Method for operating a drive train of a motor vehicle, in particular a motor car

Abstract

Method for operating a drive train (10) of a motor vehicle, when which the drive train (10) has: - a first axle (12) with at least one first wheel (18); - a second axle (14) following the first axle (12) in the longitudinal direction of the vehicle (16) with at least one second wheel (22); - at least one first drive device (24) assigned to the first axle (12), by means of which the first wheel (18) can be driven; - at least one second drive device (26) assigned to the second axle (14), by means of which the second wheel (22) can be driven; and - a first control unit (32) by means of which at least one braking torque for braking the motor vehicle can be adjusted, in that the first control unit (32) is designed to control at least one service brake of the motor vehicle and thereby implement an anti-lock braking system of the motor vehicle; characterized by the fact that the drive train (10) has a second control unit (34) in addition to the first control unit (32), by means of which the drive devices (24, 26) can be controlled in order to adjust a respective torque to be provided by the respective drive device (24, 26) for driving the respective wheel (18, 22), wherein: ◯ by means of the first control unit (32) a distribution of a total torque requested by the driver of the motor vehicle to the drive devices (24, 26) is determined; ◯ at least one distribution signal, which characterizes the determined distribution, is provided by the first control unit (32) and received by the second control unit (34); and ◯ the second control unit (34) depending on the received distribution signal controls the drive devices (24, 26) in such a way that the torques are provided by the drive devices (24, 26) and in total correspond to the total torque; ◯ wherein the first control unit (32) is used to perform drive slip control of the drive devices (24, 26), ◯ wherein the first control unit (32) limits at least one of the torques to a maximum first value during at least a first time interval, which is lower than a maximum second value of the at least one torque permitted by the first control unit (32) during a second time interval different from the first time interval, ◯ wherein by means of the second control unit (34) a second distribution of the total torque requested by the driver of the motor vehicle to the drive devices (24, 26) is determined, which differs from the distribution, and the second distribution is overridden by the first distribution.

Description

[0001] The invention relates to a method for operating a drive train of a motor vehicle, in particular a motor vehicle.

[0002] Drivetrains for motor vehicles, such as cars, and motor vehicles with such drivetrains are already well known from the general state of the art and in particular from series vehicle construction. The drivetrain has, for example, two axles arranged consecutively or one behind the other in the vehicle's longitudinal direction, each with its own drivable wheels. The wheels can be driven, for example, by a drive unit of the drivetrain, in particular such that the drive unit provides a total torque. In this case, for example, the total torque is distributed among the axles and thus among the wheels. Such a distribution of the total torque among the axles is usually space-consuming, costly, and weight-intensive.

[0003] DE 10 2004 049 324 A1 discloses a method for controlling and regulating driving dynamics in motor vehicles with hybrid drives. Furthermore, WO 2011 / 128024 A1 discloses a method for operating a motor vehicle. DE 10 2015 106 746 A1 discloses a method for controlling the brake bias in a vehicle braking system that has both friction braking devices and regenerative braking devices.

[0004] The object of the present invention is therefore to provide a method and a drive train for a motor vehicle so that a torque distribution to axles of the drive train can be realized particularly advantageously.

[0005] This object is achieved according to the invention by a method having the features of patent claim 1. Advantageous embodiments of the invention are specified in the dependent claims.

[0006] A first aspect of the invention relates to a method for operating a drive train of a motor vehicle, for example a motor vehicle, in particular a passenger car. The drive train has a first axle which comprises at least one first wheel. The first axle preferably comprises at least or exactly two first wheels, which are preferably spaced apart from one another in the transverse direction of the vehicle. The drive train also has at least one second axle following the first axle in the longitudinal direction of the vehicle, so that the axles are arranged one after the other or one behind the other in the longitudinal direction of the vehicle. The second axle comprises at least one second wheel. The second axle preferably comprises at least or exactly two second wheels, which are spaced apart from one another, for example in the transverse direction of the vehicle.The wheels are ground contact elements by which the motor vehicle can be or is supported downwards on a roadway in the vertical direction of the vehicle. In other words, it is preferably provided that the motor vehicle is supported downwards on the roadway in the vertical direction of the vehicle via the wheels, wherein preferably during the method or during the method, the motor vehicle travels along the roadway so that the wheels roll along the roadway. Thus, the method is preferably carried out while the motor vehicle is traveling.

[0007] The drive train further comprises at least one first drive device assigned to the first axle, by means of which the first wheel or wheels can be driven. The drive train also comprises at least one second drive device assigned to the second axle, by means of which the second wheel or wheels can be driven. Preferably, the first drive device is assigned exclusively to the first axle with respect to the axles, so that, with respect to the first wheel and the second wheel, only the first wheel or wheels can be driven by means of the first drive device.Furthermore, it is preferably provided that the second drive device is assigned exclusively to the second axle with respect to the axles, so that exclusively the second wheel can be driven by means of the second drive device with respect to the first wheel and the second wheel. In other words, preferably exclusively the first wheels can be driven by means of the first drive device with respect to the first wheels and the second wheels, and preferably exclusively the second wheels can be driven by means of the second drive device with respect to the first wheels and the second wheels. In this case, it is particularly preferably provided that the axles are mechanically, in particular permanently, decoupled from one another, so that no mechanical, torque-transmitting coupling is provided between the axles.Thus, for example, the first drive device cannot drive the second axle or the second wheels, and the second drive device preferably cannot drive the first axle or the first wheels. In other words, the drive devices are preferably axle-specific drive devices or axle-specific motors, wherein, with respect to the axles, the respective axle-specific motor can only drive the axle to which the respective motor is assigned.

[0008] The drive train further comprises a first control unit, also referred to as a brake control unit (BSG). At least one braking torque for braking the motor vehicle can be adjusted by means of the first control unit. The feature that a braking torque for braking the motor vehicle can be adjusted by means of the first control unit is to be understood, for example, that the first control unit, in particular via at least one actuator, can effect the braking torque by means of which the motor vehicle can be braked or acceleration of the motor vehicle can be prevented, and thus, for example, a current speed of the motor vehicle can be kept at least substantially constant.

