WO2024193838A1

WO2024193838A1 - Electromechanical braking system for a motor vehicle and method for operating an electromechanical braking system in a motor vehicle

Info

Publication number: WO2024193838A1
Application number: PCT/EP2023/079614
Authority: WO
Inventors: Gabor ORDASI
Original assignee: Thyssenkrupp Presta Ag; Thyssenkrupp Ag
Priority date: 2023-03-22
Filing date: 2023-10-24
Publication date: 2024-09-26
Also published as: DE102023107227A1

Abstract

The present invention relates to a method for operating an electromechanical braking system (110) in a motor vehicle, wherein the braking system (110) has at least one input unit (113, 114), via which a braking command is transmitted, and at least two brake devices (1, BU), which each comprise a brake actuator (4, BM) with at least one electric servomotor (41, 42), wherein the brake devices (1, BU) are each associated with a wheel brake control unit (120, BC) and a wheel speed sensor unit (121), wherein for a respective brake device (1, BU) the associated wheel speed sensor unit (121) provides a wheel speed (P2) to the associated wheel brake control unit (120, BC), said wheel brake control unit (120, BC) is provided with a substitute wheel speed (EP1) for the wheel speed (P2) provided by the associated wheel speed sensor unit (121), wherein said wheel brake control unit (120, BC) controls the brake actuator (4, BM) taking into account the wheel speed (P2) provided by the associated wheel speed sensor unit (121) in order to implement the transmitted braking command in normal operation, and the wheel brake control unit (120, BC) controls the brake actuator (4, BM) taking into account the provided substitute wheel speed (EP1) in order to implement the transmitted braking command in the event of a fault with respect to the provision of the wheel speed (P2) by the associated wheel speed sensor unit (121). The invention also relates to a braking system (110) designed, in particular, to be operated by such a method.

Description

Electromechanical braking system for a motor vehicle and method for operating an electromechanical braking system in a motor vehicle

The invention relates to an electromechanical braking system for a motor vehicle, comprising at least one input device for transmitting a braking command, at least two braking devices, each of which is assigned a wheel speed sensor unit which is designed to provide a wheel speed to the assigned braking device, wherein the braking devices each comprise a brake actuator which has at least one electric servomotor. Furthermore, the invention relates to a method for operating an electromechanical braking system in a motor vehicle, wherein the braking system has at least one input unit via which a braking command is transmitted, and at least two braking devices, each of which comprises a brake actuator with at least one electric servomotor.

Such a braking system comprises at least two electromotive braking devices, each of which is assigned to a wheel of a motor vehicle that is to be braked. This is therefore also referred to as a braking unit or wheel brake. An electromotive braking device has an electromotive brake actuator that is supported on the chassis of a motor vehicle relative to the rotation of the wheel to be braked and that has at least one electric servomotor. This acts via an actuator on a braking part, for example a brake pad, which can be brought into braking engagement with a counter-braking part attached to the wheel to be braked, for example a brake disk, by rotating the actuator. During braking engagement, frictional contact is generated between the braking part and the counter-braking part, with the braking torque generated by friction being greater the higher the adjustment force exerted by the actuator in the adjustment direction. In the prior art, such braking systems are known, for example, from DE 10 2017 123 266 A1, US 6,397,981 B1 or US 6,081,081 A. According to the disclosure of US 6,081,081 A, each brake actuator can be controlled individually by the central control unit. This makes it possible to activate each braking device separately to optimize the braking effect.

The braking system is controlled electrically. A braking command, in particular an electrical braking command, to initiate a braking process can be generated manually by an input unit, in particular a brake pedal or a parking brake switch, and additionally or alternatively by an automated input unit, in particular an anti-lock braking system (ABS for short) or an automatic drive system (ADS for short).

Taking such a braking specification into account, the servomotors of the brake actuators can be controlled and braking devices can be brought into braking intervention.

The optimum braking torque, which can achieve the shortest possible braking distance, if possible without locking the wheels, can be determined from the target values given with the braking command and other actual parameters relevant to the braking process, in particular wheel position, wheel speed, electric current of the servomotor, braking force, vehicle speed and/or other actual parameters. In the prior art, it is known, for example from US 6,317,675 B1, to provide at least the values for the braking command and possibly other values to a central control unit, which can be referred to synonymously as an ECU (ECU: Electronic Control Unit). This control unit uses a predetermined control algorithm to determine the control currents required for the servomotors of all brake actuators, which are required to generate defined wheel braking torques. The wheel speed is an actual parameter of particular importance that should always be provided to convert the braking command into a corresponding braking intervention of a respective braking device in order to prevent a brake failure, even a partial brake failure. To increase the reliability, US 6,410,993 Bl discloses a two-circuit or multi-circuit circuit arrangement for a safety-critical control system, such as brake-by-wire, wherein each circuit of the circuit arrangement contains a complete microprocessor system that processes the input data redundantly and provides an error detection signal (FAIL) when an error or a discrepancy between the redundantly generated data processing results occurs.

Against this background, it is an object of the present invention to provide an improved electromechanical braking system and an improved method for operating an electromechanical braking system, wherein the reliability is advantageously increased and in particular the reliability of the provision of a wheel speed is improved in a cost-effective manner.

