WO2023208779A1

WO2023208779A1 - Method for operating an electric drive system for a motor vehicle

Info

Publication number: WO2023208779A1
Application number: PCT/EP2023/060497
Authority: WO
Inventors: Marco Ebersbach; Rico Janke
Original assignee: Mercedes-Benz Group AG
Priority date: 2022-04-28
Filing date: 2023-04-21
Publication date: 2023-11-02
Also published as: DE102022001489B3

Abstract

The invention relates to a method for operating an electric drive system (110) of a motor vehicle, wherein the electric drive system (110) comprises a first electric machine (12) and at least a first vehicle wheel (16) that is couplable to the first electric machine (12), wherein when a first temperature threshold of the first electric machine (12) is exceeded, a first torque of the first electric machine (12) is limited. The electric drive system (110) comprises a second electric machine (14), wherein the second electric machine (14) is torque-transmittingly coupled or couplable to the first vehicle wheel (16) or to a second vehicle wheel (18), wherein a disconnect clutch (22) is designed to torque-transmittingly couple the first electric machine (12) to or decouple said machine from the first wheel vehicle (16). When a second temperature threshold of the first electric machine (12) is exceeded, and if the disconnect clutch (22) is in working order, the disconnect clutch (22) is opened for the purpose of decoupling the first electric machine (12) from the first motor vehicle (16), wherein the first vehicle wheel (16) and/or the second vehicle wheel (18) are driven by the second electric machine (14).

Description

Method for operating an electric drive system for a motor vehicle

The invention relates to a method for operating an electric drive system for a motor vehicle according to the preamble of patent claim 1.

The DE 102016220 536 A1 and the DE 102020203669 A1 each disclose methods for operating an electrical machine of a motor vehicle as known, whereby when a temperature threshold of the electrical machine is exceeded, a power or a torque of the electrical machine is limited to the electrical To protect the machine from thermal damage.

The object of the present invention is to provide an operating method for an electric drive system for a motor vehicle, in which, on the one hand, a high level of component protection and, on the other hand, at the same time a high level of traffic safety and comfort are achieved.

This object is achieved by a method for operating an electric drive system of a motor vehicle with the features of patent claim 1. Advantageous embodiments with useful developments of the invention are specified in the remaining claims.

It is based on a method for operating a motor vehicle with an electric drive system, wherein the electric drive system has a first electric machine and at least one vehicle wheel that can be coupled to the first electric machine.

For example, the first electric machine and the vehicle wheel are parts of an electric axle of the motor vehicle. Typically, for example, the first electric machine has a single-speed gearbox or a multi-speed gearbox coupled via an axle gear to the first vehicle wheel or to two first vehicle wheels. The input gear or the multi-speed gear and/or the axle gear can be parts of a first gear.

In a known manner, an operating method is assumed in which a first torque of the first electrical machine is limited when a first temperature threshold of the first electrical machine is exceeded.

According to the invention, on the one hand, a second electric machine is provided, wherein the second electric machine is coupled or can be coupled in a torque-transmitting manner to the first vehicle wheel or to a second vehicle wheel.

Furthermore, according to the invention, a separating clutch is provided, wherein the separating clutch is designed to couple or decouple the first electric machine with the first vehicle wheel in a torque-transmitting manner.

Furthermore, the method according to the invention provides that, if a second temperature threshold of the first electrical machine is exceeded and if the separating clutch is functional, the separating clutch is opened for the purpose of decoupling the first electrical machine from the first vehicle wheel, the first vehicle wheel and / or the second vehicle wheel can be driven by the second electric machine. According to the invention, the second temperature threshold is greater than the first temperature threshold.

The method according to the invention makes it possible, on the one hand, to operate the electric drive system in such a way that the first electric machine is maximally protected from thermal damage, but on the other hand to ensure drive power even during the protective measure, thereby ensuring both traffic safety and comfort is.

The second electric machine can be coupled or can be coupled, for example, to the first vehicle wheel or to the first vehicle wheels.

For example, the second electric machine can be coupled or can be coupled to the first vehicle wheel via the input gearbox mentioned above as an example or the multi-speed gearbox. The second electrical machine can therefore be part of the same electrical axis to which the first electrical machine also belongs.

The second electrical machine can also be part of another electrical axle, thus a second electrical axle, of the motor vehicle, the second electric axle has a second motor vehicle wheel. For example, the second electric machine can be coupled or can be coupled to the second motor vehicle wheel via a second transmission.

