Method for Generating Braking Power by Actuating at Least One Electric Braking Motor in a Vehicle Parking Brake

Abstract

In a method for generating braking power by actuating at least one electric braking motor in a vehicle parking brake comprising two control devices, in the event of a failure of a first control device/braking motor unit, braking power is generated automatically via a second control device/braking motor unit if the vehicle speed is lower than a threshold value and/or if a characteristic value in the vehicle (e.g. the ignition status) indicates that the vehicle is at or is about to come to a standstill, but preferably only once a defined time interval has elapsed.

Claims

1. A method for generating braking power, the method comprising: actuating at least one electric braking motor in a vehicle parking brake of a vehicle, the vehicle parking brake having at least two controllers configured to control at the least one electric braking motor; and automatically activating, in response to a failure of a first controller-braking motor pair, a second controller-braking motor pair to generate braking power if at least one of (i) one of a vehicle speed of the vehicle and a corresponding driving state variable of the vehicle is less than an assigned limit value, and (ii) a characteristic variable of the vehicle indicates one of an existing vehicle standstill and an imminent vehicle standstill.

2. The method as claimed in claim 1, wherein: a first controller of the at least two controllers and a first electric braking motor of the at least one electric braking motor form the first controller-braking motor pair; and a second controller of the at least two controllers and a second electric braking motor of the at least one electric braking motor form the second first controller-braking motor pair.

3. The method as claimed in claim 2, wherein: the first controller is a master controller and the second controller is a slave controller; and the master controller is configured to, after evaluation of a vehicle state of the vehicle, forward control information to the slave controller.

4. The method as claimed in claim 1, wherein the characteristic variable indicating the one of the existing vehicle standstill and imminent vehicle standstill is at least one of an ignition state of the vehicle, a state of a door contact switch of the vehicle, a state of a seat occupancy detector of the vehicle, and a state of a belt lock of the vehicle.

5. The method as claimed in claim 1, wherein the one of the existing vehicle standstill and imminent vehicle standstill is detected in response to both (i) the one of the vehicle speed and the corresponding driving state variable being less than the assigned limit value and (ii) the characteristic variable adopting a value indicating the one of the existing vehicle standstill and imminent vehicle standstill.

6. The method as claimed in claim 5, wherein the automatically activating the second controller-braking motor pair to generate braking power occurs only after a defined period of time has elapsed since detecting the one of the existing vehicle standstill and imminent vehicle standstill.

7. The method as claimed in claim 5, further comprising: automatically removing, following the automatically activating the second controller-braking motor pair to generate braking power, the braking power in response to detecting a wish to drive off.

8. The method as claimed in claim 7, wherein the wish to drive off is detected in response to a drive torque of the vehicle exceeding an assigned limit value.

9. A vehicle parking brake for holding a vehicle at a standstill, the vehicle parking brake comprising: at least one electric braking motor; and at least two controllers configured to: actuate the at least one electric braking motor; and automatically activate, in response to a failure of a first controller-braking motor pair, a second controller-braking motor pair to generate braking power if at least one of (i) one of a vehicle speed of the vehicle and a corresponding driving state variable of the vehicle is less than an assigned limit value, and (ii) a characteristic variable of the vehicle indicates one of an existing vehicle standstill and an imminent vehicle standstill.

10. The vehicle parking brake as claimed in claim 9, wherein the at least one electric braking motor is configured to displace a brake piston towards a brake disc.

11. The vehicle parking brake as claimed in claim 9, wherein the vehicle parking brake is part of a braking system that also includes a hydraulic brake.

12. The vehicle parking brake as claimed in claim 11, wherein the braking system is part of a vehicle.

13. A vehicle comprising: a vehicle parking brake configured to hold the vehicle at a standstill, the vehicle parking brake comprising: at least one electric braking motor; and at least two controllers configured to: actuate the at least one electric braking motor; and automatically activate, in response to a failure of a first controller-braking motor pair, a second controller-braking motor pair to generate braking power if at least one of (i) one of a vehicle speed of the vehicle and a corresponding driving state variable of the vehicle is less than an assigned limit value, and (ii) a characteristic variable of the vehicle indicates one of an existing vehicle standstill and an imminent vehicle standstill.

14. The method as claimed in claim 1, wherein the method is performed by the at least two controllers by executing a computer program stored on a non-transitory computer readable medium.

