Brake blending in electric vehicles with recuperation and friction brake

Abstract

In a method for determining a braking characteristic (14) for a brake arrangement (8) of a vehicle (4), a speed profile (24) for a simulated journey (26) of the vehicle (4) and a braking characteristic (14) is provided in a simulation arrangement (2), and for a particular number of passes (D): the journey (26) of the vehicle (4) is simulated and quality parameters (30a-c) for the currently applicable braking characteristic (14) are determined, wherein the braking characteristic (14) is changed between passes (D), after completion of the passes (D) a selected value (W1-3a-c) of a quality parameter (30a-c) is determined and the underlying braking characteristic (14) is provided for storage in the real vehicle (4), wherein the brake arrangement (8) has a friction brake (10) and a recuperation brake (12), wherein the braking characteristic (14) has a limit speed (VG) and a gradient (ST), wherein above the limit speed (VG) the vehicle (4) is braked only by means of the recuperation brake (12) and below the limit speed (VG) as the speed decreases (vIST) the proportion (ARB) the friction brake (10) contributes to the braking increases in accordance with the gradient (ST) and the recuperation brake (12) proportion (ARE) reduces accordingly.

Description

[0001] Brake blend in electric vehicles with recuperation and friction brakes

[0002] The invention relates to a braking arrangement in or of electric vehicles, i.e., vehicles with an electric drive. The invention is based on the assumption that the braking arrangement of such vehicles includes a regenerative brake, i.e., a brake for regenerative braking, and a friction brake.

[0003] A vehicle is known from US 2009 / 0118887 A1. This vehicle comprises a drivetrain system and a friction braking system that transmits traction torque to a drivetrain. The drivetrain system includes a torque machine and an energy storage device connected to the torque machine, wherein the torque machine transmits traction torque to the drivetrain. A method for controlling regenerative braking and friction braking includes monitoring a vehicle operating point, determining a braking torque request, and determining a regenerative braking motor torque ratio based on the vehicle operating point, wherein the regenerative braking motor torque ratio is non-linearly dependent on the vehicle operating point, and applying the friction brake based on the regenerative braking motor torque ratio and the braking torque request.

[0004] The object of the invention is to provide improvements with regard to such a brake arrangement.

[0005] The object is achieved by a method according to patent claim 1. Preferred or advantageous embodiments of the invention and other categories of the invention emerge from the further claims, the following description and the attached figures. The method is in particular a computer-implemented method. The method serves to determine one or more braking characteristics for a braking arrangement of a vehicle. The vehicle is in particular a motor vehicle or automobile, in particular a passenger car. The vehicle contains an electric drive, in particular an electric motor, and is in particular a fully electric vehicle (BEV, Battery Electric Vehicle) or a hybrid electric vehicle ((P)HEV, (Plugin) Hybrid Electric Vehicle), which in addition to the electric drive also has a combustion drive, e.g. a gasoline or diesel engine.

[0006] The braking system includes a friction brake and a regenerative braking system. The latter is part of the electric drive or motor. In other words, the regenerative braking system, such as the motor, can recover electrical energy from the vehicle's deceleration during coasting and feed it back into a traction battery, for example.

[0007] The braking characteristic curve to be determined has a variable limit speed and gradient and, if necessary, other variable parameters. In the vehicle, the braking characteristic curve has the following functionality: If braking is required above the limit speed, the vehicle is braked exclusively using the regenerative braking. Below the limit speed, the proportion (X) of the friction brake in the required total braking power increases with decreasing speed according to the gradient, starting at 0% of the respective braking power up to 100% of the respective braking power. The proportion of the regenerative braking decreases accordingly with decreasing speed (100% - X). Both braking components always add up to 100% of the required braking power. In particular, the following applies: from orBelow a minimum speed, the proportion of regenerative braking is 0%, and the vehicle is decelerated exclusively by the friction brake. The minimum speed can also be zero. "Gradient" here refers specifically to a classic linear gradient of the braking characteristic. However, a more complex braking characteristic can also be present, e.g., a generally rising and possibly also falling curve. The "gradient" then degenerates into a general parameter / set of parameters that describes a corresponding characteristic curve.

[0008] In the method, the following is carried out in a simulation arrangement simulating the vehicle (which is at least partially, in particular completely, computer-implemented):

[0009] First, a speed profile is provided. The speed profile describes the temporal progression of a target vehicle speed over time for a simulated vehicle journey.

