction unit. An electromechanical parking brake has an electric drive unit for this purpose, which can be controlled by a parking brake control device such that the drive unit mechanically moves or retracts at least one brake element of the friction brake against the friction unit.Due to self-locking caused by a gearbox with a large gear ratio (i > 100), the brake element can remain pressed against the friction unit even after the drive unit is switched off.

[0006] In its unactuated state—that is, when the driver is not pressing the brake pedal and / or no driver assistance system is generating hydraulic brake pressure—a hydraulic service brake establishes a specific clearance between the brake element and the friction unit. This clearance must be large enough to prevent the brake element and friction unit from touching, as otherwise a residual braking torque would be present even when the service brake is not applied, reducing the vehicle's efficiency.

[0007] However, brake caliper designs optimized for residual braking torque result in a correspondingly large clearance, i.e., a large gap, leading to a longer pedal travel and a deterioration of the overall brake system's volume balance. At the same time, increased clearance also affects the brake pedal characteristics, as the driver must first overcome this clearance before the friction brakes engage.

[0008] From DE 10 2013 218 401 A1, a method for operating a motor vehicle is known in order to reduce the free play of a friction brake by means of a parking brake during autonomous or semi-autonomous operation of the motor vehicle. An operating state of the motor vehicle is awaited or detected as an activation signal for the parking brake. This operating state can, for example, be the deceleration of the motor vehicle. In this case, the service brake is first hydraulically activated or put into operation, and then it is checked whether the deceleration of the motor vehicle is sufficient. If insufficient deceleration is detected by the parking brake, the entire braking operation is implemented using the parking brake. The invention is based on the objective of efficiently operating a hydraulic service brake of a motor vehicle.

[0009] The problem is solved by the subject matter of the independent patent claims. Advantageous embodiments of the invention are described by the dependent patent claims, the following description, and the figure.

[0010] The invention provides a method for operating an electromechanical parking brake or handbrake of a motor vehicle. By means of this method, the hydraulic service brake of the motor vehicle can be assisted by the parking brake while the vehicle is in motion. The electromechanical parking brake can be constructed in a manner known per se, i.e., a control device of the parking brake moves at least one brake element of the friction brake (for example, at least one brake pad) relative to a friction unit of the friction brake (for example, a brake disc) on at least one friction brake of the motor vehicle, for example, a caliper brake of each of the front wheels, by controlling an electric drive unit of the parking brake. The movement of the at least one brake element thus occurs independently of the brake pressure of the hydraulic service brake of the motor vehicle.In other words, by controlling or operating the drive unit, the friction brake can be adjusted or activated even when the service brake is not engaged. The movement of at least one brake element relative to the friction unit thus occurs as a superimposed movement, which can occur in conjunction with a movement resulting from the application of the hydraulic service brake. The parking brake moves at least one brake element mechanically, for example by means of a spindle, and not hydraulically.

[0011] To operate the hydraulic service brake more efficiently, the electromechanical parking brake is used according to the invention. For this purpose, it is also operated while the vehicle is in motion. During driving, the distance between the brake element and the friction unit is changed by the parking brake through the actuation of the drive unit. This change or adjustment of the distance occurs depending on at least one brake actuation signal, which is dependent on the application of the service brake. Thus, if the service brake is applied, the parking brake is also controlled or operated. The hydraulic service brake can be actuated in two different ways, for example. Firstly, a driver can actuate a brake pedal of the hydraulic service brake. Secondly, a driver assistance system can actuate the hydraulic service brake.Such a driver assistance system could be, for example, an electronic stability control (ESC) or an electric brake booster.

[0012] The invention offers the advantage that the air gap, i.e., the distance between the brake element and the friction brake, can be changed or adjusted during driving by means of the electromechanical parking brake, particularly dynamically or depending on the driving situation. Thus, the air gap can be varied or adjusted for efficient operation of the hydraulic service brake while driving.

