Method for actuating a brake system in a vehicle

Abstract

The invention relates to a method for actuating a brake system in a vehicle, the brake system comprising a hydraulic vehicle brake and an electromechanical brake device, the electromechanical brake device being actuated in the event of a partial or complete failure of a brake booster unit of the hydraulic vehicle brake, and the electromechanical braking force is increased in multiple stages.

Description

Technical Field

[0001] The invention relates to a method for actuating a brake system in a vehicle, wherein the brake system comprises a hydraulic vehicle brake equipped with a brake booster unit and at least one electromechanical brake device equipped with an electric brake motor for generating an electromechanical braking force. Background Art

[0002] DE 102004004992 A1 describes a parking brake system in a vehicle, wherein a clamping force for fixing the vehicle in a stationary state is generated by an electric brake motor in that the electric brake motor moves a brake piston against a brake disk. The parking brake system can be integrated into a hydraulic vehicle brake. In normal braking operation, the hydraulic brake fluid presses the brake piston against the brake disk.

[0003] A method for operating a motor vehicle brake system, which is equipped with a hydraulic brake device, an electromechanical brake device and a brake pedal, is known from DE 10 2018 210 021. In the event of a failure of the hydraulic brake device, an electromechanical braking force is applied by the electromechanical brake device to decelerate the motor vehicle.

[0004] A method for operating a motor vehicle brake system is known from DE 102018208877 A1, which is equipped with a hydraulic brake device, an electromechanical brake device, a brake pedal as a first operating device and a button as a second operating device, wherein, in the event of a failure of the hydraulic brake device, an electromechanical braking force is generated by means of the electromechanical brake device to decelerate the motor vehicle, regardless of which of the two operating devices is operated. Summary of the invention

[0005] The method according to the invention relates to a vehicle having a hydraulic vehicle brake, which is braked by the hydraulic vehicle brake in normal braking operation by applying hydraulic brake pressure to wheel brake devices of the hydraulic vehicle brake so that a brake piston moves toward a brake disk in the direction of the wheel brake device.

[0006] Furthermore, the hydraulic vehicle brake has at least one brake booster unit for increasing the brake pressure generated by the driver. The brake booster unit is preferably electrically actuable, for example by means of an electrically actuable actuator, which is advantageously connected downstream of the master brake cylinder of the vehicle brake. The electrically actuable actuator is, for example, a plunger, which is driven by an electric motor. The plunger moves brake fluid into one or more brake circuits of the hydraulic vehicle brake and builds up hydraulic brake pressure.

[0007] In principle, the brake booster unit can also be designed to be non-electrically actuatable, for example hydraulically actuatable.

[0008] Furthermore, at least some of the wheel brakes of the hydraulic vehicle brake are each equipped with an electromechanical brake device with an electric brake motor, in particular the wheel brake devices on the left and right wheels of the rear axle of the vehicle. The electromechanical brake device with the electric brake motor can be actuated when the vehicle is parked in order to electromechanically generate a parking brake force that permanently immobilizes the vehicle. In a preferred embodiment, the electric brake motor of the electromechanical brake device acts on the same brake piston as the hydraulic vehicle brake.

[0009] In the method for operating a brake system according to the invention, in the event of a partial or complete failure of the brake booster unit of a hydraulic vehicle brake, an electromechanical brake device is operated in addition to the hydraulic brake force during the braking process. This is done by increasing the electromechanical brake force in multiple stages, wherein the electromechanical brake force remains constant or at least approximately constant in each stage. The electromechanical brake force is thus established according to a step function. It has been shown that this approach can significantly improve the brake force regulation. Dead times that could affect the brake force regulation are eliminated or at least reduced. Even if the brake booster of a hydraulic vehicle brake fails or partially fails, the brake force regulator for the hydraulic vehicle brake and the electromechanical brake device can continue to be used.

[0010] According to an advantageous embodiment, a maximum electromechanical brake force assistance is provided, wherein each electromechanical brake force level corresponds to a defined percentage of the maximum electromechanical brake force assistance. For example, the maximum electromechanical brake force assistance is provided at a deceleration of 4 m / s. 2 The value of the maximum electromechanical brake force assistance may be determined according to vehicle regulations and / or according to the current driving situation, for example as a function of current driving state variables and operating variables such as current vehicle speed or vehicle load. The different stages of the electromechanical brake force build-up may be different percentage values ​​of the maximum electromechanical brake force assistance, wherein both equidistant distances between the stages and different distances between the stages are possible.