[0010] Furthermore, an initial braking characteristic curve is provided, as described above, which has certain (starting) values ​​for the limit speed and the gradient and possibly other parameters, if available.

[0011] The following steps are then carried out for a certain number of passes:

[0012] In each run, the vehicle's journey is simulated based on the speed profile and the current braking characteristic curve. The actual speed at which the vehicle is currently moving is simulated. When the vehicle is simulated to decelerate while driving, only the use of the regenerative braking is simulated if the actual speed is above the limit speed. If the currently simulated actual speed is below the limit speed, the braking is simulated based on the use of the regenerative braking and the friction braking, depending on the current point on the characteristic curve (actual speed and the corresponding distribution of braking between the two brakes). Depending on the gradient, the proportion of friction braking increases and the proportion of regenerative braking decreases as the actual speed decreases.

[0013] In each run, the simulated journey is evaluated during or at the end of the simulation: Based on at least one quality criterion, a respective value of at least one quality parameter is determined for the currently applicable braking characteristic. Specifically, a value is determined for each quality parameter based on a respective quality criterion. The quality parameter describes the quality of the braking characteristic in the vehicle during the simulated journey. The quality criterion is used to determine the value of the quality parameter during the journey based on determined simulation values, for example, actual speed, actual acceleration, actual distance traveled, etc.

[0014] The number of iterations can be specified or determined dynamically during the execution of the procedure based on a termination criterion. For example, a termination criterion checks whether the previous iterations have already delivered the desired values ​​for a quality criterion.

[0015] Between each run, a modified braking characteristic is generated by changing at least the limit speed and / or the gradient (or other parameters, if available) of the braking characteristic. After the corresponding change, a new run is started with the modified braking characteristic, and the journey is simulated again with the same speed profile.

[0016] After all runs have been completed, at least one of the values ​​of one of the quality parameters is determined as a selected value with an associated quality parameter based on an evaluation criterion. For example, this could be a highest or lowest numerical value, or a numerical value that most closely corresponds to a desired specification or a specific target value.

[0017] At least those braking characteristics that formed the basis for the selected values ​​and quality parameters in the simulation, i.e., that led to them, are provided as selected and real braking characteristics. The real braking characteristics are intended or are configured for storage in the real vehicle. Optionally, in addition to the braking characteristics, the values ​​or quality parameters that characterize the corresponding braking characteristics are also provided.

[0018] Simulations can also be performed with different speed profiles.

[0019] The real braking characteristics determined using this method are calculated and numerical data (braking characteristics and optionally associated values / quality parameters). These have a real technical effect. This effect is achieved when the data is used according to its intended technical purpose. This technical purpose here is the use / storage and utilization as real braking characteristics or values ​​of quality parameters in a real braking system of a real vehicle.

[0020] The braking characteristics or values / quality parameters, as data generated by a numerical simulation, are specifically adapted for the intended technical application. They are data, namely braking characteristics, for controlling a technical device, namely the actual braking arrangement in the real vehicle, for use in the real vehicle. There, the actual braking effect is then generated based on the braking characteristic, allowing, for example, a driver to select a desired braking characteristic (e.g., "sporty," "energy-saving," etc.) based on the quality parameters or their values, if several braking characteristics have been stored for selection in the vehicle.

[0021] The invention is based on the practical observation that brake bidding (the transition from braking torque via pure recuperation of the electric motor to pure braking torque via the friction brakes, i.e., disc brakes, drum brakes, etc.) is implemented differently depending on the vehicle manufacturer. It would be desirable to also implement a brake bidding strategy for a multi-disk brake (complementary brake) integrated into the drivetrain.

[0022] According to the invention, a methodology is provided for determining the optimal brake biending strategy (brake characteristic curve) of electric vehicles for two (recuperation and friction brake) and also for more than two brake systems (friction brake with at least two partial brakes, e.g. wheel brake and complementary brake).

[0023] According to the invention, it is possible to evaluate the brake bidding for the friction brake (wheel brake and / or complementary brake) in conjunction with the recuperation of the electric motor. This allows different brake bidding strategies (characteristic curves) to be evaluated with regard to reliability, efficiency, and comfort (quality parameters). This creates the possibility of creating an optimized brake bidding strategy with a friction brake (wheel brake and / or complementary brake) for each recuperation-capable electric vehicle by adapting the vehicle parameters (brake characteristic curve, but also vehicle data underlying the simulation).

