Method for torque-based operation of an inverter of an electric drive of a vehicle, in particular a commercial vehicle, inverter, electric drive, vehicle, in particular commercial vehicle, computer program and / or computer-readable medium

Abstract

The invention relates to a method (100) for torque-based operation of an inverter (23) of an electric drive (21) of a vehicle (200a), in particular a commercial vehicle (200b), said electric drive being set up for regenerative braking (NB), having a control unit (24), which is connected to the inverter (23) and different from the inverter (23), for controlling a friction brake device (30) and / or the electric drive (21), wherein the method (100) comprises: using the inverter (23) to measure (110) an actual speed (NEM) of the electric drive (21); using the control unit (24) to ascertain (120) a speed limit (NTAR) determined based on a target speed (VWL) for a wheel (210) which is able to be driven by the electric drive (21); using the control unit (24) to determine (130) an updated speed limit (NLIM) as a function of the speed limit (NTAR) and the actual speed (NEM); and operating (140) the inverter (23) at a reduced torque (T) based on the updated speed limit (NLIM).

Description

[0001] Method for the torque-based operation of an inverter of an electric drive of a vehicle, in particular a commercial vehicle, inverter, electric drive, vehicle, in particular a commercial vehicle, computer program and / or computer-readable medium

[0002] The invention relates to a method for the torque-based operation of an inverter of an electric drive of a vehicle, in particular a commercial vehicle, configured for regenerative braking, having a control unit that is different from the inverter and connected to the inverter for controlling a friction brake device and / or the electric drive. The invention also relates to an inverter for an electric drive of a vehicle, in particular a commercial vehicle, an electric drive, a vehicle, in particular a commercial vehicle, and a computer program and / or computer-readable medium.

[0003] In other words, the invention particularly relates to trucks and trailers optionally equipped with an electronically controlled braking system (EBS or TEBS) and with at least one electrically driven axle with an electric drive (eDrive - central drive or wheel-individual drive) that can be operated as a wear-free continuous brake and, during deceleration, enables the recovery of braking energy in the form of electrical energy (recuperation). The electric drive typically comprises a drive control unit, also called an eDrive ECU, an inverter with an internal inverter control unit, an electric motor, and an optionally switchable transmission.

[0004] To ensure stability, the effective torque and slip (both drive and brake slip) on the driven axle(s) must be limited in certain situations. This requires coordination between the electric drive and the braking system, which typically monitors and controls driving stability, for example, through an anti-lock braking system (ABS) and electronic stability control (ESC), including active rollover protection (ARP) and yaw rate control. In stability- and slip-critical deceleration situations, the state of the art deactivates the electric drive by the friction brake control unit, and solely the friction brakes or the friction brake device are used for control. This is because conventional continuous braking (so-called retarders) cannot be controlled precisely and dynamically enough due to their dynamic nature.

[0005] However, the electric drive lacks the necessary dynamics and precision, so that the potential for recuperation and, in particular, for improving braking performance and stability is not fully exploited.

[0006] If the electric drive is operated with slip control in certain driving and / or braking situations, close coordination between the electric drive and the braking system and its stability control is necessary. It must be ensured that the achieved slip values ​​and torques are high enough to achieve recuperation, achievable deceleration during braking, and / or propulsion during acceleration, but at the same time remain below a stability-critical maximum value, particularly to achieve sufficient lateral control. The overall slip behavior is heavily dependent on the friction pairing between the tires and the surface, including dynamic changes in the surface and its coefficient of friction, and the load and static and dynamic axle load distribution.

[0007] DE 10 2016 208 766 A1 discloses a method for operating a motor vehicle, wherein an automated driving process is carried out, wherein a first braking device is used for the automated deceleration of the motor vehicle, wherein at least one operating parameter of the motor vehicle is detected during the automated driving process, wherein it is checked whether the at least one operating parameter fulfills a predetermined test criterion, and wherein the motor vehicle is automatically decelerated with a second braking device if the at least one operating parameter does not fulfill the test criterion.

[0008] EP 3 299 230 A1 discloses an integrated brake control section that generates a target braking force and a target wheel speed equivalent value of each electric brake device as target values ​​and transmits the target braking force and the target wheel speed equivalent value to a target value transmitter. An electric brake control device of each electric brake device includes a braking force controller that controls an electric motor according to the target braking force, a wheel speed controller that controls the electric motor in accordance with the target wheel speed equivalent value, and a control switch. The control switch switches between the use of the braking force controller and the use of the wheel speed controller in accordance with a predetermined condition.

[0009] Slip control by means of the friction brake device, also called service brake, or by means of one or more electric drives is known from the prior art.

[0010] One advantage of controlling the friction brake system is that the friction brake system has access to essential information relevant to driving stability and can implement braking interventions in a coordinated manner. For example, with traction control (ASR), on a road surface with different friction coefficients per wheel (p-split condition or MU-split condition or MU-split scenario), control can be achieved by holding the spinning wheel at a lower friction coefficient using braking intervention.

