METHOD FOR CONTROLLING A HYDRAULIC BRAKE SYSTEM DURING A REGENERATIVE BRAKING PROCESS, HYDRAULIC BRAKE SYSTEM, COMPUTER PROGRAM PRODUCT, CONTROL UNIT AND MOTOR VEHICLE

Abstract

A method for controlling a hydraulic brake system where a hydraulic fluid is displaced in the direction of at least two-wheel brakes by means of a brake cylinder. One of the at least two-wheel brakes is at least partially hydraulically isolated from the brake cylinder in order to adapt the at least two-wheel brakes with regard to their hydraulic braking force to an incipient or present wheel load distribution. In addition or alternatively, in the method, it is furthermore the case that at least one volume fraction of the hydraulic fluid is displaced between the at least two wheel brakes in order to adapt the at least two wheel brakes with regard to their hydraulic braking force to a changing wheel load distribution over the course of the braking process and/or to a changing generator braking torque over the course of the braking process.

Claims

1. A method for controlling a hydraulic brake system during a regenerative braking process, wherein a hydraulic fluid is or has been displaced in the direction of at least two wheel brakes by means of a brake cylinder, and wherein at least one volume fraction of the hydraulic fluid is displaced between the at least two wheel brakes in order to adapt the at least two wheel brakes with regard to their hydraulic braking force to a changing wheel load distribution over the course of the braking process and/or to a changing generator braking torque over the course of the braking process.

2. A method for controlling a hydraulic brake system during a regenerative braking process, wherein, by means of a brake cylinder, a hydraulic fluid is displaced in the direction of at least two wheel brakes and one of the at least two wheel brakes is at least partially hydraulically isolated from the brake cylinder in order to adapt the at least two wheel brakes with regard to their hydraulic braking force to an incipient or present wheel load distribution.

3. The method as defined in claim 2, wherein an isolation valve is adjusted in the direction of a closed state in order to at least partially hydraulically isolate the one-wheel brake from the brake cylinder.

4. The method as defined in claim 3, wherein the isolation valve is adjusted into the closed state in order to fully hydraulically isolate the one-wheel brake from the brake cylinder.

5. The method as defined in claim 3, wherein, after the adjustment of the isolation valve in the direction of the closed state, the isolation valve is adjusted in the direction away from the closed state in order to relieve the other of the at least two wheel brakes of load with regard to its hydraulic braking force.

6. The method as defined in claim 1, wherein one of the at least two wheel brakes is a front wheel brake which is configured to be assigned to a front vehicle wheel, the other wheel brake is a rear wheel brake which is configured to be assigned to a rear vehicle wheel, and, in the regenerative braking process, a generator braking torque effected by an electric machine acts on the rear vehicle wheel.

7. The method as claimed in claim 2, wherein one of the at least two wheel brakes is a front wheel brake which is configured to be assigned to a front vehicle wheel, the other wheel brake is a rear wheel brake which is configured to be assigned to a rear vehicle wheel, and, in the regenerative braking process, a generator braking torque effected by an electric machine acts on the rear vehicle wheel, and wherein the at least partially hydraulically isolated wheel brake is formed by the rear wheel brake.

8. A hydraulic brake system for a motor vehicle, comprising: a brake cylinder and at least two wheel brakes which are each hydraulically connected via a feed line to the brake cylinder, wherein the brake cylinder is configured to displace a hydraulic fluid in the direction of the at least two wheel brakes, and the at least two wheel brakes are configured to exert a hydraulic braking force by means of the hydraulic fluid; an isolation valve which is fluidically assigned to one of the feed lines and which is configured to close the one feed line; a control unit which is connected in signal-exchanging fashion to the isolation valve and which is configured to, in the presence or upon an onset of an actuation of the brake cylinder, and in particular in the presence or upon an onset of a generator braking torque of an electric machine, activate the isolation valve for adjustment in the direction of a closed state in order to at least partially hydraulically isolate the associated wheel brake from the brake cylinder and thus adapt the at least two wheel brakes with regard to their braking force to an incipient or present wheel load distribution.

