DE102009039347A1 - Method for operation of motor vehicle, particularly hybrid vehicle, involves providing total brake torque of braking of motor vehicle proportionately by electrical machine of motor vehicle - Google Patents

Abstract

The method involves providing a total brake torque of braking of a motor vehicle proportionately by an electrical machine of the motor vehicle. A target point is determined, to which a continuous termination of proportionate determination of the total brake torque by the electrical machine is begun.

Description

The invention relates to a method for operating a motor vehicle according to the preamble of patent claim 1.

Such methods are well known. So revealed the DE 10 2005 032 196 A1 a drive device for a motor vehicle having an internal combustion engine, an electric machine coupled to the internal combustion engine, with a transmission device and with a control device, wherein the control device is designed such that in the case of a braking request, the requested total braking torque is at least partially provided by the electric machine, and wherein, in a present braking request with a constant total braking torque and carried out during concerns this braking request change the gear ratio, the electric machine is driven such that the changing due to the change in transmission total braking torque is at least partially balanced.

This drive device, like the well-known, such drive devices, especially in hybrid vehicles, has the disadvantage that a transition from braking by the electric machine to braking by another service brake system, in particular by a friction brake system, is implemented inadequately comfortable , In such a transition occurs often noticeable for occupants of the vehicle jerk, which greatly adversely affects the comfort of the vehicle.

It is therefore an object of the present invention to provide a method for operating a motor vehicle, which allows increased driving comfort of the motor vehicle.

This object is achieved by a method for operating a motor vehicle having the features of patent claim 1. Advantageous embodiments with expedient and non-trivial developments of the invention are specified in the dependent claims.

An inventive method for operating a motor vehicle, in particular a hybrid vehicle, in which a total braking torque of a braking of the motor vehicle is provided at least partially by at least one electric machine of the motor vehicle, characterized in that a time is determined, to which a substantially continuous termination of the at least partial provision of the total braking torque is started by the electric machine. The determination of this time point allows a continuous termination of the at least partial provision of the total braking torque by the electric machine, which means that this proportionate provision by the electric machine is not terminated abruptly or abruptly, but continuously decreasing. This termination can follow, for example, a ramp-shaped course, which is why this termination can also be referred to as ramp-out. The continuous termination from the determined time thus enables a comfortable and for occupants of the motor vehicle little to no noticeable termination of the at least proportionate provision of the total braking torque by the electric machine, which means a significant increase in comfort for occupants of the motor vehicle.

The time is determined, for example, at least as a function of a vehicle speed, a vehicle deceleration and / or a torque component of the electric machine to the total braking torque. In this case, for example, a limit value for the vehicle speed can be predetermined, which is read out or determined, for example, from a characteristic map or the like, in which the continuous termination of the at least partial provision of the total braking torque by the electric machine is to be ended or terminated. In the time between the determined time and this limit value of the vehicle speed, the described ramping out of the at least partial provision of the total braking torque by the electric machine takes place, whereby the comfort described for the occupants is realized.

If after the occurrence of the determined time, a torque component of another service brake system, in particular a friction brake system of the motor vehicle to the total braking torque increases, this has the advantage that thereby, for example, by a driver of the motor vehicle, required braking up to a standstill of the motor vehicle and efficient is made possible with a high delay with simultaneous realization of a comfortable, there is no or only slightly noticeable transition from the at least partially providing the total braking torque by the electric machine to provide the total braking torque through the other service brake system.

In the mentioned moments proportions of The electrical machine or the further service brake system can likewise be braking torque requests of the electric machine or of the further service brake system that are determined in a control device of the motor vehicle or are requested by the control device, for example from corresponding actuators.

In any case, the method according to the invention makes it possible to comfortably end the at least partial provision of the entire braking torque by the electric machine or a transition from this provision to an at least partial provision of the total braking torque by the further service brake system, without the undesired jerk described above by the motor vehicle, which is advantageous in particular when braking the motor vehicle in its standstill insofar as there must be a transition from the at least proportionate provision of the entire braking torque by the electric machine to the complete provision of the entire braking torque by the further service brake system.

Further advantages, features and details of the invention will become apparent from the following description of several preferred embodiments. It is understood that additional steps may be added or steps omitted, as well as the steps performed in a different order without departing from the scope of the invention.