[0024] Brake bidding of the friction brake (especially the complementary brake) can be implemented using a simplified ramp control (limit speed and linear gradient) that regulates the intervention of the friction brake / complementary brake during the braking process starting at a specific point in time (below the limit speed) with a specific gradient. The ramp controls the intervention of the friction brake (wheel brake or complementary brake) (ramp function = braking characteristic curve). Using the methodology according to the invention, various brake bidding strategies (different intervention of the friction brake depending on the actual vehicle speed) can be evaluated by adapting the ramp function. By storing the vehicle parameters (used in the simulation), these can be modified to investigate brake bidding strategies with regard to reliability, efficiency, and comfort for various recuperative electric vehicles.

[0025] The invention is based on the following considerations: Depending on the electric vehicle, the efficiency of recuperation is insufficient to generate the necessary (a certain predetermined) braking torque for constant deceleration at (below) a certain speed during braking, which is why the friction brake (including the complementary brake) must intervene. In reality, however, the friction brake in recuperation-capable electric vehicles already intervenes at higher speeds (below the speed limit) to ensure greater reliability and comfort. There are various options for the friction brake to intervene (brake biending strategies).

[0026] The invention, or rather the method / model / simulation system, enables the application of a target speed profile. In the simulation, the following applies: The electric motor is controlled via a simulated PID controller based on the delta between the target and (simulated current) actual speed (actual speed less than target speed: electric motor should drive; actual speed greater than target speed: electric motor should decelerate through recuperation). The PID controller of the friction brake (wheel brake and / or complementary brake) is controlled via the delta between the target and actual acceleration (target acceleration less than actual acceleration: friction brake should engage). In addition, a ramp function (slope of the braking characteristic curve) controls the speed-dependent intervention of the friction brake.This returns the value zero (0%) for higher speeds (greater than the limit speed) so that the entire braking torque is generated through recuperation, and increases with decreasing speed (lower limit speed) to the value 1 (100%) in order to increase the share of the friction brake in the braking process (brake biending) or to take over completely (100%). This ramp can be varied (gradient, limit speed, other parameters) to easily investigate different brake biending strategies. The electric motor and wheel and / or complementary brake supply a drive or braking force, from which, together with the driving resistance forces, the actual acceleration and actual speed can be calculated / simulated as output. The actual acceleration and actual speed are then fed back into the simulated control to calculate the delta between the target and actual state.

[0027] Different brake binding strategies can be evaluated using the criteria reliability, efficiency and comfort (quality criteria).

[0028] "Reliability" describes the deviation of the distance traveled (simulated actual distance) during a simulated braking from the target distance (determined from the target speed), which allows the response and controllability of the blending of the two or three braking systems to be evaluated.

[0029] "Efficiency" is assessed based on total energy consumption (energy absorbed by the traction motor, and possibly also by the combustion engine in (P)HEVs). If energy consumption is higher, less energy can be recuperated with the corresponding brake-bidding strategy.

[0030] "Comfort" is assessed based on the jerk (derivative of the vehicle's acceleration) at the start of the braking. A greater jerk means that passengers feel a sudden force (such as when you begin to brake and are slightly pushed out of your seat), which is something to be avoided.

[0031] This evaluation methodology allows the simple evaluation of brake biending strategies for two or more braking systems using the ramp function in order to set an optimized brake biending strategy for different electric vehicles.

[0032] Model studies show that, for the same vehicle, a greater amount of recuperated energy can be achieved during partial load braking by blending with the complementary brake than with the conventional wheel brake, which can be considered an advantage of the complementary brake.

[0033] In a preferred embodiment, within the method, after completion of the steps described above, at least the provided real braking characteristics, and optionally also at least one of the associated values / quality parameters, are stored in the real vehicle. This results in a concrete technical use, materialization, or implementation of the simulation results / data determined by the method described above.

[0034] In a preferred embodiment, the reliability of the braking characteristic is determined as a quality parameter. This determination is made using the distance traveled by the vehicle while driving as a quality criterion. Alternatively or additionally, the efficiency of the braking characteristic is determined as a quality parameter. This is made using the energy absorbed by the drive system while driving as a quality criterion. Alternatively or additionally, the comfort of the braking characteristic is determined as a quality parameter. This is made using the time derivative of the vehicle's acceleration while driving as a quality criterion. All of this involves simulated data / quantities. Corresponding quality parameters are particularly meaningful for braking characteristic curves. The determination based on the described quality criteria is particularly easy to carry out during the simulation.

