Method for decelerating a vehicle

Abstract

A method for decelerating a vehicle includes actuating an electric brake motor of an electromechanical braking mechanism in an event of a failure of a hydraulic vehicle brake to produce a braking force in an event of a failure of the hydraulic vehicle brake. The method further includes producing a decelerating torque in the drive train of the vehicle in the event of the failure of the hydraulic vehicle brake. The vehicle includes a brake system. The brake system has the hydraulic vehicle brake and the electromechanical braking mechanism with the electric brake motor.

Claims

1. A method for decelerating a vehicle including a brake system, the brake system including a hydraulic vehicle brake and an electromechanical braking mechanism with an electric brake motor, the method comprising: actuating the electric brake motor of the electromechanical braking mechanism to produce a braking force against a brake disc in an event of a failure of the hydraulic vehicle brake; and operating the drive train of the vehicle in a manner that produces a decelerating torque in the drive train in the event of the failure of the hydraulic vehicle brake, wherein the decelerating torque produced by the drive train is maintained beyond a time at which the braking force is made available in the electromechanical braking mechanism.

2. The method as claimed in claim 1, further comprising: actuating the electric brake motor in the event of the failure of the hydraulic vehicle brake only when the vehicle is moving below a speed limit; and producing the decelerating torque in the drive train of the vehicle in the event of the failure of the hydraulic vehicle brake only when the vehicle is moving below the speed limit.

3. The method as claimed in claim 1, wherein the method is carried out in a parking mode.

4. The method as claimed in claim 1, further comprising: following the failure of the hydraulic vehicle brake firstly actuating the electromechanical braking mechanism and secondly adjusting the drive train such that the decelerating torque is produced.

5. The method as claimed in claim 1, further comprising: engaging the lowest possible gear in an automatic transmission in the vehicle.

6. The method as claimed in claim 1, further comprising: turning off a combustion engine in the drive train to produce the decelerating torque.

7. The method as claimed in claim 1, further comprising: switching an electric motor in the drive train to a generator mode to produce the decelerating torque.

8. The method as claimed in claim 1, further comprising: accelerating an electric motor in the drive train against a direction of travel to produce the decelerating torque.

9. The method as claimed in claim 1, further comprising: locking a central differential between a front axle and a rear axle of an all-wheel drive vehicle to produce the decelerating torque.

10. The method as claimed in claim 1, wherein the electric brake motor is controlled by a regulating unit or a control unit.

11. A vehicle comprising: a brake system including a hydraulic vehicle brake and an electromechanical braking mechanism having an electric brake motor; a drive train; and a regulating unit configured to carry out a method for decelerating the vehicle, the method including actuating the electric brake motor of the electromechanical braking mechanism to produce a braking force against a brake disc in an event of a failure of the hydraulic vehicle brake, and operating the drive train of the vehicle in a manner that produces a decelerating torque in the drive train in the event of the failure of the hydraulic vehicle brake, wherein the decelerating torque produced by the drive train is maintained beyond a time at which the braking force is made available in the electromechanical braking mechanism.

12. A method for decelerating a vehicle including a brake system, the brake system including a hydraulic vehicle brake and an electromechanical braking mechanism with an electric brake motor, the method comprising: actuating the electric brake motor of the electromechanical braking mechanism to produce a braking force against a brake disc in an event of a failure of the hydraulic vehicle brake; operating the drive train of the vehicle in a manner that produces a decelerating torque in the drive train in the event of the failure of the hydraulic vehicle brake; and engaging the lowest possible gear in an automatic transmission in the vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and advantageous embodiments are to be found in the further claims, the description of the figures and the drawings. In the figures:

(2) FIG. 1 shows an all-wheel drive vehicle in a schematic representation,

(3) FIG. 2 shows a section through an electromechanical holding brake for a vehicle, with which the clamping force is produced by means of an electric brake motor,

(4) FIG. 3 shows a process schema with steps of the method for decelerating the vehicle in the parking mode in the event of a failure of the hydraulic vehicle brake, shown for a vehicle with front or rear drive,

(5) FIG. 4 shows a further process schema for decelerating a vehicle in the parking mode, shown for an all-wheel drive vehicle,

(6) FIG. 5 shows a further process schema for decelerating a vehicle in the parking mode, shown for a vehicle with an electromotive drive.

