DE10338046B4 - Automotive braking system with an active brake booster and integrated ESP and / or EDS and / or ASR functionality - Google Patents

Abstract

Motor vehicle brake system with two brake circuits and integrated ESP and / or EDS and / or ASR functionality, comprising: - a wheel brake (36) per vehicle wheel, - two controllable valves (30, 31) for selectively setting the brake pressure to the Wheel brakes (36) of the brake circuits, - an active brake booster (1), and - control means (19) for controlling the valves of the wheel brakes (36) and the brake booster (1), - wherein the ESP and / or EDS and / or ASR functionality solely by the activation of the active brake booster (1) and the wheel brakes (36) associated valves (30, 31) is effected, characterized in that the active brake booster is an electromechanical brake booster (1), in at least one of the brake circuits a pre-pressure sensor (18) upstream of the valves (30, 31) of the wheel brakes (36) is provided which detects the brake pressure generated by the brake booster (1), the signals d Form pressure sensor (18) are included in a control loop to set the pressure level generated by the brake booster (11) and the brake pressures applied to the individual wheel brakes (36).

Description

The invention relates to a motor vehicle brake system according to the preamble of patent claim 1.

Such a brake system is out DE 44 38 722 A1 and continue off DE 195 38 974 A1 known. In both cases, a brake operation is possible regardless of the driver.

For braking heavy vehicles, the driver's foot force is usually insufficient, so they are usually equipped with a brake booster. Brake booster usually work with a negative pressure generated by the engine and / or an additional vacuum pump, such as in DE 44 38 722 A1 the case is. In this case, the pressure difference between the engine pressure and the ambient pressure is used to apply in addition to the driver's foot force, an amplifying force on the piston rod of a master cylinder.

With increasing vehicle mass, however, the diameter of the brake booster increases sharply. For very heavy vehicles tandem brake booster are therefore used. In diesel engines, direct-injection FSI engines or Valvetronic engines, however, virtually no negative pressure is available on the engine. For this reason, electric motors or negative pressure pumps driven by the internal combustion engine are used in these engines. However, these and the necessary tubing require space, increase the vehicle weight and are expensive in terms of manufacturing and assembly.

The problem of lack of vacuum is according to DE 44 38 722 A1 bypassed by throttling the vehicle engine.

DE 195 38 974 A1 suggests for this purpose a hydraulic pressure source.

Furthermore are out DE 32 31 353 C2 and DE 100 57 557 A1 Electromechanical brake booster known.

The invention has for its object to provide a structurally simple, as little controllable valves requiring, easy to install motor vehicle brake system.

For this purpose, a motor vehicle brake system with the features of claim 1 is proposed. It is assumed that the following considerations.

Contemporary automotive brake systems of conventional design include an anti-lock braking system (ABS). This has the task of selectively reducing a brake pressure caused by the driver via the brake pedal at one or more wheel brakes in order to prevent the respective vehicle wheels from locking. At none of the wheel brakes so that a brake pressure applied, which is greater than the predetermined by the driver via the brake pedal brake pressure. Depending wheel brakes each have an inlet valve and an exhaust valve are provided. This allows the brake pressure to be set individually on each wheel brake. In total, this results in eight valves in the hydraulic system between the wheel brakes and the electromechanical brake booster for ensuring the ABS functionality.

Adding to the braking system further functionalities, such as an electronic differential lock (EDS), a traction control (ASR) or an electronic stability program (ESP), it is necessary to build in the brake system, a greater pressure on the wheel brakes, as he from the driver is currently specified. In a dual-circuit braking system for this purpose usually two additional valves are present per brake circuit, so that the brake system with these four so-called switching valves has a total of twelve valves.