[0035] In a preferred variant of this embodiment, a braking distance of the vehicle is selected as the distance traveled as the basis for reliability or its determination in the quality criterion. Reliability is determined based on a deviation of an actual braking distance from a predetermined target braking distance. Reliability or its value thus describes a measure of how well the vehicle can implement a braking request in order to achieve the shortest possible braking distance. The actual / target braking distance is a portion of the actual / target distance covered by the vehicle in the simulation that is attributable to one braking application. In a preferred embodiment, the method is carried out for a vehicle that has a combination brake consisting of a wheel brake and a complementary brake as a friction brake.A complementary brake is one that is not located locally on a single wheel, but acts centrally on at least two wheels in a drivetrain. In particular, a complementary brake is coupled to a motor shaft of the electric traction motor. This thus serves to complement the braking of the traction motor. "Complementary" therefore means that the braking action takes place alongside or in addition to the regenerative braking or regenerative operation of the traction motor.

[0036] Thus, the method can also be used to assess or evaluate braking characteristics for their quality in a vehicle with a combination brake and to find the desired braking characteristics.

[0037] In a preferred variant of this embodiment, the method provides a braking characteristic curve that also includes a particularly variable partial characteristic curve or sub-characteristic curve. The partial characteristic curve describes a distribution of the braking by the friction brake between the wheel brake and the complementary brake. The partial characteristic curve can be fixed, but is also, in particular, variable. The partial characteristic curve can describe a speed-dependent or speed-independent distribution between the wheel brake and the complementary brake.

[0038] In other words, by changing the partial characteristic curve, a change can occur within the friction brake in the interaction between the wheel brake and the complementary brake (if possible). Between two runs in the process, a modified braking characteristic curve is then generated by changing the limit speed and / or the gradient and / or (if changeable) the partial characteristic curve or its parameters. Thus, the influence of different configurations of the combination brake in the friction brake can also be investigated and evaluated in the process. In other words, the "braking characteristic curve" is then, in particular, a set of characteristic curves / characteristic curves. A braking characteristic curve as described above for controlling the components of the friction brake and the regenerative brake is then only one part of the characteristic curve field. The second braking characteristic curve (partial characteristic curve) then serves to distribute the friction braking power between the wheel brake and the complementary brake.In the process, at least one change to the set of characteristics is then made between two runs.

[0039] The partial characteristic curve can also describe a speed-independent division between the wheel brake and the complementary brake.

[0040] In a preferred embodiment, the vehicle's travel is simulated by determining an actual acceleration of the vehicle as the leading actual variable in the process based on contributions from the drive system and the braking system, as well as the vehicle's driving resistance. Contributions from the drive system and the braking system depend on the target speed or the driving profile. The vehicle's driving resistance is at least predetermined, but optionally also dependent on the target speed. "Leading actual variable" means that further actual variables are then derived from the actual acceleration in the simulation. For example, an actual speed of the vehicle is derived by integrating the actual acceleration; an actual distance traveled by the vehicle is derived by integrating the actual speed; and a characteristic value for perceptible jerking (change in acceleration over time) in the vehicle is derived by time-deriving the actual acceleration.

[0041] In particular, a force acting on the vehicle is first determined from the contributions of the drive system, braking arrangement and driving resistances, and the acceleration is then determined based on the evaluation of the force with the vehicle mass (inertia). The actual acceleration can be determined particularly easily and reliably using the method, and further actual values ​​can be generated particularly easily from this. In a preferred embodiment, an actual acceleration is simulated or determined in the method. The time-integrated actual acceleration forms the basis for the actual speed of the braking characteristic. In particular, the actual acceleration is determined as the leading actual variable in the method, as explained above. This makes it particularly easy to determine the actual speed on which the braking characteristic is based.

[0042] In a preferred embodiment, braking by the friction brake in the vehicle is only simulated if a determined actual braking acceleration (its magnitude) is less than a target braking acceleration (its magnitude) derived from the target speed. In other words, braking is only simulated if a negative actual acceleration is present (braking acceleration) and only if this is lower than the target braking acceleration, i.e., without the use of the friction brake, a desired target braking of the vehicle according to the speed profile cannot be achieved or reached. Only when the friction brake is used does it apply according to the braking characteristic curve, as explained above.