The starting point is a hybrid vehicle with at least one electric machine in its drive train, which can be operated as a generator during braking in order to recover energy (recuperation). During a recuperation, the hybrid vehicle is slowed down at the same time. The drive train has, for example, a hybrid control unit which controls or regulates an interaction of the components of the drive train.

Furthermore, the hybrid vehicle has a further service brake system, for example in the form of a disc brake system, which can divide a total braking torque of a braking request of a driver of the hybrid vehicle in deceleration by the disc brake system, which is a friction brake, and the drive train with the electric machine and this distribution controls or regulates. A sum of a total torque requirement, which is provided by the friction brake and the recuperation, always corresponds to the driver's request. The described distribution of the total torque request is regulated, for example, by a control unit of the further service brake system, which is referred to below as the brake control unit.

The interaction between the hybrid control unit and the brake control unit works because the hybrid control unit constantly calculates a maximum braking torque through recuperation and transmits it to the brake control unit. This means more braking torque by recuperation, so by the electric machine, a higher energy recovery. The brake control unit requests, depending on the driver's request, a braking torque by recuperation in a suitable height of the hybrid control unit, which is provided by this.

Both controllers are connected for example by a data line. For a transmission of information between the control units, for example, a time T_ue is required.

Characteristic of braking by recuperation is that a requested braking torque is set by recuperation after a time T_h. Accordingly, it is characteristic of the further service brake system that a requested braking torque is set by the friction brake after a time T_b.

When braking in the standstill of the hybrid vehicle from a certain vehicle speed, a transition from a maximum use of a braking torque by recuperation to the exclusive use of a braking torque by the friction brake is needed. This takes place in such a way that, starting from a vehicle speed at which the transition is or must be completed, a time is determined, in addition to which the above-described ramping out of braking by recuperation is started or must begin. This is done for example on the basis of a gradient, which is defined in Newton meters per second [Nm / s] and the vehicle deceleration [m / s ² ] during braking.

The characteristic curve of available braking torque through recuperation versus vehicle speed is a hyperbola plotted in a two-dimensional Cartesian four-quadrant coordinate system at abscissa-plotted vehicle speed and at zero-decelerating vehicle speed at which the braking torque is plotted by recuperation is approaching toward infinity and approaching the abscissa when the vehicle speed approaches zero relative to positive vehicle speed values. This means that when braking with decreasing vehicle speed, the available braking torque increases by recuperation, with a steadily steeper gradient. A request for braking torque by recuperation, for example by the mentioned control device follows this course.

At the time when the ramping out of braking by recuperation, so the at least proportionately providing the total torque request by the electric machine, the gradient of the requested braking torque changes from strong increase to rapid decrease due to recuperation. It is difficult for the drive train of the hybrid vehicle to follow this course.

For the further service brake system, ie for the friction brake, this means to switch from a reduction in the braking torque by the friction brake to an increase. Due to physical inertia of an actuator of the friction brake, however, this can only be done with a time delay. For a timely compensation of the behavior of the recuperation also a rapid change of brake pressure reduction of the friction brake on brake pressure build-up is required. If the described determination according to the invention of the time at which the ramp-up of the at least partial provision of the total braking torque by the electrical machine is started already has the advantage that a considerable increase in comfort is already possible, the following aspect of the invention makes possible a further comfort enhancement.

Thus, the further service brake system already calculates from vehicle speed, vehicle deceleration and the amount of the requested braking torque by recuperation when the ramp-out of the braking torque by recuperation is started. This calculation is now extended to the effect that, on the basis of the signals mentioned above, it is additionally determined when the ramping-out is started after the lapse of a predefinable or adjustable time period T_rest. Upon reaching this time, ie within this period, a further increase in the requirement of braking torque is prohibited by recuperation, so the braking torque held by recuperation substantially equal, for example, compared to a state before falling below a limit, or even lowered.

This involves capping a torque peak of the brake torque by recuperation since the amount of the demand is not further increased. Both the drive train with the electric machine and the further service brake system are set in a constant state, from which the response time during subsequent overramping, that is, the transition from the provision of the total braking torque by the electric machine to provide the total braking torque by the further service brake system , is less and less scatters.

T_ruhe is selected according to physical characteristics of the service brake system and powertrain such that actuators of the service brake system and powertrain have reached a steady state before said overramping begins.

