Method for operating a motor vehicle braking system with an electro-hydraulic service brake and a mechanical parking brake, as well as a motor vehicle braking system

Abstract

Method for operating a braking system of a motor vehicle equipped with a wheel slip control device, wherein the braking system comprises an electro-hydraulic service brake designed to generate braking forces independently of operator input, and a mechanical or electromechanical parking brake that can be actuated by means of an actuating element, wherein an operator's request to actuate the parking brake is detected and subsequently, during the actuation of the parking brake, a hydraulic pressure of the service brake is generated which acts on at least one wheel of the motor vehicle that can be braked by the parking brake and is sufficient to block the at least one wheel of the motor vehicle that can be braked by the parking brake during a journey of the motor vehicle.The hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it if a brake light switch is inactive and the main hydraulic pressure of the service brake is less than a predefinable main hydraulic pressure threshold value, and the hydraulic pressure of the service brake is reduced again during the application of the parking brake to assist it in such a way that at least one blocked wheel is no longer blocked as soon as the brake light switch is active or the main hydraulic pressure of the service brake is greater than the predefinable main hydraulic pressure threshold value.

Description

[0001] The present invention relates to a method for operating a braking system of a motor vehicle equipped with a wheel slip control device, wherein the braking system is an electro-hydraulic service brake configured to generate braking forces independently of operator input, and comprises a mechanical or electromechanical parking brake that can be actuated by means of an actuating element, according to the preamble of claim 1. The invention further relates to a braking system for a motor vehicle according to the preamble of claim 10.

[0002] It is generally known that parking brakes on motor vehicles are equipped with separate operating elements, such as handbrake levers or foot levers. Parking brakes can be purely mechanical, connected, for example, to the operating element inside the vehicle via a cable. The operator, for example, the driver, actsuates the operating element by pulling the handbrake lever upwards or pushing the foot lever downwards, thereby generating a torque at the handbrake lever or foot lever. This torque is converted into a tensile force via the cable, which in turn generates the clamping force of the parking brake. In electromechanical parking brakes, the force generated by the operator is replaced by an electromechanical force. Such parking brakes can then be engaged and disengaged by means of an electrical switch.Parking brakes are generally designed and suitable to hold the vehicle stationary by mechanical means, for example, even on an inclined road surface. The parking brake usually acts on the rear wheels of the vehicle.

[0003] The service brake allows the driver to reduce the vehicle's speed or bring it to a complete stop with graduated braking force. Modern vehicles are now equipped with an electrically controlled service brake system to enable not only anti-lock braking (ABS) but also automatic braking functions independent of driver input, such as traction control (ASR) or electronic stability control (ESP). The service brake system typically includes a suitably designed electro-hydraulic service brake, which may be equipped with an electro-hydraulic control unit and / or an electronically controlled brake booster, or implemented as a so-called "brake-by-wire" system. ABS, ASR, ESP functions, and similar systems are implemented by a wheel slip control unit, also referred to here as a wheel slip control device.

[0004] While the ABS function of the service brake system actively prevents the vehicle's wheels from locking when the service brake is applied, the parking brake is also generally not designed to lock the vehicle's wheels, such as the rear wheels, while the vehicle is in motion. Particularly on dry asphalt, i.e., a road surface with a high coefficient of friction, the parking brake torque that can be applied via the parking brake actuator may not be sufficient to lock the corresponding vehicle wheels. This is especially true for parking brakes that act on the vehicle's disc brakes, which are themselves actuated by the service brake.To cause the wheels to lock using such parking brakes, a high force is required that cannot usually be applied by an average operator using the conventional parking brake actuation element.

[0005] Another known parking brake concept, which allows the transmission of higher braking forces via the actuating element to the wheels braked by the parking brake, particularly the rear wheels, of the vehicle, provides a separate brake drum within a disc brake that is normally actuated by the service brake. The parking brake acts upon this separate drum. However, even with this brake concept, the desired locking of the wheels braked by the parking brake cannot always be guaranteed under all operating conditions of the vehicle. Furthermore, such a parking brake concept involves increased manufacturing effort and consequently higher costs.

