DE102013223163A1 - Method for controlling a brake system - Google Patents

Abstract

The invention relates to a method for controlling a brake system of a motor vehicle, which has at least one electric machine on the wheels of a driven axle, which can be operated as a drive or generator, wherein the wheels at least the drive axle wheel brakes, the braking force are increased or decreased independently of the driver can. According to the invention, at least one curve size such as a steering wheel angle and / or a lateral acceleration and / or a yaw rate is measured by means of at least one sensor, and when a brake request occurs, it is checked whether the braking request takes place during a quasi-stationary cornering, and in this case is for a vehicle Rear drive on the outside wheel of the drive axle generates a greater braking force than on the inside wheel of the drive axle and for a vehicle with front-wheel drive on the outside wheel of the drive axle generates a smaller braking force than on the inside wheel of the drive axle. Furthermore, the invention relates to a motor vehicle.

Description

The invention relates to a method according to the preamble of claim 1 and a motor vehicle according to the preamble of claim 12.

Vehicles with at least partially electric propulsion often have environmental advantages over conventional vehicles that are powered exclusively by an internal combustion engine, but because of the limited capacity of currently available batteries they have a significantly lower range than conventional vehicles. By braking force generated by the driver, the braking force is first generated via the or the / as / s electric / n / drive operated as a generator, the kinetic energy of the vehicle during braking at least partially converted into electrical energy and stored; thus extends the range of a vehicle with electric drive.

Thus, the energy recovery or recuperation takes place with the highest possible efficiency, the brake force distribution between the front and rear axle is often - deviating from an ideal in terms of driving stability brake force distribution - chosen such that only acts on the axis connected to an electric drive, a braking force or the vehicle deceleration is generated only by the electric drive operated as a generator. When the electric drive acts, for example, on the rear axle, in particular on a road surface with a low coefficient of friction when braking in a curve, significant deviations from a neutral driving behavior may occur; The vehicle oversteers and can get into skidding. For an untrained driver, an oversteering vehicle is difficult or impossible to control.

From the DE 10 2004 061 107 A1 It is known, the electric-regenerative brake (the electric drive) to specify a maximum target braking torque (or a maximum braking force), which is calculated variably from the driving situation of the motor vehicle. In this case, the existing sensor system of a vehicle dynamics control system is preferably used to evaluate the current driving dynamic situation and a limit is set, up to which the generator may contribute to the braking effect. Furthermore, the maximum deviation of the brake force distribution of the usual design is determined depending on the situation.

The object of the present invention is to allow a recuperation with high efficiency at a constant driving behavior of the vehicle.

This object is achieved by a method for controlling a brake system according to claim 1.

Thus, a method for controlling a brake system of a motor vehicle is provided, which has at least one electric machine on the wheels of a drive axle, which can be operated as a drive or a generator, wherein the wheels at least the drive axle wheel brakes, the braking force of the wheel individually increases or decreases independently of the driver can be. According to the invention at least one curve size such as a steering wheel angle and / or a lateral acceleration and / or a yaw rate is measured by means of at least one sensor, and when a brake request occurs, it is checked whether the braking request takes place during a quasi-stationary cornering, and in this case becomes the outside wheel of the drive axle generates a larger or smaller braking force than on the inside wheel of the drive axle.

On the basis of the signals of at least one sensor so a curve size is measured, which allows both the detection of cornering and the assignment of the inside of the curve and the outside wheel. In vehicles with a vehicle dynamics control system, sensors for measuring a steering wheel angle, a lateral acceleration and a yaw rate are present in any case, so that an evaluation of the signals of these sensors can be carried out with little effort and without additional costs. In a quasi-stationary cornering, which can be detected, for example, based on a consistently struck steering wheel and fixed vehicle speed, the required yaw moment to compensate for a caused by the strong on the drive axle displaced braking force deviation from the desired or usual driving behavior can be determined or estimated.

