DE102020213414A1 - Procedure for waking up a braking system - Google Patents

Abstract

The invention relates to a method for controlling a hydraulic brake system (1) having a master brake cylinder (3), a linear actuator (5), a hydraulic pump 5 (26) and at least one wheel brake (6, 7, 8, 9), the hydraulic Brake system (1) is woken up from a rest state by exerting a force on the brake master cylinder (3). In order to be able to implement a soft pedal feel as well as a brake booster, a flow-open hydraulic connection is established between the linear actuator (5) and the master brake cylinder (3), and the linear actuator (5) is controlled to generate a counterforce which is applied to the master brake cylinder ( 3) the force exerted is directed in the opposite direction and the hydraulic pump (26) is connected to the at least one wheel brake (6, 7, 8, 9) in an open-flow manner and is controlled in order to shift hydraulic volume into the at least one wheel brake (6, 7, 8, 9). .

Description

The invention relates to a method for controlling a hydraulic brake system with a master brake cylinder, a linear actuator, a hydraulic pump and at least one wheel brake, the hydraulic brake system being awakened from an idle state by exerting a force on the master brake cylinder, in particular by actuating a brake pedal.

In the course of the automation of motor vehicles, it is necessary to install multiple redundancies in safety-critical systems such as braking systems. Especially with fully automatic driving, the driver fails as a fallback to generate a braking force. Modern hydraulic brake systems therefore often have two or more independent actuators for building up hydraulic pressure in the wheel brakes. Typically, a linear actuator is combined with a hydraulic pump as two different types of actuators to exploit their respective advantages. However, as the last fallback level, direct access by the driver to the wheel brakes is usually still provided. In order to achieve this, the hydraulic valves are typically designed in such a way that, in the de-energized state, they establish a connection between a master brake cylinder, and thus the brake pedal, with the wheel brakes. In the event of a complete failure of the brake system control with the power supplies of the hydraulic valves, at least the mechanical functionality of the brake system is guaranteed.

Since the hydraulic valves have a power requirement that is not negligible, the brake system is put into a rest state when not in use, especially when the vehicle is parked and the ignition is deactivated. If one of several wake-up criteria is met, the brake system is switched from the idle state back to an operating state. One of the wake-up criteria is the application of force to the brake pedal. When the braking system is awakened from the rest state by applying a force to the brake pedal, the hydraulic valves are generally not initially in the preferred state for normal braking function.

Depending on the hydraulic connection, either a hard pedal feel can occur when the brake pedal is awoken or there is still no brake booster available.

Since the braking force can only be regulated very poorly by the driver when the pedal feels hard and the braking force applied by the driver may be insufficient without brake booster, such a system is not in an optimal state immediately after waking up.

It is therefore the object of the invention to specify a method with which optimal functionality is already available when the brake system is woken up from an idle state.

The object is achieved by a method according to the invention as claimed in claim 1, in which the hydraulic brake system is woken up from an idle state by exerting a force on the master brake cylinder. As soon as a pedal actuation is detected, a hydraulic connection open to flow is established between the linear actuator and the brake master cylinder. Thus, hydraulic volume is shifted into the linear actuator by actuating the master brake cylinder. The linear actuator is controlled in such a way that it generates a counterforce which opposes the force exerted on the master brake cylinder. The force on the master cylinder generates hydraulic pressure, which is directed through the open-flow connection into the linear actuator. This is pushed back by the hydraulic pressure, which means that a volume of brake fluid is pressed into the linear actuator. The counterforce is now designed in such a way that it counteracts this movement, but only to the extent that the linear actuator moves further back under the effect of the pressure from the master brake cylinder. The proportions between the force exerted on the master brake cylinder and the counterforce of the linear actuator depend on the active surfaces of the linear actuator and the master brake cylinder. The force acting on the linear actuator results from multiplying the hydraulic pressure prevailing there by the effective area of the displaceable piston of the linear actuator. The counterforce built up by the linear actuator, which results from the motor torque of the linear actuator, is chosen to be smaller than this force.