To solve this problem, a method for operating an electromechanical braking system in a motor vehicle and an electromechanical braking system according to the independent claims are proposed. Further advantageous embodiments of the invention are described in the dependent claims and the description and shown in the figures. The proposed solution provides a method for operating an electromechanical braking system in a motor vehicle, wherein the braking system has at least one input unit via which a braking command is transmitted, and at least two braking devices, each of which comprises a brake actuator with at least one electric servomotor, wherein the braking devices are each assigned a wheel brake control unit and a wheel speed sensor unit. For a respective braking device, the assigned wheel speed sensor unit provides a wheel speed to the assigned wheel brake control unit, and this wheel brake control unit is provided with a substitute wheel speed for the wheel speed provided by the assigned wheel speed sensor unit. According to the invention, in order to implement the transmitted braking command in normal operation, this wheel brake control unit controls the brake actuator taking into account the wheel speed provided by the assigned wheel speed sensor unit, and in the event of a fault in relation to the provision of the wheel speed from the assigned wheel speed sensor unit, this wheel speed sensor unit controls the brake actuator taking into account the substitute wheel speed provided. In particular, it is provided that the replacement wheel speed is not determined with the wheel speed sensor unit assigned to the wheel in question and preferably also not with one of the identically designed redundant wheel speed sensor units assigned to the wheel in question. In this respect, the replacement wheel speed is in particular a parameter that approximates the actual wheel speed of a wheel and in particular can even match it, but in relation to which certain deviations from the actual wheel speed are certainly accepted. Advantageously, the brake actuator can be further controlled in this way, in particular with regard to the corresponding control algorithm without deviation from normal operation, by advantageously using the replacement wheel speed for the wheel in question as a parameter instead of the wheel speed of the wheel in question in the event of a fault. According to one embodiment, the replacement wheel speed can only be provided if a fault has occurred. In particular, however, it is provided that the replacement wheel speed for each wheel is also determined and provided in fault-free normal operation. It is also advantageous to carry out a diagnosis, in particular a plausibility check, with respect to the wheel speed provided by the associated wheel speed sensor unit using the substitute wheel speed in normal operation. In this way, a problem with respect to one of the wheel speed sensor units and/or with respect to determining the substitute wheel speed can advantageously be detected at an early stage. According to an advantageous embodiment, it is provided that the wheel brake control units are connected to one another via a data transmission system, in particular a communication bus, further in particular a CAN bus, for exchanging data. The wheel brake control unit assigned to a braking device is advantageously provided with a wheel speed from at least one of the wheel speed sensor units that is not assigned to this braking device as a substitute wheel speed via the data transmission system. In this case, the substitute wheel speed is a wheel speed measured on another wheel. In a four-wheeled motor vehicle, the wheel speeds of the other wheels are made available as a substitute wheel speed, in particular to a first braking device assigned to a wheel. In particular, processing and weighting of the three wheel speeds for the three other wheels is also provided as a function of current driving parameters, with a mathematically determined substitute wheel speed being determined for this first braking device from the three wheel speeds detected by sensors. In this embodiment, a failure of the sensor detection of a wheel speed for a first wheel is thus advantageously compensated for by detecting the wheel speed of the other wheels of the motor vehicle.

A further advantageous embodiment provides that the input unit of the braking system is connected to the respective wheel brake control units via a communication connection for transmitting the braking specification, wherein the wheel brake control unit assigned to a braking device is provided with the wheel speed provided to this wheel brake control unit as a substitute wheel speed by one of the other wheel brake control units via the communication connection. The communication connection between the input unit of the braking system and the wheel brake control unit is advantageously not implemented via a communication bus, so that in particular in the event of a fault in the communication bus that prevents a wheel speed from being provided to a first wheel brake control unit by the other wheel brake control units via the communication bus, the wheel speed can still be provided as a substitute wheel speed via the communication connection. In particular, it is provided that the communication connection between the input unit and the respective wheel brake control unit is a line cable, preferably a sensor cable.

Advantageously, the braking command is transmitted in a first frequency range via the communication link and the replacement wheel speed in a second Frequency range is transmitted via the communication connection, the second frequency range being a frequency range that differs from the first frequency range. In particular, the first frequency range is in a 1 kHz range and the second frequency range is in a 100 kHz range. In particular, the first frequency range and the second frequency range are far enough apart that the signal for the braking command and the signal for the substitute wheel speed do not interfere with one another. Preferably, the braking command is transmitted as a first signal via the communication connection to the wheel brake control units, and the substitute wheel speed is transmitted via the communication connection as a second signal modulated onto the first signal, the first signal being transmitted in particular in the first frequency range and the second signal being transmitted in particular in the second frequency range. Advantageously, the respective wheel brake control unit providing the substitute wheel speed modulates the substitute wheel speed as the second signal and the receiving wheel brake control unit demodulates the second signal. The input unit of the brake system is also advantageously a brake pedal or a brake pedal sensor included in the brake pedal, which transmits a brake pedal position as a brake command in analog or digital form, with the transmission of the brake command as a first signal and the transmission of the substitute wheel speed as a second signal taking place in particular via sensor cables leading from the brake pedal sensor to the wheel brake control units as a communication connection. Each wheel brake control unit therefore advantageously has a galvanic connection to the input unit, in particular to the brake pedal sensor. This brake pedal sensor preferably automatically sends the information relating to a brake command via the pedal position. The brake pedal sensor can be an analog or digital sensor. Each wheel brake control unit preferably has a receiver interface, which receives the brake command from the brake pedal sensor as a first signal. Furthermore, the receiver interface is advantageously set up to feed a signal into the communication connection, which can in particular be formed by the pedal sensor line, preferably by modulation. Advantageously, the wheel brake control units can exchange information with other control units by means of this modulation, and thus in particular transmit a wheel speed. In the event that a wheel brake control unit does not receive any information regarding a current wheel speed from the associated wheel speed sensor, for example because the cable or the sensor is defective, the wheel brake control unit can advantageously request the wheel speed from the other wheel brake control units via the data transmission system, which can in particular be designed as a CAN bus, and have it provided as a replacement wheel speed, or this wheel brake control unit can advantageously Communication connection, in particular the cable of the brake pedal sensor, receives the signal and decodes the modulated signal that comes from the other wheel brake control units in order to arrive at the substitute wheel speed. In this respect, even in the event of a fault in the data transmission system, a substitute wheel speed can advantageously be provided to a wheel brake control unit via the communication connection between the wheel brake control units and the input unit.

According to a further advantageous embodiment, it is provided that at least one of the braking devices comprises a brake disc, wherein the wheel brake control units assigned to such a braking device with a brake disc determine the substitute wheel speed or a further substitute wheel speed based on vibrations of the brake disc. It is therefore provided in particular that, according to this embodiment, additionally or alternatively a substitute wheel speed is determined for the wheel in question, wherein this substitute wheel speed is not determined by one of the wheel speed sensor units. Instead, it is advantageously exploited that a speed of the associated wheel can be deduced from a vibration of the brake disc.

Advantageously, the wheel brake control unit assigned to a braking device with a brake disc detects a ripple current caused by vibrations of the brake disc and due to mechanical coupling in the at least one servomotor of the braking device and advantageously determines the equivalent wheel speed or the further equivalent wheel speed based on the detected ripple current, in particular based on a frequency of the detected ripple current. Advantageously, use is made of the fact that a small distance between the brake disc and the brake pads couples the mechanical movement to the servomotor, in particular via the brake pad, brake piston, slide, motor shaft, motor and current caused in the motor. The vibration causes a ripple in the motor current, i.e. a ripple current. Since the wheel brake control unit assigned to the servomotor measures the motor current in particular, it is advantageously provided that the wheel brake control unit measures and evaluates the ripple in the current. Advantageously, the wheel speed is estimated by the wheel brake control unit based on the ripple frequency.