[0011] During the build-up, different numbers of steps of the electromechanical braking force can be taken into account. Preferably, at least three steps or at least four steps are specified, which are sufficient to achieve an improved braking force regulation. If necessary, at least seven steps or at least ten steps can also be specified. Both a fixed number of steps and different numbers of steps can be specified, in particular depending on current driving state variables and operating variables, such as the current vehicle speed or vehicle load.

[0012] The shortest actuation time for each stage to change from one stage to the next is advantageously at least 20 milliseconds, preferably at least 50 milliseconds. This ensures a targeted setting of the stages. The shortest actuation time can be fixed or variably specified, in particular depending on current driving state variables and operating variables, such as the current vehicle speed or vehicle load.

[0013] The current actuation time of each stage may depend on state variables or operating variables of the vehicle, such as the voltage in the vehicle electrical system or the motor speed of the brake motor. Preferably, all stages have the same actuation time. Alternatively, different stages may also have actuation times of different lengths.

[0014] According to another advantageous embodiment, the maximum electromechanical brake force assistance is set to a value below the maximum possible mechanical brake force. This ensures that the maximum electromechanical brake force assistance is at most a level that avoids wheel locking. The maximum electromechanical brake force assistance represents an upper limit within which the electromechanical brake force can be built up in stages.

[0015] According to a further advantageous embodiment, the electromechanical braking force depends on the actuation level of the brake pedal and is limited to a maximum electromechanical braking force assistance when a brake pedal actuation limit value is reached. For example, a defined pedal force, for example 200 N, is specified as the brake pedal actuation limit value, with which the brake pedal is actuated. Alternatively, a defined pedal travel when the brake pedal is actuated can also be specified.

[0016] In another preferred embodiment, the electromechanical braking force is only generated when the hydraulic brake pressure in the hydraulic vehicle brake reaches or exceeds a minimum pressure (e.g. 5 bar). Within the minimum pressure, the hydraulic vehicle brake is only actuated and the electromechanical braking force is only generated when the minimum pressure is exceeded. However, below the minimum hydraulic pressure, the electric brake motor can be actuated without generating an electromechanical braking force in order to reduce the free travel until the brake pads come into contact with the brake disc. The reduction of the free travel can be associated with the additional condition that the hydraulic brake pressure is greater than zero or that the brake pedal travel is greater than zero.

[0017] Alternatively, the electric brake motor can also remain unactivated when the minimum hydraulic pressure falls below.

[0018] In principle, the brake control mechanism can be maintained even if the vehicle hydraulic brake and the electromechanical brake are actuated simultaneously. When the slip of one wheel of the vehicle increases, the electromechanical braking force acting on this wheel is preferably reduced first, and the hydraulic braking force generated is only reduced subsequently if a further reduction in the braking force is required.

[0019] According to another advantageous embodiment, the electromechanical braking force is built up and released in multiple stages, for example at the end of a braking process or when the braking force is reduced. The step-by-step reduction of the electromechanical braking force during release also facilitates the braking force regulation. However, if necessary, the electromechanical braking force can also be released in one step without intermediate stages, in particular when the driver completely withdraws the brake pedal.

[0020] The invention also relates to a control device, which is equipped with means for carrying out the above-described method. These means include at least one storage unit, at least one calculation unit, a control device input and a control device output. The control device can be used to control adjustable components of a hydraulic vehicle brake and / or an electromechanical brake device. If necessary, a plurality of control devices can be provided, one of which is assigned to the hydraulic vehicle brake and another to the electromechanical brake device.

[0021] The invention also relates to a brake system in a vehicle, wherein the brake system is equipped with a hydraulic vehicle brake and an electromechanical brake device with an electric brake motor and is also equipped with at least one control device as described above for actuating adjustable components of the brake system.

[0022] The present invention also relates to a vehicle having the above brake system, which is particularly a vehicle with at least two axles driven by a motor, such as a passenger car or a truck.

