DE102020123689A1 - Method and device for operating a motor vehicle in a warm-up mode and motor vehicle - Google Patents

Abstract

The invention relates to a method and a device for operating a motor vehicle and a corresponding motor vehicle. In the method, a warming-up requirement for a component of the motor vehicle is detected. A first electrical machine of the motor vehicle is then operated as a motor to generate a total output power that includes a required drive power for driving a first axle of the motor vehicle and an additional power that goes beyond that. A second electrical machine is operated as a generator on a second axle of the motor vehicle with part of the additional power to generate a charging current for a battery of the motor vehicle. In this case, heat loss resulting from the motor-driven generation of the additional power by the first electrical machine and the corresponding generator-type operation of the second electrical machine is used to heat up the at least one component.

Description

The present invention relates to a method for operating a motor vehicle with two electrical machines and a device for a corresponding motor vehicle for corresponding automatic activation of the electrical machines. Furthermore, the present invention relates to a correspondingly equipped and set up motor vehicle.

It is known that operation or the respective operating properties of various components of motor vehicles can be temperature-dependent. For example, a temperature that is too high, i.e. overheating, can lead to damage or derating, i.e. a power limitation to protect against overheating, can be necessary. On the other hand, if the temperatures are too low, performance can be restricted and/or wear can be increased. The latter applies, for example, to lubricants or components lubricated by a lubricant, as well as to batteries, in particular traction batteries, ie drive energy stores in electrically operated motor vehicles. There is thus a motivation to enable or ensure reliable, situation-dependent correct temperature control of vehicle components.

This is for example from the DE 10 2018 211 662 A1 a method for operating a drive train of a motor vehicle is known. The drive train there comprises a first electrical machine for driving a first axle and a second electrical machine for driving a second axle, as well as an electrical storage device connected thereto and a control device. In the method, a current state of charge of the memory and a request from the control device to drive the second axle via the second machine are determined. If the state of charge corresponds to at least a first limit state of charge, the second machine is driven exclusively by providing first electrical energy from the accumulator. If the current state of charge is less than the first limit state of charge, the second machine is driven at least by second electrical energy provided by generator operation of the first machine. This is intended to enable energy-efficient use of the storage system overall. Due to the fact that part of the energy for driving the second machine is provided by the first machine and therefore does not have to be supplied by the store, its thermal load can also be reduced.

The object of the present invention is to enable efficient operation of a multi-motor electric motor vehicle.

According to the invention, this object is achieved by the subject matter of the independent patent claims. Further configurations and developments of the present invention are specified in the dependent patent claims, in the description and in the drawing.

The method according to the invention serves for the, in particular automatic, operation of a motor vehicle. A warming-up requirement for at least one component of the motor vehicle is automatically recognized. This can mean or include, for example, that a temperature of the at least one component is determined and based on this it is determined that this temperature is below a predetermined target or operating temperature which, for example, enables particularly efficient operation of the at least one component. Likewise, the need for heating can be detected, for example, when the motor vehicle is put into operation with a cold start, that is to say, for example, after at least a predetermined standstill or rest time.

Furthermore, in the method, a first electric machine of the motor vehicle is operated as a motor to generate a total output power. This total power output includes a drive power requested--for example by a driver of the motor vehicle--to drive a first axle of the motor vehicle and an additional power going beyond that. The requested drive power is therefore necessary in order - without any other additional resistance - to meet a driver's request with regard to the drive or propulsion of the motor vehicle or, for example in autonomous or semi-autonomous operation of the motor vehicle, to achieve or set a specific speed of the motor vehicle. A correspondingly higher speed of the motor vehicle could result from the additional power that goes beyond that. However, this is not the case here, since in the method a second electrical machine on a second axle of the motor vehicle is operated as a generator with part of the additional power to generate a charging current for a battery of the motor vehicle. In this case, heat loss resulting from the motor-driven generation of the additional power by the first electrical machine and the corresponding generator-type operation of the second electrical machine is used to heat up the at least one component. In other words, a resistance is provided by the generator operation of the second electrical machine, which increases the Speed of the motor vehicle beyond the driver's request or an automatic request prevented by the additional service. Rather, part of the additional power is converted here into heat for heating the at least one component and a remaining part of the additional power is taken up by the second electrical machine and fed to the battery.

The at least one component that is to be heated up here by this operation of the two electric machines can in principle be or include any component or device of the motor vehicle whose operation or operating properties are temperature-dependent, in particular with regard to efficiency and performance and/or wear and tear. For example, the component to be heated may be or include the battery. This can be the case in particular if the battery is a traction battery of the motor vehicle from which the first electrical machine is fed or supplied.

