DE102015206184A1 - Parking brake for a motor vehicle with a brake booster and method for performing a parking brake operation - Google Patents

Abstract

The invention relates to a method for performing a parking brake operation in a motor vehicle with an automated parking brake and a service brake, wherein the service brake has a brake booster and the brake booster in a deceleration braking a defined characteristic for a gain of a braking force, wherein the characteristic of the brake booster in the implementation the parking brake operation is changed, and a parking brake, a brake booster and a control device, which are arranged and have means to perform the method.

Description

State of the art

The font EP 1 604 128 B1 describes a brake circuit with main service brake and a parking brake of the type with blocking means which are activated by a source of pressurized fluid, wherein the source of pressurized fluid is a source of pressurized brake fluid for actuating the main service brake having a master cylinder which is actuated by an active pneumatic servo motor for brake assistance belonging to the brake circuit.

Furthermore, the patent application describes DE 10 2014 222 197 A1 a method for carrying out a parking brake operation in a motor vehicle with a hydraulic service brake and an automated parking brake, which is characterized in that each parking brake operation after the activation of the parking brake braking force is at least partially generated by the vehicle occupant.

The font DE 10 2010 001 355 A1 describes a vacuum brake booster which acts on a master cylinder with an assisting force and a method for its operation. The assistance force of the brake booster can be adjusted via an adjusting device and via a main control valve. Thus, the brake booster is operable in two modes of operation, wherein in a first mode of operation the assisting force is adjusted by the adjusting means and in a second mode of operation by the main control valve.

Disclosure of the invention

Automated parking brakes require powerful actuators (actuators) to provide power for a locking process. This results in high costs for the customer. New types of actuator concepts could reduce costs. However, these concepts must ensure that the requirements for a parking brake operation are met. In particular, a fast power and high braking forces must be made possible. The object is therefore to develop a method by means of which the braking force generation can be carried out according to the requirements of the parking brake operation, as well as suitable components to implement such a method and to apply.

This object is solved by the features of the independent claims. Further developments of the invention are specified in the dependent claims.

A method is provided for performing a parking brake operation in a motor vehicle having an automated parking brake and a service brake, the service brake having a brake booster. According to the invention it is provided that the brake booster in a deceleration braking process has a defined characteristic for a gain of a braking force and the characteristic of the brake booster in the implementation of the parking brake operation is changed.

In particular, a deceleration braking operation is understood to mean a regular service braking operation by means of a hydraulic service brake in order to decelerate and stop a vehicle. A parking brake operation is used in particular to secure the vehicle at a standstill. An automated parking brake (also called automated or automatic parking brake) takes over the generation or supports the driver in generating the braking force required for the locking process and allows holding the generated braking force. For this purpose, the required braking force is set to the braking device in a first step, for example. By hydraulic pressure and in a second step, the generated braking force is set. The amount of braking power required depends on several factors, such as vehicle weight, slope of the holding plane or temperature of the brake discs. The braking force generated via the brake piston pressing the brake pads to the brake disc; Therefore, it can also be spoken of a clamping force. The braking force thereby allows a holding force to keep the vehicle in the parked position. The parking brake has for fixing the generated braking force, for example, a self-locking locking mechanism. This can be configured as an electric motor with a spindle gear. In an alternative embodiment, valves can also permanently lock in a generated pressure to achieve a parking brake function.

According to the invention, a brake booster (BKV) is provided. In particular, the BKV is designed as a pneumatic vacuum brake booster. A BKV helps the driver to build up braking power. In particular, the reinforcement of a pressure applied by the driver, for example by means of the foot brake pedal, is to be understood as assistance. Alternatively, the support can also be designed as independent and driver-independent pressure generation. This can also be used in (partially) autonomous parking brake systems. The characteristic of a BKV describes the ratio of the output force to the input force. In the case of driver-independent pressure generation, the characteristic generally describes the force generation process. This characteristic can be represented by a (possibly kinked) force-displacement curve. The path can be represented by the deflection of the associated with the Fußbremspedal piston rod.

