Patent Publication Number: US-2021162966-A1

Title: Motor vehicle brake system, method for operating same and control appliance therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a national stage of International Application No. PCT/EP2018/070015, filed Jul. 24, 2018, the disclosure of which is incorporated herein by reference in its entirety, and which claimed priority to German Patent Application No. 102017008948.5, filed Sep. 25, 2017, the disclosure of which is incorporated herein by reference in its entirety 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of motor vehicle brake systems in general. Specifically, the operation of a motor vehicle brake system in the event of failure of a driving dynamics regulation system is described. 
     BACKGROUND 
     Known hydraulic motor vehicle brake systems, which are configured as brake-by-wire (BBW) systems or are equipped with an electric brake boost (EBB) system, comprise an electrically controllable actuator which, in service brake mode, generates a hydraulic pressure on the wheel brakes of the motor vehicle or boosts a hydraulic pressure generated by the driver. To this end, deceleration of a vehicle, requested by the driver via a brake pedal, is sensor-detected and converted into a control signal for the electrically controllable actuator. 
     Brake systems of this type normally also comprise a master cylinder which can be mechanically actuated by means of the brake pedal and via which hydraulic fluid can likewise be delivered to the wheel brakes. The master cylinder, which can be actuated by means of the brake pedal, produces a redundancy in relation to the electrically controllable hydraulic pressure generator of the BBW or EBB system, which is vital for reasons of operational safety. Motor vehicle brake systems for autonomous or partially autonomous driving are designed with redundancy, especially since the driver is not necessarily located inside the vehicle (e.g. in remote-controlled parking—RCP—mode). 
     Modern brake systems furthermore comprise a driving dynamics regulation system (also known as electronic stability control, ESC), which comprises, for example, one or more functions such as anti-slip regulation (ASR), an anti-lock brake system (ABS) or an electronic stability program (ESP). There are demands for the driving dynamics regulation system to be designed with redundancy. In other words, at least rudimentary driving dynamics regulation should still be possible in the event of a loss of function of the driving dynamics regulation system to enable the vehicle stability or the deceleration capacity to be at least partially maintained. 
     SUMMARY 
     The present disclosure is based on the object of specifying a motor vehicle brake system which has a redundancy in the event of a loss of function of the driving dynamics regulation system. 
     According to a first aspect, a motor vehicle brake system is specified. The brake system comprises a driving dynamics regulation system, which is designed to carry out a wheel-specific regulating intervention on each of a plurality of vehicle wheels, and an electrically controllable actuator, which is designed to generate or boost a service brake force. The brake system further comprises a control, which is designed, in the event of an identified loss of function of the driving dynamics regulation system, to select one of at least two vehicle wheels on which a regulating intervention by the driving dynamics regulation system would be required in each case and to electrically control the actuator on the basis of a regulating intervention determined for the selected vehicle wheel. 
     The brake system can be a hydraulic, a pneumatic, a mechanical or a regenerative brake system. Combinations thereof are also conceivable (e.g. a hydraulic regenerative brake system). 
     The electrically controllable actuator can be part of an EBB system (for brake boosting) or a BBW system (for brake force generation). The actuator can comprise an electric motor and a transmission connected downstream of the electric motor. In a hydraulic brake system, a cylinder-piston arrangement or other device for hydraulic pressure generation can be connected downstream of the transmission. 
     In one realization, the brake system is configured as a BBW system, which comprises the actuator, and/or is equipped with an EBB system, which comprises the actuator. In one design, the brake system is provided with an electrically controllable vacuum brake booster, which functions as the actuator. 
     The BBW system can provide a constant mechanical decoupling of a brake pedal from a master cylinder of the brake system. This mechanical decoupling can be overridden in favor of mechanical push-through (PT) in the event of an error in the BBW system. 
     The EBB system (including the electrically controllable vacuum brake booster) cannot provide such a mechanical decoupling, or can only provide it in certain cases (e.g. with regenerative braking), wherein, in the case of the mechanical coupling, a force acting on the master cylinder by means of the brake pedal is boosted using the actuator. 
     The service brake force can be requested by a driver via a brake pedal. The service brake force can also be requested by a system for autonomous or partially autonomous driving. The service brake force is conventionally used for braking the moving vehicle and therefore differs functionally from the brake force generated by an emergency brake (e.g. an electric parking brake, EPB), for example. 
     The electrical control of the actuator on the basis of a regulating intervention determined for the selected vehicle wheel can comprise regulation on the basis of a parameter measured at the selected vehicle wheel. The measured parameter can also be used as a regulating variable. Such a parameter can be, for example, a wheel speed or a wheel velocity. Further or other parameters can be analyzed within the framework of the regulating intervention. 
     In one implementation, the control is designed to control the actuator on the basis of an anti-slip regulation intervention determined for the selected vehicle wheel. In the case of a hydraulic brake system, brake pressure regulation can take place for this purpose, which comprises, for example, pressure-decrease, pressure-build-up and pressure-holding phases. 
     According to one variant, the control is designed to select the vehicle wheel with the greatest slip. According to a further development, the control is designed to select the wheel with the (e.g. relatively) greatest slip, for which one or more further conditions are fulfilled. The further condition can refer, for example, to a particular vehicle side or a particular vehicle axle (e.g. front axle or rear axle). The further condition can additionally or alternatively refer to wheel-related roadway coefficients of friction. In such a further development, of all the vehicle wheels on which a regulating intervention by the driving dynamics regulation system would be required, it is not necessarily the wheel with the greatest absolute slip which is selected. 
