Brake control device for a vehicle and method for operating a brake control device for a vehicle

Abstract

The present invention provides a brake control system (10) for a vehicle (F), comprising a control system (SE) connected to a brake booster device (BV) and an electric machine (EM) of the vehicle, the control system (SE) being set up to recognize a malfunction or failure of the brake booster device (BV) and to recognize a minimum value (minM1) of a first brake torque (M1) of the electric machine (EM) as a generator brake torque, the minimum value (minM1) of the first brake torque (M1) corresponding to a brake torque having a minimum absolute value at all vehicle speeds that can be generated by the electric machine (EM), and the control system being set up to operate the electric machine (EM) such that at least the minimum value (minM1) of the first brake torque (M1) is generated by the electric machine (EM) for a brake request when a malfunction or failure of the brake booster device (BV) is recognized.

Description

[Technical field]

[0001] The present invention relates to a brake control for a vehicle and to a method of operating a brake control for a vehicle. [Background technology]

[0002] Conventional drive concepts in electrically operated vehicles can utilize electric machine braking action, for which brake force generators or brake boosters are known that can be electronically controlled when braking action is required.

[0003] As is known, hydraulic braking systems are available for vehicles, and there are a variety of brake systems, particularly with regard to brake force boosting. In the event of a brake system failure, the brake force boosting may be lost, and the driver may generate hydraulic pressure through the brake pedal at a mechanical fallback level, which may be converted into vehicle deceleration by the wheel brakes.

[0004] An electric vehicle is accelerated by an electric motor and can recover energy by the electric motor when braking (recuperation). To recover energy, the electric motor generates a resistive torque (corresponding to its hyperbolic power), which can decelerate the vehicle accordingly. Recuperation is usually controlled by the brake system in order to ensure or at least increase driving stability and also because the braking torque of the electric motor is highly dependent on the rotational speed and therefore on the vehicle speed. However, drivers often want to achieve a constant deceleration (residual hydraulic or electromechanical braking torque), which may require a controlled generation of the braking torque. In the event of a brake system failure, recuperation is therefore usually also deactivated in many cases.

[0005] Patent Document 1 describes a drive train for a vehicle capable of all-wheel drive. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2013 / 083243A1 Brochure Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a brake control device for a vehicle as claimed in claim 1 and a method for operating a brake control device for a vehicle as claimed in claim 7.

[0008] Preferred developments are the subject of the dependent claims. [Means for solving the problem]

[0009] The idea behind the present invention is to provide a brake control device for a vehicle and a method for operating a brake control device for a vehicle, which is able to improve the deceleration output of the vehicle by generating a generator brake torque in the event of a malfunction or inoperation of the brake booster device.

[0010] The advantage is that the mechanical fallback level can assist in deceleration and improve this in the event of a brake force augmentation failure, by utilizing additional generator braking torque, which allows the same pedal force to result in a stronger vehicle deceleration than would be possible without the generator braking torque.

[0011] In this case, there is an advantage that the current capacity of the electric machine as a generator can be taken into consideration, and the deceleration ratio (the ratio of the generator to the brake torque) can be taken into consideration.

[0012] According to the present invention, a brake control device for a vehicle, capable of controlling the braking action of the vehicle, comprises a control device connected or connectable to a brake booster device and an electric machine of the vehicle, the control device is set up to recognize a malfunction or failure of the brake booster device and to recognize and / or recognize a minimum value of a first brake torque of the electric machine as a generator brake torque, the minimum value of the first brake torque corresponding to a brake torque having a minimum absolute value at all vehicle speeds that can be generated by the electric machine, and the control device is set up to operate the electric machine such that at least the minimum value of the first brake torque is generated by the electric machine for a brake request when a malfunction or failure of the brake booster device is recognized.

[0013] The malfunction may be a total or partial malfunction of the function of the brake booster device. The malfunction may be any possible malfunction that may lead to a limitation of the brake force boosting or any other type of malfunction.

[0014] The generator brake torque may decrease with increasing vehicle speed, and may be determined or pre-determined over a range of permitted speeds for the vehicle, e.g., set by road traffic regulations or by the manufacturer, with a minimum value being determined or pre-determined over all speeds. The brake request may be made by the driver or by the control unit (autonomously).

[0015] A braking action may be a braking process on a vehicle to slow down the rotation of the wheels, for example by friction torque and / or generator brake torque and / or some other manner of braking force on the vehicle.

[0016] At this time, deceleration based on the setting in the vehicle can be pursued, and this setting may be selectable by the user to be arbitrarily low or high (strong).