9. The brake system as defined in claim 8, wherein the control unit is configured to, in the presence of an actuation of the brake cylinder and in particular in the presence of a generator braking torque of the electric machine, activate the isolation valve for adjustment in the direction away from the closed state in order to adapt the at least two wheel brakes with regard to their hydraulic braking force to a changing wheel load distribution over the course of the braking process and/or to a changing generator braking torque over the course of the braking process.

10. The brake system as defined in claim 8, wherein the control unit is configured to, in the presence of an actuation of the brake cylinder, activate the isolation valve for adjustment in the direction away from the closed state in a manner dependent on a change in the wheel load distribution and/or a changing generator braking torque.

11. The brake system as defined in claim 8, wherein one of the at least two wheel brakes is a front wheel brake, which is configured to be assigned to a front vehicle wheel, and the other wheel brake is a rear wheel brake, which is configured to be assigned to a rear vehicle wheel.

12. The brake system as defined in claim 11, wherein the isolation valve is a constituent part of an anti-lock braking system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Further details and features of the present disclosure will emerge from the following description of two exemplary embodiments on the basis of the drawing. In the drawing:

[0049] FIG. 1 shows a possible embodiment of a hydraulic brake system, which is suitable for carrying out a regenerative braking process, in a schematic illustration, and

[0050] FIG. 2 shows a further possible embodiment of a hydraulic brake system, which is suitable for carrying out a regenerative braking process, in a schematic illustration.

DETAILED DESCRIPTION

[0051] FIG. 1 shows a possible embodiment of a hydraulic brake system 10 which is suitable for being used for example in a motor vehicle, in particular a passenger motor vehicle, a heavy goods vehicle or a motorcycle. In FIG. 1, the hydraulic brake system 10 is illustrated by way of example in conjunction with two vehicle wheels 100, 200. The hydraulic brake system 10 is configured to be able to perform a regenerative braking process. In the regenerative braking process, the kinetic energy of the motor vehicle is utilized in order to drive an electric machine 50 in generator mode and thereby generate electrical energy. The electrical energy can be utilized for example to charge an electrical energy store of the motor vehicle.

[0052] By way of example, in FIG. 1, the electric machine 50 is assigned to one of the vehicle wheels 100, 200, in particular to the vehicle wheel 200, in order to illustrate that the electric machine 50 is driven by the movement of the vehicle, that is to say by the rotation of the vehicle wheel 200. The electric machine 50 is preferably a constituent part of an electric drive of the motor vehicle, which serves for example for driving the vehicle wheel 200. During a regenerative braking process, the electric drive is utilized as a generator.

[0053] The hydraulic brake system 10 comprises at least one, preferably at least two, wheel brakes 28, 30, which can be assigned to in each case one vehicle wheel. For example, the one wheel brake 28 is are to one vehicle wheel 100, and the other wheel brake 30 to the vehicle wheel 200. For example, the one vehicle wheel 100 is a front wheel, and the other vehicle wheel 200 is a rear wheel. In this respect, the one wheel brake 28 may be a front wheel brake 1, and the other wheel brake 30 may be a rear wheel brake 2.

[0054] Preferably, the at least two wheel brakes 28, 30 are each hydraulically connected via a feed line 20.1, 20.2 to a brake cylinder 16. For example, the feed lines 20.1, 20.2 are hydraulically connected via a common line portion 20.3 to the brake cylinder 16. The brake cylinder 16 is configured to displace a hydraulic fluid in the direction of the at least two wheel brakes 28, 30. The at least two wheel brakes 28, 30 are each configured to exert a braking force, for example in the form of a friction force, on the associated vehicle wheel 100 or 200 respectively by means of the hydraulic fluid. The hydraulic brake system 10 is preferably assigned a brake pedal 12, by means of which the brake cylinder 16 is to be actuated. The brake cylinder 16 is preferably assigned a reservoir 18 for the purposes of storing hydraulic fluid for the hydraulic brake system 10 in the reservoir. The reservoir 18 may have an inlet opening in order to be refilled or filled via the inlet opening.