In addition, the hydraulic pump is connected to the at least one wheel brake in an open-flow manner and is controlled in order to shift hydraulic volume into the at least one wheel brake. Thus, the linear actuator does not function as a pressurization device, but as a simulator to create a soft pedal feel, with the actual task of the linear actuator, to generate braking pressure in the wheel brakes, being taken over by the hydraulic pump.

In a preferred embodiment of the invention, the hydraulic braking system includes a plurality of hydraulic valves and the rest The state of the brake system is a state in which the hydraulic valves of the brake system are in their respective de-energized state. In the idle state, the energy consumption of the braking system is therefore minimal or even zero. This ensures that an energy store in the vehicle, such as a vehicle battery, still has enough energy to be able to start the vehicle safely even after it has been stationary for a long time.

In a further preferred embodiment of the invention, the counterforce is determined based on an actuation variable. For example, the actuation variable can be measured by a computing unit, for example via a sensor, and the associated counterforce can be determined using a computing rule or a stored characteristic curve. This counterforce can then be generated by the linear actuator, in that it is driven, for example, with a motor torque that is necessary for this purpose or is regulated to a corresponding power or current consumption.

In a particularly preferred embodiment of the invention, the counterforce increases as the actuation variable increases, for example by suitably selecting the calculation rule or characteristic curve. As a result, the pedal has an increasingly hard pedal feel when it is actuated. This simulates the normal reaction of a mechanical braking system. Such behavior allows the brake pressure to be metered very precisely by the driver.

In a further particularly preferred embodiment of the invention, in a first range of the actuation variable, the counterforce has a first ratio to the actuation variable, and in a second range of the actuation variable, the counterforce has a second ratio to the actuation variable. In the case of a characteristic curve, this can thus be divided into at least two areas with different gradients. However, such behavior can also be implemented by a suitable calculation rule. In particular, the actuation magnitude may be greater in the second range than in the first range and the second ratio may be greater than the first ratio. In other words, a characteristic curve becomes steeper in the range of larger values of the actuation variable. However, this behavior can also be implemented by means of a calculation rule or other regulations and/or data.

In a further particularly preferred embodiment of the invention, the actuation variable includes a brake pedal position, a linear actuator position and/or a master brake cylinder pressure. All of these variables can be used to determine whether and how hard a driver has pressed a brake pedal. A suitable sensor system can be provided for this purpose. The brake pedal position can be determined using a pedal travel sensor on the brake pedal. The linear actuator position can be realized via a corresponding position sensor on the piston, a sensor of a motor of the linear actuator or in software by storing the movements made starting from a zero position. The master cylinder pressure can be measured by means of a hydraulic pressure sensor in the brake system, which at the time of the measurement is open to flow with the master brake cylinder or is arranged directly in it.

In a further preferred embodiment of the invention, the open-flow hydraulic connection between the linear actuator and the master brake cylinder is produced by opening a hydraulic valve. In normal operation, the linear actuator and brake master cylinder are typically separate from one another since they serve as alternative sources of pressure. However, a flow-open connection for carrying out the method according to the invention can be established in a simple manner by appropriate switching of the hydraulic valve(s) located in between.

In a further preferred embodiment of the invention, the hydraulic pump is controlled as a function of a braking request variable. Thus, a brake pressure and thus the braking force is regulated as required.

In a particularly preferred embodiment of the invention, the brake request variable includes a brake pedal position, a linear actuator position and/or a master brake cylinder pressure. The braking request variable can thus be selected from the same group as the actuation variable. It can therefore be identical to the actuation size or a different size can be selected. The variables can be determined as already explained for the actuation variable.

