Method for controlling a generator braking torque of an electric drive for a vehicle, in particular a utility vehicle, computer program and / or computer-readable medium, control device, electric drive or electric braking system and vehicle, in particular utility vehicle

Abstract

The invention relates to a method (100) for controlling a generator braking torque (25) of an electric drive (21) for a vehicle (300a), in particular a utility vehicle (300b), wherein the method (100) includes: detecting (110) a braking requirement (55) for braking the vehicle (300a), in particular the utility vehicle (300b), using a target braking torque (56); and controlling (120) the generator braking torque (25) depending on the target braking torque (56) and on a trigger condition (60), wherein control (120) is carried out within a plurality of cycles (Z), wherein a generator braking torque (25) provided by the electric drive (21) is changed (26) within a cycle (Z), wherein each of the cycles (Z) comprises a first partial cycle (SZ1) and a second partial cycle (SZ2), and wherein, in the first partial cycle (SZ1), the change (26) comprises reducing (27) the generator braking torque (25) and, in the second partial cycle (SZ2), the change (26) comprises increasing (28) the generator braking torque (25).

Description

[0001] Method for controlling a generator braking torque of an electric drive for a vehicle, in particular a commercial vehicle, computer program and / or computer-readable medium, control unit, electric drive or electric braking system and vehicle, in particular a commercial vehicle

[0002] The invention relates to a method for regulating a generator braking torque of an electric drive for a vehicle, in particular a commercial vehicle. The invention also relates to a computer program and / or computer-readable medium, a control unit for a vehicle, in particular a commercial vehicle, an electric drive or an electric braking system for a vehicle, in particular a commercial vehicle, and a vehicle, in particular a commercial vehicle.

[0003] The invention relates in particular to the field of vehicles, in particular commercial vehicles, including trailers, with an electronically controlled braking system (electronic brake system, EBS, or trailer electronic brake system, TEBS) and at least one axle electrically driven by an electric drive (eDrive) via a central drive and / or a wheel-individual drive, wherein the electric drive is configured for regenerative braking. In other words, the electric drive can be operated as a wear-free continuous brake and thereby enables the recovery of braking energy in the form of electrical energy (recuperation) during deceleration. A generator braking torque has a decelerating effect on one or more wheels of the vehicle.

[0004] DE 10 2019 135 087 A1 discloses a method for slip control of a vehicle wheel driven by an electric drive, comprising at least the following steps: controlling the electric drive of the vehicle wheel with an actual drive torque in a torque control in a torque control step, determining a wheel speed and a wheel slip of the vehicle wheel and evaluating the wheel slip using an instability criterion to determine whether instability exists, if instability is detected, direct or indirect transition to slip control of the wheel slip to a target slip by controlling the electric drive, determining whether an end criterion for ending the slip control is met, if the end criterion is met, returning to the torque control in the torque control step. In this case, drive control can be combined with ABS control. In this way, electrical braking orRecuperation can be superimposed with a subordinate friction braking with a constant torque. Thus, if a vehicle wheel is prone to locking, friction braking via the wheel brake can be controlled by means of an ABS control process via the central brake control unit (ABS control unit), with the wheel hub motor simultaneously operating, particularly for recuperation.

[0005] DE 10 2012 217 679 A1 discloses a slip-controlled braking system for an electrically driven motor vehicle, comprising friction brakes on the wheels of at least one axle, which are controlled by a friction brake control device, at least one electric machine which is connected to at least one wheel and is controlled by an electric drive control device, means for detecting a deceleration request, in particular a brake pedal with a pedal angle sensor, a wheel slip control device and a torque distribution device.The means or means for detecting a deceleration request is or are connected to the wheel slip control device, which specifies target braking torques for each wheel in accordance with the deceleration request, wherein the wheel slip control device is connected to a torque distribution device which is connected to the friction brake control device and the electric drive control device and specifies friction braking requests to the wheel slip control device in accordance with the target braking torques.

[0006] Friction brake control unit and generator braking requests are specified to the electric drive control unit. Further information relating to driving dynamics is transmitted by a condition observer to the wheel slip control unit. The electric drive control unit sends the currently applied generator braking torque(s) and / or the maximum generable generator braking torque(s) to the torque distribution unit, and the distribution between friction braking requests and generator braking requests is carried out taking into account the currently applied and / or maximum generable generator braking torque(s). For high recuperation of braking energy and a related range increase of an electrically powered vehicle, the electric drive must be able to provide the highest possible generator braking torque with corresponding slip values. The friction brake can also be active during particularly heavy braking.If the slip becomes too high during braking, the braking torque must be limited to avoid locking.