[0023] The invention also relates to a computer program product with a program code, which is designed to implement the above-mentioned method steps. The computer program product runs in the above-mentioned control device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further advantages and expedient embodiments are apparent from the further claims, the description of the figures and the drawings.

[0025] Figure 1 A schematic diagram of a hydraulic vehicle brake is shown with a brake booster forming an actuator, wherein the wheel brake device of the vehicle brake on the rear axle of the vehicle is additionally designed as an electromechanical brake device with an electric brake motor,

[0026] Figure 2 shows a cross-sectional view of an electromechanical brake device with an electric brake motor,

[0027] Figure 3 A flow chart with method steps is shown for generating an additional electromechanical braking force in the event of a partial or complete failure of a brake booster unit of a hydraulic vehicle brake.

[0028] Figure 4 Shows the connection Figure 3Flow chart of FIG. 1 with a control loop for limiting the electromechanical braking force.

[0029] In the figures, identical components are provided with the same reference numerals. DETAILED DESCRIPTION

[0030] Figure 1 The brake system in the vehicle shown in the figure comprises a hydraulic vehicle brake 1 having a front axle brake circuit 2 and a rear axle brake circuit 3 for supplying brake fluid under hydraulic pressure to and controlling the wheel brake device 9 on each wheel of the vehicle. In another embodiment, the brake circuits can also be constructed diagonally. The two brake circuits 2 and 3 are connected to a common master brake cylinder 4, which is supplied with brake fluid via a brake fluid storage container 5. The master brake cylinder piston in the master brake cylinder 4 is operated by the driver via a brake pedal 6, and the pedal stroke applied by the driver is measured by a pedal stroke sensor 7. Between the brake pedal 6 and the master brake cylinder 4 is a brake booster 10, which, for example, comprises an electric motor, which is preferably operated via a transmission device of the master brake cylinder 4 (intelligent booster, iBooster). The brake booster 10 forms an electrically controllable actuator for influencing the brake pressure. The intelligent booster 10 forms a brake booster unit.

[0031] The actuating movement of the brake pedal 6 measured by the pedal travel sensor 7 is transmitted as a sensor signal to the control device 11, in which an actuating signal is generated for actuating the brake booster 10. The brake fluid supply of the wheel brake device 9 is carried out in each brake circuit 2, 3 via different switching valves, which are part of the brake hydraulic system 8. The brake hydraulic system 8 also includes a hydraulic pump, which is a component of the electronic stability program (ESP).

[0032] The brake boosting can be performed additionally or alternatively by means of an electrically actuatable actuator which is connected downstream of master brake cylinder 4 of vehicle brake 1 .

[0033] The vehicle brake 1 is provided with an additional hydraulic supply line 24 which connects the brake fluid reservoir 5 to the outlet valve of the wheel brake device 9 .

[0034] Figure 2 , which is arranged on a wheel on the rear axle of the vehicle. The wheel brake device 9 is part of the hydraulic vehicle brake 1 and is supplied with brake fluid 22 from the rear axle brake circuit. The wheel brake device 9 also has an electromechanical brake device, which, like the hydraulic vehicle brake 1, is part of the brake system in the vehicle and is preferably used to immobilize the vehicle when stationary, but can also brake the vehicle when it is moving.

[0035] The electromechanical brake device comprises a brake caliper 12 with a clamp 19, which meshes (übergreift, overlaps) with a brake disk 20. As an adjustment mechanism, the brake device has a DC electric motor as a brake motor 13, whose rotor shaft drives the spindle 14 in rotation, on which a spindle nut 15 is supported. When the spindle 14 rotates, the spindle nut 15 moves in the axial direction. The spindle nut 15 moves in the brake piston 16, which is the carrier of the brake pad 17, which is pressed against the brake disk 20 by the brake piston 16. On the opposite side of the brake disk 20, there is another brake pad 18, which is fixedly held on the clamp 19. The brake piston 16 is sealed on its outer side in a fluid-tight manner relative to the housing that accommodates the brake piston by a surrounding sealing ring 23.

[0036] In the brake piston 16, the spindle nut 15 can move axially forward in the direction of the brake disk 20 when the spindle 14 rotates, or can move axially backward up to the stop 21 when the spindle 14 rotates in the opposite direction. In order to generate the clamping force, the spindle nut 15 acts on the inner end face of the brake piston 16, thereby pressing the brake piston 16, which is axially displaceably supported in the brake device, against the facing end face of the brake disk 20 with the brake pad 17.