The determined yaw moment is expediently implemented via a wheel-independent driver-independent increase or reduction of the braking forces in the wheels of the drive axle. A wheel-individual driver-independent change in the braking forces can be carried out, for example, in a known electro-hydraulic control device of a brake system, which is a pressure source such as an electric having driven piston pump and two each of a wheel brake of the drive axle associated with solenoid valves. By then an arranged between the wheel brake and the pressure source inlet valve of a wheel brake is closed, the brake pressure in the other wheel can be increased individually. A wheel-individual driver-independent change of the braking force on an axle is thus understood here that the braking force in a first wheel brake can be changed, while the braking force in a second wheel brake of the drive axle is at least kept equal or even can be lowered.

It is advantageous if, for a vehicle with rear-wheel drive, a greater braking force is generated on the outer wheel of the drive axle than on the inner wheel of the drive axle. In a rear-wheel drive vehicle, the inside wheel of the drive axle is greatly relieved in a curve, and thus can transmit a lower braking force than the outside wheel. Thus, there is a tendency for the rear of the vehicle to "break out", i. the vehicle oversteers. By braking the outside of the wheel of the rear axle, which has a greater Austient force and thus larger transmittable transverse forces than the inside wheel, the existing coefficient of friction can be optimally used without loss of cornering force.

Furthermore, it is advantageous if a smaller braking force is generated for a vehicle with front-wheel drive on the outside wheel of the drive axle than on the inside wheel of the drive axle. In principle, when braking a weight shift to the front axle, which can be transmitted to this larger lateral forces. Thus, it is not critical in terms of driving stability to generate a yaw moment in the screwing by the front wheel is braked more inside the curve.

Many factors are already known in the design of the chassis. Thus, based on the present brake request and preferably an estimated coefficient of friction, the required yaw moment can be determined in a feedforward control, without having to recognize a clear deviation between the desired and measured behavior of the vehicle as in a vehicle dynamics control.

Conveniently, a change quantity is determined from the signals of the sensor (s) as a temporal change of a curve size. A quasi-stationary cornering is preferably detected when at least one measured curve size exceeds a predetermined curve threshold value and the change quantity falls below a predetermined change threshold value. In this case, a first curve size such as the yaw rate and the temporal change of a second curve size, such as the steering wheel angular velocity as a change over time of the steering angle. Furthermore, it may be provided to allow changes up to a predetermined maximum value or to carry out the method according to the invention even with a slow change of the cornering.

Preferably, a coefficient of friction of the road is determined, and the difference between the braking force on the outside wheel of the drive axle and the braking force on the inside wheel of the drive axle is selected in accordance with the determined coefficient of friction. In this case, known methods for friction coefficient estimation can be used. Expediently, a coefficient of friction once determined is maintained for a predefined period of time or the duration of a journey until a slip control is required on the basis of a consideration of one or more wheel speeds or a slip inspection. In general, clearly asymmetric braking forces can be applied to the drive axle on a high coefficient of friction.

Particularly preferably, the coefficient of friction of the roadway is determined from a consideration of the requested braking force, a measured lateral acceleration and / or at least one measured wheel speed of a wheel of the drive axle, in particular based on a characteristic curve. By considering the braking behavior during a first braking of the curve, an estimate of the coefficient of friction based on a consideration of braking force, lateral acceleration and slip can be made, in particular assuming an in-plane cornering.

Particularly preferably, a value for the lateral forces on the front and / or rear axle is calculated on the basis of the determined coefficient of friction and the braking forces on the front and rear axles. As soon as a value for the coefficient of friction has been determined during a journey, a simple calculation of the lateral forces can be carried out by changing the braking force by, in particular, keeping all parameters except the requested braking deceleration or the braking forces at the front and rear axles constant.

Most preferably, the difference between the braking force on the outside wheel of the drive axle and the braking force on the inside wheel of the drive axle in accordance with the determined Side forces selected, wherein preferably also the steering angle is taken into account. Thus, an optimally adapted to the current driving situation braking force difference can be determined.