This is implemented, for example, such that the condition "no increase in the requirement of braking torque by recuperation" in comparison of an actual requirement of braking torque by recuperation or actual vehicle speed is set with a limit value, which is permanently calculated, for example. If the actual signal exceeds the limit value, then the prohibition of increasing occurs, from which point onwards the demand for braking torque by recuperation is kept or lowered the same as before it was undershot.

An increase in the requirement of braking torque through recuperation is only permitted again when the described prohibition is canceled by an independent condition.

The calculation of the described limit value, which limit value is present, for example, as vehicle speed, takes place, for example, according to: v _{no increase} = v _exhausted + (a _car · M _{rain demand} / G _ramp ) - a _car · T_rest where G _{ramp is} the positive gradient of the reduction of the demand for braking torque by recuperation in [Nm / s]. V is the vehicle _speed at which the ramping down of the at least partial provision of the total braking torque by the electric machine will be ended. a _vehicle is the deceleration of the vehicle and thus a negative value. M _{rain demand} refers to the requirement of braking torque by recuperation, which is also a negative value.

Another aspect of the invention relates to a further improvement of the transition from braking with braking torque by recuperation to pure braking by the friction brake.

Especially when braking downhill there is the problem that the braking does not lead to a similar extent to a deceleration of the vehicle. With a modulation of the braking request, the driver can accelerate the hybrid vehicle while it is braking and the at least partial provision of the total braking torque by the electric machine is in the described ramp-down operation.

This would increase the amount of requested braking torque through recuperation. To avoid any, resulting Comfort impairment is ensured in this aspect of the invention that when ramping down this ramp, ie the course of the completion of the at least proportionate provision of the total braking torque by the electric machine, only in one direction (decreasing braking torque by recuperation) is traversed while minimizing the effects of noise the corresponding signals. For this purpose, the ramping out of braking by recuperation is defined as the system state.

As soon as it is determined that the ramp-down has to be started, ie the corresponding condition exists, the system consisting of the electric machine and the friction brake is switched to ramp-off. From this point on, an increase in the demand for braking torque due to recuperation is no longer permitted. The statement that the ramp-down must be commenced correlates with the time determined according to the invention.

This means that with a reduction of the braking torque by recuperation and subsequent increase, for example, re-increase, the vehicle speed of the amount of braking torque request by recuperation is kept constant.

For example, to exit the system state of ramping, the vehicle speed must exceed a threshold that is well above the vehicle speeds in which the ramp down is performed. If the system state Ausrampen reset, doing the increase in the request of braking torque by recuperation is not on the ramp of ramping down, but over a defined gradient up to the value that the further service brake system or its control unit under the given conditions as available braking torque by recuperation , Braking request of the driver determined as target value.

To avoid a sudden success of ramping down when reaching or falling below the described vehicle speed as a limit, in which therefore the ramping must be completed, provides a further aspect of the invention that a further Ausrampbedingung introduced and a determination of a maximum allowable value for the requirement of Braking torque is performed by recuperation by minimum value formation of both conditions.

The new condition is a gradient which is defined as the maximum permissible braking torque by recuperation per vehicle speed unit, ie km / h, above the vehicle speed at which the braking torque due to recuperation, that is braking by recuperation, will or will have been completely canceled out. This ensures that the requirement of braking torque due to recuperation when the defined vehicle speed is reached is always reduced to zero Nm as a limit value. The slope of the additional gradient is to be chosen so that the ramping out of braking by recuperation before stopping the hybrid vehicle for most of the braking on the deceleration condition.

Another aspect of the invention for increasing the comfort in a transition from braking by recuperation to the brakes by the further service brake system, in particular before reaching the standstill of the hybrid vehicle to increase the demand for braking torque through the friction brake and in synchronism the requirement braking torque by recuperation to reduce substantially the same amount.

This aspect of the invention now relates to a compensation of any different response of the actuator for braking by recuperation, so for example the electric machine, and braking by the other service brake system, so for example the friction brake.