[0055] To boost an actuating force input by means of the brake pedal 12, for example by a driver of the motor vehicle, a brake force booster 14 may be provided. The brake force booster 14 preferably boosts the actuating force in a known manner in accordance with a pneumatic, electrohydraulic or electromechanical principle. In order, for automatic vehicle control, to actuate the brake cylinder independently of an actuation of the brake pedal by the driver, it is also possible for an electrically controlled brake force booster (EBB; Electronic Brake Booster) to be provided.

[0056] The hydraulic brake system 10 preferably furthermore comprises at least one, for example two, isolation valve(s) 22, 24, of which the one isolation valve 22 is assigned to the one feed line 20.1 and the other isolation valve 24 is assigned to the other feed line 20.2 and which are each configured to close the associated feed line 20.1 or 20.2. For example, it is the intention, by means of the one isolation valve 22, for the one wheel brake 28 to be able to be at least partially or entirely hydraulically isolated from the brake cylinder 16. For example, it is the intention, by means of the other isolation valve 24, for the other wheel brake 30 to be able to be at least partially or entirely hydraulically isolated from the brake cylinder 16.

[0057] The isolation valves 22, 24 are preferably each provided for adjustment between a closed position and an open position in order to close or shut off, in particular entirely or at least partially close or shut off, the associated feed line 20.1 or 20.2. Preferably, in the closed position of the respective isolation valve 22 or 24, the associated feed line 20.1 or 20.2 is shut off, in particular fully shut off or at least largely or substantially shut off, and, in the open position, the associated feed line 20.1 or 20.2 is open, in particular substantially open or fully open.

[0058] Preferably, the hydraulic brake system 10 furthermore has at least one, for example two, return lines 32.1, 32.2, of which the one return line 32.1 is assigned to the one wheel brake 28 and the other return line 32.2 is assigned to the other wheel brake 30. The return lines 32.1 and 32.2 each serve for returning at least one volume fraction of the hydraulic fluid from a region positioned downstream of the respectively associated isolation valve 22 or 24 into a region positioned upstream of the respectively associated isolation valve 22 or 24. For example, the return lines 32.1 and 32.2 are each connected in terms of flow by way of one end to the associated feed line 20.1 or 20.2 in a region between the associated isolation valve 22 or 24 and the associated wheel brake 28 or 30. Preferably, the return lines 32.1 and 32.2 are connected in terms of flow by way of another end to the associated feed line 20.1 or 20.2 in a region between the associated isolation valve 22 or 24 and the brake cylinder 16. In this way, at least one volume fraction of the hydraulic fluid can be returned from the associated wheel brake 28 or 30 into the respective feed line 20.1 or 20.2, bypassing the associated isolation valve 22 or 24.

[0059] The region positioned downstream is to be understood in particular to mean that receiving volume of the brake system 10 for receiving hydraulic fluid which is positioned downstream of the isolation valve 22 or 24 under consideration as viewed in the flow direction with respect to the feed line 20.1 or 20.2 under consideration, that is to say in the direction from the brake cylinder 16 to the wheel brake 28 or 30 under consideration. For example, the region positioned downstream comprises a hydraulic receiving volume of the associated feed line 20.1 or 20.2 which is positioned downstream of the isolation valve 22 or 24 under consideration, and/or comprises a hydraulic receiving volume of the wheel brake 28 or 30 under consideration.

[0060] The region positioned upstream is to be understood in particular to mean that receiving volume of the brake system 10 for receiving hydraulic fluid which is positioned upstream of the isolation valve 22 or 24 under consideration as viewed in the flow direction with respect to the feed line 20.1 or 20.2 under consideration, that is to say in the direction from the brake cylinder 16 to the wheel brake 28 or 30 under consideration. For example, the region positioned upstream comprises a hydraulic receiving volume of the associated feed line 20.1 or 20.2 which is positioned upstream of the isolation valve 22 or 24 under consideration and/or comprises a hydraulic receiving volume of the brake cylinder 16 and/or of the reservoir/replenishment vessel 18 for the hydraulic fluid.