It is advantageous if the increase or decrease in the braking force on the inside wheel of the drive axle, and the reduction or increase in the braking force on the outside wheel of the drive axle are equal in magnitude. As a result, the total braking force on the drive axle and thus the vehicle deceleration remains constant, whereby the control can remain structurally simple.

ermittelt, wobei

F ^_y,f

eine Seitenkraft an der Vorderachse,

F ^_y,r

eine Seitenkraft an der Hinterachse,

B_f

eine Bremskraft an der Vorderachse,

δ

einen Einschlagwinkel der gelenkten Räder,

l_f

einen Abstand zwischen Vorderachse und Schwerpunkt,

l_r

einen Abstand zwischen Hinterachse und Schwerpunkt, und

s_r

eine Spurbreite der Hinterachse bezeichnen.

In particular, for a vehicle with rear-wheel drive, the difference ΔB _r between the braking force on the outside wheel of the rear axle and the braking force on the inside wheel of the rear axle according to

determined, where

F ^ _{y, f}

a lateral force on the front axle,

F ^ _{y, r}

a lateral force on the rear axle,

B _f

a braking force on the front axle,

δ

a steering angle of the steered wheels,

l _f

a distance between the front axle and the center of gravity,

l _r

a distance between the rear axle and the center of gravity, and

s _r

indicate a track width of the rear axle.

ermittelt, wobei

F ^_y,f

eine Seitenkraft an der Vorderachse,

F ^_y,r

eine Seitenkraft an der Hinterachse,

B_f

eine Bremskraft an der Vorderachse,

δ

einen Einschlagwinkel der gelenkten Räder,

l_f

einen Abstand zwischen Vorderachse und Schwerpunkt,

l_r

einen Abstand zwischen Hinterachse und Schwerpunkt, und s_f eine Spurbreite der Vorderachse bezeichnen.

For a vehicle with front-wheel drive, the difference ΔB _f between the braking force on the outside wheel of the front axle and the braking force on the inside wheel of the front axle in particular according to

determined, where

F ^ _{y, f}

a lateral force on the front axle,

F ^ _{y, r}

a lateral force on the rear axle,

B _f

a braking force on the front axle,

δ

a steering angle of the steered wheels,

l _f

a distance between the front axle and the center of gravity,

l _r

a distance between the rear axle and the center of gravity, and s _f denote a track width of the front axle.

With regard to an efficient recuperation, it is advantageous if a braking force demand is converted up to a predetermined maximum braking force only at the wheels of the drive axle, as long as the slip at the drive wheels is below a slip threshold value.

The invention further relates to a motor vehicle, in particular with four wheels and two axles, which has at least one electric machine on the wheels of a drive axle, which can be operated as a drive or generator, comprising wheel brakes on the wheels at least the drive axle, the braking force increases wheelindividually driver independently or can be lowered, which has an electronic control unit with a computing unit that performs a method according to the invention.

The inventive method can also be implemented in a vehicle with hybrid drive, in which therefore the wheels of one of several axes are temporarily driven by an internal combustion engine.

Further preferred embodiments will become apparent from the subclaims and the following description of an embodiment with reference to figures.

Show it

1 a schematic representation of the driving behavior in a generator braking a front-wheel drive vehicle,

2 a schematic representation of the driving behavior in a generator braking a rear-wheel drive vehicle,

3 the force acting on a front-wheel drive vehicle during generator braking, and

4 the forces acting on a rear-wheel drive vehicle during generator braking.

1 shows a schematic representation of the driving behavior of a front-wheel drive vehicle during a generator braking. Under front-driven here is understood that the wheels of the front axle are connected to one or more electric machines; Even in a hybrid vehicle, it is assumed that the electric drive is the drive decisive for the handling behavior in the braked case. The front-wheel drive vehicle may have both a central electric motor which acts on both wheels of the front axle, and two electric motors each associated with a wheel of the front axle, in particular wheel hub motors. A solid line shows the driver's desired driving behavior, which is set at a high coefficient of friction and / or at a braking force distribution which is ideal in terms of driving stability. If the vehicle is braked at low friction only on the front wheels to ensure recuperation with high efficiency, so the vehicle follows the dashed line shown.