[0037] For the hydraulic braking force, the hydraulic pressure of the brake fluid 22 from the hydraulic vehicle brake 1 acts on the brake piston 16. The hydraulic pressure can also play an auxiliary role when the vehicle is stationary when the electromechanical brake device is actuated, so that the total braking force is composed of the component provided by the electric motor and the hydraulic component. During vehicle travel, either only the hydraulic vehicle brake, or the hydraulic vehicle brake and the electromechanical brake device, or only the electromechanical brake device is active to generate the braking force. The control signals for actuating the adjustable components of the hydraulic vehicle brake 1 and the electromechanical wheel brake device 9 are generated in the control device 11.

[0038] Figure 3 A flow chart with method steps is shown for generating an additional electromechanical braking force in the event of a failure of a brake booster unit of a hydraulic vehicle brake. Figure 3 Refers to a braking situation in which the hydraulic vehicle brake is actuated but the brake booster (e.g., smart booster 10 or plunger) fails completely or at least partially. In this case, the braking force initiated by the driver by actuating the brake pedal is not or has not been sufficiently increased, so that the driver must press the brake pedal harder to achieve the same deceleration value compared to a complete hydraulic vehicle brake.

[0039] In the starting state according to method step 30, it is assumed that the above-mentioned partial or complete failure of the brake booster unit in the hydraulic vehicle brake has occurred. In the following method step 31, it is queried whether the hydraulic vehicle brake has been actuated, in particular by actuating the brake pedal. If not, then after the "No" branch ("N"), the process returns to the first method step 30 and checks again at periodic intervals whether the brake pedal has been actuated. If, on the other hand, the result of the query in step 31 shows that the driver has indeed actuated the brake pedal, then after the "Yes" branch ("Y"), the process proceeds to the next method step 32.

[0040] In method step 31 , as an alternative to actuation of the brake pedal, it may also be queried whether a braking force request has been made in any other way, in particular by an automatically operating driver assistance system.

[0041] In method step 32, it is queried whether the hydraulic brake pressure exceeds a first lower threshold value. If not, then after the "No" branch, the method returns to the starting point. However, if the current hydraulic brake pressure exceeds the lower threshold value, a minimum requirement must be assumed, which triggers subsequent actions.

[0042] In this case, the “yes” branch is followed by the next method step 33 , in which the free travel is reduced by actuating the electromechanical braking device until the brake pad comes to bear against the brake disk.

[0043] If necessary, the free travel can be reduced below the lower limit value, which represents the minimum pressure. This has the advantage that the dead time during the electromechanical braking force connection can be reduced as the braking demand increases.

[0044] After the electromechanical brake device has been pre-positioned in method step 33, a further query is made in the next method step 34 whether a second brake pressure limit value has been exceeded, which is higher than the first brake pressure lower limit value according to method step 32. If not, then the method returns to method step 32 after the "No" branch. However, if the current brake pressure exceeds the limit value according to method step 34, then after the "Yes" branch, the next step 35 is continued, in which the electromechanical brake device is actuated by controlling the electric brake motor 13 and an electromechanical brake force is generated in addition to the hydraulic brake force. This can compensate for a partial or complete failure of the brake booster unit in the hydraulic vehicle brake.

[0045] Figure 4The method shows that in method step 35 an electromechanical brake device is activated with a control circuit for limiting the maximum electromechanical braking force generated. After the electromechanical braking force is activated in step 35, a query is made in the next step 36 whether the wheel slip on the relevant wheel generating the electromechanical braking force exceeds a threshold value. If so, the "yes" branch is followed to step 37, according to which the electromechanical braking force is automatically reduced in the electromechanical brake device. The method then returns to step 36 and inquires again at periodic intervals whether the wheel slip on the relevant wheel exceeds a threshold value.