3 shows by way of example that in the post-published DE 103 27 553 A1 shown brake system in which the inlet and outlet valves for the ABS functionality with the reference numerals for 30 ' and 31 ' Marked are. Each brake circuit has two additional valves 32 ' and 33 ' intended. When an Electronic Stability Program (ESP) responds, these additional valves become 32 ' and 33 ' energized. The valve 32 ' separates thereby the direct connection between the master brake cylinder 3 ' and the wheel brakes 36 ' from. Below this valve 32 ' Thus, a greater pressure by the return pump also present in the brake system 34 ' be set up as specified by the driver. The additional, additional changeover valve 33 ' serves to brake fluid for this pressure build-up from the expansion tank 35 ' of the master cylinder 3 ' through the master cylinder 3 ' suck it through. Would these changeover valves be 32 ' and 33 ' not available, so would the return pumps 34 ' Although the ESP pressure build up. However, this would then via a sniffer bore in the connection between the master cylinder 3 ' and the brake fluid reservoir 35 ' flow away. To prevent this, the valve becomes 32 ' switched to its locked position. Through the parallel check valve 36 ' however, the driver may have a greater brake pressure per foot in every situation build up as the return pumps 34 ' provide.

According to the invention can on the additional switching valves 32 ' and 33 ' be waived. An actuation of the return pumps 34 ' to increase the pressure is eliminated. This allows a structurally simple braking system with an active brake booster and integrated ESP or EDS or ASR functionality. A presentable by the controllable valves anti-lock braking system is not affected.

According to the invention here is an electromechanical brake booster used. As a result, the gain can be selectively influenced by a corresponding control of the brake booster.

If the required admission pressure is built up solely by means of the electromechanical brake booster, namely by a driver's foot force actuation and / or by the control device, the entire hydraulic system for all wheel brakes only needs to perform the function of a pressure reducer, as in an anti-lock brake system, at each wheel brake to set the desired pressure. But this is the hydraulic circuit of an anti-lock brake system in the brake system sufficient to represent, for example, the functionality of an electronic stability program. In addition to a reduction in the number of valves required additional simplification results in terms of the required lines in the hydraulic system. Overall, this leads to a significant cost reduction of a brake system with an active brake booster and integrated ESP or EDS or ASR functionality.

In the course of a further simplification of the brake system, a single admission pressure sensor may be provided, which is connected upstream of the valves of the wheel brakes in order to detect the brake pressure generated by the brake booster. The signals from this form of pressure sensor are included in a control loop to adjust the pressure level generated by the brake booster and the brake pressures applied to the individual wheel brakes. For reasons of redundancy and error detection, a second pressure sensor can be provided in the other brake circuit.

In its simplest embodiment, this results in a hydraulic system between the wheel brakes and the electromechanical brake booster, which manages with only eight controllable valves. Compared to the above-described prior art, this results in considerable cost advantages.

Advantageous embodiments of the invention are the subject of further claims.

Preferably, the controller is configured to set an admission pressure greater than or equal to the largest brake pressure required on one of the wheel brakes in the event of a response of the EDS / ASR / ESP functionality to the electro-mechanical brake booster. This form is adjusted on all four wheels with the wheel-specific intake and exhaust valves to the desired wheel pressure in the control. The return pump is in operation as in ABS operation. The hydraulic system thus only assumes the function of a wheel-specific admission pressure reducer.

In an advantageous embodiment, an electromechanical brake booster is used in the present invention, as in the above DE 103 27 553 A1 is disclosed. Its content is incorporated in the present application with respect to the brake booster and its control. However, other electromechanical brake booster can be used instead of this brake booster.

According to an advantageous embodiment of the invention, the electromechanical brake booster comprises a piston rod for direct connection of a brake pedal with a piston of a master cylinder, an electric motor with a stator and a rotor, both of which are arranged concentrically around the piston rod, and a spindle drive with a rotatably mounted, axially movable spindle screw which is driven via the rotor of the motor and starts when activating the motor for brake booster against a driver and presses it in the direction of the master cylinder.

In this surprisingly simple way succeeds the modularization of the electromechanical brake booster. This can be used in series production of motor vehicles, regardless of the selected internal combustion engine, the same master cylinder with subsequent braking system. In engines that do not generate sufficient negative pressure, can be installed instead of working with vacuum brake booster, the inventive electromechanical brake booster, without this being associated with an additional adjustment effort. The brake booster according to the invention is readily connectable to conventional master cylinder.