Such systems generally have dead times which are necessary to represent the corresponding torque requirements also for the actual deceleration of the vehicle. So if the powertrain, so for example, the electric machine, and the other service brake system different response, it is provided to maintain or further increase the comfort that the requirement of braking torque of the faster-reacting system made dependent on an achieved actual braking torque of the slower system becomes. In the following concrete example, this is the further service brake system. The example is also analogous to the case transferable, if the powertrain, so the electric machine, the slower system. In addition to the determined above-described, determined time point t0 at which the ramp-out of the braking by recuperation and the time T_ruhe, a further period of time T_feedback is introduced, which is a period for a feedback-based ramping. The following steps of this example assume a constant driver request for a braking torque. An increase or a reduction of the driver's wish would initially only affect the amount of the desired braking torque by the friction brake during ramping.

In a first step, the request for braking torque by recuperation is not further increased at a time tx, ie, it is left as it was before the time or lowered, wherein the time tx is a time T_ruhe + T_feedback before t0.

In a second step, after the time T_ruhe has elapsed, the requirement of braking torque is increased by the friction brake with the predetermined or determined gradient. The requirement of braking torque by recuperation, so the requirement for the drive train with the electric machine remains unchanged.

In a third step, as soon as the actual braking torque by the friction brake (for example, determined from measured braking pressures of the system) increases, the requirement of braking torque by recuperation reduced by the same amount.

If the actual braking torque through the friction brake does not rise steadily, but sink briefly during the transition, so in a fourth step, the requirement of braking torque is kept constant by recuperation and not increased.

In a fifth step, the transition or the overramping is completed when the target braking torque is reduced to zero by recuperation. It should be noted at this point that the transition can also be described as overramping, since the increase in braking by the friction brake is also carried out continuously, for example following a ramp-like course.

If the actual braking torque through the friction brake does not rise sufficiently quickly, the setpoint braking torque is nevertheless reduced by recuperation through a hard ramp-out curve or ramp-out ramp in a sixth step. This case does not occur with appropriate tuning of the parameters.

To further improve this process and thus to further increase comfort is provided in a further aspect of the invention that an assumed, linear relationship between the brake pressure and the braking torque of the friction brake is replaced by a non-linear relationship, especially at very low brake pressures, for example between zero and five bars. With a brake pressure build-up above zero bar, resistances to components of the friction brake, such as brake calipers (rollback) and elasticities of brake lines, must first be overcome before the braking torque builds up through the friction brake.

To illustrate the non-linear relationship, for example, a characteristic curve is used in which intermediate values are interpolated. Such a characteristic with a nominal factor of 100 Nm / bar has, for example, the following values: 0 bar 0 Nm 1 bar 0 Nm 2.5 bar 200 Nm 4 bar 400 Nm 100 bar 10000 Nm

In a further aspect of the invention, a reaction time of the faster system, ie the system with the lower response time, is taken into account. Such a system represents a controlled system, so that a slow controlled system and a fast controlled system can be given, and thus in the above example, the fast control system of the drive train with the electric machine and the slower controlled system is the friction brake.

According to a further aspect of the invention, both the requested and the actual torque of the slower controlled system are used to determine the requirement of braking torque to the fast controlled system. This means that the torque requirement for braking torque by recuperation is composed of an interpolation of two Ausrampkurven.

This avoids that by determining the specification of braking torque to the fast controlled system alone based on the requirement of braking torque to the slower controlled system leads to an unintentionally early implementation of the requested torque by the faster control system. It is also avoided that by determining the specification of braking torque to the fast controlled system alone based on the already implemented by the slower controlled system braking torque leads to an unintentionally late implementation of the requested torque by the faster control system.

The combination of the two signals can be done in different ways.

One possible implementation is to use both signals proportionally; the weighting is carried out as a percentage. The requirement of braking torque to the fast controlled system is provided with a so-called compensation factor.

0% compensation corresponds to a reduction in the requirement of braking torque by Recuperation based on the desired value of the braking torque by the friction brake. 100% compensation corresponds to a reduction based on the actual value of the braking torque by the friction brake, as described in the specific example.

For all values in between, the requirement of desired braking torque is determined by recuperation as interpolation of these two limit curves. With appropriate adjustment of the compensation factor, this time delay for conversion is virtually eliminated.

Further advantages, features and details emerge from the drawing. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the figure description and / or shown alone in the figure can be used not only in the respectively indicated combination but also in other combinations or in isolation without the scope of the invention to leave.

