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

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

[0001] Electromechanical braking system for a motor vehicle and method for operating an electromechanical braking system in a motor vehicle

[0002] 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 designed to provide a wheel speed to the assigned braking device, wherein the braking devices each comprise a brake actuator having 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 comprising a brake actuator with at least one electric servomotor.

[0003] Such a braking system comprises at least two electromotive braking devices, each assigned to a wheel of a motor vehicle 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 supported on the chassis of a motor vehicle relative to the rotation of the wheel to be braked, which actuator 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 disc, by rotating the actuator. During braking engagement, frictional contact is generated between the braking part and the counter-braking part, whereby the braking torque generated by friction increases the higher the adjusting force exerted by the actuator in the adjustment direction.Such braking systems are known in the prior art, for example, from DE 10 2017 123 266 A1, US Pat. No. 6,397,981 B1, or US Pat. No. 6,081,081 A. According to the disclosure of US Pat. No. 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.

[0004] The braking system is controlled electrically. A braking command, in particular an electrical braking command, to initiate a braking operation can be generated manually via an input unit, in particular a brake pedal or a parking brake switch, and additionally or alternatively via an automated input unit, in particular an anti-lock braking system (ABS) or an automatic drive system (ADS).

[0005] 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.

[0006] 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 ​​​​provided with the braking command and other actual parameters relevant to the braking process, in particular wheel position, wheel speed, electrical 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, if necessary, other values ​​to a central control unit, which can be synonymously referred to as an ECU (ECU: Electronic Control Unit). This control unit determines the control currents required for the servomotors of all brake actuators to generate defined wheel braking torques according to a predetermined control algorithm.The wheel speed is a particularly important actual parameter that should always be available to convert the braking command into a corresponding braking intervention of a respective braking device in order to prevent brake failure, even partial brake failure. To increase reliability, US Pat. No. 6,410,993 B1 discloses a dual-circuit or multi-circuit circuit arrangement for a safety-critical control system, such as brake-by-wire. Each circuit of the circuit arrangement contains a complete microprocessor system that redundantly processes the input data and delivers an error detection signal (FAIL) if an error or a discrepancy occurs between the redundantly generated data processing results.

[0007] 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.

[0008] To achieve this object, 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, as well as illustrated 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 comprising 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 associated wheel speed sensor unit provides a wheel speed to the associated wheel brake control unit, and this wheel brake control unit is provided with a substitute wheel speed for the wheel speed provided by the associated wheel speed sensor unit. According to the invention, in order to implement the transmitted braking command during normal operation, this wheel brake control unit controls the brake actuator taking into account the wheel speed provided by the associated wheel speed sensor unit. In the event of a fault with respect to the provision of the wheel speed by the associated wheel speed sensor unit, this wheel speed sensor unit controls the brake actuator taking into account the provided substitute wheel speed.In particular, it is provided that the substitute wheel speed is not determined using the wheel speed sensor unit assigned to the wheel in question, and preferably also not using one of the identically designed redundant wheel speed sensor units assigned to the wheel in question. In this respect, the substitute wheel speed is in particular a parameter which approximates the actual wheel speed of a wheel and in particular can even coincide with it, but with regard to which certain deviations from the actual wheel speed are certainly acceptable. Advantageously, the brake actuator can thereby be further controlled, in particular with regard to the corresponding control algorithm, without deviating from normal operation, by advantageously using the substitute 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 substitute wheel speed can only be provided if a fault has occurred. In particular, however, it is provided that the substitute wheel speed for each wheel is also determined and provided during fault-free normal operation. Further advantageously, using the substitute wheel speed during normal operation, a diagnosis, in particular a plausibility check, is carried out with regard to the wheel speed provided by the assigned wheel speed sensor unit. In this way, a problem with regard to one of the wheel speed sensor units and / or with regard to the determination of the substitute wheel speed can advantageously be detected at an early stage. According to one advantageous embodiment, it is provided that the wheel brake control units are connected to one another via a data transmission system, in particular a communications 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 at 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 sensory detection of a wheel speed for a first wheel is thus advantageously compensated by detecting the wheel speed of the other wheels of the motor vehicle.