[0061] Preferably, the return line 32.1, 32.2 each have a pressure dissipation valve 34 or 36 respectively. Preferably, the return lines 32.1, 32.2 have a common line portion 32.3, which is fluidically assigned a pump 38 and an accumulator 42. The pump 38 is configured to convey at least one volume fraction of the hydraulic oil, in particular in a return direction 70. Preferably, by means of a conveying action of the pump 38 in the return direction 70, the at least one volume fraction of the hydraulic fluid is conveyed in the direction of the region positioned upstream. The accumulator 42 is configured to store at least one volume fraction of the hydraulic fluid, in particular to store the same under pressure, in particular to buffer-store the same.

[0062] The respective pressure dissipation valve 34 or 36 is configured to open and close the respectively associated return line 32.1 or 32.2. The respective pressure dissipation valve 34 or 36 is preferably provided for adjustment between a closed position and an open position in order to open, in particular entirely or at least partially open, the associated return line 32.1 or 32.2. Preferably, in the open position of the respective pressure dissipation valve 34 or 36, the associated return line 32.1 or 32.2 is open, in particular at least partially open or fully open, and, in the closed position, the respective return line 32.1 or 32.2 is closed or shut off, in particular entirely shut off or at least largely or substantially shut off. Preferably, as viewed in the return direction 70 of the hydraulic fluid, the respective pressure dissipation valve 34 or 36, the pump 38 and the accumulator 42 are arranged in the sequence in which the respective pressure dissipation valve 34 or 36 comes first, and is followed either by the pump 38 or the accumulator 42. By opening the corresponding return line 32.1 or 32.2, the accumulator 42 is thus filled with the returned volume fraction of the hydraulic fluid.

[0063] Preferably, the hydraulic brake system 10 furthermore comprises a control unit 48, in particular an electrical control unit, for activating the isolation valves 22, 24 and/or the pressure dissipation valves 34, 36 and/or the pump 38. For example, for this purpose, the control unit 48 is connected in signal-exchanging fashion to the isolation valves 22, 24 and/or to the pressure dissipation valves 34, 36 and/or to the pump 38 via a corresponding signal line 61 or 62 or 63 or 64 or 65 respectively, in particular electrical signal line. Preferably, the isolation valves 22, 24 and/or the pressure dissipation valves 34, 36 and/or the pump 38 has in each case one electrical receiver unit in order to process the control signals transmitted by the control unit 48 and initiate or perform a corresponding actuation of the isolation valve 22 or 24 or of the pressure dissipation valve 34 or 36 or of the pump 38 respectively.

[0064] For example, for this purpose, the pump 38 may have a corresponding actuating device, such as for example an electric drive motor M, which is activated by the control line 65 and which acts on the pump 38, in particular on a working cylinder of the pump 38, via a mechanical and/or hydraulic and/or electromagnetic actuation connection 67. Preferably, both control signals and state signals, for example signals with information items regarding monitored or detected parameters, are to be transmitted via the signal lines 61, 62, 63, 64, 65.

[0065] The control unit 48 is preferably connected in signal-exchanging fashion to the electric machine 50 for example via a signal line 60, in order to transmit control signals from the control unit 48 to the electric machine 50 and/or conversely in order to transmit control signals or signals containing information items regarding an operating state of the electric machine 50, for example, to the control unit 48. For this purpose, the electric machine 50 may have a control unit 52 which communicates via the signal line 60 with the control unit 48 and which activates, in particular directly activates, the electric machine 50.

[0066] Preferably, the control unit 48 is furthermore connected in signal-exchanging fashion via a signal line 66 to a sensor element assigned to the brake pedal 12, in particular a pedal travel sensor 46. The pedal travel sensor 46 serves for detecting a pedal travel of the brake pedal 12. Via the signal connection between the pedal travel sensor 46 and the control unit 48, the control unit 48 can take into consideration information items relating to the pedal travel.