DETAILED DESCRIPTION

(7) FIG. 1 shows an all-wheel drive vehicle 20 with hydraulic vehicle brakes 21 on each vehicle wheel 22. The drive train of the vehicle 20 is formed by a combustion engine 23 and an automatic transmission 24 connected downstream thereof.

(8) The vehicle 20 can comprise a hybrid drive with an electric drive motor 25 that is joined by a flange to the automatic transmission 24. The drive movement of the combustion engine 23 and possibly of the electric drive motor 25 is transmitted to the front axle 26 of the vehicle and via a central differential 28 to the rear axle 27.

(9) The adjustable components of the vehicle 20, in particular the hydraulic vehicle brake 21, the components of the drive train with the combustion engine 23, the automatic transmission 24 and optionally the electric drive motor 25 and the central differential 28 are adjusted by means of final control signals of a regulating or control unit 12.

(10) The vehicle 20 is further fitted with an electromechanical braking mechanism with an electric brake motor, which is used as a parking or holding brake for producing a clamping force that holds the vehicle at a standstill. Such an electromechanical braking mechanism 1 is represented in FIG. 2.

(11) The electromechanical braking mechanism 1 comprises a brake caliper 2 with a claw 9 that overlaps a brake disk 10. As a final control element, the holding brake 1 comprises a d.c. electric motor as a brake motor 3, the rotor shaft of which rotationally drives a spindle 4 on which a spindle nut 5 is rotatably supported. During rotation of the spindle 4, the spindle nut 5 is displaced axially. The spindle nut 5 moves within a brake piston 6 carrying a brake lining 7 that is pressed by the brake piston 6 against the brake disk 10. On the opposite side of the brake disk 10 there is a further brake lining 8 that is held positionally fixedly on the claw 9.

(12) During a rotary movement of the spindle 4, the spindle nut 5 can move axially forwards towards the brake disk 10 within the brake piston 6 or during an opposite rotary movement the spindle 4 can move axially rearwards until reaching a stop 11. To produce a clamping force, the spindle nut 5 acts on the inner rear face of the brake piston 6, whereby the brake piston 6, which is axially movably mounted in the electromechanical braking mechanism 1, is pressed with the brake lining 7 against the facing end surface of the brake disk 10.

(13) The brake motor 3 is also actuated by the regulating or control unit 12 that is installed in the vehicle. The regulating or control unit 12 provides as an output a supply voltage U.sub.so that is applied to the electric brake motor 3.

(14) The holding brake and the hydraulic vehicle brake 21 both act on the brake piston 6. During actuation of the hydraulic vehicle brake 21, the rear of the brake piston 6 facing the brake motor is subjected to hydraulic fluid under pressure.

(15) In FIG. 3, a process schema for decelerating a vehicle in the parking mode is represented for the case in which the hydraulic vehicle brake fails during a parking process, which may be at least partly carried out in an automated manner. The vehicle comprises as a drive a combustion engine to which an automatic transmission is coupled. In the vehicle, only either the rear axle or the front axle is driven.

(16) First, in the first step 30 of the method the failure of the hydraulic vehicle brake is detected. In order to still be able to decelerate the vehicle without an accident, in the next step 31 of the method the electromechanical braking mechanism is started, by means of which a clamping force that decelerates the vehicle to a standstill is produced electromechanically.

(17) In addition, by means of the drive train of the vehicle a decelerating torque is produced to shorten the braking process. For this purpose, in the next step 32 of the method a check is made as to whether the setting of the automatic gearbox is in the drive position. If this is not the case, the no branch (N) is then followed to the step 33 of the method, in which the lowest gear in the automatic transmission is engaged by means of final control signals of a regulating or control unit. The process is then continued to the next step 34 of the method.

(18) If the result of the query in the step 32 is that the setting of the automatic gearbox is in the drive position, the yes branch Y is immediatelypossibly after engaging the lowest gearadvanced to the step 34, in which the drive motor that is implemented as a combustion engine in the vehicle is turned off. In combination with the lowest gear, which is set in the automatic transmission, a high engine drag torque is acting, by means of which the vehicle is additionally decelerated.