[0006] In certain situations, such as dangerous or threatening situations, or in motorsport, it is desirable for the driver to execute a so-called handbrake turn, or simply a handbrake turn. This maneuver induces extreme drift angles, i.e., oversteer, to enable a 180° turn in the shortest possible time or to navigate particularly tight or challenging U- and S-curves. The rear wheels are immediately locked by the parking brake, causing the vehicle to break away. In motorsport, for example, it is common practice to equip vehicles with special, extra-long parking brake levers to generate the necessary torque to lock the wheels.Purely hydraulic parking brakes are also known from the motorsport sector, but these are not approved for road use, as these hydraulic parking brakes use the same hydraulic circuit as the service brake.

[0007] Generic methods for operating a braking system of a motor vehicle equipped with a wheel slip control device are disclosed, for example, in DE 196 32 863 A1 or DE 102 47 653 A1, wherein the braking system is an electro-hydraulic service brake designed to generate braking forces independently of operator input, and comprises a mechanical or electromechanical parking brake that can be actuated by means of an actuating element and acts in particular on the rear wheels of the motor vehicle, wherein an operator's request to actuate the parking brake is detected and subsequently, during the actuation of the parking brake, a hydraulic pressure of the service brake is generated which acts on at least one wheel of the motor vehicle that can be braked by the parking brake, in particular a rear wheel, and is sufficient.to block at least one wheel of the motor vehicle that can be braked by the parking brake while the motor vehicle is in motion.

[0008] Furthermore, US patent 2014 / 0129107 A1 discloses an electro-hydraulic service brake in which the wheels of a non-driven vehicle axle can be secured against rolling away when stationary by selectively building up and maintaining hydraulic pressure in the service brake circuits of these wheels, depending on the driver actuation of a switch. This capability can be used to cause the wheels of the driven vehicle axle to spin, for example, to increase the temperature of the spinning tires before driving off.

[0009] Furthermore, DE 10 2010 062 816 A1 describes an electro-hydraulic service brake in which the occurrence of a negative coefficient of friction of the road surface is monitored during a braking operation, wherein the amplification of a brake booster is set to a smaller value when a braking maneuver is detected on a road surface with a negative coefficient of friction than in the case of a braking maneuver on a road surface without a negative coefficient of friction.

[0010] US patent 2010 / 0114445 A1 discloses a driver assistance system that can perform autonomous braking upon detecting an obstacle in a vehicle's path. To reduce the braking reaction time, it is proposed that, in the case of a hydraulic or electro-hydraulic service brake, the brakes be pre-tensioned using an ABS pump of an ESP unit.

[0011] EP 2 342 110 B1 discloses the use of an electromechanical service brake on the front axle of a vehicle and an electrohydraulic service brake on the rear axle of the vehicle. Braking forces can also be generated on the rear axle independently of operator input by means of an ESP unit.

[0012] Furthermore, US patent 6,254,202 B1 discloses an electro-hydraulic vehicle service brake with an ABS control unit. During emergency braking, additional brake pressure can be generated by a pump within the ABS unit, supplementing the brake pressure normally produced by a master cylinder.

[0013] DE 10 2007 028 070 A1 describes an electro-hydraulic service brake for a motor vehicle with a regenerative braking unit and an electric machine for driving / braking the motor vehicle, wherein the regenerative braking unit, during a regenerative braking process, does not feed a volume of hydraulic fluid corresponding to the braking request into the wheel brakes, but stores it in a hydraulic fluid pressure accumulator of the regenerative braking unit.

[0014] Finally, the article “Electrohydraulic Brake System - The First Approach to Brake-by-Wire Technology” by Wolf-Dieter Jonner et al., SAE Technical Paper 960991, 1996, describes the general structure of so-called brake-by-wire braking systems.

[0015] DE 10 2014 203 889 A1 describes a method for operating a braking system in which, by actuating a second control element different from the service brake, a braking force is built up exclusively on the wheels of an axle, in particular the rear axle, in such a way that they lock.

[0016] Against this background, the present invention aims to improve a method for operating a braking system comprising an electro-hydraulic service brake and a mechanical or electromechanical parking brake of a motor vehicle equipped with a wheel slip control device, such that a simplified and safe execution of a handbrake turn is possible with such motor vehicles. Furthermore, the method should not require any mechanical modifications compared to such and already known braking systems.

[0017] This problem is solved by a method having the features of claim 1 and by a braking system having the features of claim 10. Further particularly advantageous embodiments of the invention are disclosed in the dependent claims.