[0013] The parking brake reduces the clearance before or at the beginning of a braking process initiated by the hydraulic service brake, thereby improving the response of the friction brake to the application of the brake pedal or the activation of a driver assistance system. The brake element can thus be moved closer to the friction unit by the parking brake at the start of hydraulic service brake application, depending on the actuation signal. Preferably, when the actuation signal indicates service brake application, the parking brake's drive unit is activated to set the distance between the brake element and the friction unit to a predetermined value. Therefore, at the start of service brake application, the clearance is set by the parking brake, i.e., the predetermined distance is present.This allows, for example, the described offset value to be compensated for or reversed, and / or a so-called knockback (rebound) of the brake element to be compensated for. A knockback can be caused by lateral runout of the friction unit or by the driving style of the vehicle. Using the invention, brake pads can, for example, be readjusted or returned to a predetermined normal dimension (i.e., the specified distance value). When a brake pedal is actuated, this shortens the pedal travel by which the driver must move the brake pedal to bring the brake element into initial contact with the friction unit. The aforementioned actuation signal can also predictively signal an impending application of the service brake. If the service brake is then actually applied, the specified distance value will already be set.Predictive signaling of an impending action can be generated, for example, depending on the release of the accelerator pedal of the motor vehicle and / or environmental detection by the motor vehicle, which detects objects in the driver's path of the motor vehicle.

[0014] The invention also includes further developments whose features result in additional advantages.

[0015] A conventional parking brake can have the problem that it only offers two positions or states: an open position and a closed position. To allow for flexible adjustment of the distance between the brake element and the friction unit, it is therefore preferred that the control device actuates the drive unit based on a position signal received from a position sensor. This position sensor signals a relative change in position of a component of the drive unit or of a transmission coupling the drive unit to the brake element. For example, the position sensor can signal the rotational position of a gear in the transmission or a change in the rotational position of the gear. Such a position sensor can be provided, for example, by a Hall sensor or Hall effect sensor.The position signal can therefore also detect an intermediate position between the open and closed positions, and the drive unit can be stopped in this intermediate position, for example, to precisely set a predetermined distance between the braking element (brake pad) and the friction unit (brake disc). Thus, a continuous change in the distance between the braking element and the friction unit can be detected or monitored, and a predetermined distance can be set. Alternatively, instead of a relative change in position, the position signal can also indicate or record the absolute position of the component of the drive unit or the transmission. However, monitoring the relative change in position has the advantage that no calibration is necessary and wear of the braking element has no influence on the position signal.

[0016] One way to support the hydraulic service brake using the parking brake is to increase the clearance after a braking operation, thereby reducing the residual braking torque of the friction brake. For example, a brake piston of a caliper brake can be actively retracted (increased) using the parking brake. Preferably, when the service brake's actuation signal indicates the end of service brake application (i.e., the end or completion of a braking operation), the parking brake's drive unit is then activated to increase the clearance by a predetermined offset value. This clearance is the same as that set or generated by the service brake itself when it is not actuated.The clearance, i.e., the distance between the brake element and the friction unit, is increased by the electric drive unit by moving at least one brake element away from the friction unit by the offset value. By using an offset value, i.e., by causing a relative change in the position of at least one brake element with respect to the friction unit, this improved design can also be combined with an automatic adjustment of the clearance caused by the hydraulic service brake, as can be provided in a known manner to compensate for wear.

[0017] The aforementioned distance value, to which the gap between the brake element and the friction unit is set at the beginning or predictively before the hydraulic service brake is applied via the parking brake, is preferably user-selectable. For this purpose, the distance value is determined based on a driving mode signal from a vehicle control unit. Thus, the vehicle user has a driving mode selection available, which determines the brake pedal characteristic with respect to the free play. For example, a choice can be made between a comfort free play and a sport free play, with the comfort free play being greater than the sport free play. This, in turn, adjusts the response behavior of the service brake.

