EP4297998A1

EP4297998A1 - Method for braking a vehicle and braking system

Info

Publication number: EP4297998A1
Application number: EP21820491.5A
Authority: EP
Inventors: Frank Overzier
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-02-23
Filing date: 2021-11-25
Publication date: 2024-01-03
Also published as: JP2024506568A; US20240025386A1; CN116867693A; DE102021104249A1; WO2022179723A1; KR20230150829A

Abstract

The invention relates to a method (M) for braking a vehicle, comprising: sensing (M1) a braking request signal which represents a target deceleration of the vehicle; generating (M21), by means of a first pressure generating device (10), a hydraulic brake pressure in a wheel-brake cylinder (1) based on the sensed braking request signal, which pressure generating device is hydraulically connected to the wheel-brake cylinder (1); detecting (M3) a fault state of the first pressure generating device (10); determining (M4) a replacement braking request signal, if a fault state of the first pressure generating device (10) is detected, wherein the replacement braking request signal is determined based on a target deceleration known at a predetermined time before the detection of the fault state; and generating (M5), by means of a brake pressure control system (120), a replacement brake pressure in the wheel-brake cylinder (1) based on the determined replacement braking request signal, which brake pressure control system has a second pressure generating device (20) which is hydraulically coupled to the wheel-brake cylinder. The invention also relates to a method (M) for braking a vehicle, in which the replacement braking request signal is determined based on a target deceleration, known at a predetermined time before the detection of the fault state, based on a braking torque generated by an electric machine kinematically coupled to a wheel of the vehicle. A further aspect of the invention relates to a braking system (100) for a vehicle.

Description

description

title

METHOD OF BRAKING A VEHICLE AND BRAKING SYSTEM

technical field

The present invention relates to a method for braking a vehicle and a braking system for a vehicle.

State of the art

Hydraulic braking systems are typically used in road vehicles such as cars or trucks. Increasingly, such hydraulic brake systems are operated according to a "brake-by-wire" principle, with actuation of a brake pedal being detected by sensors and a braking request being determined from this, which represents a desired deceleration of the vehicle. A hydraulic pressure is then determined from the braking request, which is generated by means of a pressure generating device, such as an electrically driven plunger, in a wheel brake cylinder for braking a wheel of the vehicle.

Furthermore, brake systems of road vehicles usually have brake pressure control systems for wheel-specific brake pressure control, e.g. to perform an anti-lock braking function (ABS). Typically, such brake pressure control systems have their own pressure generation device and a valve arrangement for wheel-specific pressure variation.

If the pressure generation device fails in brake systems operating according to the brake-by-wire principle, a master brake cylinder, which can be actuated by the brake pedal, typically becomes hydraulic connected to the wheel brake cylinder so that the required braking pressure can be generated manually.

DE 102014225 954 A1 describes a brake system in which a pressure generation device of a brake pressure control system, which is set up to generate wheel-specific brake pressures, takes over the generation of the desired brake pressure if a first externally controlled pressure generation device fails.

Disclosure of Invention

According to the invention, a method for braking a vehicle having the features of claim 1, a method for braking a vehicle having the features of claim 10 and a braking system having the features of claim 12 are provided.

According to a first aspect of the invention, a method for braking a vehicle is provided. The method includes detecting a brake request signal which represents a target deceleration of the vehicle, for example based on an actuation of a brake actuation device, generating a hydraulic brake pressure in a wheel brake cylinder based on the detected brake request signal using a first pressure generating device which is hydraulically connected to the wheel brake cylinder Detecting a fault condition of the first pressure generating device, determining a replacement braking request signal when a fault condition of the first pressure generating device is detected, wherein that

Substitute braking request signal is determined based on a target deceleration known at a predetermined point in time before the error state is detected, and generating a substitute brake pressure in the wheel brake cylinder based on the determined substitute braking request signal by means of a brake pressure control system, which has a second pressure generating device hydraulically coupled to the wheel brake cylinder. According to a second aspect of the invention, a method for braking a vehicle includes detecting a braking request signal, which represents a target deceleration of the vehicle, for example based on an actuation of a brake actuation device, generating a braking torque by means of an electric machine kinematically coupled to a wheel of the vehicle based on the brake request signal, provision of a first pressure generation device hydraulically connected to a wheel brake cylinder for generating a brake pressure in the wheel brake cylinder based on the brake request signal, detection of a fault state of the first pressure generation device, determination of a substitute brake request signal if a fault state of the first pressure generation device is detected, with the

Substitute braking request signal is determined based on a target deceleration known at a predetermined point in time before the detection of the fault condition based on the braking torque generated by the electric machine, and generating a substitute brake pressure in the wheel brake cylinder based on the determined substitute braking request signal by means of a brake pressure control system, which sends a pressure hydraulically to the wheel brake cylinder coupled second pressure generating device.

According to a third aspect of the invention, there is provided a braking system for a vehicle. The braking system includes a sensor for detecting a braking request or braking request signal, a wheel brake cylinder for generating a frictional force on a wheel of the vehicle, a first pressure generating device which is hydraulically coupled to the wheel brake cylinder and is set up to generate a hydraulic pressure in the wheel brake cylinder, a Brake pressure control system with a second pressure generating device which is hydraulically coupled to the wheel brake cylinder and set up to generate a hydraulic pressure in the wheel brake cylinder independently of the first pressure generating device, and a control system which is signal-connected to the actuation sensor, the first pressure generating device and the brake pressure control system and set up for this purpose is to cause the braking system to carry out a method according to the first aspect of the invention. If the method according to the third aspect of the Invention is performed, the control system can in particular have an interface for connection to the electrical machine.