[0018] It should be noted that the features listed individually in the following description can be combined in any technically sensible way and demonstrate further embodiments of the invention.

[0019] According to the invention, a method for operating a braking system of a motor vehicle equipped with a wheel slip control device is disclosed, wherein the braking system comprises an electro-hydraulic service brake configured to generate braking forces independently of operator input, and a mechanical or electromechanical parking brake that can be actuated by means of an actuating element and, in particular, acts on the rear wheels of the motor vehicle. In the method according to the invention, an operator's request to actuate the parking brake is detected, and subsequently, during the actuation of the parking brake, hydraulic pressure is generated by the service brake, which acts on at least one wheel of the motor vehicle that can be braked by the parking brake, in particular a rear wheel, and is sufficient to block the at least one wheel of the motor vehicle that can be braked by the parking brake while the motor vehicle is in motion.

[0020] However, according to the invention, the hydraulic pressure of the service brake is only generated to assist the parking brake during its application if a brake light switch is inactive and the main hydraulic pressure of the service brake is below a predefinable threshold value. This ensures that the service brake does not engage to assist the parking brake, as described in the invention, if the driver intends to perform conventional braking using the service brake. The main hydraulic pressure threshold is preferably set within a range of 0 to 10 bar.

[0021] Furthermore, as soon as the driver of the vehicle applies the service brake during the handbrake maneuver – i.e., the brake light switch is activated or the hydraulic pressure of the service brake exceeds the predefined hydraulic pressure threshold – the hydraulic pressure of the service brake, generated for the specific intervention on the wheels braked by the parking brake, particularly the rear wheels, is preferably reduced during the application of the parking brake in such a way that the one or more locked wheels are no longer locked. The specific intervention of the service brake for performing the handbrake maneuver is thus terminated, which, among other things, significantly improves the safety of performing the handbrake maneuver.

[0022] A wheel slip control device within the meaning of the present invention is, in particular, a device or system for controlling the wheel slip of a motor vehicle using the electro-hydraulic service brake to improve driving stability, as can be implemented, for example, in the form of an anti-lock braking system (ABS), traction control (ASR), yaw control (AYC), and / or electronic stability program (ESP). Such systems comprise various electrical, hydraulic, and electro-hydraulic components, such as an electronically controlled brake booster, one or more hydraulic pumps, electrically controlled valves, hydraulic accumulators, and the like, as well as usually an electronic control unit for controlling these components to perform one or more of the aforementioned functions.The electro-hydraulic control of the service brake thus enables, in particular, the generation of braking forces independent of operator input. These wheel slip control devices and electro-hydraulically controlled brakes are known, which is why they will not be discussed further here.

[0023] The parking brake according to the invention can be a purely mechanical parking brake, which, for example, acts on the corresponding wheels, in particular the rear wheels, of the motor vehicle via a cable operated by an operator using an actuating element, both to engage and to release the brake, or it can be an electromechanical parking brake in which the force generated by the operator at the actuating element is replaced by an electromechanical force. According to the invention, the actuating element can be a foot lever or, preferably, a handbrake lever. In particular, in the case of electromechanical parking brakes, the actuating element can also be an electrical switch by which the parking brake is actuated.

[0024] Since the inventive method, after recognizing the operator's request to apply the parking brake and during its application, can cause at least one wheel of the motor vehicle, in particular at least one rear wheel, to lock by applying the braking force required for locking from the electro-hydraulic service brake, it is possible, even though the motor vehicle is equipped with a wheel slip control device that essentially prevents wheel slip during normal operation, to also perform a handbrake turn with the motor vehicle. In other words, during the handbrake turn, that is, limited to this specific case, 100% wheel slip of at least one wheel, in particular at least one rear wheel, of the motor vehicle is temporarily permitted.The electro-hydraulic service brake then assists the parking brake in such a way that at least one wheel of the vehicle braked by the parking brake can be locked. At the latest when the parking brake is released or deactivated via the actuating element, the hydraulic pressure of the service brake used to lock the at least one wheel is reduced. Subsequently, the wheel slip control system regulates the slip of all wheels of the vehicle again in the conventional manner.