[0017] An operating state of the electric machine as a generator can then be determined, which may correspond to the extent to which the electric machine can apply a generator brake torque at that moment or generally, e.g., across all speeds that the machine is capable of generating. For example, when the speed of the vehicle increases, the first brake torque that can be generated may be less than when the speed is lower. Across all speeds of the vehicle, a minimum value of the first brake torque that may be at least applicable when the electric machine operates as a generator can be determined.

[0018] Then, depending on knowledge of the capabilities of the electric machine as a generator, i.e. as a device for generating a generator brake torque, the first brake torque can be increased and / or decreased, for example adaptively adaptable and dynamically over time, to reach a setting for the first brake torque, for example to reach at least a minimum value or as a sum with a second brake torque of another brake device.

[0019] In other words, it can be estimated what percentage of the set total braking torque at the vehicle can be provided by the generator at all times or under the current (to be estimated) conditions, and to what percentage the other (second) braking torque can be reduced, since a minimum value may always be applicable if no faults occur in the electric machine or in other components of the drive or brake system.

[0020] The vehicle may be a passenger car having a drive which may include an electric machine.

[0021] In the event of a failure or malfunction of the brake booster and / or at the mechanical fallback level, the electric machine (electric motor) of the vehicle can be regarded as a kind of separate brake circuit, and its possible brake action can be utilized in addition to the hydraulic brake action. Depending on the hyperbolic power of the electric motor, only a minimum torque is possible at high rotational speeds, so that the available brake torque can be set accordingly (or the higher the power of the electric motor, the higher the brake torque at high rotational speeds or vehicle speeds). There is also the option of always demanding from the electric motor only a deceleration that is possible even at high speeds, in particular only a minimum value. Such torque, which is preferably always available under the normal functioning of the electric machine and the associated components of the brake control device, can be taken into account for designing the brake action at the fallback level, or there is also the option of demanding a higher (first) generator brake torque at low speeds in order to further reduce the pedal force required for the vehicle brake action and therefore the difference in the brake action between the standard state (with brake booster) and when a fault occurs. For example, the deceleration achievable at the mechanical fallback level is, for example, 2.44 m / s under a pedal force of 500 N, either by the second brake torque alone, or by the minimum value alone, or by both combined. 2 It could be.

[0022] In a preferred embodiment of the brake control device, the brake control device includes a pedal sensor device and / or the control device is connected to the pedal sensor device and is set up to determine operation of a brake pedal and / or an accelerator pedal in the vehicle, and the control device is set up to infer a braking request by the driver from operation of the brake pedal and / or the accelerator pedal.

[0023] The operation can be performed by the driver.

[0024] In a preferred embodiment of the brake control device, the pedal sensor device is set up to recognize the pressure and / or force and / or position of the brake pedal and / or the accelerator pedal and the control device is set up to deduce the degree of braking request from the pressure and / or force and / or position of the brake pedal and / or the accelerator pedal and to generate this at least partially by the electric machine as a first brake torque.

[0025] The degree may correspond to an adjustment angle or deflection of the pedal from the rest position and reflects the strength of the required braking action, and depending on the degree of the required braking torque and the resulting strength of the braking action, it can be generated by the electric machine alone, if a minimum value is sufficient, or if the electric machine is operating at a speed lower than that for generating the minimum value and can generate a first braking torque correspondingly higher than the minimum value, or it can be generated together with a second braking torque, for example of a hydraulic or other brake system.

[0026] In a preferred embodiment of the brake control device, the control device is further set up to recognize the release of the accelerator pedal and to request a constant first brake torque from the electric machine, which is greater than or equal to a minimum value, and / or to recognize operation of the brake pedal via a pedal sensor device and to generate the first brake torque depending on the degree of braking request, and / or to recognize operation of the brake pedal via a further sensor mechanism and to request a constant first brake torque which is greater than or equal to a minimum value, and / or to recognize operation of the brake pedal via a further sensor mechanism and to request the first brake torque according to a predefined characteristic curve.

[0027] The brake torque that can be generated depending on the degree can be realized, for example proportionally, by conversion from the force actually generated by the driver at the brake pedal using a scaling factor, which can be determined depending on the electric machine and the achievable minimum value, can be adaptively changed or can be set.

[0028] In a preferred embodiment of the brake control device, the control device is connected to the hydraulic brake equipment and / or the further brake equipment and is set up to generate, in the hydraulic brake equipment and / or the further brake equipment, a second brake torque which, together with a minimum value of the first brake torque, produces a predetermined overall brake torque at the vehicle upon braking request.

