Braking system and method for operating a braking system

Abstract

A braking system (10) for a vehicle is specified, wherein the braking system (10) is designed for the selective pressurization and pressure relief of at least two pressure connections (12a, 12b, 12c, 12d) for brake actuators (14a, 14b, 14c, 14d). The braking system (10) comprises an electrofluidic braking module (16) with an electrically actuatable pressure generating unit (18), a master cylinder module (26) comprising a fluidic brake master cylinder (28) actuatable by a brake pedal (38), wherein the electrofluidic braking module (16) and the master cylinder module (26) are coupled to the pressure connections (12a, 12b, 12c, 12d) via at least one selection valve (44, 46).The brake system (10) further comprises a control unit (64) configured to control the electrofluidic brake module (16) and the at least one selection valve (44, 46) to apply pressure to the pressure connections (12a, 12b, 12c, 12d) and to control the electrofluidic brake module (16) to increase a fluid pressure in the master cylinder module (26) while the at least one selection valve (44, 46) is in the first switching position. Furthermore, a method for operating a brake system (10) is specified.

Description

[0001] The invention relates to a braking system for a vehicle and a method for operating a braking system.

[0002] The braking system is designed for the selective application and depressurization of at least two pressure connections for brake actuators, wherein each pressure connection can be coupled to an associated brake actuator of a wheel of the vehicle. The braking system comprises an electrofluidic brake module with an electrically actuated pressure generation unit, wherein the electrofluidic brake module is fluidly coupled to all pressure connections at least in a normal operating mode, such that the pressure connections can be selectively pressurized and depressurized. The braking system further comprises a master cylinder module comprising a fluidic brake master cylinder that can be actuated by the brake pedal, wherein the master cylinder module is fluidly coupled to all pressure connections in a fallback mode, such that the pressure connections can be selectively pressurized and depressurized.

[0003] Such braking systems are known from the prior art. A brake actuator, for example, is a brake caliper that interacts with a brake disc. The brake actuator, in particular, has a fluidic slave cylinder.

[0004] In a normal operating mode, i.e. in an operating mode in which there are no defects or malfunctions in the braking system, the pressure connections are either pressurized or relieved of pressure by means of the electrofluidic braking module.

[0005] If driver interaction is intended in this normal operating mode, in particular if a driver command is to be queried in this normal operating mode, the master cylinder module also participates. However, the master cylinder module and in particular the brake pedal serve only to detect the driver command. In this context, the master cylinder module interacts with a known simulator unit designed to generate a restoring force on the brake pedal. The master cylinder module is not fluidically coupled to the pressure ports in normal operating mode. Such a normal operating mode is used in particular in combination with a non-autonomous operating mode of an assigned vehicle.

[0006] In this context, due to the lack of fluidic coupling between the master cylinder module and pressure connections, one also speaks of a brake-by-wire system or brake-by-wire operation.

[0007] In the event that driver interaction is not desired or not planned in normal operating mode, the master cylinder module's involvement is not required. Such a normal operating mode is used in particular in combination with an autonomous or semi-autonomous operating mode of an associated vehicle.

[0008] When the braking system is started by a driver turning on the ignition, the master cylinder module is initially connected to the pressure ports. In this state, the driver may be standing on the brake pedal, which causes hydraulic fluid to be pumped to the pressure ports. If, after the start-up process has been completed and the brake pedal is depressed, the connection from the master cylinder module to the pressure ports is closed, there is a hydraulic fluid deficit in the master cylinder module, which means that the brake pedal must first be depressed a certain amount during braking before a counterforce generated by the simulator unit can be perceived on the brake pedal. In this context, this is also referred to as pedal fallout. This can be irritating for the driver.

[0009] It is therefore an object of the present invention to provide a braking system with improved feedback behavior.

[0010] This object is achieved according to the invention by a braking system for a vehicle, wherein the braking system is designed for the selective pressurization and depressurization of at least two pressure connections for brake actuators, wherein each pressure connection can be coupled to an associated brake actuator of a wheel of the vehicle. The braking system comprises a brake pedal for detecting a driver's braking request, an electrofluidic brake module with an electrically actuated pressure generation unit, and a master cylinder module comprising a fluidic brake master cylinder that can be actuated by the brake pedal. The electrofluidic brake module and the master cylinder module are coupled to the pressure connections via at least one selection valve.In a de-energized state, the at least one selection valve is preloaded in a first switching position, in which both the electrofluidic brake module and the master cylinder module are fluidly connected to the pressure ports. In an energized state, the at least one selection valve is in a second switching position, in which the electrofluidic brake module is fluidly connected to the pressure ports and a connection from the master cylinder module to the pressure ports is blocked.