[0009] 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 command, 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 further 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, particularly in the event of a communication bus malfunction that prevents the other wheel brake control units from providing a wheel speed to a first wheel brake control unit 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.

[0010] Advantageously, the braking command is transmitted in a first frequency range via the communication connection, and the substitute wheel speed is transmitted in a second frequency range via the communication connection, wherein the second frequency range 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 sufficiently far apart that the signal for the braking command and the signal for the substitute wheel speed do not interfere with each other.Preferably, the braking command is transmitted as a first signal via the communication link to the wheel brake control units, and the substitute wheel speed is transmitted via the communication link as a second signal modulated onto the first signal, wherein the first signal is transmitted in particular in the first frequency range and the second signal is 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.Further advantageously, the input unit of the braking system is a brake pedal or a brake pedal sensor enclosed by the brake pedal, which transmits a brake pedal position as a braking command in analog or digital form, wherein the braking command is transmitted as a first signal and the equivalent wheel speed is transmitted as a second signal, 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 advantageously has a galvanic connection to the input unit, in particular to the brake pedal sensor. This brake pedal sensor preferably automatically transmits the information relating to a braking 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 braking command from the brake pedal sensor as a first signal.Furthermore, the receiver interface is advantageously configured to feed a signal into the communication connection, which can be formed in particular by the pedal sensor line, preferably by modulation. Advantageously, the wheel brake control units can exchange information with other control units using 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 substitute wheel speed, or this wheel brake control unit can advantageously receive the signal via the communication connection, in particular the cable of the brake pedal sensor, and decode 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.

[0011] 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 equivalent wheel speed or a further equivalent wheel speed based on vibrations of the brake disc. It is therefore particularly provided that, according to this embodiment, additionally or alternatively, an equivalent wheel speed is determined for the wheel in question, wherein this equivalent wheel speed is not determined by one of the wheel speed sensor units. Instead, it is advantageously exploited that a rotational speed of the associated wheel can be deduced from a vibration of the brake disc.

[0012] 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, 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 induced in the motor, is utilized. 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 current ripple. Advantageously, the wheel brake control unit estimates the wheel speed based on the ripple frequency.

[0013] It is further advantageously provided that, during normal operation, a K1 (K1: artificial intelligence), in particular a K1 of the wheel brake control unit or a K1 of a higher-level motor vehicle control unit, trains the determination of the substitute wheel speed or the further substitute wheel speed based on the ripple current detected 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.

[0014] 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 input 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 due to the robust design that is less sensitive to external interference and the possibility of redundantly distributing control functions between the central control unit and the wheel brake control units.In particular, anti-lock braking (ABS) control can be carried out decentrally and independently of the central control unit by the wheel brake control unit together with the associated wheel speed sensor unit. This can further increase operational reliability.

[0015] It is advantageous for each of the wheel brake control units to be 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 from 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 considered and processed, in particular the electric current of the servo motor, braking force, and / or vehicle speed.A further advantage of the method is that the signals supplied by the wheel speed sensor (wheel position sensor) can be processed virtually in real time in the decentralized wheel brake control units of the braking devices. This allows for increased processing speed and operational reliability, as well as a redundant control design.

[0016] Furthermore, according to an advantageous embodiment, 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, upon exceeding which the first drive wheel slips smoothly relative to the second drive wheel, wherein to actuate the first actuator, the first drive wheel and the second drive wheel are driven synchronously such that the second actuator remains unactuated, and to actuate the second actuator, the second drive wheel is driven and the first drive wheel is stopped relative to it such 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 motor, and correspondingly the second actuator can be driven by a second electric actuator motor.

[0017] During normal braking operation, the first and second drive wheels advantageously rotate synchronously. This can be achieved, on the one hand, by driving the first and second drive wheels with synchronized drive torques by the first and second actuators. 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 idly 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 immobilizing 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 that is greater than the clutch torque. This rotates the second drive wheel relative to the first drive wheel, and by actuating the second actuator, the air gap can be continuously and precisely adjusted, so that continuously progressive wear of the brake element or brake pad can be optimally compensated.