In a curve, the course of the vehicle is determined by the side forces acting on the axles. In the case of an unbraked or braked with an ideal braking force distribution cornering acts on the front axle, the side force F _{y, f0} and at the rear axle, the side force F _{y, r0} ; the vehicle follows the course shown as a solid line (the name of the forces is used throughout the figures). In the case of generator braking at a low coefficient of friction, the braking forces on the front wheels, the left front wheel force B _{f, l} and the right front wheel force B _{f, r} cause a reduction of the side forces, in particular on the inside wheel, which has lower contact forces , Thus, of the side forces F _{y, f} and F _{y, r} acting in this case _{, in} particular the lateral force on the front axle is reduced. This results in a yaw moment about the vertical axis of the vehicle, which causes an understeer or a relation to the driver's request to the outside of the curve rotated, dashed course shown.

2 shows a schematic representation of the driving behavior of a rear-wheel drive vehicle during generator braking, with rear-driven refers to the fact that the wheels of the front axle are connected to a central electric motor or each wheel of the rear axle is connected to an associated electric motor, in particular a wheel hub motor. A solid line shows the driver's desired driving behavior, which is set at a high coefficient of friction and / or at a braking force distribution which is ideal in terms of driving stability. If the vehicle is braked at low friction only on the rear wheels to ensure high efficiency recuperation, the vehicle follows the dashed line shown.

The side forces on the axles which determine the course of the vehicle correspond again to the lateral force F _{y, f0} at the front axle and the lateral force F _{y, r0} at the rear axle in the case of unbraked or braked braking with an ideal braking force distribution. these cause the vehicle to follow the course shown as a solid line. In the case of generator braking, the braking forces on the rear wheels, the force B _{r, l} acting on the left rear wheel and the force B _{r, r} acting on the right rear wheel cause a reduction of the lateral forces, in particular on the inside wheel, which has lower contact forces. Thus, of the side forces F _{y, f} and F _{y, r} acting in this case _{, in} particular the lateral force on the rear axle is reduced. This results in a yaw moment about the vertical axis of the vehicle, which causes a relation to the driver's request to the inside of the curve turned dashed lines shown.

The yawing moment that amplifies the rotation of the vehicle in the direction of the curve can also result in a skidding of the vehicle. Therefore, the case of an oversteering vehicle is particularly dangerous for inexperienced drivers. The discussed oversteer also occurs in a comparison with the in 1 Case shown higher coefficient of friction, since the wheels of the rear axle when braking in principle have a lower contact force against the wheels of the front axle.

In terms of driving stability and thus driving safety unchanged yaw behavior of the vehicle during a braking operation is required. The method according to the invention makes it possible to ensure stable driving behavior during braking in a curve and to maintain a constant braking effect, ie the relationship between the driver braking requirement and the effective vehicle deceleration remains the same.

Based on 3 showing the forces acting on a front-wheel drive vehicle during generator braking, a first embodiment of the invention will be explained.

In a first step, it is checked whether there is a quasi-stationary cornering. Depending on the existing sensors, a measured curve size such as steering wheel angle, lateral acceleration, yaw rate or yaw rate can be viewed to detect cornering. The presence of quasi steady-state cornering can be determined by the temporal change of a measured curve size. It may also be provided to consider a first curve size for the detection of a cornering and the temporal change of a second curve size as a measure of the presence of quasi-stationary conditions. For example, quasi-stationary cornering may be detected when the yaw rate is greater than a predetermined turn threshold and the amount of steering angular velocity is less than a change threshold (preferably 150 ° / sec). If the vehicle has a vehicle dynamics control system, quasi-stationary cornering can be detected from the driving situation recognition of the vehicle dynamics control and / or an estimated curve radius.