[0011] The braking system comprises a control unit configured to control the electrofluidic brake module and the at least one selection valve for pressurizing the pressure connections. The control unit is also configured to control the electrofluidic brake module to increase a fluid pressure in the master cylinder module while the at least one selection valve is in the first switching position.

[0012] By activating the electrofluidic brake module with the selector valve open, the control unit ensures that sufficient hydraulic fluid is present in the master cylinder module during a normal braking operation to ensure adequate counterforce across the entire pedal travel. In other words, pressure equalization takes place in the master cylinder module. This creates clearly perceptible feedback for the driver on the brake pedal.

[0013] The control unit is particularly configured to detect an actuation of the brake pedal and to control the electrofluidic brake module to increase the fluid pressure in the master cylinder module when the brake pedal is actuated during a start-up process of the brake system. This means that the brake pedal was already actuated while the brake system was still de-energized. The brake pedal is consequently moved back to its original position by means of the electrofluidic brake module. The driver perceives this as the brake pedal being pushed back if they continue to place their foot on the brake pedal. This resetting of the brake pedal prevents a reduced fluid pressure from prevailing in the master cylinder module.

[0014] A braking system start-up process refers to the braking system starting up when the ignition or, in the case of an electric vehicle, the start switch is activated.

[0015] In another scenario, it is conceivable that activating the electrofluidic brake module with the selection valve open during the braking system's start-up process requires an increased actuation force to operate the brake pedal, thus preventing the driver from moving the brake pedal during the start-up process. The increased actuation force is selected such that the driver can overcome the counterforce acting on the brake pedal if necessary to decelerate the vehicle.

[0016] For example, in the first switching position of the at least one selection valve, the electrofluidic brake module is fluidly connected to the pressure ports and to the master cylinder module via a check valve that blocks the flow toward the electrofluidic brake module. This allows braking pressure to build up at the pressure ports during the starting process, preventing the vehicle from rolling away during the starting process. In particular, this ensures that a braking force acts on the vehicle wheels during pressure equalization in the master cylinder module, in the event that the driver actually intended to apply braking force by pressing the brake pedal during the starting process.

[0017] According to one embodiment, a displacement sensor and / or a pressure sensor are provided, which are configured or are configured to detect a brake pedal actuation and / or a fluid pressure in the master cylinder module. The control unit is configured to stop actuation of the electrofluidic brake module when the brake pedal is in its initial position and / or when a defined fluid pressure is reached in the master cylinder module. This prevents an excessively high fluid pressure from building up in the master cylinder module.

[0018] The braking system can comprise a simulator unit which is fluidically connected to the master cylinder module and which is configured to generate a restoring force for the brake pedal, wherein a simulation valve is arranged between the simulator unit and the master cylinder module, wherein the simulation valve is preloaded in a de-energized state in a first switching position in which a fluid flow from the master cylinder module to the simulator unit is blocked, and the simulation valve is open in an energized state. The simulator unit can actively generate a restoring force perceptible on the brake pedal. Since the simulator unit can be optionally fluidically connected to or fluidically separated from the master cylinder module via the simulation valve, it is possible to determine when exactly the simulation unit is involved in generating the restoring force.

[0019] Preferably, the control unit is configured to control the simulation valve while the electrofluidic brake module is controlled to increase the fluid pressure in the master cylinder module. Thus, pressure equalization can also occur in the simulator unit by controlling the electrofluidic brake module.

[0020] The object is further achieved according to the invention by a method for operating a braking system as described above. In a first method step, the braking system is started, in particular by actuating an ignition. After restarting the braking system, the control unit controls the electrofluidic braking module while the at least one selection valve is in the first switching position, whereby hydraulic fluid is delivered to the pressure ports and to the master cylinder module. Subsequently, the control unit controls the at least one selection valve, so that the electrofluidic braking module and the master cylinder module are fluidically separated from one another, and the master cylinder module is separated from the pressure ports.

[0021] As already explained in connection with the braking system according to the invention, this ensures that sufficient hydraulic fluid is present in the master cylinder module to ensure sufficient counterforce on the brake pedal over the entire pedal travel during a braking operation.