[0025] The method according to the invention is particularly preferably implemented in the form of a computer-executable program within the wheel slip control device, for example, within the ESP control unit. Accordingly, no mechanical modifications to the vehicle's braking system, in particular neither to the service brake nor the parking brake, nor additional components for the braking system are required. Only the programming of the corresponding control unit needs to be adapted to the implementation of the method according to the invention.

[0026] The generation of hydraulic pressure for locking at least one wheel of the vehicle while driving is preferably achieved by means of at least one hydraulic pump of the wheel slip control device, for example, an ABS and / or ESP hydraulic pump. In this way, the vehicle components already present for the braking system can advantageously also be used to carry out the method according to the invention, i.e., to initiate and execute the handbrake turn. No additional components are required.

[0027] The operator's request to engage the parking brake is preferably detected by a sensor, usually already present in the vehicle, which monitors the actuation or movement of the handbrake or foot lever. If an electrical switch is used to activate the parking brake, the operator's request to engage the parking brake is immediately apparent from the actuation of the switch, making it unambiguous and easy to detect. It is also conceivable that the vehicle may be equipped with an additional actuating element specifically designed to initiate a handbrake reversal, such as a separate handbrake lever or a separate switch, in addition to the conventional handbrake or foot lever. In this case, the operator's request to engage the parking brake is immediately recognizable from the actuation of this specific actuating element.

[0028] An advantageous embodiment of the invention provides that the hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it when the vehicle is within a predefinable speed range. Preferably, the speed range is defined by a predefinable lower speed threshold and a predefinable upper speed threshold. This ensures that the handbrake turning maneuver only takes place within a speed range in which a controlled handbrake turn by a (skilled) driver is possible. Preferably, the lower speed threshold can be set in a range of 0 to 50 km / h and the upper speed threshold in a range of 0 to 300 km / h.

[0029] According to a further advantageous embodiment of the invention, the hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it if the lateral acceleration of the vehicle is greater than a predefinable first lateral acceleration threshold and / or the yaw acceleration of the vehicle is greater than a predefinable yaw acceleration threshold. Preferably, the first lateral acceleration threshold can be in a range of 0 to 10 m / s². 2 and the yaw acceleration threshold in a range of 0 to 200 deg / s 2The handbrake turning maneuver, i.e., the locking of at least one wheel, particularly the rear wheel, of the vehicle, is initiated only when the driver, by actuating the control element and steering into a curve (resulting in lateral or yaw acceleration), indicates even more clearly that they intend to perform a handbrake turning maneuver. However, when the parking brake is engaged while the vehicle is traveling straight ahead, no specific intervention occurs via the electro-hydraulic service brake on the wheels braked by the parking brake, particularly the rear wheels, to assist it in accordance with the invention. Only the braking torque generated by the parking brake is effective.

[0030] Preferably, the hydraulic pressure of the service brake is reduced again during the application of the parking brake to assist it, as soon as the lateral acceleration of the motor vehicle is less than a predefinable second lateral acceleration threshold value, which is preferably in a range of 0 to 10 m / s². 2 can be determined. In this case, the special engagement of the service brake on the wheels braked by the parking brake, in particular the rear wheels, of the motor vehicle to assist it is terminated, so that only the parking brake, as long as it is applied, exerts a braking force on the corresponding wheels, in particular the rear wheels.

[0031] A further advantageous embodiment of the invention provides that the hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it when the sign of the yaw rate is equal to the sign of the change in the steering wheel angle over time. This ensures that the driver of the motor vehicle steers in the direction of the vehicle's rotation about its vertical axis and thus indicates the execution of the handbrake turn.

[0032] Furthermore, the hydraulic pressure of the service brake is preferably reduced during the application of the parking brake to assist it, as soon as the steering wheel angle exceeds a predefinable steering wheel angle threshold and the sign of the steering wheel angle is not the same as the sign of the yaw rate. In this way, the intervention of the service brake on the wheels braked by the parking brake, particularly the rear wheels, of the vehicle, as provided for in the invention, is terminated as soon as the driver of the vehicle exceeds a certain degree of steering counter-steering. As long as the parking brake remains applied, it continues to act, but on its own, on the corresponding wheels, particularly the rear wheels, of the vehicle. The steering wheel angle threshold can preferably be set in a range of 0° to 500°.