     The control can be designed to analyze the roadway coefficients of friction associated with the vehicle wheels and to select the vehicle wheel on the basis of the roadway coefficient-of-friction analysis. The roadway coefficient of friction is also denoted by the Greek letter μ. 
     The control can therefore be designed to determine a high coefficient-of-friction side of the vehicle on the basis of the roadway coefficient-of-friction analysis and to select the vehicle wheel with the greatest slip on the high coefficient-of-friction side. The control can also be designed, when the roadway coefficients of friction at all vehicle wheels are each below a threshold value, to select the vehicle wheel with the greatest slip. The control can further be designed, when the roadway coefficients of friction at all vehicle wheels are each above a threshold value, to select a rear wheel. In the latter case, the control can be designed to carry out the regulating intervention on the selected rear wheel in such a way that, for the selected rear wheel, a coefficient-of-friction limit is prevented from being exceeded. 
     In general, the control can be designed to determine a yaw rate (e.g. by receiving a parameter indicating the yaw rate). In this case, the control can further be designed to carry out at least one of the following steps: select the vehicle wheel on the basis of the determined yaw rate and/or carry out the regulating intervention on the basis of the determined yaw rate. 
     In one variant, the control is designed to recognize oversteering on the basis of the yaw rate and to select a wheel on the inside of the turn or a rear wheel. The control can also be designed to determine understeering on the basis of the yaw rate and to select a wheel on the outside of the turn or a front wheel. 
     The control is, for example, further designed to also carry out the regulating intervention determined for the selected vehicle wheel on at least one non-selected vehicle wheel. In this case, the control can be designed, when carrying out the regulating intervention determined for the selected vehicle wheel on the at least one non-selected vehicle wheel, to permit locking of the at least one non-selected vehicle wheel. 
     In one implementation, the control is designed to identify a requirement for a regulating intervention on each of the at least two vehicle wheels. In this connection, the control can analyze one or more sensor-measured parameters and, on the basis of this analysis, identify whether or not a regulating intervention is required on a particular vehicle wheel. The regulating intervention can then be carried out with continued analysis of the one or more parameters (which then serve e.g. as regulating variable(s)). 
     The control can be designed to identify the regulating-intervention requirement on the basis of slip recognition for the respective vehicle wheel. In general, the control can be designed to identify the regulating-intervention requirement on the basis of at least one parameter measured at the respective vehicle wheel (e.g. wheel speed or wheel velocity). Additionally or alternatively, the control can be designed to identify the regulating-intervention requirement on the basis of at least one of the following parameters: yaw rate, steering angle, lateral acceleration, longitudinal acceleration, wheel speed, wheel velocity. 
     The control can further be designed to identify the loss of function of the driving dynamics regulation system. The loss of function can be identified by receiving an error signal or (alternatively) monitoring the driving dynamics regulation system. The loss of function can be caused, for example, by failure of a hydraulic, mechanical or electrical component of the driving dynamics regulation system. This includes a pump, valves etc. 
     The brake system can further comprise a control device, which is associated with the driving dynamics regulation system, and a second control device, which is associated with the electrically controllable actuator, wherein the control is implemented in the second control device. The second control device can be a control device for an electric brake booster or for a brake-by-wire system or for autonomous or partially autonomous driving. 
     A second aspect relates to a method for operating a motor vehicle brake system having a driving dynamics regulation system, which is designed for carrying out a wheel-specific regulating intervention on each of a plurality of vehicle wheels, and an electrically controllable actuator, which is designed to generate or boost a brake force. The method comprises, in the event of an identified loss of function of the driving dynamics regulation system, selecting one of at least two vehicle wheels on which a regulating intervention by the driving dynamics regulation system would be required in each case, and electrically controlling the actuator on the basis of a regulating intervention determined for the selected vehicle wheel. 
     The method can further comprise method steps which correspond to the functions of the control described here. 
     Likewise described control device or system made up of a plurality of control devices, comprising at least one processor and at least one memory, wherein the at least one memory contains program code for carrying out the method presented here when it is run on the at least one processor. The control device or system made up of a plurality of control devices is an exemplary implementation of the control described here. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further aspects, details and advantages of the present disclosure are revealed in the description below of exemplary embodiments with reference to the figures, which show: 
         FIG. 1  an exemplary embodiment of a motor vehicle brake system; 
         FIG. 2  an exemplary embodiment of a control device system for the brake system according to  FIG. 1 ; and 
         FIG. 3  a flow chart of an exemplary embodiment of a method for operating the brake system according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The hydraulic circuit diagram of an exemplary embodiment of a hydraulic motor vehicle brake system  100  is shown in  FIG. 1 . It should be pointed out that the present solution is not restricted to a hydraulic brake system, but will merely be discussed by way of example with the aid of a hydraulic brake system. 