The next step is expediently to determine or estimate the coefficient of friction μ 1 of the roadway. In this case, it may be provided to set a braking force difference between the inside wheel of the drive axle and the outside wheel of the drive axle only when the determined or estimated coefficient of friction falls below a predetermined adhesion threshold value. On a roadway with a high coefficient of friction and a significant deviation from the ideal brake force distribution is unproblematic. If the vehicle has a transverse acceleration sensor and wheel speed sensors, it can be determined from a comparison of the applied braking force, the measured slip on a wheel or both wheels of the drive axle or a consideration of the measured wheel speeds, in particular on the assumption that there is travel on the plane individual vehicle wheels, a coefficient of friction estimated or determined by a characteristic curve. Corresponding characteristics can be determined from driving tests and are expediently stored in a non-volatile memory of an electronic control unit of a brake system. By thus taking into account the wheel speeds, in particular the drive axis, at the beginning of the measurement, a coefficient of friction can at least be estimated. It is advantageous then to maintain this and to calculate in the course of the braking process with a change in the braking request, the applied lateral forces on the drive axle and non-driven axle. The braking request or the braking force can preferably be determined in a hydraulic brake system with a pressure sensor arranged between the master brake cylinder and the wheel brakes. In principle, a pedal travel or pedal angle sensor can also be used. Other methods known per se for estimating the coefficient of friction can also be used.

The next steps of calculation of the braking force difference will be made with reference to FIG 3 explaining in which the forces acting on a vehicle with front-wheel drive forces are shown in braking in a curve. The presence of a quasi steady-state cornering means that the vehicle is in equilibrium about the vertical axis and the total yaw moment T ₀ about the vertical axis through the center of gravity is 0 (and thus the yaw rate is constant): T ₀ = F _{y, f 0} · l _f - F _{y, r} 0 · l _r ≈ 0 (1)

Here, l _f denotes the distance between the front axle and the center of gravity of the vehicle and l _r the distance between the rear axle and the center of gravity of the vehicle. The center of gravity indicated by the black circle is between the two axes, so the sum of l _f and l _r corresponds to the distance l between the front and rear axles. The braking forces B _f on the front axle and B _r on the rear axle must cause a vehicle deceleration according to the driver request. In a vehicle with a regenerative braking system, a variable FA corresponding to the driver request is expediently detected with a pedal travel, pedal angle or pedal force sensor.

The distribution of the braking forces between the front and rear axles is generally based on the ideal in terms of driving stability braking force distribution. For efficient recuperation, however, it is necessary for small delays up to the maximum by the one or more generators implementable Deceleration to implement the braking force as completely as possible on the front axle. Therefore, the braking forces at the front and rear axles are determined according to a suitable distribution function on the basis of the detected driver requirement FA: B _f = F _distribution (FA) (2) B _r = F _distribution (FA) (3)

In a further step, an estimation of the lateral forces on the front and rear axle takes place on the basis of a tire model and the determined coefficient of friction μ 1: F ^ _{y, f} = F (B _f , μ ^) (4) F ^ _{y, r} = F (B _r , μ ^) (5)

The braking forces on the non-driven axle, in a vehicle with front-wheel drive so the rear axle are expediently divided equally:

On the drive axle, so the front axle, the braking forces are divided asymmetrically. Furthermore, the sum of the braking forces B _{f, l} on the left front wheel and B _{f, r} on the right front wheel must be considered to be the total braking force desired according to the driver's braking request the front axle corresponds to: B _{f, l} + B _{f, r} = B _f (7)

For the in 3 shown driving situation results in the required yaw moment T according to the following formula: T = (F ^ _{y, f} - B _f sin δ) · l _f - F _{y, r} · l _r + (B _{f, l} - B _{f, r} ) · s _f cos δ = 0 (8)

Here, δ denotes the steering angle of the steered front wheels and s the track width of the front axle. Since the total braking force of the front axle must remain the same in the asymmetric braking, the lowering of the braking force on the outer wheel takes place by the same amount as the increase of the braking force on the inner wheel:

To apply the required yaw moment, the following brake torque difference ΔB _{f is} required:

Apart from geometric factors and the driver's braking request, the difference in the braking forces of the two front wheels (driving wheels) .DELTA.B _f is thus mainly dependent on the changes in the lateral forces of the two axles during braking. Appropriately, therefore, even during a braking process, a new estimate of the coefficient of friction, if, for example, the slip behavior deviates significantly from the expected based on the estimated coefficient of friction behavior, ie, for example, a significant drop in one or more wheel speeds at a previously assumed close to 1 coefficient of friction.