[0007] However, there is the problem that slip depends on the axle load and the road surface or on the coefficient of friction between the road surface and a wheel of the vehicle. Dynamic changes in axle load lead to a change in slip that needs to be regulated for a given torque. If the road surface changes, the p-slip curve (see Figure 1 ) changes, possibly resulting in a changed maximum adhesion at which maximum power transmission in the longitudinal direction is possible. This raises the question of which fixed and / or operationally adjusted setpoint the slip should be limited to and / or regulated. If the slip is too high and therefore too close to the maximum adhesion, the tire no longer provides any or insufficient lateral guidance and the vehicle becomes unstable.In the unstable region of the p-slip curve, i.e., at slip values ​​greater than the slip value at the maximum adhesion, self-reinforcing effects also occur, as the potential power transmission decreases again with increasing slip. If the slip is too low, the adhesion potential, and thus efficiency and braking distance, remain unused.

[0008] With purely slip-based control, there is also the problem that the vehicle reference speed must be known with sufficient accuracy to calculate the individual wheel slip. Otherwise, for example, in a braking situation, either braking distance is wasted if the calculated vehicle reference speed is too high, or the vehicle becomes unstable if the calculated vehicle reference speed is too low. In the drive case, as well as in the braking case when the electric drive is used alone for regenerative braking, the vehicle reference speed is typically known via the freely rotating front axle. However, with simultaneous braking intervention on all axles, especially when no ABS control is active, the vehicle reference speed can only be estimated.

[0009] When braking, a control principle is well known, particularly for pneumatic anti-lock braking systems (ABS). ABS essentially uses the change in wheel speed or wheel acceleration over time to detect when a wheel has locked and initiate control. This makes ABS robust with respect to the reference speed, as wheel speed / acceleration is independent of the reference speed. When control begins according to ABS, braking force is initially reduced via a friction brake, so that a locked wheel starts moving again without braking, resulting in positive wheel acceleration. Braking force is then built up again until a tendency to lock is again detected by wheel deceleration. This makes ABS likewise robust with respect to varying surfaces, as braking force is built up until the tendency to lock is reached.In other words, the vehicle "rolls back and forth" within an interval of slip values ​​that are smaller than the slip value at maximum adhesion. At the same time, lateral control and steerability are maintained during the unbraked rolling phases. The disadvantage is that at times no braking force is applied, resulting in wasted braking distance.

[0010] The object of the invention is to enrich the state of the art and enable improved control for braking a vehicle, in particular a commercial vehicle. One embodiment of the invention can achieve the object of achieving braking control that is robust against possible errors in the reference speed and changing road surfaces, and opens up the possibility of generating a continuous and, if possible, continuous braking torque.

[0011] This object is achieved by a method according to claim 1 and the subject matter according to the further independent claims. The subclaims specify preferred developments of the invention.

[0012] According to the invention, a method for controlling a

[0013] Generator braking torque of an electric drive for a vehicle, in particular a commercial vehicle. The method comprises: detecting a braking request for braking the vehicle, in particular a commercial vehicle, with a target braking torque; regulating the generator braking torque as a function of the target braking torque and a trigger condition, wherein the regulating takes place within a plurality of cycles, wherein a generator braking torque provided by the electric drive is changed within a cycle, wherein each of the cycles comprises a first sub-cycle and a second sub-cycle, and wherein in the first sub-cycle the change comprises a reduction of the generator braking torque and in the second sub-cycle the change comprises an increase of the generator braking torque.

[0014] The vehicle, in particular a commercial vehicle, is referred to below as the "vehicle." The vehicle includes wheels that can be braked by regenerative braking with the generator braking torque provided by the electric drive. A driver and / or an automated driving function can provide or trigger a braking request that causes the vehicle, an axle of the vehicle, and / or one of the wheels to be braked with the desired braking torque by the electric drive and / or a friction brake device.

[0015] The generator braking torque is controlled depending on the target braking torque and a trigger condition, and within a plurality of cycles. The trigger condition is a condition that initiates the control. If the trigger condition is met, the control takes place. If, however, the trigger condition is not met, the control can be omitted. A cycle is a finite time interval other than zero, in which the control takes place according to a predetermined pattern or scheme. Within a cycle, the generator braking torque provided by the electric drive is changed systematically and in a rule-based manner. It was recognized that the total braking torque can be controlled effectively and reliably by controlling the generator braking torque.Several cycles are run to control the generator braking torque, allowing for comparatively short cycles while utilizing the comparatively high control dynamics of the electric drive compared to other braking systems. The use of the electric drive to provide the generator braking torque provides a control system comparable to ABS. Due to the dynamics and control quality of the electric drive, this already leads to improved controllability of the generator braking torque compared to ABS, thus decelerating the vehicle.