[0018] It is advantageous that the first drive wheel and the second drive wheel are torque-locked by the friction clutch to create a synchronous drive. Synchronous drive of the two drive wheels by the servomotors is not required. Any torque differences can be compensated within specified tolerances.

[0019] 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 drive 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 opposite to the spring force. This results in a relatively high clutch torque. If, however, only the second drive wheel is rotated to adjust the air gap, the spring force alone acts, so that a lower clutch torque is set. This facilitates the adjustment of the air gap.

[0020] The braking system for a motor vehicle further proposed to achieve the object mentioned above 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 designed to provide a wheel speed to the assigned braking device, wherein the braking devices each comprise a brake actuator having at least one electric servomotor. A wheel brake control unit for controlling the respective brake actuator is assigned to each braking device, 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.Advantageously, in the event of a malfunction in the provision of the wheel speed, control can continue, specifically using the substitute wheel speed instead of the actual wheel speed. This increases reliability at low cost. Particularly advantageously, the braking system is designed for operation according to a method according to the invention.

[0021] 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.

[0022] 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 disc. 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).

[0023] Advantageously, the braking system comprises at least two wheel brake control units separate from the central control unit. These can be electrically controlled by the central control unit using control signals. By providing at least two wheel brake control units, each associated with a braking device and connected to a brake actuator, 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.

[0024] Each wheel brake control unit can be controlled by the central control unit with target braking values ​​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 decentralized brake control. This enables simpler and shorter cabling, particularly from 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 manufacturing and assembly costs. Furthermore, sensitivity to external interference can be reduced.The decentralized design of the brake control allows for greater redundancy, thus further increasing operational reliability.

[0025] A wheel brake control unit can preferably be integrated with the braking device. This allows for a compact, safe, and easy-to-install design. 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, or in a two-wheeled vehicle with two braking devices, two wheel brake control units can be provided.

[0026] It is preferred that a wheel brake control unit is connected to at least one brake actuator. A wheel brake control unit ensures the control of the brake actuator(s) with a defined target control signal in order to generate a defined braking torque for the wheel assigned to the respective braking device.

[0027] It is advantageous for each of the wheel brake control units to be connected to an electric actuator. The wheel brake control unit can control the actuator with electrical target control values ​​of the control current. Two or more actuators of a braking device can also be connected to one wheel brake control unit.

[0028] 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 respective wheel to be braked, in particular a wheel speed sensor unit. This can be designed to detect parameters (actual values) relevant to a braking operation, in particular wheel position, wheel speed, vehicle speed, and / or slip, and to transmit 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 braking 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 need for the central control unit means that operational reliability and redundancy can be increased.

[0029] 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 other sensor device with the target values ​​of a braking command transmitted from the central control unit to the wheel brake control unit and controls the servomotor(s) of the brake actuator accordingly to achieve the target values.

[0030] 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 along an axis by the actuating device 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 clutch device is arranged between the first drive wheel and the second drive wheel, wherein the clutch device is preferably designed as a friction clutch with a friction element that can be frictionally connected to a counter-friction element in clutch engagement.

[0031] Further advantageous details, features, and design details of the invention are explained in more detail in connection with the exemplary embodiments shown in the figures (hereinafter referred to as Figure).

[0032] Fig. 1 shows an embodiment of a braking system of a motor vehicle designed according to the invention in a schematic, isolated representation;

[0033] Fig. 2a shows a schematic representation of another exemplary embodiment of a braking system designed according to the invention in normal operation; Fig. 2b shows a schematic representation of the exemplary embodiment of a braking system designed according to the invention according to Fig. 2a in the event of a malfunction;

[0034] Fig. 3 shows a schematic perspective view of an embodiment of a braking device of a braking system designed according to the invention;

[0035] Fig. 4 is a side view of the braking device according to Fig. 3;

[0036] Fig. 5 shows a section QQ through the braking device according to Fig. 3;

[0037] Fig. 6 shows a first actuator of the braking device according to Fig. 3 in a schematic perspective view; and

[0038] Fig. 7 is an enlarged detailed view of the adjusting device from Fig. 5.