[0011] In contrast, especially with wheel-specific drives, control via the electric drive offers the advantage of allowing fast and precise speed and / or torque control internally. If control is performed via the braking system and thus on a separate control unit, this always involves an additional communication path, usually via a vehicle bus, such as a CAN bus, with corresponding dead times and delays.

[0012] EP 3 995 370 A1 proposes the application of speed limits for slip control. The wheel-specific speed limits calculated by the "Motion Management System" are transmitted to the "Motion Support System." There, the torque is limited according to the current speed and the speed limits. The torque is transmitted as a control signal and physically implemented.

[0013] A state-of-the-art inverter offers the ability to dynamically specify a maximum or minimum permissible speed, i.e., a speed limit, via a connected control unit in parallel with the target torque. Even before this speed limit is reached, the inverter internally reduces its torque (derating) so that the speed limit cannot be exceeded in steady-state conditions. This speed-dependent torque reduction is typically used to limit a vehicle's top speed.

[0014] For slip control, the advantage is that in the event of slip, the inverter can react very quickly based on a resolver signal that is directly connected to the inverter. No additional control units or communication links, such as a fieldbus (CAN), are integrated into the control loop.

[0015] The disadvantage, however, is that the inverter only knows the actual speed of the electric drive from the resolver signal, but not the wheel speed, especially in central drives with a differential. For central drives in a MU-split scenario, the speed limit must be appropriately adjusted by another control unit based on the wheel speeds in order to be able to control the wheel on a side with a lower friction coefficient (low-p side). Furthermore, the speed-dependent torque limitation (derating) implemented on the inverter reduces the torque even before the received speed limit is reached. This means that a certain offset always remains between the actual and a target speed. This means that the inverter does not operate optimally.

[0016] The object of the invention is to enrich the state of the art. In one embodiment of the invention, the object is achieved by providing an improved operating strategy for operating an inverter of an electric drive. 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.

[0017] According to the invention, a method is provided for the torque-based operation of an inverter of an electric drive of a vehicle, in particular a commercial vehicle, configured for regenerative braking, having a control unit that is different from the inverter and connected to the inverter for controlling a friction brake device and / or the electric drive. The method comprises: detecting an actual speed of the electric drive by the inverter; determining a speed limit determined based on a target speed for a wheel drivable by the electric drive by the control unit; determining a tracked speed limit by the control unit as a function of the speed limit and the actual speed; and operating the inverter with a reduced torque based on the tracked speed limit.

[0018] The vehicle, in particular a commercial vehicle, is referred to below as the "vehicle." In other words, a distributed slip control system between a control unit and the inverter is proposed, based on suitable tracking of the speed limit. It was recognized that, due to the nature of the prior art, the actual speed of the inverter is not set in such a way that the wheel reaches the target speed, since a transmittable torque always results, resulting in an offset or difference. By feedbacking the speeds, the speed limit can be adjusted so that the inverter can operate effectively.

[0019] The actual speed of the electric drive can be detected by the inverter, for example in the case of a wheel-individual drive, via the inverter or its resolver signal in order to exploit the dynamic advantages of the inverter.

[0020] The target speed can define the wheel speed to be controlled. Determining the target speed can be based, in particular, on a slip limit. The slip limit can describe a maximum positive slip during propulsion or a maximum negative slip during braking. The target speed can be determined based on the actual vehicle speed and the actual wheel speed and can thus be effectively determined by the control unit. The tracked speed limit can be defined such that the wheel reaches the target speed.

[0021] The adjusted speed limit can be determined in order to operate the inverter with the reduced torque. The speed limit can be adjusted in such a way that the target speed is reached despite a reduction in torque by derating to the reduced torque in accordance with the adjusted speed limit. The reduced torque can be a torque reduced compared to a target torque. By adhering to the defined specifications for driving and / or deceleration via the slip limit or the target speed, driving stability is ensured and the target speed at the wheel is reached. At the same time, the high control quality and dynamics of an internal inverter control system are optimally utilized.In the case of a central drive, i.e. when several wheels are driven by the inverter, it may be necessary to adjust the speed limit based on the speed of the wheel that slips more or more, which is done by the control unit.

[0022] Preferably, the reduced torque is determined based on a difference between the tracked speed limit and the actual speed of the electric drive. This means that the tracked speed limit defines the derating instead of the original speed limit. This allows the target speed to be reached, and the offset between the target speed and the actual wheel speed can be reduced or decreased. Optionally, the reduced torque can be linearly dependent on a speed difference between the actual speed and the tracked speed limit, defining a dependency that can be effectively implemented in the inverter.