[0029] In order to generate the total torque, at least a minimum value can then be provided by the electric machine, and if the current operating conditions of the electric machine allow, a first brake torque greater than the minimum value can also be provided to better support the mechanical fallback level, in which case the total brake torque can be higher or the proportion of the second brake torque can be reduced.

[0030] In a preferred embodiment of the brake control device, the controller is connected to a vehicle battery and is set up to recognize or determine a state of charge of the battery and / or recognize or determine acceptable overload operation of the electric machine, and request a first brake torque greater than a minimum value for a predetermined time based on acceptable overload operation of the electric machine and / or request a first brake torque greater than the minimum value under acceptable overload conditions of the battery.

[0031] Under such a request from the brake system and / or brake control device, the electric machine can be operated in a temporary overload operation to at least temporarily increase the currently possible total brake torque or the first brake torque. Furthermore, there is an option for the electric drive to temporarily allow a slightly increased battery charge state. The maximum charge state is usually selected so that the best service life of the battery is guaranteed. In rare error situations, it can be temporarily abandoned, especially under tolerable overload conditions that are known for the battery and that do not temporarily lead to damage to the battery or that may at least be equally tolerable for overload operation. The maximum possible generator brake torque is communicated to the brake system, so that the maximum possible deceleration can be realized in this way.

[0032] The braking arrangement may include friction brakes or any other type of non-generator brake.

[0033] Furthermore, in addition to the signal for the determination of the driver's braking desire, it is preferable to use further quantities, which contain information about the dynamic driving conditions and on which the required brake torque can be adapted. In particular when a brake torque is required at the rear axle, the maximum braking effect in the given situation can thereby be achieved while maintaining or at least improving vehicle stability. Such signals can be, for example, wheel speed signals and / or steering angle and / or yaw rate and / or lateral acceleration. The first and / or second brake torque can be adapted accordingly. In addition, the hydraulic generation at the individual wheels can be reduced (braking force distribution or ABS function), in particular in order to compensate for any restrictions on the adjustment accuracy that may arise by means of a further regulator for the generation of the brake torque (for example the automatic parking brake APB). Taking into account such driving dynamic conditions can be possible, for example, insofar as corresponding and necessary signals are available and the brake control unit can still process them in order to set the generator brake torque accordingly and adaptively. If the brake control system is no longer able to process such signals accordingly, the generator control unit can itself generate a constant, low regenerative torque, like an engine brake torque, as soon as the accelerator pedal is released. This constant, low regenerative brake torque can be selected so that it remains stable in any driving state of the vehicle and that the driven axle is taken into account accordingly.

[0034] According to the invention, in a method for operating a brake control device for a vehicle in order to control the braking action of the vehicle, a braking request and / or a need to perform a braking action by the brake control device according to the invention is recognized, a malfunction or inoperability of the brake booster device is recognized, a minimum value of a first braking torque of the electric machine as a generator braking torque is determined, the minimum value of the first braking torque corresponding to a braking torque having a smallest absolute value at all vehicle speeds that can be generated by the electric machine, and in the event of a malfunction or inoperability of the brake booster device and in the event of a braking request and / or a need for a braking action, at least the minimum value of the first braking torque is generated by the electric machine.

[0035] There may be a need to control and execute braking actions by means of a brake control device and / or brake equipment.

[0036] In a preferred embodiment of the method, in response to a braking request due to pedal actuation on the brake pedal and / or the accelerator pedal, the pressure and / or force and / or position of the brake pedal and / or the accelerator pedal are recognized by a pedal sensor device and / or a further sensor mechanism, the degree of the braking request is estimated from the pressure and / or force and / or position of the brake pedal and / or the accelerator pedal and a first braking torque is generated which is constant or dependent on said degree.

[0037] The further sensor mechanism may be a sensor typically used for a vehicle, acceleration, force, pedal movement or pedal pressure, a navigation system, or any other type of sensor mechanism. The further sensor mechanism may be an independent sensor mechanism, e.g., prepared and operated independently from the pedal sensor and other components of the vehicle and / or brake control device.

[0038] In a preferred embodiment of the method, the release of the accelerator pedal is recognized and a constant first brake torque greater than or equal to a minimum value is requested from the electric machine and / or actuation of the brake pedal is recognized via a pedal sensor device and the first brake torque is generated depending on the degree of braking demand and / or actuation of the brake pedal is recognized via a further sensor mechanism and a constant first brake torque greater than or equal to a minimum value is requested and / or actuation of the brake pedal is recognized via a further sensor mechanism and the first brake torque is requested in accordance with a predefined characteristic curve.

