Electric drive device for driving a motor vehicle and method for operating an electric drive device

Abstract

The invention relates to an electric drive device (100) for driving a motor vehicle, comprising at least a first electric machine (10) and a second electric machine (20). According to the invention, the first electric machine (10) is designed as a separately excited synchronous machine, and the second electric machine (20) is designed as a permanently excited synchronous machine, wherein the second electric machine (20) has magnets that are substantially free of at least heavy rare earth elements. The invention further relates to a method for operating an electric drive device (100).

Description

[0001] The invention relates to an electric drive device for driving a motor vehicle and a method for operating an electric drive device.

[0002] Many magnetic materials, especially neodymium-iron-boron magnets, such as those used in permanent-magnet synchronous machines for traction applications, are demagnetized by the combination of high temperature and high opposing magnetic field. This places high demands on the coercive field strength of the magnetic material. This requirement is typically met by alloying the heavy rare earth elements dysprosium, terbium, and holmium. This makes the magnet expensive.

[0003] DE 10 2017 220 685 A1 discloses a method and a device for operating an electric machine to deliver a predetermined torque and a predetermined speed. The method serves to measure a temperature of the electric machine and, based on this, trigger an active short circuit if a temperature threshold is exceeded. If the temperature threshold is exceeded, demagnetization of the magnets of the electric machine is prevented by reducing the maximum torque.

[0004] DE 10 2019 130 334 A1 discloses a method for protecting permanent magnets of a permanent-magnet synchronous machine in a vehicle from demagnetization. If a predetermined rotor temperature of the permanent-magnet synchronous machine is exceeded, operation of the permanent-magnet synchronous machine is suppressed in areas of the speed / torque characteristic map of the permanent-magnet synchronous machine where the field strength of a counter-field generated by an active short circuit of the permanent-magnet synchronous machine would exceed the coercive field strength of the permanent magnets.

[0005] An object of the invention is to provide an improved electric drive device for driving a motor vehicle.

[0006] A further object is to provide a method for operating an improved electric drive device.

[0007] The above-mentioned objects are solved by the features of the independent claims.

[0008] Advantageous embodiments and advantages of the invention emerge from the further claims, the description and the drawing.

[0009] The invention is based on an electric drive device for driving a motor vehicle with at least a first electric machine and a second electric machine.

[0010] According to the invention, the first electrical machine is designed as a separately excited synchronous machine and the second electrical machine as a permanently excited synchronous machine, wherein the second electrical machine has magnets which are substantially free of at least heavy rare earth elements.

[0011] Heavy rare earth elements, or heavy rare earth metals, are elements with an atomic number in the periodic table of elements between 64 and 71, such as terbium, dysprosium, and holmium. They ensure temperature stability of the magnets of a permanent magnet synchronous machine and offer stability against demagnetization by induced magnetic fields.

[0012] However, the proposed electric drive system advantageously eliminates the need for such materials, as the availability of such materials may be limited and these materials are expensive, thus increasing the cost of manufacturing the permanent-magnet synchronous machine. If permanent-magnet synchronous machines use magnets that are essentially free of at least heavy rare earth elements, more cost-effective electric drive systems can be used in vehicle drives.

[0013] According to an advantageous embodiment of the electric drive device, the second electric machine can have magnets that are essentially free of rare earth elements. This allows for the implementation of an electric drive device that is even more cost-effective to manufacture and independent of the procurement of rare earth elements.

[0014] According to an advantageous embodiment of the electric drive device, the first electric machine and the second electric machine can be connected to a first or second axle of the motor vehicle. In particular, the first electric machine and the second electric machine can be connected to the first or second axle of the motor vehicle via a common transmission unit with a clutch. Thus, a two-wheel drive motor vehicle can advantageously be driven with the proposed drive device having two electric machines.

[0015] According to an advantageous embodiment of the electric drive device, the first electric motor can be connected to a first axle, in particular a rear axle, and the second electric motor can be connected to a second axle, in particular a front axle, of the motor vehicle. Thus, a four-wheel drive motor vehicle can advantageously be driven with the proposed drive device having two electric motors.

