Method for Operating a Vehicle Comprising an Electro-Hydraulic Brake System, and Electro-Hydraulic Brake System of a Vehicle

Abstract

Please substitute the new Abstract submitted herewith for the original Abstract: The invention relates to operating a vehicle having an electro-hydraulic brake system. The vehicle can be operated in a manual and an autonomous driving mode. The brake system is divided into a first and a second hydraulic brake circuit. The two brake circuits can be hydraulically decoupled from one another by a circuit separating valve. The two brake circuits are each assigned to hydraulically enable at least one respective wheel brake of the vehicle. A brake pedal is brought into an at least partially actuated position during an autonomous driving mode.

Claims

1. to 13. (canceled)

14. A method for operating a vehicle with an electrohydraulic brake system comprising a first and second hydraulic brake circuit that are each assigned to hydraulically enable at least one respective wheel brake of the vehicle, the method comprising: hydraulically decoupling the first brake circuit of the brake system from the second brake circuit; separating the second brake circuit from an actuating cylinder that is actuatable by a brake pedal; producing a hydraulic connection between the actuating cylinder and the at least one wheel brake assigned to the first brake circuit; separating the hydraulic connection of the first brake circuit from a hydraulic pressure source that is controllable by a control unit; switching an outlet valve assigned to the at least one wheel brake of the first brake circuit into an opened position, in which the outlet valve produces a hydraulic connection between the at least one wheel brake of the first brake circuit and a brake fluid vessel; conveying hydraulic brake fluid from the actuating cylinder via the first brake circuit and via the opened outlet valve at the at least one wheel brake into the brake fluid vessel; and evacuating hydraulic fluid from a pressure chamber of the actuating cylinder, which is assigned to the first brake circuit, wherein the vehicle is operable in a manual and an autonomous driving mode; and during an autonomous driving mode, the brake pedal is brought into an at least partially actuated position.

15. The method according to claim 14, wherein a second pressure chamber of the actuating cylinder, which is assigned to the second brake circuit, is evacuated via the following steps: separating the second brake circuit of the brake system from the first brake circuit; separating the first brake circuit from the actuating cylinder that is actuatable by the brake pedal; producing a hydraulic connection between the actuating cylinder and the at least one wheel brake assigned to the second brake circuit; separating the hydraulic connection of the second brake circuit from a hydraulic pressure source that is controllable by a control unit; switching an outlet valve assigned to the at least one wheel brake of the second brake circuit into an opened position, which outlet valve produces a hydraulic connection between the at least one wheel brake and a brake fluid vessel; conveying hydraulic brake fluid from the actuating cylinder via the second brake circuit and via the opened outlet valve at the at least one wheel brake into the brake fluid vessel; and evacuating hydraulic fluid from the second pressure chamber of the actuating cylinder, which is assigned to the second brake circuit.

16. The method according to claim 14, wherein the brake pedal is arrested in the actuated position.

17. The method according to claim 14, wherein the first and second brake circuits are separated from one another by a circuit-separating valve.

18. The method according to claim 14, wherein in the case of a braking intervention, during the actuation of the brake pedal into an actuated position, the second brake circuit is hydraulically coupled to the hydraulic pressure source that is controllable by a control unit.

19. The method according to claim 14, wherein in the event of a manual driving mode being detected, the brake pedal is brought back into a non-actuated position again.

20. The method according to claim 14, wherein the brake pedal is brought back into its non-actuated position by a force store element.

21. The method according to claim 14, wherein the brake pedal is brought into an actuated position with a maximum speed such that no noticeable vehicle deceleration occurs.

22. An electrohydraulic brake system of a vehicle operable both in a manual and in an autonomous driving mode, comprising: a first and a second hydraulic brake circuit hydraulically decouplable from one another by a circuit-separating valve, each being assigned to enable at least one respective wheel brake of the vehicle; an actuating cylinder actuatable by a brake pedal; hydraulic pressure source controllable by an electronic open-loop and/or closed-loop control unit by a pressure in which the at least one wheel brake of one of the first and second hydraulic brake circuits is controllable in an autonomous driving mode of the vehicle; an actuating valve to produce a hydraulic connection between the actuating cylinder and two or more wheel brakes assigned to a common brake circuit of the first and second hydraulic brake circuits, and a brake pedal actuator or a driver by which the brake pedal is movable into an at least partially actuated position, wherein the wheel brakes of the vehicle are assigned to one outlet valve that is controllable by the electronic open-loop and/or closed-loop control unit; and in the opened state, the one outlet valve produces a hydraulic bypass of brake fluid into a brake fluid vessel.

23. The electrohydraulic brake system according to claim 22, wherein the first brake circuit is formed: by rear wheel brakes of the vehicle; or by front wheel brakes of the vehicle; or by a front wheel brake on the left-hand vehicle side and a rear wheel brake on the right-hand vehicle side; or by a front wheel brake on the right-hand vehicle side and a rear wheel brake on the left-hand vehicle side; and the second brake circuit is formed by the remaining wheel brakes.

