Drive unit for an electric vehicle and method for operating a drive unit

Abstract

The invention relates to a drive unit (10) for an electric vehicle (2), comprising a plurality of electric motors (21, 22, 23, 24) for driving the electric vehicle (2), a plurality of power electronics (41, 42, 43, 44) for controlling the electric motors, a plurality of battery cells (31, 32, 33, 34) for storing electrical energy, and at least one coupling region (12, 13), wherein each of the electric motors can be connected to each of the battery cells by means of at least one coupling region via one of the power electronics. The invention also relates to a method for operating the drive unit according to the invention, wherein each of the electric motors is connected to exactly one of the battery cells by means of the at least one coupling region via exactly one of the power electronics.

Description

Technical Field

[0001] The invention relates to a drive unit for an electric vehicle, the drive unit comprising a plurality of electric motors for driving the electric vehicle. The invention also relates to a method for operating a drive unit according to the invention. Background Art

[0002] It is apparent that in the future, battery cells will be used more and more, especially in electric vehicles, which place high demands on the reliability, efficiency, safety and service life of the battery cells. Battery cells with lithium-ion battery cells are particularly suitable for such applications. These battery cells are characterized in particular by high energy density, thermal stability and extremely low self-discharge.

[0003] Here, the electric vehicle has a drive unit having a plurality of electric motors for driving the electric vehicle, which are supplied with electrical energy by a battery unit. The battery unit has a plurality of battery cells, which are connected in series and / or in parallel with each other. In addition, the battery unit includes a battery controller for controlling and monitoring the individual battery cells. Here, the battery controller is in communication connection with a central control unit.

[0004] A drive unit of the type described is disclosed in DE 10 2010 062 227 A1 for an electric vehicle. In one embodiment, a first electric motor is provided for driving a first wheel axle and a second electric motor is provided for driving a second wheel axle. In another embodiment, four electric motors are provided for driving each wheel of the electric vehicle.

[0005] During acceleration, the electric motor draws electrical energy from the battery cells. During braking, the electric motor of such an electric vehicle acts as a generator and feeds the generated regenerative energy back into the battery cells. If a plurality of battery cells are provided, the individual battery cells may have different states of charge (SoC=State of Charge). In optimal operation of the drive system, the battery cells should be used during charging and discharging in such a way that the states of charge of the individual battery cells remain at least approximately the same.

[0006] A drive unit for an electric vehicle is known from US 2003 / 0146737 A1. The drive unit comprises an electric motor for driving the electric vehicle and has a battery unit, which is connected to the electric motor via power electronics. The battery unit comprises a plurality of individual batteries connected in series. With the aid of a multiplexer, the individual batteries can be charged and discharged individually. This makes it possible to adapt the different charge states of the individual batteries to one another. Summary of the invention

[0007] A drive unit for an electric vehicle is provided. The drive unit comprises a plurality of electric motors for driving the electric vehicle. For example, an electric motor for driving a wheel axle can be provided respectively, or an electric motor for driving each wheel of the electric vehicle can be provided respectively.

[0008] According to the invention, the drive unit also comprises a plurality of power electronics for driving a plurality of electric motors. The drive unit also comprises a plurality of battery cells for storing electrical energy. The power electronics each comprises, for example, an inverter or an inverter which generates a three-phase AC voltage for the electric motor from a DC voltage provided by the battery cells.

[0009] According to the invention, the drive unit also comprises at least one coupling region. In this case, each of the electric motors can be connected to each of the battery cells via one of the power electronics by means of the at least one coupling region. Thus, the individual electric motors can be selectively connected to the individual battery cells.

[0010] According to an advantageous embodiment of the invention, the drive unit comprises a coupling region close to the motor, by means of which each of the electric motors can be connected to each of the power electronics, wherein each of the power electronics is fixedly connected to one of the battery cells, for example.

[0011] According to another advantageous embodiment of the present invention, the drive unit comprises a coupling region close to the battery, by means of which each of the power electronic devices can be connected to each of the battery cells. Here, for example, each of the power electronic devices is fixedly connected to one of the electric motors.

[0012] According to another advantageous design of the present invention, the drive unit comprises a coupling region close to the motor and a coupling region close to the battery, wherein each of the electric motors can be connected to each of the power electronic devices by means of the coupling region close to the motor, and wherein each of the power electronic devices can be connected to each of the battery cells by means of the coupling region close to the battery. Therefore, each of the power electronic devices can be connected to any battery cell and any electric motor.

