METHOD FOR OPERATING A VEHICLE BRAKE SYSTEM, CONTROL UNIT, AND VEHICLE

Abstract

A method for operating a vehicle brake system including a brake booster and an electronic traction control device, which is used as a fallback level in a malfunction of the brake booster. The position of an accelerator pedal is ascertained when a malfunction of the brake booster is detected, and under the precondition that the accelerator pedal is released, a predefined initial pressure is built up in a pressure chamber of a master brake cylinder of the vehicle brake system with the aid of the traction control device so that a deceleration of the vehicle is induced. A control unit which is designed to carry out the method, and a vehicle having a vehicle brake system and a control unit, are also described.

Claims

1-10. (canceled)

11. A method for operating a vehicle brake system, the vehicle brake system including a brake booster and an electronic traction control device, which is used as a fallback level in a malfunction of the brake booster, the method comprising: detecting a malfunction of the brake booster; ascertaining a position of an accelerator pedal; and under a precondition that the accelerator pedal is released, building up a predefined initial pressure in a pressure chamber of a master brake cylinder of the vehicle brake system using the traction control device so that a deceleration of the vehicle is induced.

12. The method as recited in claim 11, wherein the pressure buildup to the initial pressure is controlled in its timing using the traction control device.

13. The method as recited in claim 11, further comprising: ascertaining a position of a brake pedal of the vehicle brake system; wherein when an operation of the brake pedal is detected, a prepressure generated in the pressure chamber of the master brake cylinder by the operation of the brake pedal is taken into account in the pressure buildup in the pressure chamber of the master brake cylinder.

14. The method as recited in claim 13, wherein in a detected operation of the brake pedal, a pressure, which corresponds to a prepressure boosted by a factor plus the initial pressure, is built up in the pressure chamber of the master brake cylinder using the traction control device.

15. The method as recited in claim 13, wherein to ascertain the position of the brake pedal, the pressure in the pressure chamber of the master brake cylinder is measured.

16. The method as recited in claim 11, wherein a further fallback level is established, using binary information.

17. The method as recited in claim 11, wherein after the pressure buildup to the initial pressure in the pressure chamber of the master brake cylinder, the position of the accelerator pedal is ascertained again and if the accelerator pedal is operated, the pressure is reduced, the pressure reduction being controlled in its timing using the traction control device.

18. The method as recited in claim 11, wherein the malfunction of the brake booster is detected using a control unit of the traction control device, which is connected in a data-transmitting manner to the brake booster via a CAN bus.

19. A control unit configured to operate a vehicle brake system, the vehicle brake system including a brake booster and an electronic traction control device, which is used as a fallback level in a malfunction of the brake booster, the control unit configured to: detect a malfunction of the brake booster; ascertain a position of an accelerator pedal; and under a precondition that the accelerator pedal is released, build up a predefined initial pressure in a pressure chamber of a master brake cylinder of the vehicle brake system using the traction control device so that a deceleration of the vehicle is induced.

20. A vehicle, comprising: a vehicle brake system including a brake booster and an electronic traction control device; and a control unit configured to operate the vehicle brake system, the control unit configured to: detect a malfunction of the brake booster, ascertain a position of an accelerator pedal, and under a precondition that the accelerator pedal is released, build up a predefined initial pressure in a pressure chamber of a master brake cylinder of the vehicle brake system using the traction control device so that a deceleration of the vehicle is induced.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows a flow diagram for the graphical representation of a typical sequence of a method according to an example embodiment of the present invention.

[0022] FIG. 2 shows a schematic representation of the deceleration and acceleration characteristic via the accelerator and/or brake pedal position according to the related art and according to a first example embodiment of the present invention.

[0023] FIG. 3 shows a schematic representation of the deceleration and acceleration characteristic via the accelerator and/or brake pedal position according to the related art as well as according to a first and a second example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0024] To begin with, a typical method sequence of a method according to an example embodiment of the present invention is described based on the flow diagram shown in FIG. 1.