The BKV can be advantageously used both in the context of the deceleration braking process as well as when performing the parking brake operation. The change according to the invention of the characteristic of the BKV in the parking brake operation can be configured as an increase in the force-displacement characteristic. Furthermore, an increase in the maximum power assist (gain of the vacuum) and / or a faster power build-up (increase the dynamics of the vacuum build-up) can be set. This results in a stronger and faster braking force assistance in a parking brake operation than in a regular service brake operation, for example. Delay brake operation. While in a deceleration braking process especially a sensitive control is necessary, the parking brake focused on the direct, fast and low-cost for the driver achieving the required holding power for the present holding situation. This can be advantageously achieved by the method according to the invention.

In one embodiment, the brake booster comprises at least one vacuum chamber and a working chamber, wherein a first connection of the working chamber is formed at atmospheric pressure to generate the characteristic of the brake booster in a deceleration braking operation and to change the characteristic in a parking brake operation, a second connection of the working chamber with atmospheric pressure is trained.

By this is meant that to achieve the regular characteristics of the BKV an initial connection with the environment exists. The compound is in particular a pneumatic connection. This first connection of the working chamber with atmospheric pressure is formed by a main control valve. The circuit of the main control valve is subject to a geometric relationship of the components and the deflection of the input rod. The opening width of the main control valve is therefore dependent on how far the driver moves the input rod by means of the foot brake pedal. In an advantageous embodiment, a further connection possibility between the working chamber and the atmospheric pressure is additionally present. When a parking brake operation is activated, this connection opens. This results in a change in the characteristics of the BKV. Advantageously, this connection can be activated as needed and independently of the first connection. Furthermore, this can make it possible to activate both connections in parallel.

In an advantageous development, the brake booster on a switchable or controllable valve, wherein the second connection of the working chamber is formed by means of the valve with atmospheric pressure.

By this is meant that in addition to the main control valve, another valve is used, which forms an independent connection between the working chamber and the ambient pressure surrounding the system. The use of switching valves allows opening and closing of the connection. Alternatively, if control valves are used, the connection may have a continuous transition, i. allow a partial opening. In particular, electromagnetic valves are provided. By using switchable or adjustable valves, the further connection can be activated independently of the deflection of the input rod. It is advantageously possible to open and close the valves on the basis of signals. For this example, evaluated signals from sensor units, such as brake light switch, pressure information of the master cylinder or displacement sensors on the brake pedal or the piston rod can be used.

In an alternative embodiment, the characteristic of the brake booster is changed when at least one defined activation condition is met.

This means that the characteristic of a BKV in the context of a parking brake operation is only changed if a specified condition is fulfilled or assumed to be fulfilled. Such a condition may be, for example, a specific environmental situation, such as the inclination of the plane in which the vehicle is located or conditions in the vehicle, such as exceeding a temperature of the brake discs or conditions that are met by an action of the driver. If a defined condition is not met, there is no change in the characteristic. This can avoid that the driver is confronted with unwanted or unfamiliar system reactions. Furthermore, an unnecessary component load can be avoided by reducing the adaptation processes, in particular at high pressures and fast component movements. Furthermore, it can be provided to change the characteristic only if a plurality of defined conditions are met.

In a further development, it is provided that the characteristic of the brake booster is changed when an activation of the parking brake operation and an actuation of the service brake have taken place.