It is further advantageously provided that during normal operation a Kl (Kl: Artificial Intelligence), in particular a Kl of the wheel brake control unit or a Kl of a higher-level motor vehicle control unit, determines the replacement wheel speed or the other substitute wheel speed based on the ripple current recorded for a braking device, taking into account the wheel speed provided by the wheel speed sensor unit assigned to this braking device. This advantageously improves the assignment of a vibration to a wheel speed. The substitute wheel speed is thus advantageously better approximated to an actual wheel speed.

A further advantageous embodiment of the method provides that the braking devices are connected to a central control unit which is designed for connection to the at least one input unit, wherein a braking command is entered by at least one of the input units into the central control unit, which controls the brake actuators with control signals, wherein the central control unit outputs control signals to at least two wheel brake control units, each assigned to a braking device, which each control a brake actuator of the respective braking device. One advantage of the method designed in this way is that improved operational reliability can be achieved through the decentralized control architecture, in particular through the robust design that is less sensitive to external interference and the possibility of redundant distribution of control functions to the central control unit and the wheel brake control units. In particular, anti-lock control (ABS) can be carried out by the wheel brake control unit together with the associated wheel speed sensor unit in a decentralized manner and independently of the central control unit. This allows further increased operational reliability to be achieved.

It is advantageous that each of the wheel brake control units is transmitted actual signals from a wheel speed sensor unit of the respective braking device. According to a control specification, the control of the respective brake actuator is regulated in the respective wheel brake control unit taking into account the actual signals of the wheel speed sensor unit, such as in particular wheel position and/or wheel speed, so that the target values specified by the braking command are realized. The wheel speed sensor unit preferably provides the actual signals of the measured parameters in real time. Actual values provided by other sensor devices can also be taken into account and processed, in particular electric current of the servomotor, braking force and/or vehicle speed. A further advantage of the method is that the processing of the signals provided by the wheel speed sensor (wheel position sensor) can take place practically in real time in the decentralized wheel brake control units of the braking devices. This can result in increased Processing speed and operational reliability as well as a redundant design of the control system can be realized.

Furthermore, according to an advantageous embodiment, it is provided that the braking device has an actuating device which can be coupled to the at least one actuating motor and comprises a first actuating drive and a second actuating drive coupled in series therewith, and which acts on a braking part which can be brought into braking engagement with a counter-braking part in the direction of an axis, wherein the first actuating drive has a first drive wheel which can be driven in rotation and to which a first drive torque can be applied for actuation, and the second actuating drive has a second drive wheel which can be driven in rotation and is coaxial with the first drive wheel and to which a second drive torque can be applied for actuation, wherein a coupling device is arranged between the first drive wheel and the second drive wheel. Preferably, the clutch device is designed as a friction clutch and has a predeterminable clutch torque, when exceeded, the first drive wheel slips relative to the second drive wheel, wherein to actuate the first actuator, the first drive wheel and the second drive wheel are driven synchronously so that the second actuator remains unactuated, and to actuate the second actuator, the second drive wheel is driven and the first drive wheel is brought to a standstill relative to it so that the friction clutch slips and the first actuator remains unactuated. To adjust the first actuator, an actuating torque can be coupled into the first drive wheel by means of a first electric actuator, and the second actuator can be driven accordingly by a second electric actuator.

In normal braking operation, the first and second drive wheels are advantageously rotated synchronously. This can be achieved by driving the first and second drive wheels with synchronized drive torques by the first and second servomotors. On the other hand, the second drive wheel can be driven synchronously by the clutch device when the first drive wheel is driven, as long as the transmitted drive torque remains below the clutch torque. In this operating mode, the second actuator advantageously remains unactuated and rotates as a whole together with the brake element. In this design variant with the friction clutch, the clutch device can slip continuously and evenly when the clutch torque is exceeded in order to adjust the air gap between the brake part and the counter-brake part. This can be achieved in particular by fixing the drive wheel of the first actuator, in particular by a brake or a corresponding control of the first drive motor, while the second drive motor applies a second drive torque to the second drive wheel, which is greater than the clutch torque. As a result, the second drive wheel is rotated relative to the first drive wheel, and by operating the second actuator, the air gap can be continuously and precisely adjusted so that continuously advancing wear of the brake element or the brake pad can be optimally compensated.

It is advantageous that the first drive wheel and the second drive wheel are coupled in a torque-locking manner to generate a synchronous drive by the friction clutch. This does not require the two drive wheels to be driven synchronously by the servomotors. Any torque differences can be compensated within specified tolerances.

It can advantageously be provided that a higher clutch torque is specified when the first actuator is actuated than when the second actuator is actuated. The first actuator is actuated by synchronous driving of the first and second drive wheels. The friction element and the counter-friction element are preloaded against each other by the spring force of the spring element, and in addition the adjusting force of the first actuator acts in the opposite direction to the spring force. This results in a relatively high clutch torque. However, if only the second drive wheel is turned to adjust the air gap, the spring force alone acts, so that a lower clutch torque is set. This makes adjusting the air gap easier.

The braking system for a motor vehicle, which is further proposed to solve the problem mentioned at the outset, comprises at least one input device for transmitting a braking command, at least two braking devices, each of which is assigned a wheel speed sensor unit which is designed to provide a wheel speed to the assigned braking device, wherein the braking devices each comprise a brake actuator which has at least one electric servomotor. A wheel brake control unit is assigned to each braking device for controlling the respective brake actuator, wherein the wheel brake control unit is designed to control the brake actuator taking into account the wheel speed provided by the assigned wheel speed sensor unit, and is further designed to control the brake actuator taking into account a substitute wheel speed for the wheel speed provided by the assigned wheel speed sensor unit. In this respect, the control can advantageously continue to take place in the event of a fault with regard to the provision of the wheel speed, namely then with the replacement wheel speed instead of the wheel speed. In this way, the reliability is increased at low cost. The braking system is particularly advantageously designed for operation according to a method designed according to the invention.

A further advantageous embodiment of the braking system provides that the braking devices are connected to a central control unit which is designed to be connected to the at least one input unit, and the wheel brake control units are connected to the central control unit.

A braking device, which can also be referred to as a braking unit or wheel brake, is assigned to each wheel of the vehicle. Each braking device has a brake actuator with at least one electric servomotor, which can exert an adjusting force on a braking part, in particular a brake pad, via an adjusting device. This allows the braking part to be brought into braking engagement with a counter-braking part assigned to the wheel, in particular a brake disk. The braking devices can be activated by input units, which can have manual input devices such as a brake pedal or a parking brake switch, and additionally or alternatively automated input units such as an anti-lock braking system (ABS) or an automatic drive system (ADS). The input units are advantageously electrically connected to the central control unit. The central control unit is designed in particular as an ECU (ECU: Electronic Control Unit).