[0016] According to a further aspect of the invention, a method for operating an electric drive device is proposed, at least comprising a first operating mode in which the motor vehicle is driven by operation of the second electric machine, wherein the first electric machine remains switched off; a second operating mode in which the motor vehicle is driven by operation of the first electric machine, wherein the second electric machine remains switched off; a third operating mode in which the motor vehicle is driven by operation of the second electric machine and the first electric machine, wherein a torque is predominantly provided by the second electric machine;and a fourth operating mode, in which the motor vehicle is driven by operation of the second electric machine and the first electric machine, with torque being provided predominantly by the first electric machine. A respective operating mode to be set is selected depending on a current torque requirement and / or depending on a current rotational speed of a rotor of at least one of the first or second electric machines.

[0017] Advantageously, the proposed method can be used to operate an electric drive device that uses magnets in permanent-magnet synchronous machines that are essentially free of at least heavy rare-earth elements. By shifting the load, in particular depending on the magnet temperature, into different operating modes from the second electric machine, which is designed as a permanent-magnet synchronous machine, to the first electric machine, which is designed as a separately excited synchronous machine, the magnets of the permanent-magnet synchronous machine, which are essentially free of at least heavy rare-earth elements, can be protected from operation at excessively high temperatures.

[0018] According to an advantageous embodiment of the method, the first operating mode can be activated when a torque request falls below a torque threshold and the current speed falls below a first speed threshold. The second operating mode can be activated when the current speed exceeds a second speed threshold. The third operating mode can be activated when the current torque request exceeds the torque threshold. The fourth operating mode can be activated when the current speed exceeds the first speed threshold.

[0019] Thus, the magnets of the permanent-magnet synchronous machine, which are essentially free of at least heavy rare earth elements, can be protected from operation at excessively high temperatures due to load shifts from the second electrical machine, which is designed as a permanent-magnet synchronous machine, in the first, third or fourth operating mode of the permanent-magnet synchronous machine, to the first electrical machine, the separately excited synchronous machine.

[0020] According to an advantageous embodiment of the method, when the electric drive device is operated in the first operating mode and a determined temperature, in particular rotor temperature or magnet temperature, in the second electric machine exceeds a temperature threshold, the first electric machine can be switched on and the load transferred to it. Thus, the magnets of the permanent-magnet synchronous machine, which are essentially free of at least heavy rare earth elements, can be protected from operation at excessively high temperatures.

[0021] According to an advantageous embodiment of the method, when the electric drive device is operated in the third operating mode and a determined temperature in the second electric machine exceeds the temperature threshold, the torque provided by the first electric machine can be increased while the second electric machine is shut down. Thus, the magnets of the permanent-magnet synchronous machine, which are essentially free of at least heavy rare earth elements, can be protected from operation at excessively high temperatures.

[0022] According to an advantageous embodiment of the method, when the electric drive device is operated in the fourth operating mode and a determined temperature in the second electric machine exceeds the temperature threshold, the torque provided by the first electric machine can be increased while the second electric machine is shut down. Thus, the magnets of the permanent-magnet synchronous machine, which are essentially free of at least heavy rare earth elements, can be protected from operation at excessively high temperatures.

[0023] According to an advantageous embodiment of the method, switching on and / or off the first and / or second electric machine can be continuously controlled after a determined exceedance of the temperature threshold. This ensures continuous propulsion of the motor vehicle.

[0024] According to an advantageous embodiment of the method, a total final value of the torques provided by the second electric machine and the first electric machine after a determined exceedance of the temperature threshold can correspond to at least a total initial value of the torques provided before the determined exceedance of the temperature threshold. This allows the motor vehicle to be operated efficiently without impairing the drive behavior. The maximum torque when the second electric machine is completely switched off is limited by the maximum torque of the first electric machine.

[0025] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an exemplary embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will expediently consider the features individually and combine them into further meaningful combinations.