[0018] The method assumes that the aforementioned actuation signal signals the activation of the service brake and thus the beginning and / or end of the actuation, in order to then control the parking brake drive unit. Several further developments of the invention address the question of which actuation signal can be used. An activity signal from a brake light of the vehicle can be received as an actuation signal. Such an activity signal has the advantage that when the brake pedal is actuated, this is signaled before a pressure change significant for the braking process occurs in the master cylinder of the service brake. Thus, the activity signal is available at an early stage when the brake pedal is actuated. Additionally or alternatively, a sensor signal from a brake pedal travel sensor can be evaluated as an actuation signal, i.e., the movement of the brake pedal can be directly detected.Additionally or alternatively, a trigger signal from a predictive brake request detection system can be received as an actuation signal. A brake request can be predictively detected, for example, based on a change in accelerator pedal travel, such as by means of an accelerator pedal travel sensor. Such a trigger signal can be generated, for example, by an electromechanical brake booster. Additionally or alternatively, a control signal from a driver assistance system and / or a recuperation control system can be received as an actuation signal. Such a control signal has the advantage that it can be generated before the actual application of the service brake by the driver assistance system or the recuperation control system.The use of a control signal has the advantage that the parking brake can be combined or coordinated with the recuperation of an electric drive and / or blending (transition from recuperation to friction braking).

[0019] So far, training courses have been described that provide for adjusting the air gap of the friction brake using the parking brake.

[0020] Another advanced modification proposes using the parking brake for emergency braking. A hydraulic service brake typically has more than one hydraulic brake circuit. If one of these circuits fails, applying the service brake results in asymmetrical braking of the vehicle. To counteract this so-called "pulling to one side," one modification proposes that, upon receiving a failure signal indicating a brake circuit failure in one of the hydraulic service brake circuits, and provided the activation signal indicates driver-initiated service brake application (e.g., pressing the brake pedal), the failed brake circuit is at least partially compensated for by activating the parking brake's drive unit. In other words, the friction brake that remains inactive due to the failed brake circuit is applied or engaged by the parking brake.Automated detection of a failed brake circuit is state of the art.

[0021] Another advanced system utilizes the parking brake to increase braking power if the service brake's own brake booster is no longer sufficient. In this system, upon receiving a fault signal indicating a failure of the service brake booster and / or pump, and provided the activation signal indicates driver engagement of the service brake, additional braking force is generated by activating the parking brake's drive unit. This means the distance between the brake element and the friction unit of the friction brake is reduced to zero by the parking brake, and then an additional braking force is applied to the friction unit via the brake element by the drive unit. This compensates for the failure of the primary brake booster and / or the service brake pump, resulting in redundant brake force amplification based on the parking brake.Another advantage of this is that the master brake cylinder can be made larger in diameter than if the parking brake were not used to compensate for a failed brake booster. This allows the required pedal force at the brake pedal to remain constant even when the brake booster is out. The parking brake can be used as a redundancy or as a replacement for the pump by having its control unit activate the parking brake drive unit in response to an intervention signal from a driver assistance system.

[0022] This allows the vehicle to be provided without an ESC pump (ESC - Electronic Stability Control) or at least compensate for a failure of the ESC pump.

[0023] To operate an electromechanical parking brake according to the invention, the invention also provides a control device for such a brake. This control device can be configured as the parking brake's control unit. The control device includes a processor configured to execute an embodiment of the method according to the invention. The processor can include a microcontroller. Furthermore, program code for the processor can be provided, configured to execute the embodiment of the method when carried out by the processor. The program code can be stored in a data memory of the processor.

[0024] Equipping an electromechanical parking brake with the control device according to the invention results in a parking brake for a motor vehicle according to the invention. This parking brake has, in a known manner, at least one drive unit configured to move at least one brake element (e.g., a brake pad) of a respective friction brake of the motor vehicle relative to a friction unit (e.g., a brake disc) of the friction brake. In other words, the parking brake can provide a drive unit for one or more friction brakes. A friction brake can, for example, be designed as a caliper brake. A drive unit can be based on an electric motor.

[0025] The parking brake according to the invention particularly preferably includes a position sensor configured to signal a relative change in position and / or an absolute position of a component of the drive unit itself or of a transmission coupling the drive unit to the brake element. Such a position sensor can, for example, be configured to signal the position of a gear in the transmission or a change in the gear's position. A Hall sensor or Hall effect sensor can, for example, be provided as the position sensor.

[0026] An embodiment of the invention is described below. The single figure (Fig.) shows a schematic representation of an embodiment of the motor vehicle according to the invention.