     The brake system  100  comprises an assembly  110  for hydraulic pressure generation, which can be coupled to a brake pedal (not shown), and a hydraulic control assembly  120  (also known as a hydraulic control unit, HCU) with two separate brake circuits I. and II. The brake system  100  further comprises four wheel brakes. Two of the four wheel brakes  130  are associated with the brake circuit I., whilst the two wheel brakes  130  are associated with the brake circuit II. The association of the wheel brakes  130  with the brake circuits I. and II. takes place according to a diagonal allocation in such a way that the wheel brakes  130 A and  130 B at the right rear wheel (HR) and at the left front wheel (VL) are associated with the brake circuit I., whilst the wheel brakes  130 C and  130 D at the left rear wheel (HL) and at the right front wheel (VR) are associated with the brake circuit II. Any other allocation of the wheel brakes  130  to the brake circuit I. and II. would be likewise conceivable. 
     In the present exemplary embodiment, the brake system  100  further comprises an optional electric parking brake (EPB) with two electromechanical actuators  140 A,  140 B which can be electrically controlled separately from one another. In  FIG. 1 , the actuators  140 A,  140 B are each merely indicated in the form of an electric motor. It goes without saying that the actuators  140 A,  140 B comprise further components, for example a transmission, via which the actuators  140 A,  140 B act for example on brake cylinders. 
     The two actuators  140 A,  140 B are associated with different wheel brakes of the four wheel brakes  130 . Specifically, the actuator  140 A is associated with the wheel brake  130 A of the right rear wheel (HR), whilst the actuator  140 B is associated with the wheel brake  130 C of the left rear wheel (HL). Of course, in other variants, the two actuators can also be associated with the wheel brakes  130 B,  130 D of the right front wheel (VR) and the left front wheel (VL). 
     The assembly  110  for hydraulic pressure generation comprises a master cylinder  110 A and can be operated according to the EBB and/or the BBW principle. This means that, incorporated in the assembly  110 , there is an electrically controllable actuator in the form of a hydraulic pressure generator  110 B which is designed to boost or generate a hydraulic pressure for at least one of the two brake circuits I. and II. This hydraulic pressure generator  110 B comprises an electric motor, which acts directly or indirectly on the master cylinder  110 A for hydraulic pressure generation via a mechanical transmission (not shown). Indirect action can take place for example hydraulically (for instance, in that the transmission acts on a plunger arrangement whereof the output is hydraulically coupled to an input of the master cylinder  110 A). 
     The HCU  120  comprises a driving dynamics regulation system (also referred to as an ESC system) for carrying out regulating interventions on the wheel brakes  130 , which, in the present example, is designed with two circuits. In other exemplary embodiments, the driving dynamics regulation system can also be designed in a known manner, with one circuit. 
     Specifically, the two-circuit driving dynamics regulation system according to  FIG. 1  comprises a first electrically controllable hydraulic pressure generator  160  in the first brake circuit I. and a second electrically controllable hydraulic pressure generator  170  in the second brake circuit II. Each of the two hydraulic pressure generators  160 ,  170  comprises an electric motor  160 A,  170 B and a pump  160 B,  170 B which can be actuated by the electric motor  160 A,  170 B. Each of the two pumps  160 B,  170 B can be designed as a multi-piston pump, as a gear pump or in another manner. Each pump  160 B,  170 B has a blocking action contrary to its delivery direction, as illustrated with the aid of the blocking valves at the output and input of the pumps  160 B,  170 B. Since the speed of each of the electric motors  160 A,  170 A is adjustable, the delivery quantity of each of the pumps  160 B,  170 B can also be adjusted by controlling the associated electric motor  160 A,  170 A accordingly. 
     The two electric motors  160 A,  170 A—and therefore the two hydraulic pressure generators  160 ,  170 —can be controlled independently of one another. This means that each of the two hydraulic pressure generators  160  and  170  can build up a hydraulic pressure independently of the other hydraulic pressure generator  170  or  160  in the respective brake circuit I. or II. This redundancy is advantageous in relation to safety considerations. 
     The brake system  100  operates by means of a hydraulic fluid, which is partly stored in three reservoirs  110 C,  190 ,  200 . Whilst the reservoir  110 C is an unpressurized reservoir, which forms part of the assembly  110 , the other two reservoirs  190 ,  200  are each integrated as pressure accumulators (e.g. as low pressure accumulators, LPA) in one of the two brake circuits I., II. The two hydraulic pressure generators  160  and  170  are each capable of sucking hydraulic fluid out of the associated reservoir  190  or  200  or out of the central reservoir  110 C. 
     The reservoir  110 C has a greater capacity than each of the two reservoirs  190 ,  200 . However, the volume of the hydraulic fluid stored in each of the two reservoirs  190 ,  200  is at least sufficient to enable a vehicle to also be brought safely to a stop in the event of a required brake pressure regulation on one or more of the wheel brakes  130  (e.g. in the event of ABS-assisted emergency braking). 
     The brake circuit I. comprises a hydraulic pressure sensor  180 A, which is arranged on the input side of the brake circuit I. in the region of its interface with the assembly  110 . The signal of the hydraulic pressure sensor  180 A can be analyzed in association with a control of the hydraulic pressure generator  110 B integrated in the assembly  110  and/or the hydraulic pressure generator  160  integrated in the brake circuit I. The analysis and control takes place by means of a control device system  300  shown merely schematically in  FIG. 1 . A further hydraulic pressure sensor  180 B is integrated accordingly in the brake circuit II. 
     As shown in  FIG. 1 , the two brake circuits I. and II. are constructed identically in terms of the components integrated therein and the arrangement of these components. For this reason, only the construction and the mode of operation of the first brake circuit I. will be explained in more detail below. 