One of the ideas on which the invention is based is to use a brake pressure control system to compensate for a failure of the pressure-generating device in a braking system in which the hydraulic brake pressure is generated using a pressure-generating device that is externally operated or not kinematically coupled to a brake-actuating device, such as a brake pedal or a brake lever , which is intended to be used, for example, to perform an ABS or ESP function, with the brake pressure control system on detection of a failure or fault condition of the

Pressure generating device initially adjusts a brake pressure, which corresponds to a brake pressure known before the detection of the failure or is equivalent to a braking torque generated by an electric machine. This means that it is not necessary to resort to detecting a brake request signal generated, for example, by the driver, but instead a brake pressure is first automatically set that corresponds to a desired target deceleration known at a specific, past point in time. This substitute braking pressure is thus generated exclusively on the basis of the ascertained or correspondingly generated substitute braking request signal, in which case the substitute braking request signal can in particular be constant, at least for a predetermined period of time. The present invention can be used both for purely hydraulic braking, braking in which the braking torque is generated partly by an electric machine operated as a generator and partly hydraulically or by means of the wheel brake cylinder, and purely regenerative braking, in which the braking torque is initially is generated entirely by an electric machine operated as a generator. In the last-mentioned case or according to the second aspect of the invention, the first pressure-generating device is kept available in order, for example, to intervene as a backup or as a supplement. If the first pressure generating device fails during purely regenerative braking before it generates brake pressure in the wheel brake cylinder, the regenerative braking is ended and the brake pressure control system generates the brake pressure in the wheel brake cylinder based on the last valid one Braking torque generated by the electrical machine before the failure of the first pressure-generating device.

A fault condition of the first pressure generating device, which can be, for example, a plunger driven by an electric motor, can generally be detected when the pressure generating device is no longer able to set the desired brake pressure. This can be the case, for example, if the pressure-generating device itself is defective, e.g. because the electric motor overheats or is damaged in some other way, or if the pressure-generating device does not receive an actuation signal. The latter case can occur, for example, if the detection of the brake request signal no longer works or if the determination of the brake pressure, e.g. with the help of a control unit, no longer works.

An advantage of the invention is that immediately after failure of the first pressure generating device, a brake pressure can be generated by means of the second pressure generating device of the brake pressure control system based on a braking request known before the failure. This means that there is no need to wait for the driver to react, which could be e.g. depressing the brake pedal or pulling the brake lever. Thus, the braking distance can be advantageously shortened.

Advantageous refinements and developments result from the further dependent claims and from the description with reference to the figures of the drawing.

According to some specific embodiments, it can be provided that the detection of a brake request signal includes the detection of an actuation of a brake actuation device. For example, the adjustment travel of a brake pedal or a brake lever can be detected using an actuation sensor, with the brake request signal being generated based on the detected adjustment travel. Other types of actuation detection are also conceivable, for example the detection of a pressure that is generated in a simulator by actuating the brake actuation device. General can the detection of the brake request signal based on an actuation of a brake actuation device.

According to some specific embodiments, it can be provided that the determination of the substitute braking request signal includes a determination of an adjustment travel of a brake actuation device at the predetermined point in time before the error state is detected. The travel of the brake actuation device, such as a pedal or lever, can be determined in particular with a travel sensor, as already explained. The determined travel can be recorded in a time-resolved manner and the detected values can be stored for a predetermined, in particular a sliding period of time, so that even if the travel sensor and/or the first pressure-generating device fails, the last valid values can be accessed, which are then used to determine the Replacement brake request are used. In this way, security is further improved.

According to some specific embodiments, provision can be made for the determination of the substitute braking request signal to include determination of a brake pressure in the wheel brake cylinder at the predetermined point in time before the error state is detected. For example, in a hydraulic path that connects the first pressure-generating device to the wheel brake cylinder, the pressure can be detected by means of a sensor, in particular time-resolved, with the detected values being able to be stored for a predetermined, in particular sliding, period of time, so that even if the first Pressure generating device can be accessed on the last valid values, which are then used to determine the replacement braking request. In this way, security is further improved.

According to some specific embodiments, the method can include generating a braking torque by means of an electric machine kinematically coupled to a wheel of the vehicle based on the braking request signal. This can be advantageous, for example, in electrically driven vehicles or hybrid vehicles, with the desired target deceleration taking place partly by operating the electric machine as a generator and partly with the help of the wheel brake cylinder. The hydraulic brake pressure that is Wheel brake cylinders by the first and/or the second

Pressure generating device is generated, thus also depends on what proportion of the target deceleration delivers the electric machine.

According to some specific embodiments, it can be provided that the substitute braking torque is determined based on the braking torque generated by the electric machine. For example, a control unit of the electrical machine, e.g. power electronics, can output a machine control signal representing the braking torque generated by the electrical machine to the control system of the hydraulic brake system, which uses this machine control signal to determine which braking torque must be generated by the friction brake cylinder.

According to some specific embodiments, it can be provided that the brake pressure control system has a first control unit which actuates the second pressure generating device, and a fault condition of the first pressure generating device is detected using a control signal which is sent to the first control unit. For example, an error state can be detected if the control signal is absent or if an error signal is sent to the first control unit instead of the control signal. The first control unit can in particular have a processor unit, eg with one or more CPUs, FPGAs, ASICS or the like, and a data memory, in particular a non-volatile data memory such as an HDD memory or an SSD memory. For example, software can be stored in the data memory, which can be executed by the processor unit in order to output output signals, in particular actuating signals, to the second pressure generating device and optionally to valves in order to actuate them. The output signals can be generated, for example, based on the control signal and/or based on a pressure signal which represents a current pressure present on a suction side of the second pressure generating device. The first control device can be set up, for example, the pressure generating device, optionally in cooperation with a To cause valve assembly to perform an anti-lock function and / or to a wheel-specific variation of the brake pressure.