Description

[0028] Further advantages and expedient designs can be found in the further claims, the description of the figures and the drawings. In the figures:

[0029] FIG. 1 shows a schematic representation of a hydraulic vehicle brake with wheel brake units that are additionally equipped with an electric braking motor as part of a parking brake,

[0030] FIG. 2 shows a section through a parking brake with an electric braking motor,

[0031] FIG. 3 shows a basic representation of the parking brake with two electric braking motors and one control unit each,

[0032] FIG. 4 shows a flow chart with process steps for generating braking power by applying the parking brake if a component of the parking brake has failed.

[0033] In the figures, the same components are provided with the same reference characters.

[0034] The braking system represented in FIG. 1 for a vehicle comprises a hydraulic vehicle brake 1 with a front axle brake circuit 2 and a rear axle brake circuit 3 for supplying and controlling wheel brake units 9 on each wheel of the vehicle with brake fluid under hydraulic pressure. The brake circuits may also be formed as two diagonal brake circuits, each with a front wheel and a diagonally arranged rear wheel.

[0035] The two brake circuits 2, 3 are connected to a common master brake cylinder 4, which is implemented as a tandem cylinder and is supplied with brake fluid via a brake fluid reservoir 5. The main brake cylinder piston inside the master brake cylinder 4 is operated by the driver by means of the brake pedal 6, wherein the pedal travel exerted by the driver is measured by a pedal travel sensor 7. Between the brake pedal 6 and the master brake cylinder 4 there is a brake booster 10, which includes, for example, an electric motor, which operates the master brake cylinder 4 via a gearbox (iBooster). The brake booster 10 is an active brake component for influencing the hydraulic brake pressure.

[0036] The control movement of the brake pedal 6 measured by the pedal travel sensor 7 is transmitted as a sensor signal to a control unit 11 of the braking system, in which control signals are generated for controlling the brake booster 10. The wheel brake units 9 are supplied with brake fluid in each brake circuit 2, 3 via different switching valves, which together with other units are part of the brake hydraulics 8. The brake hydraulics 8 also include a hydraulic pump, which is part of an electronic stability program (ESP) to which another control unit is assigned. The hydraulic pump is also an active brake component for influencing the hydraulic braking pressure.

[0037] In FIG. 2 a wheel brake unit 9, which is disposed on wheels on the rear axle of the vehicle, is shown in detail. The wheel brake unit 9 is part of the hydraulic brake 1 and is supplied with brake fluid 22 from the rear axle brake circuit. The wheel brake unit 9 also comprises an electromechanical braking device which is part of a holding or parking brake for holding a vehicle but can also be used to slow down the vehicle when the vehicle is moving, in particular at lower vehicle speeds below the speed limit. Such wheel brake units 9 may also be disposed, where appropriate, on the wheels of the front axle of the vehicle.

[0038] The electromechanical braking device comprises a brake caliper 12 with a claw 19 that engages around a brake disc 20. As a control element, the braking device has a motor-gear unit with a DC electric motor as a braking motor 13, the rotor shaft of which rotationally drives a spindle 14 on which a spindle nut is mounted 15 rotationally fixedly. When the spindle 14 is rotated, the spindle nut is displaced 15 axially. The spindle nut 15 moves within a brake piston 16 that is the carrier of a brake pad 17 that is pressed against the brake disc 20 by the brake piston 16. On the opposite side of the brake disc 20 there is another brake pad 18, which is held stationary on the claw 19. The brake piston 16 is sealed pressure-tight on its outside relative to the accommodating housing by an enclosing sealing ring 23.

[0039] When the spindle 14 is rotating the spindle nut 15 can move axially forwards within the brake piston 16 towards the brake disc 20 or can move axially rearwards until reaching an end stop 21 during an opposite rotational movement of the spindle 14.

[0040] To generate clamping power, the spindle nut 15 acts on the inner end face of the brake piston 16, whereby the axially movable brake piston 16 is pressed with the brake pad 17 against the facing end face of the brake disc 20. The spindle nut 15 is a transmission element between the braking motor and the brake piston.

[0041] For hydraulic braking power, the hydraulic pressure of the brake fluid 22 from the hydraulic vehicle brake 1 acts on the brake piston 16. The hydraulic pressure may also be effective with the vehicle at a standstill when the electromechanical braking device is operated in support, so that the total braking power is composed of the electromotive component and the hydraulic component. While the vehicle is travelling, either only the hydraulic brake is active, or both the hydraulic brake and the electromechanical braking device are active or only the electromechanical braking device is active to generate braking power. The control signals for controlling both the adjustable components of the hydraulic vehicle brake 1 as well as the electromechanical braking device are generated in the control unit 11, 24, which is the control unit 11 of the brake booster 10 (iBooster), or the ESP control unit 24.