     In the brake circuit I., a plurality of valves which can be actuated by electromagnets are provided, which, in the unactuated, i.e. electrically non-controlled state, assume the basic positions illustrated in  FIG. 1 . In these basic positions, the valves couple the assembly  110 , in particular the master cylinder  110 A, to the wheel brakes  130 . Therefore, even in the event of a loss of function (e.g. a failure) of the energy supply and an associated failure of the hydraulic pressure generator  110 B, the driver can still build up a hydraulic pressure on the wheel brakes  130  by means of the brake pedal acting on the master cylinder  110 A. However, in the case of an EBB implementation, this hydraulic pressure is then not boosted or, in the case of a BBW implementation, a mechanical coupling of the brake pedal to the master cylinder  110 A takes place (push-through, PT, mode). In BBW mode, on the other hand, the master cylinder  110 A is fluidically decoupled from the brake circuit I. in a known manner. 
     The multiplicity of valves comprises two 2/2-way valves  210 ,  220 , which permit an uncoupling of the two wheel brakes  130 A and  130 B from the assembly  110 . Specifically, the valve  210  is provided to uncouple the wheel brakes  130 A,  130 B from the assembly  110  in the electrically controlled state when, by means of the hydraulic pressure generator  160 , a regulating intervention is carried out on at least one of the two wheel brakes  130 A,  130 B. In its electrically controlled state, the valve  220  enables hydraulic fluid to be sucked or fed out of the reservoir  110 C (e.g., in the case of a sustained regulating intervention, if the reservoir  190  is to be emptied completely). A decrease in pressure at the wheel brakes  130 A,  130 B is further possible in this electrically controlled state, in that a return flow of hydraulic fluid from the wheel brakes  130 A,  130 B into the unpressurized reservoir  110 C is enabled. 
     The hydraulic connection of the wheel brakes  130 A,  130 B to the assembly  110  and the hydraulic pressure generator  160  is determined by four 2/2-way valves  230 ,  240 ,  250 ,  260  which, in the unactuated, i.e. electrically non-controlled state, assume the basic positions illustrated in  FIG. 1 . This means that the two valves  230  and  260  each assume their throughflow position, whilst the two valves  240  and  250  each assume their blocking position. The two valves  230  and  240  form a first valve arrangement associated with the wheel brake  130 B, whilst the two valves  250  and  260  form a second valve arrangement associated with the wheel brake  130 A. 
     As explained below, the two valves  210  and  220 , the two valve arrangements  230 ,  240  and  250 ,  260  and the hydraulic pressure generator  160  are each designed to be controlled for wheel brake pressure-regulating interventions on the respective wheel brake  130 A,  130 B. The control of the two valves  210  and  220 , the two valve arrangements  230 ,  240  and  250 ,  260  and the hydraulic pressure generator  160  within the framework of the regulating interventions takes place by means of the control device system  300 . The control device system  300  implements, for example, the wheel brake pressure-regulating interventions of driving dynamics regulation, wherein the driving dynamics regulation according to the present disclosure also includes an anti-lock brake system (ABS) and/or anti-slip regulation (ASR) and/or an electronic stability program (EPB) and/or brake pressure regulation for adaptive cruise control (ACC). 
     Anti-lock regulation involves preventing the wheels from locking during braking. To this end, it is necessary to modulate the hydraulic pressure in the wheel brakes  130 A,  130 B individually. This takes place by adjusting successively alternating pressure-build-up, pressure-holding and pressure-decrease phases, which are realized by suitably controlling the valve arrangements  230 ,  240  and  250 ,  260  associated with the two wheel brakes  130 B and  130 A and possibly the hydraulic pressure generator  160 . 
     During a pressure-build-up phase, the valve arrangements  230 ,  240  and  250 ,  260  each assume their basic position, so that an increase in the brake pressure in the wheel brakes  130 A,  130 B (as in the case of BBW braking) can take place by means of the hydraulic pressure generator  160 . For a pressure-holding phase at one of the wheel brakes  130 B and  130 A, only the valve  230  or  260  is controlled, i.e. brought into its blocking position. Since control of the valve  240  or  250  does not take place in this case, it remains in its blocking position. The corresponding wheel brake  130 B or  130 A is thus hydraulically uncoupled so that a hydraulic pressure applied in the wheel brake  130 B or  130 A is held constant. In a pressure-decrease phase, both the valve  230  or  260  and the valve  240  or  250  are controlled, i.e. the valve  230  or  260  is brought into its blocking position and the valve  240  or  250  is brought into its throughflow position. Hydraulic fluid can therefore flow out of the wheel brake  130 B or  130 A in the direction of the reservoir  110 C and  190  in order to lower a hydraulic pressure applied in the wheel brake  130 A or  130 B. 
     Other regulating interventions in normal braking mode take place in an automated manner and typically independently of an actuation of the brake pedal by the driver. Such automated regulations of the wheel brake pressure take place, for example, in association with anti-slip regulation, which prevents individual wheels from spinning during a starting procedure via targeted braking, driving dynamics regulation in a narrower sense, which adapts the vehicle behavior in the limit range to the driver request and the roadway conditions via targeted braking of individual wheels, or adaptive cruise control, which, amongst other things, maintains a distance between the vehicle in question and a vehicle in front via automatic braking. 
     When executing automatic hydraulic pressure regulation, a hydraulic pressure can be built up on at least one of the wheel brakes  130 A or  130 B by controlling the hydraulic pressure generator  160 . In this case, the valve arrangements  230 ,  240  or  250 ,  260  associated with the wheel brakes  130 B,  130 A hydraulic pressure generator  160  firstly assume their basic positions shown in  FIG. 1 . Fine adjustment or modulation of the hydraulic pressure can be undertaken by controlling the hydraulic pressure generator  160  and the valves  230 ,  240  or  250 ,  260  associated with the wheel brakes  130 B or  130 A accordingly, as explained by way of example above in association with the ABS regulation. 