[0027] The embodiment described below is a preferred embodiment of the invention. In this embodiment, the described components each represent individual features of the invention that can be considered independently of one another. Each of these features further develops the invention independently and can therefore be considered part of the invention individually or in a combination other than that shown. Furthermore, the described embodiment can also be supplemented by other features of the invention already described.

[0028] The figure shows a motor vehicle 10, which could be, for example, a car, in particular a passenger car or truck. A wheel 11 is shown, which could be a front or rear wheel, by means of which the motor vehicle 10 can roll over a surface. A friction brake 12 can be provided in the wheel 11, which can be designed, for example, as a caliper brake with a brake caliper 13 and a brake disc. The brake disc is generally referred to as a friction unit 14. The brake caliper 13 can have brake pads, which are generally referred to as brake elements 15. The friction brake 12 can be used both as a service brake 10 for braking the motor vehicle 10 while driving and as a parking brake 17 to prevent the motor vehicle 10 from rolling when switched off.

[0029] The service brake 16 can additionally comprise at least one hydraulic brake circuit 18, in which a brake pressure P can be set in a known manner, for example, by a master cylinder 19. Depending on the brake pressure P, a brake piston 20 of the friction brake 12 can be moved hydraulically. The brake piston 20 can press the brake elements 15 against the friction unit 14 in a known manner, thereby effecting friction braking of the wheel 11. In the unactuated state of the service brake 16, the brake elements 15 have a distance 21 greater than 0 from the brake disc 14. The distance 21 represents the clearance of the friction brake 13.

[0030] The parking brake 17 can act mechanically on the brake piston 20. For this purpose, an electric drive unit 22 can be provided, which, via a gearbox 23 and a spindle 23', can also move the brake piston 20. This also allows the brake elements 15 to be pressed against or moved relative to the friction unit 14, independently of the hydraulic brake circuit 16. The drive unit 22 can be an electric motor. The drive unit 22 can be controlled by a control device 24 of the parking brake 17. The control device 24 can be designed as a control unit.

[0031] The example of the friction brake 12 shown for wheel 11 can also be provided or intended for use on another wheel of the motor vehicle 10 or on both front wheels and rear wheels of the motor vehicle 10.

[0032] The master cylinder 19 can be adjusted or actuated by a brake booster (BKV) in a known manner. The brake booster (BKV) can, for example, be actuated by the driver via a brake pedal (BP). Additionally or alternatively, a driver assistance system 25 can control a pump (not shown) to adjust the brake pressure (P) without driver intervention. An example of such a pump is an ESC pump.

[0033] When the service brake 16 is applied, a brake light 26 can be activated in a manner known per se. An activity signal 27, indicating the state of the brake light 16, can be provided to the control device 24. Additionally or alternatively, a brake pedal travel sensor 28 can signal a sensor signal 29 concerning the position of the brake pedal BP to the control device 24. Additionally or alternatively, the driver assistance system 25 can provide a control signal 30 to the control device 24, signaling to the control device 24 that the service brake 16 has been applied by the driver assistance system 25. The driver assistance system 25 can, for example, provide cruise control.

[0034] Signals 27, 29, 30 each represent an actuation signal to indicate actuation of the hydraulic service brake 16.

[0035] The control device 24 can also receive a position signal 32 from a position sensor 31 of the parking brake 17, which signals or correlates with a change in position or location of, for example, a component of the transmission 23.

[0036] In a manner known per se, the control device 24, when the motor vehicle 10 is parked or switched off, can move or press the brake elements 15 against the friction unit 14 by activating or operating the drive unit 22. The brake elements 15 then remain in this position, for example due to self-locking of the transmission 23, thus blocking the rolling motion of the wheel 11. To release the parking brake 17, the drive unit 22 can be operated in the opposite direction, thereby moving the brake elements 15 away from the friction unit 14, allowing the wheel 11 to roll freely.

[0037] During a journey of the motor vehicle 10, the position or orientation of the brake elements 15 can also be adjusted by means of the parking brake 14, so that the value of the distance 21 can be set.

