DE102021213466A1 - Retractable brake pedal - Google Patents

Abstract

The invention relates to a hydraulic brake system having a brake pedal (1) coupled to a master brake cylinder (2) for actuating wheel brakes (8a, 8b, 8c, 8d), which can be moved into an end position for autonomous driving mode by an external actuator, and a valve arrangement for controlling the hydraulic flow in the brake system and a control unit (12) for controlling the valve arrangement. According to the invention, the control unit (12) is set up to create a flow-open connection between the master brake cylinder (2) and a brake fluid reservoir (4) when the brake pedal (1) is retracted by actuating the valve arrangement.

Description

The invention relates to a hydraulic brake system having a brake pedal coupled to a master brake cylinder for actuating wheel brakes, which can be moved into an end position for an autonomous driving mode by an external actuator, a valve arrangement for controlling the hydraulic flow in the brake system, and a control unit for regulating the valve arrangement .

In addition to autonomous operation, current self-driving vehicles can also be controlled purely manually by a driver. However, a brake pedal required for this disturbs the driver in autonomous operation. It is therefore provided in such brake systems to fold away the brake pedal for autonomous operation. This pedal movement is typically performed around the normal pivot axis of the brake pedal, which also allows the movement of the brake pedal when the driver brakes.

Corresponding brake systems typically work in a brake-by-wire mode if they do not work in an autonomous mode. This means that the actuation of the brake pedal is detected and translated into a driver's brake request, which is used as the basis for a hydraulic pressure build-up in the wheel brakes of the hydraulic brake system. For this purpose, such a brake system has an electrical pressure supply device. However, the retraction of the brake pedal for the transition to the autonomous mode should not be interpreted as a driver braking request and lead to vehicle braking. However, the mechanical decoupling of the brake pedal required for this is complex and expensive. Braking systems for an autonomous driving mode also often have extended redundancy, since the driver is the last fallback. For this purpose, a second pressure supply device is installed for at least some of the wheel brakes, which takes over the pressure build-up to decelerate the vehicle in the event of a fault.

It is the object of the present invention to create a brake system for autonomous vehicles with a retractable brake pedal, which can be produced easily and inexpensively.

The object is achieved by a brake system according to claim 1 in that the control unit is set up to establish a flow-open connection between the master brake cylinder and a brake fluid reservoir when the brake pedal is retracted by actuating the valve arrangement. The brake system can receive a signal, in particular via a communication interface, which announces or requests the retraction of the brake pedal. This signal can be received directly from the external actuator or from a higher-level control unit. The brake system can then signal readiness to retract the brake pedal to the external actuator or the control unit as soon as this is available. The brake pedal is retracted by pivoting it about the normal pivot axis.

In a preferred embodiment, the control unit is also set up to decouple the master brake cylinder from the wheel brakes by closing a master brake cylinder valve after the brake pedal has reached the end position. This means that the hydraulic pressure in the brake system cannot have any repercussions on the brake pedal with the external actuator.

In a further preferred embodiment, the control device is set up to establish the open-flow connection via outlet valves of the wheel brakes. Thus, no additional valves are necessary and the brake system can be designed to be particularly cost-effective.

In a further preferred embodiment, the control unit is also set up to implement a pressure request at the wheel brakes while the brake pedal is being retracted. The transition from a manual mode to an autonomous mode can be carried out without any problems while driving, since the brake system is always ready for use. For example, in a half-by-wire mode, the pedal retraction can be continued and braked with a pressure supply device designed as a linear actuator on the rear axle become.

In a particularly preferred embodiment, the retraction of the brake pedal is paused while the pressure request is being implemented and then continued. The control device can be set up to send corresponding signals to pause and/or continue to the external actuator.

In an alternative particularly preferred embodiment, the open-flow connection is established via outlet valves of at least one first wheel brake and a pressure requirement is implemented using a pressure supply device on at least one second wheel brake. This division can either be provided as a standard case or otherwise all outlet valves can be open. Then only when there is a print request is there a switch to this division.