24. The electrohydraulic brake system according to claim 22, wherein the actuating cylinder comprises a first and a second pressure chamber, wherein the first brake circuit is assigned to the first pressure chamber and the second brake circuit is assigned to the second pressure chamber.

25. The electrohydraulic brake system according to claim 22, comprising: a manually-actuatable unlocking device by which the brake pedal situated in an at least partially actuated position is unlockable into a non-actuated position.

26. The electrohydraulic brake system according to claim 22, wherein the brake pedal is mechanically coupled to an accelerator pedal such that, in the autonomous driving mode of the vehicle, the accelerator pedal is likewise held in an actuated position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] FIG. 1 schematically shows a circuit diagram of the layout of a brake circuit of an electrohydraulic brake system with a two-piston actuating cylinder during evacuation of the first pressure chamber of the actuating cylinder during the movement of the brake pedal into an actuated position, whereas

[0069] FIG. 2 schematically shows a circuit diagram of the layout of a brake circuit of an electrohydraulic brake system with a two-piston actuating cylinder during evacuation of the second pressure chamber of the actuating cylinder.

DETAILED DESCRIPTION OF THE DRAWINGS

[0070] The electrohydraulic brake system comprises in this case a two-piston actuating cylinder Z which is actuatable by a brake pedal P. The actuating cylinder Z again comprises two pressure chambers DK, SK, which each form a brake circuit. Thus, the system comprises a first and a second hydraulic brake circuit, which two brake circuits are hydraulically decouplable from one another via in each case one circuit-separating valve V.sub.m, V.sub.B2.

[0071] Here, each brake circuit can be hydraulically connected to two different wheel brakes R of the vehicle. The brake circuit of the first pressure chamber DK, also referred to as a so-called pressure rod circuit, is hydraulically assigned to the wheel brake R.sub.HL of the left-hand rear wheel of the vehicle and to the wheel brake R.sub.VR of the right-hand front wheel of the vehicle. Thus, the two wheel brakes R.sub.HL, R.sub.VR can be hydraulically controlled and operated via the pressure rod circuit.

[0072] The second brake circuit of the second pressure chamber SK, which is also referred to as a so-called floating-piston circuit, is assigned to the remaining wheel brakes R, to the wheel brake R.sub.VL of the left-hand front wheel and R.sub.HR of the right-hand rear wheel of the vehicle.

[0073] During a brake-by-wire braking process, the actuating cylinder Z is normally hydraulically decoupled from the wheel brakes R. Instead, the braking operation at the individual wheel brakes R occurs via a generation of external power, in this case via a hydraulic pressure source D which is controlled by an electric motor M and via a control unit. This means that the muscle power of the driver by actuation of the brake pedal P acts only as a fall-back level in the event of a failure of the brake-by-wire.

[0074] Here, the vehicle is operable in a manual and in an autonomous driving mode.

[0075] During a manual driving operation, when the driver themself performs the driving and thus braking task, the brake pedal P, when it is actuated by the driver, acts via a pedal rod on an actuating cylinder Z. Here, firstly, the deceleration demand of the driver is detected electronically via a suitable sensor arrangement S 1, and secondly, a hydraulic actuation of a pedal feel simulator S is preferably performed. The pedal feel simulator S may, for example, likewise constitute a pressure cylinder or else a spring arrangement which, in a brake-by-wire operating mode, provides the driver with feedback or a resistance for the purposes of feedback of the brake actuation. The pressure acting in a simulator chamber is in this case hydraulically independent of a pressure level in the wheel brakes R, which is set by a, for example, electric-motor-powered drive M.

[0076] The actual brake pressure required for the braking of the wheel brakes R is generated via the hydraulic pressure source D or pressure provision device, which is controlled in open-loop or closed-loop fashion by the electronic open-loop and closed-loop control unit, and a pressure valve arrangement V.sub.P2, V.sub.P1 of the brake system.

[0077] Here, in particular, an electric motor M serves as drive or as pump.

[0078] In the autonomous driving mode of the vehicle, if the vehicle (at least partially) performs the driving task, the brake-by-wire closed-loop pressure control is performed in a manner dependent on data from a multiplicity of different vehicle sensor arrangements.

[0079] If the brake pedal is now brought into an actuated position, according to the above-described method implementation mode of operation of the brake system, a pedal travel sensor arrangement S1 would detect the brake pressure desired by the driver and a control unit would initiate a braking process at the wheel brakes R through suitable control of the hydraulic pressure source D. The brake system would, in the normal situation, initiate a braking operation.

[0080] In this case, however, the driver actuates the brake pedal P without a braking intervention being desired. Instead, it is provided that the brake pedal P is brought into an actuated position such that, while the vehicle is in an autonomous driving mode, the driver is provided with more legroom in the footwell.