The braking system advantageously has at least two wheel brake control units that are separate from the central control unit. These can be electrically controlled by the central control unit using control signals. In other words, because at least two wheel brake control units are provided, each of which is assigned to a braking device and connected to a brake actuator, it is provided that at least two braking devices each have their own wheel brake control unit, which is connected to the central control unit and to the brake actuator.

Each wheel brake control unit can be controlled by the central control unit with target braking values that are generated from a braking command received from the input devices. The advantageous combination of the central control unit with at least two decentralized wheel brake control units assigned to the wheels enables a decentralized brake control system. This enables simpler and shorter cabling. enables, in particular, a wheel sensor, in particular a wheel position sensor, in particular a wheel speed sensor, which is assigned to a wheel and can be connected directly to the wheel brake control unit of the braking device also assigned to the wheel. This advantageously reduces the manufacturing and assembly costs. In addition, the sensitivity to external interference can be reduced. The decentralized design of the brake control also enables a higher level of redundancy to be achieved, so that operational reliability can be further increased.

A wheel brake control unit can preferably be integrated with the braking device. This allows a compact, safe and easy-to-assemble design to be realized. Preferably, each of the braking devices has a wheel brake control unit, for example, in a four-wheeled vehicle with four braking devices, four wheel brake control units can be provided accordingly, or in a two-wheeled vehicle with two braking devices, two wheel brake control units can be provided accordingly.

It is preferred that a wheel brake control unit is connected to at least one brake actuator. A wheel brake control unit ensures that the brake actuator(s) are controlled with a defined target control signal in order to generate a defined braking torque for the wheel assigned to the respective braking device.

It is advantageous that each of the wheel brake control units is connected to an electric servomotor. The wheel brake control unit can control the servomotor with electrical target control values of the control current. Two or more servomotors of a braking device can also be connected to a wheel brake control unit.

In particular, it can be provided that each wheel brake control unit is connected to a sensor device. The sensor device can preferably comprise a wheel sensor assigned to the wheel to be braked, in particular a wheel speed sensor unit. This can be designed to detect parameters (actual values) relevant to a braking process, in particular wheel position, wheel speed, vehicle speed and/or slip, and to forward them to the wheel brake control unit. Furthermore, a sensor device can be provided for detecting the electric current of the servomotor, the braking force, and the like. Preferably, each of the braking devices has a sensor device, preferably at least one wheel sensor, in particular a Wheel speed sensor unit. One advantage is that the sensor unit, in particular a wheel speed sensor unit assigned to the respective brake unit, can be connected with less effort. The fact that relevant parameters can be measured on the wheel to be braked and fed directly to the wheel brake control unit without the central control unit being connected in between can increase operational reliability and redundancy.

It can be provided that each wheel brake control unit has a control unit. The electrical control unit advantageously compares the actual values of a wheel sensor or another sensor device with the target values of a braking specification transmitted from the central control unit to the wheel brake control unit and controls the servomotor(s) of the brake actuator accordingly in order to achieve the target values.

According to a further advantageous embodiment of the braking system, the braking device comprises an actuating device and a braking part connected thereto, which can be adjusted by the actuating device along an axis and brought into braking engagement with a counter-braking part, wherein the actuating device has a first actuating drive and a second actuating drive coupled in series therewith, wherein the first actuating drive has a first drive wheel that can be driven in rotation, and the second actuating drive has a second drive wheel that can be driven in rotation and is coaxial with the first drive wheel, wherein a coupling device is arranged between the first drive wheel and the second drive wheel, wherein the coupling device is preferably designed as a friction clutch with a friction element that can be frictionally connected to a counter-friction element in coupling engagement.

Further advantageous details, features and design details of the invention are explained in more detail in connection with the embodiments shown in the figures (hereinafter: figure).

Fig. 1 shows an embodiment of a braking system of a motor vehicle designed according to the invention in a schematic, isolated representation;

Fig. 2a shows a schematic representation of a further embodiment of a braking system designed according to the invention in normal operation; Fig. 2b shows a schematic representation of the embodiment of a braking system designed according to the invention according to Fig. 2a in the event of a malfunction;

Fig. 3 shows a schematic perspective view of an embodiment of a braking device of a braking system designed according to the invention;

Fig. 4 is a side view of the braking device according to Fig. 3;

Fig. 5 is a section Q-Q through the braking device according to Fig. 3;

Fig. 6 shows a first actuator of the braking device according to Fig. 3 in a schematic perspective view; and

Fig. 7 is an enlarged detailed view of the adjusting device from Fig. 5.

In the various figures, identical parts are generally provided with the same reference symbols and are therefore sometimes only explained in connection with one of the figures.

Fig. 1 shows a schematic, isolated perspective partial view of a chassis 100 of a motor vehicle. This comprises steerable wheels 101, which are mounted on a frame part of the body 102 of the motor vehicle on pivotable steering knuckles 103. In this embodiment, a steering system of the motor vehicle comprises a steering shaft 104, on the rear end of which in the direction of travel a steering wheel 105 is attached as a manual steering input. The steering shaft 104 is connected to a steering gear 106, which is connected to the steering knuckles 103 via tie rods 107 to generate a steering angle.

In this exemplary embodiment, an electromechanical braking system 110 of the motor vehicle has a brake pedal 113 attached to the body 102 with an associated brake pedal sensor, the brake pedal 113 being a manual input unit for transmitting a braking command. The brake pedal 113 is only shown schematically in Fig. 1. Furthermore, in this exemplary embodiment, the braking system 110 comprises an automated input unit 114 which is connected to a central control unit 112 of the braking system 110. This input unit 14 can output external control signals to the central control unit 112 for controlling the braking system 110. Furthermore, the braking system 110 shown in Fig. 1 comprises a braking device 1 for each of the two wheels 101 shown in Fig. 1. Each of these has a brake caliper 3 which is attached to and supported on the motor vehicle body 102. A brake disk 2 is attached to a wheel 101 in a rotationally fixed manner as a counter-braking part, which is gripped by the brake caliper 3 which is fixed relative to it and has brake pads not explicitly shown here. Furthermore, the braking devices 1 each have a brake actuator with an electric servomotor and a wheel brake control unit 120 for controlling the respective brake actuator. Each of the wheels 101 and thus each of the braking devices 1 is assigned a wheel speed sensor unit 121 which is designed to provide the assigned braking device 1 with a wheel speed of the assigned wheel 101, which is used by the wheel brake control unit 120 for controlling the respective brake actuator. Furthermore, the wheel brake control unit 120 is designed to control the respective brake actuator on the basis of a provided substitute wheel speed, which is particularly advantageous if no wheel speed can be provided due to a fault in relation to the wheel speed sensor unit 121 of the wheel brake control unit. Various options are provided for providing the substitute wheel speed, some of which will also be discussed below with reference to the other figures. One variant in this regard provides that the wheel speeds provided by the wheel speed sensor units 121 are made available for retrieval via a data transmission system 111 of the motor vehicle, in particular via a CAN bus of the motor vehicle. For example, for a braking device 1 shown on the left side in Fig. 1 of the associated

Wheel brake control unit 120 provides as a substitute wheel speed the wheel speed determined by the wheel speed sensor unit 121, which is assigned to the braking device 1 on the right side in Fig. 1, via the data transmission system 111.