In a particularly preferred embodiment, a second pressure supply device is provided, which implements the pressure requirement at the at least one first wheel brake. This means that all wheel brakes are used for braking even when the brake pedal is retracted, thus minimizing the braking distance.

In a further preferred specific embodiment, the control unit is set up to implement parameterization of a pedal counterforce by varying the number of open outlet valves. Accordingly, the control unit adjusts the number of open exhaust valves in order to achieve a specified pedal counterforce or a corresponding hydraulic pressure.

In a further particularly preferred embodiment, the control unit is also set up to implement parameterization of the pedal counterforce by regulating the inlet valves of the wheel brakes. For this purpose, an electrical holding current of the intake valves is regulated by means of a corresponding characteristic curve to such a value that a required dynamic pressure is established.

In a further preferred embodiment, the control unit is set up to control the valve arrangement when the brake pedal is retracted, to cyclically establish a flow-open connection between a pressure sensor and a pressure-free reservoir, and to carry out an adjustment of the pressure sensor. Thus, the accuracy of the pressure sensor is improved, so that braking can be implemented exactly according to a requirement.

In a further preferred embodiment, the control unit is set up to establish a flow-open connection between the pressure supply device and the brake fluid reservoir when the brake pedal is retracted and there is no braking request. Thus, volume variations, for example from thermal expansion, can be compensated.

In a further preferred embodiment, the control unit is set up to monitor pedal retraction and to output an error message if there are deviations from normal behavior. The monitoring can in particular include the brake pedal position and/or the hydraulic pressure in the master brake cylinder.

In a further preferred embodiment, the control unit is set up to communicate data from the brake system to the external actuator. This can use the already existing sensors of the brake system for running in and therefore does not have to have any additional sensors.

The object is also achieved by a method for controlling a hydraulic brake system having a brake pedal coupled to a master brake cylinder for actuating wheel brakes, the brake pedal being moved into an end position for an autonomous driving mode by an external actuator, with the brake pedal being retracted by means of a Valve assembly of the brake system is made a flow-open connection between the master cylinder and a brake fluid reservoir.

• 1 zeigt schematisch eine erfindungsgemäße Bremsanlage mit dem Volumenfluss beim Einfahren des Bremspedals in einer ersten Ausführungsform,
• 2 zeigt schematisch eine erfindungsgemäße Bremsanlage mit dem Volumenfluss beim Einfahren des Bremspedals in einer zweiten Ausführungsform,
• 3 zeigt schematisch eine erfindungsgemäße Bremsanlage mit dem Volumenfluss beim Einfahren des Bremspedals in einer dritten Ausführungsform;

Further features, advantages and possible applications of the invention also result from the following description of exemplary embodiments and the drawings. All of the described and/or illustrated features belong to the subject matter of the invention, both individually and in any combination, even independently of their summary in the claims or their back-references.

• 1 shows schematically a brake system according to the invention with the volume flow when the brake pedal is retracted in a first embodiment,
• 2 shows schematically a brake system according to the invention with the volume flow when the brake pedal is retracted in a second embodiment,
• 3 shows schematically a brake system according to the invention with the volume flow when the brake pedal is retracted in a third embodiment;

This in 1 The brake system shown for a motor vehicle includes four hydraulically actuated wheel brakes 8a-8d. The brake system comprises a master brake cylinder 2 that can be actuated by means of an actuating or brake pedal 1, a travel simulator or a simulation device 3 that interacts with the master brake cylinder 2, a pressure medium reservoir 4 that is at atmospheric pressure, an electrically controllable pressure supply device 5, and a valve arrangement comprising wheel-specific brake pressure modulation valves, which for example, are designed as inlet valves 6a-6d and outlet valves 7a-7d. Furthermore, the brake system includes at least one electronic control and regulation unit 12 for controlling the electrically actuable components of the brake system.

For example, wheel brake 8a is on the left front wheel (FL), wheel brake 8b is on the right front wheel (FR), wheel brake 8c is on the left Rear wheel (RL) and the wheel brake 8d assigned to the right rear wheel (RR).

