Method for operating a drive unit for a motor vehicle and corresponding drive unit

Abstract

A method for operating a drive system for a motor vehicle comprising several electric machines operatively connected to different wheel axles and / or wheels of the motor vehicle, wherein individual torques for each of the electric machines are determined and set on the electric machines from a drive input from a driver of the motor vehicle and / or a driver assistance device and at least one machine parameter of the electric machines and a state parameter of an environment, such that for different values ​​of the machine parameter and / or the state parameter, the individual torques are different from one another for the same drive input, wherein an efficiency of the electric machines is used as the machine parameter and the individual torques are determined such that at least one first of the electric machines is operated with a higher efficiency than another second of the electric machines.characterized in that a coefficient of friction between at least one of the wheels and a surface is used as a state parameter of the environment, wherein the drive input is distributed more evenly among the individual torques the smaller the coefficient of friction is.

Description

[0001] The invention relates to a method for operating a drive device for a motor vehicle, which has a plurality of electric machines that are operatively connected to different wheel axles and / or wheels of the motor vehicle, wherein individual torques for each of the electric machines are determined and set on the electric machines from a drive specification of a driver of the motor vehicle and / or a driver assistance device and at least one machine parameter of the electric machines and a state parameter of an environment, so that for different values ​​of the machine parameter and / or the state parameter, the individual torques are different from one another for the same drive specification, wherein an efficiency of the electric machine is used as the machine parameter and the individual torques are determined such that at least a first of the electric machines is operated with a higher efficiency than another,second of the electric machines. The invention further relates to a drive device for a motor vehicle.

[0002] For example, EP 2 444 273 A1 is known from the prior art. This document relates to an engine control device for an electrically powered motor vehicle with a first motor for driving the front wheels of the motor vehicle and a second motor for driving the rear wheels of the motor vehicle.The engine control device comprises an engine drive control device which distributes a target torque requested for the motor vehicle and controls the first and second motors, a determination device which detects a period of time over which a drive torque distributed to one of the first and second motors corresponds to or is greater than a reference torque which is predetermined for one of the first and second motors, and which determines whether the detected period of time corresponds to or is longer than a predetermined period of time, and a drive torque distribution control device which, if the detected period of time corresponds to or is greater than the predetermined period of time, lowers the drive torque distributed to one of the first and second motors below the reference torque and increases a drive torque distributed to the other of the first and second motors.

[0003] Furthermore, the prior art includes the document DE 11 2013 007 547 T5 and the non-patent literature Michael Eckert: Energy-optimal vehicle dynamics control of multi-engine electric vehicles, Volume 31, D-76131 Karlsruhe: KIT Scientific Publishing, April 17, 2015 - ISBN 978-3-7315-0332-3.

[0004] The drive device serves to drive the motor vehicle, i.e., to provide a torque directed toward driving the motor vehicle. Driving can include, for example, accelerating and / or decelerating the motor vehicle and / or maintaining a constant speed. The drive device is assigned to the motor vehicle or forms a component of the motor vehicle. The drive device has several electrical machines, which can be driven, for example, by means of electrical energy extracted from an energy storage device.

[0005] For example, in a first operating mode, the electrical energy extracted from the energy storage device is supplied to at least one of the electrical machines or several of the electrical machines, while in a second operating mode, at least one other of the electrical machines is operated as a generator, with the electrical energy generated by the generator being temporarily stored in the energy storage device. The second operating mode corresponds to a recuperation operating mode.

[0006] Of course, it is also possible to generate the electrical energy required to operate the electrical machines in another way on board the motor vehicle, in particular using a separate generator, which is driven, for example, by an internal combustion engine. Additionally or alternatively, a fuel cell device can be provided to generate the electrical energy. The electrical energy thus generated can be used directly to operate at least one of the electrical machines or, alternatively, can be temporarily stored in the energy storage device.

[0007] The electric machines of the drive device are operatively connected to different wheel axles and / or wheels of the motor vehicle. Each wheel axle of the motor vehicle is preferably assigned a plurality of wheels, which are arranged in particular at opposite ends of the respective wheel axle. In principle, the motor vehicle can have any number of wheel axles, but two wheel axles are usual for passenger vehicles, namely a front axle and a rear axle. It can now be provided that at least a first of the electric machines is assigned to a first of the wheel axles, i.e. serves to drive the wheels assigned to this wheel axle. For this purpose, for example, the wheels are rigidly and / or permanently operatively connected to the first electric machine. Preferably, at least one transmission, in particular a differential gear, is provided between the electric machine and the wheels of the wheel axle.At least a second of the electric motors, however, is assigned to a second of the wheel axles. The above applies analogously to this.