[0038] By means of the position sensor 31, the control device 24 can not only set the closed or open state of the parking brake 17, but at least an intermediate position. This allows the brake piston 20 of the friction brake 13 to be retracted, for example, during driving after a braking operation, i.e., after the service brake 16 has been applied, so that the residual braking torque, caused by insufficient clearance between the brake element 15 and the friction unit 14, can be reduced to as low as 0 Nm. This contributes to reducing the CO2 emissions of the motor vehicle 10.

[0039] However, if the brake piston 20 is retracted too far, resulting in excessive clearance, the next braking action would lead to a longer brake pedal travel of the brake pedal BP when the driver applies the service brake 16. The volume balance of the brake system would also deteriorate.

[0040] When a braking request is detected, as signaled, for example, by the activity signal 27 and / or sensor signal 29 and / or status signal 30, the control device 24 can use the drive unit 22 to move the brake elements 15 closer to the friction unit 14, so that only a smaller hydraulic free travel is felt in the brake pedal BP than without the operation of the drive unit 22. Similarly, the brake elements 15 can be moved closer to the friction unit 14 after a so-called knockback caused by lateral runout of the brake disc. The retraction of the brake piston 20 caused by the knockback can be detected, for example, by a sensor and reversed before the next braking action, depending on one of the described actuation signals 27, 29, 30. As a result, no increase in pedal travel is perceptible to the driver.

[0041] In combination with a glare-sensitive braking system for a gradual transition between recuperation into the battery and friction braking operation, coupling via the control device 24 is also possible. Depending on the battery status, braking can be performed with hydraulic assistance or purely hydraulically. The air clearance can be adjusted to the current operating condition by setting the distance 21 using the parking brake 17.

[0042] The driver assistance system 25 and / or a travel sensor on an accelerator pedal of the motor vehicle 10 can also predictively detect an impending application of the service brake 16 (brake request) and subsequently generate an actuation signal for the control device 24, whereupon this can control the drive unit 22 to set or prepare the distance 21.

[0043] The parking brake 17 can be operated in different application levels by means of the control device 24. For example, by adjusting the brake elements 15 to varying degrees relative to the friction unit 14, either a comfort-oriented brake pedal (soft brake pedal characteristic) or a particularly short, very sporty brake pedal (sporty brake pedal characteristic) can be selected, for example, via a driving mode button on a control unit 10 of the vehicle. The software application effort can be implemented by the control device 24, for example, by means of a processor unit 33 of the control device 24.

[0044] A further advantage arises from the mitigation of emergency situations. In the event of a brake circuit failure in brake circuit 18, not only can the braking performance be increased, but a rollover of the vehicle 10 can also be prevented if a driver applies the brake pedal BP or a driver assistance system 25 initiates or performs braking. Rollover can occur with a diagonal distribution of brake circuits (design X) and the failure of one of the brake circuits.

[0045] In the event of a failure of a brake booster 23, for example a vacuum brake booster, the braking force can be increased by the parking brake 17 via the drive unit 22, so that a predetermined maximum pedal force at the brake pedal BP is still sufficient to generate a predetermined braking force at the wheel 11. Due to this redundancy of the brake force amplification provided by the brake booster 23 on the one hand and the parking brake 17 on the other, the master brake cylinder 19 can also have a larger diameter than if there were no redundancy, but only the brake booster 23, thus further improving the volume efficiency of the brake system.

[0046] The parking brake 17 can also be coupled with the driver assistance system 25, so that the driver assistance system 25 can control the parking brake 17 for a braking intervention and thereby selectively brake wheels, e.g. for vehicle dynamic stabilization or deceleration of the vehicle 10.

[0047] In summary, the brake clearance can be actively adjusted by setting the distance 21. By adjusting the distance 21 based on a relative movement, such as that detected by the displacement sensor 23, this adjustment is also independent of wear. By resetting the brake clearance at the beginning of an application of the service brake 16, a reduction in CO2 emissions from the braking system can be achieved without increasing the travel of the brake pedal BP. A driving mode can also be used to select either a comfort-oriented or an extremely sporty pedal feel at the brake pedal BP.