[0013] A method for operating a drive unit for an electric vehicle according to the invention is also provided. In this case, each of the electric motors is connected to exactly one of the battery cells by means of the at least one coupling region via exactly one of the power electronics. In this case, each of the electric motors is connected to another battery cell.

[0014] In driving operation, in particular when accelerating the electric vehicle, each of the electric motors is therefore supplied with electrical energy from the other battery cell. In regenerative operation, in particular when braking the electric vehicle, each of the electric motors provides a regenerative current. In this case, each of the electric motors feeds electrical energy into the other battery cell.

[0015] During the regenerative operation, the regenerative currents provided by the individual electric motors may differ from one another. The regenerative currents of the electric motors may also fluctuate during the regenerative operation. The charge states of the individual battery cells may also differ from one another. Furthermore, during the regenerative operation, the charge states of the individual battery cells change.

[0016] According to a preferred development of the invention, the regenerative current currently provided by each of the electric motors is therefore measured during the regenerative mode, and the current state of charge of each of the battery cells is also measured.

[0017] According to an advantageous embodiment of the invention, the electric motor which currently provides the greatest regenerative current is connected to the battery cell having the lowest state of charge.

[0018] According to a further advantageous embodiment of the invention, the electric motor which currently provides the smallest regenerative current is connected to the battery cell having the highest state of charge.

[0019] According to a preferred development of the present invention, the charging current flowing into each of the battery cells is limited to a predefined limit value. The charging current is preferably limited in a plurality of stages as a function of time.

[0020] Preferably, the charging current flowing into the battery cell is limited to a first limit value until the first time period ends. After the first time period ends until the second time period ends, the charging current flowing into the battery cell is limited to a second limit value. Here, the first limit value is greater than the second limit value.

[0021] Preferably, after the second time period has expired, the charging current flowing into the battery cell is limited to a third limit value. In this case, the second limit value is greater than the third limit value.

[0022] The mentioned limit values ​​are not necessarily fixed. The mentioned limit values ​​may depend, for example, on the temperature and / or the state of charge of the individual battery cells.

[0023] In the drive unit for an electric vehicle according to the present invention, each of the electric motors for driving the electric vehicle can be flexibly connected to any battery cell for storing electric energy. With the aid of the coupling region, it is particularly possible to connect each of the electric motors to another battery cell. If the number of the electric motors is equal to the number of the battery cells, a clear assignment of the electric motors to the battery cells can be achieved by corresponding connections.

[0024] The method according to the invention for operating a drive unit according to the invention for an electric vehicle can adapt the charge states of the individual battery cells to one another. The electric motor and the battery cells can be connected to one another in such a way that battery cells with a higher charge state are preferably discharged before battery cells with a lower charge state, and battery cells with a lower charge state are preferably charged before battery cells with a higher charge state. As a result, all battery cells are loaded more or less uniformly and age more or less quickly. If all battery cells have more or less the same charge state, the charging process of the battery cells at an external charging station can also be carried out efficiently and simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention are explained in more detail with the aid of the drawings and the following description.

[0026] in:

[0027] Figure 1 shows a schematic diagram of an electric vehicle having a drive unit according to a first embodiment,

[0028] Figure 2 shows a schematic diagram of an electric vehicle having a drive unit according to a second embodiment,

[0029] Figure 3 shows a schematic diagram of an electric vehicle having a drive unit according to a third embodiment,

[0030] Figure 4 A schematic diagram showing the coupling region,

[0031] Figure 5 shows an exemplary regenerative current of an electric motor,

[0032] Figure 6 shows an exemplary charge state of a battery cell before the end of a first time period,

[0033] Figure 7shows an exemplary state of charge of the battery cell after the first time period ends and before the second time period ends, and

[0034] Figure 8 An exemplary charge state of the battery cell after the end of the second time period is shown. DETAILED DESCRIPTION

[0035] In the following description of embodiments of the invention, identical or similar elements are denoted by the same reference numerals, wherein a repeated description of these elements is omitted in individual cases. The figures merely schematically illustrate the subject matter of the invention.

[0036] Figure 1 The schematic diagram of an electric vehicle 2 with a drive unit 10 according to a first embodiment is shown. The electric vehicle 2 comprises two drive axles and a total of four drive wheels 92. The drive wheels 92 of the axles can each be driven via a common differential 94.

[0037] The drive unit 10 includes a first electric motor 21, a second electric motor 22, a third electric motor 23, and a fourth electric motor 24 for driving the electric vehicle 2. The first electric motor 21 and the second electric motor 22 drive two of the drive wheels 92 through one of the differentials 94. The third electric motor 23 and the fourth electric motor 24 drive the other two of the drive wheels 92 through another differential 94. The four electric motors 21, 22, 23, 24 are configured in a three-phase manner.