[0022] According to one embodiment, the control unit detects whether the brake pedal is depressed during the start-up process of the braking system and activates the electrofluidic brake module while the at least one selection valve is in the first switching position. The control unit stops the activation of the electrofluidic brake module until the brake pedal is depressed again and simultaneously activates the at least one selection valve when the brake pedal has reached its initial position, thereby disconnecting the master cylinder module from the pressure ports. This means that as soon as pressure equalization is complete, the control unit disconnects the master cylinder module from the pressure ports, thereby returning the braking system to its normal operating state, so that during subsequent braking processes, the pressure at the pressure ports is varied solely by the electrofluidic brake module.

[0023] During the activation of the electrofluidic brake module, the simulation valve can be activated, which supplies hydraulic fluid to the simulation unit. This allows pressure equalization to occur in the simulation unit, as already described in connection with the braking system.

[0024] The selector valve can remain permanently activated during braking system operation from the initial activation, so that the master cylinder module is permanently disconnected from the pressure ports, requiring pressure equalization only when the braking system is started. This simplifies the electronic control of the braking system.

[0025] Only in the event of a power failure can the master cylinder module be connected to the pressure ports by eliminating the control of the selection valve, which allows hydraulic access from the master cylinder module to the pressure ports.

[0026] Further advantages and features of the invention will become apparent from the following description and from the accompanying single drawing, to which reference is made. Fig. 1 shows a braking system 10 for a vehicle.

[0027] In the illustrated embodiment, the braking system 10 is designed to be used in a vehicle having a total of four wheels.

[0028] Accordingly, the brake system 10 comprises four pressure connections 12a, 12b, 12c, 12d, which in the present case are designed as hydraulic pressure connections.

[0029] The pressure port 12a is coupled to a brake actuator 14a, which is assigned to one of the vehicle's wheels. For example, the brake actuator 14a is a front-left brake actuator.

[0030] The pressure port 12b is coupled to a brake actuator 14b, which is also assigned to one of the vehicle's wheels. For example, the brake actuator 14b is a rear right brake actuator.

[0031] The pressure port 12c is coupled to a brake actuator 14c. This is also assigned to one of the vehicle's wheels. For example, brake actuator 14c is a front right brake actuator.

[0032] The pressure port 12d is coupled to a brake actuator 14d, which is also assigned to one of the vehicle's wheels. For example, the brake actuator 14d is a rear left brake actuator.

[0033] The braking system 10 is designed to selectively apply pressure to or relieve pressure from each of the pressure ports 12a, 12b, 12c, 12d. Pressure relief refers to the removal of previously applied pressure.

[0034] In this way, the brake actuators 14a, 14b, 14c, 14d can be actuated by means of the brake system 10.

[0035] For this purpose, the braking system 10 comprises an electrofluidic braking module 16 with an electrically actuated pressure generating unit 18.

[0036] This has a pressure chamber 20 which can be selectively pressurized or relieved of pressure by means of a displaceable piston 22.

[0037] For this purpose, the piston 22 is bidirectionally coupled to an electrically actuated spindle drive 24.

[0038] Furthermore, a master cylinder module 26 is provided.

[0039] This comprises a fluidic, i.e. here hydraulic, brake master cylinder 28 with a primary piston 30 and a secondary piston 32. The primary piston 30 defines a first pressure chamber 34 within the brake master cylinder 28 and the secondary piston 32 defines a second pressure chamber 36.

[0040] The primary piston 30 and the secondary piston 32 are also displaceable within the brake master cylinder 28 by means of a brake pedal 38. In other words, the brake master cylinder 28 can be actuated by means of the brake pedal 38.

[0041] In this way, pressure can be generated or pressure can be released in the pressure chambers 34, 36.

[0042] The brake pedal 38 is used to detect a driver’s braking request.

[0043] The first electrofluidic brake module 16 and the master cylinder module 26 are both coupled to a fluid reservoir 40. This ensures that sufficient brake fluid is always available to the first electrofluidic brake module 16 and the master cylinder module 26.

[0044] The braking system 10 shown in the figures comprises two braking circuits.

[0045] A first brake circuit serves to selectively supply or relieve pressure to pressure ports 12a and 12b. A second brake circuit serves to selectively apply or relieve pressure to pressure ports 12c and 12d.