[0026] Showing: Fig. 1 a system overview of an electric drive device for driving a motor vehicle with at least a first electric machine and a second electric machine according to an embodiment of the invention; Fig. 2 a system overview of an electric drive device according to a further embodiment of the invention; Fig. 3 shows a speed / torque diagram of a method for operating the electric drive device according to an embodiment of the invention; Fig. 4 a derating behavior of the electric drive device in the first operating mode; Fig. 5 a derating behavior of the electric drive device in the third operating mode; and Fig. 6 a derating behavior of the electric drive device in the fourth operating mode.

[0027] In the figures, identical or similar components are designated by the same reference numerals. The figures are merely examples and are not to be construed as limiting.

[0028] Fig. 1 shows a system overview of an electric drive device 100 for driving a motor vehicle with at least a first electric machine 10 and a second electric machine 20 according to an embodiment of the invention.

[0029] The first electrical machine 10 is designed as a separately excited synchronous machine, and the second electrical machine 20 is designed as a permanently excited synchronous machine. The second electrical machine 20 has magnets that are essentially free of at least heavy rare earth elements.

[0030] Heavy rare earth elements such as terbium, dysprosium, and holmium typically ensure temperature stability of the magnets of a permanent-magnet synchronous machine and offer resistance to demagnetization caused by induced magnetic fields. Using magnets in permanent-magnet synchronous machines that are essentially free of at least heavy rare earth elements allows for more cost-effective electric drive systems in vehicle drives.

[0031] In an alternative embodiment, the second electric machine 20 could even comprise magnets that are essentially free of rare earth elements. This allows permanent magnet synchronous machines to be manufactured even more cost-effectively.

[0032] In the Fig. In the embodiment shown in Figure 1, the two electric machines 10, 20 are mechanically coupled to the first or second axle 32, 36 of the motor vehicle via a common transmission unit 40 with a clutch. The transmission unit 40 can have at least one summing gear, a transmission, a clutch, and a differential.

[0033] The two electrical machines 10, 20 are supplied with power by a power electronics unit 80 via corresponding alternating current (AC) controllers 82, 83, for example, so-called AC busbars. The two electrical machines 10, 20 can be controlled independently via the power electronics unit 80.

[0034] The axle 32, 36 is mechanically connected to wheels 84 of the motor vehicle.

[0035] In Fig. Figure 2 shows an alternative embodiment of an electric drive system with two driven axles 32, 36. The first axle 32 may represent the rear axle 34, while the second axle 36 represents the front axle 38.

[0036] The first electric machine 10 is mechanically coupled to the front axle 38 via a transmission unit 42 and is electrically supplied by power electronics 80 via an AC busbar 82. The transmission unit 42 can have at least one differential and a transmission ratio.

[0037] The second electric machine 20 is mechanically coupled to the rear axle 34 via a transmission unit 44 and is electrically supplied by power electronics 81 via an AC busbar 83. The transmission unit 44 can have at least one differential, a transmission ratio, and a clutch.

[0038] The two electrical machines 10, 20 can be controlled independently via the respective power electronics 80, 81. Both power electronics units 80, 81 can also be configured as a single power electronics unit.

[0039] Fig. Figure 3 shows a speed / torque diagram of a method for operating the electric drive device 100 according to an embodiment of the invention. A torque 50 is plotted against the speed 60.

[0040] The proposed method comprises a first operating mode 1, in which the motor vehicle is driven by operation of the second electric machine 20, wherein the first electric machine 10 remains switched off.

[0041] The method comprises a second operating mode 2, in which the motor vehicle is driven by operation of the first electric machine 10, wherein the second electric machine 20 remains switched off.

[0042] The method further comprises a third operating mode 3, in which the motor vehicle is driven by operation of the second electric machine 20 and the first electric machine 10, wherein a torque 50 is predominantly provided by the second electric machine 20.

[0043] The method further comprises a fourth operating mode 4, in which the motor vehicle is driven by operation of the second electric machine 20 and the first electric machine 10, wherein a torque 50 is predominantly provided by the first electric machine 10.

[0044] A selection of a respective operating mode 1, 2, 3, 4 to be set is made depending on a current requirement of a torque 50 and / or depending on a current speed 60 of a rotor of at least one of the first or second electric machines 10, 20.