[0042] The parking brake contains an electromechanical braking device in accordance with FIG. 2 on each of the vehicle's two rear wheels. The ESP control unit 24 is assigned to a braking device, for example on the left rear wheel, wherein the control unit 11 of the brake booster 10 is assigned to the other braking device.

[0043] In FIG. 3 the parking brake is shown schematically. The parking brake comprises the two electromechanical braking devices 25a and 25b on the left and right rear wheels of the vehicle, wherein a respective electric braking motor 13a, 13b belongs to each electromechanical braking device 25a, 25b. The braking device 25a is, for example, the braking device on the left rear wheel and the braking device 25b is the braking device on the right rear wheel of the vehicle.

[0044] The braking device 25a includes the ESP control unit 24 and the braking device 25b includes the iBooster control unit 11 to control the respective braking motors 13a or 13b. Each control unit 11, 24 comprises a standstill management unit 26a, 26b, a logic unit 27a, 27b and a hardware unit 28a, 28b. The standstill management unit 26a, 26b receives signals from other units 29 and 30 in the vehicle, wherein the unit 29 is a parking brake switch and the unit 30 is a vehicle sensor or a vehicle environment sensor. The standstill management unit 26a in the ESP control unit 24 receives signals from both the parking brake switch 29 and the sensor system 30. The standstill management unit 26b of the iBooster control unit 11, on the other hand, receives only signals of the sensor system 30, but not of the parking brake switch 29.

[0045] The logic unit 27a, 27b in the control unit 11, 24 contains the control logic for controlling the respective braking motors 13a, 13b and is implemented in particular as software in the control units.

[0046] The hardware units 28a, 28b include the power electronics for application to the braking motors 13a, 13b, for example H-bridges.

[0047] By actuating the parking brake switch 29, the driver can manually generate a trigger signal for activating the parking brake with both electromechanical braking devices 25a and 25b. The trigger signal of the parking brake switch 29 is fed to the standstill management unit 26a in the ESP control unit 24 as an input signal. The trigger signal is normally transmittedin the case of full functionality of both control units 11, 24from the standstill management unit 26a of the ESP control unit 24 to the standstill management unit 26b of the iBooster control unit 11, so that the trigger signal is available in both control units 11, 24 and the relevant electric braking motors 13a, 13b are controlled accordingly by both control units 11, 24.

[0048] In the event of a failure of a control unit, the respective braking motor also fails, but the functionality of the other electromechanical braking device remains, provided that the second control unit remains intact.

[0049] In the event of a failure of the iBooster control unit 11, if there is a trigger signal the first electromechanical braking device 25a is controlled by the ESP control unit 24, which acts on the electric braking motor 13a by means of the power electronics 28a.

[0050] In the event of a failure of the ESP control unit 24, the second electric braking motor 13b of the second electromechanical braking device 25b can be controlled by the iBooster control unit 11. However, in this case, the trigger signal of the parking brake switch 29 is not available, so that an alternative trigger signal must be generated, which is obtained from the vehicle sensor system or the vehicle environment sensor system 30. For example, information about the vehicle's standstill can be obtained from the vehicle's drive engine or from the environment sensors and can be used as a trigger signal.

[0051] If necessary, the sensor system 30 also includes another input system in the vehicle, for example a touch-sensitive screen, by means of which the driver can trigger the actuation of the parking brake independently of the parking brake switch 29.

[0052] Various other units can also be controlled by the control units 11, 24. For example, brake lights 31a, 31b can be operated when actuating one or both electromechanical braking devices 25a, 25b. Further communication between the braking devices 25a, 25b takes place via interface units 32a, 32b. Each control unit also provides information to a respective diagnostic unit 33a, 33b. In the case of an automatic parking operation or in the case of other braking operations where appropriate, the ESP control unit 24 can be used to provide a hydraulic braking power boost by means of the ESP pump 34 and the iBooster control unit 11 can be used to provide an electromechanical boost by means of the brake booster or the iBooster 10.