Active operation to warm up the at least one component can advantageously bring it up to operating temperature particularly quickly, that is to say, for example, into a predefined target temperature range. As a result, improved efficiency, improved performance or the ability to call up power and/or reduced wear can be achieved. In this case, this can be achieved in particular by devices that are already present in the motor vehicle, namely the two electrical machines. As a result, if necessary, additional expense for a separate heating device for the at least one component can be saved. This can advantageously save cost, weight, maintenance effort and complexity.

Heat is inevitably generated by operating the electrical machines with the load caused by the additional power or increased load, but here a part of the energy used for this purpose that is not converted into heat is advantageously recuperated, ie recovered, by the generator operation of the second electrical machine. Compared to the use of a separate heating device, this can enable heating that is particularly efficient overall. If the component to be heated is the battery, heat is also advantageously generated directly in the battery by the charging current fed into the battery by the second electrical machine. As a result, the battery can be warmed up particularly efficiently, effectively and quickly, i.e. brought to operating temperature.

The operation or the corresponding control of the electrical machines, for example by setting the additional power, can therefore be used to control corresponding heat flows that are inevitably associated therewith.

In a further embodiment of the present invention, an electric machine coupled to a rear axle of the motor vehicle is used or assigned as the first or second electric machine and, correspondingly, an electric machine coupled to a front axle of the motor vehicle is used or assigned as the second or as the second first electric machine automatically dynamically depending on a current operating situation of the motor vehicle. In particular, the respective uses or assignments can take place or be carried out depending on a respective driving state and/or a respective environmental condition, ie a type or a state of an environment of the motor vehicle. In other words, depending on the operating situation, the electric machine on the rear axle or the electric machine on the front axle can be operated as the first electric machine, ie as a motor for driving the motor vehicle. The respective other electrical machine, ie coupled to the respective other axle, is then operated accordingly as the second electrical machine, ie as a generator.

Different driving states can be, for example, starting from a standing start, accelerating, driving at a constant speed, or the like. The environmental situation can be characterized, for example, by an incline or incline of a subsurface on which the motor vehicle is driving, a type or a condition of a surface on which the vehicle is driving, for example a road surface, or the like. By taking corresponding operating situations into account, the present inventive method for heating the at least one component can advantageously be used in various situations, for example while simultaneously ensuring particularly good traction or driving stability of the motor vehicle. For example, when starting or accelerating on a level, asphalted and dry road, the electric machine on the rear axle can be used as the first electric machine, that is to say it can be operated. On the other hand, when driving up an incline with a snow-covered road surface, the electric machine on the front axle can be used or operated as the first electric machine, ie as a motor. The possibility proposed here to determine depending on the situation, i.e. to set or select which of the electric mechanical machines of the motor vehicle as a motor and which of the electrical machines is operated as a generator, improved flexibility in the operation of the motor vehicle and thus, for example, improved safety can advantageously be achieved.

In a further embodiment of the present invention, the additional power is automatically set depending on the heating requirement and a predetermined derating curve of at least one component of the motor vehicle in order to cover the heating requirement, in particular as quickly as possible, and at the same time to avoid derating of the at least one component. This component can be the component to be heated or a component that is separate from it. For example, the component to be heated can be a traction battery of the motor vehicle and the component described here can be power electronics coupled to the traction battery, such as an inverter. In particular, the heating requirement can not only be determined here, but also quantified, for example in the form of a temperature difference or a temperature change to be achieved for the at least one component. For this purpose, a model of at least the component to be heated can be specified and taken into account, which assigns a necessary amount of heat or energy to a temperature change to be achieved. Likewise, another heat requirement of the motor vehicle, for example for a passenger compartment or interior of the motor vehicle, a current ambient temperature, a vehicle temperature and/or the like can be taken into account.

The vehicle temperature can be, for example, a coolant temperature, a temperature of the traction battery and/or a drive of the motor vehicle, an oil temperature and/or the like.

The adaptation or setting of the additional power proposed here can advantageously, for example, enable a particularly good compromise between particularly rapid heating of the at least one component and minimization of a thermal load on the at least one component and thus ultimately optimal performance and/or flexibility in the operation of the motor vehicle.

To define or set the additional service, a corresponding rule or assignment table or a corresponding characteristic map can be specified, for example stored in a computer-readable data memory of the motor vehicle. Such a specification or such a characteristic diagram can specify, for example, that a greater additional power is used when there is a greater need to warm up, but a lower additional power is used when the vehicle and/or ambient temperature is relatively high.