[0023] Preferably, the tracked speed limit is determined such that the actual speed of the inverter corresponds to the speed limit. This ensures that the inverter reaches the speed limit and can thus adjust to the target speed of the wheel. The speed limit is preferably determined taking into account an actual wheel speed related to the wheel and an actual vehicle speed of the vehicle, in particular a commercial vehicle. This enables wheel-specific control. Based on the actual vehicle speed and the actual wheel speed, the speed limit can be determined while observing a slip limit to be maintained.

[0024] Preferably, the adjusted speed limit is determined such that the speed of a wheel of the vehicle, in particular a commercial vehicle, that slips more than another wheel corresponds to the target speed. The wheel that slips more and the other wheel can be driven by the inverter (central drive). This ensures that the wheels adhere to a slip limit, thus enabling effective and safe operation of the vehicle, in particular a commercial vehicle. It is advantageous for the adjusted speed limit to be determined by the friction brake control unit, since the friction brake control unit knows the wheel speeds and / or wheel speeds.

[0025] Preferably, the reduced torque is a drive torque or a braking torque. This allows the inverter to be operated to accelerate the wheel according to the drive torque or decelerate it according to the braking torque.

[0026] Preferably, the method comprises the step of transmitting the reduced torque from the inverter to a friction brake control unit. The reduced torque can be transmitted to the friction brake control unit in order to be able to perform a braking intervention taking the reduced torque into account. For example, the reduced torque and a friction brake torque can generate respective deceleration and braking torque components based on a braking request.

[0027] The control unit is preferably a friction brake control unit or a drive control unit. The friction brake control unit can provide essential information for the control, such as the target speed. The drive control unit can define specifications regarding the target torque and / or the derating for the inverter.

[0028] According to a further aspect of the invention, an inverter for an electric drive of a vehicle, in particular a commercial vehicle, is provided. The inverter is configured to carry out the method described here. The inverter can be configured to carry out steps of the method described as optional and / or advantageous in order to achieve a corresponding technical effect.

[0029] According to a further aspect of the invention, an electric drive for a vehicle, in particular a commercial vehicle, is provided. The electric drive comprises the inverter described here. The electric drive and / or the inverter can be configured 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 vehicle, in particular a commercial vehicle, is provided. The vehicle has the inverter described here or the electric drive described here. The vehicle, the inverter, and / or the electric drive can be configured to perform 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, a computer program and / or computer-readable medium is provided. The computer program and / or computer-readable medium comprises instructions which, when the program or instructions are executed by a computer, cause the computer to carry out the method described here and / or the steps of the method described here. The computer program and / or computer-readable medium can comprise instructions to carry out steps of the method described as optional and / or advantageous in order to achieve a corresponding technical effect. Further advantages and features of the invention as well as their technical effects emerge from the figures and the description of the preferred embodiments shown in the figures.

[0032] Fig. 1 is a schematic representation of an overview of a vehicle, in particular a commercial vehicle, according to an embodiment of the invention;

[0033] Fig. 2 is a schematic representation of a calculation process according to the prior art;

[0034] Fig. 3 is a schematic representation of a calculation sequence according to a method according to an embodiment of the invention;

[0035] Fig. 4 is a schematic representation of speeds as a function of time to illustrate an effect of a method according to an embodiment of the invention;

[0036] Fig. 5 is a schematic representation of a dependency of torque and an actual speed of an electric drive according to an embodiment of the invention;

[0037] Fig. 6 is a schematic representation of a dependency of torque and an actual speed of an electric drive according to an embodiment of the invention;

[0038] Fig. 7 is a schematic representation of a relationship between slip and friction coefficient;

[0039] Fig. 8 is a schematic representation of several alternative topologies of a vehicle, in particular a commercial vehicle, for carrying out a method according to an embodiment of the invention; and

[0040] Fig. 9 is a schematic representation of a method according to an embodiment of the invention.

[0041] Figure 1 shows a schematic representation of an overview of a vehicle 200a, in particular commercial vehicle 200b, according to an embodiment of the invention.

[0042] The vehicle 200a, in particular commercial vehicle 200b, is referred to below as vehicle 200a, 200b. The vehicle 200a, 200b is a land vehicle and, for example, a truck, a bus, a trailer, and / or a multi-unit vehicle. The vehicle 200a, 200b has an electric drive 21. The vehicle 200a, 200b further has a friction brake device 30. The friction brake device 30 is an electric braking system or an electronically controlled braking system. In an embodiment not shown, the friction brake device 30 is a pneumatic and / or hydraulic braking system. The friction brake device 30 has a friction brake control unit 24a.