[0009] The drive train further comprises a second control unit, also referred to as a drive control unit (ASG), provided in addition to the first control unit. The drive devices can be controlled by means of the second control unit, whereby a respective torque, to be provided by the respective drive device and also referred to as an individual torque, can be set for driving the respective wheel or axle. The respective control unit is an electronic computing device, with the control units preferably being designed as individual structural units. In other words, the control units are preferably designed separately from one another and are thus separate units, which can, for example, be spaced apart from one another.

[0010] In order to be able to implement a torque distribution among the axles in a particularly advantageous manner, in particular in a particularly cost-effective, space-saving, and weight-efficient manner, the method according to the invention provides that the first control unit (brake control unit) determines the distribution of a total torque requested by the driver of the motor vehicle among the drive devices and thus among the axles. The driver requests the total torque, for example, by correspondingly actuating, in particular moving, a control element designed, for example, as a pedal, in particular as an accelerator pedal, and arranged, for example, in the interior of the motor vehicle.The total torque, also referred to as the total torque, is thus, for example, a request from the driver, also referred to as the driver's command, which expresses the desire, by operating the control element, for the total torque to act on the wheels or axles as a whole. The aim of the method is to comply with the driver's command and to allow the total torque to act on the axles or wheels as a whole, i.e., to adjust it. This is possible in a particularly advantageous manner using the method according to the invention.

[0011] In the method, at least one, in particular electrical or electronic, distribution signal, which characterizes the distribution determined by the brake control unit, is provided by the first control unit and received by the second control unit (drive control unit). In this way, the distribution, which is or was determined by means of the brake control unit, is communicated to the drive control unit. Furthermore, the method provides that the drive control unit, depending on the received distribution signal, controls the drive devices and thus operates them, in particular controls or regulates them, in such a way that the torques, also referred to as individual torques, are provided by the drive devices and, in sum, correspond to the total torque.In other words, the drive devices are controlled by the drive control unit in dependence on the received distribution signal in such a way that the drive devices provide the individual torques in such a way that the individual torques in sum correspond to the total torque.

[0012] In the method according to the invention, the distribution of the total torque to the axles is not carried out, or not only carried out, by the drive control unit; rather, the distribution of the total torque to the axles is carried out by the brake control unit. This allows for a holistic approach, since the brake control unit usually already has all the input and output variables relevant for the distribution of the total torque, also referred to as torque distribution, at its disposal. This allows it to carry out, for example, brake-internal functions such as traction control, engine overrun torque control, and an electronic stability program. Since the brake control unit now also distributes the total torque to the axles according to the invention, the distribution of the total torque to the axles can be implemented with only a small number of components, thus saving costs, space, and weight.In addition, an on-board network, via which, for example, the control units communicate and thus, for example, the distribution signal is transmitted, can be kept particularly simple and therefore cost-effective. In particular, an additional control unit used in addition to the brake control unit and in addition to the drive control unit to implement the distribution of the total torque can be avoided, so that the number of parts and thus the weight and installation space requirement of the drive train can be kept particularly low. In addition, a particularly advantageous four-wheel or all-wheel drive can be realized by the method according to the invention, since, for example, the first wheels can be driven or are driven by means of the first drive device and the second wheels can be driven, in particular simultaneously, by means of the second drive device.

[0013] Furthermore, the method according to the invention enables, on the one hand, particularly safe operation and, on the other hand, particularly efficient operation of the motor vehicle. In this regard, the method according to the invention makes it possible to drive only the wheel(s) of one of the axles for as long as possible by means of the drive device assigned to one axle, while the other axle, or the wheel(s) of the other axle, are not driven by the drive device assigned to the other axle.Through the inventive distribution of the total torque by the brake control unit and thus through the holistic approach, a four-wheel or all-wheel drive distribution can pursue the approach of maximum longitudinal dynamics or maximum traction, so that switching from two-wheel drive to all-wheel or four-wheel drive is possible only when, and preferably only when, required, for example, by a corresponding request from the driver. Otherwise, the drivetrain can be operated with two-wheel drive, which allows energy consumption to be kept particularly low.

[0014] With all-wheel drive, both the wheels of one axle and the wheels of the other axle are driven by the drive system, in particular simultaneously, thus ensuring particularly dynamic and safe operation. In particular, it is possible to implement the driver's request by redistributing the power to the other axle, even in the event of axle limitations on one of the axles, as long as this is physically possible and sensible. Excessive axle limitations can thus be avoided, so that in at least almost every driving situation, the driver's request can be met with regard to the provision of the total torque required by the drivetrain. This has a positive effect on both traction and thus on the safety as well as the driving dynamics of the vehicle.

[0015] The distribution of the total torque between the axles or drive units is understood to mean both driving and thus traction operation of the drive train as well as overrun operation or recuperation operation. Thus, for example, the respective individual torque can be a positive torque, by means of which the respective wheel and thus the motor vehicle as a whole is driven and thereby, for example, positively accelerated. Furthermore, it is conceivable that the respective individual torque is a negative torque and thus, for example, a recuperation torque or a braking, drag, or overrun torque, which is set or brought about, for example, in particular by means of the respective drive unit, and by means of which the motor vehicle is braked or prevented from accelerating.In traction mode, the respective wheel is driven by the drive device, and in push mode, for example, the respective drive device is driven by the respective wheel.