     The hydraulic pressure regulation takes place by means of the control device system  300  generally depending, on the one hand, on sensor-detected parameters (e.g. wheel speeds, yaw rate, lateral acceleration, etc.) describing the vehicle behavior and, on the other hand, sensor-detected parameters (e.g. actuation of the brake pedal, steering-wheel angle, etc.) describing the driver request, where present. A deceleration request by the driver can be identified, for example, by means of a position sensor, which is coupled to the brake pedal or an input element of the master cylinder  110 A. As the measured variable describing the driver request, it is alternatively or additionally possible to use the brake pressure generated in the master cylinder  110 A by the driver, which is then detected by means of the sensor  180 A (and the corresponding sensor  180 B associated with the brake circuit II.) and possibly plausibility-checked. The deceleration request can also be initiated by a system for autonomous or partially autonomous driving. 
       FIG. 2  shows an exemplary embodiment of the control device system  300  of  FIG. 2 . As shown in  FIG. 2 , the control device system  300  comprises a first control device  302 , which is designed to control the hydraulic pressure generator  160  and the EPB actuator  140 A, and a second control device  304 , which is designed to control the hydraulic pressure generator  170  and the EPB actuator  140 B. As explained in association with  FIG. 1 , this control can take place on the basis of a multiplicity of sensor-detected measured variables. In another exemplary embodiment, the two control devices  302  and  304  could also be combined to form a single control device, in particular in the case of a one-circuit configuration of the driving dynamics regulation system. 
     In the exemplary embodiment according to  FIG. 2 , the two control devices  302  and  304  are designed as a spatially cohesive control device unit  306 . The two control devices  302  and  304  can therefore be accommodated in a common housing, but comprise separate processors  302 A,  304 A for processing the measured variables and for controlling the respectively associated components  140 A,  160  and  140 B,  170 . For data exchange, for example in association with the plausibility-checking of measured variables and/or control signals, the corresponding processors  302 A,  304 A of the two control devices  302 ,  304  are communicatively connected to one another via a processor interface  308 . The processor interface  308  in the exemplary embodiment is designed as a serial/parallel interface (SPI). 
     The control device system  300  further comprises a third control device  310 , which is designed to control the hydraulic pressure generator  110 B integrated in the assembly  310  and therefore, in particular, the electric motor thereof. Depending on the configuration of the brake system  100 , this control can take place according to the EBB principle or the BBW principle. The control device  310  can form a spatially cohesive control device unit with the two other control devices  302  and  304 , or it can be provided at a spacing from these. In one realization, a housing of the control device  310  is integrated in the assembly  110 . In a system for autonomous or partially autonomous driving, the control device system can comprise a further control device (not illustrated in  FIG. 2 ), which implements the corresponding functions. 
     As shown in  FIG. 2 , two parallel electric supply systems K 30 - 1  and K 30 - 2  are provided in the present exemplary embodiment (in other exemplary embodiments, in particular in a one-circuit configuration of the driving dynamics regulation system, only one of these supply systems K 30 - 1  and K 30 - 2  could be present). Each of these two supply systems K 30 - 1  and K 30 - 2  comprises a voltage source and associated voltage supply lines. In the exemplary embodiment according to  FIG. 2 , the supply system K 30 - 1  is designed to supply the EPB actuator  140 A and the hydraulic pressure generator  160 , whilst the parallel supply system K 30 - 2  is designed to supply the other EPB actuator  140 B and the hydraulic pressure generator  170 . In another exemplary embodiment, the EPB actuator  140 A and the hydraulic pressure generator  160  could additionally (i.e. redundantly) be supplied by the supply system K 30 - 2 , and the EPB actuator  140 B and the hydraulic pressure generator  170  could additionally be supplied by the supply system K 30 - 1 . The system redundancy is thus further increased. 
     Each of the three control devices  302 ,  304  and  310  (and an optional control device for autonomous or partially autonomous driving), is supplied redundantly both via the supply system K 30 - 1  and via the supply system K 30 - 2 . To this end, each of the control devices  302 ,  304 ,  310  can be provided with two separate supply connections, which are each associated with one of the two supply systems K 30 - 1  and K 30 - 2 . 
     As further shown in  FIG. 2 , two parallel communication systems Bus 1  and Bus 2  are provided redundantly, which, in the exemplary embodiment, are each designed as a vehicle bus (e.g. according to the CAN or LIN standard). The three control devices  302 ,  304  and  310  (and an optional control device for autonomous or partially autonomous driving) can communicate with one another via each of these two communication systems Bus 1 , Bus 2 . In another exemplary embodiment, only one bus system (e.g. Bus 1 ) could be provided. 
     In the exemplary embodiment according to  FIG. 2 , the control of the components  140 A,  160  and  140 B,  170  takes place by means of the two control devices  302  and  304  and the control of the hydraulic pressure generator  110 B integrated in the assembly  110  takes place by means of the control device  310  (or by means of the optional control device for autonomous or partially autonomous driving) in such a way that the corresponding control device  302 ,  304 ,  310  switches the power supply for the corresponding component on or off and possibly modulates it (e.g. via pulse-width modulation). In another exemplary embodiment, one or more of these components, in particular the EPB actuators  140 A,  140 B can be connected to one or both of the communication systems Bus 1 , Bus 2 . In this case, the control of these components by means of the associated control device  302 ,  304 ,  310  then takes place via the corresponding communication system Bus 1 , Bus 2 . In this case, the corresponding component can further be continuously connected to one or both of the supply systems K 30 - 1 , K 30 - 2 . 
     An exemplary embodiment of a method for operating the brake system  100  according to  FIG. 1  is explained below with reference to the flow chart  400  according to  FIG. 3 . The method can be carried out by means of the control device system  300  illustrated in  FIG. 2  or a control device system configured in another manner. In particular, the method (e.g. as a program code forming the basis of the method) can be implemented in the control device  310  and/or a control device (not illustrated in  FIG. 2 ) for autonomous or partially autonomous driving. 