Preferably, the driver is provided directly on the piston rod. In an advantageous embodiment of the driver can also be formed dome-shaped or convex. The dome-shaped or convex shape serves to compensate for the angular movements of the piston rod in response to the pedal travel.

The control of the electromechanical brake booster and for the other functionalities are preferably integrated in a common control device, regardless of whether a control or regulation is provided. Preferably, the necessary calculations for controlling the electric motor are made by one of the processors of the control device for the brake hydraulics. However, it is also possible to implement the control of the electromechanical brake booster in a separate, modular control unit.

In an advantageous embodiment of the invention, a brushless electric motor is used on the brake booster. As a result, the outer dimensions of the brake booster according to the invention can be kept low.

Preferably, an electric motor is used, in which the rotor has at least one permanent magnet and the stator has at least one energizable coil. Such a motor is extremely compact and also has a low rotating mass, so that the boosting force is effective very quickly.

The control of the electric motor in a normal braking can be done via a simple control or via a control system. In the former case, a sensor for detecting the pedal force acting on the piston rod is provided on the brake booster or on the brake pedal. The current of the electric motor is set with a gain factor, for example, proportional to the detected pedal force.

In the case of control, in addition to a sensor for detecting the pedal force acting on the piston rod, there is further provided a sensor for detecting the actual total force from the pedaling force and the boosting force. From the pedal force then a setpoint for the total force is calculated. The difference to the detected actual total force is compensated by the electric motor.

In this case, the actual total force can be measured directly on the piston rod with a sensor. Alternatively, it is also possible to calculate the actual total force from the form detected by the pressure sensor.

According to a further advantageous embodiment of the invention, the spindle drive used is self-locking. In the event of a failure of the electric motor, this can be used to reset the brake pedal.

For this purpose, a separate return spring can be provided, which pushes the spindle screw back to its original position. Preferably, however, the restoring force for the spindle drive is generated solely by the hydraulic back pressure of the master cylinder and a pedal return spring, whereby the structure of the brake booster remains simple.

As a spindle drive, for example, a roller screw or a ball screw can be provided.

The invention will be explained in more detail with reference to an embodiment shown in the drawing. The drawing shows in:

1 1 is a schematic view of a brake system according to the invention with an electromechanical brake booster and associated hydraulic, shown in longitudinal section;

2 a representation of the control of the electric motor of the electromechanical brake booster, and in

3 a schematic view of a conventional brake system in a representation according to 1 ,

The embodiment in 1 shows an electromechanical brake booster 1 when installed between a brake pedal 2 and a tandem master cylinder 3 , In this case, the electromechanical brake booster 1 a continuous piston rod 4 for direct connection of the brake pedal 2 with a primary piston 5 of the master cylinder 3 on.

Furthermore, the electromechanical brake booster 1 a brushless electric motor 6 with a stator 7 and a rotor 8th on, concentrically around the piston rod 4 are arranged. A likewise concentric to the piston rod 4 arranged spindle drive comprises a rotatably mounted, but axially movable spindle screw 9 which over the rotor 8th of the motor 6 is driven. When the motor is activated 6 For the brake booster the spindle screw runs 9 against a driver 10 at. The driver 10 is at its to the piston rod 4 facing side convex to angular movements of the piston rod 4 compensate for the pedal travel.

In amplifier mode, the spindle screw presses 9 on the at the piston rod 4 provided driver 10 and thus the piston days 4 together with brake pedal 2 in the direction of the master cylinder 3 ie in 1 to the left. For this purpose, the driver applied pedal force with a force sensor 11 on the piston rod 4 measured. Depending on the detected force, the coils of the stator 7 of the electric motor 6 energized. As a result, the rotor starts 8th , which is provided here with permanent magnets to rotate. About with the rotor 8th firmly connected or integrally formed outer sleeve 12 and bullets 13 of the ball screw drive moves the spindle screw 9 in a translational movement in the direction of the tandem master cylinder 3 to. The spindle screw 9 is rotationally fixed, but stored without translation to the structure. Once the spindle screw 9 the driver 10 touches it pushes it together with the foot force of the piston rod 4 on the primary cylinder 5 , A floating piston 14 transfers in known manner the pressure from the primary circuit in the secondary circuit of the brake system.