[0043] This allows particularly realistic vehicle behavior to be simulated, and the friction brake is not unnecessarily simulated in the vehicle if braking is also possible via the recuperation brake or otherwise (driving resistance / friction).

[0044] The object of the invention is also achieved by a device / system for data processing, comprising means for carrying out (the steps) of the method according to the invention.

[0045] The object of the invention is also achieved by a computer program or computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the invention / the steps of the method according to the invention. The object of the invention is also achieved by a computer-readable medium, in particular a storage medium, comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the invention / the steps of the method according to the invention.

[0046] The device / system for data processing, the computer program or computer program product, the computer-readable medium, in particular storage medium and at least some of their possible embodiments as well as the respective advantages have already been explained in connection with the method according to the invention.

[0047] Further features, effects, and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention and the accompanying figures. Each of these figures shows a schematic diagram:

[0048] Figure 1 shows a simulation arrangement for a vehicle,

[0049] Figure 2 shows the braking characteristic curve from Figure 1 in detail,

[0050] Figure 3 is a flow chart for a method executed in the simulation setup of Figure 1.

[0051] Figure 1 shows a simulation setup 2 in which a vehicle 4 is simulated. The simulation setup is computer-implemented, i.e., implemented as a computer program on a computer (not shown in detail).

[0052] The vehicle 4 has an electric drive system 6, in this case an electric motor. The vehicle 4 also has a braking arrangement 8. The braking arrangement 8 includes a friction brake 10 and a regenerative braking system 12. The regenerative braking system 12 is part of the drive system 6 and is implemented in that the electric motor, when the vehicle 4 is coasting, absorbs the kinetic energy of the vehicle 4 and converts it into electrical energy, thereby actively braking the vehicle 4. The recovered energy is fed back into a drive battery (not shown) of the vehicle 4.

[0053] In the example, vehicle 4 includes a friction brake 10, which is designed as a combination brake 50, which in turn includes a wheel brake 52 and a complementary brake 54. Each wheel brake 52 acts on a single wheel (not shown) of vehicle 4. The complementary brake 54 acts jointly on all wheels of the all-wheel-drive vehicle 4 by braking the entire drive train (not shown) of vehicle 4. Specifically, the complementary brake 54 is a multi-disk brake coupled to a motor shaft (not shown) of the electric motor.

[0054] The brake arrangement 8 has a brake characteristic curve 14, here a ramp function, or the brake characteristic curve 14 is assigned to the brake arrangement 8.

[0055] Figure 2 shows the braking characteristic curve 14 in detail. This representation is purely qualitative. The braking characteristic curve 14 has a limit speed VG and a gradient ST. In the example, the braking characteristic curve 14 is linear. The braking characteristic curve 14 assigns a respective braking torque MB to a current actual speed vIST of the vehicle 4, which is to be generated by the braking arrangement 8 on the vehicle 4.

[0056] In addition to the braking characteristic curve 14, Figure 2 also shows the conditions for an exemplary specific braking torque 20 required across the entire possible actual speed range of the vehicle 4. Also plotted in Figure 2 is the maximum braking torque 22 (recuperation) that is available or can be delivered by the recuperation brake 12 for all speeds vIST. Therefore, the recuperation brake 12 cannot deliver more braking torque than the maximum braking torque 22 in any situation of the vehicle 4. During a braking operation for the vehicle 4, the recuperation brake 12 can therefore also be used alone for actual speeds vIST greater than the limit speed VG in order to fully deliver the required braking torque 20. The use of the friction brake 10 is therefore not necessary here, since the required braking torque 20 is below the maximum possible braking torque 22.

[0057] However, below the limit speed VG, the maximum possible braking torque 22 of the recuperation brake 12 is no longer sufficient to generate the required braking torque 20. The use of the friction brake 10 is therefore necessary if the braking torque 20 is to be achieved.

[0058] According to the braking characteristic curve 14 shown in solid lines, the friction brake 10 is only activated for values ​​of the actual speed vIST below the limit speed VG. Above the limit speed VG, a proportion ARE of 100% of the required braking torque MB is provided by the recuperation brake 12. Below the limit speed VG, this proportion ARE decreases linearly. The example shows a situation with a proportion ARE of 60% at a specific actual speed vIST that is current at a simulation time.