[0039] In the various figures, identical parts are generally provided with the same reference symbols and are therefore sometimes explained only in connection with one of the figures.

[0040] 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 pivoting steering knuckles 103. In this exemplary embodiment, a steering system of the motor vehicle comprises a steering shaft 104, at 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.

[0041] 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, wherein the brake pedal 113 is a manual input unit for transmitting a braking command. The brake pedal 113 is shown only schematically in Fig. 1. Furthermore, in this exemplary embodiment, the braking system 110 comprises an automated input unit 114 connected to a central control unit 112 of the braking system 110. This input unit 114 can output external control signals for controlling the braking system 110 to the central control unit 112. 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. This braking device 1 has a brake caliper 3, which is attached to and supported on the motor vehicle body 102.A brake disc 2 is rotatably mounted on each wheel 101 as a counter-brake component, which is gripped by the brake caliper 3, which is fixed relative to the wheel 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 associated braking device 1 with a wheel speed of the associated 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 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 be discussed in more detail 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 in Fig. 1, the associated

[0042] Wheel brake control unit 120 provides 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, as a substitute wheel speed via the data transmission system 111.

[0043] 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. Furthermore, the braking system 110 in this exemplary embodiment comprises a first input unit 113 and a second input unit 114, each of which can transmit a braking command to the braking system 110 for implementation by the braking devices 1 (BUI, BU2, BU3, BU4). The input unit 114 can, in particular, be assigned to a driver assistance system and can be signal-connected to the braking system 110 via a data transmission system 111, in particular a CAN bus of the motor vehicle.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 particularly designed 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 therefrom and take it into account for the control of the respective brake actuator 4 of the braking system 110.

[0044] In the exemplary embodiment shown in Fig. 2a and Fig. 2b, each of the four braking devices 1 (BU1, 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 (S1, S2, S3, S4) is connected to each wheel brake control unit 120, which transmits actual values ​​of the rotational position and wheel speed P1, P2, P3, P4 to the respective wheel brake control unit 120 (BC1, BC2, BC3, BC4) in real time during travel in normal operation as 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.

[0045] 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 during trouble-free normal operation, as shown in Fig. 2a. Thus, for example, in trouble-free normal operation, the wheel brake control unit BC1 can receive a wheel speed PI from the wheel speed sensor 121 (S1); 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) 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 (S1).Accordingly, in normal operation, the wheel brake control unit BC2 controls the associated brake actuator 4 (BM2) to implement the transmitted braking command, taking into account the wheel speed P2 provided by the associated wheel speed sensor unit 121 (S2). Similarly, the wheel brake control units BC3 and BC4 control the associated brake actuators 4 (BM3) and 4 (BM4).

[0046] 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 P1, 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. Thus, in this exemplary embodiment, it is 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 transmitting 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.

[0047] In the normal operation illustrated 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 infer a malfunction of a sensor 121, for example in the case of deviations that exceed a tolerance threshold. In the event that a malfunction occurs with regard 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 provided substitute wheel speed EPI. Such a malfunction case is outlined in Fig. 2b with regard 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 link 135 and thus 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. By way of example, Fig. 2b also shows a diagram of a first signal Sgl as a PWM signal for a braking command with a modulated second signal Sg2 for the substitute wheel speed EPI.

[0048] Furthermore, in this exemplary embodiment, the wheel brake control units 120 (BC1, BC2, BC3, BC4) 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 from the central control unit 112. According to a variant embodiment not shown here, however, this central control unit 112 can also be omitted.

[0049] An advantageous embodiment of the brake actuator 4 is explained in further detail below with reference to Fig. 3, Fig. 4, and Fig. 5. Each 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 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.

[0050] 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 exemplary 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) rotatable about a wheel axis R. A brake caliper 3 engages around 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.