In a further preferred embodiment of the invention, the brake system comprises a simulator unit, which is connected to the master brake cylinder via a hydraulic valve that is closed when de-energized, the simulator valve. The task of the simulator is to simulate a suitable pedal feel in brake-by-wire mode. The simulator could therefore also generate a soft pedal feel when the brake system is woken up, but is typically decoupled from the master brake cylinder and thus the brake pedal in the idle state due to the normally closed valve. If the brake system is woken up by pressing the brake pedal, the brake pedal has already been activated pressure on the simulator valve. For cost reasons, this is usually designed in such a way that it cannot open under pressure. Thus, the simulator is not available immediately upon waking from sleep to create a soft pedal feel. However, since the simulator function is made available by the linear actuator according to the invention, the simulator valve can be of inexpensive design.

In a further preferred embodiment of the invention, a hydraulic connection between the master brake cylinder and the wheel brake is closed, so that in particular there is no flow-open connection between the master brake cylinder and the wheel brake. The brake pressure in the wheel brakes, which is made available by the hydraulic pump, can therefore not get into the master brake cylinder, which could affect the brake pedal and lead to unwanted feedback.

In a further preferred embodiment of the invention, the master brake cylinder is designed as a tandem master brake cylinder with two chambers, only one chamber being connected to the linear actuator in an open-flow manner, while the other chamber has no open-flow connection to the linear actuator. This is sufficient to ensure acceptable pedal feel while saving the cost of another connection.

The object is also achieved by a brake system comprising a master brake cylinder, a linear actuator, a hydraulic pump and at least one wheel brake, a control device of the brake system being provided which is set up to carry out one of the methods described above.

In a preferred embodiment of the brake system according to the invention, the control device comprises at least a first control unit and a second control unit, the first control unit being set up to control the hydraulic pump and the second control unit being set up to control the linear actuator. Additional redundancy is provided by dividing the activation between two separate control units. If one of the control units fails, the other pressurization device can still ensure that braking pressure can be built up in the wheel brakes independently of the driver.

• 1 zeigt schematisch eine erfindungsgemäße Bremsanlage,
• 2 zeigt eine Kennlinie der Gegenkraft;

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,
• 2 shows a characteristic of counterforce;

In 1 a hydraulic brake system 1 is shown, with which the method according to the invention can be carried out. The brake system 1 is equipped with an extended redundancy, as is required for autonomous driving. The brake system 1 works in a normal operating mode according to the brake-by-wire method. In this case, the driver exerts a braking force on a master brake cylinder 3 which is designed as a tandem master brake cylinder 3 . As a result, hydraulic volume is shifted via an open simulator valve 10 into a simulator 4, which generates a pedal feel. In the embodiment shown, only one chamber of the
Tandem brake master cylinder 3 connected to the simulator 4, while the second chamber only presses against a closed first check valve 21. The first shut-off valve 21 connects the tandem master brake cylinder 3 to a first sub-circuit of the brake system 1, which includes the wheel brakes 8, 9 of the rear left and front right wheels with the respective inlet valves 14 and outlet valves 15. A second shut-off valve 22 connects the tandem master brake cylinder 3 to the second sub-circuit of the brake system 1. The second sub-circuit of the brake system 1 includes the wheel brakes 6, 7 of the rear right and front left wheels with the respective inlet valves 14 and outlet valves 15. Also the second shut-off valve 22 is closed in normal operating mode. In the embodiment shown, the first and second pitch circles are constructed essentially symmetrically. A different distribution of the wheel brakes 6, 7, 8, 9 on the first and second pitch circle, for example with both front wheel brakes in the first pitch circle and the rear wheel brakes in the second pitch circle, is also possible.

Also provided in the brake system 1 is a linear actuator 5 which is connected to the first partial circuit via a first supply valve 19 and is connected to the second partial circuit via a second supply valve 20 . The first supply valve 19 separates the first sub-circle from the linear actuator 5 and the second supply valve 20 separates the second sub-circle from the linear actuator 5. Due to the symmetrical design, the second sub-circle can also be understood as the first sub-circle and the first sub-circle as the second sub-circle within the meaning of the invention. In a normal operating mode, the first supply valve is 19 and the second Supply valve 20 is opened so that the linear actuator 5 can deliver brake fluid to all wheel brakes 6, 7, 8, 9. The brake fluid flows out of the linear actuator 5, through an open changeover valve 25 of the respective sub-circuit and the inlet valve 14 of the respective wheel brakes 6, 7, 8, 9. The pump isolating valves 24 of the two sub-circuits are closed in normal operating mode. The braking force is thus generated by the linear actuator 5 .