[0016] It has proven particularly advantageous if the first control unit determines the distribution as a function of at least one dynamic parameter that characterizes the driving dynamics of the motor vehicle. The driving dynamics or the dynamic parameter include, for example, an acceleration acting on the motor vehicle, in particular in the vehicle's longitudinal and / or transverse directions, which is detected, for example, by means of an acceleration sensor. Alternatively or additionally, the dynamic parameter can include a pitch and / or roll and / or yaw of the motor vehicle and thus, for example, a yaw rate. This makes it possible to ensure particularly advantageous driving behavior of the motor vehicle in a space-saving, weight-saving, and cost-effective manner.

[0017] To implement the holistic approach described above particularly advantageously, the first control unit is designed to control at least one service brake of the motor vehicle. This provides the brake control unit with advantageous input or control variables, allowing the brake control unit to not only advantageously control the service brake but also advantageously distribute the total torque.

[0018] The brake control unit essentially has the following functions or is used to implement the following functions: The first of these functions is the implementation of an anti-lock braking system (ABS). Here, for example, the brake control unit can control or actuate the service brake accordingly to implement an anti-lock braking system. A second of these functions is the implementation of an electronic differential lock (EDL). A third of these functions is the implementation of the aforementioned acceleration skid control. A fourth of these functions is the implementation of engine drag torque control. A fifth of these functions is the implementation of an electronic stability control (ESC), which is also known as an electronic stability system.The electronic stability system can, for example, change or influence braking torques specified by the driver, in particular for each wheel, and / or build them up actively and for each wheel, in particular independently of the driver or without any action by the driver.

[0019] It has proven particularly advantageous if the dynamic parameter includes at least one coefficient of friction, which characterizes the friction between at least one of the wheels and the aforementioned road surface on which the motor vehicle is supported via the at least one wheel. This embodiment is based on the finding that the brake control unit can already have information about the coefficient of friction available, or that the coefficient of friction can be determined particularly advantageously by the brake control unit, since the brake control unit already has input variables available that allow for simple and rapid determination of the coefficient of friction.By taking the coefficient of friction into account, for example, excessive and unnecessary axle limitation can be avoided and / or the total torque can be distributed between the axles in such a way that the total torque desired by the driver is provided by the drive system as a whole, without, however, leading to a loss of deceleration or stability on one of the axles and / or to excessive limitation of the respective axle. Limiting or the limitation of the respective axle means that, at least during a first period of time, a maximum torque acting on the respective axle or on the respective wheel of the respective axle is or is reduced compared to a second period of time that is different from the first period of time. This can, for example, avoid unfavorable driving conditions.

[0020] With regard to the aforementioned redistribution and with regard to a possible limitation of at least one of the axles, the following advantage can be achieved through the holistic approach and thus through the brake control unit determining the distribution of the total torque to the drive device: For example, a basic distribution is first determined, in particular by the brake control unit. The basic distribution can initially be determined such that the torques to be provided by the drive devices correspond to the total torque. For example, a maximum first torque acting on one of the axles is permitted, in particular during a first time interval or initially, in particular by the brake control unit, so that the drive device assigned to one axle may only provide or exert the first torque on that one axle.If, for example, a limitation of one axle occurs based on the basic distribution, in particular by the brake control unit, then, for example, a maximum second torque acting on one axle and lower than the first torque is permitted, in particular by the brake control unit, during a second time interval following the first time interval, so that the drive device assigned to one axle may only provide or exert a maximum of the second torque on one axle. One axle is thus limited to the second torque during the second time interval, which is, for example, lower than the first torque by a limiting torque, in particular a predetermined or predefinable one. The limiting torque is specified, for example, by the brake control unit.

[0021] By limiting one axle in this way, excessive slip on one axle can be avoided, for example, so that this limitation is carried out, for example, as part of a traction control system, which is carried out in particular by the brake control unit.

[0022] Typically, such a limitation of one axle, also known as axle limitation, also leads to a limitation of the other axle, so that the total torque desired by the driver cannot usually be provided by the drive train or the drive devices. In other words, the drive train can then usually only provide a drive torque that is lower than the desired total torque. This can now be avoided by the holistic approach. The holistic approach makes it possible to avoid excessive limitation of the other axle when limiting one axle, in particular by distributing or redistributing the limiting torque from one axle to the other axle and thus to the drive device assigned to the other axle.During this redistribution, the torque to be provided by the drive device assigned to the other axle is increased by the limiting torque, in particular based on the basic distribution and the torque initially determined within the framework of a basic distribution and to be provided by the drive device assigned to the other axle, in such a way that, during or despite the limitation, the torques provided or to be provided by the drive devices correspond in total to the total torque. If the limiting torque is 20 Newton meters, for example, the torque determined by the basic distribution and to be provided by the other axle is increased by 20 Newton meters.The redistribution is preferably also carried out taking into account excessive slip on the other axle or in such a way that excessive slip on the other axle is also avoided by the redistribution.

[0023] On the one hand, this prevents excessive slip on the axles, thus achieving particularly high or optimal traction of the vehicle and, consequently, particularly safe operation. On the other hand, it ensures that the drive systems and thus the drivetrain provide the total torque desired by the driver in almost every driving situation, thus enabling particularly high driving dynamics.

[0024] According to the invention, the second control unit determines a second distribution of the total torque requested by the driver of the motor vehicle to the drive device and thus to the axles, which distribution differs from the first distribution. This makes it possible to pursue different distribution objectives through the different distributions. As previously explained, the first distribution determined by the brake control unit, for example, aims at particularly advantageous driving dynamics and thus, for example, at actually being able to provide the total torque desired by the driver in at least almost every situation.Preferably, the second division aims, for example, to achieve the lowest possible energy consumption of the motor vehicle and thus a particularly high degree of efficiency or the most efficient possible operation of the motor vehicle.

[0025] Thus, it is preferably provided that the second control unit determines the second division as a function of at least one efficiency parameter that relates to low-energy operation of the motor vehicle. The first division can ensure that both particularly dynamic operation and particularly efficient and thus low-energy operation of the motor vehicle can be realized.