In a further embodiment of the present invention, the additional service is limited to a maximum of a predetermined portion of a remaining service. This residual power corresponds to a difference between a maximum power that can be generated by the first electrical machine as intended or according to specifications and the respective drive power. The specified proportion is less than 100%. The magnitude of the remaining power can therefore vary dynamically during operation of the motor vehicle, depending on the drive power required in each case. By limiting the additional power, a reserve power is available, that is, a power reserve is kept free. This can, for example, enable particularly fast operation or implementation of an increase in the demand for drive power or particularly fast and reliable retrieval of power for another device in the motor vehicle, for example an electrically operated or triggered safety device in the motor vehicle. Just as the remaining power can vary with changing drive power, the additional power can also vary accordingly during operation of the motor vehicle, contrary to the requested drive power. As a result, the stated advantages of the warming-up operation, ie the described operation of the electric machines for warming up the components, can be achieved in a particularly flexible and situation-appropriate manner, in particular without impairing driving operation that is obvious to a particular vehicle occupant.

In a further embodiment of the present invention, the additional service is varied according to a predetermined time course or profile. In particular, it can be provided that the additional power is initially increased or increased relatively slowly, for example over many seconds or several minutes, up to a maximum value. This maximum value can then be retained for a predetermined period of time—absolutely or dynamically. The additional power can then be reduced again. As a result, when the temperature of the component is initially particularly low, excessive loads can be avoided, then a particularly rapid warm-up can be achieved by the maximum value and then derating or overheating can be avoided by the subsequent reduction in the additional power. As a result, an overall implementation of the mentioned in a particularly simple manner Advantages of the warm-up operation can be achieved particularly gently and reliably.

In a further embodiment of the present invention, the demand for drive power is monitored. If an increase in the drive power is detected or if it is approaching a specified threshold value, the additional power is then automatically reduced - possibly down to 0. In this way, for example, if there is sufficient remaining power available, maximum power and speed of heating can be achieved or used and if the required drive power increases an impairment of the driving performance or the implementation of the corresponding driver request can be avoided.

A further aspect of the present invention is a device for a motor vehicle for automatically controlling two electrical machines of the motor vehicle coupled to different axes in a warm-up mode for warming up at least one component of the motor vehicle. The device according to the invention is set up for automatically carrying out or executing at least one embodiment of the method according to the invention. For this purpose, the device according to the invention can comprise, for example, a processor device, such as a microchip, processor or controller, as well as a computer-readable data memory connected thereto. A program code or computer program can then be stored in this data memory, which encodes or implements the described sequences or method steps of the method according to the invention and can be executed by the processor device in order to cause the device or the motor vehicle to carry out the method. Such a data memory or such a computer program can in turn be specific aspects of the present invention. The device can be designed, for example, as a control unit of the motor vehicle. The device according to the invention can have an input interface and an output interface for receiving or outputting data or signals. For example, temperature data can be received via the input interface and control signals for controlling the electrical machines can be output via the output interface. For this purpose, the device can be connected to an on-board network of the motor vehicle, for example.

Another aspect of the present invention is a motor vehicle that has two electric machines coupled to different axles of the motor vehicle and a device according to the invention for automatically controlling the electric machines to heat up at least one component, in particular a traction battery, of the motor vehicle. The motor vehicle according to the invention can therefore in particular be the motor vehicle mentioned in connection with the method according to the invention and/or in connection with the device according to the invention. Accordingly, the motor vehicle according to the invention can have some or all of the properties and/or features mentioned in these contexts.

In one development of the present invention, the motor vehicle has at least a first liquid circuit for cooling at least one of the electrical machines, ie a first cooling circuit, and a second liquid circuit coupled in a thermally conductive manner to the component to be heated. The first liquid circuit is thermally coupled by a heat exchanger to the second liquid circuit, that is to say heat-transferring, in particular heat-conducting. Heat generated or arising as a result of the operation of the first electrical machine can therefore be transported through the first liquid circuit to the heat exchanger and transferred through it into the second liquid circuit. This heat can then be transported to the component to be heated through the second liquid circuit. This heat transport via two different liquid circuits enables a particularly flexible temperature control of the at least one electrical machine thermally coupled to the first liquid circuit on the one hand and the at least one component on the other hand. In this way, a particularly efficient, effective and/or gentle operation of the motor vehicle as a whole can also be made possible outside of the warm-up operation.

