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

Abstract

The present disclosure relates to a method for controlling a hydraulic brake system during a regenerative braking process. In the method, a hydraulic fluid is displaced in the direction of a wheel brake by means of a brake cylinder. In the method, furthermore, at least a volume fraction of the hydraulic fluid is conducted via a pressure dissipation valve into an accumulator, an isolation valve is adjusted in the direction of a closed state in order to at least partially hydraulically isolate the wheel brake from the brake cylinder, and at least a volume fraction of the hydraulic fluid is conveyed out of the wheel brake by means of a pump. The present disclosure furthermore comprises a hydraulic brake system for a motor vehicle, a computer program product, a control unit and a motor vehicle.

Claims

1. A method for controlling a hydraulic brake system during a regenerative braking process, wherein a hydraulic fluid is displaced in the direction of a wheel brake by means of a brake cylinder, and wherein the method comprises the steps whereby at least a volume fraction of the hydraulic fluid is conducted via a pressure dissipation valve into an accumulator, an isolation valve is adjusted in the direction of a closed state in order to at least partially hydraulically isolate the wheel brake from the brake cylinder, and at least a volume fraction of the hydraulic fluid is conveyed out of the wheel brake by means of a pump.

2. The method as claimed in claim 1, wherein the hydraulic fluid is displaced from the brake cylinder in the direction of the wheel brake, the at least one volume fraction of the hydraulic fluid is simultaneously or subsequently conducted via the pressure dissipation valve into the accumulator, the isolation valve is adjusted in the direction of the closed state simultaneously with, or in a manner offset in terms of time in relation to, the conducting of the at least one volume fraction onward into the accumulator, and the at least one volume fraction of the hydraulic fluid is conveyed out of the wheel brake by means of the pump simultaneously with or subsequently to the adjustment of the isolation valve.

3. The method as claimed in claim 1, wherein the isolation valve is adjusted into the closed state in order to hydraulically fully isolate the wheel brake from the brake cylinder.

4. The method as claimed in claim 2, wherein the isolation valve is adjusted into the closed state in order to hydraulically fully isolate the wheel brake from the brake cylinder.

5. The method as claimed in claim 1, wherein such a volume fraction of the hydraulic fluid is conveyed out of the wheel brake by means of the pump that no braking force acts at the wheel brake.

6. The method as claimed in claim 4, wherein such a volume fraction of the hydraulic fluid is conveyed out of the wheel brake by means of the pump that no braking force acts at the wheel brake.

7. A hydraulic brake system for a motor vehicle, comprising: a brake cylinder and a wheel brake which are hydraulically connected to one another via a feed line, wherein the brake cylinder is configured to displace a hydraulic fluid in the direction of the wheel brake, and the wheel brake is configured to exert a hydraulic braking force by means of the hydraulic fluid; an isolation valve which is fluidically assigned to the feed line and which is configured to close the feed line; a return line for returning at least a volume fraction of the hydraulic fluid from a region positioned downstream of the isolation valve into a region positioned upstream of the isolation valve; a pressure dissipation valve, a pump and an accumulator, which are fluidically assigned to the return line, wherein the pump is configured to convey at least a volume fraction of the hydraulic fluid, the accumulator is configured to store at least a volume fraction of the hydraulic fluid, and the pressure dissipation valve is configured to open the return line; a control unit which is connected in signal-exchanging fashion to the isolation valve, the pressure dissipation valve and the pump and which is configured such that, 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 force of an electric machine, the control unit activates the pressure dissipation valve for opening and activates the isolation valve for closing, in order to at least partially hydraulically isolate the wheel brake from the brake cylinder, and furthermore activates the pump to impart a conveying action, in order to lower a residual braking force which has a braking action on the wheel brake.

8. The brake system as claimed in claim 7, wherein the control unit is configured such that, 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 force of the electric machine, the control unit activates the pressure dissipation valve for opening, subsequently or simultaneously activates the isolation valve for closing, and, subsequently to or simultaneously with the activation of the isolation valve, activates the pump to impart a conveying action.