[0067] The control unit 48 is preferably configured such that, in the presence or upon an onset of an actuation of the brake cylinder 16 and in particular in the presence or upon an onset of a generator braking torque originating from the electric machine 50, the control unit activates at least one of the pressure dissipation valves 34, 36 for opening and the associated isolation valve 22 or 24 for adjustment in the direction of a closed state, and furthermore activates the pump 38 for imparting a conveying action. The control unit 48 is preferably also configured such that, in the presence or upon an onset of an actuation of the brake cylinder 16 and in particular in the presence or upon an onset of a generator braking torque originating from the electric machine 50, the control unit activates the two pressure dissipation valves 34, 36 for opening and the two associated isolation valves 22, 24 for adjustment in the direction of a closed state, and furthermore activates the pump 38 for imparting a conveying action. Preferably, the control unit 48 is configured such that, in the presence or upon an onset of an actuation of the brake cylinder 16, and in particular in the presence or upon an onset of a generator braking torque at least one of the pressure dissipation valves 34, 36 is activated for opening, the associated isolation valve 22 or 24 is subsequently or simultaneously activated for closing, and the pump 38 is activated, for imparting a conveying action, subsequently to or simultaneously with the activation of the isolation valve 22 or 24.

[0068] In order to identify or detect a presence or an onset of an actuation of the brake cylinder 16, the control unit 48 utilizes, for example, information items from the pedal travel sensor 46. In order to identify or detect a presence of a generator braking torque of the electric machine 50, the control unit 48 utilizes, for example, signals from sensor elements which provide information items relating for example to the operating state of the electric machine 50. In addition or alternatively, it is also possible for the electric machine 50 to be utilized directly, for example by virtue of the control unit 48 using information items from the control unit 52 of the electric machine 50 for this purpose. If the control unit 48 identifies or detects that the electric machine 50 is not operating in the generator mode, for example because the electric machine 50 is still electrically energized, the control unit 48 may be configured to output a control command to the electric machine 50 to switch into the generator mode.

[0069] In order to perform a regenerative braking process without or substantially without hydraulic braking force action, the hydraulic brake system 10 may provide the following mode of functioning: An actuation of the brake pedal 12 or an incipient actuation of the brake pedal 12 is identified or detected by the control unit 48. The pressure dissipation valve 34 and/or the pressure dissipation valve 36 is hereupon activated for opening by the control unit 48. This results in an adjustment of the pressure dissipation valve 34 and/or of the pressure dissipation valve 36 from the closed position (FIG. 1) toward its open position and thus an opening of the return line 32.1 and/or of the return line 32.2. As a result of the actuation of the brake pedal 12, a displacement of a hydraulic fluid from the brake cylinder 16 in the direction of the wheel brakes 28, 30 is effected via the feed lines 20.1, 20.2. Owing to the opened return line 32.1 and/or the opened return line 32.2, at least one volume fraction of the hydraulic fluid is conducted into the accumulator 42, such that a hydraulic braking force corresponding to the displacement of the hydraulic fluid is not generated at the wheel brake 28 and/or the wheel brake 30.

[0070] By means of the actuation of the brake pedal 12, a braking force demand is input, which must be matched by generation of a braking force. For this purpose, the drag torque originating from the electric machine 50 is utilized, which acts as a braking force on the moving system, in particular the vehicle wheel 200. If, for example, the braking force demand is covered by this generator braking force originating from the electric machine 50, the opening of the pressure dissipation valve 34 or 36 is performed to such an extent that no or substantially no hydraulic braking force acts at the associated wheel brake 28 or 30. If, for example, the braking force demand is higher than the generator braking force, the opening of the pressure dissipation valve 34 or 36 is performed such that, at the associated wheel brake 28 or 30, such a level of hydraulic braking force is built up, owing to the displacement of the hydraulic fluid, that the hydraulic braking force and the generator braking force give rise to an overall braking force which corresponds or at least approximately corresponds to the braking force demand.

[0071] After the activation of the pressure dissipation valve 34 or 36 or after the opening of the pressure dissipation valve 34 or 36, the associated isolation valve 22 or 24 is activated for closing by the control unit 48. This results in an adjustment of the associated isolation valve 22 or 24 from its open position (FIG. 1) in the direction of its closed position and thus to a shutting-off of the associated feed line 20.1 or 20.2. In this way, the associated wheel brake 28 or 30 is hydraulically isolated from the brake cylinder 16. Furthermore, the pump 38 is activated, for imparting a conveying action, by the control unit 48. As a result of the conveying action by the pump 38, a volume fraction of the hydraulic fluid that is still situated in the wheel brake 28 or 30 in question is conveyed out to such an extent that no braking force or substantially no braking force acts at the wheel brake 28 or 30 in question, in order that, in this way, the wheel brake 28 in question is placed in a hydraulically unpressurized state. When the actuation of the brake pedal 12 has been ended, the pressure dissipation valve 34 or 36 is activated for closing, and the associated isolation valve 22 or 24 is activated for opening. The pump 38 still imparts a conveying action until such time as the accumulator 42 has been evacuated.