[0051] A brake actuator 4 is attached to the brake caliper 3. The brake actuator 4 comprises an adjusting device 5 that 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 adjusting 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, based on vibrations of the brake disc 2, a substitute wheel speed for a wheel speed measured by a wheel sensor unit 121. This takes advantage of the fact that the vibrations of the brake disc occur in a range between ±0.01 mm ... 1 mm (mm: millimeters) during normal operation of the braking device 1 in a moving motor vehicle.Due to mechanical coupling via the very small air gap between brake disc 2 and brake pad, which can be in the tenths 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, which will be explained below, and can therefore also detect the resulting ripple current and evaluate it with regard to a wheel speed. It can be provided that a wheel brake control unit 120 transmits a frequency of a detected ripple current and a wheel speed determined by 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 association of the frequency of the ripple current with a corresponding wheel speed. Advantageously, in the event of a failure of the wheel speed sensor unit 121, the detected frequency of the ripple current can then be used to provide the wheel brake control unit 120 with a substitute wheel speed, 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.

[0052] 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 disc 2 is arranged axially between two brake pads 31 and 32. One brake pad 31 is firmly supported on the brake caliper 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 defined by the axis A to generate the braking engagement on the brake disc 2, as indicated by the arrow in Fig. 5.

[0053] In the unactuated state of the braking device 1, the already mentioned axial air gap L is located between the brake disc 2 and the adjustable brake pad 32, which is shown schematically in Fig. 5 as exaggeratedly wide.

[0054] 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 axially coupled thereto (with respect to the axis A) and has a spindle drive.

[0055] The first actuator 6, which in the example shown is designed as a ramp bearing, comprises a drive-side cam disc 61 and an output-side cam disc 62, which are axially and rotationally fixedly supported on the brake actuator 4. Balls 63 are arranged between the cam discs 61 and 62. As can be seen in the schematically isolated view of Fig. 6, the cam discs 61 and 62 have axially opposite, ramp-like raceways 64, which are inclined to the axis A and between which balls 63 can roll. A rotation of the output-side cam disc 62, in Fig. 6 above, relative to the fixed drive-side cam disc 61 - as schematically indicated by the curved arrows - leads to a linear adjustment of the output-side cam disc 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.

[0056] The cam disk 62 is connected to a coaxial gear 65, which is designed as a spur gear and forms a drive wheel within the meaning of the invention. The gear 65 is in gear engagement with a first electric actuator 41. This enables the rotating drive of the cam disk 62 and thus 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 on the output side, 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.

[0057] 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 may, for example, have radially projecting projections or teeth that engage axially displaceably in axial slots of the hub part 74.

[0058] The gear 75, like the gear 65, can 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 actuation of the second actuator 7. The threaded spindle 71 is axially connected via a thrust bearing 43, for example, an axial roller bearing as shown, to a thrust piece 44, to which the movable brake pad 32 is attached, as can be seen in Fig. 5. The thrust piece 44 can also be referred to as a piston.

[0059] The clutch device according to the invention comprises a friction element 8, which is designed as a coaxial, conical extension extending from the cam disc 62 toward the second actuator 7. The conical extension has a conical friction surface 81 arranged externally on an outer cone. The friction element 81 can preferably be formed integrally with the cam disc 62 / spindle nut 72.

[0060] In clutch engagement, the friction element 8 is frictionally coupled to a counter-friction element 9. The conical projection axially engages a corresponding conical opening in 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 abut one another in a frictionally engaged manner, 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 axially displaceably in corresponding slots 76 in the hub part 74 or the gear 75. A spring element 93 is arranged between the gear 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 clutch torque of the friction clutch formed by the friction element 8 and the counter friction element 9.

[0061] 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 disc 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 them using 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.

[0062] 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, causing the friction clutch to slip continuously. Accordingly, the second actuator 7 is adjusted evenly, allowing the width of the air gap L to be continuously adjusted and adapted, for example, to compensate for wear on the brake pad 32.

[0063] The braking devices shown in Fig. 3 to Fig. 7 are designed as floating caliper brakes, also known 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 is movable 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.