According to some specific embodiments, it can be provided that the first pressure generating device is actuated by a second control unit based on the brake request signal, with the second control unit generating the first control signal and sending it to the first control unit. The second control unit can in particular have a processor unit, e.g. with one or more CPUs, FPGAs, ASICS or the like, and a data memory, in particular a non-volatile data memory such as an HDD memory or an SSD memory. For example, software can be stored in the data memory, which can be executed by the processor unit in order to output output signals, in particular actuating signals, to the first pressure generating device and optionally to valves in order to actuate them. For example, the second control unit, based on the brake request signal, which e.g

Brake actuation device coupled travel sensor can be output, determine the brake pressure and press the first pressure generating device accordingly. The second control device can communicate to the first control device, e.g. Optionally, the first control device can store the control signals received from the second control device in its data memory for a specific, flexible period of time, so that in the event of an error state of the pressure generating device, the stored values can be accessed in order to be able to more easily determine the replacement braking request signal.

According to some specific embodiments, it can be provided that the generation of the replacement brake pressure includes the generation of a linear, a stepwise, and/or a progressive or a degressive increase in pressure in the wheel brake cylinder.

According to some embodiments, it can be provided that by actuating the brake actuation device, which, for example, as already explained, brake pedal or a brake lever, a hydraulic reset pressure is generated in a reset simulator by means of a master brake cylinder, and where, if a fault condition of the first pressure generating device is detected, the master brake cylinder is hydraulically coupled to the wheel brake cylinder, and the first pressure generating device is preferably hydraulically separated from the wheel brake cylinder becomes. The master brake cylinder can be hydraulically connected to and disconnected from the wheel brake cylinder, for example by a first isolating valve. The first pressure generating device can be hydraulically connected to and disconnected from the wheel brake cylinder in a similar manner by a second isolating valve. If the first pressure generating device is in an operative state, the first isolating valve is closed and the master brake cylinder, which is kinematically coupled to the brake actuation device, is thereby hydraulically separated from the wheel brake cylinder. In the event of an error condition of the first pressure generating device, the first isolating valve is opened and optionally the second isolating valve is closed. This hydraulically connects the master brake cylinder to the wheel brake cylinder. As a result, the driver no longer only feels the restoring force of the simulator on the brake actuation device, but rather the actually prevailing brake pressure. In addition, the opening of the first isolating valve leads to a volume displacement from the wheel brake cylinder into the master brake cylinder and thus to a drop in brake pressure. This would have to be compensated by the driver by further actuation of the brake actuation device, for example by depressing the brake pedal. However, since according to the invention the brake pressure control system can completely take over the pressure generation at least temporarily and sets the last known brake pressure, the driver is given more time to react, which advantageously improves the operating comfort and safety.

According to some specific embodiments, it can be provided that the replacement braking pressure is generated for a predetermined first period based on the determined replacement braking request signal and the replacement braking request signal is then reduced to zero within a transition period, in particular linearly, with the replacement braking pressure during the transition period being based on a sum of the Substitute brake request signal and the detected brake request signal is generated by means of the brake pressure control system. Accordingly, after reaching the replacement braking pressure, which is set based on the replacement braking request signal, the replacement braking request signal is reduced, which at the same time leads to a reduction in the replacement braking pressure. In order to keep the deceleration of the vehicle constant, this reduction must be compensated for by actuating the brake actuation device and thus generating a corresponding braking request signal. A transition sequence is thus provided in which the substitute braking request signal is increasingly reduced, for example linearly reduced.

According to some embodiments of the brake system, the sensor for detecting the braking request signal can be an actuation sensor, which is designed to detect an actuation, in particular a travel, of a brake actuation device. The detection of a travel, e.g. a pedal or a brake lever, is advantageously relatively fail-safe. In addition, the actuation signals detected by an actuation sensor can be converted and stored in a simple manner, which makes it easier to generate the substitute braking request signal.

The features and advantages disclosed herein for one aspect of the invention are also disclosed for the other aspects of the invention and vice versa.

The invention is explained below with reference to the figures of the drawings. From the figures show:

Figs. 1A, 1B show a schematic representation of a hydraulic circuit diagram of a brake system according to an exemplary embodiment of the invention;

Fig. 2 is a schematic representation of a flowchart of a

Method according to an embodiment of the invention;

Fig. 3 is a qualitative representation of the curves of a brake pressure, a

Travel of a brake pedal and a braking request during a method according to an embodiment of the invention; and

Fig. 4 is a qualitative representation of the curves of a brake pressure, a

Travel of a brake pedal and a braking request during a method according to a further embodiment of the invention.

In the figures, the same reference symbols designate identical or functionally identical components, unless otherwise stated.

In the figs. 1A and 1B, a braking system 100 for a vehicle is shown schematically, in particular for a road vehicle such as a car, a bus or a truck. The brake system 100 has at least one wheel brake cylinder 1, a braking force generation arrangement 110, a brake pressure control system 120 and a control system 130. The braking force generating arrangement 110 is shown in FIG. 1A, the brake pressure control system 120 is shown in FIG. 1B. Portions of the control system 130 can be found in both Figures 1A and 1B.

As shown in FIG. 1B by way of example, one wheel brake cylinder 1 can be provided for each wheel. The wheel brake cylinder 1 is designed to convert a hydraulic pressure into a movement of a friction lining in order to press it against a friction piece 101 coupled to the wheel with a contact pressure force proportional to the hydraulic pressure, so that a friction or braking force inhibiting the rotation of the wheel is produced.

As shown in FIG. 1A , the braking force generating arrangement 110 has an actuation sensor 30 and a first pressure generating device 10 . Optionally, the braking force generation arrangement 110 can also have a brake master cylinder 12 kinematically coupled to a brake pedal 2 and a reservoir 15 for holding brake fluid. Instead of a brake pedal 2, a brake lever or, in general, a brake actuation device could also be provided. For reasons of clarity, reference is made below to a brake pedal 2, although the invention is not limited thereto. The actuation sensor 30 is used to detect a braking request, which represents a target deceleration of the vehicle. For example, actuation sensor 30 can be a travel sensor that is set up to detect a travel or displacement of a brake pedal 2 that can be actuated by a driver.