[0008] Additionally or alternatively, it can be provided that the electric machines are directly assigned to the wheels of the motor vehicle. In this respect, for example, at least one of the electric machines is assigned to each of the wheels, thus implementing an independent wheel drive. Of course, not all wheels of the motor vehicle have to be driven at least temporarily; rather, the motor vehicle can have non-driven wheels in addition to the at least temporarily driven wheels. If a drive specification is present, for example in the form of a specified torque, this can be distributed evenly among the electric machines in order to achieve uniform drive or propulsion of the motor vehicle.

[0009] It is an object of the invention to propose a method for operating a drive device for a motor vehicle, which has advantages over known methods, in particular enables optimal adaptation of the drive device to current driving conditions and / or operating conditions of the motor vehicle.

[0010] This is achieved according to the invention with a method having the features of claim 1. It is provided that a coefficient of friction between at least one of the wheels and a surface is used as a state parameter of the environment, wherein the drive specification is distributed more evenly between the individual torques, the smaller the coefficient of friction is.

[0011] The drive specification, which is present, for example, in the form of the specified torque, is specified by the driver and / or the driver assistance device. The drive specification is thus present as a setpoint for the drive device and is adjusted thereon. The drive device determines the individual torques from the drive specification and at least one further parameter, for example the machine parameter and / or the state parameter. Such an individual torque is determined for each of the electrical machines and adjusted thereon. The individual torques thus represent setpoint torques for the electrical machine. The electrical machines are subsequently controlled such that they provide an actual torque corresponding to the respective individual torque.

[0012] The machine parameter of the electrical machines corresponds, for example, to a state variable of at least one of the electrical machines. Of course, multiple machine parameters can be used to determine the individual torques, preferably at least one machine parameter for each electrical machine, in particular exactly one machine parameter. In addition to or as an alternative to the machine parameter, the at least one state parameter can be used. The state parameter relates either to the motor vehicle or to the environment; in this respect, it can be present as a motor vehicle state parameter or as an environment state parameter. The state parameter of the motor vehicle corresponds, for example, to a state variable of the motor vehicle itself and is independent of the motor vehicle's environment. The state parameter of the environment, on the other hand, directly relates to the environment and, at most, indirectly to the motor vehicle.

[0013] When determining the individual torques, the drive specification and the at least one machine parameter or the at least one state parameter, in particular only the drive specification on the one hand and the machine parameter and / or the state parameter on the other, serve as input variables, while the individual torques are available as output variables. Additionally, in particular exclusively, the variables mentioned below can be used. The individual torques are determined in such a way that for different values ​​of the machine parameter and / or the state parameter, the individual torques differ from one another, even if the drive specification is the same.

[0014] For example, for one and the same drive specification, it can be provided that, for a first value of the machine parameter or the state parameter, the individual torques of several of the electrical machines, in particular all electrical machines, are identical, so that the drive specification is distributed evenly among the electrical machines or at least some of the electrical machines. For a second value of the machine parameter or the state parameter, which differs from the first value, however, the individual torques or at least several of the individual torques should be different from one another.

[0015] Accordingly, the drive input is distributed unevenly among the individual torques or the electric motors, so that the wheel axles or the wheels of the vehicle are subjected to different drive torques by the electric motors, corresponding to the individual torques. Of course, at least one of the electric motors can also be completely deactivated, i.e., provide no torque or a torque of 0 Nm.

[0016] This procedure is, of course, independent of the orientation or sign of the individual torques. Thus, the described method can be used both for accelerating and decelerating the motor vehicle and / or for maintaining the motor vehicle's speed constant. In particular, if different individual torques result from the machine parameter and / or the state parameter, it can be provided that the individual torques differ not only in their magnitude but also in their sign.

[0017] For example, it may be provided that one of the electric machines provides a single torque aimed at accelerating the motor vehicle, and another of the electric machines provides a single torque aimed at decelerating the motor vehicle. In this case, it may be provided, for example, that the decelerating electric machine is operated as a generator and thus generates electrical energy, which is used directly to operate the accelerating electric machine, in particular bypassing the energy storage device.

[0018] In addition to the machine parameter or the state parameter, a currently active driving profile can be used to determine the individual torques. The driving profile determines, for example, whether an efficient or sporty driving style should be implemented using the drive system. The driving profile can be set, for example, by the driver of the vehicle using a suitable control device. Using the described method, the best possible efficiency can be achieved during acceleration or deceleration of the vehicle.

[0019] In a further embodiment of the invention, it is provided that the electrical machines are designed identically or for different rated speeds and / or rated torques. In principle, the electrical machines can be designed in any desired manner. However, several of the electrical machines, in particular all electrical machines, are preferably designed identically. Alternatively, however, several of the electrical machines, in particular all electrical machines, can be designed differently, in particular for different rated speeds and / or different rated torques.