This is to be understood that in this embodiment, two conditions must be met, so that a change in the characteristics of the BKV takes place. On the one hand, the parking brake must be activated and, on the other hand, the service brake must be actuated. The activation of the parking brake operation can be carried out, for example, by the driver by means of an actuation of the parking brake button. In an alternative embodiment, an activation of the parking brake operation can be automatically detected by the vehicle, such as when detecting a parking maneuver or a specific speed profile or reaching a target position in the navigation. The operation of the service brake can advantageously be done by the driver. The determination of the operation of the service brake can be done, for example, on the basis of the signal of the brake light switch. Alternatively, a determination by means of a displacement sensor on the brake pedal or the piston rod or based on pressure information in the master cylinder or brake circuit. An identification of the operation of the service brake occurs when a defined path, or a defined pressure threshold is exceeded. A combination of the two features appears advantageous in several respects: Advantageously, the assistance is started by means of a change in the characteristic only when both the parking brake operation has been activated and the driver moves the brake pedal to a defined extent. Furthermore, by the additional actuation of the service brake by the driver, a force superposition of the force generated by the driver as well as the force generated by the BKV for the parking brake operation can take place.

In an advantageous embodiment, the method is further characterized in that in a parking brake operation, a substantial amount of force of the braking force by means of an actuator of the service brake, in particular by means of the brake booster, is generated.

This is to be understood that a force generator, in particular a pressure generator, the service brake provides a significant contribution to the generation of the braking force necessary for the parking brake operation. The force assistance by the driver must therefore not be essential. Furthermore, the power contribution of the parking brake, in particular of the electric motor of the parking brake is reduced. This can be advantageously adapted to the design of the components of the parking brake. The components can therefore be made smaller, lighter and cheaper. Due to the reduced dimensions of the electric actuator of the parking brake, and the output stage of the control unit for the control of the actuator can also be designed smaller and therefore more cost-effective.

In an alternative advantageous embodiment, during a parking brake operation, a hydraulic braking force generated by means of the brake booster is supported by means of a further force generator, in particular by means of an ESP pump.

By this is meant that multiple actuators can be combined to produce the required clamping force. Advantageously, an electric, in particular controllable, actuator can be used as an additional force generator. For example, the generation of a hydraulic pressure by the BKV and additionally by the ESP pump. The first actuator is a modified brake booster as described above. This actuator is the main pressure. The second actuator is e.g. the ESP pump. This actuator only has to provide the necessary pressure difference in order to generate a sufficient clamping force for the locking process and is thus charged only slightly more. A structural modification can be avoided.

A combination of several actuators of the service brake can, for example, also take place exclusively in special situations. In addition to the regular requirements for the provision of a holding force in the parking brake case (parking case) may arise in the presence of high gradients or high brake disc temperatures or high loading extraordinary demands on the required clamping force, which are taken into account in the design of the system. By combining and utilizing multiple actuators of the service brake, the residual force to be applied by the parking brake can be kept very low. As a result, an interpretation of their components, in particular of the electric motor and transmission, also carried to lower forces.

In an advantageous embodiment it is provided that the brake booster has a controllable vacuum generator.

By this is meant that a required vacuum source of the vacuum chamber can not be represented only by a gasoline engine and a suction tube. Advantageously, an adjustable vacuum generator, in particular an electric vacuum pump, can also be used here. Depending on requirements, different levels of negative pressure can be generated hereby. By setting a specific pressure for the parking brake operation, the characteristic of the BKV can be changed. As a result, for example, advantageously a rapid generation of the required braking force can be made possible.

In an advantageous manner, the method is characterized in that an adjustable negative pressure generator generates a greater negative pressure in a parking brake operation than in a deceleration braking operation.

This is understood to mean that the characteristic of the BKV is changed in a regular braking process by generating a greater negative pressure by means of the electric vacuum pump in a parking brake operation.

Under a greater negative pressure, a more pronounced vacuum, i. a lesser pressure understood. The increased negative pressure leads to an increase in power transmission and to an increase in support for the driver. In a parking brake operation, therefore, a higher braking force will be provided by the BKV than in a deceleration operation. For use in the context of parking brake operation is advantageously provided to operate the vacuum pump with maximum power. In this way, a suitable for the desired target achievement vacuum can be generated in the vacuum chamber of the BKV. In this case, only a very small force from the driver by means of the Fußbremspedals to generate the necessary clamping force is zuusteuern.