The master brake cylinder 12 is kinematically coupled to the brake pedal 2 and can be actuated by it. By moving the brake pedal 2, brake fluid is transported out of the master brake cylinder 12. As shown by way of example in FIG. 1A, the master brake cylinder 12 can be hydraulically coupled to a reset simulator 14, which generates a reset force that is proportional to the actuating travel of the pedal 2. Furthermore, the master brake cylinder 12 can be hydraulically coupled to and separated from the wheel brake cylinder 1 via first isolating valves 13A. 1A shows an example of a state in which the first isolating valves 13A are open and the master brake cylinder 12 is thus hydraulically coupled to the wheel brake cylinder 1 . The first isolating valves 13A can be switchable solenoid valves, for example, which are open when de-energized.

As shown in Fig. 1A by way of example, the first pressure generating device 10 can be designed, for example, as a plunger 11 which has a piston 11B which can be displaced by a motor, in particular an electric motor 11A. The first pressure generating device 10 is hydraulically connected to the wheel brake cylinder 1 . In particular, the first pressure-generating device 10 can be hydraulically coupled to and separated from the wheel brake cylinder 1 via second isolating valves 13B, as is shown by way of example in FIGS. 1A, 1B. 1A shows a state, purely by way of example, in which the second isolating valves 13B are closed and the first pressure-generating device 10 is thus hydraulically separated from the wheel brake cylinder 1 . The second isolating valves 13B can be switchable solenoid valves, for example, which are normally closed.

The brake pressure control system 120 is generally used to set a wheel-specific brake pressure, for example, to perform an anti-lock function, such as eg ABS or ESP. As shown schematically in FIG. 1B, brake pressure control system 120 includes a second pressure-generating device 20, which can be actuated independently of first pressure-generating device 10. As shown by way of example in FIG. 1B, the second pressure generating device 20 can have, for example, a pump 21 for each two wheels or wheel brake cylinders 1, the pumps 21 being actuated by a common motor 22, for example an electric motor. However, it is also conceivable that one pump 21 is provided for each wheel or wheel brake cylinder 1 . As shown schematically in FIG. 1B, the pump 21 is arranged in a hydraulic path which connects the first pressure generating device 10 and, when the first isolating valves 13A are open, the master brake cylinder 12 to the respective wheel brake cylinder 1. As is also shown schematically and purely by way of example in Fig. 1B, the brake pressure control system 120 can have an inlet valve 23 and an outlet valve 24 for each wheel brake cylinder 1, with the inlet valve 23 being arranged in a hydraulic path which connects a pressure outlet of the pump 21 to the wheel brake cylinder 1 connects, and wherein the inlet valve 23 is arranged in a hydraulic path which connects a suction inlet of the pump 21 with the wheel brake cylinder 1. The inlet and outlet valves 23, 24 can in particular be switchable solenoid valves, so that by operating the second pressure generating device 20 and actuating the inlet and outlet valves 23, 24, wheel-specific brake pressure adjustment is possible.

In particular, the control system 130 can have a first control unit 131 and a second control unit 132 . In principle, however, it is also conceivable to provide only one control unit. The control units 130 can, in particular, be a processor unit (not shown), e.g. with one or more CPUs, FPGAs, ASICS or the like, and a data memory (not shown), in particular a non-volatile data memory such as an HDD memory or an SSD memory exhibit. For example, software can be stored in the data memory, which can be executed by the respective processor unit in order to generate output signals. The first and the second control unit 131, 132 are signal-connected, for example by a data bus 133 such as a CAN bus. Furthermore, the actuation sensor 30 is connected to the first and/or the second control unit 131, 132, for example via the data bus 133 or another wireless or wired connection. The first pressure generating device 10 is also signal-connected to the second pressure generating device 20 and optionally to the inlet and outlet valves 23, 24. This signal connection can also be implemented, for example, via the data bus 133 or another wired or wireless connection. The second control unit 132 is signal-connected to the first pressure-generating device 10 and to the first and second isolating valves 13A, 13B, for example via the data bus 133 or another wired or wireless connection. The control system 130 is thus signal-connected to the actuation sensor 30, the first pressure generating device 10 and the brake pressure control system 120. Optionally, the control system 130 can also be signal-connected to an electric machine 150, eg via the data bus 133 or another wired or wireless connection. The electric machine 150 is kinematically coupled to one or more wheels of the vehicle and can be operated both as a motor and as a generator. For example, the first and/or the second control unit 131, 132 can have an interface for connection to the electrical machine 150.

The sequence of a method M for braking a vehicle is shown schematically in FIG. 2 . This method M can be carried out in particular with the aid of the braking system 100 explained above. In particular, the control system 130 can be set up to cause the braking system 100 to carry out this method M. Therefore, the method M is described below with reference to the process shown in Figs. 1A and 1B will be discussed.

In a first step M1 of the method, a braking request signal, which represents a target deceleration of the vehicle. For example, the brake request signal can be detected based on the actuation of brake pedal 2 or generally a brake actuation device, for example with the aid of travel sensor 30. In a further step M21, by means of the first

Pressure generating device 10 generates a brake pressure in the wheel brake cylinder 1 based on the detected brake request signal. For example, second control unit 132 can use the detected brake request signal to determine the brake pressure that must be set in the wheel brake cylinder to achieve the desired deceleration, and output a corresponding actuation signal to first pressure-generating device 10 in order to cause it to set the brake pressure. As an alternative or in addition to step M21, a braking torque is generated in a step M22 by means of electric machine 150, which is kinematically coupled to a wheel of the vehicle, based on the braking request signal. In particular, in the case of an electrically powered vehicle or a hybrid vehicle, the electric machine 150 driving the wheel can be operated as a generator to brake the vehicle. It should be noted that the braking force generation arrangement 110 and the brake pressure control system 120 are also provided when purely regenerative braking is carried out exclusively using the electric machine 150, e.g. in the event that the braking torque generated by the electric machine 150 is not sufficient to achieve the desired deceleration of the vehicle.