The separating clutch mentioned can be designed as a known positive or frictional clutch.

The separating clutch can be arranged at any point of a torque flow between the first electric machine and the first vehicle wheel and is designed to interrupt or enable this torque flow.

The torque flow refers to a sequence of mechanical transmission of torque between the first electric machine and the first vehicle wheel. For example, with regard to the torque flow, a rotor shaft of the first electric machine, the first transmission and the first vehicle wheel are arranged one after the other in the order mentioned.

For example, the separating clutch can be arranged between the first electric machine and the first transmission with regard to the torque flow. The separating clutch can also be arranged inside the first transmission. The separating clutch can be one of several gear clutches of the transmission if the transmission is designed as a multi-speed transmission. The separating clutch can also be a set of several switching elements. With regard to the torque flow, the separating clutch can also be arranged between the first transmission and the first vehicle wheel.

The first temperature threshold of the first electrical machine means a threshold value for a first temperature of the first electrical machine. The first temperature of the first electrical machine is a temperature measured at any point on the first electrical machine or a temperature calculated for the first electrical machine. The first temperature can be, for example, a rotor temperature, a stator temperature, an inverter temperature or a temperature of a cooling system of the first electrical machine. However, the first temperature can also be a temperature calculated according to a temperature model. The first electrical machine thus comprises at least a stator, a rotor, an inverter or power electronics and a cooling system. The first temperature threshold can be a single fixed value. However, it can also be a characteristic curve or a characteristic field of temperature threshold values, whereby the first temperature threshold can assume different values, for example depending on an ambient temperature or depending on other parameters.

The second temperature threshold of the first electrical machine means a second threshold value for a further temperature of the first electrical machine.

According to an advantageous development, it is provided that a vehicle speed is limited when a defect in the separating clutch is detected and when a third temperature threshold of the first electric machine is exceeded. The third temperature threshold is advantageously greater than the second temperature threshold.

Overall, in comparison to known methods, a limitation of the vehicle speed and an associated reduction in safety and comfort can initially be avoided. Only when several component problems are detected, i.e. when there is a risk of component destruction, is the vehicle speed limited. By limiting the vehicle speed, further heating of the first electric machine can be counteracted.

A further advantageous development of the invention provides that the first electrical machine is de-energized after the separating clutch has been opened. After the second temperature threshold has been exceeded and the separating clutch has been opened, the first electrical machine can be shut down, whereby a further increase in temperature can be avoided.

The vehicle speed is advantageously limited by setting a maximum vehicle speed, with a power output of the first electric machine and/or the second electric machine being limited in such a way that the maximum vehicle speed is not exceeded. In addition, a braking device of the electric drive system can also be activated in such a way that the maximum vehicle speed is not exceeded. In addition, generator operation of the second electric machine can also be activated in such a way that the maximum vehicle speed is not exceeded. The detection of the defect in the separating clutch can in particular be a detection of a blockage of the separating clutch in the closed state. This can be a mechanical jamming of the separating clutch or a defect in an actuator of the separating clutch. Mechanical jamming of the separating clutch can be detected, for example, using a sensor for sensing a state of the separating clutch. Alternatively, mechanical jamming can also be detected using a plausibility check.

Advantageously, when the third temperature threshold is exceeded depending on the vehicle speed, a known zero torque control of the first electrical machine takes place, whereby a current flow in the first electrical machine is minimized and thus a further increase in temperature is minimized.

A display element for displaying messages for a driver of the motor vehicle is advantageously provided, with the limitation of the vehicle speed being displayed for the driver when the third temperature threshold and the associated limitation of the vehicle speed are exceeded.

If a fourth temperature threshold of the first electric machine is exceeded, the motor vehicle is advantageously shut down by limiting the vehicle speed to 0 km/h. Advantageously, the limitation of the vehicle speed to 0 km/h does not occur suddenly, but rather as part of a shutdown process, with the impending limitation of the vehicle speed to 0 km/h being displayed to the driver by means of the display element. The fourth temperature threshold is advantageously greater than the third temperature threshold. The fourth temperature threshold is chosen so that there is a risk of a vehicle fire or a similar danger.

The decommissioning process advantageously initially includes a warning message to the driver. It is then advantageously ensured that the first electric machine no longer provides any drive torque. Subsequently, an intervention in a torque control of the second electric machine advantageously takes place, whereby it is advantageously possible to continue driving with the previously set limitation of the vehicle speed for a certain time in order, for example, to be able to complete an overtaking process that has begun. When the second temperature threshold of the first electrical machine is exceeded, a first error message is advantageously stored in an error memory of a control and regulating device. When the fourth temperature threshold of the first electrical machine is exceeded, a second error message is advantageously stored in the error memory. The first error message and the second error message can advantageously be distinguished, for example, by selecting different error codes.