[0026] According to the invention, the first control unit (brake control unit) performs traction control (ASR) of the drive system. This allows the previously described holistic approach to be implemented particularly advantageously, since the brake control unit is used not only to distribute the total torque but also for traction control.

[0027] According to the invention, during traction control, the first control unit limits at least one of the individual torques to a maximum first value during at least a first time period, which is lower than a maximum second value of the at least one torque permitted by the first control unit during a second time period different from the first time period. Thus, an axle limitation takes place in order to avoid, for example, a loss of traction or grip. However, the first division makes it possible to shift this axle limitation to the other axle, so that overall, i.e., the sum of the individual torques, makes it possible to provide the total torque desired by the driver across the axles. This ensures particularly dynamic and, at the same time, safe operation.

[0028] A further embodiment is characterized in that the first control unit performs drag torque control of the drive systems, also known as overrun torque control. If the driver requests a drag or overrun torque, for example, by abruptly releasing the accelerator pedal, the respective drag torque can be adjusted by the drag torque control. This can prevent, for example, an excessively abrupt buildup of excessive drag torque, thus avoiding unfavorable driving situations.

[0029] It has proven particularly advantageous if the first control unit, during drag torque control, limits at least one of the individual torques to a maximum first value during at least a first time period, which is lower than a maximum second value of the at least one individual torque permitted by the first control unit during a second time period different from the first time period. Here, too, axle limitation takes place within the framework of drag torque control, whereby a loss of traction can be avoided. Nevertheless, by appropriately distributing the total torque, the axle limitation, which takes place on one of the axles, for example, can be shifted to the other axle, so that the total torque desired by the driver can be guaranteed, in particular also during overrun or in the case of overrun.

[0030] In order to achieve a particularly advantageous distribution of the total torque, a further embodiment of the invention provides that at least one of the drive devices, in particular both drive devices, comprises or comprise at least one electric machine. The distribution determined by means of the first control unit sets, for example, a recuperation torque and thus a recuperation mode of the electric machine, which is operated as a generator in recuperation mode. In recuperation mode, the electric machine is in overrun mode, with the electric machine or generator being driven by at least one of the wheels of the axle to which the electric machine is assigned. The generator thereby provides electrical energy, which can be stored, for example, in an energy storage device of the motor vehicle.By activating recuperation mode, particularly efficient operation can be achieved. Furthermore, a particularly advantageous distribution of the total torque can be achieved, so that the total torque desired by the driver can be provided in at least almost every driving situation.

[0031] In order to be able to divide the total torque particularly advantageously, it is provided in a further embodiment of the invention that the first control unit determines the division as a function of a driving profile selected by the driver and / or as a function of a state of an electronic stability program selected by the driver and / or as a function of whether the motor vehicle is coupled to a trailer and / or as a function of a change in the position of the control element brought about by the driver.

[0032] Finally, it has proven particularly advantageous that a mechanical, torque-transmitting coupling of the axles is omitted or not provided. In other words, the axles are mechanically decoupled from each other, especially permanently.

[0033] A second aspect relates to a drive train for a motor vehicle, wherein the drive train is designed to carry out a method according to the invention. For this purpose, the drive train comprises a first axle which has at least one first wheel. The drive train further comprises a second axle which follows the first axle in the vehicle longitudinal direction and which has at least one second wheel. The drive train further comprises at least one first drive device assigned to the first axle, by means of which the first wheel can be driven. Furthermore, the drive train comprises at least one second drive device assigned to the second axle, by means of which the second wheel can be driven. In addition, the drive train comprises a first control unit, by means of which at least one braking torque for braking the motor vehicle can be adjusted.Furthermore, the drive train comprises a second control unit provided in addition to the first control unit, by means of which the drive devices can be controlled in order to thereby set a respective torque provided by the respective drive device and also referred to as an individual torque for driving the respective wheel. The first control unit is designed to determine a distribution of a total torque requested by the driver of the motor vehicle between the drive device and thus between the axles. The first control unit is designed to provide at least one distribution signal that characterizes or defines the determined distribution.The second control unit is designed to receive the distribution signal and, depending on the received distribution signal, to control the drive devices in such a way that the drive devices provide the individual torques and the torques in total correspond to the total torque.

[0034] The invention also includes further developments of the drive train according to the invention that have features already described in connection with the further developments of the method according to the invention. For this reason, the corresponding further developments of the drive train according to the invention are not described again here.

[0035] The invention also includes combinations of the features of the described embodiments.

[0036] An exemplary embodiment of the invention is described below. It shows: Fig. 1 a schematic representation of a drive train according to the invention; Fig. 2 a flowchart illustrating a method according to the invention; and Fig. 3 shows a further diagram illustrating the method according to the invention.

[0037] The exemplary embodiment explained below is a preferred embodiment of the invention. In the exemplary embodiment, the described components of the embodiment each represent individual, independently considered features of the invention, which also further develop the invention independently of one another and are thus also to be considered as components of the invention, either individually or in a combination other than that shown. Furthermore, the described embodiment can also be supplemented by further features of the invention already described.

[0038] In the figures, functionally identical elements are provided with the same reference numerals.

[0039] Fig. Figure 1 shows a schematic representation of a drive train 10 for a motor vehicle, in particular a passenger car. The drive train 10 has at least or exactly two axles 12 and 14 arranged one behind the other in the vehicle's longitudinal direction and thus in succession, wherein the axle 12 is also referred to as the first axle and the axle 14 is also referred to as the second axle. The vehicle's longitudinal direction is Fig. 1 by a double arrow 16. The axle 12 has at least or exactly two first wheels 18 spaced apart from one another in the transverse direction of the vehicle, which are, for example, front wheels of the motor vehicle. Thus, the axle 12 is, for example, a front axle of the motor vehicle. In Fig. In Figure 1, the vehicle's transverse direction is illustrated by a double arrow 20. The axle 14 has at least or exactly two second wheels 22, which are spaced apart from each other in the vehicle's transverse direction. The wheels 22 are, for example, rear wheels of the motor vehicle, so that the axle 14 is, for example, a rear axle of the motor vehicle.