To the associated outputs 15 and 16 of the tandem master cylinder 3 is a hydraulic system 17 connected, which this with the wheel brakes 36 combines. The hydraulic system 17 includes two diagonal brake circuits, each with two wheel brakes 36 , Every wheel brake 36 is a controllable inlet valve 30 and a controllable outlet valve 31 assigned. One return pump each 34 each brake circuit ensures that the brake pedal does not fall slowly in the slip control mode of the brake hydraulics. Furthermore, in at least one of the brake circuits is a pressure sensor 18 arranged over that of the brake booster 1 provided and at the intake valves 30 attached form is measured. About a control device shown only schematically 19 is taking into account one from the driver via the brake pedal 2 predetermined braking request and other vehicle parameters including the measured form the functionality of an anti-lock braking system (ABS) provided. The intake valves 30 and exhaust valves 31 are for this purpose by the controller 19 accordingly selectively controlled.

A special feature of the brake system shown is that provided for the anti-lock brake hydraulic circuit after 1 without the addition of further valves solely by means of the electromechanical brake booster 1 provides additional functionalities that require a brake pressure that is above that of the driver via the brake pedal 2 predetermined pressure level is or is displayed when the driver, the brake pedal 2 not activated. Examples of such functionalities are an electronic stability program (ESP), a traction control system (ASR) or an EDS. The control algorithms required for this purpose are in the control device 19 stored.

The required pre-pressure in the EDS / ASR / ESP case, in contrast to the in 3 illustrated prior art instead of by the return pumps 34 ' now through the electromechanical brake booster 1 carried out. These are the coils of the stator 7 energized. The rotor 8th and drives over the spindle nut 9 the driver 10 in 1 to the left. In the brake system thus pressure is built up. The brake booster provides a sufficiently high pre-pressure available on all four wheels via the respective intake and exhaust valves 30 . 31 is adjusted to the pressure desired there. The pre-pressure must be at least as large as the maximum of all desired brake pressures at the wheel brakes 36 , The return pump is in operation to prevent slow decay of the brake pedal. According to the invention in this situation, the in 3 still existing changeover valves 32 ' and 33 ' be waived. In this case, the hydraulic system needs 17 for all wheel brakes 36 only perform the function of a pressure reducer, as is usual in an anti-lock braking system, to each wheel brake 36 to set the desired brake pressure.

Thus, the hydraulic connection of an anti-lock braking system is sufficient, for example, to carry out the tasks of an electronic stability program (ESP). Only the form sensor 18 is still required for the scheme. As a result, this results in a functional extension while saving four valves. This and the associated, reduced piping within the hydraulic system 17 means a significant cost savings. The illustrated hydraulic system 17 comes with only eight controllable valves 30 respectively. 31 out. In this case, in each case an inlet valve and an outlet valve can be structurally combined to form a unit, for example to a known 3/3-valve or a flow valve.

The driving dynamics sensors of an ESP, where yaw rate and lateral acceleration (in some cases also longitudinal acceleration) are measured, can be fed into the control unit of the electromechanical brake booster 1 structurally integrated. The data of these sensors can be evaluated by the processor of a brake booster controller with. The transmission of this data to the ESP can be done via a bus system, eg a CAN bus. This makes it possible to save an additional control unit or housing for the vehicle dynamics sensors.

At a Fremdkraftbremsung the brake pedal 2 attracted to the bulkhead of the vehicle. If the driver also wants to brake himself, can this through the pedal force sensor 11 determined and taken into account in the braking force generation.

Should the electromechanical brake booster 1 not working or de-energized, the driver can press the brake with his foot alone. Because the driver 10 transmits only compressive forces, disturbs the electromechanical brake booster 1 not here.

In contrast to vacuum brake boosters, the electromechanical brake booster works 1 even if the combustion engine is switched off. In this case, he receives his electrical energy from the starter battery.