Advantageously, not only the limitation of the vehicle speed is displayed by means of the display element, but also the limitation of the torque that occurs after the second temperature threshold of the first electric machine is exceeded.

The invention is explained in more detail with reference to the drawings described below, in which the same reference numbers stand for the same elements or parameters. The drawing shows in:

1 shows a schematic representation of a motor vehicle with a first embodiment of an electric drive system;

2 shows a schematic representation of a motor vehicle with a second embodiment of an electric drive system;

3 shows a flowchart for a method for operating the electric drive system according to the first embodiment or the second embodiment;

Fig. 4 is a functional diagram showing dependencies of essential parameters of the method.

1 shows a motor vehicle 30 with an electric drive system 10 in a first embodiment, as is suitable for implementing the method according to the invention. The electric drive system 10 has a first electric machine 12 and a second electric machine 14. Both electrical machines each have, among other things and not shown in detail, a rotor, a stator and an inverter. Both electric machines 12, 14 are coupled or can be coupled to first vehicle wheels 16 via a transmission 20. The first electric machine 12 can be coupled and decoupled from the first vehicle wheels 16 by means of a separating clutch 22. In the first exemplary embodiment, the first separating clutch 22 is arranged between the first electric machine 12 and the transmission 20 with respect to a torque flow flowing between the first electric machine 12 and the first vehicle wheels 16. The second electric machine 14 is permanently coupled to the transmission 20 in the first exemplary embodiment.

To detect a temperature T of the first electrical machine 12, the electrical drive system 10 has a temperature sensor 24. In the schematic representation, the temperature sensor 24 stands for a rotor temperature sensor or a stator temperature sensor or an inverter temperature sensor or also for a temperature calculation model.

Both the temperature sensor 24, as well as the electrical machines 12, 14, as well as the transmission 20, as well as an actuator (not shown) of the separating clutch 22 are connected to a control and regulating device 26 via connecting lines 28. The connecting lines can be sensor lines, data lines or control lines for actuators. The control and regulating device 26 can be a single electronic control device. The control and regulating device 26 is advantageously a network of individual control devices that communicate with one another via data lines.

The transmission 20 advantageously and not shown in detail has at least one gear ratio, particularly advantageously several switchable gear ratios, and an axle gear.

2 shows a motor vehicle 30 with an electric drive system 110 in a second embodiment, which is also suitable for implementing the method according to the invention.

The motor vehicle 30 has two drive axles, namely a first drive axle 32 and a second drive axle 34. The first vehicle axle 32 has first vehicle wheels 16, which are driven by the first electric machine 12 via a transmission 120. The second vehicle axle 34 has second vehicle wheels 18, which are driven by the second electric machine 14 via a transmission 220. The gears 120, 220 of the first drive axle 32 and the second drive axle 34 can differ in detail from each other and also from the gear 20 of the first embodiment, but the differences are irrelevant to the invention and its advantageous developments.

A separating clutch 22, 36 is provided for both drive axles 32, 34, namely the separating clutch 22 for coupling the first electrical machine 12 to the first vehicle wheels 16 and a second separating clutch 36 for coupling the second electrical machine 14 to the second vehicle wheels 18.

3 shows a flowchart for a method for operating the electric drive system according to the first embodiment or the second embodiment.

The method is expediently carried out in the form of a computer program in the control and regulating device 26 equipped for these purposes.

The process begins with a starting step START, in which, for example, basic conditions under which the process can actually run are checked.