(19) In the following step 35 of the method, the query is carried out as to whether the vehicle is already at a standstill. If this is still not the case, the no branch is then returned to the start of the query according to step 35 and the query is run through again at cyclical intervals.

(20) After the vehicle is at a standstill, the yes branch is then advanced to the step 36, in which a query is carried out as to whether the desired target clamping force has been achieved in the electromechanical braking mechanism. This ensures that for different parking conditions, possibly even for parking the vehicle on a slope, a sufficiently high clamping force is acting in the electromechanical braking mechanism that holds the vehicle permanently. If the query in the step 36 indicates that the target clamping force has not yet been reached, the no branch is again returned to the start of the query and the query is run through again at cyclical intervals. In the meantime, an increasing clamping force is built up in the electromechanical braking mechanism.

(21) If the query in the step 36 reveals that the target clamping force has been achieved, the yes branch is then advanced to the step 37, with which the method is terminated. A sufficiently high clamping force is acting in the electromechanical braking mechanism and the vehicle is at a standstill.

(22) The process of the method according to FIG. 3 concerns a vehicle with a combustion engine drive and a driven vehicle axle. In FIG. 4, by contrast, a process of the method for an emergency stop in the automatic parking mode of a vehicle with a combustion engine, an automatic transmission and an all-wheel drive is represented for the case in which the hydraulic vehicle brake fails. The same steps of the method as in FIG. 3 are provided with the same reference characters.

(23) Similarly to FIG. 3, in FIG. 4 the failure of the hydraulic vehicle brake is also detected in the step 30 and the emergency stop is initiated in the step 31 by first starting the electromechanical braking mechanism.

(24) In the subsequent step 100, a query is carried out as to whether the central differential between the front axle and the rear axle is unlocked. If this is the case, the yes branch is then advanced to the step 101 and the central differential is locked, whereupon the process is advanced to the next step 32. If on the other hand the query in the step 100 reveals that the central differential is locked, the locking position already exists and the no branch is then advanced directly to the next query 32.

(25) The next steps of the method 32 through 37 correspond to those of FIG. 3. In the step 32, the gearbox setting is queried, and the lowest gear in the gearbox is engaged in the step 33 if necessary. In the step 34, the combustion engine is turned off, and in the step 35 the query is carried out as to whether the vehicle is stationary. In the step 36 a query is carried out as to whether the target clamping force in the electromechanical braking mechanism has already been achieved. In the step 37, the method is terminated after the target clamping force has been set and the vehicle is at a standstill.

(26) In FIG. 5, a process of the method for decelerating a vehicle in the parking mode in the event of a failure of the hydraulic vehicle brake for a vehicle with an electromotive drive is represented. The same steps of the method as in FIGS. 3 and 4 are also provided with the same reference characters in FIG. 5.

(27) In the step 30, the failure of the hydraulic vehicle brake is detected, whereupon in the step 31 the emergency stop is initiated and the electromechanical braking mechanism is started. In the subsequent step 200, a query is carried out as to whether the vehicle is moving forwards or moving rearwards. If the vehicle is moving, the yes branch then branches to the step 201 and the electric drive motor is accelerated opposite to the direction of motion of the vehicle. As a result, a torque that decelerates the vehicle is produced by means of the electric drive motor. Following the step 201, the process again returns to the query according to step 200 and checks again at cyclical intervals whether the vehicle is still moving.

(28) If the query in the step 200 reveals that the vehicle is at a standstill, the no branch is then advanced to the step 202 and the actuation of the electric drive motor is adjusted to prevent acceleration of the vehicle from a standstill in the opposite direction. If, however, the vehicle is standing on an upslope and no adequate clamping force is available by means of the electromechanical braking mechanism, the electric drive motor is actuated in the step 202 in such a manner that a force that compensates the downhill force is produced in the drive motor.

(29) The steps 36 and 37 correspond to those from FIGS. 3 and 4. In the step 36, a query is carried out as to whether the target clamping force has been achieved in the electromechanical braking mechanism. If this is the case, the electric drive motor is turned off in the step 37 and the method is terminated.