In a further embodiment of the present invention, the motor vehicle has a common liquid circuit which is thermally, ie heat-transferring, in particular thermally conductive, coupled both to at least one of the two electrical machines and to the at least one component to be heated. In other words, the heat generated by the at least one electrical machine can be absorbed by a heat transport medium circulating in the common liquid circuit and transported by it directly to the at least one component. As a result, a particularly effective and efficient heat transport or heat transfer from the electrical machine to the component to be heated can be achieved.

As a liquid or medium of the liquid circuits mentioned, for example, water, Glycol, a mixture thereof, a saline solution, an oil or the like can be used.

Further features of the invention can result from the claims, the figures and the description of the figures. The features and feature combinations mentioned above in the description and the features and feature combinations shown below in the description of the figures and/or in the figures alone can be used not only in the combination specified in each case, but also in other combinations or on their own, without going beyond the scope of the invention to leave.

In the single figure, the drawing shows a schematic representation of a motor vehicle with two electrical machines.

With the electric vehicles that are becoming increasingly widespread nowadays, it can be observed that a nominal output of widely used high-voltage storage devices and thus a vehicle output can be restricted depending on the temperature. This can affect both drive functions and all other vehicle functions that require electrical energy, such as interior heating or a driving dynamics stabilization program.

To reduce this problem shows 1 a schematic representation of an electric motor vehicle 10 with a rear axle 12 and a front axle 14. To drive the rear axle 12, a first electric machine 16 is arranged on this present. In addition, the motor vehicle 10 has a second electric machine 18 which is arranged on the front axle 14 . The electrical machines 16, 18 are therefore mechanically or force-transmittingly coupled to the respective axis 12, 14.

Furthermore, the motor vehicle 10 has a traction battery 20 for feeding or supplying at least one of the electrical machines 16, 18 with an operating current. In addition, a liquid system 22 of the motor vehicle 10 is indicated here schematically, which can function as a heat transfer or cooling circuit. The liquid system 22 comprises one or more liquid lines, indicated here schematically, which is or are routed along the electric machines 16, 18 and through the traction battery 20, as well as a heat exchanger 24 coupled thereto. The liquid system 22 can also comprise one or more liquid circuits.

Schematically indicated here on the electrical machines 16, 18 and the traction battery 20 temperature sensors 26 are arranged for measuring a respective current temperature.

Motor vehicle 10 also has a control device 28 with a processor 30 and a computer-readable data memory 32 connected thereto. The control unit 28 is set up here to control a warm-up operation, in which the traction battery 20 is to be warmed up to a predetermined operating temperature by appropriate activation of the electrical machines 16, 18, for example after a cold start of the motor vehicle 10. For this purpose, the control unit 28 is present via a schematic indicated electrical system of the motor vehicle 10 at least with the two electrical machines 16, 18 and the traction battery 20, in particular with the temperature sensors 26, connected to transmit signals or data.

In order to warm up the traction battery 20, an entanglement of a drive of the motor vehicle 10, ie an entangled operation of the electric machines 16, 18, is used in the present case. In the present example, the first electric machine 16 is operated as a motor to drive the rear axle 12 . The first electric machine 16 generates a requested drive power 34 which is converted into propulsion of the motor vehicle 10 via the rear axle 12 . In addition, the first electrical machine 16 also generates an additional power 36.

In contrast, the second electric machine 18 is operated as a generator on the front axle 14 . This results in a power loss both in the driving first electric machine 16 or on the rear axle 12 and in the second electric machine 18 or on the front axle 14 , which leads to the traction battery 20 heating up. A part of the additional power 36 that is not converted into heat is converted into a charging power 38 , ie a charging current for charging the traction battery 20 , by the second electric machine 18 operated as a generator.

Overall, therefore, a requested propulsion of the motor vehicle 10 is implemented, since the additional power 36 is only used to generate heat and to overcome an additional resistance generated by the generator operation of the second electric machine 18, but not to generate additional speed of the motor vehicle 10. This is to be seen in comparison to operation without the additional power 36, in which the second electric machine 18 is decoupled from the front axle 14 or, for example, rotates freely or idling, or the first electric machine 16 and the second electric machine 18 each with one Share of the drive power 34 is operated as a motor.

In the present case, motor vehicle 10 is therefore driven by first electric machine 16 via rear axle 12 . The drive power 34 generated or delivered by the first electric machine 16 is increased by the additional power 36 to a total output power above a power retrieved or requested by the driver of the motor vehicle 10, for example, the front axle 14 or the second electric machine 18 with the additional power 36, that is, a difference between the total output power and the drive power 34 desired or called up by the driver is operated as a generator.