[0020] For example, the at least one electric machine assigned to the first wheel axle can be different from the at least one electric machine assigned to another, second wheel axle. In particular, the electric machine assigned to a rear axle will be designed for a higher rated torque than the electric machine assigned to a front axle. Analogously, electric machines assigned to the rear wheels of the motor vehicle can be identical, but designed for higher rated torques than identical electric machines assigned to the front wheels. If at least one electric machine is mentioned in this description, this can mean exactly one electric machine or, alternatively, several electric machines.

[0021] The invention provides that an efficiency of the electric machine is used as a machine parameter, and the individual torques are determined such that at least a first of the electric machines is operated with a higher efficiency than another, second of the electric machines. In particular, the first electric machine is operated at optimal efficiency, while at least one other of the electric machines, for example, all other electric machines, is operated with an efficiency that lies below its respective optimal efficiency. Alternatively, at least one of these electric machines can also be deactivated.

[0022] Within the scope of a further embodiment of the invention, it is provided that an acceleration, a steering angle and / or a wheel slip of at least one of the wheels is used as a state parameter of the motor vehicle. The acceleration can, for example, be a longitudinal acceleration or a lateral acceleration of the motor vehicle. The steering angle is the angle currently set by means of a steering device. The wheel slip is the wheel slip currently occurring at at least one of the wheels or a value which is determined from the wheel slip of the wheels or the driven wheels of the motor vehicle. For example, at least one of the mentioned variables, in particular several of the mentioned variables or all of the mentioned variables, is / are input into the determination of the individual torques.For example, when the steering angle is different from 0°, i.e. when the motor vehicle is cornering, it may be provided that the outer wheels of the motor vehicle are driven with greater individual torques than the inner wheels of the motor vehicle.

[0023] A particularly preferred embodiment of the invention provides that a longitudinal acceleration and / or a lateral acceleration of the motor vehicle is used as the acceleration. Such an embodiment has already been mentioned above. The longitudinal acceleration is the acceleration of the motor vehicle in the direction of a longitudinal axis of the motor vehicle, while the lateral acceleration is the acceleration in the transverse direction, i.e., in a direction perpendicular to the longitudinal direction and parallel to a ground surface or a floor plane of the motor vehicle.

[0024] The invention provides that a coefficient of friction between at least one of the wheels and a surface is used as an environmental condition parameter. The ambient temperature is the temperature outside the motor vehicle. It is measured, for example, using a suitable measuring device. The coefficient of friction, which can also be referred to as the friction coefficient, is a measure of the frictional force between the wheel and the surface in relation to the contact force, i.e., the wheel contact force.

[0025] For example, it can be provided that at an ambient temperature below a certain temperature threshold and / or a friction coefficient below a certain friction threshold, the deviation between the individual torques is selected to be smaller than at a higher ambient temperature or a higher friction coefficient. Preferably, the temperature threshold for the ambient temperature is selected such that if it is undershot, it can be assumed that the surface of the motor vehicle has a low friction coefficient, caused, for example, by ice. Accordingly, it is expedient to apply the drive input evenly to the surface via the wheel axles or wheels of the motor vehicle. According to the invention, the lower the ambient temperature and / or the friction coefficient, the more evenly the drive input is distributed among the individual torques.

[0026] Preferably, it is provided that if the ambient temperature falls below the temperature threshold and / or if the friction coefficient falls below the friction threshold, the drive specification is distributed evenly among the individual torques, while if the ambient temperature is above the temperature threshold or the friction coefficient is above the friction threshold, an increasing deviation between the individual torques is permitted with increasing ambient temperature and / or increasing friction coefficient.

[0027] Within the scope of a further embodiment of the invention, it is provided that the individual torques are optimized based on the machine parameter and / or the state parameter. The optimization is carried out, for example, in such a way that a value of the machine parameter and / or a value of the state parameter assumes an optimal value. In the case of the machine parameter, it can be provided, for example, that the efficiency is optimized. In this case, it can be provided that the overall efficiency of the drive device, for example, the average efficiency of all electrical machines, is considered.

[0028] To optimize overall efficiency, it may be provided that the individual torque of a first of the electric machines is increased to increase its efficiency, while the individual torque of a second of the electric machines is reduced, in particular to zero. While this may result in a deterioration in the respective efficiency of one or more of the electric machines, this is offset by an improvement in the efficiency of the first electric machine, so that the overall efficiency of the drive system increases.

[0029] A preferred embodiment of the invention provides that if an actual efficiency of one of the electrical machines deviates from a target efficiency, the individual torque of the electrical machine is changed by a torque difference such that the actual efficiency approaches the target efficiency, wherein the torque difference is taken into account when determining the individual torque of at least one other of the electrical machines. The actual efficiency is the current efficiency of the electrical machine. For example, a maximum efficiency of the electrical machine is used as the target efficiency.