The master brake cylinder 2 has a master brake cylinder piston 15 in a housing 16, which delimits a hydraulic pressure chamber 17, and represents a single-circuit master brake cylinder 2. The pressure chamber 17 accommodates a return spring 9, which positions the piston 15 in an initial position when the master brake cylinder 2 is not actuated. The pressure chamber 17 is connected to the pressure medium reservoir 4 via radial bores formed in the piston 15 and a corresponding pressure compensation line 41 , which can be shut off by a relative movement of the piston 15 in the housing 16 . The pressure chamber 17 is on the other hand connected by means of a hydraulic line section (also referred to as the first supply line) 22 to a brake supply line 13 to which the input ports of the inlet valves 6a-6d are connected. Thus, the pressure chamber 17 of the master brake cylinder 2 is connected to all inlet valves 6a-6d.

In the pressure compensation line 41 or in the connection between the pressure chamber 17 and the pressure medium reservoir 4, for example, no hydraulic valve, in particular no electrically or hydraulically actuated valve and no check valve, is arranged.

Alternatively, a diagnostic valve, in particular one that is normally open, can be contained in the pressure compensation line 41 or between the master brake cylinder 2 and the pressure medium reservoir 4, preferably a parallel connection of a normally open diagnostic valve with a check valve that closes toward the pressure medium reservoir 4.

The valve arrangement can also include other hydraulic valves. A separating valve 23 is arranged between the supply line 22 connected to the pressure chamber 17 and the brake supply line 13 or the pressure chamber 17 is connected to the brake supply line 13 via the first supply line 22 with a separating valve 23 . The isolating valve 23 is designed as an electrically actuable, preferably normally open (SO), 2/2-way valve. The hydraulic connection between the pressure chamber 17 and the brake supply line 13 can be shut off by the isolating valve 23 .

A piston rod 24 couples the pivoting movement of the brake pedal 1 as a result of a pedal actuation with the translational movement of the master brake cylinder piston 15, the actuation path of which is detected by a displacement sensor 25, which is preferably designed redundantly. As a result, the corresponding piston travel signal is a measure of the brake pedal actuation angle. It represents a driver's braking request.

A pressure sensor 20 connected to the first supply line 22 detects the pressure built up in the pressure chamber 17 by a displacement of the piston 15 . This pressure value can also be evaluated to characterize or determine the driver's braking request. As an alternative to a pressure sensor 20, a force sensor 20 can also be used to determine the driver's braking request.

According to the example, the simulation device 3 is designed hydraulically and is hydraulically coupled to the master brake cylinder 2 . The simulation device 3 essentially has, for example, a simulator chamber 29, a simulator rear chamber 30 and a simulator piston 31 separating the two chambers 29, 30 from one another. The simulator piston 31 is supported on a housing by an elastic element 33 (eg simulator spring) arranged in the (for example dry) simulator rear chamber 30 . According to the example, the hydraulic simulator chamber 29 is connected to the pressure chamber 17 of the master brake cylinder 2 by means of a simulator release valve 32 that can preferably be actuated electrically and is preferably closed when de-energized.

The braking system or the braking system comprises an inlet valve 6a-6d and an outlet valve 7a-7d for each hydraulically actuated wheel brake 8a-8d, which are hydraulically interconnected in pairs via central connections and connected to the wheel brake 8a-8d. The inlet valves 6a-6d are each connected in parallel with a non-return valve, which opens towards the brake supply line 13. The outlet connections of the outlet valves 7a-7d are connected to the pressure medium reservoir 4 via a common return line 14.

The electrically controllable pressure supply device 5 is designed as a hydraulic cylinder-piston arrangement (or a single-circuit, electrohydraulic actuator) or linear actuator, the piston 36 of which can be actuated by a schematically indicated electric motor 35 with the interposition of a rotation-translation gear 39, also shown schematically. The piston 36 delimits the single pressure chamber 37 of the pressure supply device 5. A rotor position sensor, indicated only schematically, which serves to detect the rotor position of the electric motor 35 is denoted by the reference number 44.