The power loss additionally generated by the additional power 36 in the electric drive system of the motor vehicle 10 introduces heat into the liquid system 22 and possibly directly within the traction battery 20. The liquid system 22, for example a cooling system of the motor vehicle 10, thermally couples the electric machines 16, 18 with the traction battery 20, so that the heat entered is ultimately entered into the traction battery 20 to warm it up.

A particularly large warming effect can be achieved by using this activation of the electrical machines 16, 18 by the control unit 28, for example at particularly cold temperatures of the devices of the motor vehicle 10 when driving off, i.e. when the motor vehicle 10 is started up, when there is a need for heating and a heating time for the traction battery 20 is particularly large due to the thermal resistance in the cooling connection.

For example, the traction battery 20 and the electrical machines 16, 18 can be designed for a continuous output of about 60 kW. In such an operation, a power loss can amount to 10% of the total or maximum power, for example, so that the activation of the electrical machines 16 , 18 proposed here can generate several kilowatts of heat output to warm up the traction battery 20 .

Overall, the examples described show how a warm-up strategy for a drive train of an electric vehicle with two drive axles can be implemented.

Reference List

10

motor vehicle

12

rear axle

14

front axle

16

first electric machine

18

second electric machine

20

traction battery

22

liquid system

24

heat exchanger

26

temperature sensors

28

control unit

30

processor

32

data storage

34

drive power

36

additional service

38

charging power

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102018211662 A1 [0003]

Claims (10)

Method for operating a motor vehicle (10), in which - A need to heat up at least one component (20) of the motor vehicle (10) is automatically detected, - a first electric machine (16) of the motor vehicle (10) is operated as a motor to generate a total output power, which includes a required drive power (34) for driving a first axle (12) of the motor vehicle (10) and an additional power (36) going beyond that, - a second electrical machine (18) on a second axle (14) of the motor vehicle (10) is operated as a generator with part of the additional power (36) to generate a charging current (38) for a battery (20) of the motor vehicle (10), And thereby - A through the motor generation of the additional power (36) by the first electrical machine (16) and the corresponding generator operation of the second electrical machine (18) resulting heat loss is used to heat the at least one component (20). procedure after claim 1 , characterized in that using an electric machine (16) coupled to a rear axle (12) of the motor vehicle (10) as the first (16) or second electric machine (18) and correspondingly using one coupled to a front axle (14) of the Motor vehicle (10) coupled electric machine (18) as the second (18) or first electric machine (16) automatically dynamically depending on a current operating situation of the motor vehicle (10), in particular a driving condition and / or an environmental condition. Method according to one of the preceding claims, characterized in that the additional power (36) is set automatically depending on the heating requirement and a predetermined derating curve of at least one component of the motor vehicle (10) in order to cover the heating requirement and at the same time derating the at least one to avoid components. Method according to one of the preceding claims, characterized in that the additional power (36) is limited to at most a predetermined proportion of less than 100% of a residual power, the residual power being a difference between a maximum power that can be generated by the first electrical machine (16) and the corresponding drive power. Method according to one of the preceding claims, characterized in that the additional power (36) is varied according to a predetermined time profile. Method according to one of the preceding claims, characterized in that the demand for drive power is monitored and the additional power (36) is automatically reduced when an increase is detected or when a predetermined threshold value is approached. Device (28) for a motor vehicle (10) for automatically activating two electrical machines (16, 18) of the motor vehicle (10) coupled to different axles (12, 14) in a warm-up mode for warming up at least one component (20) of the motor vehicle (10 ), wherein the device (28) is set up for automatically carrying out a method according to one of the preceding claims. Motor vehicle (10), having two electrical machines (16, 18) coupled to different axles (12, 14) of the motor vehicle (10) and a device (28). claim 7 for automatically controlling the electrical machines (16, 18) to heat up at least one component (20), in particular a traction battery, of the motor vehicle (10). Motor vehicle (10) after claim 8 , characterized in that the motor vehicle (10) has at least one first liquid circuit (22) for cooling at least one of the electrical machines (16, 18) and a second liquid circuit (22) coupled in a thermally conductive manner to the component (20) to be heated, the first Liquid circuit (22) is thermally coupled by a heat exchanger (24) to the second liquid circuit (22). Motor vehicle (10) after claim 8 or 9 , characterized in that the motor vehicle (10) has a common fluid circuit (22) which is thermally coupled both to at least one of the electrical machines (16, 18) and to the component (20) to be heated.

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