[0038] The drive unit 10 also includes a first battery cell 31, a second battery cell 32, a third battery cell 33 and a fourth battery cell 34 for storing electrical energy. The drive unit 10 further includes a first power electronic device 41, a second power electronic device 42, a third power electronic device 43 and a fourth power electronic device 44 for controlling the electric motors 21, 22, 23, 24. The power electronic devices 41, 42, 43, 44 each include, for example, an inverter or an inverter, which generates a three-phase AC voltage for supplying power to the electric motors 21, 22, 23, 24 from the DC voltage provided by the battery cells 31, 32, 33, 34.

[0039] The drive unit 10 comprises a coupling region 12 close to the motor. By means of the coupling region 12 close to the motor, each of the electric motors 21, 22, 23, 24 can be connected to each of the power electronic devices 41, 42, 43, 44. The drive unit 10 comprises a coupling region 13 close to the battery. By means of the coupling region 13 close to the battery, each of the battery cells 31, 32, 33, 34 can be connected to each of the power electronic devices 41, 42, 43, 44.

[0040] Each of the power electronics 41, 42, 43, 44 can be connected to any battery cell 31, 32, 33, 34 and to any electric motor 21, 22, 23, 24 by means of the coupling regions 12, 13. Thus, each of the electric motors 21, 22, 23, 24 can be connected to each of the battery cells 31, 32, 33, 34 via one of the power electronics 41, 42, 43, 44. The respective electric motors 21, 22, 23, 24 can thus be selectively connected to the respective battery cells 31, 32, 33, 34.

[0041] Each of the battery cells 31, 32, 33, 34 has a battery controller for controlling and monitoring the battery cells of the battery cells 31, 32, 33, 34. The drive unit 10 includes a central control unit 50 which is in communication connection with the battery controller and the power electronics 41, 42, 43, 44.

[0042] In regenerative operation, in particular when braking electric vehicle 2 , first electric motor 21 provides a first regenerative current IR1 , second electric motor 22 provides a second regenerative current IR2 , third electric motor 23 provides a third regenerative current IR3 , and fourth electric motor 24 provides a fourth regenerative current IR4 .

[0043] The power electronic devices 41, 42, 43, 44 convert the regenerative currents IR1, IR2, IR3, IR4, which are three-phase alternating currents, into charging currents IL1, IL2, IL3, IL4, which are direct currents. Here, the first charging current IL1 flows into the first battery cell 31, the second charging current IL2 flows into the second battery cell 32, the third charging current IL3 flows into the third battery cell 33, and the fourth charging current IL4 flows into the fourth battery cell 34.

[0044] Figure 21 shows a schematic diagram of an electric vehicle 2 having a drive unit 10 according to a second specific embodiment. The drive unit 10 according to the second specific embodiment is largely identical to the drive unit 10 according to the first specific embodiment. The differences are discussed below.

[0045] The drive unit 10 according to the second embodiment comprises a coupling region 12 close to the electric motor, but does not comprise a coupling region 13 close to the battery. Therefore, each of the electric motors 21, 22, 23, 24 can be connected to each of the power electronics 41, 42, 43, 44. Each of the power electronics 41, 42, 43, 44 is fixedly connected to one of the battery cells 31, 32, 33, 34.

[0046] Figure 3 1 shows a schematic diagram of an electric vehicle 2 having a drive unit 10 according to a third specific embodiment. The drive unit 10 according to the third specific embodiment is largely identical to the drive unit 10 according to the first specific embodiment. The differences are discussed below.

[0047] The drive unit 10 according to the third embodiment comprises a coupling region 13 close to the battery, but does not comprise a coupling region 12 close to the motor. Therefore, each of the battery cells 31, 32, 33, 34 can be connected to each of the power electronics 41, 42, 43, 44. Each of the power electronics 41, 42, 43, 44 is fixedly connected to one of the electric motors 21, 22, 23, 24.

[0048] Figure 4 A schematic diagram of the coupling regions 12 , 13 is shown. The coupling regions 12 , 13 are connected to the electric motors 21 , 22 , 23 , 24 and to the battery cells 31 , 32 , 33 , 34 via power electronics 41 , 42 , 43 , 44 (not shown here).

[0049] For the coupling region 12 close to the motor, the power electronics 41, 42, 43, 44 are arranged between the coupling region 12 close to the electric motor and the battery cells 31, 32, 33, 34. The coupling region 12 close to the motor is connected to the electric motors 21, 22, 23, 24 and to the power electronics 41, 42, 43, 44 in a three-phase manner.