[0016] Each of the cycles comprises a first sub-cycle and a second sub-cycle. In principle, each cycle can thus be considered as consisting of two sub-intervals. In the first sub-cycle, the change involves reducing the generator braking torque, and in the second sub-cycle, the change involves increasing the generator braking torque. For example, by reducing the generator braking torque, a slip that meets the trigger condition is reduced by reducing the generator braking torque in the first sub-cycle, only to then be increased again in the second sub-cycle until the cycle ends.

[0017] In other words, a targeted temporal modulation, for example a ramp-like build-up and release, of the braking torque generated by the electric drive is used to adapt the control system to the road surface or substructure and to achieve sufficient independence from or robustness with respect to the reference speed. Due to the good response time of the electric drive, the control / modulation cycles can be much shorter than in conventional pneumatic ABS. In principle, this makes it possible to generate a braking torque that is ideally permanent. The braking distance and braking performance are improved while maintaining stability. Regenerative braking is possible. Self-adaptation to the road surface can occur, as the braked wheel or axle is specifically overbraked until the tendency to lock is detected. Ideally, the maximum adhesion is reached and detected.The total braking torque can be adjusted by changing the generator braking torque.

[0018] Preferably, the generator braking torque is changed in such a way that the generator braking torque does not change sign within a cycle. This maintains a residual generator braking torque and prevents tooth flank changes in the electric drive's gearbox. This protects the electric drive's mechanical components and increases its service life.

[0019] Preferably, a new cycle begins when the trigger condition is met. This means that when the trigger condition is met again, for example, when the generator braking torque increases or when the road surface friction coefficient changes, the generator braking torque is immediately reduced. For this purpose, the previous cycle can be aborted in favor of a new cycle. This is particularly advantageous when road surface characteristics change and / or the driving situation changes. The new cycle can follow the previous cycle immediately, i.e., without a time lag, to enable rapid control.

[0020] Preferably, the change occurs according to a variable rate of change. The rate of change can depend on the target braking torque and on variables related to the trigger condition. This allows for situation-appropriate control.

[0021] Preferably, the rate of change depends on a road surface characteristic and / or driving condition. For example, when driving on a relatively smooth road surface, the generator braking torque can be reduced relatively quickly, while when driving on a less smooth road surface, the generator braking torque can be reduced more slowly. This allows for situation-appropriate control. The rate of change can be constant or variable within a sub-cycle.

[0022] Preferably, the rate of change is limited such that the trigger condition is not met within a predetermined cycle section. The cycle section is a time interval within a cycle, in particular within the second sub-cycle. This enables particularly reliable and safe deceleration. The cycle section can be determined by inertial properties and / or kinematic properties of the electric drive. Preferably, within one of the cycles, the reduction occurs at a first rate of change and the increase occurs at a second rate of change, wherein the first rate of change differs in magnitude from the second rate of change. The different rates of change enable flexible changes within a cycle. This allows a given difference in the generator braking torque to occur at different time intervals.Preferably, the first rate of change is smaller in magnitude than the second rate of change, so that, for example, when the trigger condition is met, the generator braking torque can be reduced comparatively slowly, thus avoiding an excessive reduction in the generator braking torque. This can prevent braking potential from going unused.

[0023] Preferably, a braking torque change affecting the generator braking torque occurs within one of the cycles, and the control takes place taking into account a previous braking torque change from a previous cycle. The braking torque change can be defined as a difference between the generator braking torque at the beginning of the cycle and a minimum generator braking torque within the cycle. The generator braking torque is controlled as a function of the braking torque change from the previous cycle. For example, rates of change for changing the generator braking torque in the current cycle can be based on the rates of change from the previous cycle. This allows a suitable estimate of parameters for controlling the generator braking torque to be achieved for the current cycle.

[0024] Preferably, the braking torque change is selected taking into account a first threshold condition relating to the previous braking torque change. The first threshold condition can be dependent on a current generator braking torque and / or a control capacity of the electric drive. If the threshold condition is met, for example if the braking torque change is less than a predetermined threshold, control is carried out in such a way that the generator torque is reduced compared to the previous cycle, since the road surface has less grip and less torque can be released. If the threshold condition is not met, for example if the braking torque change is greater than a predetermined threshold, control is carried out in such a way that the generator torque is increased compared to the previous cycle, since the road surface has better grip and more torque can be released.