[0040] The drive train 10 has a first drive device 24, which, with respect to the axles 12 and 14, is exclusively assigned to the axle 12. Thus, with respect to the wheels 18 and 22, the drive device 24 is exclusively assigned to the wheels 18, so that, with respect to the axles 12 and 14, only the axle 12 can be driven by means of the drive device 24. In other words, with respect to the wheels 18 and 22, only the wheels 18 can be driven by means of the drive device 24, so that, with respect to the wheels 18 and 22, the drive device 24 can only drive the wheels 18, but not the wheels 22. The drive train 10 further comprises a second drive device 26, which, with respect to the axles 12 and 14, is exclusively assigned to the axle 14.This means that the drive device 26 is assigned exclusively to the wheels 22 with respect to the wheels 18 and 22, so that by means of the drive device 26 with respect to the wheels 18 and 22 only the wheels 22, but not the wheels 18, can be driven.

[0041] The respective drive device 24 or 26 can comprise at least one or exactly one internal combustion engine, by means of which the respective wheels 18 or 20 can be driven. Alternatively or additionally, the respective drive device 24 or 26 can comprise at least one or exactly one electric machine, by means of which the respective wheels 18 or 22 can be electrically driven.

[0042] In the Fig. 1, the drive device 24 has at least or exactly one first electric machine 28, by means of which the wheels 18 can be electrically driven. Furthermore, the drive device 26 has at least or exactly one second electric machine 30, by means of which the wheels 22 can be electrically driven. Preferably, the motor vehicle is designed as an electric vehicle, in particular a battery-electric vehicle (BEV), so that the wheels 18 and 22 can be driven exclusively electrically. Alternatively, it is conceivable for the motor vehicle to be designed as a hybrid vehicle, in particular as a plug-in hybrid. The axles 12 and 14 are mechanically decoupled from one another and thus are not coupled to one another in a torque-transmitting manner, so that a mechanical, torque-transmitting coupling of the axles 12 and 14 is omitted.

[0043] For example, in order to electrically drive the respective wheels 18 or 22 by means of the respective electric machine 28 or 30, the respective electric machine is operated in motor mode and thus as an electric motor. The respective electric machine 28 or 30 is then in traction mode. In other words, in order to drive the respective wheels 18 or 22 by means of the respective drive device 24 or 26, a respective traction mode of the respective drive device 24 or 26 is set, so that in traction mode the respective wheels 18 or 22 are driven by the respective drive device 24 or 26. Furthermore, a push mode of the respective drive device 24 or 26, also referred to as towing mode, is conceivable.In the respective overrun mode, the respective drive device 24 or 26 is driven by the respective wheels 18 and 22, respectively, and thus, for example, by the kinetic energy of the moving motor vehicle. The respective overrun mode brakes the respective wheels 18 and 22, respectively, and thus slows them down or prevents them from accelerating.

[0044] The drive train 10 further comprises a first electronic control unit 32, by means of which, for example, at least one braking torque for braking the motor vehicle can be set. The braking torque is, for example, a drag torque, also referred to as a coasting torque, of the respective drive device 24 or 26, wherein the drag torque is absorbed, for example, by the respective drive device 24 or 26 in coasting mode in order to drive the respective drive device 24 or 26 in coasting mode. In particular, a service brake of the drive train can be controlled by the control unit 32.

[0045] The drive train 10 further comprises a second electronic control unit 34, which is provided in addition to the control unit 32 and is designed separately from the control unit 32. The second electronic control unit 34 is also referred to as a drive control unit (ASG). The drive devices 24 and 26 can be controlled by the control unit 34 in order to set a respective torque, which is to be provided by the respective drive device 24 or 26 and is also referred to as an individual torque, for driving the respective wheel 18 or 22. Fig. 1 it can be seen that the control units 32 and 34 are separate units.

[0046] In order to be able to realize a particularly advantageous, cost-, space-, and weight-efficient torque distribution between the drive devices 24 and 26 and thus between the axles 12 and 14, a method for operating the drive train 10 by means of the control unit 32, which is also referred to as the brake control unit (BSG), determines a total torque requested by the driver of the motor vehicle and to be provided by the drive devices 24 and 26 together or in total. For example, as part of a driver request determination, the total torque requested by the driver and thus desired is determined.The distribution of the total torque between the drive devices 24 and 26 and thus between the axles 12 and 14 is to be understood, for example, as meaning that the brake control unit determines, in particular calculates, a first partial torque to be provided by the drive device 24 and a second partial torque to be provided by the drive device 26, wherein the partial torques together result in the total torque. The partial torques can be the aforementioned individual torques, so that when the drive devices 24 and 26 provide partial torques or the individual torques, in particular simultaneously, the total torque desired by the driver is provided overall. The total torque requested by the driver is thus a driver request, also referred to as the driver command, with regard to the provision of the total torque by the drive devices 24 and 26.The respective partial torque can be zero, less than zero or greater than zero, whereby the total torque requested by the driver is greater than or less than zero or zero.

[0047] In the method, the control unit 32 provides, for example, via a Fig. 1, the on-board electrical system 36, which is shown particularly schematically, provides an electrical distribution signal which characterizes the distribution determined by the control unit 32. The distribution signal is transmitted from the control unit 32 to the control unit 34 via the on-board electrical system 36, so that the control unit 34 receives the distribution signal via the on-board electrical system 36. Depending on the received distribution signal, the control unit 34 controls the drive devices 24 and 26 such that the individual torques are provided by the drive devices 24 and 26, in particular simultaneously, and in sum correspond to the total torque. The respective individual torque can correspond to zero, be greater than zero, or less than zero, wherein, in particular, if one of the individual torques is zero, the other individual torque is greater or less than zero. The total torque is preferably a torque different from zero.If the respective individual torque is greater than zero, the respective individual torque is, for example, a traction torque, so that the drive device 24 or 26, which provides the traction torque, is operated in traction mode. If the respective individual torque is less than zero, the respective individual torque is, for example, a recuperation, braking, or drag torque, so that, for example, the drive device 24 or 26, which provides the overrun torque, also referred to as the drag torque, is operated in overrun mode and is driven, for example, by the wheels 18 or 22 of the axle 12 or 14 to which the respective drive device 24 or 26 is assigned.