[0059] The remaining 40% of the braking torque MB (100% -ARB) is provided by the friction brake 10 as the ARB component. As the actual speed vIST decreases from the limit speed VG, the ARB component therefore increases linearly from 0% to 100%. The ARE component decreases by the same amount from 100% to 0%. Both components ARB and ARB add up to 100% of the required braking torque MB at any actual speed vIST.

[0060] The simulation arrangement 2 in Figure 1 simulates the vehicle 4 and, thanks to the braking characteristic curve 14, also the braking behavior just described.

[0061] Figure 2 further shows that, in addition to the braking characteristic curve described above, a sub-characteristic curve or partial characteristic curve 56 is assigned to the braking characteristic curve 14. In other words, this is a component of the overall braking characteristic curve 14, which therefore represents a characteristic curve family or set of characteristics. The partial characteristic curve 56 describes how the component ARB of the friction brake 10 determined by the braking characteristic curve 14 is or should be divided between a component ARA of the wheel brake 52 and a component AKO of the complementary brake 54.

[0062] Both components, ARA and AKO, add up to 100%. This 100% represents the ARB share (of, for example, 40%) of friction brake 10 in the total braking torque MB. If, in this example, the ARA share is 25% and AKO is therefore 75%, wheel brake 52 contributes a total of 10%, complementary brake 54 contributes 30%, and the regenerative brake contributes 60% of the braking torque MB.

[0063] Figure 3 explains a computer-implemented method for determining one or more braking characteristic curves 14 for the vehicle 4. The method is carried out in or with the aid of the simulation arrangement 2.

[0064] In a first step S1, a speed profile 24 for a journey 26 of the vehicle 4 is provided as input for the simulation. The speed profile 24 describes the temporal progression of a target speed vSOLL of the vehicle 4 over time t. Furthermore, an initial braking characteristic curve 14, as shown in solid lines in Figure 2, is provided.

[0065] Steps 2 and 3 are now carried out for a specific number of passes D, which are indicated in the figure by an arrow. In step S2, the journey 26 of the vehicle 4 is simulated based on the speed profile 24 and the currently valid braking characteristic curves 14. In step S3, for this journey 26, a respective value Wa1, Wb1, Wc1 ("1" since this is the first pass D) of a respective quality parameter 30a-c (simulation output) for the currently valid braking characteristic curve 14 is determined based on a respective quality criterion 28a-c. The values ​​W for the simulated journey 26 of the vehicle 4 are numerically determined or generated. Since the simulation is based on the current braking characteristic curve 14, the currently determined values ​​W are assigned to this braking characteristic curve 14. In a step S4, a check is then carried out to determine whether a specific number of passes D has been reached. In the example, this is a fixed number of three.Alternatively, it could be checked whether a previously defined termination criterion for the runs D was reached, e.g. a certain value W of a certain quality parameter 30a-c was reached, which will not be explained in detail here.

[0066] Since not all passes D have been completed in this case (indicated by a cross in Figure 3), a modified braking characteristic curve 14 is generated or the braking characteristic curve 14 is modified in a step S5 between two passes D (first and second). In this case, the limit speed VG is first changed to VG' and the gradient ST to ST', which is indicated by dashed lines in Figure 2. Steps S2 to S4 are then repeated in the second pass D, and values ​​W2a-c are determined.

[0067] In a further step S5, the braking characteristic curve 14 is then modified again by changing the partial characteristic curve 56 as indicated by the dashed line. Steps S2 to S4 are then repeated in the third pass D, and values ​​W3a-c are determined.

[0068] Now, in step S4, it is determined that all three passes D have been completed (indicated by a check mark in Figure 3). Then, in a step S6, based on an evaluation criterion 32, at least one of the values ​​W of one of the quality parameters 30a-c is determined as the selected value (the quality parameter 30a-c associated with the selected value W is thus also selected).