In step M3, a fault state of the first pressure-generating device 10 is detected M3. For example, the functional state of the first pressure-generating device 10 can be determined in a step M30. In a further step M31 it can be determined whether the functional state corresponds to an error state. An error state of the first pressure generating device 10 can exist when it is no longer able to set the desired brake pressure. This can be the case, for example, if the pressure-generating device 10 itself is defective, for example because the electric motor 11 is damaged, or if the pressure-generating device 10 no longer receives an actuation signal from the second control unit 132 . The last-mentioned case can occur, for example, if the detection of the brake request signal no longer works, for example due to a defect in sensor 30, or if the determination of the brake pressure using second control unit 132 no longer works. The detecting of Error status can, for example, using the first control unit 131 by evaluating a control signal which is sent to the first control unit 131 . For example, the second control unit 132 can send the first control signal to the first control unit 131 . The first control signal can contain, for example, the brake pressure determined by second control unit 132, the brake request signal and/or a status signal that represents the functional state. First control unit 131 can thus, for example, use the functional state contained in the control signal to detect an error state of first pressure-generating device 10, using an absence of the control signal from second control unit 132, or using characteristic parameters in the control signal, such as a gradient.

If it is determined in step M31 that there is no error condition as shown in Fig.

2 denoted by the symbol , the method can return to step M30, for example. If, in step M31, it is determined that an error condition exists, as indicated by the "+" symbol in Figure 2, the method moves to steps M4 and optionally M40. In the optional step M40, the first isolating valves 13A are opened, e.g. by the second control unit 132, and the second isolating valves 13B are further optionally closed, e.g. by the second control unit 132. Thus, if an error condition of the first pressure generating device is detected, the master brake cylinder 12 hydraulically the wheel brake cylinder 1 coupled and the first pressure generating device 10 is hydraulically separated from the wheel brake cylinder 1.

In step M4, a substitute braking request signal is determined based on a target deceleration that is known at a predetermined point in time before the error state is detected. This can be done using the first control unit 131, for example. For example, this can determine an adjustment path of the brake pedal 2 at the predetermined point in time before the error state is detected. This can be done, for example, by the first control unit 131 receiving the signal from the actuation sensor 30, for example directly from the actuation sensor 30 or from the second control unit 132, and temporarily storing the values for a certain period of time. For example, you can always use the values stored for the 500 ms past the current time. A last valid value can then be used to determine the brake pressure that is to be set in the wheel brake cylinder 1 from the adjustment travel. As an alternative or in addition, determining the substitute braking request signal can include determining a brake pressure in the wheel brake cylinder 1 at the predetermined point in time before the error state is detected. For example, the first control unit 131 can be connected to a pressure sensor 31, which detects a pressure in the hydraulic path connecting the first pressure-generating device 10 to the wheel brake cylinder 1, in particular at a point in front of the suction inlet of the pump 21 of the second pressure-generating device 20, as shown in Fig 1B is shown by way of example. In this case, too, the first control unit 131 can temporarily store the values recorded by the pressure sensor 31 for a certain period of time, for example the values for the 500 ms preceding the current point in time. A last valid value can then be used as the target pressure that is to be set in the wheel brake cylinder 1 . For example, the last valid value can be a value that is a predetermined period of time ago, for example 200 ms. If, in addition to braking system 100, an electric machine 150 is operated as a generator in order to brake the vehicle, as described above, the substitute braking torque can alternatively or additionally also be determined based on the braking torque generated by electric machine 150. For example, the first control unit 131 can be connected to power electronics of the electrical machine 150 and receive the braking torque generated by the electrical machine 150 from them. This braking torque can then be used to calculate the last valid braking request and use this to determine the required hydraulic braking pressure. If the braking torque was generated exclusively by electrical machine 150 in step M22, the substitute braking torque is determined based on the braking torque generated by electrical machine 150. In this case, determining the substitute braking request signal can optionally also include determining a brake pressure in wheel brake cylinder 1 at the predetermined point in time before the error state is detected, for example using pressure sensor 31, as described above. In general, the replacement braking request signal as constant value can be determined, which corresponds to the last valid brake request signal.

In step M5, a substitute braking pressure is then generated in the wheel brake cylinder 1 based on the determined substitute braking request signal with the aid of the second pressure generating device 20 of the brake pressure control system 120 . For this purpose, the first control unit 131 outputs an actuation signal to the second pressure generating device 20 in order to cause this to adjust the determined substitute brake pressure. Furthermore, the first control unit 131 opens the inlet valve 23 and closes the outlet valve 24 of the respective wheel brake cylinder 1. For example, generating M5 the replacement brake pressure can include generating a linear, a stepwise, and/or a progressive or a degressive pressure increase in the wheel brake cylinder 1. If necessary, the generation of a braking torque can be stopped using electric machine 150 in step M5.

Optionally, in step M5, the substitute braking request signal can be generated for a predetermined first period of time based on the ascertained substitute braking request signal. During the first period of time, the substitute braking request signal can be constant, in particular. Subsequent to the first time period, the replacement braking request signal can be reduced to zero, e.g. linearly, within a transition time period. During the transition period, the replacement braking pressure is generated based on a sum of the replacement braking request signal and the detected braking request signal by means of the brake pressure control system.

An advantage of the method M described is that as soon as a failure of the first pressure-generating device is detected, a substitute braking request is determined using input variables that were determined before the failure of the first pressure-generating device. It is therefore not necessary to wait for the driver to press the brake pedal again in order to generate a new valid input value, which may be necessary, for example, if the brake pressure in the wheel brake cylinder 1 drops as a result of the opening of the first isolating valve 13A. On the basis of the replacement braking request, the control system 130 can very quickly generate a setpoint brake pressure which is at least approximately the last valid setpoint brake pressure is determined and set immediately by the brake pressure control system.