[0033] According to a further advantageous embodiment of the invention, the hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it when the coefficient of friction of the road surface is greater than a predefinable friction threshold value. In this way, it can be ensured that the specific engagement of the service brake, as defined by the invention, only occurs when it is actually necessary due to a relatively high coefficient of friction of the road surface, for example, on dry asphalt, since the braking torque that can be applied by the parking brake alone is insufficient to lock at least one wheel, in particular the rear wheel, of the vehicle.For example, the parking brake can typically be used on snow or ice to transmit sufficient braking force to lock the wheel, thus eliminating the need for intervention by the service brake as described in the invention. The friction coefficient threshold can preferably be set in a range of 0 to 1.2.

[0034] The coefficient of friction of the road surface is preferably determined or estimated by the ESP control unit of the wheel slip control system itself. For this purpose, the ESP control unit can, for example, determine during vehicle operation at what acceleration the vehicle or one of its wheels becomes unstable, from which the coefficient of friction of the road surface can be estimated. The acceleration can be determined using the ESP sensors, such as longitudinal and / or lateral acceleration sensors and / or yaw rate sensors and / or wheel speed sensors. The coefficient of friction determined in this way by the ESP control unit then serves as the input value for executing the aforementioned method according to the invention.

[0035] A further advantageous embodiment of the invention provides that the hydraulic pressure of the service brake is only generated to assist the parking brake during its application when the slip of the inside wheel, particularly the inside rear wheel, exceeds a predefinable first wheel slip threshold. This allows the system to detect that the driver intends to negotiate a curve with the parking brake engaged, thus determining the driver's request for a handbrake turn. Preferably, the first wheel slip threshold can be set within a range of 0 to 100%.

[0036] Furthermore, the hydraulic pressure of the service brake is preferably reduced again during the application of the parking brake to assist it, as soon as the slip of the inside wheel in a curve, in particular the inside rear wheel in a curve, is less than a predefinable second wheel slip threshold value. Preferably, the second wheel slip threshold value can be set in a range from 0 to 100%.

[0037] According to a further advantageous embodiment of the invention, the hydraulic pressure of the service brake is generated during the application of the parking brake to assist it, for a maximum of a predefinable engagement duration. This ensures that the specific engagement of the service brake to assist the parking brake, as defined by the invention, is terminated no later than after the engagement duration has been reached. The engagement duration is preferably definable within a range of 0 to 10 seconds.

[0038] Furthermore, an advantageous embodiment of the invention provides that, after the hydraulic pressure of the service brake is generated during the application of the parking brake to assist it, the hydraulic pressure of the service brake is reduced again during the application of the parking brake as soon as the throttle position of an engine of the motor vehicle exceeds a predefinable throttle threshold. Thus, as soon as the driver wishes to accelerate the motor vehicle again after performing the handbrake maneuver, the specific engagement of the service brake to assist the parking brake, as defined by the invention, is terminated. The throttle threshold is preferably predefinable within a range of 0 to 110%.

[0039] Furthermore, it can be advantageous to generally activate the inventive intervention of the service brake for performing the handbrake turn only after the ESP function of the vehicle has been previously deactivated by the driver. Additionally, it can also be provided that the driver must select a special drift operating mode for the vehicle so that the special intervention of the service brake to assist the handbrake turn is permitted at all.

[0040] In the case of a motor vehicle with selectable all-wheel drive (AWD), it can be advantageously provided that an AWD clutch at least partially disengages the front wheels from the rear wheels as soon as a special intervention of the service brake to assist the parking brake occurs in accordance with the invention, in order to perform the handbrake turning maneuver. Here, it can be advantageous not to fully open the AWD clutch, but merely to significantly reduce the torque it can transmit, in order to be able to return to the all-wheel drive mode of the motor vehicle as quickly as possible after the inventive intervention of the service brake for performing the handbrake turning maneuver has ended.

[0041] Particularly preferably, the service brake is applied to assist the parking brake according to the invention not just to one wheel of the vehicle, but to both rear wheels. For this purpose, both rear wheels are subjected to a definable brake pressure by means of the service brake, which is preferably definable within a range of 0 to 200 bar. Furthermore, preferably, the brake pressure applied to the inner rear wheel in a curve can be reduced by a definable factor compared to the brake pressure applied to the outer rear wheel in a curve. However, both brake pressures can also be the same. The definable factor is preferably definable within a range of 0 to 1.