9. The brake system as claimed in claim 7, wherein the isolation valve and/or the pressure dissipation valve and/or the pump and/or the accumulator are a constituent part of an anti-lock braking system.

10. The brake system as claimed in claim 8, wherein the isolation valve and/or the pressure dissipation valve and/or the pump and/or the accumulator are a constituent part of an anti-lock braking system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 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:

[0047] 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

[0048] 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

[0049] FIG. 1 shows a possible embodiment of a hydraulic brake system 10 which is used for example in a motor vehicle. In FIG. 1, the hydraulic brake system 10 is illustrated by way of example in conjunction with one vehicle wheel 100. 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. By way of example, in FIG. 1, the electric machine 50 is assigned to the vehicle wheel 100 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 100. 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 100. During a regenerative braking process, the electric drive is utilized as a generator.

[0050] The hydraulic brake system 10 comprises, for example, a brake cylinder 16 and a wheel brake 28, which are hydraulically connected to one another via a feed line 20. The brake cylinder 16 is configured to displace a hydraulic fluid in the direction of the wheel brake 28. The wheel brake 28 is configured to exert a braking force, for example in the form of a friction force, on the vehicle wheel 100 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.

[0051] 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.

[0052] The hydraulic brake system 10 preferably furthermore comprises an isolation valve 22 which is fluidically assigned to the feed line 20 and which is configured to close the feed line. For example, it is the intention in this way for the wheel brake 28 to be able to be at least partially or entirely hydraulically isolated from the brake cylinder 16. The isolation valve 22 is preferably 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 feed line 20. Preferably, in the closed position of the isolation valve 22, the feed line 20 is shut off, in particular fully shut off or at least largely or substantially shut off, and, in the open position, the feed line 20 is open, in particular substantially open or fully open.

[0053] Preferably, the hydraulic brake system 10 furthermore comprises a return line 32 which serves for returning at least a volume fraction of the hydraulic fluid from a region positioned downstream of the isolation 22 valve into a region positioned upstream of the isolation valve 22. For example, the return line 32 is connected in terms of flow by means of one end to the feed line 20 in a region between the isolation valve 22 and the wheel brake 28. Preferably, the return line 32 is connected in terms of flow by means of another end to the feed line 20 in a region between the isolation valve 22 and the brake cylinder 16. In this way, at least a volume fraction of the hydraulic fluid can be returned from the wheel brake 28 into the feed line 20, bypassing the isolation valve 22.

[0054] Preferably, the return line 32 is fluidically assigned a pressure dissipation valve 34, a pump 38 and an accumulator 42. The pump 38 is configured to convey at least a 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 a volume fraction of the hydraulic fluid, in particular to store the same under pressure, in particular to buffer-store the same.

[0055] The pressure dissipation valve 34 is configured to open and close the return line 32. The pressure dissipation valve 34 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 return line 32. Preferably, in the open position of the pressure dissipation valve 34, the return line 32 is open, in particular at least partially open or fully open, and, in the closed position, the return line 32 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 pressure dissipation valve 34, the pump 38 and the accumulator 42 are arranged in the sequence in which the pressure dissipation valve 34 comes first, and is followed either by the pump 38 or the accumulator 42. By opening the return line 32, the accumulator 42 is thus filled with the returned volume fraction of the hydraulic fluid.

[0056] Preferably, the hydraulic brake system 10 furthermore comprises a control unit 48, in particular an electrical control unit, for activating the isolation valve 22 and/or the pressure dissipation valve 34 and/or the pump 38. For example, for this purpose, the control unit 48 is connected in signal-exchanging fashion to the isolation valve 22 and/or to the pressure dissipation valve 34 and/or to the pump 38 via a corresponding signal line 61 or 62 or 63 respectively, in particular electrical signal line. Preferably, the isolation valve 22 and/or the pressure dissipation valve 34 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 of the pressure dissipation valve 34 or of the pump 38 respectively.