A lei is attached to the pressure chamber 37 of the electrically controllable pressure supply device 5 tion section (also referred to as the second supply line) 38 connected. The supply line 38 is connected to the brake supply line 13 via an electrically actuable, preferably normally closed, sequence valve 26 as part of the valve arrangement. The hydraulic connection between the pressure chamber 37 of the electrically controllable pressure supply device 5 and the brake supply line 13 (and thus the input connections of the inlet valves 6a-6d) can be opened and shut off in a controlled manner by the switching valve 26 .

The actuator pressure generated by the force of the piston 36 on the pressure medium enclosed in the pressure chamber 37 is fed into the second supply line 38 . In a “brake-by-wire” operating mode, in particular when the brake system is in a fault-free state, the supply line 38 is connected to the brake supply line 13 via the switching valve 26 . In this way, during normal braking, wheel brake pressure is built up and reduced for all wheel brakes 8a-8d by moving the piston 36 forwards and backwards.

When the pressure is reduced by moving the piston 36 back, the pressure medium previously displaced from the pressure chamber 37 of the pressure supply device 5 into the wheel brakes 8a-8d flows back into the pressure chamber 37 in the same way.

Alternatively, different wheel brake pressures can be adjusted individually for each wheel simply by means of the inlet and outlet valves 6a-6d, 7a-7d. With a corresponding reduction in pressure, the proportion of pressure medium released via the outlet valves 7a-7d flows via the return line 14 into the pressure medium reservoir 4.

Pressure medium can be sucked back into the pressure chamber 37 by moving the piston 36 back when the sequence valve 26 is closed, in that pressure medium can flow from the container 4 via the line 42 with a check valve 51 opening in the direction of flow to the actuator 5 into the actuator pressure chamber or pressure chamber 37 . According to the example, the pressure chamber 37 is also connected to the pressure medium reservoir 4 via one or more snifting holes when the piston 36 is not actuated. This connection between the pressure chamber 37 and the pressure medium reservoir 4 is separated when the piston 36 is actuated (sufficiently) in the direction of actuation 27 .

In the brake supply line 13, an electrically actuable, normally open circuit separating valve 40 is arranged, through which the brake system is divided into two hydraulic sub-circuits. Brake supply line 13 is divided into a first line section 13a, which is connected to master brake cylinder 2 (via separating valve 23), and a second line section 13b in the second hydraulic sub-circuit, which is connected to pressure supply device 5 (via switching valve 26). The first line section 13a is connected to the inlet valves 6a, 6b of the wheel brakes 8a, 8b and the second line section 13b is connected to the inlet valves 6c, 6d of the wheel brakes 8c, 8d.

When the circuit separating valve 40 is open, the brake system is designed as a single circuit. By closing the circuit separating valve 40, the brake system can be separated or divided into two hydraulic sub-circuits, brake circuits I and II, in particular controlled according to the situation. In the first brake circuit I, the master brake cylinder 2 (via the separating valve 23) is only connected to the inlet valves 6a, 6b of the wheel brakes 8a, 8b of the front axle VA, and in the second brake circuit II the pressure supply device 5 (with the connection valve 26 open) is only connected to the inlet valves 6a, 6b connected to the wheel brakes 8c and 8d of the rear axle HA.

When the circuit separating valve 40 is open, the input connections of all inlet valves 6a-6d can be supplied with a pressure by means of the brake supply line 13 which, in a first operating mode (e.g. “brake-by-wire” operating mode), corresponds to the brake pressure generated by the pressure supply device 5 is provided. The brake supply line 13 can be acted upon by the pressure of the pressure chamber 17 of the master brake cylinder 2 in a second operating mode (eg in a de-energized fallback operating mode).

The brake system advantageously includes a level measuring device 50 for determining a pressure medium level/stand in the pressure medium reservoir 4 .