[0048] Overall, this example shows how the invention can provide a functional extension of an electromechanical parking brake for active air clearance adjustment. Reference symbol list 10 motor vehicle 11 wheels 12 friction brake 13 brake calipers 14 friction unit 15 brake element 16 Hydraulic service brake 17 Electromechanical parking brake 18 brake circuit 19 main cylinders 20 brake pistons 21 Distance (air play) 22 Drive unit 23 gearboxes 23' spindle 24 Control device 25 Driver assistance systems 26 brake light 27 Activity signal 28 Brake pedal travel sensor 29 Sensor signal 30 Control signal 31 Position sensor 32 Way signal 33 Processor setup BKV brake booster BP brake pedal P Brake pressure

Claims

[1] Method for operating an electromechanical parking brake (17) of a motor vehicle (10), wherein a control device (24) of the parking brake (17) on at least one friction brake (12) of the motor vehicle (10) moves at least one brake element (15) of the friction brake (12) relative to a friction unit (14) of the friction brake (12) independently of a brake pressure (P) of a hydraulic service brake (16) of the motor vehicle (10) by means of an electrical drive unit (22) of the parking brake (17), wherein during a journey of the motor vehicle (10) a respective distance (21) between the at least one brake element (15) on the one hand and the friction unit (14) on the other hand is changed by the drive unit (22) depending on at least one brake actuation signal (27, 29, 30) of the service brake (16), characterized by, that in the event that the brake actuation signal (27, 29, 30) signals the start of an actuation or predictively an impending actuation of the service brake (16), the distance (21) is set to a predetermined distance value by controlling the drive unit (22), so that a clearance (21) is reduced by means of the parking brake (17) before or at the start of a braking process which is to be effected by the hydraulic service brake (16). [2] Method according to claim 1, wherein the drive unit (22) is controlled depending on a position signal (32) which the control device (24) receives from a position sensor (31) which signals a relative change in position and / or an absolute position of a component of the drive unit (22) or of a transmission (23) coupling the drive unit (22) with the at least one brake element (15). [3] Method according to one of the preceding claims, wherein, in the event that the at least one brake actuation signal (27, 29, 30) signals an end of an actuation of the service brake (16), by actuating the drive unit (22) an air gap (21) between the brake element (15) and the friction unit (14) caused by the service brake (16) in the unactuated state of the service brake (16) is increased by a predetermined offset value. [4] Method according to claim according to one of the preceding claims, wherein the distance value is determined as a function of a driving mode signal of an operating device of the motor vehicle (10). [5] Method according to one of the preceding claims, wherein the brake actuation signal (27, 29, 30) is an activity signal (27) of a brake light (26) of the motor vehicle (10) and / or a sensor signal (29) of a brake pedal travel sensor (28) and / or a trigger signal of a predictive brake request detection system and / or a control signal (30) of a driver assistance system (25) and / or a recuperation control system. [6] Method according to one of the preceding claims, wherein, after receiving a failure signal indicating a failure of a hydraulic brake circuit (18) of the service brake (16), in the event that the actuation signal (27, 29, 30) indicates driver-side actuation of the service brake (16), the failed brake circuit (18) is at least partially compensated by actuating the drive unit (22). [7] Method according to one of the preceding claims, wherein, after receiving a fault signal indicating a failure of a brake booster (BKV) and / or a pump of the service brake (16), in the event that the brake actuation signal (27, 29, 30) indicates driver-side actuation of the service brake (16), an additional braking force is generated by actuating the drive unit (22). [8] Method according to one of the preceding claims, wherein the control device (24) of the parking brake (17) controls the drive unit (22) depending on an intervention signal from a driver assistance system (25) for a brake intervention of the driver assistance system (25). [9] Control device (24) for an electromechanical parking brake (17), characterized by that the control device (24) has a processor device (33) configured to perform a method according to one of the preceding claims. [10] Electromechanical parking brake (17) for a motor vehicle (10) with at least one drive unit (22) for moving at least one brake element (15) of a friction brake (12) of the motor vehicle (12) with respect to a friction unit (14) of the friction brake (12), characterized by that the parking brake (17) has a control device (24) according to claim 9. [11] Parking brake (17) according to claim 10, wherein a position sensor (31) is provided which is configured to signal a relative change in position and / or an absolute position of a component of the drive unit (22) or of a transmission (23) coupling the drive unit (22) with the brake element (15).

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