[0025] Preferably, the trigger condition depends on a wheel acceleration or the wheel acceleration itself. This allows for effective detection of a wheel lock tendency. Alternatively or additionally, the trigger condition depends on a temporal change in wheel acceleration, slip, a total braking torque, and / or a temporal change in the total braking torque.

[0026] The method preferably further comprises the step of regulating a friction braking torque provided by a friction braking system as a function of a second threshold condition relating to the generator braking torque. The second threshold condition can be dependent on the control capacity of the electric drive. If the second threshold condition is met, i.e. if the generator braking torque is, for example, less than a predetermined threshold, the friction braking torque is reduced so that more braking torque can again be applied by the electric drive. Otherwise, if the second threshold condition is not met, i.e. if the generator braking torque is, for example, greater than the predetermined threshold and / or a further threshold, the friction braking torque is increased so that less braking torque needs to be applied by the electric drive and the control capacity thus increases again.

[0027] Preferably, slip-based control of the generator braking torque is applied between two cycles. It is possible to alternate between the control described above and continuous slip-based control. After one or more modulated overbrakes have been applied and it has been ensured that the optimum adhesion has been achieved in the cycles, continuous slip-based control can then be applied with knowledge of the maximum transferable torque. In this case, the cycles can be understood as test braking operations, which determine how far the (continuously) applied torque is from the maximum adhesion limit, or how far this limit is utilized, and what lateral guidance reserve currently exists.

[0028] Preferably, when the trigger condition is met, the generator braking torque is reduced to a predetermined proportion of the generator braking torque when the trigger condition is met. Thus, the generator braking torque at the time the trigger condition is met is used as a reference for a generator braking torque that is initially set by reducing it. For example, the generator braking torque can be reduced to 20% when the trigger condition is met, effectively reducing the braking torque to such an extent that safe braking is possible.

[0029] According to a further aspect of the invention, a computer program and / or computer-readable medium is provided. The computer program and / or computer-readable medium comprises instructions that, when executed by a computer, cause the computer to perform the method described here and / or the steps of the method described here. The computer program and / or computer-readable medium may comprise instructions to perform steps of the method described as optional and / or advantageous in order to achieve a corresponding technical effect.

[0030] According to a further aspect of the invention, a control unit for a vehicle, in particular a commercial vehicle, is provided. The control unit is configured to carry out the method described here. The control unit can be configured to carry out steps of the method described as optional and / or advantageous in order to achieve a corresponding technical effect.

[0031] According to a further aspect of the invention, an electric drive or an electric braking system is provided for a vehicle, in particular a commercial vehicle. The electric drive or braking system has the control unit described here. The control unit is exclusively comprised by the electric drive or braking system. Due to the control, no communication between the electric drive and the braking system is necessary. The electric drive or braking system can act as a master and initiate the control based on received information.

[0032] According to a further aspect of the invention, a vehicle, in particular a commercial vehicle, is provided. The vehicle has the control unit described here. The vehicle and / or the control unit can be configured to perform steps of the method described as optional and / or advantageous in order to achieve a corresponding technical effect.

[0033] Further advantages and features of the invention as well as its technical effects emerge from the figures and the description of the preferred embodiments shown in the figures.

[0034] Fig. 1 is a schematic representation of a p-slip curve;

[0035] Fig. 2 is a schematic representation of an overview of a vehicle, in particular a commercial vehicle, according to an embodiment of the invention;

[0036] Fig. 3 is a schematic representation of a flow chart of a method according to an embodiment of the invention; and

[0037] Fig. 4 is a schematic representation of a braking torque curve with a braking torque as a function of time.

[0038] Figure 1 shows a schematic representation of a p-slip curve 400. The coefficient of friction p is plotted as a function of slip S. The p-slip curve 400 shows two different curves 401, 402 for different surfaces. Figure 1 describes problems with slip-based control.

[0039] When a road surface changes, the p-slip curve 400 changes with a possibly changed adhesion maximum, 403, 404, at which maximum force transmission between a wheel 210 and a road surface 215 in the longitudinal direction is possible. Curve 401, shown with a solid line, is representative of a road surface 215 with higher friction than curve 402, shown with a dashed line. Accordingly, the adhesion maximum 403 of curve 401 is greater than the adhesion maximum 404 of curve 402. To the right of the adhesion maxima 403, 404, i.e., at higher slip S, there is an unstable region, as indicated by the solid-line arrow.

[0040] In curve 401, the target slip SS is too high and thus too close to the maximum adhesion 403; there is no or insufficient lateral guidance of a tire, and the vehicle 300a, 300b becomes unstable. In curve 402, the target slip SS is too low; adhesion potential, and thus efficiency and braking distance, remain unused.