If the basic conditions are met, a first test step P1 takes place, in which it is checked whether the temperature T of the first electrical machine 12 exceeds a first temperature threshold Ti. If the temperature T of the first electrical machine 12 does not exceed the first temperature threshold Ti, the result of the first test step P1 is a no decision n and the start step then takes place again. If the temperature T of the first electrical machine 12 exceeds the first temperature threshold Ti, the result of the first test step P1 is a yes decision y, and a first measure M1 is then carried out. The first measure M1 includes limiting the torque of the first electrical machine 12 to a specific maximum torque M _ma x. The maximum torque M _ma x can either be fixed or made variable depending on a requested torque, whereby it is in any case smaller than the requested torque. In the event of a yes decision in the first test step P1, a second test step P2 takes place, in which it is checked whether the temperature T of the first electrical machine 12 exceeds a second temperature threshold T2, the second temperature threshold T2 being higher than the first temperature threshold Ti. Exceeds If the temperature T of the first electrical machine does not meet the second temperature threshold T2, the result of the second test step P2 is a no decision n and the first test step P1 is then carried out again. If the temperature T of the first electrical machine 12 exceeds the second temperature threshold T2, it is also checked whether the separating clutch 22 is functional, that is, whether no error in the separating clutch 22 has been detected. If the temperature T of the first electrical machine 12 exceeds the second temperature threshold T2 and if there is no fault in the separating clutch 22, the result of the second test step P2 is a yes decision y, and a second measure M2 is then carried out. The second measure M2 includes opening the separating clutch 22 for the purpose of decoupling the first electric machine 12 from the first vehicle wheels 16. The second measure M2 advantageously includes an adjustment of a drive behavior of the second electric machine 14 by - for example in the first exemplary embodiment - a torque of the second electrical machine 14 is adjusted. Or - for example in the second exemplary embodiment - the second separating clutch (if it is not already closed) is closed and the torque of the second electric machine 14 is adjusted.

The above-mentioned detection of the error or different errors of the separating clutch 22 can be carried out in a manner known per se, for example by a status sensor such as a switch, whereby a closed or opened separating clutch 22 can be detected and can be checked for plausibility compared to a state specification for the separating clutch . The error can also be detected through diagnoses for an actuator system of the separating clutch 22. The actuator system may include an electromechanical actuator, a hydraulic actuator, a pneumatic actuator, or a combination of these.

In the event of a yes decision in the second test step P2, a first error message is advantageously stored in an error memory of the open-loop and closed-loop control device 26. The first error message contains the information about a defect or an excess temperature in the first electrical machine 12. In the event of a yes decision in the second test step P2, a third test step P3 takes place, in which it is checked whether the temperature T of the first electrical machine 12 exceeds a third temperature threshold T3, the third temperature threshold T3 being higher than the second temperature threshold T2.

If the temperature T of the first electrical machine does not exceed the third temperature threshold T3, the result of the third test step P3 is a no decision n, and the second test step P2 is then carried out again. If the temperature T of the first electrical machine 12 exceeds the third temperature threshold T3, the result of the third test step P3 is a yes decision y, and a third measure M3 is then carried out. The third measure M3 includes a limitation of a vehicle speed v. The vehicle speed v is advantageously limited by setting a speed limit v _ma x to a specific value that is greater than 0 km/h, such as the value 50 km/h. _The speed limit value v _ma

In the event of a yes decision in the third test step P3, a second error message is advantageously stored in the error memory of the open-loop and closed-loop control device 26. The second error message contains the information about a defect or a severe excess temperature in the first electrical machine 12.

In the event of a yes decision in the third test step P2, a fourth test step P4 takes place, in which it is checked whether the temperature T of the first electrical machine 12 exceeds a fourth temperature threshold T4, the fourth temperature threshold T4 being higher than the third temperature threshold T3.

If the temperature T of the first electrical machine does not exceed the fourth temperature threshold T4, the result of the fourth test step P4 is a no decision n, and the third test step P3 is then carried out again. If the temperature T of the first electrical machine 12 exceeds the fourth temperature threshold T4, the result of the fourth test step P4 is a yes decision y, and a fourth measure M4 is then carried out. The fourth measure M4 includes a limitation of the vehicle speed v to the value 0 km/h. The vehicle speed v is limited by setting the speed limit v _ma x to the value 0 km/h. The speed limit Vmax is then further processed in control and regulation functions for a drive of the electric drive system 10, 110 in such a way that, at the latest after a delay time that can be granted for safety reasons, no drive power of the electric drive system 10, 110 is anymore provided and that the vehicle, if necessary is actively braked.

In the event of a yes decision in the fourth test step P4, a third error message is advantageously stored in the error memory of the open-loop and closed-loop control device 26. The third error message contains the information about a defect or a very strong excess temperature in the first electrical machine 12.

Fig. 4 shows a functional diagram to show dependencies of essential parameters of the method.

In a first function graph 40, the maximum torque Mmax and the speed limit value v _ma x are plotted on the ordinate. On the abscissa is the temperature? applied to the first electrical machine 12. A curve with a solid line shows a course of the maximum torque M _ma x, and a dashed line shows a course of the speed limit value v _ma x, each depending on the temperature T of the first electrical machine 12.