[0064] The exemplary embodiments illustrated in the figures and explained in connection with them serve to explain the invention and are not limiting.

[0065] 1 braking device (BUI, BU2, BU3, BU4)

[0066] 100 chassis

[0067] 101 Wheel (vehicle wheel)

[0068] 102 Body

[0069] 103 Steering knuckles

[0070] 104 Steering shaft

[0071] 105 Steering wheel

[0072] 106 steering gear

[0073] 107 Tie rod

[0074] 110 Brake system

[0075] 111 Data transmission system

[0076] 112 Central control unit

[0077] 113 Brake pedal (input unit)

[0078] 114 Input unit

[0079] 120 Wheel brake control unit (BC1, BC2, BC3, BC4)

[0080] 121 Wheel speed sensor unit (SI, S2, S3, S4)

[0081] 135 Communication connection

[0082] 2 brake disc (counter brake part)

[0083] 3 brake caliper

[0084] 31, 32 Brake pad (brake part)

[0085] 4 brake actuator (BMI, BM2, BM3, BM4)

[0086] 41, 42 Actuator

[0087] 43 thrust bearings

[0088] 44 Pressure piece

[0089] 45 housings

[0090] 46 Connection device

[0091] 5 Adjusting device

[0092] 6 first actuator

[0093] 61 cam disc

[0094] 62 cam disc (integrated with spindle nut 72)

[0095] 63 ball

[0096] 64 Career

[0097] 65 Gear (first drive wheel) 7 second actuator

[0098] 71 threaded spindle

[0099] 72 spindle nut (integrated with cam disc 62)

[0100] 73 drivers

[0101] 74 Hub part

[0102] 75 gear (second drive gear)

[0103] 76 slot

[0104] 8 Friction element

[0105] 81 Friction surface

[0106] 9 Counter friction element

[0107] 91 Counter friction surface

[0108] 92 drivers

[0109] 93 spring element

[0110] Pl, P2, wheel speed

[0111] P3, P4

[0112] PI' wheel speed transmitted by a wheel brake control unit (BC1)

[0113] EPI replacement wheel speed

[0114] A axis

[0115] R wheel axle

[0116] V Adjustment direction

[0117] L Air gap

[0118] Sgl first signal

[0119] Sg2 second signal

Claims

Claims 1. 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 braking devices (1, BU), each comprising a brake actuator (4, BM) with at least one electric servomotor (41, 42), wherein a wheel brake control unit (120, BC) and a wheel speed sensor unit (121) are each assigned to the braking devices (1, BU), 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) controls the brake actuator (4, BM) taking into account the wheel speed (P) provided by the associated wheel speed sensor unit (121) 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 (EP) to implement the transmitted braking command in the event of a fault with respect to the provision of the wheel speed (P) from the associated wheel speed sensor unit (121).

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 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) is provided to the wheel brake control unit (120, BC) assigned to a braking device (1, 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 command via a communication connection (135) with the respective Wheel brake control units (120, BC) are connected, 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. The method according to claim 3, characterized in that the braking command 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 different from the first frequency range.

5. The method according to claim 3 or claim 4, characterized in that the braking command is transmitted as a first signal (Sgl) via the communication link (135) to the wheel brake control units (120, BC), and the substitute wheel speed (EP) is transmitted via the communication link (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 a 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) assigned to a braking device (1, BU) with brake disc (2) generates 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, based on the detected ripple current, the substitute wheel speed (EP) or the further substitute wheel speed (EP') is determined.

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 command is input 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 actuating motor (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 rotatably drivable first drive wheel (65) to which a first drive torque can be applied for actuation, and the second actuating drive (7) has a rotatably drivable second drive wheel (75) which 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 value is exceeded, the first drive wheel (65) slips slidingly 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 the assigned braking device (1, BU) with a wheel speed (P), 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 associated wheel speed sensor unit (121), and is further designed to control the brake actuator (4) taking into account a substitute wheel speed (EP) for the wheel speed (P) provided by the associated wheel speed sensor unit (121).

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 to be connected 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.

Images