Method and device for driver assistance

Abstract

The disclosure relates to a method for driver assistance, wherein a vehicle automatically performs a driving maneuver. In the method, a service brake of the vehicle is first actuated. Then a parking brake of the vehicle is controlled in such a way that the parking brake exerts no braking influence and that the free travel to be overcome for actuation of the parking brake is minimized. In subsequent steps, the service brake of the vehicle is released and an automatic driving maneuver is performed, wherein, if a fault or a specified event occurs, the parking brake is actuated such that the vehicle is braked to a standstill and is kept at a standstill. The disclosure further relates to a driver assistance system that is designed to perform the method.

Claims

1. A method for driver assistance in which a vehicle automatically carries out a driving maneuver, the method comprising: a) actuating a service brake of the vehicle to bring the vehicle to a standstill; b) while the vehicle is held at a standstill by the service brake, controlling a parking brake of the vehicle by (i) operating an actuator motor of the parking brake to move the parking brake from an actuated state in which the parking brake produces a clamping force in a direction of releasing the parking brake, and (ii) stopping the actuator motor as soon as the clamping force of the parking brake has been reduced, such that the parking brake has no braking effect and a free travel to be overcome for actuation of the parking brake is minimized; c) after the controlling the parking brake, releasing the service brake of the vehicle; and d) after the releasing the service brake, automatically carrying out the driving maneuver and actuating the parking brake in response to one of a fault and a predefined event occurring to brake the vehicle to a standstill and hold the vehicle at the standstill.

2. The method as claimed in claim 1, further comprising: assigning the parking brake to one of a front axle of the vehicle and a rear axle of the vehicle; and at least during step b), decoupling the service brake from the one of the front axle and the rear axle such that no effect of the service brake takes place on the one of the front axle and the rear axle assigned to the parking brake.

3. The method as claimed in claim 1, wherein the driving maneuver is a parking maneuver, the method further comprising: actuating the parking brake after a conclusion of the parking maneuver to hold the vehicle in a parking position.

4. The method as claimed in claim 1, wherein a driver takes control of the vehicle again after a conclusion of the driving maneuver, the method further comprising: actuating the service brake after the conclusion of the driving maneuver to hold the vehicle at a standstill via the service brake until the control has been taken over by the driver.

5. The method as claimed in claim 1, wherein the parking brake is configured to be electromechanically actuated.

6. The method as claimed in claim 1, further comprising: detecting whether the clamping force has been reduced by monitoring at least one of a current progression of the actuator motor and a voltage progression of the actuator motor during the control of the parking brake.

7. The method as claimed in claim 6, further comprising: detecting whether the clamping force has been reduced by detecting a change in a gradient of the current progression and disregarding a component of the change in the gradient that is induced by a switching-on of the actuator motor.

8. The method as claimed in claim 6, further comprising: detecting whether the clamping force has been reduced in response to the current progression falling below a predefined limiting value and continuously decreasing within a predefined time period.

9. The method as claimed in claim 6, further comprising: detecting whether the clamping force has been reduced in response to the current progression falling below a predefined first limiting value and an absolute value of a fluctuation of the current progression within a predefined time period falling below a predefined second limiting value.

10. A driver assistance system comprising: a control unit; a parking brake controller; and a service brake controller, wherein the control unit, the parking brake controller, and the service brake controller are configured to: a) actuate a service brake of the vehicle to bring the vehicle to a standstill; b) while the vehicle is held at a standstill by the service brake, control a parking brake of the vehicle by (i) operating an actuator motor of the parking brake to move the parking brake from an actuated state in which the parking brake produces a clamping force in a direction of releasing the parking brake, and (ii) stopping the actuator motor as soon as the clamping force of the parking brake has been reduced, such that the parking brake has no braking effect and a free travel to be overcome for actuation of the parking brake is minimized; c) after the control of the parking brake, release the service brake of the vehicle; and d) after the release of the service brake, automatically carry out a driving maneuver and actuate the parking brake in response to one of a fault and a predefined event occurring to brake the vehicle to a standstill and hold the vehicle at the standstill.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the disclosure are represented in the drawings and are described in greater detail in the following description.

(2) In the drawings:

(3) FIG. 1 shows a vehicle comprising a driver assistance system according to the disclosure,

(4) FIG. 2 shows a schematic representation of a parking brake,

(5) FIG. 3 shows a schematic representation of the method sequence, and

(6) FIG. 4 shows the control of the parking brake without hydraulic release.

DETAILED DESCRIPTION

(7) In the following description of the exemplary embodiments of the disclosure, identical or similar components and elements are designated using identical reference signs, wherein, in individual cases, a description of the components or elements is not repeated. The figures are merely a schematic representation of the subject matter of the disclosure.