In an advantageous embodiment, it is provided that the structure of the braking force by means of an increase in pressure in a braking device, which is combined with the parking brake.

Under a braking device to be understood in this context, an association of components, which represents the brake system of a wheel of the vehicle. The brake device thus includes, for example, an inflow and outflow for a brake fluid, a brake caliper (also called brake caliper) formed brake housing, and a brake piston. In contrast to this, for example, a braking system may comprise a plurality of braking devices. Furthermore, in the motor vehicle at certain braking devices, an integration of a parking brake, which is designed as a motor-on-Caliper with an electric motor driven spindle present. For example. can each be an integrated parking brake on the brake devices of the two wheels of the rear axle, while no parking brake is provided on the brake devices of the two wheels of the front axle. Advantageously, it can now be provided that in the context of the method, i. in particular to direct the pressure generated by the BKV to the braking devices, which are combined with a parking brake. There is thus a so-called pressure separation. The brake devices, which have no integrated parking brake, are not subjected to the generated hydraulic pressure. The pressure in these braking devices is thereby not further increased in the context of the method. A steering of the brake fluid can take place, for example, via a circuit of valves existing in particular in the brake system. Advantageously, a targeted focusing of the generated pressure on the relevant braking devices can be achieved by the steering of the fluid in the systems combined with parking brakes. Since the volumetric flow generated is constant, thereby faster achievement of the necessary pressure level can be achieved in these brakes, as if all braking devices are acted upon by the shifted brake fluid.

According to the invention an automated parking brake for a motor vehicle is provided with a service brake with a brake booster, wherein in a deceleration braking a defined characteristic of the brake booster for amplifying a braking force can be generated and the characteristic of the brake booster is variable when performing a parking brake operation.

This is to be understood that the parking brake is designed accordingly that, taking into account the support and increase of a braking force by the BKV at a parking brake operation, a sufficient braking force is generated. The characteristic of the BKV is changed in the performance of the parking brake operation resulting in a stronger support than in a deceleration braking operation. The changed characteristics of the BKV make it possible to adapt the parking brake to a special degree. In this case, in particular a weaker power design of the actuator and the gear unit of the parking brake is referenced, with only a small adjustment of the actuator of the service brake for replacement of the required braking force must be made. As a result, the components of the parking brake can be designed less powerful and thus smaller and cheaper.

According to the invention, a brake booster for a motor vehicle with a service brake and an automatic parking brake is provided, wherein the brake booster at least one vacuum chamber and a working chamber, wherein a first connection of the working chamber is formed to atmospheric pressure for generating a defined characteristic of the brake booster, and wherein Change of characteristics at one Parking brake operation a further, in particular switchable by means of an electromagnetic valve, connection of the working chamber with atmospheric pressure can be formed.

By this is meant that the brake booster is designed to have a changed characteristic in a parking brake operation as compared to use in a deceleration braking operation. As a result, for example, advantageously a rapid pressure build-up can take place during a locking process. Furthermore, by taking over the generation of part of the pressure required for the parking brake operation, the further pressure-generating components can be made smaller and thus less expensive. By the described embodiment, furthermore, the use of existing components of the service brake is possible, with only minor adjustments are necessary. As a result, a cost-optimized overall system can be achieved. The use of a second connection also allows for independence of force generation and assistance from the first connection, particularly when the first connection has specific restrictions, such as coupling the valve opening from the position of an input piston rod.

According to the invention, a control device is furthermore provided which has means and is designed or configured to carry out a method according to one of the preceding claims.

Further features and expediency of the invention will become apparent from the description of embodiments with reference to the accompanying figures.

embodiments

From the figures shows:

1 a schematic sectional view of a braking device with a service brake and an automated parking brake in "motor on caliper"construction; and

2 a schematic sectional view of a brake booster with a separate control valve to modify the characteristic of the brake booster

1 shows a schematic sectional view of a braking device 1 for a motor vehicle. The brake device 1 has a service brake 14 on, by means of a to be operated by the driver Fußbremspedals 13 and a service brake actuator 10 can generate a braking force for deceleration and deceleration of the vehicle. Furthermore, an automated (automatic) parking brake 15 (also called parking brake or automated parking brake called APB), which has a parking brake actuator 2 (Electric motor).