[0069] In a step S7, the underlying braking characteristics 14 assigned to the selected values ​​W (and selected quality parameters 30a-c) are provided as selected braking characteristics 14' for storage in the real vehicle 4. Optionally, the associated values ​​W are also provided together with these as selected values ​​W (and the quality parameters 30a-c') for storage. The method can end here. In a variant of the method, subsequently or additionally in a step S8, the braking characteristics 14' (associated values ​​W / quality parameters 30') provided in step S7 are stored as real braking characteristics 14, values ​​W and quality parameters 30 in the real vehicle 4. From then on, the vehicle 4 can actually use the real braking characteristics 14, values ​​W / quality parameters 30' in a real journey 26.

[0070] In detail, the procedure in simulation setup 2 is as follows:

[0071] At discrete intervals of time t, a current value of the target speed vSOLL is compared with the currently applicable actual speed vIST. The respective speed deviation dv = vSOLL - vIST is fed to the drive 6. This supplies one of the contributions 40 to a force F acting on the vehicle 4. Further contributions 40 to the force F originate from the simulated braking arrangement 8 and simulated driving resistances 42 of the vehicle 4 while driving 26. The resulting force F is offset against the vehicle mass mF and in this way an actual acceleration alST for the motor vehicle 4 is determined. This is determined here as the leading actual variable 44. This means that further actual values ​​are derived from it. In the simulation, the actual speed vIST is determined from the actual acceleration alST by time integration, and the time integration of this speed in turn produces an actual distance sIST covered by the vehicle 4.From the target speed vSOLL, a target distance sSOLL is determined by time integration, which the vehicle 4 should cover during the journey 26 based on the ideally implemented speed profile 24. A target acceleration aSOLL is determined by time differentiation. An acceleration deviation da = aSOLL - alST is determined from the target acceleration aSOLL and the actual acceleration alST. The braking characteristic curve 14 is based on the determined actual speed vIST as the time-integrated actual acceleration alST. Only if deceleration of the vehicle is desired (aSOLL less than zero) is the braking characteristic curve 14 used to decide how the required braking torque MB is distributed between the recuperation brake 12 and the friction brake 10 (therein between the wheel brake 52 and the complementary brake 54). This results in the corresponding contributions 40 of the respective brakes.Braking by the friction brake 10 is therefore only initiated if the determined actual braking acceleration alST (= actual acceleration alST, if negative, its amounts are considered) is smaller than the target braking acceleration aSOLL (= target acceleration aSOLL, if negative, its amounts) derived from the target speed vSOLL.

[0072] In the example, a reliability of the braking characteristics 14 is determined specifically as quality parameter 30a. The associated quality criterion 28a consists in comparing the actual braking distance bIST actually traveled for a braking application as the part of the actual distance alST attributable to the braking application with the corresponding target braking distance bSOLL (part of the braking distance sSOLL attributable to the braking application) (deviation ds) and evaluating it. This results in the values ​​W1 -3a. The efficiency of the vehicle 4 is determined as quality parameter 30b. Quality criterion 28b here is the determination of the total energy E that the drive system 6 absorbs during the entire simulated journey 26. This leads to values ​​W1 -3b of the quality parameter 30b. The comfort of the braking characteristics 14 is determined as quality parameter 30c.Quality criterion 28c is the time derivative of the actual acceleration alST, which allows for the detection of corresponding jerking (the steepness of the change in the actual acceleration alST over time t) when initiating or ending braking operations. This determines the corresponding values ​​W1-3c of quality parameter 30c.

[0073] List of reference symbols

[0074] 2 Simulation setup

[0075] 4 vehicle

[0076] 6 Drive

[0077] 8 Brake arrangement

[0078] 10 Friction brake

[0079] 12 Regenerative braking

[0080] 14 Braking characteristic curve

[0081] 20 braking torque (required).

[0082] 22 Braking torque (maximum, recuperation)

[0083] 24 speed profile

[0084] 26 ride

[0085] 28a-c Quality criterion

[0086] 30a-c Quality parameters

[0087] 32 Evaluation criteria

[0088] 40 posts

[0089] 42 Driving resistances

[0090] 44 current size (leading)

[0091] 50 combination brake

[0092] 52 Wheel brake

[0093] 54 Complementary brake

[0094] 56 Partial characteristic curve

[0095] VG speed limit

[0096] ST gradient

[0097] VIST Actual speed

[0098] MB braking torque

[0099] ARE share (regenerative braking)

[0100] ARB share (friction brake)