In a last step, the braking forces on the wheels of the drive axle must be established by a braking system of the motor vehicle. This may be a hydraulic brake system, as for example from the DE 10 2011 003 346 A1 is known. The wheel brakes can alternatively be realized as electromechanical friction brakes, wherein different friction brakes can also be used, as for example in the EP 2 342 110 B1 is disclosed. Depending on the configuration of the electric drive, there are various possibilities for how the different braking forces can be realized on the two drive wheels:

If the drive axle of the vehicle has two electric motors, with each wheel being assigned an engine, the asymmetrical braking forces can be generated by means of recuperative braking if the motors can supply the requested braking forces during generator operation. If the total braking force on the front axle exceeds the maximum available generator braking force, both generator and friction brake system are expediently activated in order to provide the desired deceleration in the combination.

If the vehicle has only one central motor connected to both wheels of the drive axle, only the common or equal portion of the braking force on the two drive wheels can reach up to (B _f -ΔB _f ) = 2 * min (B _{f, l} , B _{f , r} ), be applied via a recuperative braking, up to the maximum of the electric motor available braking torque. The asymmetric braking forces and beyond the generator delay portions of the braking force are realized by the friction brake system.

Based on 4 showing the force acting on a rear-wheel drive vehicle during generator braking forces, a second embodiment of the invention will be explained. The first step of detecting a quasi-stationary cornering is basically the same as described in the first embodiment. The second step of an estimate or determination of the coefficient of friction can also take place by means of methods known per se. In the following, therefore, only the distribution of the braking forces in the case of at least one electric machine connected to the rear axle will be discussed.

In order to ensure efficient recuperation, in a vehicle with rear-wheel drive expediently the rear axle brakes more than the front axle, in particular up to a predetermined maximum deceleration. The deceleration of the non-driven front wheels is symmetrical. To counteract an oversteer tendency, the outside rear wheel is subjected to a greater braking force than the inside rear wheel. In sum, the different braking forces on the two rear wheels must furthermore correspond to the total braking force determined on the basis of the predetermined distribution function and the driver demand: B _{r, l} + B _{r, r} = B _r (12)

The required yaw moment to compensate for the oversteer can according to T = (F ^ _{y, f} - B _f sin δ) · l _f - F _{y, r} · l _r + (B _{f, l} - B _{f, r} ) · s _r = 0 (13) where s _r denotes the track width of the rear axle. For the required braking forces B _{r, l} on the left rear wheel and B _{r, r} on the right rear wheel is obtained with a symmetrically applied braking force difference ΔB _r on the rear axle:

The braking forces are discussed as discussed above for the front axle by suitable control of electric drive and / or braking system.

An inventive method allows by an asymmetric deceleration of the wheels of the drive axle, the usual handling despite a required for efficient recuperation deviation from the (under driving stability aspects) optimal brake force distribution.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102004061107 A1 [0004]
• DE 102011003346 A1 [0049]
• EP 2342110 B1 [0049]

Claims (15)