[0030] If the actual efficiency deviates from the target efficiency, in particular if it is lower than this, the individual torque of the electrical machine should be changed such that the actual efficiency approaches the target efficiency. The individual torque is changed by the torque difference. In order to keep the total torque generated by the electrical machines, which results from the sum of the individual torques, equal to the drive specification, it is therefore necessary to reduce the individual torque of at least one other electrical machine. For example, the torque difference is deducted from the individual torque of a single other electrical machine. However, it can also be provided that the torque difference is divided proportionally between several individual torques of several other electrical machines and deducted proportionally from them.

[0031] Finally, within the scope of a further embodiment of the invention, it can be provided that the determination of the individual torques is additionally carried out taking into account a multi-axle drive request. The multi-axle drive request can, for example, be specified by the driver of the motor vehicle and / or the driver assistance device. In the case of the driver, this is provided, for example, by means of a suitable control element. When the multi-axle drive request is present, a torque directed towards driving the motor vehicle is to be applied to several wheel axles or to the wheels of several wheel axles. This means that when the multi-axle drive request is present, the drive specification is to be distributed more evenly across the individual torques of the electric machine, i.e., without the multi-axle drive request.

[0032] In particular, when a multi-axle drive requirement is present, the individual torques are selected such that the drive input is distributed between the front axle and the rear axle of the motor vehicle, or rather the corresponding individual torques, based on a constant distribution factor. When a multi-axle drive requirement is present, preferably wheels of several wheel axles are subjected to a torque directed toward driving the motor vehicle—in the case of a conventional motor vehicle, this would mean two front wheels and two rear wheels.

[0033] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method described above, wherein the drive device has a plurality of electrical machines which are operatively connected to different wheel axles and / or wheels of the motor vehicle.It is provided that the drive device is designed to determine individual torques for each of the electrical machines from a drive specification of a driver of the motor vehicle and / or a driver assistance device and at least one machine parameter of the electrical machines and a state parameter of an environment and to set them on the electrical machines, so that for different values ​​of the machine parameter and / or the state parameter with the same drive specification the individual torques are different from one another, wherein an efficiency of the electrical machines is used as the machine parameter and the individual torques are determined in such a way that at least a first one of the electrical machines is operated with a higher efficiency than another second one of the electrical machines.It is further provided that a coefficient of friction between at least one of the wheels and a surface is used as a state parameter of the environment, whereby the drive specification is distributed more evenly between the individual torques, the smaller the coefficient of friction is.

[0034] The advantages of such a design of the drive device and such a procedure have already been pointed out. Both the drive device and the method can be further developed according to the above explanations, so reference is made to these in this regard.

Claims

[1] Method for operating a drive device for a motor vehicle, which has a plurality of electrical machines that are operatively connected to different wheel axles and / or wheels of the motor vehicle, wherein individual torques for each of the electrical machines are determined from a drive specification of a driver of the motor vehicle and / or a driver assistance device and at least one machine parameter of the electrical machines and a state parameter of an environment and are set on the electrical machines, so that for different values ​​of the machine parameter and / or the state parameter with the same drive specification, the individual torques are different from one another, wherein an efficiency of the electrical machines is used as the machine parameter and the individual torques are determined in such a way,that at least a first of the electrical machines is operated with a higher efficiency than another second of the electrical machines, , characterized by that a coefficient of friction between at least one of the wheels and a surface is used as a state parameter of the environment, whereby the drive specification is distributed more evenly between the individual torques, the smaller the coefficient of friction is. [2] Method according to claim 1, characterized by that the electrical machines are designed identically or for different rated speeds and / or rated torques. [3] Method according to one of the preceding claims, characterized by that the individual torques are optimized based on the machine parameter and / or the condition parameter. [4] Method according to one of the preceding claims, characterized bythat if an actual efficiency of one of the electrical machines deviates from a target efficiency, the individual torque of the electrical machine is changed by a torque difference such that the actual efficiency approaches the target efficiency, wherein the torque difference is taken into account when determining the individual torque of at least one other of the electrical machines. [5] Method according to one of the preceding claims, characterized by that the determination of the individual torques is also carried out taking into account a multi-axis requirement. [6] Drive device for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive device has a plurality of electric machines which are operatively connected to different wheel axles and / or wheels of the motor vehicle, wherein the drive device is designed to determine individual torques for each of the electric machines from a drive specification of a driver of the motor vehicle and / or a driver assistance device and at least one machine parameter of the electric machines and a state parameter of an environment and to set them on the electric machines, so that for different values ​​of the machine parameter and / or the state parameter with the same drive specification, the individual torques are different from one another, wherein an efficiency of the electric machines is used as the machine parameter and the individual torques are determined in such a way,that at least a first of the electrical machines is operated with a higher efficiency than another second of the electrical machines, , characterized by that a coefficient of friction between at least one of the wheels and a surface is used as a state parameter of the environment, whereby the drive specification is distributed more evenly between the individual torques, the smaller the coefficient of friction is.