[0043] The vehicle 200a, 200b according to Figure 1 has a plurality of wheels 210, 210'. The wheels 210 are arranged on a roadway. A torque T, mediated by the roadway and effected by the electric drive 21 and the friction brake device 30, can act on each of the wheels 210 as a drive torque T+ or a braking torque T-. The roadway can be subject, in particular, to local changes. For example, the roadway can have different surfaces at different locations, thus leading to different friction values ​​or friction coefficients MU between the roadway and the wheels 210, 210' (see also Figure 7). Different slip S can occur at the wheels 210, 210'. The slip S can be calculated from an actual wheel speed VW of the respective wheel 210, 210' and an actual vehicle speed WEH.The wheels 210, 210' may have a different slip S from each other, whereby one of the wheels 210 may be referred to as a wheel 210 with greater slippage than the other of the wheels 210'.

[0044] The electric drive 21 is configured for regenerative braking NB. In this case, the braking torque T- can be applied and mechanical energy of the wheels 210, 210' can be converted into electrical energy 262. The electrical energy 262 can be applied to an energy storage device 260 of the vehicle 200a, 200b to increase its charge level 261.

[0045] The electric drive 21 is configured to generate the drive torque T+ or the braking torque T-, which can lead to an acceleration or deceleration of the vehicle 200a, 200b or one of the wheels 210, 210'. The friction brake device 30 is configured to apply a braking torque T- to one or more of the wheels 210, 210'. The electric drive 21, as a so-called central drive, is configured to apply a torque T to one or more wheels 210, 210' of an axle (not shown). In another embodiment (not shown), the electric drive 21 is configured to apply a torque T to exactly one wheel 210, 210'.

[0046] The dynamics of each of the wheels 210, 210' can be characterized by a measurable wheel acceleration or deceleration and / or a temporal change in the wheel acceleration. The wheel deceleration and / or the temporal change in the wheel acceleration can be detected by measured values ​​from a wheel speed sensor (not shown) and / or by control information from the electric drive 21.

[0047] The electric drive 21 comprises an inverter 23 and a drive control unit 24b. The drive control unit 24b can be referred to as an eDrive ECU. The drive control unit 24b is configured to operate the inverter 23 based on control specifications and to read control information from the inverter 23. The inverter 23 can detect an actual speed NEM of the electric drive 21 and transmit it to the drive control unit 24b. The drive control unit 24b can specify a target torque TT and a tracked speed limit NLIM to the inverter 23. The tracked speed limit NLIM can include a lower limit NLIM- and / or an upper limit NLIM+. The inverter 23 is configured to set the actual speed NEM based on the specifications; in this case, the inverter 23 can apply a reduced torque TR before and / or upon reaching the speed limit NTAR and / or a tracked speed limit NLIM.The actual speed NEM of the electric drive 21 detected by the inverter 23 is translated into the actual wheel speed VW, VW' directly in the case of a wheel-individual drive or indirectly via a transmission in the case of a central drive.

[0048] The drive control unit 24b and the friction brake control unit 24a are control units 24 of the vehicle 200a, 200b. The control units 24 are different from the inverter 23 and an inverter-internal control unit (not shown). Each of the control units 24, i.e., the drive control unit 24b and the friction brake control unit 24a, is configured to communicate with the inverter 23 to operate the inverter 23.

[0049] The vehicle 200a, 200b or the inverter 23 and / or the control units 24 are configured to carry out the method 100 described with reference to Figure 9. For this purpose, the control unit 24 can determine the tracked speed limit NLIM as described with reference to Figures 3 to 6 in order to operate the inverter 23 accordingly. Communication between the inverter 23 and the control unit(s) 24, or an architecture as described with reference to Figure 8, can be provided.

[0050] Figure 2 shows a schematic representation of a calculation process according to the prior art. Figure 2 illustrates a friction brake control unit 24a and a drive control unit 24b. Figure 2 is described with reference to the nomenclature or designations according to Figure 1.

[0051] According to Figure 2, the friction brake control unit 24a detects a slip limit L, an actual wheel speed VW, and an actual vehicle speed WEH. From this, the friction brake control unit 24a determines a target speed VWL for a wheel 210, 210', i.e., a wheel-specific speed v. For example, the target speed VWL for the wheel 210, 210' is calculated in the drive case using the equation VWL = WEH / (1 - L) and in the braking case using the equation VWL = WEH x (1 - L).

[0052] The friction brake control unit 24a transmits the target speed VWL for the wheel 210, 210' to the drive control unit 24b. The drive control unit 24b detects the actual speed NEM of the electric drive 21 via the inverter 23 or its resolver and calculates a speed limit NTAR for operating the inverter 23. The speed limit NTAR can be interpreted as an inverter-related speed v or converted into one. The inverter 23 is operated based on the speed limit NTAR.

[0053] Figure 3 shows a schematic representation of a calculation sequence according to a method 100 according to one embodiment of the invention. Figure 3 illustrates a friction brake control unit 24a and a drive control unit 24b. Figure 3 is described with reference to Figure 1 and its description.