[0072] Preferably, the control unit 48 is furthermore configured to, in the presence or upon an onset of an actuation of the brake cylinder 16, and in particular in the presence or upon an onset of a generator braking torque of the electric machine 50, activate one of the isolation valves 22, 24 for adjustment in the direction of a closed state in order to at least partially hydraulically isolate the associated wheel brake 28 or 30 from the brake cylinder 16 and thus adapt the two wheel brakes 28, 30 with regard to their braking force to an incipient or present wheel load distribution which is present in the motor vehicle during the course of the braking process. Preferably, the control unit 48 is configured to, in the presence or upon an onset of an actuation of the brake cylinder 16, and in particular in the presence or upon an onset of a generator braking torque of the electric machine 50, activate the isolation valve 24, which is assigned to the rear wheel brake 2, for adjustment in the direction of a closed state in order to at least partially hydraulically isolate the rear wheel brake 2 from the brake cylinder 16 and thus adapt the rear wheel brake 2 and the front wheel brake 1 with regard to their braking force to an incipient or present wheel load distribution of the motor vehicle during the braking process.

[0073] Preferably, the control unit 48 is furthermore configured to, in the presence of an actuation of the brake cylinder 16 and in particular in the presence of a generator braking torque of the electric machine 50, activate one of the isolation valves 22, 24 for adjustment in the direction away from the closed state in order to adapt the two wheel brakes 28, 30 with regard to their hydraulic braking force to a dynamic wheel load distribution which is encountered in the motor vehicle during the course of the braking process. Preferably, the control unit 48 is configured to, in the presence of an actuation of the brake cylinder 16 and in particular in the presence of a generator braking torque of the electric machine 50, activate the isolation valve 24, which is assigned to the rear wheel brake 2, for adjustment in the direction away from the closed state in order to adapt the front wheel brake 1 and the rear wheel brake 2 with regard to their hydraulic braking force to a dynamic wheel load distribution of the motor vehicle which is encountered during the course of the braking process and/or to a changing generator braking torque over the course of the braking process. For example, the control unit 48 is configured to, in the presence of an actuation of the brake cylinder 16, activate the isolation valve 24, which is assigned to the rear wheel brake 2, for adjustment in the direction away from the closed state in a manner dependent on a temporally changing generator braking torque of the electric machine 50 in order to adapt the front wheel brake 1 and the rear wheel brake 2 with regard to their hydraulic braking force to a dynamic wheel load distribution of the motor vehicle which is encountered during the course of the braking process.

[0074] In order to perform a regenerative braking process with hydraulic braking force action, the hydraulic brake system 10 may provide a mode of functioning which is described below on the basis of the example of the front wheel brake 1, which is assigned to a front wheel of the motor vehicle, and the rear wheel brake 2, which is assigned to a rear wheel of the motor vehicle: An actuation of the brake pedal 12 or an incipient actuation of the brake pedal 12 is identified or detected by the control unit 48 and, for example, the electric machine 50 is in the generator mode or a generator mode is incipient. The isolation valve 24 assigned to the rear wheel brake 2 is hereupon activated by the control unit 48 in order to adjust the isolation valve in the direction of a closed state and in this way at least partially hydraulically isolate the associated wheel brake 30 from the brake cylinder 16.

[0075] As a result of the actuation of the brake pedal 12, a displacement of a hydraulic fluid from the brake cylinder 16 in the direction of the front wheel brake 1 and of the rear wheel brake 2 is effected via the feed lines 20.1, 20.2. The displacement of the hydraulic fluid results in a higher hydraulic braking force at the front wheel brake 1 in relation to the rear wheel brake 2. An increased hydraulic vehicle braking torque is achieved in this way, because a focus is placed on the wheel load distribution of the motor vehicle that takes effect at least in the initial phase of the braking process. This braking situation is promoted in that the rear wheel 200 is additionally acted on by the generator braking torque provided by the electric machine 50.