[0039] This characteristic curve may be a non-linear characteristic curve, for example for the first brake torque or for the generator capacity of the electric machine.

[0040] In this way, in the event of a fault in the brake system and / or in the event of a malfunction or failure of the brake booster device, the electric machine can be incorporated into the braking of the vehicle based on various options.

[0041] As soon as the driver fully releases the accelerator pedal, the electric machine can be activated to generate a first brake torque that is constant regardless of brake pedal operation, which acts similarly to the (boosted) engine brake torque of an internal combustion engine.

[0042] Furthermore, as soon as the driver operates the brake pedal, a driver braking request can be recognized via a pedal travel sensor (PTS), which is available in the brake system and may be included in or connected to the brake control unit, and the control unit can request a corresponding first brake torque from the electric machine via an interface. This brake torque can be changed depending on the driver braking request (as sensed via the PTS) up to the maximum available or available first brake torque. A prerequisite here can be that the PTS sensor and the ECU (control unit) are still functional at least to that extent.

[0043] Furthermore, as soon as the driver operates the brake pedal, the driver's braking wish can be recognized via a pressure sensor (DS) that is available in the brake system and that may be included in or connected to the brake control unit, and the control unit can request a corresponding first braking torque from the electric machine via the interface. This first braking torque can be varied depending on the driver's braking wish (as sensed via the DS) up to the maximum available or available first braking torque. A prerequisite here can be that the PTS sensor and the ECU (control unit) are still functional at least to that extent.

[0044] Requirements relating to the brake system may also be applied in connection with the brake control device and vice versa.

[0045] Brake pedal actuation can also be sensed by an independent sensor mechanism (separate sensor mechanism) at the brake pedal (e.g., BLS). When the brake pedal actuation is recognized, an electric machine can generate a constant braking torque.

[0046] The driver's braking command can be sensed by an independent sensor mechanism (e.g., a pedal stroke sensor) at the brake pedal. Depending on the driver's braking command (brake pedal stroke), the electric machine can generate a braking torque that is proportional to the driver's braking command or that is set via a non-linear characteristic curve.

[0047] The electric machine can thus generate a constant braking torque, a braking torque proportional to the brake pedal position, and / or a braking torque defined by a non-linear characteristic curve, and this first braking torque can then be superimposed on the hydraulic braking torque generated by the driver when operating the brake pedal, thereby enabling the vehicle to decelerate more strongly than would be possible with the hydraulic braking torque alone.

[0048] It may further be preferable to request a second brake torque via one or more further regulators in addition to the generator brake torque. This may be, for example, an electric parking brake or an engine brake torque of an internal combustion engine. The control device can then coordinate these brake torques and request them in such a way that the best possible braking action and metering possibilities can be achieved for the driver. This may be possible for the vehicle's brake system and brake control device insofar as the desired deceleration can be determined from the signals of the above-mentioned sensors and / or by the electric machine.

[0049] Furthermore, the electric drive and / or any other regulators used can report / determine via the interface the currently possible first and / or second braking torques and thus make optimal use of the possible braking effect.

[0050] In a preferred embodiment of the method, a second brake torque is generated upon a braking request in the hydraulic brake installation and / or in a further brake device, which together with the minimum value of the first brake torque results in a predetermined overall brake torque of the vehicle.

[0051] A determination of the second brake torque currently available may be made and / or an estimate of the second brake torque that will be available in the near future may be made, and the overall brake torque that can be generated may be known.

[0052] In a preferred embodiment of the method, the operating state of the electric machine and the first braking torque of the electric machine which can be produced therefrom can be determined continuously or at predetermined time intervals.

[0053] The brake control system may also be characterized by the features and advantages listed in connection with the method, and vice versa.

[0054] Other features and advantages of the embodiments of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

[0055] The invention will now be explained in more detail with reference to embodiments illustrated in the schematic diagrams of the drawings. [Brief description of the drawings]

[0056] [Figure 1] 1 is a schematic diagram showing a brake control device according to one embodiment of the present invention. [Diagram 2] 4 is a graph showing braking torque in an electric machine. [Diagram 3] 1 is a block diagram illustrating method steps of a method for operating a brake control system for a vehicle, according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] In the drawings, the same reference numerals represent the same components or components with the same functions.