[0041] Figure 2 shows a schematic representation of an overview of a vehicle 300a, in particular commercial vehicle 300b, according to an embodiment of the invention.

[0042] The vehicle 300a, in particular the commercial vehicle 300b, is referred to below as the vehicle 300a, 300b. The vehicle 300a, 300b is a land vehicle and, for example, a truck, a bus, a trailer, and / or a multi-unit vehicle.

[0043] The vehicle 300a, 300b is configured to perform the method 100 described with reference to Figures 3 and 4. For this purpose, the vehicle 300a, 300b, in the embodiment shown in Figure 2, has an electric drive 21, a control unit 250, and a friction brake system 40.

[0044] The control unit 250 is configured to receive and evaluate a braking request 55 for braking the vehicle 300a, 300b with a target braking torque 56. The braking request 55 can comprise a signal triggered, for example, by a pedal actuation and / or an actuation of a retarder lever by a driver of the vehicle 300a, 300b and / or by an automated driving function, which is transmitted, for example, via a vehicle bus (not shown) to the control unit 250. The control unit 250 comprises a processor 251 and a memory 252 for processing and storing information. The control unit 250 is thus configured to carry out the steps of the method 100 described in Figures 3 and 4. In particular, a threshold condition 59, a trigger condition 60, and a second threshold condition 42 are stored in the memory 252.

[0045] In the embodiment shown in Figure 2, the control unit 250 is connected to the electric drive 21 and the friction brake system 40 in order to exchange control information 150 with the electric drive 21 and the friction brake system 40, in particular to receive measured values ​​and to send control signals.

[0046] The electric drive 21 is configured for regenerative braking NB. The electric drive 21 can generate a generator braking torque 25, which can lead to a deceleration of the vehicle 300a, 300b. The electric drive 21 can effect a change 26, in particular a reduction 27 and an increase 28, of the generator braking torque 25.

[0047] The friction brake system 40 is an electric brake system 43 or an electronically controlled brake system and can apply a friction brake torque 41. In an embodiment not shown, the friction brake system 40 is a pneumatic and / or hydraulic brake system.

[0048] The vehicle 300a, 300b according to Figure 2 has a plurality of wheels 210. The wheels 210 are arranged on a roadway 215. A total braking torque 320, mediated by the roadway 215 and effected by the electric drive 21 and the friction braking system 40, can act on each of the wheels 210. The total braking torque 320 is the sum of the generator braking torque 25 and the friction braking torque 41.

[0049] The electric drive 21 can be configured as a so-called central drive to apply the generator braking torque 320 to a plurality of wheels 210 of an axle (not shown). In the embodiment shown in Figure 2, the electric drive 21 is configured to apply the generator braking torque 320 to each individual wheel, whereby Figure 2 only schematically illustrates the braking of a wheel 210. The dynamics of each of the wheels 210 can be characterized by a measurable wheel acceleration 310 and a temporal change in the wheel acceleration 311. The wheel acceleration 310 and / or the temporal change in the wheel acceleration 311 can be detected by measured values ​​from a wheel speed sensor (not shown) and / or by control information 150 of the electric drive 21. The effective total braking torque 320 creates a slip 312 between the wheel 210 and the road surface 215. The slip 312 can be determined, for example, by wheel speeds.

[0050] The electric drive 21 is configured to perform the method for estimating the coefficient of friction described in German patent application 10 2022 114 084.9, filed June 3, 2022, which was not yet published at the time of filing. For this purpose, the electric drive is configured to apply a temporally predetermined excitation torque to the wheel 210, wherein the excitation torque is applied to the wheel 210 periodically at a frequency; and to determine a slip change as a function of the excitation torque, wherein the slip change is determined taking the frequency into account.

[0051] Figure 3 shows a schematic representation of a flow chart of a method 100 according to an embodiment of the invention. The method 100 is a method 100 for regulating a generator braking torque 25 of an electric drive 21 for a vehicle 300a, 300b. Such a vehicle 300a, 300b is shown in Figure 2. Figure 3 will be described with reference to Figure 2.

[0052] The method 100 includes detecting 110 a braking request 55 for braking the vehicle 300a, 300b with a target braking torque 56. The target braking torque 56 is a target value for the total braking torque 320. However, the applicable total braking torque 320 may be limited, for example, due to a high slip S and / or a low coefficient of friction p (see Figure 1), which may result in braking with the target braking torque 56 not being possible. Braking then occurs with a total braking torque 320 that is less than the target braking torque 56. For this purpose, the generator braking torque 25 is regulated 120.