     The method begins in step  402  with the identification of a loss of function of the driving dynamics regulation system. For example, a loss of function (including a failure) of one of the two control devices  302 ,  304  (or both control devices  302 ,  304 ) can therefore be identified. A loss of function (including a failure) of one of the two (or both) hydraulic pressure generators  160 ,  170  can also be identified in step  402 . It goes without saying that, in the case of a one-circuit driving dynamics regulation system, only one control device  302  or  304  and only one hydraulic pressure generator  160  or  170  will be present, which means that a loss of function thereof is all the more serious. The loss of function can be identified, for example, in that the corresponding control device  302 ,  304  no longer communicates at all or in that the corresponding control device  302 ,  304  communicates an error message. The error message can be attributed, for example, to the loss of function of one of the hydraulic pressure generators  160 ,  170  or one of the valves shown in  FIG. 1 . 
     After identifying the loss of function in step  402  (or previously or at the same time), it is identified in step  404  that a regulating intervention is required at two or more of the vehicle wheels VL, HR, VR, HL (c.f.  FIG. 1 ). The identification of a regulating-intervention requirement at the respective wheel can take place by analyzing wheel signals (e.g. wheel speeds or wheel velocities). The wheel signals can be received by the control device  310 , for example via the bus system Bus 1 . If available, further parameters can be additionally or alternatively used for recognizing the regulating-intervention requirement (e.g. yaw rate, steering angle, lateral acceleration and/or longitudinal acceleration). These further parameters can also be received, for example, via the bus system Bus 1 . 
     In step  404 , a slip calculation is, in particular, carried out on the basis of the wheel signals. The slip calculation is based on the calculation of a deviation of an individual wheel velocity from the vehicle velocity. The vehicle velocity can be determined with the aid of the wheel velocity of a slip-free wheel or in another manner (e.g. on the basis of a satellite-based positioning system). 
     A roadway coefficient of friction for each wheel can further take place via the wheel velocities, the yaw rate or both in step  404  in order to identify a regulating-intervention requirement. It is thus possible, in particular, for different roadway coefficients of friction on different vehicle sides to be identified (i.e. a so-called split μ identification can be carried out). Vehicle stability identification (e.g. according to an ESP) can further be identified in step  404  based on the yaw rate (if available) in order to identify a regulating-intervention requirement. 
     As already mentioned, the steps  402  and  404  can be carried out in any order or also at the same time. 
     If, in step  404 , a plurality of vehicle wheels are determined at which a regulating intervention is to be carried out (e.g. since it has been identified that a slip threshold value has been exceeded for a plurality of vehicle wheels), a selection of one of these vehicle wheels takes place in step  406 . Specifically, the vehicle wheel selected is the one at which a regulating intervention promises the best results in terms of vehicle safety. The background to this selection is the fact that, with a loss of function of the driving dynamics regulation system, multi-channel regulating interventions are usually no longer possible. Multi-channel regulating interventions are understood to be those regulating interventions which take place at two or more vehicle wheels at the same time. However, the option of a one-channel regulating intervention by means of the actuator, which is conventionally used for (“one-channel”) service braking, is instead available. In the brake system according to  FIG. 1 , this is the hydraulic pressure generator  100 B comprising the electric motor. Of course, in the driving dynamics regulation system according to  FIG. 1 , which is designed with two circuits, it may be that there is only a loss of function of one of the two regulating circuits, which means that the selection in step  406  can be restricted to the two vehicle wheels of the affected regulating circuit. 
     For more sustained regulation, the selection according to step  406  can be also be repeated once or a plurality of times in order to select different wheels in succession. However, it may also be that the selection in step  406  selects the same vehicle wheel a plurality of times. 
     After one of the affected vehicle wheels has been selected in step  406 , control of the actuator, such as the hydraulic pressure generator  1006  according to  FIG. 1 , which comprises the electric motor, takes place in step  408  on the basis of a regulating intervention determined for the selected vehicle wheel. It should be pointed out that the regulating intervention determined for the selected vehicle wheel can also act on one or more vehicle wheels other than the selected vehicle wheel (or the associated wheel brake  130 ) since more than one wheel brake  130  can be fluidically coupled to the hydraulic pressure generator  1006 . However, in this case, for example, locking of the non-selected wheel can be taken into account. If, for example, an anti-slip regulation intervention, which relates to the slip prevailing at the selected vehicle wheel, is carried out, the hydraulic pressure adjusted in this case by the actuator can lead to locking of one or more non-selected vehicle wheels (irrespective of whether a regulating intervention is even required there). 
     In the hydraulic brake system  100  according to  FIG. 1 , the regulating intervention can, in general, comprise hydraulic pressure regulation. 
     Several selection options according to step  406  and (one-channel) control options according to step  408  are listed in the table below. The slip and coefficient-of-friction recognition can be carried out on the basis of wheel signals. The regulating procedure can likewise be carried out on the basis of wheel signals. If one or more further parameters are available, for example the yaw rate, these can be taken into account both for the wheel selection and for the regulation. 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                   
                 Selection/regulating 
               