[0058] FIG. 1 shows a schematic diagram of a brake control system according to one embodiment of the present invention.

[0059] A brake control device 10 for a vehicle F, capable of controlling the vehicle's braking action, has a control device SE connected or connectable to a brake booster device BV and to an electric machine EM of the vehicle, the control device SE is set up to recognize a malfunction or failure of the brake booster device BV and to recognize and / or recognize a minimum value minM1 of a first brake torque M1 of the electric machine EM as a generator brake torque, the minimum value minM1 of the first brake torque M1 corresponding to a brake torque having a smallest absolute value at all vehicle speeds that can be generated by the electric machine EM, and the control device is set up to operate the electric machine EM such that at least the minimum value minM1 of the first brake torque M1 is generated by the electric machine EM for a brake request when a malfunction or failure of the brake booster device BV is recognized. The brake control device 10 may include a pedal sensor device PS and / or in the brake control device a control device SE may be connected to the pedal sensor device PS, the brake control device being set up to determine operation of the brake pedal and / or accelerator pedal of the vehicle, and the control device SE being set up to estimate a braking request by the driver from operation of the brake pedal and / or accelerator pedal.

[0060] Furthermore, in the hydraulic brake installation HB of the vehicle and / or in a further brake installation WB to which the brake control device 10 and its control device SE may be connected, a second brake torque M2 can be generated upon braking demand, which together with the minimum value minM1 of the first brake torque can result in a predetermined overall brake torque in the vehicle.

[0061] FIG. 2 shows a graph of the braking torque on an electric machine.

[0062] 2a shows the dependence of the first braking torque M1 on the speed of the vehicle, converted into the angular speed ω that the electric machine can generate itself and that the electric machine can rotate with when the vehicle is moving. The maximum speed ω at which the minimum value of the first braking torque minM1 can be generated is then max can be defined.

[0063] At speeds lower than this, it is advantageous to be able to generate a higher first brake torque based on the hyperbolic output, e.g. due to the system design in the vehicle (electric machine and / or battery charging), the maximum torque M1 max can also be defined, and for overload operation the hyperbola can be shifted to P0.

[0064] In FIG. 2b, the accelerator pedal GP and the brake pedal BP (from the respective sensor mechanisms) are shown versus time t. The accelerator pedal GP may be released between t1 and tn. During this time, a constant first brake torque M1 can be generated by the electric machine. If the brake pedal BP is then actuated between t2 and t3, a constant additional torque can be added to the first brake torque, for example to a minimum value minM1, as in the bottom diagram of FIG. 2b. Alternatively, a modified additional torque can also be generated for the first brake torque, adapted to the degree of deflection or pressure at the brake pedal BP (third diagram). This can start at t2 or at a later time t4 and end at t3.

[0065] FIG. 3 illustrates a block diagram of method steps of a method for operating a brake control system for a vehicle according to one embodiment of the present invention.

[0066] In a method for operating a brake control device for a vehicle in order to control the braking action of the vehicle, a braking request and / or a need to perform a braking action by the brake control device according to the invention is recognized S1, a malfunction or inoperability of the brake booster device is recognized S2, a minimum value of a first braking torque of the electric machine as a generator braking torque is determined S3, the minimum value of the first braking torque corresponds to the braking torque having the smallest absolute value at all vehicle speeds that can be generated by the electric machine, and in the event of a malfunction or inoperability of the brake booster device and in the event of a braking request and / or a need for a braking action, at least the minimum value of the first braking torque is generated S4 by the electric machine.

[0067] Although the present invention has been fully described above with reference to preferred embodiments, the present invention is not limited thereto but can be modified in various ways. [Explanation of symbols]

[0068] 10 Brake control device BV Brake booster device EM Electrical Machinery F vehicle M1 First brake torque M2 Second brake torque minM1 Minimum value PS Pedal Sensor Device SE Control Unit WB Separate brake system

Claims

1. A brake control device (10) for a vehicle (F) capable of controlling the braking action of the vehicle, comprising: A control device (SE) connected or connectable to a brake booster device (BV) and an electric machine (EM) of a vehicle, said control device (SE) comprising: Recognizing a malfunction or failure of the brake booster device (BV), is set up to recognize and / or know a minimum value (minM1) of a first brake torque (M1) of the electric machine (EM) as a generator brake torque, the minimum value (minM1) of the first brake torque (M1) corresponding to a brake torque having a minimum absolute value at all vehicle speeds that can be generated by the electric machine (EM), and the control device A brake control device set up to operate the electric machine (EM) such that at least the minimum value (minM1) of the first brake torque (M1) is generated by the electric machine (EM) for a brake request when a malfunction or failure of the brake booster device (BV) is recognized.