[0053] Each control unit 11, 24 with an assigned braking motor forms a control unit/braking motor unit for generating braking power, in particular for holding the vehicle at a standstill. In the event of a failure of a control unit/braking motor unit, the remaining intact control unit/braking motor unit can generate braking power. The failure in one of the control unit/braking motor units may include both the associated control unit and the associated braking motor. In addition, it is possible that the communication between the control units 11, 24 is interrupted, so that no signal can be transmitted from the control unit 24 to the control unit 11.

[0054] In FIG. 4 a flow chart with various process steps for generating braking power by actuating the parking brake in the event that a control unit/braking motor unit or communication between the control units has failed is shown in detail. The procedure automatically activates the remaining control unit/braking motor unit, provided that the vehicle speed is below a limit value or that a characteristic variable in the vehicle indicates an existing or imminent vehicle standstill.

[0055] According to FIG. 4, first, in a first process step 40, a checked is made as to whether a control unit/braking motor unit has failed or the communication between the control units is interrupted. The failure of a control unit/braking motor unit may relate to both the failure of a control unit and the failure of a braking motor or an interruption in signal and current transmission. If the check in the first process step 40 shows that there is in fact a failure of a control unit/braking motor unit or an interruption of communication between the control units, the Yes branch (Y) is consequently advanced to the next process step 41. Otherwise, the full functionality is available, and the No branch (N) is consequently returned to the check according to process step 40, which is re-run at cyclic intervals.

[0056] In process step 41, which is passed through in the event of a fault in the parking brake, a query is carried out as to whether the vehicle speed or a corresponding driving state variable is less than an assigned limit value. The limit value is advantageously of the order of 10 km/h.

[0057] In addition or alternatively to considering the driving state variable, a characteristic variable can also be considered that indicates an existing or imminent vehicle standstill, for example the ignition state of the drive engine in the vehicle, the state of a door contact switch, in particular on the driver's door, the state of a seat occupancy detection unit for the driver's seat or the state of a seat belt lock for the driver's belt. It is also possible to take into account the state of a contact switch on the trunk. If the corresponding characteristic variable indicates a stationary vehicle or an imminent vehicle standstill, for example with the driver's door open or the boot lid open, this information may also be used for the method according to the invention of automatic control of the intact control unit/braking motor unit. In a preferred design, both the vehicle speed is checked for being below the assigned limit value and one or more parameters indicating an existing or imminent vehicle standstill will be taken into account. This increases reliability and plausibility with regard to the automatic generation of braking power.

[0058] If the query in step 41 shows that the vehicle speed has not fallen below the assigned limit value and/or the parameters in the vehicle under consideration do not indicate an existing or imminent vehicle standstill, then consequently the No branch is returned to the beginning of process step 41 and this step is re-run at cyclic intervals. Otherwise, if a condition or the various conditions in step 41 are met, the Yes branch is consequently advanced to the next step 42.

[0059] If the yes output of the query is reached in process step 41, the conditions are in principle met that the intact control unit/braking motor unit can be activated automatically, and the braking power can be generated. For comfort reasons, however, a further time delay is taken into account, which is the subject of the process step 42. In this case, waiting for a defined period of time after the detection of the vehicle's standstill is carried out before the braking power is automatically generated by the control unit/braking motor unit. By waiting for the time period in process step 42, a higher degree of driving comfort is achieved, especially during a parking or unparking process in the vehicle.

[0060] If the query in step 42 shows that a defined time span has not yet elapsed, the No branch returns to the beginning of step 42 and this step 42 is re-run at cyclic intervals. If, on the other hand, the query shows that the defined period of time has elapsed, the Yes branch is consequently moved to the next process step 43, in which the intact control unit/braking motor unit is activated, and braking power is generated automatically.

[0061] In the following process step 44, conditions are queried that lead to a discontinuation of the braking power generation by the parking brake. The automatic braking power generation by the parking brake is also automatically removed again if one or more corresponding termination conditions are met, which are checked in process step 44. This is the drive torque of the drive engine in the vehicle, for example. If the drive torque does not exceed an assigned limit value, the braking power of the parking brake is maintained and consequently the No branch is again returned to the beginning of the query in step 44 and the query is re-run at cyclic intervals. If, on the other hand, the query in step 44 indicates that the drive torque exceeds the assigned limit value, it must be assumed that the vehicle journey is to be resumed, whereupon the Yes branch is consequently advanced to the step 45 and the braking power of the parking brake is automatically removed again.