Fig. 2a and Fig. 2b each show a schematic diagram of a chassis 100 with an exemplary embodiment of a braking system 110 designed according to the invention. The motor vehicle has four wheels 101, each of which is assigned a braking device 1 (BUI, BU2, BU3, BU4) of the braking system 110. In this exemplary embodiment, the braking system 110 further comprises a first input unit 113 and a second input unit 114, which can each transmit a braking command to the braking system 110 for implementation by means of the braking devices 1 (BUI, BU2, BU3, BU4). The input unit 114 can in particular be assigned to a driver assistance system and connected to the braking system 110 via a data transmission system 111, in particular a CAN bus of the motor vehicle. be connected in terms of signaling. In this exemplary embodiment, however, the input unit 113 is a brake pedal or a brake pedal sensor assigned to the brake pedal, which is designed in particular to detect an actuation of the brake pedal by a vehicle user and to transmit it as a braking command via the communication connections 135, which in this exemplary embodiment are sensor lines, to the wheel brake control units 120 (BC1, BC2, BC3, BC4) of the braking system 110. When the brake pedal is actuated, the brake pedal sensor 113 advantageously detects the brake pedal position, in particular in real time, so that the respective wheel brake control unit 120 (BC1, BC2, BC3, BC4) can preferably also derive the acceleration of the brake pedal during actuation and take this into account for the control of the respective brake actuator 4 of the braking system 110.

In the embodiment shown in Fig. 2a and Fig. 2b, each of the four braking devices 1 (BUI, BU2, BU3, BU4) has a brake actuator 4 (BMI, BM2, BM3, BM4) and a wheel brake control unit 120 (BC1, BC2, BC3, BC4). A wheel speed sensor 121 (SI, S2, S3, S4) is connected to the wheel brake control unit 120, which outputs actual values of the rotational position and wheel speed PI, P2, P3, P4 to the respective wheel brake control unit 120 (BC1, BC2, BC3, BC4) in real time during travel in normal operation shown in Fig. 2a. The respective wheel brake control unit 120 (BC1, BC2, BC3, BC4) is preferably integrated with the braking device 1 and electrically connected to the brake actuator 4, which has respective electric servomotors 41, 42 via which a braking intervention can be controlled.

Each of the four wheel brake control units 120 (BC1, BC2, BC3, BC4) can receive a wheel speed PI, P2, P3, P4 from the associated wheel speed sensor 121 in a trouble-free normal operation, as shown in Fig. 2a. The wheel brake control unit BC1 can therefore, for example, receive a wheel speed PI from the wheel speed sensor 121 (Sl) in a trouble-free normal operation; the wheel brake control unit BC2 can receive a wheel speed P2 from the wheel speed sensor 121 (S2), etc. In normal operation, the wheel brake control unit BC1 then controls the associated brake actuator 4 (BMI) in order to implement the braking command transmitted by the input unit 113 or the input unit 114, taking into account the wheel speed PI provided by the associated wheel speed sensor unit 121 (Sl). Accordingly, in normal operation, the wheel brake control unit BC2 controls the associated brake actuator 4 (BM2) to implement the transmitted brake command, taking into account the values of the associated wheel speed sensor unit 121 (S2). provided wheel speed P2. In the same way, the wheel brake control units BC3 and BC4 control the associated brake actuators 4 (BM3) and 4 (BM4).

In this exemplary embodiment, however, it is not only provided that the wheel brake control units 120 (BC1, BC2, BC3, BC4) receive a braking command from the input unit 113 via the respective communication connection 135, wherein the braking command from the input unit 113 is preferably transmitted as a first signal Sgl in a first frequency range of the order of 1 kHz. This is because it is also provided that the wheel brake control units 120 (BC1, BC2, BC3, BC4) comprise a modulation unit with which the wheel brake control units 120 (BC1, BC2, BC3, BC4) make a wheel speed PI, P2, P3, P4 received from the associated wheel speed sensor 121 (SI, S2, S3, S4) available as a second signal Sg2 via the communication connections 135 to at least one of the other wheel brake control units 120 (BC1, BC2, BC3, BC4), in particular by modulating the second signal Sg2 onto the first signal Sgl, which preferably takes place in a second frequency range of the order of 100 kHz, and is shown schematically in the diagram in Fig. 2b. In particular, it can be provided that the central control unit 112 specifies which of the wheel brake control units 120 (BC1, BC2, BC3, BC4) makes the received wheel speed Pl, P2, P3, P4 available as a second signal Sg2 via the communication connections 135 to the other wheel brake control units 120 (BC1, BC2, BC3, BC4) as a substitute wheel speed EPI. In this exemplary embodiment, it is thus provided that the wheel brake control unit BC1 makes a wheel speed PI received from the associated wheel speed sensor unit S1 available to the other wheel brake control units BC2, BC3 and BC4 as a substitute wheel speed EPI via the sensor lines 135 as a signal Sg2 (referred to as PI' in Fig. 2b). The assignment of sending and receiving wheel brake control units 120 can be changed by the central control unit 112, in particular varied cyclically. In particular, all detected wheel speeds can also be sent via the communication connection 135, wherein different frequency bands are then preferably assigned to the wheel brake control units.