[0053] The regulation 120 of the generator braking torque 25 takes place as a function of the target braking torque 56 and a trigger condition 60, wherein the regulation 120 takes place within a plurality of cycles Z, see Figure 4. Within a cycle Z, a change 26 of the generator braking torque 25 provided by the electric drive 21 takes place, wherein each of the cycles Z comprises a first sub-cycle SZ1 and a second sub-cycle SZ2. In the first sub-cycle SZ1, the change 26 comprises a reduction 27 of the generator braking torque 25, and in the second sub-cycle SZ2, the change 26 comprises an increase 28 of the generator braking torque 25. Optionally, the cycle has a third sub-cycle (not shown), wherein a constant generator braking torque 25 is provided in the third sub-cycle. Thus, no change in the generator braking torque 25 takes place in the third sub-cycle. The regulation 120 is described in more detail with reference to Figure 4.

[0054] To control 120 the generator braking torque 25, the control unit 250 sends corresponding control information 150 to the electric drive 21.

[0055] The method 100 according to Figure 3 further comprises the step of controlling 130 a friction braking torque 41 provided by a friction braking system 40 as a function of a second threshold condition 42 relating to the generator braking torque 25. The second threshold condition 42 depends on the control capacity of the electric drive 21. If the second threshold condition 42 is met, i.e., if the generator braking torque 25 is less than a predetermined threshold, the friction braking torque 41 is reduced. Otherwise, if the second threshold condition 42 is not met, i.e., if the generator braking torque 25 is greater than the predetermined threshold and / or another threshold, for example, the friction braking torque 41 is increased. To control 120 the friction braking torque 41, the control unit 250 sends corresponding control information 150 to the friction braking system 40.Figure 4 shows a schematic representation of braking torque curves 450 with a braking torque M as a function of time t. A curve 451, represented by a dotted line, shows the dependence of the friction braking torque 41 on time t. A curve 452, represented by a solid line, shows the total braking torque 320 as the sum of the friction braking torque 41 and the generator braking torque 25 as a function of time t. The generator braking torque 25 as such is not represented in Figure 4. A curve 453, represented by a dashed line, shows a maximum total braking torque 322 as the sum of the friction braking torque 41 and the maximum available generator braking torque 25. Figure 4 serves to further describe the method 100 according to Figure 4.

[0056] The braking torque curves 450 shown as an example in Figure 4 are characterized by four ordered times t1, t2, t3, t4, more precisely a first time t1, a second time t2, a third time t3 and a fourth time t4.

[0057] Initially and until the first time t1, the control of the braking torque M is passive, ie the electric drive 21 applies a constant generator braking torque 25 to a wheel 210 and the friction braking torque 41 behaves according to a braking request 55 and increases in the example shown.

[0058] Between the first time t1 and the fourth time t4, the control 120 according to Figure 3 is active. As can be seen in Figure 4, the control 120 takes place in several cycles Z. Within a cycle Z, a change 26 of a generator braking torque 25 provided by the electric drive 21 takes place, wherein each of the cycles Z comprises a first sub-cycle SZ1 and a second sub-cycle SZ2. In the first sub-cycle SZ1, the change 26 comprises a reduction 27 of the generator braking torque 25, and in the second sub-cycle SZ2, the change 26 comprises an increase 28 of the generator braking torque 25.

[0059] At time t1, a trigger condition 60 is met. Upon fulfillment 125 of the trigger condition 60, a new cycle Z begins. Upon fulfillment 125 of the trigger condition 60, a reduction 27 of the generator braking torque 25 to a predetermined proportion of the generator braking torque 25 occurs upon fulfillment 125 of the trigger condition 60. The trigger condition 60 depends on a wheel acceleration 310, a temporal change in the wheel acceleration 311, a slip 312, a total braking torque 320, and / or a temporal change 321 in the total braking torque 320.

[0060] The generator braking torque 25 is changed in such a way that the generator braking torque 25 does not experience a change in sign within a cycle Z. This means that the total braking torque 25 always remains greater than the friction braking torque 41 according to curve 451.