In the second function graph 42, a state DCU _open of the separating clutch 22 is plotted on the ordinate. The state DCU _open of the separating clutch 22 can assume two different values: 0 for a closed separating clutch 22 and 1 for an open separating clutch 22. The temperature T of the first electrical machine 12 is again plotted on the abscissa of the second function graph 42, where the scaling the abscissa of the two function graphs 40, 42 should be the same.

4 shows that at temperatures T of the first electrical machine 12, which are smaller than the first temperature threshold Ti, a specific value for a maximum torque M _ma x of the first electrical machine 12 is already predetermined. If the temperature T of the first electrical machine 12 exceeds the first temperature threshold Ti, the maximum torque M _ma x is set to lower values. In the method exemplary embodiment of FIG. 4, the maximum torque M _ma less torque and therefore always less drive power is available. If the second temperature threshold T2 is exceeded, the separating clutch 22 is opened, which is reflected in the state DCU _0P en of the separating clutch 22.

If the third temperature threshold T3 is exceeded, the speed limit v _ma x is limited to, for example, 50 km/h. If the fourth temperature threshold T4 is exceeded, the speed limit Vmax is limited to 0 km/h.

With the method according to the invention, it is possible to maintain the availability of the electric drive system 10, 110 as much as possible even in the event of technical malfunctions or defects, so that the greatest possible safety for occupants of the motor vehicle can be achieved.

Reference symbol list

10, 110 Electric drive system

12 first electric machine

14 second electric machine

16 first vehicle wheel

18 second vehicle wheel

20, 120, 220 gears

22 separating clutch

24 temperature sensor

26 control and regulation device

28 connecting line

30 motor vehicle

32 first drive axle

34 second drive axle

36 second separating clutch

40 first function graph

42 second function graph

DCUopen State of the separating clutch

M1 first measure

M2 second measure

M3 third measure

M4 fourth measure n no decision

P1 first test step

P2 second test step

P3 third test step

P4 fourth test step

START Start step

T temperature

T 1 first temperature threshold

T2 second temperature threshold

T3 third temperature threshold

T4 fourth temperature threshold y yes decision

Claims

Claims Method for operating a motor vehicle (30) with an electric drive system (10, 110), the electric drive system (10, 110) having a first electric machine (12) and at least one first vehicle wheel (12) which can be coupled to the first electric machine (12). 16), wherein when a first temperature threshold (Ti) of the first electrical machine (12) is exceeded, a first torque of the first electrical machine (12) is limited, characterized in that the electrical drive system (10, 110) has a second electrical machine ( 14), wherein the second electric machine (14) is coupled or can be coupled in a torque-transmitting manner to the first vehicle wheel (16) or to a second vehicle wheel (18), wherein a separating clutch (22) is designed to connect the first electric machine (12). to couple or decouple with the first vehicle wheel (16) in a torque-transmitting manner, whereby if a second temperature threshold (T2) of the first electric machine (12) is exceeded and if the separating clutch (22) is functional, the separating clutch (22) for the purpose of decoupling the first electric machine (12) is opened by the first vehicle wheel (16), the first vehicle wheel (16) and/or the second vehicle wheel (18) being driven by the second electric machine (14), the second temperature threshold (T2 ) is higher than the first temperature threshold (Ti). Method according to claim 1, characterized in that when a defect in the separating clutch (22) is detected and when a third temperature threshold (T3) of the first electrical machine (12) is exceeded Vehicle speed (v) is limited, the third temperature threshold (T3) being greater than the second temperature threshold (T2). Method according to claim 1, characterized in that after opening the separating clutch (22), the first electrical machine (12) is switched off. Method according to claim 2, characterized in that when the third temperature threshold (T3) is exceeded, a zero torque control of the first electrical machine (12) takes place as a function of the vehicle speed (v). Method according to one of the preceding claims, characterized in that if a fourth temperature threshold (T4) of the first electric machine (12) is exceeded, the vehicle speed (v) is limited to 0 km/h. Method according to claim 5, characterized in that the fourth temperature threshold (T4) is greater than the third temperature threshold (T3). Method according to claim 1, characterized in that after the second temperature threshold (T2) of the first electrical machine (12) is exceeded, a first error message is saved. Method according to claim 7, characterized in that a display element is provided for displaying messages for a driver of the motor vehicle, the limitation of the torque being displayed by means of the display element after the second temperature threshold (T2) of the first electric machine (12) has been exceeded.