For example, the hydraulic components, namely the master brake cylinder 2, the simulation device 3, the pressure supply device 5, the valve arrangement with the hydraulic valves 6a-6d, 7a-7d, 23, 26, 40 and 32 and the hydraulic connections including the brake supply line 13 together located in a hydraulic control unit 60 (HCU). The electronic control and regulation unit (ECU) 12 is assigned to the hydraulic control and regulation unit 60 . Hydraulic and electronic control and regulation units 60 , 12 are preferably designed as one unit (HECU). In this case, the pressure sensor 19 is viewed from the pressure chamber 37 of the pressure supply device 5 arranged behind the switching valve 26.
In a normal operating mode, the separating valve 23 is closed and the connection valve 26 and the circuit separating valve 40 are opened, so that the hydraulic pressure in all wheel brakes 8a to 8d is set by the linear actuator 5.

The connection to the front wheel brakes 8a, 8b is routed through a further brake unit 54, each with a switching valve 59a, 59b, which is open during normal operation. For reasons of redundancy, the further brake unit comprises a further pressurization device 57, which is designed as two hydraulic pumps 57a, 57b with a common motor. The hydraulic pumps 57a, 57b are connected on the suction side via a normally closed pump isolating valve 58a, 58b to an associated low-pressure accumulator 55a, 55b, which in turn has a connection to the brake fluid reservoir 4. The low-pressure accumulators 55a, 55b are also connected to the associated wheel brakes 8a, 8b via a further valve 56a, 56b.

The hydraulic pump 57 and the linear actuator 5 can be controlled by two separate control units.

The principle of hydraulic support for pedal retraction is in 1 shown. If the control unit 12 receives a signal which announces or requests a retraction of the brake pedal 1, it switches the valve arrangement in such a way that a flow-open connection is established between the master brake cylinder 2 and the brake fluid reservoir. In particular, a simulator valve 3 is closed, an isolating valve or master cylinder valve 23 is open, and inlet valves 6 and outlet valves 7 of at least one wheel brake 8 are open. The volume flow from the master brake cylinder 2 shown with a thicker line is diverted into the container 4 through open outlet valves 7a, 7b of the front axle (upper two wheel brakes 8a, 8b). In the variant shown, the inlet valves 6c, 6d and outlet valves 7c, 7d of the rear axle are not used and the circuit separating valve 40 is closed. This basic principle can easily be applied in a pressureless idle state. From a hydraulic point of view, only the dynamic pressure acts as a counterforce to the pedal movement. Neither the simulator 3 nor the pressure-volume properties of the entire hydraulic system affect the counterforce.

When brake pedal 1 has reached the end position, master brake cylinder valve 23 between master brake cylinder 2, in particular with simulator 3, and the rest of the hydraulic brake system is closed so that system pressures do not act unnecessarily on brake pedal 1 and the external actuator.

• Die einfachste hydraulische Lösung ist ein Pausieren des Pedaleinfahrens. Die Bremsanlage schaltet durch Schließen des Hauptzylinderventils 23 in eine By-Wire Betriebsart und regelt mit dem Linearaktuator 5 den Systemdruck an beiden Achsen. Der externen Pedalaktuator wird dazu über eine Kommunikationsschnittstelle gestoppt. Alternativ könnte das Simulatorventil 32 geöffnet werden, um das Volumen in den Simulator 3 umzuleiten. Der externe Pedalaktuator müsste dann aber gegen eine größere Gegenkraft arbeiten.

It cannot be ruled out that a sudden need for pressure regulation, i.e. a pressure requirement, arises during the pedal retraction movement and has to be implemented. Therefore, this invention provides in particular the following three embodiments in order to be able to represent braking during pedal retraction:

• The simplest hydraulic solution is to pause pedal retraction. The brake system switches to a by-wire operating mode by closing the master cylinder valve 23 and regulates the system pressure on both axles with the linear actuator 5 . For this purpose, the external pedal actuator is stopped via a communication interface. Alternatively, the simulator valve 32 could be opened to divert the volume into the simulator 3. The external pedal actuator would then have to work against a larger counterforce.