(8) FIG. 1 shows a vehicle 1 comprising a driver assistance system 10. The driver assistance system 10 includes a control unit 12 which is connected to a parking brake controller 14 and a service brake controller 16. In further embodiments, the parking brake controller 14 and the service brake controller 16 can also be combined in one control unit.

(9) The service brake controller 16 controls a service brake 21 of the vehicle 1. The service brake 21 comprises four brake pistons 25, wherein a rear axle 26 and a front axle 28 of the vehicle 1 are each acted on by two brake pistons 25. The brake pistons 25 are each acted on via a hydraulic system 24, wherein the hydraulic system 24 is connected to valves 18, 19 which are controlled by the service brake controller 16.

(10) The parking brake controller 14 is connected to a parking brake 20 of the vehicle 1. The parking brake 20 includes two actuator motors 22, each of which actuates a spindle 32. The spindle 32 works together with a nut 34, see FIG. 2, on the brake piston 25 in order to have a braking effect. To this end, the particular spindle 32 is driven by the actuator motor 22, and therefore the nut 34 is moved toward the brake piston 25 and presses the nut against the brake piston 25.

(11) The control unit 12 is also configured for automatically carrying out a driving maneuver. To this end, the control unit 12 is connected to surroundings sensors 30, via which the control unit 12 can receive data concerning the surroundings of the vehicle 1. Moreover, the control unit 12 includes two connections to further systems of the vehicle 1, which are not represented in FIG. 1. It is provided, in particular, that the control unit 12 can generate a steering angle for the automatic implementation of a driving maneuver and can act on a drive of the vehicle 1. For the purpose of decelerating or braking the vehicle 1, the service brake 21 of the vehicle 1 can be acted on by the control unit 12 and by the service brake controller 16.

(12) FIG. 2 shows a schematic representation of a parking brake 20. The parking brake 20 comprises a brake caliper 40 including a gripping device 46 which engages over a brake disk 42. The parking brake 20 comprises, as the actuator, an actuator motor 22 which rotationally drives a spindle 32, on which a nut 34 is rotatably mounted. During a rotation of the spindle 32, the nut 34 is axially displaced. The nut 34 moves within the brake piston 25 which is the carrier of a brake pad 44 which is pressed against the brake disk 42 by the brake piston 25. Another brake pad 45, which is fixedly held on the gripping device 46, is located on the opposite side of the brake disk 42.

(13) Within the brake piston 25, during a rotary motion of the spindle 32 axially forward, the nut 34 can move in the direction toward the brake disk 42 and, during an opposing rotary motion of the spindle 32 axially backward, the nut can move axially rearward until it reaches a stop 48. In order to generate a clamping force, the nut 34 acts upon the inner end face of the brake piston 25, whereby the axially displaceably mounted brake piston 25 including the brake pad 44 is pressed against the facing end face of the brake disk 42.

(14) FIG. 3 schematically shows the sequence of one preferred embodiment of the method.

(15) The method begins at a start point 100. In a first step 101, the service brake 21 of the vehicle 1 is decoupled from the rear axle 26 of the vehicle 1. To this end, the valves 18, 29 are controlled, wherein the valves assigned to the rear axle 26 are closed, and therefore a pressure build-up for the hydraulic system 24 is possible only at the front axle 28.

(16) The pressure build-up in the service brake 21 takes place in the subsequent or simultaneously occurring step 102, and therefore a braking effect acts on the front axle 28 via the hydraulic system 24 and the brake piston 25.

(17) Simultaneously therewith, or afterward, the parking brake 20 of the vehicle 1 is controlled in the next step 104. If the parking brake 20 has not yet been actuated, the parking brake is now actuated, in order to initially have a braking effect on the rear axle 26. Subsequent thereto, the parking brake 20 is released until the braking effect has been reduced but there is still no free travel present. If the parking brake 20 is designed as an electromechanical brake, the spindle is driven via the actuator motor 22 during the release of the parking brake 20, and therefore the spindle becomes detached from the brake piston 25. The actuator motor 22 is stopped as soon as the braking effect has been completely reduced, wherein there is no clearance yet between the nut 34, which is moved by the spindle 32, and the brake piston 25, i.e., there is still no free travel between the nut 34 and the brake piston 25. Alternatively, the parking brake can be controlled in this step in such a way that the actuator motor is controlled in the direction of locking and is braked in a timely manner, and therefore the free travel has been completely eliminated, but a braking effect does not yet take place.

(18) Subsequent thereto, in a step 106, the vehicle 1 is automatically guided. For example, the vehicle 1 automatically parks in a parking space or unparks from a parking space. A check for faults takes place during the implementation of the automatic driving maneuver, according to step 108 of the method.