The figure shows a diagram in which is shown in a braking of a hybrid vehicle with an electric machine, a transition from at least partially providing a total braking torque by the electric machine for at least partially providing the total braking torque by a friction brake.

The figure shows a diagram 10 in which, in the case of braking of a hybrid vehicle with an electric machine, a transition from an at least partial provision of a total braking torque by the electric machine to an at least partial provision of the total braking torque by a friction brake is shown. On an abscissa 12 of the diagram 10 is the vehicle speed of the hybrid vehicle plotted while on an ordinate 14 of the diagram 10 an axis torque is plotted, which correlates with corresponding braking torques of the electric machine or the friction brake. Since the transition shown is braking, the acceleration of the hybrid vehicle is negative and the vehicle speed decreases. Therefore, the corresponding braking torques are negative.

In a simplified way, said transition is a transition from braking by the electric machine to braking by the friction brake, which is embodied, for example, as a disc brake system. The transition takes place continuously and obeys a ramp-shaped course, which is why the transition is also referred to as over ramps. As is known, in the braking by the electric machine of the hybrid vehicle, recovery of energy, which is called recuperation, takes place.

If the hybrid vehicle is braked to a standstill as a result of a driver request, this is a limit value 16 the vehicle speed provided, in which the continuous termination of braking by the electric machine, ie their ramps must be completed. Depending on the vehicle speed, the vehicle deceleration and an amount of a request of braking torque by recuperation becomes a time 18 determines at which the ramping out of braking by recuperation is started. The time 18 go a first time span 20 and a second time span 22 in front. The timespan 20 takes into account different responses of the electric machine and the friction brake and thus different times to provide the corresponding braking torque by recuperation or by the friction brake. A requirement of braking torque by the faster-reacting system is thus dependent on an actual braking torque of the slower system.

The request of braking torque is effected for example by a control device of the hybrid vehicle, which transmits the corresponding request of braking torque to the corresponding system, from which the request for braking torque is then provided according to the reaction time of the system. Hence the time span 20 referred to as T_feedback.

The timespan 22 is provided to enable the friction brake and the electric machine or corresponding actuator in a substantially constant state in which they have a steady state. This allows a calming of the system and a comfortable since little to no noticeable transition.

A course 24 represents a request of braking torque by recuperation, in which the limit 16 is safely adhered to, during a course 26 represents a request of desired braking torque by the friction brake. As can be seen, the demand for braking torque by recuperation is reduced with decreasing vehicle speed, while the demand for braking torque by the friction brake is increased. Both requirements follow a ramp-shaped course, which illustrates the above-described name overramping for this transition.

A course 28 represents an actual course of the braking torque by the friction brake, which of the course 26 the requirement of braking torque by the friction brake deviates, since in particular at low brake pressures, a linear relationship between brake pressure and braking torque is no longer given by the friction brake and / or the friction brake has a slower response and thus a higher reaction time than the electric machine. Since in the present example, the friction brake has a higher response time and thus a higher reaction time than the electric machine and thus the braking by recuperation, the ramp-off of the request for braking torque by recuperation is based on the actual course 28 the braking torque through the friction brake. In the diagram 10 is a compensation factor 100%, which means that the requirement of braking torque is increased by recuperation by the amount by which the actual braking torque of the friction brake actually decreases.

This means that the ramping out of the demand for braking torque by recuperation or braking by recuperation itself on the course 28 and thus based on the actual braking torque through the friction brake.

Follow as in the diagram 10 illustrated the requirement of braking torque by recuperation the course 32 , so is the ramping out of braking by recuperation at a vehicle speed 34 completed.

0% compensation factor would mean that the ramping out of braking by the electric machine would follow the course 24 and thus the request of braking torque by recuperation follows, so therefore at the compensation factor of 0%, the ramp-out of the request of braking torque by recuperation on the course 26 the requirement of desired braking torque by the friction brake and not the actual actual braking torque (curve 18 ) of the friction brake is based.

For values of the compensation factor between 0 and 100%, a corresponding progression of the demand for braking torque is made by recuperation by interpolation of the curves 24 and 32 determined, which therefore represent as limit curves of this interpolation.

Hard ramping up according to the course 24 In any case, make sure that to the limit 16 the vehicle speed is stopped braking by recuperation.