The outlet valves 15 of the individual wheel brakes 6, 7, 8, 9 can be opened to reduce the pressure in the wheel brakes 6, 7, 8, 9, for example in the case of ABS control. The brake fluid then flows through the respective outlet valve 15 into a low-pressure reservoir 27 of the respective pitch circuit.

Both sub-circuits each have a hydraulic pump 26 which is connected to a changeover valve 25, a pump isolating valve 24 and a low-pressure accumulator 27. In a fallback level, the switching valves 25 can be closed and the pump isolating valves 24 can be opened. If the hydraulic pumps 26 are then activated, this brake fluid is pumped into the wheel brakes 6 , 7 , 8 , 9 . The hydraulic pumps 26 thus increase the braking pressure exerted by the driver via the tandem master brake cylinder 3 .

The first pitch circle and the second pitch circle are thus constructed essentially in parallel. The system pressure in the first partial circle can be determined by a pressure measuring device 16 . In addition, a further pressure measuring device 17 is arranged on the tandem master brake cylinder 3 in order to determine the brake pressure exerted by the driver. A connection between the second partial circuit and the reservoir 2 can be established by means of an anti-cavitation valve 23 . This can be switched in particular when the volume of brake fluid in the brake circuit is to be reduced.

1 shows the hydraulic valves of the brake system 1 in their de-energized state, as this is assumed at rest. When waking up from the idle state, the hydraulic valves should be put into their operating state and therefore at least partially energized. As already mentioned, the supply valves 19, 20 would be opened and the check valves 21, 22 closed in normal operation, so that a braking pressure could be built up by the linear actuator 5 and sent to the wheel brakes 6, 7, 8, 9. The pedal feel would be generated by the simulator 4, which would have to be connected to the master brake cylinder by switching the simulator valve 10. However, if the brake system 1 is woken up by the actuation of the brake pedal, then there is already pressure on the master brake cylinder 3 and thus on the simulator valve 10 . Therefore, the simulator valve 10 cannot open.

According to the invention, the simulator valve 10 is left closed. Instead, the check valves 21, 22 and the supply valves 19, 20 are opened and the switching valves 25 are closed. There is thus a connection between master brake cylinder 3 and linear actuator 5 and, separately from this, a connection between hydraulic pumps 26 and wheel brakes 6, 7, 8, 9. Based on the pedal position, which is measured by a pedal travel sensor, linear actuator 5 is now activated To generate counter force, which acts as a simulator and creates a soft pedal feel. For this purpose, a suitable counterforce is selected based on a characteristic curve for each pedal position and the linear actuator 5 is controlled to generate this counterforce. At the same time, also based on the pedal position, the hydraulic pump is controlled to generate hydraulic pressure in the wheel brakes 6, 7, 8, 9. Full functionality is thus already ensured when the brake system 1 is woken up. In the event of a subsequent reduction in pressure at the master brake cylinder, the simulator valve 10 can then be opened and, if the opening is successful, the other valves can be put into their state for normal operation.

In 2 a characteristic curve is shown which, for each pedal position 28, directly indicates a motor torque 29 of the linear actuator 5 required for the counterforce. In a first area 30, the pedal is still very soft, since increasing pedal travel is accompanied by only a slight increase in motor torque 29 and thus in the counterforce of linear actuator 5. In a second area 31, the characteristic curve becomes significantly steeper, so that even with a small movement, the motor torque 29 and thus the counterforce of the linear actuator 5 increase sharply. The pedal feel is much harder here.