[0054] According to Figure 3, in a first step the friction brake control unit 24a detects a slip limit L and an actual vehicle speed WEH and determines the target speed VWL for a wheel 210, 210' as described with reference to Figure 2. In a second step the friction brake control unit 24a detects the actual wheel speed VW and determines a target speed VTAR for the electric drive 21, for example in the drive case using the equation VTAR = max (VWL + 1 / 2 x min(VWJinks - VWL; VW_right -VWL), WEH + VOFFS), with an offset speed VOFFS, an actual wheel speed VWJinks of a left wheel 210, 210', an actual wheel speed VW_right of a right wheel 210, 210, and the minimum function min(). The target speed VTAR is a wheel-related speed v.

[0055] The friction brake control unit 24a transmits the target speed VTAR to the drive control unit 24b. In a first step, the drive control unit 24b uses the target speed VTAR to determine a speed limit NTAR related to the inverter 23. In a second step, the drive control unit 24b detects the actual speed NEM of the electric drive 21 and, taking the speed limit NTAR into account, calculates a tracked speed limit NLIM for operating the inverter 23.

[0056] According to one variant (see Figure 8 (A)), the friction brake control unit 24a can calculate the target speed VTAR taking into account the actual wheel speed VW_left of the left wheel 210, 210' and the actual wheel speed VW_right of the right wheel 210, 210, as well as the slip limit L. The friction brake control unit 24a sends the target speed VTAR to the drive control unit 24b. The drive control unit 24b calculates the tracked speed limit NLIM therefrom such that the actual speed NEM of the electric drive 21 reaches the tracked speed limit NLIM.

[0057] According to a further variant, particularly suitable for a central drive (see also Figure 8 (A)), the friction brake control unit 24a can calculate the target speed VTAR taking into account the slip limit L. The friction brake control unit 24a reads the actual wheel speed VWJinks of the left wheel 210, 210' and the actual wheel speed VW_right of the right wheel 210, 210 and uses this to calculate an axle-related, tracked speed limit VLIM such that the actual wheel speeds VWJinks, VW_right maintain and / or reach the target speed VTAR. The tracking is based on the wheel speeds. The friction brake control unit 24a sends the tracked speed limit VLIM to the drive control unit 24b. The drive control unit 24b converts the tracked speed limit VLIM into the tracked speed limit NLIM.The drive control unit 24b sends the tracked speed limit NLIM to the inverter 23, whereby no tracking is carried out by the drive control unit 24b.

[0058] The tracked speed limit NLIM can be understood as an inverter-related speed v or converted into one. For example, the tracked speed limit NLIM is calculated using the equation NLIM = NTAR + K x int (NTAR-NEM) dt, where K is an optionally constant gain factor and int (...) dt is an integral over time t . The integration limits can depend on the torque T, which is the maximum or minimum possible. The tracked speed limit NLIM is calculated in such a way that the speed limit NTAR is only shifted far enough that the maximum of the speed difference-dependent derating curve (see Figures 5 and 6) is at the level of the speed limit. In this way, the entire torque can still be released within the speed limit, if required, for example for a wheel 210 on a road surface with a high friction coefficient MU.

[0059] Inverter 23 is operated based on the tracked speed limit NLIM. Anti-windup conditions can be inserted for the integrating component to prevent the integrator from integrating beyond plausible values. The integration limits can be dependent on the maximum or minimum possible torque T.

[0060] Figure 4 shows a schematic representation of speeds v as a function of time t to illustrate an effect of a method 100 according to an embodiment of the invention. Figure 4 is described with reference to Figures 1 and 3. The lower curve of Figure 4 shows the actual vehicle speed WEH with a strong solid line. The vehicle 200a, 200b accelerates. The actual vehicle speed WEH increases.

[0061] Two dashed lines indicate target speeds VWL for a wheel 210, 210'. The target speeds VWL for the wheel 210, 210' are obtained, for example, as described with reference to Figures 2 and 3, from the slip limit L and the actual vehicle speed WEH, with the lower of the two curves of the target speeds VWL for the wheel 210, 210' illustrating the braking case and the upper of the two curves of the target speeds VWL for the wheel 210, 210' illustrating the driving case.

[0062] The actual wheel speed VW, VW' should be within the two curves of the target speeds VWL for wheel 210, 210' to enable stable, reliable, and effective operation of the vehicle 200a, 200b. This means that at any time t, the actual wheel speed VW, VW' should be between the target speeds VWL for wheel 210, 210'.

[0063] A dotted line represents the wheel speed VW of a wheel 210 that initially slips less. The dotted line with the wheel speed VW is initially within the target speeds VWL for wheel 210, 210.

[0064] A strong solid line (upper curve) represents a wheel speed VW' of a wheel 210 with greater slippage. The wheel speed VW' initially exceeds the target speeds VWL for wheel 210, 210', is therefore too high and must be regulated.