To enable always safe reducing the brake pressure to zero, is the electromechanical brake booster 1 or its transmission formed self-locking. Otherwise, in the event of a power failure in braking mode, the electromechanical brake booster would 1 remain in position during power failure and continue to build up brake pressure. Accordingly, the spindle drive is designed so that already by the hydraulic counter-pressure and / or a pedal return spring 21 a sufficient restoring force is built up, which the electromechanical brake booster 1 moves back to zero position. However, it can also be an additional return spring on the brake booster 1 be provided.

For the electric motor 6 For example, instead of the above-mentioned motor, a brushless DC motor, a three-phase motor, an asynchronous motor, a stepping motor, or a conventional DC motor may also be used. In order to determine the amplification produced by the engine, the information needed first of all as information about how much the driver would like to brake without the assistance of the amplification is input as a system input variable. For this purpose, in principle, the pedal travel or the pedal force of the brake pedal 2 be measured. Preferably, one will select the pedal force, because by the firm connection of the pedal 2 with the piston rod 4 the pedal travel would always represent the displacement of foot force and amplifier power. Also would be in case of failure of a hydraulic circuit of the tandem master cylinder 3 the pedal 2 pivoted forward and would falsely signal a braking request from the driver.

For a pure pre-control operation during normal braking, a fixed ratio of foot force F _F and gain force F _{V is} specified. This is z. B. the current i of the electric motor 6 adjusted in proportion to the driver's foot force F _F. As will be explained in more detail below, the proportionality factor k can be changed as a function of the speed and / or the loading. It does not necessarily have to be constant, but can be increased at high pedal forces or high pedal speeds, such. B. in a panic braking or with a brake assistant.

Alternatively, at the electromechanical brake booster 1 also be provided a force control, as in 2 is shown. In this case, another sensor is needed which measures the actual sum force F _actual from foot force F _F and amplifier force F _V , or only the amplifier force F _V alone. For this purpose, the signal of the admission pressure sensor is preferred 18 of the hydraulic system 17 used, the measured pressure is proportional to the actual sum force F _Ist . For safety reasons, for the purpose of redundancy in the second brake circuit also a form sensor 18 be installed, which is used in case of failure of the first circle.

In the regulation, the foot force F _{F of} the driver with the sensor 11 measured. This is multiplied by an optionally variable amplification factor k or k (v). The sum of driver's foot force F _F and boosting force F _V is the control _setpoint F _setpoint . Actual value is the actual total force F _actual or one from the admission pressure sensor 18 calculated force. From both the control difference can be determined. The electric power of the electric motor 6 is via an example in the control device 19 implemented controller 23 regulated according to the rule difference.

The brake booster k is variably possible in pilot control operation and in control operation. Thus, for example, depending on the driving speed at high driving speeds, a high gain k (v) can be set. This gives the driver the feeling of a powerful, well-decelerating brake. At low driving speeds, especially when parking, the gain k (v) may be reduced to improve the driver's ability to fine tune. Any faults in the brake system can be indicated to the driver by a slight reduction in the gain factor (eg from 5 to 4). He will notice this by having to apply a higher pedaling force for the same deceleration. Alternatively, the gain k may easily pulsate.

Also, z. B. when loading or in the team operation, the gain k can be increased. Thus, compared to the empty vehicle by a pure feedforward control in dependence on the estimated mass of the vehicle or train always the same pedal force delay function can be displayed.

In an external power braking, as occurs for example in an ESP intervention, the amplifier power is adjusted so that the pressure generated by the amplifier and driver foot is at least so large that it corresponds to the maximum of all four desired wheel brake pressures. On the three remaining wheels can be controlled via a pressure model by clocking their valves 30 respectively. 31 lower wheel pressures are set.

The electromechanical brake booster 1 also makes it possible to make the braking system artificially yielding in a frontal crash. This can be triggered by a crash sensor 22 , z. B. an airbag sensor, through the electromechanical brake booster 1 Pressure to be built in the brake system. In an accident, the piston rod 4 and the brake pedal 2 pulled forward. The pedal 2 gives way to the driver's foot and can reduce the severity of injury to the leg. In addition, the vehicle is artificially delayed further beyond the actual accident in order to reduce the risk of possible secondary collisions. The pressure can then be reduced again via a ramp, so that the pedal 2 slowly moved back to its zero position. In this operating state, where appropriate, in the hydraulic system 17 existing low-pressure accumulator 24 to be used as additional elasticities. For the brake fluid is thus an additional volume ready, causing the brake pedal 2 continues to swing forward.