In the figs. 3 and 4 these and other advantages of the method M described become clear. 3 shows four diagrams (A), (B), (C), (D), in which the abscissa is the time axis valid for all diagrams (A)-(D). The current brake pressure in wheel brake cylinder 1 is plotted on the ordinate of diagram (A). The current desired braking signal or the current substitute desired braking signal is plotted on the ordinate of diagram (B). The travel of the brake pedal 2 is plotted on the ordinate of the diagram (C). A is plotted on the ordinate of the diagram (D). The diagrams (A)-(D) shown in Fig. 3 show the course of braking that is carried out with the braking system 100 described above according to the method M described, the deceleration of the vehicle being carried out entirely or at least partially by the braking system 100 t will.

At the point in time t0 drawn in FIG. 3, the brake pressure is generated by means of the first pressure generating device 10 in the manner described above. That is, steps M1, M21 and M3 are executed. As can be seen in diagram (C) of FIG. 3, the pedal 2 is kept shifted by a constant travel. Accordingly, the desired braking shown in diagram (B) of FIG. 3 and the counterforce on pedal 2 shown in diagram (D) of FIG. 3 are constant. Accordingly, the first pressure generating device 10 generates a constant brake pressure in the wheel brake cylinder 1, as shown in diagram (A) of FIG.

At time t1, an error state of first pressure generating device 10 is detected when step M3 is executed. Therefore, the first isolation valves 13A are opened and the second isolation valves 13B are preferably closed, as described above. Diagram (A) of FIG. 3 shows the further progression of the brake pressure, which is generated by the execution of method M by means of brake pressure control system 120, in a full line. The dashed line shown in diagram (A) of FIG. 3 shows the brake pressure that the brake pressure control system 120 would generate if it were based solely on the brake request signal and not on the Substitute brake request signal would be actuated. As can be seen in diagram (A) of FIG. 3, the brake pressure drops abruptly at time t1, since brake fluid flows at high pressure into master brake cylinder 12 as a result of the opening of first isolating valves 13A. Accordingly, the pedal 2 is pushed back (diagram (C) of Fig. 3) and the counterforce on the pedal 2 increases (diagram (D) of Fig. 3). Due to the change in the pedal travel 2, the desire to brake also decreases, as can be seen in diagram (B) in FIG. It can optionally also be provided that upon detection of a fault condition in braking force generating arrangement 110 or in first pressure generating device 10, the braking request signal is initially generated based on the pressure detected by pressure sensor 31, for example because actuation sensor 30 has failed. In this case, too, the braking request would be reduced at time t1, since the braking pressure is reduced as a result of the opening of the first isolating valve 13A. In diagram (B), the dashed line shows the braking request that would result solely from the actuation of brake pedal 2, which corresponds to the braking request signal. The dash-dotted line in diagram (B) of FIG. 3 shows the substitute braking request signal which is generated in step M4 of method M explained above.

As can be seen from the dashed line in diagram (B) in FIG. 3, the substitute braking request signal is generated from point in time t2 (step M4 of method M). The delay at time t1 results, for example, from the evaluation or computing time that control system 130, in particular first control unit 131, requires in order to determine the substitute braking request signal. As can be seen in diagram (B) of FIG. 3, the substitute braking request signal is generated in such a way that it corresponds to the last valid braking request signal before time t1. Due to the substitute braking request signal, the second pressure generation device 20 of the brake pressure control system 120 begins to build up the brake pressure in the wheel brake cylinder 1 again, with the brake pressure that was present in the wheel brake cylinder 1 before the failure of the first pressure generation device being reached again at time t4, as can be seen in the course of the full line can be seen in diagram (A) of FIG. The period of time t24 between the times t2 and t4 can thus be referred to as the reaction time of the brake pressure control system 120. As can be seen from the dashed line in diagram (A) of Fig. 3, without this described method M the pressure continue to fall until time t3 there is an equilibrium between the counterforce on the brake pedal 2 and the brake pressure. The driver then needs a certain reaction time to press the pedal 2 further down again, which occurs again from time t5, as can be seen in diagrams (C) and (D) of FIG. The period of time t25 between the time t2 and t5 can thus be regarded as the reaction time of the driver.

In the diagrams (A)-(C), the dashed line shows the profile that would result without the method M described above if only the actuation of the pedal 2 is used to generate the brake request signal. As can be seen from the course of the dashed lines in diagrams (C) and (D) of FIG. 3, from time t5 onwards the travel of pedal 2 is increased again due to the increase in pedal force. Accordingly, the braking request signal is determined and the braking request increases again, as can be seen from the dashed line in diagram (B) of Fig. 3, causing brake pressure control system 120 to adjust the brake pressure accordingly, with the brake pressure being reached at time t6 , which was present before the failure of the first pressure generating device 10 (dashed line in diagram (A) of Fig. 3). The period of time t46 thus represents the shortening of the time that can be achieved by the method M described above in order to restore the brake pressure that was present before the failure of the first pressure-generating device 10 .

As shown in diagrams (B)-(D) of FIG. 3 by way of example, when the method M is executed, a transition process can be performed from time t5. As already explained, during the execution of step M5, the actual brake request signal, which is determined based on the actuation of brake pedal 2, can be ignored and only the determined substitute brake request signal can be used to generate the brake pressure in wheel brake cylinder 1, at least for a predetermined period of time, which is shown in Fig 3 corresponds to the period of time t25. In diagram (B) of FIG. 3, the double-dashed line shows a braking request that occurs in the method M described after failure of the first pressure-generating device 10 by the Actuation of the brake pedal 2 is generated, the corresponding travel of the pedal 2 and the associated pedal force in the diagrams (C) and (D) of Fig. 3 are shown as a solid line. The chain line in diagram (B) of FIG. 3 shows the substitute braking request signal. The full line in diagram (B) of FIG. 3 shows the sum of the substitute braking request signal and the braking request signal generated by actuating the brake pedal 2 . As can be seen in the diagrams (B)-(D) of Fig. 3, the replacement braking request signal can be reduced to zero from time t5 within a predetermined transition period t57 up to time t57, e.g. by a linear reduction of the replacement braking request signal, as shown in Fig. 3 shown by way of example. In order to keep the sum of the desired braking signal generated by actuating brake pedal 2 and the substitute braking command signal constant, the driver must compensate for the reduction in the substitute braking command signal by actuating pedal 2 . This is shown by way of example in FIG. 3 , the replacement braking request being reduced to zero at time t7 and the braking request signal being provided again exclusively by actuating pedal 2 . As described above, the substitute brake pressure is thus generated within the transition period t57 based on a sum of the brake request signal and the substitute brake request signal. An advantage of this procedure is that the driver does not have to actuate the pedal 2 as quickly or firmly in order to maintain the deceleration of the vehicle.