[0076] In a manner dependent on the level of the generator braking torque, which changes in a manner dependent on the speed of the motor vehicle during the braking process, that is to say changes over the course of time or of the duration of the braking process, the isolation valve 24 is now activated by the control unit 48 for adjustment in the direction away from the closed state. As a result, a greater volume fraction of the hydraulic fluid flows into the rear wheel brake 2 or, if the isolation valve was fully closed beforehand, a volume fraction of the hydraulic fluid flows into the rear wheel brake 2 in the first place, and a compensation of volume of the hydraulic fluid can thus take place between the front wheel brake 1 and the rear wheel brake 2. Thus, the hydraulic braking force of the rear wheel brake 2 increases, and the hydraulic braking force of the front wheel brake 1 decreases.

[0077] FIG. 2 shows a further possible embodiment of a hydraulic brake system 10 which is suitable for performing a regenerative braking process and which may be used for example in a motor vehicle, in particular in a passenger motor vehicle or a heavy goods vehicle. The hydraulic brake system 10 of FIG. 2 is a brake system as described in WO 2014/082885 A1. In this respect, with regard to the construction and the functionality of the hydraulic brake system 10, reference is made to the disclosure of WO 2014/082885 A1, which is hereby incorporated in its entirety into the description.

[0078] In the hydraulic brake system 10, by contrast to the hydraulic brake system 10 of FIG. 1, two brake circuits are provided, which are hydraulically separated from one another. There are preferably interactions between the two brake circuits. For example, a pressure equalization takes place via a common brake cylinder 16, such that the same brake pressure prevails in both brake circuits. The brake cylinder 16 is assigned a reservoir 18 and/or a brake force booster 14, wherein the reservoir 18 and the brake force booster 14 are dimensioned with regard to the two brake circuits. It is basically possible, in terms of function and/or construction, for the brake cylinder 16 to correspond to the brake cylinder 16, for the reservoir 18 to correspond to the reservoir 18, and for the brake force booster 14 to correspond to the brake force booster 14 of the brake system 10 of FIG. 1.

[0079] Preferably, one of the brake circuits of the brake system 10 is structurally identical and/or functionally identical to the one single brake circuit of the hydraulic brake system 10 of FIG. 1, such that components of the one brake circuit of the brake system 10 are denoted by the same reference designations. In this respect, reference is made to the description relating to the brake system 10 of FIG. 1. Preferably, the two brake circuits of the brake system 10 are of identical and/or functionally identical construction with respect to one another, such that, for the sake of simplicity and for better clarity, the other brake circuit has not been labelled with reference designations. For the sake of simplicity and for better clarity, any signal lines that are present have also been omitted in FIG. 2.

[0080] FIG. 2 illustrates four vehicle wheels, which are each assigned a wheel brake. The brake circuit under consideration comprises the wheel brakes 28 and 30, which are assigned in each case to a different vehicle wheel. The two vehicle wheels with the associated wheel brakes 28, 30 may be present at a common axle or may be assigned to different axles, for example to the front axle and to the rear axle of a motor vehicle.

[0081] FIG. 2 shows, by way of example, an assignment of the vehicle wheels to the front axle and to the rear axle in a diagonal configuration, wherein VR denotes the front right vehicle wheel, VL denotes the front left vehicle wheel, HR denotes the rear right vehicle wheel, and HL denotes the rear left vehicle wheel. By way of example, in FIG. 2, the electric machine 50 is assigned to the rear axle. The electric machine 50 interacts with the vehicle wheel at the rear left. For example, a further electric machine may be provided which interacts with the vehicle wheel at the rear right. It is also possible for the rear axle to be assigned an electric machine which is common to both vehicle wheels.