[0061] Within one of the cycles Z, a braking torque change 57 occurs relating to the generator braking torque 25. The braking torque change 57 is the difference between the generator braking torque 25 at the beginning of a cycle Z and a minimum generator braking torque 25 within the cycle Z. The control 120 takes into account a previous braking torque change 58 of a previous cycle pZ, whereby the braking torque change 58 of the previous cycle pZ is the difference between the generator braking torque 25 at the beginning of the previous cycle pZ and a minimum generator braking torque 25 within the previous cycle pZ. The braking torque change 57 is selected taking into account a first threshold condition 59 relating to the previous braking torque change 58. If the delta-M or the braking torque change 57 is small, the torque M is reduced further than in the last cycle pZ. The road surface becomes less grippy and less torque M can be released.If the delta-M is large, a higher value for the torque M, i.e., a larger first gradient 29a, can be selected. The road surface becomes more grippy, allowing more torque to be released. Alternatively or additionally, the wheel acceleration 310 can be used. In this case, the generator braking torque 25 is reduced until the wheel acceleration 310 increases again and the wheel 210 begins to accelerate at a certain rate (after a tendency to lock is detected, the wheel 210 rotates faster again).

[0062] Within each of the cycles Z, the reduction 27 occurs at a first rate of change 29a and the increase 28 occurs at a second rate of change 29b, wherein the first rate of change 29a differs in magnitude from the second rate of change 29b. The respective rate of change 29, 29a, 29b depends on a road surface characteristic and / or driving condition. In other words, the section-wise increases of the curve 452 of the total braking torque 320 in each of the cycles Z can be different from one another.

[0063] The rate of change 29 is limited such that the trigger condition 60 is not met within a predetermined cycle section SZa. In particular, the second rate of change 29b is limited in order to achieve a limited increase 28 in the second sub-cycle TZ2 as cycle section SZa. In this case, a duration of the second sub-cycle TZ2 and / or of the cycle section SZa can be predicted, which, together with the second rate of change 29b, determines whether a trigger condition 60 is likely to be met. This ensures that an excessively rapid increase in the torque M does not inadvertently lead to excessive wheel deceleration and thus trigger the trigger condition 60. The release of the torque M should only occur so quickly that the resulting (theoretical) wheel deceleration remains below the trigger condition 60.

[0064] In an embodiment not shown, the change 26 of the generator torque 25 takes place in each of the cycles Z and in each sub-cycle SZ1, SZ2 according to a variable change rate 29. This means that within the first sub-cycle SZ1 the first change rate 29a changes and / or within the second sub-cycle SZ2 the second change rate 29b changes.

[0065] If a jump in the coefficient of friction p occurs within a continuous control phase, i.e., within one of the cycles Z, this results in a jump in the wheel speed and / or wheel deceleration or wheel acceleration 310 when the generator braking torque 25 is currently and continuously applied, and can be detected via this jump. Once the change in the coefficient of friction p is detected, a direct switch to modulation and thus adaptation to the road surface 215 can be made and / or a new cycle Z can be started.

[0066] From the third time t3, the total braking torque 320 is equal to the maximum total braking torque 322. This means that the electric drive 21 can fully release a generator braking torque 25 requested by the control unit 250. If the maximum possible generator braking torque 322 was released without a trigger condition 60 occurring again, the friction braking torque 41 is increased to the currently desired value if the braking request still exists. If a trigger condition 60 occurs again during this time, a new control 120 is started with the electric drive 21. Otherwise, the control 120 is terminated.

[0067] From the fourth time point t4 onward, the control of the braking torque M is again passive, as before the first time point t1. The target braking torque 56 can be applied.

[0068] In addition, between two cycles Z, a slip-based control of the generator braking torque 25 (not shown) takes place. After one or more modulated overbrakings have taken place and it has been ensured that the optimum adhesion has been achieved in the Z cycles, continuous slip-based control can then take place with knowledge of the maximum transmittable torque M. After a defined time has elapsed, the system switches from the slip-based control back to modulation according to Figures 3 and 4 in order to perform a new adaptation to the road surface 215. Subsequently, another switch to slip-based control takes place, and so on.

[0069] Reference symbol (part of the description):