[0025] Starting from a state 10 in which the vehicle brake system is still working properly, a malfunction of a brake booster of the vehicle brake system is discovered in step 20. With the occurrence of the malfunction, the position of the accelerator pedal is ascertained in a next step 30 in order to check whether the driver is operating the accelerator pedal or whether the accelerator pedal is released. For with an operation of the accelerator pedal, the vehicle is accelerated so that a deceleration of the vehicle can be undertaken only when involving a drive train. However, this is meant to be prevented in this instance, so that no pressure is built up in a pressure chamber of a master brake cylinder with the aid of a traction control device when the accelerator pedal is operated in step 40. If it is determined in a renewed check 50 that the accelerator pedal is now released, then the position of the brake pedal is first ascertained in step 60. If it is assumed that the brake pedal is released due to an absent prepressure in the pressure chamber of the master brake cylinder, then a temporally controlled pressure buildup in the pressure chamber of the master brake cylinder to a predefined initial pressure such as to 8 bar takes place in step 70.1. If the initial pressure has been built up or state 80 been reached, then the position of the brake pedal is ascertained anew in step 90 in order to check whether the driver has now operated the brake pedal. If this is the case, then a further pressure buildup is generated in the pressure chamber of the master brake cylinder with the aid of the traction control device in step 70.2, which—added to the initial pressure—corresponds to the prepressure induced by the driver by operating the brake pedal multiplied by a factor x. If another check of the brake pedal position carried out in step 100 indicates that the brake pedal is released, then the pressure in the pressure chamber is lowered to the initial pressure so that state 80 is reached again. Next, step 30 is repeated in order to determine whether the accelerator pedal is operated again. If this is the case, then no pressure will be built up in the pressure chamber in step 40 but the pressure is actively reduced in order to allow for an acceleration of the vehicle.

[0026] With the aid of the method according to an example embodiment of the present invention, a positive change in the braking characteristic of a vehicle is achievable, which manifests itself in greater braking comfort for the driver. The acceleration characteristic of the vehicle remains unchanged in the process.

[0027] As illustrated in FIG. 2 by way of example, when the accelerator pedal is operated, the vehicle is accelerated in proportion to the position of the accelerator pedal (see graph 1, 2 in the right half of FIG. 2). If a malfunction of the brake booster is detected, it is first checked whether the accelerator pedal is operated or whether the accelerator pedal is released. If the latter is the case, then brake boosting according to the provided method of the present invention is able to be carried out. To this end, a pressure buildup to an initial force is first induced with the aid of the traction control device, i.e., regardless of whether or not the brake pedal is operated at the same time. The initial pressure is selected to be so high that a clear deceleration of the vehicle is induced (see perpendicular characteristic of graph 2 in the center of FIG. 2). If the driver operates the brake pedal, then this slowly leads to a further pressure buildup in the pressure cylinder of the master brake cylinder which, however, is low in comparison with the already generated initial pressure and thus has barely any effect on the deceleration of the vehicle (see slightly dropping slope of graph 2 in the left half of FIG. 2). Only once a certain prepressure has been reached, it is detected and boosted by a certain factor x with the aid of the traction control device (see steeply dropping slope of graph 2 in the left half of FIG. 2).

[0028] The related art is shown by graph 1. Here, the deceleration of the vehicle depends on the operation of the brake pedal by the driver. This means that the driver has to operate the brake pedal and that a certain prepressure must first be reached in the pressure chamber of the master brake cylinder before pressure boosting can be achieved with the aid of the traction control device.

[0029] A further refinement of the present invention may be gathered from FIG. 3. In FIG. 3, graph 3 symbolizes a further fallback level provided using binary information. This may be a distance-dependent information, for example, from which the brake pedal position can be derived. The required measurement is able to be carried out with the aid of a travel sensor of the brake booster. However, this assumes that the malfunction has not resulted in a complete failure of the brake booster.