[0048] The overrun mode can, in particular, be a recuperation mode of the respective electric machine 28 or 30. In recuperation mode, the electric machine 28 or 30 is operated as a generator, which is driven by the wheels 18 or 22, respectively. The generator thus converts the kinetic energy of the motor vehicle into electrical energy, which is provided by the generator. The electrical energy provided by the generator can, for example, be stored in a storage device designed to store electrical energy. The storage device can, for example, be designed as a battery, in particular as a high-voltage battery.

[0049] Fig. Figure 2 shows a flowchart illustrating the method in more detail. A block 36 in Fig. 2 illustrates, for example, that the control unit 34 (drive control unit) determines the total torque requested and thus desired by the driver, particularly as part of determining the driver's request. A block 38 illustrates that, for example, by means of the drive control unit (control unit 34), a second distribution of the total torque requested by the driver of the motor vehicle between the drive devices 24 and 26 and thus between the axles 12 and 14 is determined, which distribution differs from the previously described distribution, in particular as part of a longitudinal distribution operating strategy. The second distribution is thus, for example, a suggestion made by the control unit 34 for the distribution of the total torque between the axles 12 and 14. For example, the drive control unit proposes the second distribution with a view to the most efficient and thus energy-efficient operation of the motor vehicle.The brake control unit (control unit 32), for example, determines the first distribution with a view to achieving the highest possible driving dynamics of the motor vehicle. The first distribution, which is determined, in particular calculated, by the brake control unit, is shown in . Fig. 2 by a block 40. An arrow 42 indicates that the first division overrides or replaces the second division and that the division signal is transmitted from the brake control unit to the drive control unit. The first division determined by the brake control unit is thus implemented by the drive devices 24 and 26 through the mediation of the drive control unit, since it is not the brake control unit that controls the drive devices 24 and 26; rather, the drive control unit implements the first division determined by the brake control unit by having the drive control unit, and not the brake control unit, control the drive devices 24 and 26.

[0050] For example, a first power electronics unit is assigned to the electric machine 28, while a second power electronics unit is assigned to the electric machine 30. In order to implement the distribution of the total torque between the axles 12 and 14 determined by the brake control unit, the power electronics units are controlled by the drive control unit. Subsequently, the drive devices 24 and 26, in particular the electric machines 28 and 30, provide the respective individual torques, which together correspond to the total torque or result in the total torque. In this regard, Fig. 2 Blocks 44 and 46 so-called torque paths, via which the individual torques are finally converted by controlling the electric machines 28 and 30, wherein the control of the electric machines 28 and 30 is or was effected by the drive control unit. Furthermore, Fig. 2 a block 48 torque interventions, which are carried out by the brake control unit (control unit 34) if necessary. Fig. 2, it can be seen from an arrow 50 that the brake control unit intervenes via the torque interventions in the torque paths via which the drive control unit implements the first distribution, in order to thereby realize a particularly advantageous distribution of the wheel torque between the axles 12 and 14.

[0051] The first distribution is thus a redistribution with respect to the second distribution, since the proposal of the drive control unit is overruled or replaced by the first distribution. Since, for example, the braking torque can also be adjusted or set using the brake control unit and / or the service brake of the motor vehicle can be controlled or actuated or is controlled or actuated using the brake control unit, and since the first distribution is carried out by the brake control unit, a holistic approach is created, whereby the total torque can be distributed between axles 12 and 14 in a cost-effective, space-saving, and weight-efficient manner.In addition, the total torque desired by the driver can be provided by the drive train 10 in at least almost every driving situation, thereby achieving particularly high driving dynamics with particularly high traction and thus particularly high safety. In addition, the drive train 10 can be operated for a particularly long time, in particular with two-wheel drive for as long as possible, and thus with particularly low energy consumption. Since the total torque is distributed between the axles 12 and 14, the total torque is distributed in the vehicle's longitudinal direction, thus providing a longitudinal distribution of the total torque. The drive devices 24 and 26 are axle-individual motors between which there is no mechanical coupling. In this regard, the control units 32 and 34 ensure a quasi-virtual coupling of the axles 12 and 14, since the total torque is provided in total by the drive devices 24 and 26.Preferably, the brake control unit also carries out a traction control and a thrust torque control of the respective drive devices 24 and 26, whereby the holistic approach within the brake control unit is particularly advantageous.

[0052] Fig. 3 shows another diagram to illustrate the method and the drive train 10. In Fig. 3, a block 52 illustrates a prediction with regard to switching from two-wheel drive to four-wheel or all-wheel drive. Two-wheel drive is to be understood, for example, as meaning that, with respect to the wheels 18 and 22, only the wheels 18 or only the wheels 22 are driven. Thus, for example, the two-wheel drive can be set during a first period of time. Four-wheel or all-wheel drive is to be understood as meaning that, for example, during a second period of time different from the first period of time, both the wheels 18 and the wheels 22 are driven, in particular simultaneously. If, for example, a switch is made from two-wheel drive to all-wheel or four-wheel drive, the four-wheel or all-wheel drive is, so to speak, engaged.Block 52 illustrates a predictive engagement of the all-wheel or four-wheel drive, which for the sake of simplicity is also referred to below as all-wheel drive.