2. 2. The brake control device (10) of claim 1, further comprising a pedal sensor device (PS) and / or the control device (SE) is connected to the pedal sensor device (PS) and is set up to determine operation of a brake pedal and / or an accelerator pedal in a vehicle, and the control device (SE) is set up to estimate a braking request by a driver from operation of the brake pedal and / or the accelerator pedal.

3. 3. The brake control device (10) according to claim 2, wherein the pedal sensor device (PS) is set up to recognize the pressure and / or force and / or position of the brake pedal and / or accelerator pedal, and the control device (SE) is set up to deduce the degree of braking demand from the pressure and / or force and / or position of the brake pedal and / or accelerator pedal and to generate this at least in part as a first brake torque (M1) by the electric machine.

4. Furthermore, the control device (SE) to recognize that the accelerator pedal has been released and to request a first constant braking torque from the electric machine (EM) that is greater than or equal to the minimum value; and / or - for detecting an actuation of the brake pedal via the pedal sensor device (PS) and generating the first brake torque depending on the degree of the brake demand; and / or and / or for detecting the actuation of the brake pedal via a separate sensor mechanism and requesting a first constant brake torque greater than or equal to the minimum value. a brake pedal operation detecting means for detecting an operation of the brake pedal via a separate sensor mechanism and requesting the first brake torque in accordance with a predetermined characteristic curve; A brake control device (10) according to claim 2 or 3, set up.

5. 4. The brake control device (10) according to claim 1, wherein the control device (SE) is connected to a hydraulic brake installation and / or a further brake system and is set up to generate, in the hydraulic brake installation (HB) and / or the further brake system (WB) when a braking request is present, a second brake torque (M2) which, together with the minimum value (minM1) of the first brake torque, produces a predetermined total brake torque at the vehicle.

6. 4. The brake control device (10) according to claim 1, wherein the control device (SE) is connected to a vehicle battery and is set up to recognize or determine a state of charge of the battery and / or recognize or determine an acceptable overload operation of the electric machine (EM) and to request the first brake torque (M1) greater than the minimum value for a predetermined time based on the acceptable overload operation of the electric machine (EM) and / or to request the first brake torque greater than the minimum value in an acceptable overload condition of the battery.

7. A method of operating a brake control device (10) for a vehicle (F) for controlling the braking action of the vehicle, comprising the steps of: - a braking request and / or a need for performing a braking action is recognized (S1) by a brake control device (10) according to any one of claims 1 to 3, A malfunction or inoperability of the brake booster device (BV) is recognized (S2); a minimum value (minM1) of a first brake torque (M1) of the electric machine (EM) as a generator brake torque is determined (S3), said minimum value (minM1) of the first brake torque (M1) corresponding to a brake torque having a minimum absolute value at all vehicle speeds that can be generated by the electric machine (EM); and and generating (S4) at least said minimum value (minM1) of said first brake torque (M1) by said electric machine (EM) upon failure or malfunction of said brake booster device (BV) and upon a brake request and / or a need for a brake action.

8. 8. The method according to claim 7, further comprising: detecting a pressure and / or force and / or position of the brake pedal and / or the accelerator pedal by a pedal sensor device (PS) and / or a further sensor mechanism when a braking request is made by a pedal actuation on the brake pedal and / or the accelerator pedal; estimating a degree of the braking request from the pressure and / or force and / or position of the brake pedal and / or the accelerator pedal; and generating a first brake torque which is constant or which depends on the degree.

9. the accelerator pedal is recognized to have been released and a first constant brake torque is requested from the electric machine (EM) that is greater than or equal to the minimum value; and / or an actuation of the brake pedal is recognized via the pedal sensor device (PS) and the first brake torque is generated as a function of the degree of the brake demand; and / or and / or a first constant brake torque is requested, the first constant brake torque being greater than or equal to the minimum value, when the brake pedal is actuated via a separate sensor mechanism.

9. The method according to claim 8, further comprising detecting the actuation of the brake pedal through a further sensor mechanism and demanding the first brake torque according to a predetermined characteristic curve.

10. 8. The method according to claim 7, wherein a second brake torque (M2) is generated upon a braking request by a hydraulic brake installation (HB) and / or a further brake system (WB), which together with the minimum value (minM1) of the first brake torque results in a predetermined overall brake torque of the vehicle.

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