[0065] A target speed VTAR is shown with a dot-dashed line as described with reference to Figure 3. The target speed VTAR can be converted into the speed limit NTAR. An actual speed VEM of the electric drive 21 is shown with a weak solid line. The actual speed VEM of the electric drive 21 can be converted into the actual speed NEM of the electric drive 21. Since the wheel speed VW' exceeds the target speeds VWL for the wheel 210, 210', the actual speed VEM of the electric drive 21 must be adjusted in order to drive and / or decelerate the wheel 210' with the greater slippage less and thus to regulate the wheel speed VW' into a range between the two target speeds VWL for the wheel 210, 210'. For this purpose, the actual speed VEM of the electric drive 21 is reduced to the target speed VTAR as indicated by arrows.As also indicated by arrows, the wheel speed VW' is regulated to a value between the target speeds VWL for wheel 210, 210'. Figure 4 thus represents wheel-specific control. For this purpose, the tracked speed limit NLIM is determined taking into account the actual speed NEM in order to operate the inverter 23 with a reduced torque TR in such a way that an offset between the wheel speed VW' and the target speed VTAR is reduced or prevented. This allows only the wheel 210' with the greater slippage, for example, the faster wheel 210', to be brought to the target speed VWL, while the wheel 210 with less slippage can have a larger offset.

[0066] To calculate the speed difference between the actual wheel speed VW and the target speed VWL, the actual wheel speed VW of wheel 210 with the greater slip S can be used in central drives in order to be able to adjust wheel 210' to a low friction coefficient in p-split situations. For centrally driven axles, the friction brake system 30 monitors the realization of the desired wheel- or side-specific target slip and can ensure stability through braking interventions (see Figure 6). In the drive case, an additional braking torque T- can be generated on the low-p side in order to increase the total transmittable drive force on the high-p side. Alternatively or additionally, the electric drive 21 can specifically request braking interventions. In the braking case, an additional braking torque T- can be built up on the high-p side by the friction brake system 30.

[0067] Figure 5 shows a schematic representation of a relationship between torque T and an actual speed NEM of an electric drive 21 according to an embodiment of the invention. Figure 5 is described with reference to Figures 1, 3, and 4. It is assumed that a target torque TT is requested. The target torque TT is represented in Figure 5 by a horizontal line.

[0068] Figure 5 also illustrates a vehicle speed NV. The vehicle speed NV is defined as the speed of the electric drive 21, assuming that the vehicle 200a, 200b is traveling without slip S.

[0069] The solid line in Figure 5 represents derating, i.e. a speed-dependent reduction of the torque T implemented in the inverter 23 as a function of the actual speed NEM of the electric drive 21 according to the prior art. The torque T is reduced starting from a reference torque in such a way that the torque T becomes zero at an actual speed NEM equal to the speed limit NTAR. Since no torque T is present at the speed limit NTAR, the speed limit NTAR cannot be reached in the steady-state case. Instead, the electric drive 21 is operated at a reference speed NW, which is set without adjusting the speed limit NTAR, and at a reduced torque TR' resulting from the derating, the reference speed NW and the speed limit NTAR.

[0070] The dashed line in Figure 5 represents a torque curve resulting from derating adjusted with respect to the tracked torque NLIM. The derating of inverter 23, i.e., the (negative) slope of the speed-dependent torque curve, is known. Thus, the tracked speed limit NLIM can be selected such that inverter 23 sets the speed limit NTAR as the actual speed NEM at a reduced torque TR in order to achieve the target speed VWL for wheel 210, 210'.

[0071] Figure 6 shows a schematic representation of a relationship between torque T and an actual speed NEM of an electric drive 21 according to an embodiment of the invention. Figure 6 is described with reference to Figures 1 and 3 to 5.

[0072] The slopes of the curves shown describe the derating. During acceleration of the vehicle 200a, 200b, the torque T is initially limited via the derating curve of the drive torque T+ (solid line). If the tracked speed limit NLIM is exceeded during drive operation, the drive shaft is actively braked by a negative torque T- via the derating curve T- (dashed line).

[0073] During braking, the negative torque is initially limited by the derating curve of the braking torque T- (solid line). If the tracked speed limit NLIM is exceeded during braking, the drive shaft is actively accelerated by a positive torque T+ via the derating curve (dashed line).

[0074] Depending on the application, the derating can be adjusted if the lower limit NLIM- is undershot and / or the upper limit NLIM+ is exceeded. Such an adjustment is represented by different gradients of the curves shown. Alternatively or additionally, any functions (e.g., nonlinear or discontinuous) and / or look-up tables can be used to implement the derating. The torque TR reduced by the derating is thus, depending on the application and x-axis intercept, a drive torque T+ or a braking torque T-.