In the normal operation shown in Fig. 2a, this substitute wheel speed EPI can then be used in particular for diagnostic purposes, in particular for a comparison with the other detected wheel speeds P2, P3 and P4, in order to conclude, for example, that a sensor 121 is malfunctioning in the case of deviations that exceed a tolerance threshold. In the event that a fault occurs with respect to one of the wheel speed sensors 121 or a signal line via which a wheel speed sensor 121 transmits a wheel speed to the wheel brake control unit 120, the substitute wheel speed is used by the wheel brake control unit 120 instead of the wheel speed provided by the wheel speed sensor 121 in order to control the associated brake actuator 4 taking into account the substitute wheel speed EPI provided. Such a fault case is outlined in Fig. 2b with respect to the wheel speed sensor 121 (S2). The wheel brake control unit BC2 can therefore no longer receive a wheel speed P2 from the wheel speed sensor 121 (S2). Instead, the wheel brake control unit BC2 demodulates the signal transmitted via the communication connection 135 and in this way receives the wheel speed PI' provided by the wheel brake control unit BC1 as the substitute wheel speed EPI. The wheel brake control unit BC2 then controls the associated brake actuator 4 (BM2) taking into account the received substitute wheel speed EPI. As an example, a first signal Sgl is also shown in a diagram in Fig. 2b as a PWM signal for a brake command with a modulated second signal Sg2 for the substitute wheel speed EPI.

Furthermore, the wheel brake control units 120 (BC1, BC2, BC3, BC4) in this embodiment are advantageously designed to exchange signals with a central control unit 112 designed as an ECU and to control the brake actuator 4 taking into account further specifications by the central control unit 112. According to a design variant not shown here, this central control unit 112 can also be omitted.

An advantageous embodiment of the brake actuator 4 is explained in further detail below with reference to Fig. 3, Fig. 4 and Fig. 5. A respective brake actuator 4 advantageously has a housing 45 in which the wheel brake control unit 120 is arranged, as can be seen in Fig. 5. This has an electrical circuit which is connected to the servomotors 41, 42 and the central control unit 112. As a result, the wheel brake control unit 120 is integrated with the braking device 1.

For connecting the wheel speed sensor 121, which is schematically indicated in Fig. 2a and Fig. 2b as well as in Fig. 4 and Fig. 5, the brake actuator 4 has in particular a connection device 46, in particular an electrical plug connection arranged on the housing 45. Fig. 3 shows an embodiment of a braking device 1 of a braking system 110 designed according to the invention as a whole, wherein the braking device 1 is designed as a disc brake. This comprises a brake disc 2, which forms a counter-braking part and is connected to a vehicle wheel 101 (not shown here) that can rotate about a wheel axis R. A brake caliper 3 surrounds the two axial end faces of the brake disc 2. The brake disc 2 is designed here as a non-ventilated brake disc made of solid material. Alternatively, it can also be designed as an internally ventilated brake disc.

A brake actuator 4 is attached to the brake caliper 3. The brake actuator 4 comprises an actuating device 5 which extends axially in the direction of an axis A which is parallel to the wheel axis R and indicates the adjustment direction V of the actuating device 5. The brake actuator 4 comprises an electric servomotor 41 to which a wheel brake control unit 120 is assigned. The wheel brake control unit 120 is designed to determine a substitute wheel speed for a wheel speed measured by means of a wheel sensor unit 121 based on vibrations of the brake disk 2. This takes advantage of the fact that the vibrations of the brake disk occur in a range between ±0.01 mm ... 1 mm (mm: millimeters) when the braking device 1 is operated as intended in a moving motor vehicle. Due to mechanical coupling via the very small air gap between the brake disk 2 and the brake pad, which can be in the tenth of a millimeter range, these vibrations cause a ripple current in the servomotor 41 of the braking device 1. The mechanical coupling is particularly evident in Fig. 5. The wheel brake control unit 120 measures a current of the servomotor 41 and/or the second servomotor 42 explained below, and can therefore also detect the ripple current caused and evaluate it with regard to a wheel speed. It can be provided that a wheel brake control unit 120 sends a frequency of a detected ripple current and a wheel speed determined by means of a wheel speed sensor unit 121 assigned to the braking device 1 to a central control unit 112, for example as shown in Fig. 1, wherein a unit of the central control unit 112 uses the transmitted values to train an assignment of the frequency of the ripple current to a corresponding wheel speed. Advantageously, in the event of a failure of the wheel speed sensor unit 121, a substitute wheel speed can be provided via the detected frequency of the ripple current of the wheel brake control unit 120, which can be used to control the servo motor instead of the wheel speed from the wheel speed sensor unit 121 to implement a received braking command.

Fig. 4 shows a view of the brake caliper 3 as seen from the brake disc 2. As can be seen in the sectional view of Fig. 5 along the axis A, the brake disk 2 is arranged axially between two brake pads 31 and 32. One brake pad 31 is firmly supported on the brake calliper 3 on the side facing away from the brake actuator 4. The other brake pad 32, which forms a braking part of the braking device 1, is attached to the adjusting device 5 and can be adjusted by the latter in the axial adjustment direction V given by the axis A to produce the braking intervention on the brake disk 2, as indicated by the arrow in Fig. 5.

In the non-actuated state of the braking device 1, the axial air gap L already mentioned is located between the brake disc 2 and the adjustable brake pad 32, which is shown schematically in an exaggeratedly wide manner in Fig. 5.

The structure of the actuating device 5 is shown in Fig. 5 and in the enlarged section thereof in Fig. 7. The actuating device 5 comprises a first actuating drive 6, which has a ramp bearing, and a second actuating drive 7, which is coupled axially (with respect to the axis A) in series with the first actuating drive 6 and has a spindle drive.

The first actuator 6, which in the example shown is designed as a ramp bearing, comprises a drive-side cam disk 61 supported axially and in a rotationally fixed manner on the brake actuator 4 and a driven-side cam disk 62. Balls 63 are arranged between the cam disks 61 and 62. As can be seen in the schematically isolated view of Fig. 6, the cam disks 61 and 62 have ramp-like tracks 64 that are axially opposite one another and lie obliquely to the axis A, between which balls 63 can roll. A rotation of the output-side cam disk 62, in Fig. 6 above, relative to the fixed drive-side cam disk 61 - as schematically indicated by the curved arrows - leads to a linear adjustment of the output-side cam disk 62 in the adjustment direction V parallel to the axis A. As a result, the brake pad 32 can be brought into braking engagement by actuating the first actuator 6, as shown in Fig. 5.

The cam disk 62 is connected to a coaxial gear 65, which is designed as a spur gear and forms a drive wheel in the sense of the invention. The gear 65 is in gear engagement with a first electric servomotor 41. This enables the rotating drive of the cam disk 62 and thus an actuation of the first actuator 6. The second actuator 7, which in the example shown is designed as a spindle drive, has a Threaded spindle 71, which engages in the internal thread of a drive-side spindle nut 72. This internal thread is formed in the output-side cam disk 62 of the first actuator 6, so that the functions of the output-side cam disk 62 and the drive-side spindle nut 72 are combined in one component.