[0101] S1 -8 Step VSOLL Target speed t Time

[0102] W1-3a-c Value dv Speed ​​deviation F Force mF Vehicle mass alST Actual acceleration sIST Actual distance sSOLL Target distance aSOLL Target acceleration blST Actual braking distance bSOLL Target braking distance

[0103] E Energy

[0104] ARA share wheel brake

[0105] AKO share of complementary brake

[0106] D Passage

Claims

Patent claims 1 . Method for determining a braking characteristic curve (14) for a braking arrangement (8) of a vehicle (4) with an electric drive (6), wherein the braking arrangement (8) has a friction brake (10) and a recuperation brake (12) of the drive (6), wherein the braking characteristic curve (14) has a limit speed (VG) and a gradient (ST), wherein the vehicle (4) is braked above the limit speed (VG) exclusively with the recuperation brake (12) and below the limit speed (VG) with decreasing speed the proportion (ARB) of the friction brake in the braking increases according to the gradient (ST) and the proportion (ARE) of the recuperation brake decreases accordingly, in which - in a simulation arrangement (2) simulating the vehicle (4): - a speed profile (24) of a target speed (VSOLL) over time (t) is provided for a simulated journey (26) of the vehicle (4), - an initial braking characteristic curve (14) is provided, - for a certain number of passes (D): - the journey (26) of the vehicle (4) is simulated using the speed profile (24) and the braking characteristic curve (14), - for the journey (26) a respective value (W1-3a-c) of at least one quality parameter (30a-c) for the currently applicable braking characteristic curve (14) is determined on the basis of a quality criterion (28a-c), - whereby between two passes (D) a modified braking characteristic (14) is generated by changing the limit speed (VG) and / or the gradient (ST), - after completion of all runs (D), at least one of the values (W1 -3a-c) of one of the quality parameters (30a-c) is determined as a selected value (W1 -3a-c) and quality parameter (30a-c) based on an evaluation criterion (32), - at least the braking characteristics (14) underlying the selected values (W1 -3a-c) and quality parameters (30a-c) are provided as a real braking characteristic (14) for storage in the real vehicle (4).

2. Method according to claim 1, characterized in that at least the provided real braking characteristics (14) are stored in the real vehicle (4).

3. Method according to one of the preceding claims, characterized in that as quality parameters (30a-c) - a reliability of the braking characteristic curve (14) based on the distance (sIST) covered by the vehicle (4) during the journey (26) as a quality criterion (28a-c), and / or - an efficiency of the braking characteristic (14) based on the energy (E) absorbed by the drive (6) during travel (26) as a quality criterion (28a-c), and / or - a comfort of the braking characteristic curve (14) is determined based on the time derivative of the acceleration (alST) of the vehicle (4) during travel (26) as a quality criterion (28a-c).

4. Method according to claim 3, characterized in that a braking distance of the vehicle (4) is selected as the travel distance (sIST) on which the reliability is based, and the reliability is determined on the basis of a deviation of an actual braking distance (bIST) from a predetermined target braking distance (bSOLL).

5. Method according to one of the preceding claims, characterized in that it is carried out for a vehicle (4) which has a combination brake (50) comprising a wheel brake (52) and a complementary brake (54) as the friction brake (10).

6. Method according to claim 5, characterized in that - a braking characteristic curve (14) is provided which also contains a partial characteristic curve (56) which describes the proportions of the braking by the friction brake (10) attributable to the proportions (ARA) of the wheel brake (52) and the proportions (AKO) of the complementary brake (54), - between two passes (D) a modified braking characteristic curve (14) is generated by changing the limit speed (VG) and / or the gradient (ST) and / or the partial characteristic curve (56).

7. Method according to one of the preceding claims, characterized in that the journey (26) of the vehicle (4) is simulated in that - based on contributions (40) of the drive (6), the brake arrangement (8) and an at least predetermined driving resistance (42) of the vehicle (4) which are dependent on the target speed (VSOLL) - an actual acceleration (alST) of the vehicle (4) is determined as the leading actual value (44).

8. Method according to one of the preceding claims, characterized in that - an actual acceleration (alST) is simulated, and - the time-integrated actual acceleration (alST) is used as the actual speed (vIST) of the braking characteristic curve (14).

9. Method according to one of the preceding claims, characterized in that braking by the friction brake (10) is only simulated if a determined actual braking acceleration (alST) is smaller than a target braking acceleration (aSOLL) derived from the target speed (VSOLL).

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