[0075] Figure 7 shows a schematic representation of a relationship between slip S and friction coefficient MU. The friction coefficient MU is defined for a wheel 210, 210' and a surface contacting the wheel 210, 210'. Depending on the friction coefficient MU, a slip S illustrated by Figure 7 can be applied as drive slip or as brake slip. The relationship between slip S and friction coefficient MU in most cases exhibits a unimodal curve with a maximum, i.e., a slip S associated with the maximum friction coefficient, which occurs at a specific friction coefficient MU. The slip S associated with the maximum friction coefficient enables the best possible utilization of recuperation, the best possible acceleration and / or deceleration.

[0076] A left-hand vertical line marks a slip S that occurs when the electric drive 21 is operated at the reference speed NW described with reference to Figure 5. A right-hand vertical line marks a slip S that occurs when the electric drive 21 is operated at the tracked speed limit NLIM.

[0077] Figure 7 thus illustrates that the electric drive 21 is not operating at an optimal operating point at the reference speed NW. Tracking the actual speed NEM to the tracked speed limit NLIM results in improved operation of the electric drive 21.

[0078] Figure 8 shows a schematic representation of several alternative topologies of a vehicle 200a, in particular commercial vehicle 200b, for carrying out a method 100 according to an embodiment of the invention.

[0079] Figure 8 shows five different alternatives, which are marked by the letters (A), (B), (C), (D) and (E) and separated from each other by a vertical dashed line.

[0080] Figure 8 (A) shows the embodiment described with reference to Figure 3. The slip limit L is determined by the control unit 24 and transmitted to the friction brake control unit 24a if the control unit 24 is different from the friction brake control unit 24a. Otherwise, the transmission of the slip limit L can be omitted.

[0081] The friction brake control unit 24a receives the slip limit L and determines the target speed VTAR for the electric drive 21. The target speed VTAR can be calculated taking into account the actual wheel speed VW_left of the left wheel 210, 210' and the actual wheel speed VW_right of the right wheel 210, 210. Optionally, a tracked speed limit VLIM is calculated (see Figure 3). The friction brake control unit 24a transmits the target speed VTAR and optionally the tracked speed limit VLIM to the drive control unit 24b. The drive control unit 24b receives the target speed VTAR and optionally the tracked speed limit VLIM and determines the tracked speed limit NLIM. The drive control unit 24b initiates operation of the inverter 23 based on the tracked speed limit NLIM.

[0082] In Figure 8 (B), the control unit 24 determines the slip limit L and transmits it to the drive control unit 24b if the control unit 24 is different from the drive control unit 24b. Otherwise, the transmission of the slip limit L can be omitted. The drive control unit 24b receives the slip limit L and determines the tracked speed limit NLIM. The drive control unit 24b initiates operation of the inverter 23 based on the tracked speed limit NLIM.

[0083] In Figure 8 (C), the control unit 24 determines the slip limit L and transmits it to the friction brake control unit 24a if the control unit 24 is different from the friction brake control unit 24a. Otherwise, the transmission of the slip limit L can be omitted. The friction brake control unit 24a receives the slip limit L and determines the tracked speed limit NLIM. The friction brake control unit 24a initiates operation of the inverter 23 based on the tracked speed limit NLIM.

[0084] In Figure 8 (D), the control unit 24 determines the slip limit L and the target speed VTAR for the electric drive 21. The control unit 24 transmits the target speed VTAR to the inverter 23, which itself determines the tracked speed limit NLIM.

[0085] In Figure 8 (E), the slip limit L is determined by the control unit 24. The control unit 24 transmits the slip limit L to the inverter 23, which itself determines the tracked speed limit NLIM.

[0086] Figure 9 shows a schematic representation of a method 100 according to an embodiment of the invention. The method 100 is a method 100 for the torque-based operation of an inverter 23 of an electric drive 21 of a vehicle 200a, in particular a commercial vehicle 200b, configured for regenerative braking NB, with a control unit 24 different from the inverter 23 and connected to the inverter 23 for controlling a friction brake device 30 and / or the electric drive 21. Such a vehicle 200a, 200b is described with reference to Figure 1. Figure 9 is described with reference to Figures 1 to 8.

[0087] The method 100 comprises: detecting 1 10 an actual speed NEM of the electric drive 21 by the inverter 23. A speed limit NTAR determined on the basis of a target speed VWL for a wheel 210 drivable by the electric drive 21 is determined 120 by the control unit 24. The speed limit NTAR is determined 120 taking into account an actual wheel speed VW related to the wheel 310 and an actual vehicle speed WEH of the vehicle 200a, commercial vehicle 200b.

[0088] A tracked speed limit NLIM is determined 130 by the control unit 24 as a function of the speed limit NTAR and the actual speed NEM. The tracked speed limit NLIM is determined such that the actual speed NEM of the electric drive 21 corresponds to the speed limit NTAR. The tracked speed limit NLIM is determined such that the speed VW of a wheel 210' of the vehicle 200a, in particular of the commercial vehicle 200b, that slips more than another wheel 210 corresponds to the target speed VWL.