The above-described brake system with an electromechanical brake booster and integrated ESP or EDS or ASR functionality is characterized by a very simple and inexpensive construction. To provide the aforementioned functionalities, the pressure reducing function of an existing anti-lock braking system can be used without the need for additional valves. The required pressure build-up takes place solely by means of the electromechanical brake booster as a result of a driver foot force actuation and / or an energization commanded by the control device.

Another advantage of the brake system explained above is that the electromechanical brake booster 1 does not require any modifications to previously used brake systems without ESP functionality. Interventions in a hydraulic system equipped with ABS functionality are not necessary. Modifications are made only in the control.

The illustrated brake booster 1 is connectable as a module to conventional master cylinder. It is compact in its external dimensions and has a simple structure.

However, the invention is not limited to the illustrated embodiment, but includes all stated in the claims embodiments.

LIST OF REFERENCE NUMBERS

1

 electromechanical brake booster

2

 brake pedal

3

 Master Cylinder

4

 piston rod

5

 primary piston

6

 engine

7

 stator

8th

 rotor

9

 spindle nut

10

 takeaway

11

force sensor

12

outer sleeve

13

 Bullet

14

 secondary piston

15

 Output of the first brake circuit

16

 Output of the second brake circuit

17

 hydraulic system

18

 form sensor

19

 control devices

21

 pedal return spring

22

 crash sensor

23

regulator

24

Low-pressure accumulator

30

 intake valve

31

 outlet valve

32

 switching valve

33

 switching valve

34

 Return pump

35

 Brake fluid expansion tank

36

 wheel brake

F _F

 foot force

F _V

 boosting force

F _target

 Target total force

F _is

 Actual total force

i

 electricity

k

gain

k (v)

 Gain factor (driving speed dependent)

v

 driving speed

Superscripts referenced to refer to the same items as the corresponding reference numerals without apostrophes.

Claims (27)