               
                 Identified situation 
                 Strategy 
                 intervention 
               
               
                   
               
             
            
               
                 Split μ, high coefficient- 
                 Guiding wheels on right 
                 Only the right high 
               
               
                 of-friction side on the 
                 side. If available, the 
                 coefficient-of-friction wheels 
               
               
                 right, e.g. identified via 
                 stability observation via 
                 are observed, wherein the 
               
               
                 exceeded limit value 
                 yaw rate can limit build- 
                 high coefficient-of-friction 
               
               
                   
                 up of brake pressure. 
                 wheel with the greatest slip 
               
               
                   
                   
                 is selected. If the yaw rate 
               
               
                   
                   
                 is available, this is 
               
               
                   
                   
                 additionally used for 
               
               
                   
                   
                 pressure regulation in 
               
               
                   
                   
                 relation to the right high- 
               
               
                   
                   
                 coefficient-of-friction side. 
               
               
                   
                   
                 Locking of individual, non- 
               
               
                   
                   
                 selected wheels can be 
               
               
                   
                   
                 accepted. 
               
               
                 Split μ, high coefficient- 
                 Guiding wheels on left 
                 Only the left high 
               
               
                 of-friction side on the left, 
                 side. If available, the 
                 coefficient-of-friction wheels 
               
               
                 e.g. identified via 
                 stability observation via 
                 are observed, wherein the 
               
               
                 exceeded limit value 
                 yaw rate can limit build- 
                 high coefficient-of-friction 
               
               
                   
                 up of brake pressure 
                 wheel with the greatest slip 
               
               
                   
                   
                 is selected. If the yaw rate 
               
               
                   
                   
                 is available, this is 
               
               
                   
                   
                 additionally used for 
               
               
                   
                   
                 pressure regulation of the 
               
               
                   
                   
                 left high-coefficient-of- 
               
               
                   
                   
                 friction side. Locking of 
               
               
                   
                   
                 individual, non-selected 
               
               
                   
                   
                 wheels can be accepted. 
               
