Method for Operating a Brake System of a Vehicle

Abstract

A method for operating a brake system of a vehicle, where the vehicle has an electric machine usable for a regenerative braking of the vehicle and a drive unit usable in an overrun operation for an overrun braking of the vehicle, includes detecting an initiation of deceleration of the vehicle and detecting a driving situation suitable for regeneration. The method further includes initiating the overrun operation of the drive unit and the overrun braking of the vehicle and activating the regenerative braking so as to achieve a setpoint total regeneration torque. The regenerative braking is activated only after a limit value for a difference between an actual overrun regeneration torque by the overrun braking and a setpoint overrun regeneration torque is undershot.

Claims

1.-10. (canceled)

11. A method for operating a brake system of a vehicle, wherein the vehicle comprises an electric machine usable for a regenerative braking of the vehicle and a drive unit usable in an overrun operation for an overrun braking of the vehicle, comprising the steps of: detecting an initiation of deceleration of the vehicle; detecting a driving situation suitable for regeneration; initiating the overrun operation of the drive unit and the overrun braking of the vehicle; and activating the regenerative braking so as to achieve a setpoint total regeneration torque; wherein the regenerative braking is activated only after a limit value for a difference between an actual overrun regeneration torque by the overrun braking and a setpoint overrun regeneration torque is undershot.

12. A method for operating a brake system of a vehicle, wherein the vehicle comprises an electric machine usable for regenerative braking of the vehicle and a drive unit usable in an overrun operation for an overrun braking of the vehicle, comprising the steps of: detecting an initiation of deceleration of the vehicle; detecting a driving situation suitable for regeneration; initiating the overrun operation of the drive unit and the overrun braking of the vehicle; and activating the regenerative braking so as to achieve a setpoint total regeneration torque; wherein the regenerative braking is activated only after an actual drive torque of the drive unit reaches 0-100% of a setpoint overrun regeneration torque.

13. The method according to claim 12, wherein the regenerative braking is activated as soon as the actual drive torque reaches 60-80% of the setpoint overrun regeneration torque.

14. The method according to claim 11, wherein the overrun braking is carried out by an internal combustion engine or by the electric machine.

15. The method according to claim 12, wherein the overrun braking is carried out by an internal combustion engine or by the electric machine.

16. The method according to claim 11, wherein the vehicle is driven by an internal combustion engine and by the electric machine.

17. The method according to claim 12, wherein the vehicle is driven by an internal combustion engine and by the electric machine.

18. The method according to claim 11, wherein the vehicle is driven by the electric machine and the overrun braking is carried out by the electric machine.

19. The method according to claim 12, wherein the vehicle is driven by the electric machine and the overrun braking is carried out by the electric machine.

20. The method according to claim 11, wherein a load change or an active initiation of braking or a two-footed driving or an engine coasting is the driving situation suitable for regeneration.

21. The method according to claim 12, wherein a load change or an active initiation of braking or a two-footed driving or an engine coasting is the driving situation suitable for regeneration.

22. A brake system for a vehicle configured to carry out the method according to claim 11, comprising: an electric machine which is configured to carry out regenerative braking of the vehicle; a drive unit configured to carry out overrun braking of the vehicle in an overrun mode of the drive unit; a first control unit or a sensor unit which is configured to detect initiation of deceleration of the vehicle and a driving situation suitable for regeneration; and a second control unit which is configured to initiate regenerative braking of the vehicle.

23. An electric vehicle, comprising: an electric machine, wherein the electric vehicle is drivable by the electric machine; wherein the electric machine is configured such that overrun braking of the electric vehicle takes place in an overrun mode, regenerative braking of the electric vehicle takes place in a regeneration mode, and the regenerative braking is activated only after a limit value for a difference between an actual overrun regeneration torque by the overrun braking and a setpoint overrun regeneration torque is undershot.

24. A hybrid vehicle, comprising: an electric machine; and an internal combustion engine; wherein the hybrid vehicle is drivable by the electric machine and the internal combustion engine; wherein regenerative braking can be carried out by the electric machine in a regeneration mode, wherein overrun braking can be carried out by the internal combustion engine and/or by the electric machine in an overrun mode, and wherein the regenerative braking is activated only after a limit value for a difference between an actual overrun regeneration torque by the overrun braking and a setpoint overrun regeneration torque is undershot.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0050] The single FIGURE shows a diagram of the progression of the current braking torque (M.sub.ist) in Nm which acts on the vehicle during a method according to the invention as a function of time t.

DETAILED DESCRIPTION OF THE DRAWING

[0051] To carry out the method, the brake system of the exemplary embodiment comprises an electric motor for driving the vehicle, which can implement overrun braking of the vehicle in an overrun mode by means of an overrun torque, and can implement regenerative braking of the vehicle in the regeneration mode.

[0052] In an initial situation, the drive torque of the electric motor M.sub.ist is in a positive range (not shown in the diagram).

[0053] In a first step of the method, initiation of deceleration of the vehicle or a deceleration request is detected, for example by actuation of the brake pedal of the vehicle or by diminishing actuation or ending of actuation of an accelerator pedal. This deceleration request or this initiation of deceleration takes place at time t.sub.brems. In a following step, a driving situation suitable for regeneration is detected, i.e., it is determined by suitable sensor technology or calculations in the vehicle that regenerative braking should take place.

[0054] Subsequent to the detection of the initiation of deceleration or the deceleration request by the vehicle driver, an overrun mode of the electric motor is initiated in that the actual drive torque M.sub.ist is brought to a setpoint overrun regeneration torque M.sub.Schub. In many driving situations, however, there is a time delay Δt between the time t.sub.brems at which initiation of deceleration or a deceleration request was detected and the actual initiation of the overrun mode, that is to say the time t.sub.schub at which a negative drive torque M.sub.ist is actually initiated by an overrun mode of the electric motor.

[0055] If regenerative braking or a regeneration torque M.sub.Reku is set directly after detection of the deceleration request or the initiation of deceleration at time t.sub.brems, as indicated by the dashed line (M.sub.Reku) in FIG. 1, then an unsteady braking behavior arises since regeneration braking has already begun, while overrun regeneration has not yet begun owing to the time delay Δt. This braking behavior is felt to be unsteady and uncomfortable by a vehicle driver or vehicle occupant.

[0056] In order to avoid this disadvantage, it is envisaged that the regeneration torque M.sub.Reku for activating the regenerative braking is set only after a specified difference ΔM between the actual drive torque or actual overrun regeneration torque M.sub.ist and the setpoint overrun regeneration torque M.sub.Schub has been reached. This difference is also referred to as an activation offset ΔM.

[0057] For this purpose, a regeneration torque M.sub.Reku is superimposedor set at the electric motor at the time t.sub.Reku at which the activation offset was reached. By the setting of the regeneration torque M.sub.Reku, the regenerative braking is activated.

[0058] The total regeneration torque or total braking torque M.sub.soll is then achieved by means of the set setpoint overrun regeneration torque M.sub.Schub and the set regeneration torque M.sub.Reku.

[0059] In this way, steady braking behavior, which is perceived as comfortable by a vehicle occupant, is achieved.