The according to the diagram 10 Ramping over is done as follows:
The requirement of braking torque by recuperation is not further increased at a time, which is a sum time span from the time periods 20 and 22 before the time 18 lies.

After the lapse of time 22 If the requirement of braking torque is increased by the friction brake with a predetermined gradient, the requirement of braking torque by recuperation remains unchanged.

As soon as an actual braking torque by the friction brake (determined from measured brake pressures) increases, the requirement of braking torque is reduced by recuperation by the same amount.

If the actual braking torque does not increase steadily by the friction brake, but briefly drop during overramping, the requirement of braking torque is kept constant by recuperation and not increased.

The overramping is ended when the demand for braking torque has been reduced to 0 by recuperation, ie the set braking torque due to recuperation.

If the actual braking torque does not increase sufficiently quickly due to the friction brake, the setpoint braking torque is reduced by recuperation through a hard ramp-down curve (progression) 24 ) is still reduced, this case does not occur with appropriate tuning of the parameters.

LIST OF REFERENCE NUMBERS

10

diagram

12

abscissa

14

ordinate

16

limit

18

time

20

Period of time

22

Period of time

24

course

26

course

28

course

30

arrow

32

course

34

vehicle speed

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 102005032196 A1 [0002]

Claims (17)

Method for operating a motor vehicle, in particular a hybrid vehicle, in which a total braking torque of a braking of the motor vehicle is at least partially provided by at least one electric machine of the motor vehicle, characterized in that a time is determined at which a substantially continuous termination of at least proportional provision of the total braking torque is started by the electric machine. A method according to claim 1, characterized in that after the occurrence of the determined time, a moment proportion of a further service brake system, in particular a friction brake system, of the motor vehicle is increased to the total braking torque. Method according to one of claims 1 or 2, characterized in that the time is determined at least in dependence on a vehicle speed and / or a vehicle deceleration and / or a torque proportion of the electric machine to the total braking torque. Method according to one of the preceding claims, characterized in that the time is determined at least as a function of a time preceding the predetermined time period. A method according to claim 4, characterized in that the time period is predetermined at least in dependence on a state of the electric machine and a state of a further service brake system, in particular a friction brake system of the motor vehicle. A method according to claim 5, characterized in that the electrical machine and the further service brake system are placed in a substantially constant state during the period. Method according to one of claims 5 or 6, characterized in that within the time period of the torque component of the electric machine is reduced to the total braking torque or left substantially equal. A method according to claim 7, characterized in that the torque component of the electric machine is reduced to the total braking torque or kept substantially equal when the vehicle speed or the torque component of the electric machine falls below the total braking torque below a predetermined limit. Method according to one of the preceding claims, characterized in that after the occurrence of the determined time, at least temporarily, the torque component of the electric machine is reduced at the total braking torque or left substantially the same. A method according to claim 9, characterized in that an increase of the torque component of the electric machine is made possible at the total braking torque when the vehicle speed exceeds a predetermined limit. Method according to one of the preceding claims, characterized in that a vehicle speed is predetermined at which the substantially continuous termination of the at least partially providing the total braking torque is completed by the electric machine. Method according to one of the preceding claims, characterized in that a gradient of a maximum allowable torque component of the electric machine is given to the total braking torque per vehicle speed unit, in particular per kilometer per hour, depending on the vehicle speed at which the substantially continuous termination of at least proportional provision of the total braking torque is completed by the electric machine. Method according to Claim 2 or according to one of Claims 3 to 12, in which reference is again made to Claim 2, characterized in that the torque component of the electric machine is reduced substantially by the amount by which the torque component of the further service brake system increases in relation to the total braking torque becomes. A method according to claim 13, characterized in that the increase or reduction of the respective torque component is carried out at least in dependence on the slower reaction time of the reaction times of the electric machine and the further service brake system. Method according to one of claims 13 or 14, characterized in that the increase or the reduction of the respective torque component is carried out at least in dependence on the faster reaction time of the reaction times of the electric machine and the further service brake system. Method according to one of claims 13 to 15, characterized in that for determining the requirement of braking torque to the fast Both the requested and the actual moment of the slower controlled system can be used. Method according to Claim 2 or according to one of Claims 3 to 16, in the back reference to Claim 2, characterized in that a brake pressure of the further service brake system is determined as a function of a non-linear characteristic curve.

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