(19) If a fault is found, the sequence of the method branches off to a step 110. In response to the fault, which can be present, for example, in the form of a failure of the service brake 21, or which can be, for example, a fault in the driver assistance system 10, the parking brake 20 is actuated in a step 116, and therefore the parking brake has a braking effect on the rear axle 26 of the vehicle 1. Subsequent thereto, in a step 130, the previously decoupled parts of the service brake 21 are coupled, and therefore the service brake 21 is operated normally again. In the final step 118, the method is ended and a check can be carried out by the driver.

(20) If a fault is not found in the check in the step 108, the method branches off to the step 112 or to step 114.

(21) The method branches off to the step 112 if the implemented driving maneuver is a driving maneuver in which the driver takes over the control after conclusion of the driving maneuver. In the step 130, the previously decoupled parts of the service brake 21 are coupled, and therefore the service brake 21 is operated normally again. In the subsequent step 120, the service brake 21 is actuated, and therefore the vehicle 1 is held at a standstill by the service brake 21. Subsequent thereto, the driver can take over the guidance of the vehicle 1.

(22) If the automatically implemented driving maneuver in the step 106 is a driving maneuver in which the vehicle is to be subsequently stopped, the method branches off to the step 114. In this case as well, a coupling of the previously decoupled parts of the service brake 21 are initially coupled, in the step 130, and therefore the service brake 21 is operated normally again. Subsequent thereto, the parking brake is actuated in the step 122, in order to hold the vehicle in the target position reached after the automatic guidance.

(23) FIG. 4 shows a diagram in which a voltage U, a current I, a force F, a speed v, and a displacement s covered by the spindle 32 are plotted as a function of time t for an actuator motor 22 of the parking brake 20 of the vehicle 1. Six points in time, t1 to t6, are marked on the time axis in this case. The diagram in FIG. 4 shows the progression of the plotted variables during the release of the parking brake 20.

(24) The point in time at which the actuator motor 22 is switched on is marked in FIG. 4 using reference sign 208. This reference sign defines the beginning of the first time range 201. In the first time range 201, which runs from the point in time t1 to t2, the release of the parking brake 20 is started. In the first time range 201, a strong increase in the current I therefore occurs, and the voltage U changes as well. The speed v of the spindle 32 increases, wherein the speed 0 is marked using the arrow 216 in the representation in FIG. 4 and increases in the downward direction in the diagram. In the first time range 201, the spindle 32 has not yet covered a noteworthy displacement s, and the clamping force F also remains initially unchanged.

(25) In a second time range 202, which extends from the point in time t2 to the point in time t3, the clamping force F increasingly decreases. Thus, the covered displacement s of the spindle 32 increases. The speed v and the current I continue to increase in the second time range 202, while the voltage U remains constant.

(26) In a third time range 203, which extends from the point in time t3 to the point in time t4, a transition to a free-travel range takes place, in which the spindle 32 or the nut 34 driven by the spindle loses contact with the brake piston 25. The point at which the clamping force F begins to reduce is labeled in FIG. 4 using the reference sign 210.

(27) In the fourth time range 204, which extends from the point in time t4 to the point in time t5, the spindle 32 travels freely, i.e., the nut 34 has no contact with the brake piston 25. The clamping force F does not reduce any further, since the clamping force has reached its lowest possible value. In the absence of a timely switch-off as provided according to the method according to the disclosure, the displacement s covered by the spindle 32 continues to increase, however. This further covered displacement corresponds to the free travel. In the fourth time range 204, the voltage U, the current I, and the speed v remain essentially constant, but the covered displacement s changes.

(28) In the fifth time range 205, which extends from the point in time t5 to the point in time t6, the actuation of the actuator motor 22 is ended. The point at which the actuation of the actuator motor 22 is ended is provided with the reference sign 214. Therefore, the current I and the voltage U drop again to their original value 0, the speed v of the spindle also decreases to 0, and the covered displacement s approaches its final value.

(29) In the method provided, it is proposed according to the disclosure to control the parking brake 20 in such a way that, for example, the change in the gradient in the current I from the third time range 203 to the fourth time range 204 is detected and, in response thereto, the actuation of the actuator motor 22 is immediately ended. It is therefore provided to shorten the fourth time range 204 as compared to the representation in FIG. 4 in such a way that the spindle 32 is stopped as soon as the spindle has released the nut 34 from the brake piston 25 at the point marked with the reference sign 212, and therefore no free travel occurs.

(30) The disclosure is not limited to the exemplary embodiments described here or to the aspects emphasized therein. Rather, a plurality of modifications, which do not go beyond the normal abilities of a person skilled in the art, are possible within the scope of the disclosure.