[0046] Both the electrofluidic brake module 16 and the master cylinder module 26 are designed to supply all pressure connections 12a, 12b, 12c, 12d with pressure or to relieve them of pressure.

[0047] For this purpose, a pressure output line 42 originating from the electrofluidic brake module 16 is coupled to both a first selection valve 44 and a second selection valve 46.

[0048] Furthermore, a first pressure output line 48 of the master cylinder module 26 is coupled to the first selection valve 44 and a second pressure output line 50 of the master cylinder module 26 is coupled to the second selection valve 46.

[0049] The two selection valves 44 and 46 are designed as 3 / 2-way valves. They each have two valve inlets and one valve outlet.

[0050] The selection valves 44, 46 are also switching valves.

[0051] In a currentless state, the selection valves 44, 46 are each preloaded into a first switching position in which both the electrofluidic brake module 16 and the master cylinder module 26 are fluidically connected to the pressure connections 12a, 12b, 12c, 12d.

[0052] In particular, the pressure output lines 48 and 50 are connected to the valve output when the selection valves 44, 46 are in the first switching position.

[0053] Furthermore, in this switching position of the selection valves 44, 46, the electrofluidic brake module 16 is fluidly connected to the pressure ports 12a, 12b, 12c, 12d and to the master cylinder module 26 via a check valve 51 that blocks flow toward the electrofluidic brake module 16. In other words, the valve outlet is connected to the pressure output line 42 via the check valve 51 in such a way that flow from the pressure output line 42 toward the valve outlet is possible, but flow in the opposite direction is blocked.

[0054] The selection valves 44, 46 assume a second switching position when they are actuated, e.g. energized.

[0055] When the selection valves 44, 46 are in the second switching position, the electrofluidic brake module 16 is fluidly connected to the pressure ports 12a, 12b, 12c, 12d and a connection from the master cylinder module 26 to the pressure ports 12a, 12b, 12c, 12d is blocked.

[0056] In particular, the pressure output line 42 is connected to the valve output when the selection valves 44, 46 are in the second switching position. The pressure output lines 48, 50 are each blocked.

[0057] Furthermore, a displacement sensor 53 and pressure sensors 55 are provided, which are configured to detect brake pedal actuation and fluid pressure in the master cylinder module 26. The displacement sensor 53 is arranged, for example, at a pivot point of the brake pedal 38. The pressure sensors 55 are arranged, for example, in the pressure output lines 48, 50.

[0058] Alternatively or in addition to a displacement sensor 53, a force sensor 57 may be present.

[0059] A first pressurization line 52a is connected to the valve outlet of the first selection valve 44 and is fluidically connected to the first pressure connection 12a.

[0060] An inlet valve 54a is arranged within the first pressurization line 52a.

[0061] Furthermore, a second pressurization line 52b extends from the first selection valve 44 and is connected to the pressure port 12b. An inlet valve 54b is arranged within the pressurization line 52b.

[0062] Furthermore, the pressure connection 12a is connected to a pressure relief line 56a, which is connected via a drain valve 58a to a return line 60 leading to the fluid reservoir 40.

[0063] Similarly, the pressure connection 12b is connected to a pressure relief line 56b, which is connected to the return line 60 via a drain valve 58b.

[0064] In addition, a simulator unit 62 is connected to the pressure output line 48, which is fluidically connected to the master cylinder module 26 and which is configured to generate a restoring force for the brake pedal 38 in a manner known per se.

[0065] A simulation valve 63 is arranged between the simulator unit 62 and the master cylinder module 26, wherein the simulation valve 63 is preloaded in a de-energized state in a first switching position in which a fluid flow from the master cylinder module 26 to the simulator unit 62 is blocked, and the simulation valve 63 is open in an energized state.

[0066] A pressurization line 52c, in which an inlet valve 54c is located, branches off from the valve outlet of the second selection valve 46. The pressure connection 12c can be supplied with pressure via the pressurization line 52c.

[0067] In addition, a pressurization line 52d is provided, which extends from the valve outlet of the second selection valve 46 and in which an inlet valve 54d is positioned. The pressure connection 12d can be supplied with pressure via the pressurization line 52d.

[0068] In addition, a pressure relief line 56c is provided at the pressure connection 12c, in which a drain valve 58c is provided.

[0069] In the same way, the pressure connection 12d is connected to a pressure relief line 56d in which a drain valve 58d is provided.