[0057] 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 63 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 65. 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.

[0058] 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 48t and which activates, in particular directly activates, the electric machine 50.

[0059] Preferably, the control unit 48 is furthermore connected in signal-exchanging fashion via a signal line 64 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.

[0060] 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 force originating from the electric machine 50, the control unit activates the pressure dissipation valve 34 for opening and activates the isolation valve 22 for closing and furthermore activates the pump 38 to impart a conveying action. 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 the generator braking force, the pressure dissipation valve 34 is activated for opening, the isolation valve 22 is subsequently or simultaneously activated for closing, and, subsequently to or simultaneously with the activation of the isolation valve 22, the pump 38 is activated to impart a conveying action.

[0061] 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 force 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.

[0062] 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 onset of an actuation of the brake pedal 12 is identified or detected by the control unit 48. The pressure dissipation valve 34 is hereupon activated by the control unit 48 for opening. This results in an adjustment of the pressure dissipation valve 34 from its closed position (FIG. 1) to its open position and thus in an opening of the return line 32. 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 brake 28 is effected via the feed line 20. Owing to the opened return line 32, at least a volume fraction of the hydraulic fluid is conducted into the accumulator 42 situated there, such that a hydraulic braking force corresponding to the displacement of the hydraulic fluid is not generated at the wheel brake 28.

[0063] 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 100. 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 is performed to such an extent that no or substantially no hydraulic braking force acts at the wheel brake 28. If, for example, the braking force demand is higher than the generator braking force, the opening of the pressure dissipation valve 34 is performed such that, at the wheel brake 28, 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.

[0064] After the activation of the pressure dissipation valve 34 or after the opening of the pressure dissipation valve 34, the isolation valve 22 is activated for closing by the control unit 48. This results in an adjustment of the isolation valve 22 from its open position (FIG. 1) in the direction of its closed position and thus in a shutting-off of the feed line 20. In this way, the wheel brake 28 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 is conveyed out to such an extent that no braking force or substantially no braking force acts at the wheel brake 28, in order that, in this way, the wheel brake 28 is placed in a hydraulically unpressurized state. When the actuation of the brake pedal 12 has been ended, the pressure dissipation valve 34 is activated for closing, and the isolation valve is activated for opening. The pump 38 still imparts a conveying action until such time as the accumulator 42 has been evacuated.

[0065] 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 the hydraulic brake system 10, two hydraulically mutually separate brake circuits are provided. 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. Below, only one of the brake circuits will be referred to, wherein the other brake circuit may be of identical and/or functionally identical construction. For the sake of simplicity and for better clarity, any signal lines that are present have been omitted in FIG. 2.

[0066] 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.

[0067] The above-described components of the hydraulic brake system 10 of FIG. 1 may likewise be present in the hydraulic brake system 10. The hydraulic brake system 10 comprises for example a brake pedal 12, a brake force booster 14, a brake cylinder 16, a reservoir 18, a feed line 20, an isolation valve 22, a wheel brake 28, a return line 32, a pressure dissipation valve 34, a pump 38, an accumulator 42, a pedal travel sensor 46, a control unit 48, an electric machine 50 and a control unit 52. These components may be structurally identical and/or functionally identical to the corresponding components of the hydraulic brake system 10 of FIG. 1.