Reference List

1

braking system

2

brake fluid reservoir

3

Tandem master cylinder

4

simulator

5

linear actuator

6

wheel brake

7

wheel brake

8th

wheel brake

9

wheel brake

10

simulator valve

14

intake valve

15

outlet valve

16

system pressure sensor

17

master cylinder pressure sensor

19

First supply valve

20

Second supply valve

21

First shut-off valve

22

Second shut-off valve

23

anti-cavitation valve

24

pump isolation valve

25

switching valve

26

hydraulic pump

27

low-pressure accumulator

28

pedal travel

29

engine torque

30

First area

31

second area

Claims (14)

Method for controlling a hydraulic brake system (1) having a master brake cylinder (3), a linear actuator (5), a hydraulic pump (26) and at least one wheel brake (6, 7, 8, 9), the hydraulic brake system (1) being A force is exerted on the master brake cylinder (3) from a rest state, characterized in that a hydraulic connection open to flow is established between the linear actuator (5) and the master brake cylinder (3), and the linear actuator (5) is controlled to generate a counterforce , which is directed in the opposite direction to the force exerted on the master brake cylinder (3) and the hydraulic pump (26) being open to flow and being connected to the at least one wheel brake (6, 7, 8, 9) and controlled, hydraulic volume into the at least one wheel brake ( 6, 7, 8, 9). procedure after claim 1 , characterized in that the hydraulic brake system (1) comprises a plurality of hydraulic valves (10, 14, 15, 19, 20, 21, 22, 24, 25) and the idle state is a state in which the hydraulic valves (10, 14 , 15, 19, 20, 21, 22, 24, 25) of the brake system (1) are in their de-energized state. procedure after claim 1 or 2 , characterized in that the counterforce is generated based on an actuation variable (28). procedure after claim 3 , characterized in that the counteracting force increases as the actuation variable (28) increases. procedure after claim 3 or 4 , characterized in that in a first range (30) of the operating variable (28) the counterforce has a first ratio to the operating variable (28) and in a second range (31) of the operating variable (28) the counterforce has a second ratio to the operating variable (28), wherein in particular the actuation variable (28) in the second region (31) is greater than in the first region (30) and the second ratio is greater than the first ratio. Procedure according to one of claims 3 until 5 , characterized in that the actuation variable comprises a brake pedal position (28), a linear actuator position and/or a brake master cylinder pressure. Method according to one of the preceding claims, characterized in that the flow-open hydraulic connection between the linear actuator (5) and the master brake cylinder (3) is established by opening a hydraulic valve (19, 20), Method according to one of the preceding claims, characterized in that the hydraulic pump (26) is controlled as a function of a braking requirement variable. procedure after claim 8 , characterized in that the brake request variable includes a brake pedal position, a linear actuator position and / or a master cylinder pressure. Method according to one of the preceding claims, characterized in that the brake system (1) comprises a simulator unit (4) which is connected to the master brake cylinder (3) via a hydraulic valve (10) which is closed when de-energised. Method according to one of the preceding claims, characterized in that a hydraulic connection between the master brake cylinder (3) and the wheel brake (6, 7, 8, 9) is closed, so that in particular there is no flow-open connection between the master brake cylinder (3) and the wheel brake (6, 7, 8, 9) exists. Method according to one of the preceding claims, characterized in that the master brake cylinder is a tandem master brake cylinder (3) with two chambers, only one chamber being open to flow with the linear actuator (5). is bound, while the other chamber has no flow-open connection to the linear actuator (5). Brake system comprising a master brake cylinder (3), a linear actuator (5), a hydraulic pump (26) and at least one wheel brake (6, 7, 8, 9), characterized in that a control device of the brake system (1) is set up to Procedure according to one of Claims 1 until 12 to perform. brake position after Claim 13 , characterized in that the control device comprises at least a first control unit and a second control unit, the first control unit being set up to control the hydraulic pump (26) and the second control unit being set up to control the linear actuator (5).

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