[0045] As in Fig. 3, the first operating mode 1 is activated when a torque request 50 falls below a torque threshold 52 and the current speed 60 falls below a first speed threshold 62. In this case, only the second electric machine 20 is operated.

[0046] The second operating mode 2 is activated when the current speed 60 exceeds a second speed threshold 64. In this case, only the first electric machine 10 is operated.

[0047] The third operating mode 3 is activated when the current torque requirement 50 exceeds the torque threshold 52. The first and second electric machines 10, 20 are operated, with the second electric machine 20 covering a larger torque component.

[0048] The fourth operating mode 4 is activated when the current speed 60 exceeds the first speed threshold 62. The first and second electric machines 10, 20 are operated, with the first electric machine 10 covering a larger torque component.

[0049] Fig. 4 shows a derating behavior of the electric drive device 100 in the first operating mode 1. Load curves of the first and second electric machines 10, 20 are shown as a function of time and as a function of a magnet temperature 70 of the second electric machine 20.

[0050] The so-called derating behavior describes an operating strategy for protecting the magnets in the event of increasing heating of the magnets by a corresponding power reduction of the second electrical machine 20 while transferring load to the first electrical machine 10.

[0051] In the first operating mode 1, the motor vehicle is driven by operation of the second electric machine 20, wherein the first electric machine 10 remains switched off.

[0052] If the electric drive device 100 is operated, for example, in the first operating mode 1 and a determined temperature 70 in the second electric machine 20 exceeds a temperature threshold value 72, the first electric machine 10 is switched on.

[0053] The switching on of the first electric machine 10 and the switching off of the second electric machine 20 after a determined exceedance of the temperature threshold 72 are each continuously controlled. The first electric machine 10 continuously takes over the load from the second electric machine 20, which is continuously shut down until the first electric machine 10 takes over the full load at a maximum magnet temperature 74.

[0054] In this case, a total final value 56 of torques 50 provided by the second electrical machine and the first electrical machine after a determined exceedance of the temperature threshold value 72 corresponds to at least a total initial value 54 of the provided torques 50 before the determined exceedance of the temperature threshold value 72. In this case, the maximum total torque when the second electrical machine is completely switched off is limited by the maximum torque of the first electrical machine.

[0055] Fig. 5 shows the derating behavior of the electric drive device 100 in the third operating mode 3. In the third operating mode 3, the motor vehicle is driven by operation of the second electric machine 20 and the first electric machine 10, wherein a torque 50 is predominantly provided by the second electric machine 20.

[0056] If the electric drive device 100 is operated in the third operating mode 3 and a determined temperature 70 in the second electric machine 20 exceeds the temperature threshold 72, a provided torque 50 of the first electric machine 10 is increased, while the second electric machine 20 is switched off. At the maximum magnet temperature 74, the first electric machine 10 assumes the full load. The maximum total torque when the second electric machine is completely switched off is limited by the maximum torque of the first electric machine.

[0057] Fig.6 shows the derating behavior of the electric drive device 100 in the fourth operating mode 4. In the fourth operating mode 4, the motor vehicle is driven by operation of the second electric machine 20 and the first electric machine 10, wherein a torque 50 is predominantly provided by the first electric machine 10.

[0058] When the electric drive device 100 is operated in the fourth operating mode 4 and a determined temperature 70 in the second electric machine 20 exceeds the temperature threshold 72, a torque 50 provided by the first electric machine 10 is increased, similar to the third operating mode 3, while the second electric machine 20 is switched off. At the maximum magnet temperature 74, the first electric machine 10 assumes the full load. The maximum total torque when the second electric machine is completely switched off is limited by the maximum torque of the first electric machine. List of reference symbols 1 first operating mode 2 second operating mode 3 third operating mode 4 fourth operating mode 10 first electric machine 20 second electric machine 32 first axis 34 rear axle 36 second axis 38 front axle 40 Gear unit 42 Gear unit 44 Gear unit 50 torque 52 Torque threshold 54 Sum initial value 56 Total final value 60 rpm 62 first speed threshold 64 second speed threshold 70 Magnet temperature 72 Temperature threshold 74 maximum magnet temperature 80 Power electronics 81 Power electronics 82 AC control 83 AC control 84 wheels 90 time 100 electric drive device QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 220 685 A1