[0089] The inverter 23 is operated 140 with a reduced torque TR based on the tracked speed limit NLIM. The reduced torque TR is determined depending on a difference between the tracked speed limit NLIM and the actual speed NEM of the electric drive 21. The reduced torque TR is a drive torque T+ or a braking torque T-.

[0090] The reduced torque TR is transmitted 150 from the inverter 23 to a friction brake control unit 24a.

[0091] Reference symbol (part of the description)

[0092] 21 electric drive

[0093] 23 inverters

[0094] 24 Control unit

[0095] 24a Friction brake control unit

[0096] 24b Drive control unit

[0097] 30 Friction brake device

[0098] 100 procedures

[0099] 110 Capture

[0100] 120 Investigate

[0101] 130 Determine

[0102] 140 Operate

[0103] 150 Submit

[0104] 200a vehicle

[0105] 200b commercial vehicle

[0106] 210 wheel

[0107] 210' wheel

[0108] 260 Energy storage device

[0109] 261 Charge level

[0110] 262 electrical energy

[0111] L Slip limit

[0112] MU friction coefficient

[0113] NB regenerative braking

[0114] NEM actual speed of the electric drive

[0115] NLIM tracked speed limit

[0116] NLIM- Limit of the tracked speed limit NLIM+ Limit of the tracked speed limit

[0117] NTAR speed limit

[0118] NW reference speed

[0119] NV vehicle speed

[0120] S hatching t time

[0121] TR reduced torque

[0122] TR' reduced torque

[0123] T torque

[0124] T+ drive torque, positive torque

[0125] T- braking torque, negative torque

[0126] TT Target torque v Speed

[0127] VEM Actual speed of the electric drive

[0128] VLIM tracked speed limit

[0129] VW actual wheel speed

[0130] VW' actual wheel speed

[0131] VWL target speed for a wheel

[0132] VTAR target speed for electric propulsion

[0133] WEH Actual vehicle speed

Claims

Patent claims 1. Method (100) for the torque-based operation of an inverter (23) of an electric drive (21) of a vehicle (200a), in particular a commercial vehicle (200b), configured for regenerative braking (NB), with a control unit (24) different from the inverter (23) and connected to the inverter (23) for controlling a friction brake device (30) and / or the electric drive (21), the method (100) comprising: - detecting (110) an actual speed (NEM) of the electric drive (21) by the inverter (23); - determining (120) by the control unit (24) a speed limit (NTAR) determined on the basis of a target speed (VWL) for a wheel (210) drivable by the electric drive (21); - determining (130) a tracked speed limit (NLIM) as a function of the speed limit (NTAR) and the actual speed (NEM) by the control unit (24); and - Operating (140) the inverter (23) with a reduced torque (TR) based on the tracked speed limit (NLIM).

2. Method (100) according to claim 1, wherein the reduced torque (TR) is determined as a function of a difference between the tracked speed limit (NLIM) and the actual speed (NEM) of the electric drive (21).

3. The method (100) according to claim 1 or 2, wherein the tracked speed limit (NLIM) is determined such that the actual speed (NEM) of the inverter (23) corresponds to the speed limit (NTAR).

4. Method (100) according to one of the preceding claims, wherein the determination (120) of the speed limit (NTAR) takes into account an actual wheel speed (VW) related to the wheel (310) and an actual vehicle speed (WEH) of the vehicle (200a), in particular commercial vehicle (200b).

5. The method (100) according to claim 4, wherein the tracked speed limit (NLIM) is determined such that the speed (VW) of one more than another Wheel (210) slipping wheel (210') of the vehicle (200a), in particular commercial vehicle (200b), corresponds to the target speed (VWL).

6. Method (100) according to one of the preceding claims, wherein the reduced torque (TR) is a drive torque (T+) or a braking torque (T-).

7. Method (100) according to one of the preceding claims, wherein the method (100) comprises the step: - transmitting (150) the reduced torque (TR) from the inverter (23) to a friction brake control unit (24a).

8. Method (100) according to one of the preceding claims, wherein the control unit (24) is a friction brake control unit (24a) or a drive control unit (24b).

9. Inverter (23) for an electric drive (21) of a vehicle (200a), in particular a commercial vehicle (200b), wherein the inverter (23) is configured to carry out the method (100) according to one of the preceding steps.

10. Electric drive (21) comprising the inverter (23) according to claim 9. 1 1. Vehicle (200a), in particular commercial vehicle (200b), comprising the inverter (23) according to claim 9 and / or the electric drive (21) according to claim 10.

12. Computer program and / or computer-readable medium comprising instructions which, when the program or instructions are executed by a computer, cause the computer to carry out the method (100) and / or the steps of the method (100) according to one of claims 1 to 8.

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