[0050] For the coupling region 13 close to the battery, the power electronics 41, 42, 43, 44 are arranged between the coupling region 13 close to the battery and the electric motors 21, 22, 23, 24. The coupling region 13 close to the battery is connected to the battery cells 31, 32, 33, 34 and to the power electronics 41, 42, 43, 44 with positive and negative wires, respectively.

[0051] The coupling regions 12, 13 are constructed in a matrix manner and have a plurality of intersections. A coupling switch 15 is arranged at each intersection. If the coupling switch 15 is closed, the electric motors 21, 22, 23, 24 connected to the coupling switch 15 are connected to the battery cells 31, 32, 33, 34 connected to the coupling switch 15. The coupling regions 12, 13 are constructed in such a way that each of the electric motors 21, 22, 23, 24 is always connected to exactly one of the battery cells 31, 32, 33, 34.

[0052] Figure 5 In the form of a diagram, exemplary regenerative currents IR1, IR2, IR3, IR4 of the electric motors 21, 22, 23, 24 during regenerative operation are shown. The first regenerative current IR1 is greater than the third regenerative current IR3, the third regenerative current IR3 is greater than the second regenerative current IR2, and the second regenerative current IR2 is greater than the fourth regenerative current IR4. It is assumed below that the regenerative currents IR1, IR2, IR3, IR4 shown here remain constant over a longer period of time, in particular over a first period of time TK of, for example, 5 s, and over a second period of time TM of, for example, more than 20 s.

[0053] In addition, a first limit value GK, a second limit value GM and a third limit value GL are plotted in the diagram. In this case, the first limit value GK is greater than the second limit value GM, and the second limit value is greater than the third limit value GL. The first limit value GK corresponds to the maximum permissible charging current IL1, IL2, IL3, IL4 until the end of the first time period TK. The second limit value GM corresponds to the maximum permissible charging current IL1, IL2, IL3, IL4 after the end of the first time period TK until the end of the second time period TM. The third limit value GL corresponds to the maximum permissible charging current IL1, IL2, IL3, IL4 after the end of the second time period TM.

[0054] The first regenerative current IR1 and the third regenerative current IR3 are greater than the first limit value GK. The second regenerative current IR2 is less than the first limit value GK and greater than the second limit value GM. The fourth regenerative current IR4 is less than the second limit value GM and greater than the third limit value GL.

[0055] During the regeneration operation, the first battery cell 31 has a first charge state S1. The second battery cell 32 has a second charge state S2. The third battery cell 33 has a third charge state S3. The fourth battery cell 34 has a fourth charge state S4.

[0056] During the regeneration operation, the battery cells 31, 32, 33, 34 are charged by charging currents IL1, IL2, IL3, IL4, and the magnitudes of the charging currents IL1, IL2, IL3, IL4 depend on the regeneration currents IR1, IR2, IR3, IR4. As a result, the charging states S1, S2, S3, S4 change. The following diagram shows exemplary changes in the charging states S1, S2, S3, S4 of the battery cells 31, 32, 33, 34 over a period of time.

[0057] Figure 6 Exemplary charge states S1 , S2 , S3 , S4 of the battery cells 31 , 32 , 33 , 34 are shown before the end of a first time period TK.

[0058] The first charge state S1 is the lowest, so the first battery unit 31 is connected to the first electric motor 21. The first charging current IL1 is limited to a first limit value GK.

[0059] The second charge state S2 is the second lowest. Therefore, the second battery unit 32 is connected to the third electric motor 23. The second charging current IL2 is limited to a first limit value GK.

[0060] The fourth charging state S4 is the second highest, so the fourth battery unit 34 is connected to the second electric motor 22. The fourth charging current IL4 is not limited.

[0061] The third charging state S3 is the highest, so the third battery unit 33 is connected to the fourth electric motor 24. The third charging current IL3 is not limited.

[0062] Figure 7 Exemplary charge states S1 , S2 , S3 , S4 of the battery cells 31 , 32 , 33 , 34 are shown after the end of a first time period TK and before the end of a second time period TM.

[0063] The first charge state S1 is the lowest, so the first battery unit 31 is connected to the first electric motor 21. The first charging current IL1 is limited to a second limit value GM.

[0064] The fourth charge state S4 is the second lowest. Therefore, the fourth battery cell 34 is connected to the third electric motor 33. The fourth charging current IL4 is limited to a second limit value GM.