[0003] DE 10 2019 130 334 A1

[0004]

Claims

[1] Electric drive device (100) for driving a motor vehicle with at least a first electric machine (10) and a second electric machine (20), characterized by in that the first electrical machine (10) is designed as a separately excited synchronous machine and the second electrical machine (20) is designed as a permanently excited synchronous machine, wherein the second electrical machine (20) has magnets which are substantially free of at least heavy rare earth elements having an atomic number in the periodic table of the elements between 64 and 71. [2] Electric drive device according to claim 1, characterized by that the second electrical machine (20) has magnets which are substantially free of rare earth elements. [3] Electric drive device according to claim 1 or 2, characterized bythat the first electric machine (10) and the second electric machine (20) are connected to a first or second axle (32, 36) of the motor vehicle, in particular wherein the first electric machine (10) and the second electric machine (20) are connected to the first or second axle (32, 36) of the motor vehicle via a common transmission unit (40) and / or via a clutch. [4] Electric drive device according to claim 1 or 2 characterized by that the first electric machine (10) is connected to a first axle (32), in particular a rear axle (34), and the second electric machine (20) is connected to a second axle (36), in particular a front axle (38), of the motor vehicle. [5] Method for operating an electric drive device (100) according to one of the preceding claims, at least comprising - a first operating mode (1) in which the motor vehicle is driven by operation of the second electric machine (20), the first electric machine (10) remaining switched off; - a second operating mode (2) in which the motor vehicle is driven by operation of the first electric machine (10), the second electric machine (20) remaining switched off; - a third operating mode (3) in which the motor vehicle is driven by operation of the second electric machine (20) and the first electric machine (10), wherein a torque is predominantly provided by the second electric machine (20); - a fourth operating mode (4) in which the motor vehicle is driven by operation of the second electric machine (20) and the first electric machine (10), wherein a torque is predominantly provided by the first electric machine (10), wherein a selection of a respective operating mode (1, 2, 3, 4) to be set takes place as a function of a current requirement for a torque (50) and / or as a function of a current speed (60) of a rotor of at least one of the first or second electric machines (10, 20). [6] Method according to claim 5, wherein the first operating mode (1) is activated when a torque request (50) falls below a torque threshold (52) and the current speed (60) falls below a first speed threshold (62); wherein the second operating mode (2) is activated when the current speed (60) exceeds a second speed threshold value (64); wherein the third operating mode (3) is activated when the current torque requirement (50) exceeds the torque threshold (52); wherein the fourth operating mode (4) is activated when the current speed (60) exceeds the first speed threshold (62). [7] Method according to claim 5 or 6, wherein when the electric drive device (100) is operated in the first operating mode (1) and a determined temperature (70) in the second electric machine (20) exceeds a temperature threshold value (72), the first electric machine (10) is switched on. [8] Method according to one of claims 5 to 7, wherein when the electric drive device (100) is operated in the third operating mode (3) and a determined temperature (70) in the second electric machine (20) exceeds the temperature threshold value (72), a provided torque (50) of the first electric machine (10) is increased, while the second electric machine (20) is switched off. [9] Method according to one of claims 5 to 8, wherein switching on and / or switching off the first and / or second electrical machine (10, 20) is / are continuously controlled after a determined exceedance of the temperature threshold value (72). [10] Method according to one of claims 5 to 9, wherein a sum final value (56) of torques (50) provided by the second electrical machine (20) and the first electrical machine (10) after a determined exceeding of the temperature threshold value (72) corresponds to at least one sum initial value (54) of the provided torques (50) before the determined exceeding of the temperature threshold value (72), wherein a maximum sum torque when the second electrical machine (20) is completely switched off is limited by a maximum torque of the first electrical machine (10).

Images