[0082] As can be seen from FIG. 2, the common line portion 20.3 of the feed lines 20.1, 20.2 may be assigned a further isolation valve 26. Furthermore, a supply valve 40 may be assigned to the common line portion 32.3 of the return lines 32.1, 32.2. By means of the supply valve 40, the return lines 32.1, 32.2 can be hydraulically connected, bypassing the further isolation valve 26, to a region positioned upstream of the isolation valve 26. The hydraulic brake system 10 preferably comprises a control unit 48 which is expanded in terms of its functional scope in relation to the control unit 48 of the hydraulic brake system 10 of FIG. 1 such that the further isolation valve 26 and the supply valve 40 can also be activated.

[0083] For example, the isolation valve 26 and the supply valve 40 are a constituent part of a driving dynamics control system (ESP). For example, the control unit 48 is additionally configured for executing the hydraulic brake system 10 during a driving dynamics control process. For example, the isolation valves 22, 24 and the pressure dissipation valves 34, 36 are a constituent part of an anti-lock braking system which is provided by means of the hydraulic brake system 10. For example, the control unit 48 is additionally configured for executing the hydraulic brake system 10 during an anti-lock braking process.

[0084] In the present description, the expression pressure dissipation valve is to be understood in particular to mean a shut-off element by means of which the return line can be at least partially or fully opened, for example proceeding from a shut-off state. For example, the pressure dissipation valve has a passage for fluid, in particular the hydraulic fluid, which passage is of variable cross section. For example, the pressure dissipation valve is configured to be adjusted between a closed position and an open position, for example with regard to the passage, wherein, in the open position, the return line is at least partially or completely opened.

[0085] For example, the pressure dissipation valve is configured to be electrically or electromagnetically actuated, in order to be adjusted and/or switched, for example adjusted and/or switched in continuously variable or stepped and/or digital or analog fashion, between the closed position and the open position. For example, the pressure dissipation valve is or comprises a 2/2 directional valve; which, for example, assumes the closed position in a non-actuated state and the open position in an actuated state. If it is an electrically or electromagnetically actuated pressure dissipation valve, it is for example electrically deenergized in the non-actuated state and electrically energized in the actuated state. For example, the pressure dissipation valve is a valve with an NC function. The NC function is to be understood in particular to mean that the valve is closed in the electrically deenergized state. Such a valve may also be referred to as a normally closed NC valve. For example; the pressure dissipation valve is a preferably directly controlled solenoid valve with an NC function.

[0086] In the present description, the expression pump is to be understood in particular to mean a conveying device for conveying hydraulic fluid. For example, the pump is a rotary pump, in particular a radial piston pump or an axial piston pump. In particular, the rotary pump comprises at least one, preferably multiple, for example two to six, working piston(s), which perform(s) or can perform a reciprocating movement for the purposes of conveying the hydraulic fluid. For example, the pump comprises an electric machine, for example an electric motor, which serves for driving the pump. The electric machine is for example configured to receive electrical control signals and output corresponding control signals to the pump.

[0087] The expression accumulator is to be understood in particular to mean a hydro accumulator or hydraulic accumulator which is for example configured to store the hydraulic fluid under pressure. That volume fraction of the hydraulic fluid which is conducted to the accumulator is thus received therein counter to a resetting force of the accumulator. The accumulator may be designed such that a gas or a spring element is compressed during a process of filling with the hydraulic fluid. For example, the accumulator is a buffer accumulator which is configured to temporarily buffer-store the at least one volume fraction of the hydraulic fluid.

[0088] In the present description, the reference to a particular aspect or a particular embodiment or a particular refinement means that a particular feature or a particular characteristic described in conjunction with the respective aspect or the respective embodiment or the respective refinement is comprised at least therein but need not necessarily be comprised in all aspects or embodiments or refinements of the present disclosure. It is expressly pointed out that any combination of the various features and/or structures and/or characteristics described with regard to the present disclosure are encompassed by the present disclosure unless this is expressly or positively ruled out by the context.

[0089] The use of individual or all examples or of an exemplary phrasing in the text is intended merely to illustrate the present disclosure and does not constitute a limitation with regard to the scope of the present disclosure, unless stated otherwise. Also, no phrasing or wording of the description is to be understood as referring to an element which is not claimed but which is essential for the practical implementation of the present disclosure.