The automated parking brake 15 is designed in the illustrated embodiment as a "motor on caliper" system and with the service brake 14 combined. You could also consider this as in the system of service brake 14 integrated view. Both the automated parking brake 15 as well as the service brake 14 grip on the same brake piston 5 as well as the same caliper 6 to build up a braking force, ie a clamping force on the brake disc 7 to create. The service brake 14 is thereby actuated by the driver by means of the Fußbremspedals. The service brake is in 1 designed as a hydraulic system. In such an operation, a predetermined clamping force between the brake pads 8th . 8th' and the brake disc 7 hydraulically constructed. To build up a braking force by means of the hydraulic service brake 14 becomes a medium 11 , In particular, a substantially incompressible brake fluid 11 , in a through the brake piston 5 and the caliper 6 limited fluid space pressed. The brake piston 5 is opposite the environment by means of a seal 12 sealed.

In a structure of a clamping force by means of the service brake 14 is that of the driver by means of the foot brake pedal 13 controlled activation by a service brake actuator 10 supported. The assistance can be provided by a complete provision of the necessary force or by an increase in the force applied by the driver. The actuator 10 can by a brake booster 37 be educated. Alternatively, it is possible that the illustrated actuator 10 also involves several actuators, for example a brake booster 37 and an ESP pump.

When the service brake is activated 14 First, the free travel or the clearance must be overcome before a braking force can be built. At the end of such a preparation phase are the brake pads 8th . 8th' to the brake disc 7 applied and the force builds up with a further shift of brake fluid 11 in the direction of the brake disc. 1 shows the state of the already overcome idle and clearance, the brake pads 8th . 8th' to the brake disc 7 are created.

The braking force generated is subsequently, for example, by the electromechanical automatic parking brake 15 taken over, or handed over to this. For a takeover by means of the service brake 14 Built-up braking force through the automated parking brake 15 becomes the parking brake actuator 2 driven. The actuator 2 drives for this purpose a spindle mounted in the axial direction 3 , in particular a threaded spindle 3 , at. At the end of the spindle 3 which is the actuator 2 is turned away, is the spindle 3 with a spindle nut 4 Mistake. The spindle nut 4 and the brake piston 5 are in a caliper 6 stored, which is a brake disc 7 Pliers overlapping. The spindle nut 4 is during a rotational movement of the actuator 2 and a resulting rotational movement of the spindle 3 shifted in the axial direction and on the brake disc 7 moved. The spindle nut 4 lies in the tensioned state of the automated parking brake 15 on the brake piston 5 at.

The parking brake actuator 2 and thus the movement of the spindle drive are stopped when, for example, the spindle nut 4 on the brake piston 5 is present, or it is charged with a specific force. Is the spindle nut lying 4 on an inner end face of the brake piston 5 (also called rear of the brake piston bottom or inner piston crown) on, the parking brake 15 due to the self-locking of the spindle drive without further control of the actuator 2 a force on the brake pads 8th . 8th' , or the brake disc 7 transfer. Also, in a locked by the spindle drive brake piston 5 one by means of this position of the brake piston 5 generated clamping force to be maintained after completion of the hydraulic power supply. This can be considered a transfer, or a takeover, of the hydraulic service brake 14 to the automated electromechanical parking brake 15 be understood.

The activation of the brake actuator 2 - And possibly designed as an ESP pump brake actuator 10 - By means of a power amplifier, ie by means of a control unit 9 which may, for example, be a control unit of a vehicle dynamics system, such as ESP (electronic stability program) or another control unit.