[0053] Predictive engagement of the all-wheel drive is understood as follows: Between a starting time at which the engagement of the initially deactivated all-wheel drive begins, and an operating time at which the engagement of the all-wheel drive is, in particular, completely completed, with the operating time following the starting time, there is usually an engagement time that is required for the engagement of the all-wheel drive. With regard to the electric machines 28 and 30, the engagement time is necessary, for example, because, for example, in the two-wheel drive, the electric machine 28 is initially deactivated. This means that before the starting time or during the two-wheel drive, the electric machine 28 is initially still de-energized.Starting from the de-energized state, the electric machine 28 or 30 requires the connection time until the electric machine 28 or 30 can provide a torque and thus exert it on the wheels 18 or 22. This is due to the field structure of the electric machine 28 or 30, which is designed, for example, as an asynchronous machine. In other words, starting from its de-energized state, the electric machine 28 or 30 requires the connection time until the electric machine 28 or 30 can provide a desired torque in the form of the respective individual or partial torque. Thus, if the initially de-energized electric machine 28 is activated, i.e. energized, at the start time, the electric machine 28 can only provide a desired torque by energizing it after the connection time and thus at the operating time.

[0054] Within the framework of the predictive, i.e., anticipatory engagement of the all-wheel drive, a required time is determined, for example, by means of the brake control unit, at which the engagement of the four-wheel drive must be completed, in particular completely and / or at the latest. This requires that the required time lies in the future with respect to the determination of the required time. This means, for example, that the required time is determined during a time interval, with the required time following the time interval and thus lying in the future with respect to the time interval and being spaced apart from the time interval.

[0055] Depending on the determined demand time, the engagement of the all-wheel drive, i.e., for example, the energization of the electric machine 28, begins at the start time, in particular depending on the determined distribution, wherein the start time precedes the demand time. The demand time can, for example, coincide with the operating time, or the demand time can follow the operating time, so that the all-wheel drive is fully engaged at the latest at the demand time, in particular starting from the two-wheel drive. In other words, depending on the demand time and preferably depending on the determined distribution, the engagement of the all-wheel drive begins at the start time in such a way that the engagement of the all-wheel drive, in particular completely, is completed at the latest at the demand time.

[0056] This predictive engagement of the all-wheel drive takes place, for example, by estimating the coefficient of friction at the driven wheels 18 and 22, respectively, i.e. at those wheels 18 and 22 which are driven, in particular when the two-wheel drive is activated. This is advantageous because the other wheels 22 and 18, respectively, which are still to be engaged and thus become driven wheels, are at least almost force-free when the four-wheel drive is deactivated or when the two-wheel drive is activated. The method is carried out while the motor vehicle is traveling along a roadway and is therefore supported on the roadway in the vertical direction of the vehicle via the wheels 18 and 22. Estimation of the coefficient of friction is to be understood as determining, in particular estimating, a coefficient of friction which represents friction between the respective driven wheel 18 and 22, respectively.22 and the road surface. Since, in this case, for example, by engaging all-wheel drive, axle 12 is connected to axle 14, so that the rear wheels are or were driven during two-wheel drive, the predictive engagement of all-wheel drive occurs, for example, by estimating the friction coefficient on the rear axle and thus on wheels 22 as early as possible.

[0057] Furthermore, it is preferably provided that the all-wheel drive is implemented as a function of a driving profile selected by the driver and / or as a function of an operating state of the drive train 10 selected by the driver and / or as a function of a state of an electronic stability program selected by the driver and / or as a function of whether the motor vehicle is coupled to a trailer and / or as a function of a change in the position of a control element brought about by the driver. The control element is arranged in the interior of the motor vehicle and can be actuated, in particular moved, by the driver to request or adjust the total torque. This enables particularly efficient operation without any significant disadvantages in traction. In other words, it is possible, on the one hand, to maintain two-wheel operation for as long as possible.This ensures particularly efficient operation. On the other hand, all-wheel drive can be engaged, particularly predictively, when desired or necessary.

[0058] In addition, Fig. 3, a block 54 represents a so-called basic distribution, which is performed by the brake control unit. The brake control unit, for example, starts from the basic distribution and then performs a redistribution, illustrated by a block 56, which changes the basic distribution. The distribution signal then characterizes the redistribution, for example, so that the redistribution is, for example, the first distribution.The basic distribution occurs, for example, depending on learned friction values ​​and / or speeds and / or accelerations in the vehicle's longitudinal direction and / or depending on an estimated weight of the motor vehicle and / or a driving profile selection and / or an operating state of the drive train 10 set by the driver and / or depending on a state of the electronic stability program set by the driver and / or depending on trailer operation and / or depending on the change in the position of the accelerator pedal and / or depending on the motor vehicle's own steering behavior. The redistribution occurs, for example, depending on driving dynamics parameters that characterize the driving dynamics of the motor vehicle.The prediction illustrated by block 52 and the basic distribution illustrated by block 54, for example, use different friction coefficients to perform the prediction and the basic distribution, respectively. While the prediction, for example, uses the previously described early friction coefficient estimation and the friction coefficients determined thereby, the basic distribution uses so-called secured friction coefficients, which, in comparison to the early friction coefficient estimation, are or were determined through longer determination or observation. This enables a rapid response to be realized during the prediction by estimating the friction coefficients early or early, so that, for example, the four-wheel drive can be engaged quickly. During the basic distribution, for example, a torque shift occurs through known friction coefficient utilization.

[0059] Finally, in Fig.3, a block 58 illustrates a limitation, also referred to as limiting or axle limitation. Axle limitation occurs, for example, as a function of available axle torques and / or as a function of a specified value. Axle limitation means that the brake control unit, for example, limits at least one of the individual torques during at least a first time period to a maximum first value, which is lower than a maximum second value of the at least one individual torque permitted by the brake control unit during a second time period different from the first time period.For example, the first division makes it possible to shift or distribute a limiting torque, by which the at least one individual torque is limited and thus reduced during the first period compared to the second period, to the other axle, so that the total torque desired by the driver can be provided by the drive devices 24 and 26. This ensures, on the one hand, particularly dynamic operation and, on the other hand, particularly safe operation of the motor vehicle.