[0046] If, on the other hand, the query result in step 36 shows that the wheel slip is still below the threshold value, then after the "No" branch, the method proceeds to step 38, in which it is queried whether the current braking requirement (i.e. the braking force required by the driver) is greater than the braking force provided by the electromechanical braking device (taking into account the hydraulic braking force). If so, then after the "Yes" branch, the method returns to step 35 and adjusts the electromechanical braking device accordingly to achieve the braking requirement. On the other hand, if the braking requirement is lower than the current electromechanical braking force, then after the "No" branch, the method can proceed to step 37 to reduce the electromechanical braking force. However, the method can also return to method step 35.

[0047] exist Figure 3 and Figure 4 In the build-up of the electromechanical braking force described in , the increase is carried out in multiple stages, wherein the electromechanical braking force remains constant or at least approximately constant in each stage. For example, the shortest actuation time for switching to a higher or lower stage is 50 milliseconds. A plurality of stages, for example three, four, five or even more stages, can be specified, wherein the electromechanical braking force is increased stepwise from one stage to another. The release of the electromechanical braking force can also be carried out in stages.

Claims

1. A method for actuating a brake system in a vehicle, wherein: The brake system comprises a hydraulic vehicle brake (1) and at least one electromechanical brake device, wherein the hydraulic vehicle brake is equipped with a brake booster unit (10, 25), and the electromechanical brake device is equipped with an electric brake motor (13) for generating an electromechanical braking force, wherein, in the event of partial or complete failure of the brake booster unit (10, 25) of the hydraulic vehicle brake (1), the electromechanical brake device is operated in addition to the hydraulic braking force during the braking process, so that the electromechanical braking force is increased in multiple stages, wherein the electromechanical braking force is kept constant or approximately constant at each stage.

2. The method according to claim 1, characterized in that The brake booster unit (10, 25) in the hydraulic vehicle brake (1) can be electrically actuated.

3. The method according to claim 1 or 2, characterized in that: A maximum electromechanical brake force assistance is specified, wherein each level of the electromechanical braking force corresponds to a defined percentage of the maximum electromechanical brake force assistance.

4. The method according to any one of claims 1 to 3, characterized in that At least three stages, preferably at least seven stages, in particular ten stages, of the electromechanical braking force are provided.

5. The method according to any one of claims 1 to 4, characterized in that In order to vary the electromechanical braking force, the electromechanical brake motor is actuated within an actuation time of at least 20 milliseconds, preferably 50 milliseconds, in order to increase or decrease the braking force component of the electric motor by one step.

6. The method according to claim 5, characterized in that The actuation time depends on state variables or operating variables, such as the voltage in the vehicle electrical system or the motor speed of the brake motor (13).

7. The method according to any one of claims 1 to 6, characterized in that The maximum electromechanical brake force assistance is set to a value that is lower than the maximum possible mechanical brake force.

8. The method according to any one of claims 1 to 7, characterized in that The electromechanical braking force depends on an actuation level of the brake pedal, wherein the electromechanical braking force is limited to the maximum electromechanical braking force assistance when a brake pedal actuation limit value is reached.

9. The method according to any one of claims 1 to 8, characterized in that The electromechanical braking force is only generated when the hydraulic brake pressure in the hydraulic vehicle brake (1) reaches or exceeds a minimum pressure of, for example, 5 bar.

10. The method according to claim 9, characterized in that If the hydraulic brake pressure falls below the minimum pressure, the electric brake motor (13) is actuated to reduce the free travel until the brake pads (17, 18) come into contact with the brake disk (20).

11. The method according to any one of claims 1 to 10, characterized in that If the slip of one wheel of the vehicle increases, the electromechanical braking force acting on this wheel is reduced.

12. The method according to any one of claims 1 to 11, characterized in that When the braking process is completed or the braking force is reduced, the electromechanical braking force is released in multiple stages.

13. A control device (11) having a device for actuating adjustable components of a hydraulic vehicle brake (1) and / or an electromechanical brake device, the control device being configured to carry out a method according to claim 1.

14. Braking system in a vehicle, comprising a hydraulic vehicle brake (1) and an electromechanical brake device with an electric brake motor (13), and comprising a control device (11) according to claim 13 for actuating adjustable components of the braking system.

15. Vehicle having a brake system according to claim 14. 16 . A computer program product having a program code which is designed to carry out the method according to claim 1 , when the computer program product is run in a control device ( 11 ) according to claim 13 .

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