The diagrams (A)-(D) shown in Fig. 4 show the course of braking that is carried out with the braking system 100 described above according to the method M described, when the braking torque is initially generated exclusively by the generator operation of the electrical machine 150 is achieved (step M22 of the process M is executed).

At the point in time t0 shown in FIG. 4, the brake pressure is not generated by the first pressure generating device 10, since the electric machine alone generates the desired braking torque. This means that steps M1, M22 and M3 of method M from FIG. 2 are carried out. As can be seen in diagram (C) of FIG. 4, the pedal 2 is kept shifted by a constant travel. Accordingly, the in Diagram (B) of FIG. 4 and the counteracting force on pedal 2 shown in diagram (D) of FIG. 4 are constant.

At time t1, an error state of first pressure generating device 10 is detected when step M3 is executed. In the present case, this can be a failure of the actuation sensor 30, for example. Therefore, the first isolation valves 13A are opened and the second isolation valves 13B are preferably closed, as described above. The opening of the first isolating valve 13A causes the pedal 2 to be pushed further as a result of the driver actuating the pedal 2 (diagram (C) of FIG. 4), with the pedal force dropping due to the now missing restoring force of the simulator 14 (diagram (D) of Fig. 4). Diagram (A) of FIG. 4 shows the further progression of the brake pressure, which is generated by the execution of method M by means of brake pressure control system 120, in a full line. The dashed line shown in diagram (A) of FIG. 4 shows the brake pressure that the brake pressure control system 120 would generate if it were actuated solely on the basis of the brake request signal and not based on the substitute brake request signal. As can be seen in diagram (A) of FIG. 4, the brake pressure rises slightly at time t1, since brake fluid flows out of the master brake cylinder 12 as a result of the opening of the first isolating valves 13A and the actuation of the pedal 2. Since actuation sensor 30 fails in the present example, the braking request ceases at time t1. Provision can optionally also be made for the brake request signal to be initially generated on the basis of the pressure detected by pressure sensor 31 when a fault condition is detected in braking force generation arrangement 110 or in first pressure generation device 10 . In this case, too, the braking request at time t1 would be very small, since the opening of the first isolating valve 13A only results in pressure equalization.

As can be seen from the dashed line in diagram (B) in FIG. 4, the substitute braking request signal is generated from time t2 (step M4 of method M). The delay at time t1 results, for example, from the evaluation or computing time that control system 130, in particular first control unit 131, requires in order to determine the substitute braking request signal. As in diagram (B) of Fig. 4 can be seen, the replacement braking request signal is generated in such a way that it corresponds to the last valid braking request signal before time t1. Due to the substitute braking request signal, the second pressure generation device 20 of the brake pressure control system 120 begins to build up the brake pressure in the wheel brake cylinder 1, with the braking pressure being reached at time t4, which corresponds to the braking torque that is represented by the braking request, as can be seen from the course of the full line in the diagram (A) of Fig. 4 can be seen. For example, this braking torque can correspond to the braking torque previously generated by electric machine 150, with the generator operation of electric machine 150 being stopped. The period of time t24 between the times t2 and t4 can thus be referred to as the reaction time of the brake pressure control system 120. As can be seen from the dashed line in diagram (A) of FIG. 4, without the method M described, the pressure would initially remain constant until the driver reacts and presses the pedal 2 further down, which occurs again from time t5, like this can be seen in diagrams (C) and (D) of FIG. The period of time t25 between the time t2 and t5 can thus be regarded as the reaction time of the driver.

In diagrams (A)-(C), the dashed line shows the progression that would result without method M if only the actuation of pedal 2 is used to generate the brake request signal or the resulting pressure detected by pressure sensor 31 . As can be seen from the course of the dashed lines in diagrams (C) and (D) of FIG. 4, from time t5 onwards the travel of pedal 2 is increased again due to the increase in pedal force. Accordingly, the braking volume is shifted into wheel brake cylinder 1, the pressure detected by pressure sensor 31 increases and the actual braking request generated by the driver increases again, as can be seen from the dashed line in diagram (B) of FIG. 4, causing brake pressure control system 120 to do so is to set the brake pressure accordingly, with the brake pressure being reached at time t6, which was present before the failure of the first pressure-generating device 10 (dashed line in diagram (A) of FIG. 3). The time period t46 thus represents the shortening of the time that results from the method M described above can be achieved in order to restore the braking torque present before failure of the first pressure-generating device 10 .