Alternatively, as in 2 shown switched to a half-by-wire mode, in principle the brake pedal 1 is connected via the master cylinder 2 to the wheel brakes 8a, 8b of the front axle and the linear actuator 5 is connected to the wheel brakes 8c, 8d of the rear axle. Both axes are separated by a closed circuit separating valve 40. Due to the open outlet valves 7a, 7b of the front axle, the movement of the brake pedal still does not result in any pressure build-up on the front axle. The pressure is only built up by the linear actuator 5 on the rear axle.

2 illustrates the volume flow in half-by-wire operation during pedal-in. The volume flow from the master brake cylinder 2 into the container 4 is also shown with a bold line. The wheel brakes 8a, 8b of the front axle remain unpressurized. The pressure regulation on the wheel brakes 8c, 8d of the rear axle is represented by a dashed line.

In addition, the volumetric flow from the brake pedal can be used as a pressure source for the wheel brakes 8a, 8b of the front axle in order to adjust the wheel pressure via the wheel pressure controller. This is particularly possible when the pressure requirement on the front axle is below a maximum counter-pressure for pedal retraction. The admission pressure of the inlet valves 6a, 6b is determined by the master cylinder pressure sensor 20 and the pressure in the wheel brakes 8a, 8b is regulated based on the pressure model. For this purpose, the outlet valves 7a, 7b can be activated in a pulsed manner.

Building on the concept of 2 the second pressure supply device 57a, 57b can be added to the pressure build-up on the wheel brakes 8a, 8b of the front axle, while the master brake cylinder volume continues is discharged through the outlet valves 7a, 7b. For this purpose, changeover valves 59a, 59b and valves 56a, 56b are closed and pump isolating valves 58a, 58b are opened, so that pump 57 can draw pressure from low-pressure accumulator 55 and provide pressure in wheel brakes 8a, 8b. According to the concept shows 3 in dashed lines the high-pressure areas, which are respectively provided by the linear actuator 5 and the second pressure supply device 57a, 57b. The thick line shows the volume flow from master brake cylinder 2 into reservoir 4.

The inlet valves 6a, 6b, 6c, 6d and outlet valves 7a, 7b, 7c, 7d can be switched accordingly in order to be able to parameterize or meter the pedal counterforce when the brake pedal 1 is retracted. In order to set a minimum counterforce, all outlet valves 7a, 7b, 7c, 7d can be opened. Proceeding from this, the number of outlet valves 7a, 7b, 7c, 7d that are switched open can be varied in order to gradually increase the counteracting force. In addition, an increase in counterforce can be metered precisely if, with an open outlet valve 7a, 7b, 7c, 7d, its associated inlet valve 6a, 6b, 6c, 6d works in analog volumetric flow mode. In this case, the volume flow can be regulated in dependence on the differential pressure in the inlet valves 6a, 6b, 6c, 6d with the electrical holding current. The dynamic pressure at the inlet valve 6a, 6b, 6c, 6d and thus the counterforce of the brake pedal 1 can thus be regulated very precisely. The opening flow characteristics of the inlet valves 6a, 6b, 6c, 6d reflect the relationship between the pressure difference, electrical current and volumetric flow.

The influence of the inlet valves 6a, 6b, 6c, 6d and outlet valves 7a, 7b, 7c, 7d on the back pressure in the master brake cylinder 2 can be measured via the pressure sensor 20 and then calculated back to the pedal counterforce via the torque and effective area in the master brake cylinder 2. It is thus possible, for example, to implement a control loop in the brake system which, for example, regulates the entry speed of the pedal 1 . For this purpose, a counterforce specification is converted into a required hydraulic pressure, or a hydraulic pressure in master brake cylinder 2 is specified directly. The specification can be permanently stored in the brake system or can be received via a communication interface, for example. The electrical holding current of the inlet valves 6 or also the current of the outlet valves 7 can then be dynamically regulated so that the actual hydraulic pressure corresponds to the desired value.