[0060] Overall, it can be seen that the drive train 10 can be switched between a first operating state, in which the two-wheel drive of the drive train 10 is activated, and a second operating state, in which the four-wheel drive of the drive train 10 is activated. In order to be able to switch from one of the operating states to the other operating state, for example from the two-wheel drive to the four-wheel drive and / or from the four-wheel drive to the two-wheel drive, in a particularly needs-based and timely manner, the method for operating the drive train 10 provides that during a journey of the motor vehicle, an electronic computing device of the drive train 10 is used to determine a or the aforementioned required time at which the switching from one operating state to the other operating state must be completed at the latest.In this case, the time of demand is in the future with respect to the determination of the time of demand. The computing device can be one of the control units 32 and 34, or the computing device can comprise the control unit 32 and / or the control unit 34.

[0061] Furthermore, depending on the determined demand time, switching from one operating state to the other operating state begins at a start time prior to the demand time in such a way that the switching is completed at the latest by the demand time. Switching from one operating state to the other can be understood as engaging and / or disengaging the four-wheel drive, so that the four-wheel drive can be engaged and / or disengaged particularly advantageously by means of the method. This makes it possible, on the one hand, to operate the drive train 10 with the two-wheel drive for particularly large portions of its entire operating time, so that particularly efficient and thus low-efficiency and low-energy operation of the drive train 10 and thus of the motor vehicle as a whole can be realized.On the other hand, switching from two-wheel drive to four-wheel drive is possible then and preferably only then when this has been determined, in particular assessed, as advantageous, for example by the electronic computing device. The method enables particularly early engagement of the four-wheel drive, so that the four-wheel drive is fully engaged when required. This is required at the latest at the time required, or the computing device has determined or has determined that full engagement of the four-wheel drive is advantageous or more advantageous than two-wheel drive at the latest at the time required, particularly with regard to a safe and / or dynamic driving condition. The method enables particularly high efficiency without any disadvantages in terms of traction.In particular, the method makes it possible to maintain two-wheel drive for as long as possible and to use four-wheel drive only as long as necessary.

Claims

[1] Method for operating a drive train (10) of a motor vehicle, in which which the drive train (10) has: - a first axle (12) with at least one first wheel (18); - a second axle (14) following the first axle (12) in the vehicle longitudinal direction (16) and having at least one second wheel (22); - at least one first drive device (24) associated with the first axle (12), by means of which the first wheel (18) can be driven; - at least one second drive device (26) associated with the second axle (14), by means of which the second wheel (22) can be driven; and - a first control unit (32) by means of which at least one braking torque for braking the motor vehicle can be set, in that the first control unit (32) is designed to control at least one service brake of the motor vehicle and thereby implement an anti-lock braking system of the motor vehicle; characterized by, that the drive train (10) has a second control unit (34) provided in addition to the first control unit (32), by means of which the drive devices (24, 26) can be controlled in order to thereby set a respective torque to be provided by the respective drive device (24, 26) for driving the respective wheel (18, 22), wherein: ◯ by means of the first control unit (32) a distribution of a total torque requested by the driver of the motor vehicle between the drive devices (24, 26) is determined; ◯ at least one division signal characterising the determined division is provided by the first control unit (32) and received by the second control unit (34); and ◯ the second control unit (34) controls the drive devices (24, 26) in dependence on the received distribution signal such that the torques are provided by the drive devices (24, 26) and in sum correspond to the total torque; ◯ wherein a traction control of the drive devices (24, 26) is carried out by means of the first control unit (32), ◯ wherein the first control unit (32) limits at least one of the torques during the traction control to a maximum first value during at least a first time period, which is lower than a maximum second value of the at least one torque permitted by the first control unit (32) during a second time period different from the first time period, ◯ wherein a second distribution, different from the distribution, of the total torque requested by the driver of the motor vehicle between the drive devices (24, 26) is determined by means of the second control device (34), wherein the second distribution is overruled by the first distribution. [2] Method according to claim 1, wherein the first control unit (32) determines the division as a function of at least one dynamic parameter which characterizes a driving dynamics of the motor vehicle. [3] Method according to claim 2, wherein the dynamic parameter comprises at least one friction coefficient which characterizes a friction between at least one of the wheels (18, 22) and a road surface on which the motor vehicle is supported via the at least one wheel (18, 22). [4] Method according to claim 3, wherein the coefficient of friction is determined predictively. [5] Method according to claim 1, wherein the second control unit (34) determines the second division as a function of at least one efficiency parameter which relates to low-energy operation of the motor vehicle. [6] Method according to one of the preceding claims, wherein a drag torque control of the drive devices (24, 26) is carried out by means of the first control unit (32). [7] Method according to claim 6, wherein the first control unit (32) limits at least one of the torques during the drag torque control during at least a first time period to a maximum first value which is lower than a maximum second value of the at least one torque permitted by the first control unit (32) during a second time period different from the first time period. [8] Method according to one of the preceding claims, wherein at least one of the drive devices (24, 26) comprises an electric machine (28, 30), and wherein a recuperation torque and thereby a recuperation operation of the electric machine (28, 30) is set by the division determined by means of the first control unit (32), which is operated as a generator in the recuperation operation. [9] Method according to one of the preceding claims, wherein the first control unit (32) determines the distribution as a function of a driving profile selected by the driver and / or as a function of a state of an electronic stability program selected by the driver and / or as a function of whether the motor vehicle is coupled to a trailer and / or as a function of a change in the position of an operating element caused by the driver, by means of which the total torque can be requested by the driver. [10] Method according to one of the preceding claims, wherein a mechanical, torque-transmitting coupling of the axes (12, 14) is omitted.

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