[0068] For example, the brake pedal 12 may correspond and/or be structurally identical and/or functionally identical to the brake pedal 12, the brake force booster 14 may correspond and/or be structurally identical and/or functionally identical to the brake force booster 14, the brake cylinder 16 may correspond and/or be structurally identical and/or functionally identical to the brake cylinder 16, the reservoir 18 may correspond and/or be structurally identical and/or functionally identical to the reservoir 18, the feed line 20 may correspond and/or be structurally identical and/or functionally identical to the feed line 20, the isolation valve 22 may correspond and/or be structurally identical and/or functionally identical to the isolation valve 22, the wheel brake 28 may correspond and/or be structurally identical and/or functionally identical to the wheel brake 28, the return line 32 may correspond and/or be structurally identical and/or functionally identical to the return line 32, the pressure dissipation valve 34 may correspond and/or be structurally identical and/or functionally identical to the pressure dissipation valve 34, the pump 38 may correspond and/or be structurally identical and/or functionally identical to the pump 38, the accumulator 42 may correspond and/or be structurally identical and/or functionally identical to the accumulator 42, the pedal travel sensor 46 may correspond and/or be structurally identical and/or functionally identical to the pedal travel sensor 46, the control unit 48 may correspond and/or be structurally identical and/or functionally identical to the control unit 48, the electric machine 50 may correspond and/or be structurally identical and/or functionally identical to the electric machine 50, and the control unit 52 may correspond and/or be structurally identical and/or functionally identical to the control unit 52, of the hydraulic brake system 10 of FIG. 1. In this respect, reference is made to the description relating to the hydraulic brake system 10 of FIG. 1.

[0069] FIG. 2 illustrates four vehicle wheels, which are each assigned a wheel brake. The brake circuit under consideration comprises not only the wheel brake 28 but also a further wheel brake 30, which is assigned to a different vehicle wheel. The two vehicle wheels with the associated wheel brakes 28 and 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. 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.

[0070] The two wheel brakes 28 and 30 are jointly hydraulically connected to the feed line 20, wherein, at one end, the brake cylinder 16 is present and, at another end, the feed line 20 divides into two line portions 20.1 and 20.2, which are in each case hydraulically connected to one of the wheel brakes 28 and 30. The line portion 20.1 is assigned the isolation valve 22, and the line portion 20.2 is assigned a separate isolation valve 24. The isolation valves 22 and 24 are preferably structurally identical and/or functionally identical with respect to one another.

[0071] The return line 32 provided in the case of the hydraulic brake system 10 of FIG. 1 at least partially corresponds to the return line 32, which is assigned the pump 38 and the accumulator 42. As viewed in the direction of the wheel brakes 28 and 30, the return line 32 divides into two line portions 32.1 and 32.2, which are in each case hydraulically connected to one of the wheel brakes 28 and 30. Aside from the pressure dissipation valve 34, a further pressure dissipation valve 36 is provided, which are assigned in each case to one of the line portions 32.1, 32.2 of the return line By means of the isolation valves 22 and 24, each of the two wheel brakes 28 and 30 can be separately hydraulically isolated. By means of the pressure dissipation valves 34 and 36, it is possible, separately for each of the wheel brakes 28 and 30, for a volume fraction of a hydraulic fluid displaced by means of the brake cylinder 16 to be conducted onward in the associated line portion 32.1, 32.2 of the return line 32 in order to be stored in the accumulator 42.

[0072] Preferably, the control unit 48 is of extended functional scope in relation to the control unit 48 of the hydraulic brake system 10 in FIG. 1 such that, aside from the isolation valve 22 and the pressure dissipation valve 34, which are assigned to the wheel brake 28, it is additionally also possible for the isolation valve 24 and the pressure dissipation valve 36, which are assigned to the wheel brake 30 to be activated. The isolation valve 24 and the pressure dissipation valve 36 are preferably activatable by the control unit 48 in the same way as the isolation valve 22 and the pressure dissipation valve 34 in order to perform the above-described regenerative braking process also with respect to the wheel brake 30. 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.

[0073] As can be seen from FIG. 2, the feed line 20 may be assigned a further isolation valve 26, which is arranged in the feed line between the division into the line portions 20.1, 20.1 and the brake cylinder 16. Furthermore, a supply valve 40 may be assigned to the return line 32. By means of the supply valve 40, the return line 32 can be hydraulically connected, bypassing the further isolation valve 26, to a region positioned upstream of the isolation valve 26. 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.

[0074] 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.

[0075] 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 implantation of the present disclosure.