During pedal-in, the master cylinder valve 23 is open and the simulator valve 32 is closed. After the retraction is complete, the master cylinder valve 23 is closed and the simulator valve 32 preferably remains closed. Due to the closing of master cylinder valve 23, high system pressures that can occur during subsequent braking do not act on brake pedal 1 and thus on the external actuator.

In normal brake-by-wire operation, the hydraulic pressure in master brake cylinder 2 is used to detect a driver's braking request and thus as the basis for a brake pressure that is made available. Pedal actuations, which are sensed via the master brake cylinder pressure after the pedal has been retracted, should preferably not lead to the driver's intention being recognized.

There is also the option for the driver to cancel highly autonomous driving and switch to a manual driving mode. The driver can overrule the autonomous control by a significant pedal actuation and can thus initiate braking. For this purpose, it is provided that the end position of the brake pedal 1 still has a reserve range of movement options for the master brake cylinder 2 in the pressure build-up direction. For implementation, the brake system can, for example, recognize a driver's request when the master cylinder valve 23 and simulator valve 32 are closed, if 500N are pedaled for a predetermined period of time, for example more than 1 second. This driver request could then win against the autonomous braking functions and the hydraulic pressure could be increased to initiate braking of the vehicle.

Alternatively, in the event of a master cylinder pressure sensor error, the simulator valve 32 could be opened and a driver's request could be recognized via the pedal travel.

There is also the possibility outside of a braking maneuver, ie a pressure request, to connect the pressure sensors 19, 20 to the atmosphere so that an offset adjustment can be carried out. In previous brake systems, this is done through the open snifting holes of the master brake cylinder 2. However, since the snifting hole is closed when the brake pedal is retracted, the pressure sensors 19, 20 must be cyclically adjusted to the atmospheric pressure in a different way. For this purpose, an outlet valve 7 is opened cyclically in the idle state for the system pressure sensor 19 . For the master cylinder pressure sensor 20, an outlet valve 7 and the master brake cylinder valve 23 are opened cyclically in the idle state.

In previous braking systems, the system’s sniffer hole connection is also A pressureless state is always ensured in the idle state. Since the system is no longer connected to the atmosphere via the snifter hole when the brake pedal 1 is advanced, any residual pressures that may be present are released by opening the exhaust valve. The switching of the outlet valves 7a, 7b, 7c, 7d takes into account in particular an increased hydraulic pressure due to self-heating while driving, as well as a release of the integrated electromechanical parking brake, which is typically arranged on the wheel brakes 8c, 8d of the rear axle.

The control unit 12 can also be set up to ensure that the brake system does not switch to an idle state when the brake pedal 1 is retracted, because otherwise the required connection to the atmosphere is not given.

To improve the security of the external pedal actuation, in particular to be able to meet specific security requirements, it is possible to implement security functions in the brake system. It is thus possible, for example, to protect against unintentional pedal actuation or pedal jamming. The brake system can internally check whether an announced pedal retraction is completed correctly and quickly enough. In addition, the external pedal actuator can communicate if the pedal cannot be completely released and the brake system can compensate for the closed snifter holes.

The external actuation of the pedal by the external actuator, for example a motor, can use data from the brake system, in particular pedal travel sensor information, in its control loop. This allows pedal speed and pedal position to be controlled.

The brake system according to the invention makes it possible to retract the pedal completely with as little force as 200N, since all hydraulic counterforces are eliminated or reduced as required. Only the force of the pedal return spring and mechanical friction remain. Many requirements are thus possible without electrical or mechanical changes. Dosing and parameterization is possible and braking can still be increased when the pedal is retracted.