               
                 Homogeneous high 
                 Deceleration regulation 
                 Only the rear axle is 
               
               
                 coefficient of friction μ, 
                 via wheel pressure. 
                 observed, wherein the 
               
               
                 e.g. identified via 
                 Regulation to target 
                 coefficient-of-friction limit 
               
               
                 comparison with high 
                 deceleration e.g. 6 m/s 2 . 
                 should be prevented from 
               
               
                 coefficient-of-friction limit 
                   
                 being exceeded in a pre- 
               
               
                 value 
                   
                 controlled manner. To this 
               
               
                   
                   
                 end, e.g. the rear wheel 
               
               
                   
                   
                 which is closest to the 
               
               
                   
                   
                 coefficient-of-friction limit is 
               
               
                   
                   
                 selected (optionally 
               
               
                   
                   
                 periodically or continuously). 
               
               
                   
                   
                 Regulation takes place via 
               
               
                   
                   
                 the vehicle deceleration. 
               
               
                   
                   
                 Therefore, a further 
               
               
                   
                   
                 increase in pressure upon 
               
               
                   
                   
                 attaining e.g. 6 m/s 2  is 
               
               
                   
                   
                 prevented. Locking of 
               
               
                   
                   
                 individual non-selected 
               
               
                   
                   
                 wheels can be accepted. 
               
               
                 Homogeneous 
                 Four-wheel “Select Low” 
                 The wheel with the greatest 
               
               
                 low/average coefficient of 
                 regulation 
                 slip pushes through. The slip 
               
               
                 friction μ, e.g. identified 
                   
                 component of all wheels is 
               
               
                 via comparison with 
                   
                 monitored so that a 
               
               
                 suitable coefficient-of- 
                   
                 coefficient-of-friction 
               
               
                 friction limit value 
                   
                 transition to split μ can be 
               
               
                   
                   
                 identified (see above). If 
               
               
                   
                   
                 individual wheels go into slip 
               
               
                   
                   
                 too infrequently or never go 
               
               
                   
                   
                 into slip, the slip phase and 
               
               
                   
                   
                 slip depth of the regulated 
               
               
                   
                   
                 wheel can be increased to 
               
               
                   
                   
                 give the “too stable” wheels 
               
               
                   
                   
                 a greater brake torque. 
               
               
                 Oversteering identified 
                 Guiding wheels are 
                 Only the wheels on the 
               
               
                 (yaw rate available) 
                 wheels only on the inside 
                 inside of the turn are 
               
               
                   
                 of the turn or only rear 
                 regulated in terms of slip, 
               
               
                   
                 wheels. 
                 wherein the wheel wheel 
               
               
                   
                   
                 with the greatest slip on the 
               
               
                   
                   
                 inside of the turn can be 
               
               
                   
                   
                 selected. If desirable, the 
               
               
                   
                   
                 strategy “only regulate the 
               
               
                   
                   
                 rear wheels in terms of slip” 
               
               
                   
                   
                 can be implemented and, 
               
               
                   
                   
                 for example, the rear wheel 
               
               
                   
                   
                 with the greatest slip can be 
               
               
                   
                   
                 selected. As an option, the 
               
               
                   
                   
                 attained minimum vehicle 
               
               
                   
                   
                 deceleration is monitored 
               
               
                   
                   
                 and the pressure regulation 
               
               
                   
                   
                 is adapted to possibly 
               
               
                   
                   
                 prevent underbraking. 
               
               
                   
                   
                 Locking of individual non- 
               
               
                   
                   
                 selected wheels can be 
               
               
                   
                   
                 accepted. 
               
               
                 Understeering identified 
                 Guiding wheels are 
                 Only the wheels on the 
               
               
                 (yaw rate available) 
                 wheels only on the 
                 outside of the turn are 
               
               
                   
                 outside of the turn or 
                 regulated in terms of slip, 
               
               
                   
                 only front wheels. 
                 wherein the wheel wheel 
               
               
                   
                   
                 with the greatest slip on the 
               
               
                   
                   
                 outside of the turn can be 
               
               
                   
                   
                 selected. If desirable, the 
               
               
                   
                   
                 strategy “only regulate the 
               
               
                   
                   
                 front wheels in terms of 
               
               
                   
                   
                 slip” can be implemented 
               
               
                   
                   
                 and, for example, the front 
               
               
                   
                   
                 wheel with the greatest slip 
               
               
                   
                   
                 can be selected. As an 
               
               
                   
                   
                 option, the attained 
               
               
                   
                   
                 minimum vehicle 
               
               
                   
                   
                 deceleration is monitored 
               
               
                   
                   
                 and the pressure regulation 
               
               
                   
                   
                 is adapted to possibly 
               
               
                   
                   
                 prevent underbraking. 
               
               
                   
                   
                 Locking of individual non- 
               
               
                   
                   
                 selected wheels can be 
               
               
                   
                   
                 accepted.