As is shown by way of example in the diagrams (B)-(D) of FIG. 4 and has already been explained above in connection with FIG. As already explained, during the execution of step M5, the actual brake request signal, which is determined based on the actuation of brake pedal 2, can be ignored and only the determined substitute brake request signal can be used to generate the brake pressure in wheel brake cylinder 1, at least for a predetermined period of time, which is shown in Fig 4 corresponds to the period of time t25. In diagram (B) of FIG. 4, the double-dashed line shows a braking request that is generated in the described method M after failure of the first pressure-generating device 10 by the actuation of the brake pedal 2, with the corresponding travel of the pedal 2 and the associated pedal force in the diagrams ( C) and (D) of Fig. 4 are shown as solid lines. The dash-dotted line in diagram (B) of FIG. 4 shows the substitute braking request signal. The full line in diagram (B) of FIG. 4 shows the sum of the substitute braking request signal and the braking request signal generated by actuating the brake pedal 2 . As can be seen in the diagrams (B)-(D) of FIG. 4, the substitute braking request signal can be reduced to zero from time t5 to time t7, e.g. linearly as shown in FIG. The period between t5 and t7 is therefore referred to as the transition period t57. In order to calculate the sum of the brake request signal generated by the actuation of the brake pedal 2 and the

To keep the replacement brake request signal constant, the driver must compensate for the reduction in the replacement brake request signal by pressing pedal 2. In the example shown in FIG. 4 , the replacement braking request is at zero at time t7 and the braking request signal is again generated exclusively by actuating pedal 2 . As described above, the substitute brake pressure is thus generated within the transition period t57 based on a sum of the brake request signal and the substitute brake request signal. An advantage of this procedure is that the driver does not have to actuate the pedal 2 as quickly or firmly in order to maintain the deceleration of the vehicle. Although the present invention has been explained above by way of example using exemplary embodiments, it is not limited thereto but can be modified in many different ways. In particular, combinations of the above exemplary embodiments are also conceivable.

Claims

Expectations

A method (M) for braking a vehicle, comprising:

Detecting (Ml) a braking request signal, which represents a target deceleration of the vehicle;

Generating (M21) a hydraulic brake pressure in a wheel brake cylinder (1) based on the detected braking request signal by means of a first pressure generation device (10) which is hydraulically connected to the wheel brake cylinder (1);

detecting (M3) an error state of the first pressure generating device (10);

determining (M4) a substitute braking request signal when an error state of the first pressure generating device (10) is detected, the substitute braking request signal being determined based on a target deceleration known at a predetermined point in time before the error state is detected; and

Generating (M5) a substitute brake pressure in the wheel brake cylinder (1) based on the determined substitute braking request signal by means of a brake pressure control system (120) which has a second pressure generating device (20) hydraulically coupled to the wheel brake cylinder.

2. The method (M) according to claim 1, wherein the detection (M1) of a brake request signal includes detecting an actuation of a brake actuation device (2), and/or the determination (M4) of the substitute brake request signal includes a determination of a travel of a brake actuation device (2). the predetermined point in time prior to the detection of the fault condition.

3. The method (M) according to claim 1 or 2, wherein the determination (M4) of the replacement braking request signal is a determination of a brake pressure in Includes wheel brake cylinder at the predetermined time before the detection of the fault condition.

4. Method (M) according to any one of the preceding claims, additionally comprising:

Generating (M22) a braking torque by means of an electrical machine (150) kinematically coupled to a wheel of the vehicle based on the braking request signal.

5. Method (M) according to claim 4, wherein the substitute braking torque is determined based on the braking torque generated by the electric machine (150).

6. The method (M) according to any one of the preceding claims, wherein the brake pressure control system (120) has a first control unit (131) which actuates the second pressure generating device (20), and wherein a fault condition of the first pressure generating device (10) is detected using a control signal , which is sent to the first control unit (131).

7. The method (M) according to claim 6, wherein the first pressure generating device (10) is actuated by a second control unit (132) based on the brake request signal, the second control unit (132) generating the first control signal and sending it to the first control unit (131) sends.

8. Method (M) according to one of the preceding claims, wherein the generation (M5) of the replacement brake pressure comprises generating a linear, a gradual, and/or a progressive or a degressive pressure increase in the wheel brake cylinder (1).

9. The method (M) according to any one of claims 2 to 8, wherein by actuating the brake actuation device (2) by means of a master brake cylinder (12), a hydraulic reset pressure is generated in a reset simulator (14), and wherein, if a fault condition the first pressure generating device is detected, the master brake cylinder (12) is hydraulically coupled to the wheel brake cylinder (1), and the first pressure generating device (10) is preferably hydraulically separated from the wheel brake cylinder (1).

10. Method (M) for braking a vehicle, comprising:

Generating (M22) a braking torque by means of an electrical machine (150) kinematically coupled to a wheel of the vehicle based on the braking request signal,

Provision of a first pressure generating device (10) connected hydraulically to a wheel brake cylinder (1) for generating a brake pressure in the wheel brake cylinder (1) based on the brake request signal;

detecting (M3) an error state of the first pressure generating device (10);

Determining (M4) a substitute braking request signal when an error state of the first pressure generating device (10) is detected, the substitute braking request signal being determined based on a target deceleration known at a predetermined point in time before the error state is detected, based on the braking torque generated by the electric machine; and

11. Method (M) according to one of the preceding claims, wherein the replacement braking pressure is generated for a predetermined first period (t25) based on the determined replacement braking request signal and the replacement braking request signal is then reduced to zero within a transition period (t57), in particular linearly, wherein during of the transition period (t57) the substitute brake pressure is generated based on a sum of the substitute brake request signal and the detected brake request signal by means of the brake pressure control system (120).

12. Brake system (100) for a vehicle, comprising: a sensor (30) for detecting a braking request; a wheel brake cylinder (1) for generating a frictional force on a wheel of the vehicle; a first pressure generating device (10) which is hydraulically coupled to the wheel brake cylinder (1) and is set up to generate a hydraulic pressure in the wheel brake cylinder (1); a brake pressure control system (120) with a second pressure generating device (20) which is hydraulically coupled to the wheel brake cylinder (1) and set up to generate a hydraulic pressure in the wheel brake cylinder (1) independently of the first pressure generating device (10); and a control system (130) which is signal-connected to the actuation sensor (30), the first pressure generating device (10) and the brake pressure control system (120) and is set up to use the brake system (100) to carry out a method (M) according to one of the preceding claims to cause.

13. Brake system (100) according to claim 12, wherein the sensor for detecting the brake request signal is an actuation sensor (30) which is designed to detect an actuation, in particular a travel, of a brake actuation device (2).