Reference List

1

brake pedal

2

master cylinder

3

simulation facility

4

pressure fluid reservoir

5

print staging facility

6

a to d inlet valves

7

a to d exhaust valves

8th

a to d wheel brake

9

return spring

12

control system

13

brake supply line

14

return line

16

Housing

17

pressure chamber

19

system pressure sensor

20

master cylinder pressure sensor

22

first supply line

23

Isolation valve/master cylinder valve

24

piston rod

25

displacement sensor

26

sequence valve

29

simulator chamber

30

simulator rear chamber

31

simulator piston

32

simulator release valve

33

elastic element

35

electric motor

36

Pistons

37

pressure room

38

supply line

39

Rotation-translation gear

40

circuit isolation valve

41

pressure compensation line

42

Management

44

rotor position sensor

50

level sensor

53

check valve

54

Another braking system

55

low-pressure accumulator

56

anti-cavitation valve

57

hydraulic pump

58

pump isolation valve

59

switching valve

Claims (14)

Hydraulic brake system having a brake pedal (1) coupled to a master brake cylinder (2) for actuating wheel brakes (8a, 8b, 8c, 8d), which can be moved into an end position for an autonomous driving mode by an external actuator, a valve arrangement for controlling the hydraulic flow in the brake system and a control unit (12) for controlling the valve arrangement, characterized in that the control unit (12) is set up to open a flow connection between the master brake cylinder (2) and a brake fluid reservoir (4). brake system after claim 1 , characterized in that the control unit (12) is further set up to decouple the brake master cylinder (2) from the wheel brakes (8a, 8b, 8c, 8d) by closing a brake master cylinder valve (23) after the brake pedal (1) has reached its end position . Brake system according to one of the preceding claims, characterized in that the control unit (12) is further set up to establish the open-flow connection via outlet valves (7a, 7b, 7c, 7d) of the wheel brakes (8a, 8b, 8c, 8d). Brake system according to one of the preceding claims, characterized in that the control unit (12) is also set up to implement a pressure request at the wheel brakes (8a, 8b, 8c, 8d) while the brake pedal (1) is being retracted. brake system after claim 4 , characterized in that the retraction of the brake pedal (1) is paused during the implementation of the pressure request and is then continued. brake system after claim 4 , characterized in that the flow-open connection via outlet valves (7a, 7b, 7c, 7d) at least one first wheel brake (8a, 8b, 8c, 8d) is produced and a pressure requirement with the aid of a pressure supply device (5) at least one second wheel brake ( 8c, 8d) is implemented. brake system after claim 6 , characterized in that a second pressure supply device (57a, 57b) converts a pressure requirement at the at least one first wheel brake (8a, 8b). Brake system according to one of claims 3 until 7 , characterized in that the control unit (12) is set up to implement a parameterization of a pedal counterforce by the number of open outlet valves (7a, 7b, 7c, 7d) is varied. Brake system according to one of claims 3 until 8th , characterized in that the control unit (12) is set up to implement a parameterization of the pedal counterforce by a holding current of the inlet valves (6a, 6b, 6c, 6d) of the wheel brakes (8a, 8b, 8c, 8d) are regulated. Brake system according to one of the preceding claims, characterized in that the control unit (12) is set up to control the valve arrangement when the brake pedal (1) is retracted, to cyclically establish a flow-open connection between a pressure sensor (19, 20) and the brake fluid reservoir (4), and carry out an adjustment of the pressure sensor. Brake system according to one of the preceding claims, characterized in that the control unit (12) is set up to establish a flow-open connection between the pressure supply device (5) and the brake fluid reservoir (4) when the brake pedal (1) is retracted and there is no braking request. Brake system according to one of the preceding claims, characterized in that the control unit (12) is set up to monitor pedal retraction and to output an error message in the event of deviations from normal behavior. Brake system according to one of the preceding claims, characterized in that the control unit (12) is set up to communicate data from the brake system to the external actuator. Method for controlling a hydraulic brake system having a brake pedal (1) coupled to a master brake cylinder (2) for actuating wheel brakes (8a, 8b, 8c, 8d), the brake pedal (1) being moved to an end position by an external actuator for an autonomous driving mode is retracted, characterized in that when the brake pedal (1) is retracted, a flow-open connection is established between the master brake cylinder (2) and a brake fluid reservoir (4) by means of a valve arrangement of the brake system.

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