[0070] 21 electric drive

[0071] 25 Generator braking torque

[0072] 26 Change

[0073] 27 Reduce

[0074] 28 Increase

[0075] 29 Rate of change

[0076] 29a first rate of change

[0077] 29b second rate of change

[0078] 40 Friction brake system

[0079] 41 Friction braking torque

[0080] 42 second threshold condition

[0081] 43 electric braking system

[0082] 55 Brake request

[0083] 56 Target braking torque

[0084] 57 Braking torque change

[0085] 58 previous braking torque change

[0086] 59 Threshold condition

[0087] 60 Trigger condition

[0088] 100 procedures

[0089] 110 Capture

[0090] 120 rules

[0091] 125 Fulfill

[0092] 150 Rule information

[0093] 210 wheel

[0094] 215 Roadway

[0095] 250 control unit

[0096] 251 processor

[0097] 252 Memory 00a Vehicle 00b Commercial Vehicle 10 Wheel Acceleration

[0098] 311 temporal change of wheel acceleration

[0099] 312 slip

[0100] 320 total braking torque

[0101] 321 temporal change of the total braking torque

[0102] 322 maximum total braking torque

[0103] 400 p-slip curve

[0104] 401 Curve

[0105] 402 Curve

[0106] 403 Maximum adhesion

[0107] 404 Maximum adhesion

[0108] 450 braking torque curve

[0109] 451 Curve

[0110] 452 Curve

[0111] 453 Curve

[0112] M Braking torque p Friction coefficient

[0113] NB Regenerative braking pZ previous cycle

[0114] S slip

[0115] SS target slip

[0116] SZa cycle section

[0117] SZ1 first subcycle

[0118] SZ2 second subcycle t time t1 first time t2 second time t3 third time t4 fourth time

[0119] Z cycle

Claims

Patent claims:

1. Method (100) for controlling a generator braking torque (25) of an electric drive (21) for a vehicle (300a), in particular a commercial vehicle (300b), the method (100) comprising: - detecting (110) a braking request (55) for braking the vehicle (300a), in particular a commercial vehicle (300b), with a desired braking torque (56); - Controlling (120) the generator braking torque (25) as a function of the target braking torque (56) and of a trigger condition (60), wherein the control (120) takes place within a plurality of cycles (Z), wherein within a cycle (Z) a change (26) of a generator braking torque (25) provided by the electric drive (21) takes place, wherein each of the cycles (Z) comprises a first sub-cycle (SZ1) and a second sub-cycle (SZ2), and wherein in the first sub-cycle (SZ1) the change (26) comprises a reduction (27) of the generator braking torque (25) and in the second sub-cycle (SZ2) the change (26) comprises an increase (28) of the generator braking torque (25).

2. Method according to claim 1, wherein the generator braking torque (25) is changed such that the generator braking torque (25) does not experience a change of sign within a cycle (Z).

3. The method according to claim 1 or 2, wherein a new cycle (Z) begins when the trigger condition (60) is fulfilled (125).

4. Method according to one of the preceding claims, wherein the changing (26) takes place according to a variable rate of change (29).

5. The method according to claim 4, wherein the rate of change (29) is dependent on a road surface property and / or driving condition.

6. Method according to one of claims 4 or 5, wherein the rate of change (29) is limited such that the trigger condition (60) is not met within a predetermined cycle section (SZa).

7. Method according to one of the preceding claims, wherein within one of the cycles (Z) the reduction (27) takes place at a first rate of change (29a) and the increase (28) takes place at a second rate of change (29b), the first rate of change (29a) being different in magnitude from the second rate of change (29b).

8. Method according to one of the preceding claims, wherein within one of the cycles (Z) a braking torque change (57) relating to the generator braking torque (25) takes place, and the control (120) takes place taking into account a previous braking torque change (58) of a previous cycle (pZ).

9. The method according to claim 8, wherein the braking torque change (57) is selected taking into account a first threshold condition (59) relating to the previous braking torque change (58).

10. Method according to one of the preceding claims, wherein the trigger condition (60) is dependent on a wheel acceleration (310), a temporal change in the wheel acceleration (311), a slip (312), a total braking torque (320) and / or a temporal change (321) in the total braking torque (320).

11. Method according to one of the preceding claims, wherein the method (100) further comprises the step of: regulating (130) a friction braking torque (41) provided by a friction braking system (40) as a function of a second threshold condition (42) relating to the generator braking torque (25).

12. Method according to one of the preceding claims, wherein a slip-based control of the generator braking torque (25) takes place between two cycles (Z).

13. Method according to one of the preceding claims, wherein, upon fulfillment (125) of the trigger condition (60), a reduction (27) of the generator braking torque (25) to a predetermined proportion of the generator braking torque (25) takes place upon fulfillment (125) of the trigger condition (60).

14. Computer program and / or computer-readable medium comprising instructions which, when the program or instructions are executed by a computer cause it to carry out the method (100) and / or the steps of the method (100) according to one of claims 1 to 13.

15. Control unit (250) for a vehicle (300a), in particular a commercial vehicle (300b), wherein the control unit (250) is configured to carry out the method (100) according to one of claims 1 to 13.

16. Electric drive (21) or electric braking system (43) for a vehicle (300a), in particular a commercial vehicle (300b), comprising a control unit according to claim 15.

17. Vehicle (300a), in particular commercial vehicle (300b), comprising the control unit (250) according to claim 14 and / or an electric drive according to claim 15.

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