Driving device for electric vehicle

Abstract

To provide a driving device for an electric vehicle mounted with two electric motors, which reduces an amount of permanent magnets used in the electric motors and the number of inverters supplying power to the electric motors.SOLUTION: A driving device 10 for an electric vehicle comprises a synchronous motor 12; an induction motor 14 and a planetary gear mechanism 16. A first sun gear 20 of the planetary gear mechanism 16 is connected to the synchronous motor 12; a second sun gear 22 thereof is connected to the induction motor 14; and a carrier 24 is connected to a drive wheel 18. The synchronous motor 12 and the induction motor 14 are supplied with 3-phase alternating current power from a single inverter 42. A differential action of the planetary gear mechanism 16 causes the induction motor 14 to slip and output torque. Using one of the two motors as the induction motor reduces the amount of permanent magnets used, and controlling both motors with the single inverter reduces the number of inverters required.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a drive device for an electric vehicle, and more particularly to a drive device equipped with two electric motors. [Background technology]

[0002] The following Patent Document 1 shows a drive device for an electric vehicle equipped with two electric motors. The two electric motors are respectively connected to two sun gears of a planetary gear mechanism, and driving wheels are connected to a planetary carrier of the planetary gear mechanism. The following Non-Patent Document 1 shows a technology for driving multiple induction motors with a single inverter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-100709 A [Non-patent literature]

[0004] [Non-Patent Document 1] Yasushi Matsumoto, Satoru Ozaki, Atsuo Kawamura, "Vector Control Method of Single Inverter and Multiple Induction Machine Drive for Railway Vehicles," IEEJ Transactions on Electrical Engineering, Vol. 121, No. 7, pp. 747-755, July 2001.<URL:https: / / www.jstage.jst.go.jp / article / ieejias1987 / 121 / 7 / 121_7_747 / _pdf> Summary of the Invention [Problem to be solved by the invention]

[0005] Permanent magnet synchronous motors are often used for electric vehicle drive motors because they allow for highly accurate control of output torque and are small and high-output from the viewpoint of mountability. However, expensive rare earths are used in permanent magnets, and in higher-output motors, the amount of permanent magnets used, i.e., the amount of rare earths used, increases, making the motor expensive. In addition, there is a demand for reducing the number of inverters in drive devices equipped with multiple motors.

[0006] An object of the present invention is to obtain high output while reducing the amount of permanent magnets used in an electric motor, and to reduce the number of inverters for controlling the electric motor. [Means for solving the problem]

[0007] The drive device for an electric vehicle according to the present invention includes a synchronous motor, an induction motor, a differential transmission mechanism having three elements that rotate relative to one another, and a single inverter that supplies power to the synchronous motor and the induction motor, the three elements of the differential transmission mechanism being a first input element to which the synchronous motor is connected, a second input element to which the induction motor is connected, and an output element connected to the drive wheels.

[0008] Compared to a drive unit with two synchronous motors, it is possible to reduce the amount of permanent magnets used, and by controlling the synchronous motor and induction motor with a single inverter, it is possible to reduce the number of inverters.

[0009] In the drive device for an electric vehicle described above, the differential transmission mechanism can be configured so that the absolute value of the ratio between the relative speed of the synchronous motor with respect to the output element and the relative speed of the induction motor with respect to the output element is the ratio between the maximum torque of the induction motor and the maximum torque of the synchronous motor. The synchronous motor and the induction motor can be operated simultaneously at their maximum torque.

[0010] In the drive device for an electric vehicle described above, the maximum torque of the induction motor can be made greater than the maximum torque of the synchronous motor, which allows the amount of permanent magnets used to be reduced compared to when the maximum torque of the synchronous motor is increased.

[0011] In the drive device for an electric vehicle described above, the differential transmission mechanism may include a planetary gear mechanism, and the three elements of the planetary gear mechanism that move relative to one another may be a first input element, a second input element, and an output element.

[0012] The above-described drive device for an electric vehicle can be configured so that slip is generated in the induction motor by changing the rotation speed of the synchronous motor, and the induction motor outputs a torque according to the slip. Effect of the Invention