Method for controlling a brake system of a motor vehicle, which has at least one electric machine on the wheels of a drive axle, which can be operated as a drive or generator, wherein the wheels at least the drive axle wheel brakes, the braking force can be increased or decreased independently of the driver, characterized in that at least one curve size such as a steering wheel angle and / or a lateral acceleration and / or a yaw rate is or are measured by means of at least one sensor and that, when a braking request occurs, it is checked whether the braking request occurs during a quasi-stationary cornering, and that in this case on the outside wheel of the drive axle, a larger or smaller braking force is generated than on the inside wheel of the drive axle. A method according to claim 1, characterized in that for a vehicle with rear-wheel drive on the outside wheel of the drive axle, a greater braking force is generated than on the inside wheel of the drive axle and / or for a vehicle with front-wheel drive on the outside wheel of the drive axle generates a smaller braking force is considered to be on the inside wheel of the drive axle. A method according to claim 1 or 2, characterized in that from the signals of the sensor or a change quantity is determined as a change over time of a curve size, a quasi-stationary cornering is detected when at least one measured curve size exceeds a predetermined curve threshold and the amount of change a predetermined Change threshold falls below. Method according to one of claims 1 to 3, characterized in that a coefficient of friction of the roadway is determined, and that the difference between the braking force on the outside wheel of the drive axle and the braking force on the inside wheel of the drive axle is selected in accordance with the determined coefficient of friction. A method according to claim 4, characterized in that the coefficient of friction of the roadway from a consideration of the requested braking force, a measured lateral acceleration and / or at least one measured wheel speed of a wheel of the drive axle, is determined, in particular based on a characteristic. A method according to claim 4 or 5, characterized in that each one value for the lateral forces on the front and / or rear axle is calculated on the basis of the determined coefficient of friction and the braking forces at the front and rear axles. A method according to claim 6, characterized in that the difference between the braking force on the outside wheel of the drive axle and the braking force on the inside wheel of the drive axle is selected in accordance with the determined lateral forces, wherein preferably also the steering angle is taken into account. Method according to one of the preceding claims, characterized in that the increase or decrease in the braking force on the inside wheel of the drive axle, and the reduction or increase in the braking force on the outside wheel of the drive axle are equal in magnitude. A method according to claim 8, characterized in that for a rear-wheel drive vehicle the difference ΔB _r between the braking force on the outside wheel of the rear axle and the braking force on the inside wheel of the rear axle according to

where F ^ _{y, f is} a lateral force on the front axle, F ^ _{y, r is} a lateral force on the rear axle, B _{f is} a braking force on the front axle, δ is a steering angle of the steered wheels, l _{f is} a distance between the front axle and the center of gravity, l _{r is} a distance between the rear axle and the center of gravity, and s _{r is} a track width of the rear axle. A method according to claim 8, characterized in that for a vehicle with front-wheel drive the difference ΔB _f between the braking force on the outside wheel of the front axle and the braking force on the inside wheel of the front axle according to

where F ^ _{y, f is} a lateral force on the front axle, F ^ _{y, f is} a lateral force on the rear axle, B _{f is} a braking force on the front axle, δ is a steering angle of the steered wheels, l _{f is} a distance between the front axle and the center of gravity, l _r denotes a distance between the rear axle and the center of gravity, and s _f denotes a track width of the front axle. Method according to one of the preceding claims, characterized in that a braking force requirement is converted to a predetermined maximum braking force only at the wheels of the drive axle, as long as the slip at the drive wheels is below a slip threshold. Motor vehicle, in particular with four wheels and two axles, which has at least one electric machine on the wheels of a drive axle, which can be operated as a drive or generator, comprising wheel brakes on the wheels at least the drive axle whose braking force can be increased or decreased independently of the driver by an electronic control unit having a computing unit which carries out a method according to at least one of the preceding claims. Motor vehicle according to claim 12, characterized in that each individual wheel of the drive axle is connected to an associated electric machine, wherein the electronic control unit is configured such that the braking forces generated at the wheels of the drive axle up to a maximum deliverable braking force only from the electric machines become. Motor vehicle according to claim 12, characterized in that all wheels of the drive axle are connected to a common electric machine, wherein the electronic control unit is configured such that the braking forces are generated on the drive axle up to the braking force on the inside wheel only by the electric machine, as long as the braking force on the inside wheel is smaller than a maximum available braking force. Motor vehicle according to one of claims 12 to 14, characterized by an internal combustion engine, wherein the wheels of the drive axle and / or the wheels of the other axle are at least temporarily driven by the internal combustion engine.

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