[0065] The second charge state S2 is the second highest. Therefore, the second battery unit 32 is connected to the second electric motor 22. The second charging current IL2 is limited to a second limit value GM.

[0066] The third charging state S3 is the highest, so the third battery unit 33 is connected to the fourth electric motor 24. The third charging current IL3 is not limited.

[0067] Figure 8 Exemplary charge states S1 , S2 , S3 , S4 of the battery cells 31 , 32 , 33 , 34 are shown after the end of the second time period TM.

[0068] The first charge state S1 is the lowest, so the first battery unit 31 is connected to the first electric motor 21. The first charging current IL1 is limited to a third limit value GL.

[0069] The fourth charge state S4 is the second lowest. Therefore, the fourth battery cell 34 is connected to the third electric motor 33. The fourth charging current IL4 is limited to a third limit value GL.

[0070] The second charge state S2 is the second highest. Therefore, the second battery unit 32 is connected to the second electric motor 22. The second charging current IL2 is limited to a third limit value GL.

[0071] The third charge state S3 is the highest. Therefore, the third battery cell 33 is connected to the fourth electric motor 24. The third charging current IL3 is limited to a third limit value GL.

[0072] The invention is not limited to the embodiments described here and the aspects emphasized therein. Rather, numerous modifications are possible within the scope of the claims which are within the purview of a person skilled in the art.

Claims

1. A drive unit (10) for an electric vehicle (2), comprising: a plurality of electric motors (21, 22, 23, 24) for driving the electric vehicle (2), It is characterized in that The drive unit (10) further comprises a plurality of power electronic devices (41, 42, 43, 44) for controlling the electric motors (21, 22, 23, 24), A plurality of battery cells (31, 32, 33, 34) for storing electrical energy and at least one coupling region (12, 13), wherein Each of the electric motors (21, 22, 23, 24) can be connected to each of the battery cells (31, 32, 33, 34) by means of the at least one coupling region (12, 13) via one of the power electronic devices (41, 42, 43, 44), so that battery cells with a higher state of charge are discharged before battery cells with a lower state of charge, and battery cells with a lower state of charge are charged before battery cells with a higher state of charge.

2. The drive unit (10) according to claim 1, characterized in that The drive unit (10) comprises a coupling region (12) close to the motor, by means of which each of the electric motors (21, 22, 23, 24) can be connected to each of the power electronic devices (41, 42, 43, 44).

3. The drive unit (10) according to claim 1 or 2, characterized in that The drive unit (10) comprises a coupling region (13) close to the battery, by means of which each of the power electronic devices (41, 42, 43, 44) can be connected to each of the battery cells (31, 32, 33, 34).

4. A method for operating a drive unit (10) according to any one of claims 1 to 3, wherein each of the electric motors (21, 22, 23, 24) is connected to exactly one of the battery cells (31, 32, 33, 34) by means of the at least one coupling region (12, 13) via exactly one of the power electronic devices (41, 42, 43, 44).

5. The method according to claim 4, wherein A regenerative current (IR1, IR2, IR3, IR4) provided by each of the electric motors (21, 22, 23, 24) is measured, and a state of charge (S1, S2, S3, S4) of each of the battery cells (31, 32, 33, 34) is measured.

6. The method according to claim 5, wherein The electric motor (21, 22, 23, 24) providing the largest regenerative current (IR1, IR2, IR3, IR4) is connected to the battery unit (31, 32, 33, 34) having the lowest state of charge (S1, S2, S3, S4).

7. A method according to any one of claims 5 to 6, wherein the electric motor (21, 22, 23, 24) providing the smallest regenerative current (IR1, IR2, IR3, IR4) is connected to the battery cell (31, 32, 33, 34) having the highest state of charge (S1, S2, S3, S4).

8. The method according to any one of claims 5 to 6, wherein A charging current (IL1, IL2, IL3, IL4) flowing into each of the battery cells (31, 32, 33, 34) is limited to a predefined limit value (GK, GM, GL).

9. The method according to claim 8, wherein until the end of the first time period (TK), the charging current (IL1, IL2, IL3, IL4) is limited to a first limit value (GK), and After the first time period (TK) has ended and until the second time period (TM) has ended, the charging current is limited to a second limiting value (GM), wherein The first limit value (GK) is greater than the second limit value (GM).

10. The method according to claim 9, wherein After the second time period (TM) has ended, the charging current (IL1, IL2, IL3, IL4) is limited to a third limiting value (GL), wherein The second limit value (GM) is greater than the third limit value (GL).

Images