Motor vehicle brake system with two brake circuits and integrated ESP and / or EDS and / or ASR functionality, comprising: a wheel brake 36 ) per vehicle wheel, - two controllable valves each ( 30 . 31 ) for selective adjustment of the brake pressure at the wheel brakes ( 36 ) of the brake circuits, - an active brake booster ( 1 ), and - control devices ( 19 ) for controlling the valves of the wheel brakes ( 36 ) and the brake booster ( 1 ), Wherein the ESP and / or EDS and / or ASR functionality is controlled solely by the activation of the active brake booster ( 1 ) and the wheel brakes ( 36 ) associated valves ( 30 . 31 ), characterized in that the active brake booster is an electromechanical brake booster ( 1 ) is in at least one of the brake circuits a the valves ( 30 . 31 ) of the wheel brakes ( 36 ) upstream upstream pressure sensor ( 18 ) provided by the brake booster ( 1 ) detected brake pressure, wherein the signals of the form sensor ( 18 ) are incorporated in a control circuit in order to control the brake booster ( 11 ) and the pressure levels at the individual wheel brakes ( 36 ) to adjust applied brake pressures. Motor vehicle brake system according to claim 1, characterized in that the brake pressure is built up solely by means of the driver's foot force and / or by the active brake booster. Motor vehicle brake system according to claim 1 or 2, characterized in that the hydraulic system ( 17 ), which the wheel brakes ( 36 ) with the brake booster ( 1 ), only eight controllable valves ( 30 . 31 ) having. Motor vehicle brake system according to one of claims 1 to 3, characterized in that the valves per wheel brake ( 36 ) an inlet valve ( 30 ) and an outlet valve ( 31 ). Motor vehicle brake system according to claim 4, characterized in that the inlet valve ( 30 ) and the exhaust valve ( 31 ) are structurally combined to a combined single-outlet valve. Motor vehicle brake system according to claim 5, characterized in that the hydraulic system ( 17 ) has a total of four such combined single-outlet valve units. Motor vehicle brake system according to one of claims 1 to 6, characterized in that each brake circuit is a return pump ( 34 ) provided by the control devices ( 19 ) is controllable. Motor vehicle brake system according to one of Claims 1 to 7, characterized in that the control device ( 19 ) is configured to operate in the event of ESP response to the electro-mechanical brake booster ( 1 ) to set a brake pressure which is greater than or equal to the largest brake pressure, which at one of the wheel brakes ( 36 ) is needed. Motor vehicle brake system according to one of Claims 1 to 8, characterized in that driving dynamics sensors of an ESP are structurally integrated into the control device ( 19 ) are integrated. Motor vehicle brake system according to claim 9, characterized in that the driving dynamics sensors comprise a yaw rate and a lateral acceleration sensor. Motor vehicle brake system according to claim 10, characterized in that the driving dynamics sensors additionally comprise a longitudinal acceleration sensor. Motor vehicle brake system according to one of claims 1 to 11, characterized in that the electromechanical brake booster ( 1 ) in the following: - a piston rod ( 4 ) for the direct connection of a brake pedal ( 2 ) with a piston ( 5 ) of a master cylinder ( 3 ), - an electric motor ( 6 ) with a stator ( 7 ) and a rotor ( 8th ) concentric around the piston rod ( 4 ) are arranged, and - a spindle drive with a rotatably mounted, axially movable spindle screw ( 9 ), which via the rotor ( 8th ) of the motor ( 6 ) and when the motor is activated ( 6 ) for brake booster against a driver ( 10 ) and this in the direction of the master cylinder ( 3 ) presses. Motor vehicle brake system according to claim 12, characterized in that a sensor ( 11 ) for detecting the pedal force on the piston rod ( 4 ) is provided and the current of the electric motor ( 6 ) is set with a gain k as a function of the detected pedal force. Motor vehicle brake system according to claim 12 or 13, characterized in that a sensor ( 11 ) is provided for detecting the pedal travel and the current of the electric motor ( 6 ) is set with a gain k depending on the detected pedal travel. Motor vehicle brake system according to one of claims 12 to 14, characterized in that a sensor ( 11 ) for detecting the pedal force F _F on the piston rod (FIG. 4 ), a sensor ( 18 ) for detecting the actual sum force F _{ist is provided} from the pedal force F _F and the boosting force F _V , wherein from the pedal force F _F a target value for the sum force F _{Soll is} calculated and the Difference from the detected actual total force F _(via the motor 6 ) is corrected. Motor vehicle brake system according to claim 15, characterized in that the actual total force F _ist on the piston rod ( 4 ) is measured with a sensor. Motor vehicle brake system according to claim 15 or 16, characterized in that the actual total force F _ist from a recorded form of the admission pressure sensor ( 18 ) is calculated. Motor vehicle brake system according to one of claims 12 to 17, characterized in that the engine ( 6 ) is a brushless DC motor. Motor vehicle brake system according to one of claims 12 to 18, characterized in that the rotor ( 8th ) at least one permanent magnet and the stator ( 7 ) has at least one energizable coil. Motor vehicle brake system according to one of claims 12 to 17, characterized in that the engine ( 6 ) is a three-phase motor. Motor vehicle brake system according to one of claims 12 to 17, characterized in that the engine ( 6 ) is an asynchronous motor. Motor vehicle brake system according to one of claims 12 to 21, characterized in that the spindle drive is self-locking. Motor vehicle brake system according to one of claims 12 to 22, characterized in that the spindle drive is a roller screw drive or a ball screw drive. Motor vehicle brake system according to one of claims 12 to 23, characterized in that the restoring force for the spindle drive solely by the hydraulic counter-pressure of the master cylinder ( 3 ) and / or a pedal return spring ( 21 ) is produced. Motor vehicle brake system according to one of claims 12 to 24, characterized in that the driver ( 10 ) directly on the piston rod ( 4 ) is provided. Motor vehicle brake system according to one of claims 12 to 25, characterized in that the driver ( 10 ) is formed dome-shaped. Motor vehicle brake system according to one of claims 12 to 26, characterized in that the driver ( 10 ) is convex.

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