On as a pneumatic brake booster 37 trained service brake actuator 10 , as in 2 shown schematically, consists essentially of an amplifier housing which a first chamber 30 and a second chamber 23 having. The chambers 30 and 23 are by a movable membrane 24 separated from each other. At this membrane 24 is an amplifier body 25 appropriate. By means of the amplifier body 25 can be a piston rod 29 (Input rod of the brake booster 37 from the foot brake pedal) via a reaction disc 26 and a leadership part 34 be acted upon with an assisting force for actuating a master cylinder. The master cylinder is not in 2 illustrated, but may for example be designed as a tandem master cylinder. Between the guide part 34 and the master cylinder, an elastic element is attached, for example, a compression spring 22 , Furthermore, a piston rod 21 (Output rod from the brake booster to the master cylinder) between the guide part 34 and the master cylinder positioned. The compression spring serves to return the guide part 34 and the associated piston rod 21 ,

The second chamber 23 (so-called vacuum space or vacuum chamber) has a pneumatic connection to a vacuum generator 31 on, in 2 shown as a vacuum pump. Alternatively, a connection to a suction pipe of a gasoline engine can be provided. The first chamber 30 (so-called working space or working chamber) is via a pneumatic connection with a control device 33 and connected via this with the ambient air. About the control device 33 the connection to the ambient air can be established or interrupted. For this purpose, the control device 33 a normally closed, continuously adjustable control valve 32 (also called ventilation valve) on. This control valve is controlled by a control unit or a control unit 35 controlled. This control unit can be in the control unit 9 the parking brake be integrated.

For pneumatic brake boosters 37 are in the unactuated state, the first chamber 30 and the second chamber 23 at the same pressure level, usually at the low pressure level of the chamber 23 , By connecting the first chamber 30 with the ambient air, either via the control valve 32 or via the main control valve 27 , ambient air flows into the first chamber 30 and it sets a higher pressure. Due to the resulting pressure difference between the first chamber 30 and the second chamber 23 A force acts on a partition of the chambers, the membrane 24 (also called diaphragm). This force causes that with the membrane 24 connected amplifier body 25 moved in the direction of the master cylinder and an assisting force for pressing the brake pads 8th . 8th on the brake disc 7 generated. By means of the master cylinder is in this way the force of the brake booster 37 introduced into the hydraulic brake system.

The pneumatic brake booster 37 as described above can now be operated in two operating modes (mechanical mode, controlled mode). In mechanical mode, the regular service brake mode, the brake booster becomes 37 operated as a conventional pneumatic BKV, in which the support force of the BKV by means of the main control valve 27 is set. 'Mechanical' refers to the Opening of the main control valve 27 by the driver by moving the input rod 29 with respect to the amplifier body 25 , Through the open main control valve 27 ambient air flows through an air filter 28 in the first chamber 30 , As already described, this shifts the membrane 24 and the associated amplifier body 25 in the direction of movement of the input rod 29 , The main control valve 27 closes as soon as the desired balance of forces is reached.

Between the entrance bar 29 and the elastic member of the reaction disc 26 can be provided a free path. This free path is in the in 2 illustrated actuating situation of the brake booster 37 overcome.

As long as this free travel is not overcome, no force transfer of the applied by the driver operating force on the reaction disc 26 instead of. In this case, the driver only steps against a return spring 36 and optionally against the valve. If the free travel is overcome, for example, by appropriate, optionally controlled, moving the amplifier body 25 , or deformation of the reaction disc 26 , In addition to the assistance force of the brake booster, the driver applies a force for actuating the master cylinder.