[0070] The pressure relief lines 56c, 56d are connected to the return line 60.

[0071] In this context, the inlet valves 54a and 54c are designed as switchable check valves. In a non-actuated, e.g., de-energized, state, only a flow from the respective selection valve 44, 46 toward the associated pressure ports 12a, 12c can take place via the inlet valves 54a, 54c.

[0072] When the inlet valves 54a, 54c are actuated, e.g., energized, they are blocked. This means that no flow can pass through the pressurization lines 52a, 52c in any direction.

[0073] The inlet valves 54b, 54d are designed as 2 / 2-way valves.

[0074] The inlet valves 54b, 54d are preloaded into a first switching position, in which the respective associated pressurization line 52b, 52d can be flowed through in both directions. This position corresponds to an unactuated state.

[0075] All inlet valves 54a, 54b, 54c, 54d are switching valves.

[0076] The drain valves 58a, 58b, 58c, and 58d are all designed in the same way as 2 / 2-way valves. Again, they are switching valves.

[0077] The drain valves 58a, 58b, 58c, 58d are each preloaded into a switching position in which they act as check valves. In this context, only flow from the return line 60 toward the respective associated pressure connection 12a, 12b, 12c, 12d is permitted. The reverse flow direction is blocked.

[0078] If the drain valves 58a, 58b, 58c, 58d are switched, ie actuated, the respectively assigned pressure relief line 56a, 56b, 56c, 56d can be flowed through in both directions.

[0079] The brake system 10 also has a control unit 64, which is configured to control the electrofluidic brake module 16 and the selection valves 44, 46 for pressurizing the pressure connections 12a, 12b, 12c, 12d. Fig. For the sake of simplicity, only the signal connection of the control unit 64 to the electrofluidic brake module 16 is illustrated in Fig. 1.

[0080] In particular, the control unit 64 is configured to control the electrofluidic brake module 16 to increase a fluid pressure in the master cylinder module 26 while the at least one selection valve 44, 46 is in the first switching position.

[0081] Specifically, the control unit 64 is configured to detect an actuation of the brake pedal 38 and to control the electrofluidic brake module 16 to increase a fluid pressure in the master cylinder module 26 when the brake pedal 38 is actuated during a starting process of the brake system 10.

[0082] The control unit 64 is also configured to stop actuation of the electrofluidic brake module 16 when the brake pedal 38 is in its initial position and / or when a defined fluid pressure is reached in the master cylinder module 26.

[0083] Furthermore, the control unit 64 is configured to control the simulation valve 63, while the electrofluidic brake module 16 is controlled to increase the fluid pressure in the master cylinder module 26.

[0084] The braking system 10 can be operated as follows: First, the braking system 10 is started, in particular by actuating an ignition or a start button.

[0085] The selection valves 44, 46 and the simulation valve 63 are initially in the first switching position, since the entire braking system 10 is de-energized before starting.

[0086] After a restart of the braking system 10, the control unit 64 controls the electrofluidic braking module 16 while the at least one selection valve 44, 46 is in the first switching position, whereby hydraulic fluid is supplied to the pressure ports 12a, 12b, 12c, 12d and to the master cylinder module 26. This ensures that the brake pedal 38 is in a neutral position after the braking system 10 is restarted, even if the driver has moved the brake pedal 38 during the restart.

[0087] Since the selection valves 44, 46 are de-energized during the restart, hydraulic fluid can be pumped to the pressure ports 12a, 12b, 12c, 12d by actuating the brake pedal 38 during the restart. If the selection valves 44, 46 are then actuated while the brake pedal 38 is actuated, this results in a hydraulic fluid deficit in the master cylinder module 26, which can have a detrimental effect on the subsequent braking processes, particularly on the restoring force acting on the brake pedal 38.

[0088] For example, the control unit 64 detects, in particular using the displacement sensor 53, the pressure sensors 55 or the force sensor 57, whether the brake pedal 38 is actuated during the starting process of the braking system 10.

[0089] When the brake pedal 38 has reached its initial position, the control unit 64 stops the actuation of the electrofluidic brake module 16 and simultaneously actuates the selection valves 44, 46, thereby isolating the master cylinder module 26 from the pressure ports 12a, 12b, 12c, 12d.

[0090] Subsequently, the control unit 64 controls the at least one selection valve 44, 46, so that the electrofluidic brake module 16 and the master cylinder module 26 are fluidically separated from each other, and the master cylinder module 26 is disconnected from the pressure connections 12a, 12b, 12c, 12d. This ensures that sufficient hydraulic fluid is available in the master cylinder module 26.