The threaded spindle 71 is connected via a hub part 74 to a coaxial gear 75, which is axially fixed and rotatably mounted in the brake actuator 4. The threaded spindle is coupled to the gear 75 in a torque-locking but axially displaceable manner via drivers 73, which can have, for example, radially projecting projections or teeth that engage axially displaceably in axial slots of the hub part 74.

The gear 75 can, like the gear 65, be designed as a spur gear and is arranged coaxially adjacent to it. This gear 75 is in gear engagement with a second electric actuator 42. This enables the rotating drive of the threaded spindle 71 and thus an actuation of the second actuator 7. The threaded spindle 71 is connected axially via a thrust bearing 43, for example an axial roller bearing as shown, to a pressure piece 44 to which the movable brake pad 32 is attached, as can be seen in Fig. 5. The pressure piece 44 can also be referred to as a piston.

The clutch device according to the invention has a friction element 8, which is directed as a coaxial, conical extension from the cam disk 62 towards the second actuator 7. The conical extension has a conical friction surface 81 arranged on the outside on an outer cone. The friction element 81 can preferably be formed in one piece with the cam disk 62 / spindle nut 72.

In clutch engagement, the friction element 8 is coupled to a counter friction element 9 in a frictionally locked manner. The conical projection extends axially into a corresponding conical opening of the counter friction element 9, which has a conical friction surface 91 arranged in an inner cone. In clutch engagement, the friction surface 81 and the counter friction surface 91 are in frictionally locked contact with one another, as can be clearly seen in Fig. 7. The counter friction element 9 is coupled to the gear 75 in a torque-locking but axially displaceable manner via drivers 92, which engage in corresponding slots 76 in the hub part 74 or the gear 75 in an axially displaceable manner. A spring element 93 is arranged between the gear wheel 75 or the hub part 74 connected thereto and the counter friction element 9. The axially effective spring force of this spring element elastically braces the counter friction element 9 against the friction element 8. This generates a defined coupling torque of the friction clutch formed by the friction element 8 and the counter friction element 9.

To actuate the braking device 1, the gears 65 and 75 are rotated synchronously so that the first actuator 6 executes a working stroke in the adjustment direction V so that the brake pad 32 passes through the air gap L and comes into braking engagement with the brake disk 2. The synchronous drive of the gears 65 and 75 can be achieved by synchronizing the drive speeds of the actuator motors 41 and 42, or by driving by only one of the actuator motors 41 or 42, while the other actuator motor 42 or 41 runs idle. The frictional coupling engagement between the friction element 8 and the counter friction element 9 then ensures synchronous rotation of the gears 65 and 75. Because the friction element 8 and the counter friction element 9 are arranged entirely or at least partially within the gears 65 and 75, a particularly compact design can be realized.

To adjust the width of the air gap L, the gear 65 is fixed or blocked, in particular by appropriately controlling the first servomotor 41. The second servomotor 42 rotates the gear 75 relative to the gear 65, whereby the friction clutch continuously slips. The second actuator 7 is adjusted uniformly accordingly, whereby the width of the air gap L can also be continuously adjusted and adapted, for example to compensate for wear on the brake pad 32.

The braking devices shown in Fig. 3 to Fig. 7 are designed as floating caliper brakes, also referred to as floating caliper brakes. The brake pad 32 is pressed against the brake disc 2 by the pressure piece 44, and the brake pad 31 is pressed against the brake disc 2 by the brake caliper 3, which can be moved relative to the brake disc 2 in the direction of the axis A. Alternatively, the proposed solution can also be used with a fixed caliper brake.

The embodiments shown in the figures and explained in connection with them serve to explain the invention and are not limitative of it. List of reference symbols

1 braking device (BUI, BU2, BU3, BU4)

100 Chassis

101 Wheel (vehicle wheel)

102 Body

103 Steering knuckles

104 Steering shaft

105 Steering wheel

106 Steering gear

107 Tie rod

110 Brake system

111 Data transmission system

112 Central control unit

113 Brake pedal (input unit)

114 Input unit

120 Wheel brake control unit (BC1, BC2, BC3, BC4)

121 Wheel speed sensor unit (SI, S2, S3, S4)

135 Communication connection

2 brake disc (counter brake part)

3 Brake caliper

31, 32 Brake pad (brake part)

4 brake actuator (BMI, BM2, BM3, BM4)

41, 42 Actuator

43 Thrust bearing

44 Pressure piece

45 Housing

46 Connection device

5 Adjustment device

6 first actuator

61 Cam disc

62 Cam disc (integrated with spindle nut 72)

63 Ball

64 Career

65 Gear (first drive wheel) 7 second actuator

71 Threaded spindle

72 Spindle nut (integrated with cam disc 62)

73 Carrier

74 Hub part

75 Gear (second drive wheel)

76 Slot

8 Friction element

81 Friction surface

9 Counter friction element

91 Counter friction surface

92 carriers

93 Spring element

Pl, P2, wheel speed

P3, P4

PI' wheel speed transmitted by a wheel brake control unit (BC1)

EPI Replacement Wheel Speed

A axis

R wheel axle

V Adjustment direction

L Air gap

Sgl first signal

Sg2 second signal

Claims

1. Method for operating an electromechanical braking system (110) in a motor vehicle, wherein the braking system (110) has at least one input unit (113, 114) via which a braking command is transmitted, and at least two braking devices (1, BU), each of which comprises a brake actuator (4, BM) with at least one electric servomotor (41, 42), wherein the braking devices (1, BU) are each assigned a wheel brake control unit (120, BC) and a wheel speed sensor unit (121), wherein for a respective braking device (1, BU), the assigned wheel speed sensor unit (121) provides the assigned wheel brake control unit (120, BC) with a wheel speed (P), said wheel brake control unit (120, BC) is provided with a substitute wheel speed (EP) for the wheel speed (P) provided by the assigned wheel speed sensor unit (121), said wheel brake control unit (120, BC) to implement the transmitted braking specification in normal operation, the brake actuator (4, BM) is activated taking into account the wheel speed (P) provided by the associated wheel speed sensor unit (121), and the wheel brake control unit (120, BC) to implement the transmitted braking specification in the event of a fault in relation to the provision of the wheel speed (P) from the associated wheel speed sensor unit (121), the brake actuator (4, BM) is activated taking into account the provided substitute wheel speed (EP).