[0042] In a preferred embodiment, the method described above according to the invention is used in an electronic control unit of a wheel slip control device of a motor vehicle, in particular in an ESP control unit of the motor vehicle.

[0043] Thus, according to a further aspect of the invention, a braking system of a motor vehicle according to the invention comprises an electro-hydraulic service brake designed to generate braking forces independently of operator input, a mechanical or electromechanical parking brake that can be actuated by means of an actuating element and acts in particular on the rear wheels of the motor vehicle, and a wheel slip control device with a control unit suitable for carrying out the aforementioned method according to the invention. With regard to further embodiments, advantages, and effects of the device according to the invention, the preceding descriptions set out in connection with the description of the method according to the invention apply analogously.

Claims

[1] A method for operating a braking system of a motor vehicle equipped with a wheel slip control device, wherein the braking system is an electro-hydraulic service brake designed to generate braking forces independently of operator operation, and comprises a mechanical or electromechanical parking brake that can be actuated by means of an actuating element, wherein an operator's request to actuate the parking brake is detected and subsequently, during the actuation of the parking brake, a hydraulic pressure of the service brake is generated which acts on at least one wheel of the motor vehicle that can be braked by the parking brake and is sufficient to block the at least one wheel of the motor vehicle that can be braked by the parking brake during a journey of the motor vehicle, characterized by, that the hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it when a brake light switch is inactive and the main hydraulic pressure of the service brake is less than a predefinable main hydraulic pressure threshold, and that the hydraulic pressure of the service brake is reduced again during the application of the parking brake to assist it in such a way that at least one blocked wheel is no longer blocked as soon as the brake light switch is active or the main hydraulic pressure of the service brake is greater than the predefinable main hydraulic pressure threshold. [2] Method according to claim 1, characterized by , that the hydraulic pressure of the service brake is only generated to assist the parking brake when the vehicle is within a predefinable speed range. [3] Method according to claim 1 or 2, characterized by , that the hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it when a lateral acceleration of the vehicle is greater than a predefinable first lateral acceleration threshold and / or a yaw acceleration of the vehicle is greater than a predefinable yaw acceleration threshold, and the hydraulic pressure of the service brake is reduced again during the application of the parking brake to assist it as soon as the lateral acceleration of the vehicle is less than a predefinable second lateral acceleration threshold. [4] Method according to any one of the preceding claims, characterized by, that the hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it when the sign of the yaw rate is equal to the sign of the change in the steering wheel angle over time, and that the hydraulic pressure of the service brake is reduced again during the application of the parking brake to assist it as soon as the steering wheel angle is greater than a predefinable steering wheel angle threshold value and the sign of the steering wheel angle is not equal to the sign of the yaw rate. [5] Method according to any one of the preceding claims, characterized by , that the hydraulic pressure of the service brake is only generated during the application of the parking brake to support it when the coefficient of friction of the road surface is greater than a predefinable coefficient of friction threshold. [6] Method according to any one of the preceding claims, characterized by, that the hydraulic pressure of the service brake is only generated during the application of the parking brake to assist it when the slip of the inner wheel is greater than a predefinable first wheel slip threshold, and the hydraulic pressure of the service brake is reduced again during the application of the parking brake to assist it as soon as the slip of the inner wheel is less than a predefinable second wheel slip threshold. [7] Method according to any one of the preceding claims, characterized by , that the hydraulic pressure of the service brake is generated during the application of the parking brake to support it for a maximum of a predefinable intervention duration. [8] Method according to any one of the preceding claims, characterized by, that after the generation of the hydraulic pressure of the service brake during the application of the parking brake to support it, the hydraulic pressure of the service brake is reduced again during the application of the parking brake as soon as a throttle valve position of an engine of the motor vehicle is greater than a predefinable throttle valve threshold value. [9] Method according to any one of the preceding claims, characterized by , that at least one hydraulic pump of the vehicle's wheel slip control device is activated to generate the hydraulic pressure of the service brake during the application of the parking brake. [10] Braking system of a motor vehicle comprising an electro-hydraulic service brake designed to generate braking forces independently of operator operation, a mechanical or electromechanical parking brake which can be actuated by means of an actuating element, and a wheel slip control device with a control unit, characterized by that the control unit is configured to carry out a method according to one of the preceding claims.