[0091] In addition, the control unit 64 can control the simulation valve 63 during the activation of the electrofluidic brake module 16, thereby supplying hydraulic fluid to the simulation unit 62. This additionally ensures that sufficient hydraulic fluid is also available in the simulation unit 62.

[0092] After the start-up process is completed, the braking system 10 is operated in a normal operating mode.

[0093] During normal operation, in which the braking system is free of defects and malfunctions, the selection valves 44, 46 are each in their actuated position. In particular, the selection valves 44, 46 remain permanently actuated during operation of the braking system 10 from the initial actuation, provided no power failure occurs in the braking system 10.

[0094] The inlet valves 54a and 54c are not actuated during normal operation, ie they act as check valves.

[0095] The inlet valves 54b and 54d are also not actuated, thus releasing the associated pressurization line 52b, 52d.

[0096] Thus, the electrofluidic brake module 16 is fluidically coupled to all pressure connections 12a, 12b, 12c, 12d.

[0097] The drain valves 58a, 58b, 58c, 58d are each inactive, ie blocked for flow in the direction of the return line 60.

[0098] The master cylinder module 26 is connected to the simulator unit 62 via the pressure output line 48.

[0099] The braking system 10 can thus be operated in a so-called brake-by-wire mode. In this case, actuation of the brake pedal 38 by a driver is detected by sensors, in particular by means of the displacement sensor 53, the pressure sensor 55, and / or the force sensor 57. Based on the resulting sensor values, control commands are generated for the electrically actuated pressure generation unit 18.

[0100] On this basis, the piston 22 is displaced, for example, by an electric motor in such a way that the pressure chamber 20 is pressurized and thus each of the pressure connections 12a, 12b, 12c, 12d is pressurized.

[0101] When the pressure ports 12a, 12b, 12c, and 12d need to be relieved of pressure again, the pressure chamber 20 is relieved of pressure by moving the piston 22 in the opposite direction. This results in pressure relief at the pressure ports 12a, 12b, 12c, and 12d.

[0102] In this context, the functionality of an anti-lock braking system (ABS) can also be provided by selectively switching, i.e., opening, one or more of the drain valves 58a, 58b, 58c, 58d. This leads to a pressure reduction at the respective associated pressure connection 12a, 12b, 12c, 12d. Alternatively or additionally, one or more of the inlet valves 54a, 54b, 54c, 54d can be switched, which results in further pressure buildup at the associated pressure connection 12a, 12b, 12c, 12d being blocked.

[0103] The braking system 10 remains functional even if a defect or malfunction occurs in the first electrofluidic braking module 16. This operating mode is referred to as fallback mode.

[0104] In this context, the selection valves 44, 46 are transferred to their de-actuated state. This occurs either, e.g., in the event of a power failure, due to the preload of the selection valves 44, 46 or by the defined removal of an actuation signal. The inlet valves 54a, 54b, 54c, 54d and the outlet valves 58a, 58b, 58c, 58d are also each in their de-actuated state. This is also achieved via the respective preload or by a defined shutdown.

[0105] Overall, no external energy supply is required to move the valves into the above-mentioned switching positions.

[0106] In particular, in this state, by actuating the brake pedal 38, pressure can be built up in the pressure chambers 34, 36, which is then made available to all pressure ports 12a, 12b, 12c, 12d via the selection valves 44, 46. This means that hydraulic flow from the master cylinder module 26 to the pressure ports 12a, 12b, 12c, 12d is possible.