2. Method according to claim 1, characterized in that the wheel brake control units (120, BC) are connected to one another via a data transmission system (111) for exchanging data, wherein the wheel brake control unit (120, BC) assigned to a braking device (1, BU) is provided with a wheel speed (P) from at least one of the wheel speed sensor units (121) which is not directly assigned to this braking device (120, BU) as a substitute wheel speed (EP) via the data transmission system (111).

3. Method according to one of the preceding claims, characterized in that the input unit (113, 114) of the braking system (110) for transmitting the braking specification via a communication connection (135) with the respective Wheel brake control units (120, BC), wherein the wheel brake control unit (120, BC) assigned to a braking device (1, BU) is provided with the wheel speed (P) provided to this wheel brake control unit (120, BC) as a substitute wheel speed (EP) by one of the further wheel brake control units (120, BC) via the communication connection (135).

4. Method according to claim 3, characterized in that the braking specification is transmitted in a first frequency range via the communication connection (135) and the substitute wheel speed (EP) is transmitted in a second frequency range via the communication connection (135), wherein the second frequency range is a frequency range deviating from the first frequency range.

5. Method according to claim 3 or claim 4, characterized in that the braking specification is transmitted as a first signal (Sgl) via the communication connection (135) to the wheel brake control units (120, BC), and the substitute wheel speed (EP) is transmitted via the communication connection (135) as a second signal (Sg2) modulated onto the first signal (Sgl).

6. The method according to claim 5, characterized in that the respective wheel brake control unit (120, BC) providing the substitute wheel speed (EP) modulates the substitute wheel speed (EP) as the second signal (Sg2) and the receiving wheel brake control unit (120, BC) demodulates the second signal (SG2).

7. Method according to one of the preceding claims, characterized in that the input unit (113) is a brake pedal sensor which transmits a brake pedal position as a braking command in analog or digital form.

8. Method according to one of the preceding claims, characterized in that at least one of the braking devices (1, BU) comprises a brake disc (2), wherein the wheel brake control units (120, BC) assigned to such a braking device (1, BU) with brake disc (2) determine the substitute wheel speed (EP) or a further substitute wheel speed (EP') based on vibrations of the brake disc (2).

9. Method according to claim 8, characterized in that the wheel brake control unit (120, BC) associated with a braking device (1, BU) with brake disc (2) has a Vibrations of the brake disc (2) and ripple current caused by mechanical coupling in the at least one servomotor (41, 42) of the braking device (1, BU) are detected and the substitute wheel speed (EP) or the further substitute wheel speed (EP') is determined based on the detected ripple current.

10. The method according to claim 9, characterized in that during normal operation a Kl trains the determination of the substitute wheel speed (EP) or the further substitute wheel speed (EP') based on the ripple current detected for a braking device (1, BU) taking into account the wheel speed (P) provided by the wheel speed sensor unit (121) assigned to this braking device (1, BU).

11. Method according to one of the preceding claims, characterized in that the braking devices (1, BU) are connected to a central control unit (112) which is designed for connection to the at least one input unit (113, 114), wherein a braking specification is entered by at least one of the input units (113, 114) into the central control unit (112), which controls the brake actuators (4) with control signals, wherein the central control unit (112) outputs control signals to at least two wheel brake control units (120, BC), each assigned to a braking device (1, BU), which each control a brake actuator (4) of the respective braking device (1, BU).

12. Method according to one of the preceding claims, characterized in that the braking device (1) has an actuating device (5) which can be coupled to the at least one servomotor (41, 42, BM), comprising a first actuating drive (6) and a second actuating drive (7) coupled in series therewith, and which acts on a braking part (32) which can be brought into braking engagement with a counter-braking part (2) in the direction of an axis (A), wherein the first actuating drive (5) has a first drive wheel (65) which can be driven in rotation and to which a first drive torque can be applied for actuation, and the second actuating drive (7) has a second drive wheel (75) which can be driven in rotation and is coaxial with the first drive wheel (65) and to which a second drive torque can be applied for actuation, wherein a coupling device is arranged between the first drive wheel (65) and the second drive wheel (75).

13. Method according to claim 12, characterized in that the coupling device is designed as a friction clutch (8, 9) and has a predeterminable coupling torque, when this limit is exceeded, the first drive wheel (65) slips relative to the second drive wheel (75), wherein to actuate the first actuator (6), the first drive wheel (65) and the second drive wheel (75) are driven synchronously so that the second actuator (7) remains unactuated, and to actuate the second actuator (7), the second drive wheel (75) is driven and the first drive wheel (65) is brought to a standstill relative thereto so that the friction clutch slips and the first actuator (6) remains unactuated.

14. Braking system (110) for a motor vehicle, comprising at least one input device (113, 114) for transmitting a braking command, at least two braking devices (1, BU), each of which is assigned a wheel speed sensor unit (121) which is designed to provide a wheel speed (P) to the assigned braking device (1, BU), wherein the braking devices (1, BU) each comprise a brake actuator (4) which has at least one electric servomotor (41, 42), characterized in that the braking devices (1, BU) are each assigned a wheel brake control unit (120, BC) for controlling the respective brake actuator (4), wherein the wheel brake control unit (120, BC) is designed to control the brake actuator (4) taking into account the wheel speed (P) provided by the assigned wheel speed sensor unit (121), and is further designed to take into account a substitute wheel speed (EP) for the wheel speed (P) provided by the assigned wheel speed sensor unit (121) provided wheel speed (P) to control the brake actuator (4).

15. Braking system (110) according to claim 14, characterized in that the braking system (110) is designed for operation according to a method according to one of claims 1 to 13.

16. Braking system (110) according to claim 14 or claim 15, characterized in that the braking devices (1, BU) are connected to a central control unit (112) which is designed for connection to the at least one input device (113, 114), and the wheel brake control units (120, BC) are connected to the central control unit (112).

17. Braking system (110) according to one of claims 14 to 16, characterized in that the braking device (1, BU) comprises an adjusting device (5) and a braking part (32) connected thereto, which can be adjusted by the adjusting device (5) along an axis (A) and can be brought into braking engagement with a counter-braking part (2), wherein the adjusting device (5) has a first actuator (6) and a second actuator (7) coupled in series therewith, wherein the first actuator (6) has a first drive wheel (65) which can be driven in rotation, and the second actuator (7) has a second drive wheel (75) which can be driven in rotation and is coaxial with the first drive wheel (65), wherein a clutch device (8, 9) is arranged between the first drive wheel (65) and the second drive wheel (75), wherein the clutch device is preferably designed as a friction clutch (8, 9) with a friction element (8) which can be frictionally connected to a counter friction element (9) in clutch engagement.