[0081] For this purpose, in a first step as illustrated in FIG. 1, the floating-piston circuit SK is hydraulically decoupled from the actuating cylinder via the valve V.sub.B 1. The pressure-rod circuit DK is simultaneously opened by electrical energization of the valve V.sub.B2, wherein a hydraulic connection is produced between the first pressure chamber DK and the left-hand rear-wheel brake R.sub.HL and the right-hand front-wheel brake R.sub.VR of the vehicle. The outlet valves V.sub.A2 to the left-hand rear-wheel brake R.sub.HL and to the right-hand front-wheel brake R are opened, such that hydraulic fluid which flows from the first pressure chamber in the direction of the wheel brakes R.sub.HL, R.sub.VR as a result of the actuation of the brake pedal P is discharged through the outlet valves V.sub.A2 into the brake fluid vessel B. The second pressure chamber SK (the floating-piston circuit) is decoupled from the wheel brakes, for which reason no braking operation occurs at the left-hand front-wheel brake R.sub.VL and at the right-hand rear-wheel brake R.sub.HR.

[0082] Thus, no noticeable vehicle deceleration occurs upon actuation of the brake pedal P.

[0083] In a further step, after the first pressure chamber DK of the actuating cylinder Z has been evacuated as can be seen in FIG. 1, the pressure-rod circuit DK is, as can be seen in FIG. 2, now hydraulically decoupled by closure of the valve V.sub.B2, such that, in the event of further actuation of the brake pedal P, no vehicle deceleration caused by a pressure build-up in the second pressure chamber SK occurs. For the evacuation of the second pressure chamber SK, the valve V.sub.B1 is therefore opened, and the floating-piston circuit SK is thus produced. The outlet valves V.sub.A1 of the left-hand front-wheel brake R.sub.VL and of the right-hand rear-wheel brake R.sub.HR are opened. In the case of further actuation of the brake pedal P into an actuated position, the hydraulic fluid in the floating-piston circuit SK now flows in the direction of the two wheel brakes R.sub.YL and R.sub.HR through the outlet valves V.sub.A1 into the brake fluid vessel B. No noticeable vehicle deceleration occurs via the second brake circuit, the floating-piston circuit SK.

[0084] In order that a braking operation can occur at any time during the actuation of the brake pedal P into an actuated position, always at least two wheel brakes, in the first step (illustrated in FIG. 1) the wheel brakes R.sub.HR and R.sub.VL and in the second step (illustrated in FIG. 2) the wheel brakes R.sub.HL and R.sub.VR, are controllable and actuatable via the hydraulic pressure source D. For this purpose, in the respective steps (FIG. 1 and FIG. 2), depending on which pressure chamber is presently being evacuated, the connection to the respective wheel brakes R and to the hydraulic pressure source D is produced via a valve V.sub.P2 (in step 2) or V.sub.P1 (in step 1). At those wheel brakes R at which a braking operation is to occur (depending on which step of the evacuation the actuating cylinder finds itself), the outlet valves V.sub.A1 (in step 1) and V.sub.A2 (in step 2) are closed, such that hydraulic fluid can flow from the hydraulic pressure source D into the respective wheel brake R.

[0085] It can thus be ensured that, during the entire process of the evacuation of the two pressure chambers DK, SK of the actuating cylinder Z, autonomous braking of the vehicle via at least two wheel brakes R can be performed.

[0086] After the two steps (step 1 in FIG. 1 and step 2 in FIG. 2) of the evacuation of the actuating cylinder Z have taken place and the brake pedal P is in an actuated position, it is provided that the brake pedal P is held in said actuated position, via a suitable locking mechanism, during the entire period in which the vehicle is in the autonomous driving mode.

[0087] If the vehicle changes back into a manual driving mode, then the arresting of the brake pedal P in the actuated position can be released. A spring arrangement which is, for example, already present in the actuating cylinder Z can then ensure the resetting force required for the movement of the brake pedal P into a non-actuated position. The valves V.sub.B2 and V.sub.B1 are then closed, and the driver can then again operate the brake system by actuating the brake pedal P in the conventional manner.

[0088] It is advantageously to be noted here that, during the evacuation process of the actuating cylinder Z or during the actuation of the brake pedal in accordance with the stated steps 1 and 2, the control unit takes into consideration the fact that the travel sensor 51 for detecting the brake pedal travel and the plausibility diagnostic means S2 for comparing the desired pressure with possible disturbance variables are suppressed or deactivated. After the method has been completed and the brake pedal is brought into a non-actuated position again, the sensor arrangements 51 and S2 should then be functional. The valve VS for producing a hydraulic connection between the brake force simulator S and the brake circuits SK, DK remains closed during the entire method according to FIG. 1 and FIG. 2.