Claims

[1] Brake system (10) for a vehicle, wherein the brake system (10) is designed for selectively applying and relieving pressure to at least two pressure connections (12a, 12b, 12c, 12d) for brake actuators (14a, 14b, 14c, 14d), wherein each pressure connection (12a, 12b, 12c, 12d) is connectable to an associated brake actuator (14a, 14b, 14c, 14d) of a wheel of the vehicle, comprising a brake pedal (38) for detecting a driver's braking request, an electrofluidic brake module (16) with an electrically actuated pressure generating unit (18), a master cylinder module (26) comprising a fluidic brake master cylinder (28) which can be actuated by the brake pedal (38), wherein the electrofluidic brake module (16) and the master cylinder module (26) are coupled to the pressure connections (12a, 12b, 12c, 12d) via at least one selection valve (44, 46), wherein the at least one selection valve (44, 46) is preloaded in a currentless state into a first switching position in which both the electrofluidic brake module (16) and the master cylinder module (26) are fluidically connected to the pressure connections (12a, 12b, 12c, 12d), and wherein the at least one selection valve (44, 46) is in a second switching position in an energized state, in which the electrofluidic brake module (16) is fluidically connected to the pressure connections (12a, 12b, 12c, 12d) and a connection from the master cylinder module (26) to the pressure connections (12a, 12b, 12c, 12d) is blocked, wherein the brake system (10) has a control unit (64) which is configured to control the electrofluidic brake module (16) and the at least one selection valve (44, 46) for pressurizing the pressure connections (12a, 12b, 12c, 12d), and wherein the control unit is configured to control the electrofluidic brake module (16) to increase a fluid pressure in the master cylinder module (26) while the at least one selection valve (44, 46) is in the first switching position. [2] Braking system (10) according to claim 1, characterized by in that the control unit is configured to detect an actuation of the brake pedal (38) and to control the electrofluidic brake module (16) to increase a fluid pressure in the master cylinder module (26) when the brake pedal (38) is actuated during a starting process of the brake system (10). [3] Braking system (10) according to one of the preceding claims, characterized by in that in the first switching position of the at least one selection valve (44, 46), the electrofluidic brake module (16) is fluidically connected to the pressure connections (12a, 12b, 12c, 12d) and to the master cylinder module (26) via a check valve (51) blocking in the direction of the electrofluidic brake module (16). [4] Braking system (10) according to one of the preceding claims, characterized by that a displacement sensor (53) and / or a pressure sensor (55) is present, which are configured or which are configured to detect a brake pedal actuation and / or a fluid pressure in the master cylinder module (26), wherein the control unit (64) is configured to stop actuation of the electrofluidic brake module (16) when the brake pedal (38) is in its initial position and / or when a defined fluid pressure in the master cylinder module (26) is reached. [5] Braking system (10) according to one of the preceding claims, characterized byin that the brake system (10) comprises a simulator unit (62) which is fluidically connected to the master cylinder module (26) and which is designed to generate a restoring force for the brake pedal (38), wherein a simulation valve (63) is arranged between the simulator unit (62) and the master cylinder module (26), wherein the simulation valve (63) is prestressed in a de-energized state into a first switching position in which a fluid flow from the master cylinder module (26) to the simulator unit (62) is blocked, and the simulation valve is open in a energized state. [6] Braking system (10) according to claim 5, characterized by that the control unit (64) is configured to control the simulation valve (63) while the electrofluidic brake module (16) is controlled to increase the fluid pressure in the master cylinder module (26). [7] Method for operating a braking system (10) according to one of the preceding claims, comprising the following steps: - the braking system (10) is started, in particular by actuating an ignition, - the control unit (64) controls the electrofluidic brake module (16) after a restart of the brake system (10), while the at least one selection valve (44, 46) is in the first switching position, whereby hydraulic fluid is delivered to the pressure connections (12a, 12b, 12c, 12d) and to the master cylinder module (26), - the control unit (64) then controls the at least one selection valve (44, 46) so that the electrofluidic brake module (16) and the master cylinder module (26) are fluidically separated from one another and the master cylinder module (26) is separated from the pressure connections (12a, 12b, 12c, 12d). [8] Method according to claim 7, characterized byin that the control unit (64) detects whether the brake pedal (38) is actuated during the starting process of the braking system (10) and the control unit (64) activates the electrofluidic brake module (16) while the at least one selection valve (44, 46) is in the first switching position, and wherein the control unit (64) stops the actuation of the electrofluidic brake module (16) until the brake pedal (38) is actuated again and simultaneously activates the at least one selection valve (44, 46) when the brake pedal (38) has reached its starting position, whereby the master cylinder module (26) is separated from the pressure connections (12a, 12b, 12c, 12d). [9] Method according to claim 7 or 8 for operating a braking system (10) according to one of claims 5 and 6, characterized by that during the activation of the electrofluidic brake module (16) the simulation valve (63) is activated, whereby hydraulic fluid is conveyed to the simulation unit (62). [10] Method according to one of claims 7 to 9, characterized by that the selection valve (44, 46) remains permanently activated during operation of the braking system (10) from the first activation.

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