In the controlled mode, the parking brake mode, the brake booster 37 operated according to the procedure of the invention. The driver operates in the presence of a Feststellbremswunsches at standstill of the vehicle, the parking brake button. At the same time or within a defined period of time, he also actuates the brake pedal 13 , Pressing the brake pedal 13 is by one, in 2 Sensor not shown detected. For this purpose, the brake light switch can be used. The sensor data is used to control the device 33 with the control valve 32 head for. Through the open main control valve 32 ambient air flows into the first chamber 30 , As already described, this shifts the membrane 24 and the associated amplifier body 25 in the direction of movement of the input rod 29 , This can already at a slight actuation of the brake pedal 13 a clamping force on the brake device 1 be set. Upon another actuation of the brake pedal 13 In addition, as described in the mechanical mode, the main control valve 27 open. The characteristic of the brake booster 37 This results in consideration of both valves 27 . 32 , Is the vacuum generator 31 When the parking brake is activated, for example when the parking brake button is actuated or when the brake pedal is actuated, it can be operated with maximum power in order to obtain the desired characteristic of the brake booster.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1604128 B1 [0001]
• DE 102014222197 A1 [0002]
• DE 102010001355 A1 [0003]

Claims (13)

Method for carrying out a parking brake operation in a motor vehicle with an automated parking brake ( 15 ) and a service brake ( 14 ), whereby the service brake ( 14 ) a brake booster ( 37 ) characterized in that the brake booster ( 37 ) has a defined characteristic for a gain of a braking force in a deceleration braking operation and the characteristic of the brake booster is changed in the implementation of the parking brake operation. Method according to Claim 1, characterized in that the brake booster ( 37 ) at least one vacuum chamber ( 23 ) and a working chamber ( 30 ), wherein a first connection of the working chamber ( 30 ) with atmospheric pressure for generating the defined characteristic of the brake booster ( 37 ) is formed in a decelerating brake operation, and for changing the characteristic in a parking brake operation, a second connection of the working chamber ( 30 ) is formed at atmospheric pressure. Method according to Claim 2, characterized in that the brake booster ( 37 ) a switchable or controllable valve ( 32 ), wherein by means of the valve ( 32 ) the second connection of the working chamber ( 30 ) is formed at atmospheric pressure. Method according to one of the preceding claims, characterized in that the characteristic of the brake booster ( 37 ) is changed if at least one defined activation condition is met. Method according to one of the preceding claims, characterized in that the characteristic of the brake booster ( 37 ) is changed when an activation of the parking brake operation and an operation of the service brake ( 14 ) is done. Method according to one of the preceding claims, characterized in that in a parking brake operation, a substantial amount of force of the braking force by means of an actuator ( 10 ) the service brake ( 14 ), in particular by means of the brake booster ( 37 ), is produced. Method according to one of the preceding claims, characterized in that in a parking brake operation, a means of the brake booster ( 37 ) Hydraulic braking force is supported by means of another force generator, in particular by means of an ESP pump. Method according to one of the preceding claims, characterized in that the brake booster ( 37 ) an adjustable vacuum generator ( 31 ) having. Method according to one of the preceding claims, characterized in that a controllable vacuum generator ( 31 ) generates a greater negative pressure in a parking brake operation than in a deceleration braking operation. Method according to one of the preceding claims, characterized in that the structure of the braking force by means of an increase in pressure in a brake device ( 1 ), which with the parking brake ( 15 ) is combined. Automated parking brake ( 15 ) for a motor vehicle with a service brake ( 14 ) with a brake booster ( 37 ), wherein in a deceleration braking process, a defined characteristic of the brake booster ( 37 ) can be generated for a gain of a braking force, characterized in that the characteristic of the brake booster ( 37 ) is variable when performing a parking brake operation. Brake booster ( 37 ) for a motor vehicle with a service brake ( 14 ) and an automated parking brake ( 15 ), wherein the brake booster ( 37 ) at least one vacuum chamber ( 23 ) and a working chamber ( 30 ) wherein a first connection of the working chamber ( 30 ) to atmospheric pressure to produce a defined characteristic of the brake booster ( 37 ) is formed, characterized in that for changing the characteristic in a parking brake operation another, in particular by means of an electromagnetic valve ( 32 ) switchable, connection of the working chamber ( 30 ) can be formed with atmospheric pressure. Control unit ( 9 . 35 ), which comprises means and is designed to carry out a method according to one of the preceding claims.

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