[0013] By reducing the amount of permanent magnets used in the synchronous motor and by reducing the number of inverters, it is possible to provide an inexpensive drive unit. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing a schematic configuration of a drive device according to an embodiment of the present invention; [Diagram 2] FIG. 4 is a collinear diagram showing the speed relationships among three elements of the planetary gear mechanism of the present embodiment. [Diagram 3] FIG. 2 is a diagram showing torque characteristics of a synchronous motor and an induction motor. [Figure 4] FIG. 2 is an explanatory diagram of control of the output torque of an induction motor by controlling a synchronous motor, showing an initial state in which the synchronous motor and the induction motor are unloaded. [Diagram 5] FIG. 1 is an explanatory diagram of control of the output torque of an induction motor by controlling a synchronous motor, showing a state in which the synchronous motor accelerates and slip occurs in the induction motor. [Figure 6] FIG. 2 is an explanatory diagram of control of the output torque of an induction motor by controlling a synchronous motor, showing a state in which the output torque of the synchronous motor and the induction motor are stable. [Figure 7] FIG. 10 is an explanatory diagram of control of the output torque of the induction motor by controlling the synchronous motor, showing a state in which a higher output torque is obtained. [Figure 8]FIG. 2 is a diagram showing a vector representation of each parameter related to a synchronous motor. [Figure 9] FIG. 13 is a diagram showing vector representations of parameters related to a synchronous motor, showing a case where the driving torque is equal and the driving voltage is small (a) and large (b). [Figure 10] FIG. 2 is a diagram showing vector representations of various parameters related to a synchronous motor, and in particular shows changes in drive current, total interlinkage magnetic flux, and drive voltage due to drive torque. [Figure 11] This is a collinear diagram of a device that combines a synchronous motor and an induction motor with different outputs. [Figure 12] FIG. 12 is a diagram showing the torque characteristics of the device of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing a schematic configuration of a drive device 10 for an electric vehicle according to this embodiment. The drive device 10 includes a synchronous motor 12 and an induction motor 14 that drive the vehicle. The synchronous motor 12 may be a permanent magnet field type synchronous motor. The outputs of the synchronous motor 12 and the induction motor 14 are transmitted to drive wheels 18 via a planetary gear mechanism 16, which is a differential mechanism.

[0016] Planetary gear mechanism 16 includes three elements that rotate relatively around a common rotation axis with a predetermined relationship. The three elements are a first sun gear 20 that is an input element to which synchronous motor 12 is connected, a second sun gear 22 that is an input element to which induction motor 14 is connected, and a planetary carrier 24 (hereinafter referred to as carrier 24) that is an output element to which drive wheels 18 are connected. Second sun gear 22 meshes with a plurality of outer pinions 26 rotatably supported by carrier 24. First sun gear 20 meshes with a plurality of inner pinions 28 rotatably supported by carrier 24, and each of inner pinions 28 meshes with one outer pinion 26.

[0017] Planetary gear mechanism 16 is a compound planetary gear mechanism including a first planetary gear train consisting of a first sun gear 20, an inner pinion 28, and an outer pinion 26, and a second planetary gear train consisting of a second sun gear 22 and an outer pinion 26. The first planetary gear train is a double-pinion type planetary gear train, and the second planetary gear train is a single-pinion type planetary gear train.

[0018] The first sun gear 20 is connected to the output shaft of the synchronous motor 12 via a first input gear pair 30. The second sun gear 22 is connected to the output shaft of the induction motor 14 via a second input gear pair 32. The first sun gear 20 and the second sun gear 22 may be directly connected to the output shafts of the synchronous motor 12 and the induction motor 14, respectively, without using gear pairs. The carrier 24 includes an integrated output gear 34, which meshes with a ring gear 38 of a final reduction gear 36. The power of the synchronous motor 12 and the induction motor 14 output via the planetary gear mechanism 16 is transmitted from the ring gear 38 to a differential 40 of the final reduction gear 36, and is further distributed to the left and right drive wheels 18.

[0019] The synchronous motor 12 and the induction motor 14 are supplied with power from a battery 44 via a common inverter 42 (during power running). DC power from the battery 44 is converted to three-phase AC power in the inverter 42 and supplied to the synchronous motor 12 and the induction motor 14. Since the synchronous motor 12 and the induction motor 14 are supplied with power from the common inverter 42, the voltage and frequency of the supplied AC power are common. Each phase current of the three-phase AC power supplied from the inverter 42 to the synchronous motor 12 is detected by a synchronous motor current sensor 46. The rotation speed of the synchronous motor 12 is detected by a synchronous motor rotation speed sensor 48, which is, for example, a resolver. Each phase current of the three-phase AC power supplied from the inverter 42 to the induction motor 14 is detected by an induction motor current sensor 50. The rotation speed of the induction motor 14 is detected by an induction motor rotation speed sensor 52, which is, for example, a resolver. The detected phase currents and rotation speeds of the synchronous motor 12 and the induction motor 14 are sent to a control device 54. The control device 54 controls the outputs and rotation speeds of the synchronous motor 12 and the induction motor 14 in response to the driver's operation and driving conditions such as the vehicle speed. The control device 54 feedback-controls the synchronous motor 12 and the induction motor 14 based on the detected current values ​​and rotation speeds.

[0020] FIG. 2 is a so-called nomographic diagram showing the relationship between the rotational speeds of the three elements of the planetary gear mechanism, that is, the first sun gear 20, the second sun gear 22, and the carrier 24. In the figure, the rotational speed of the first sun gear 20 is shown on the S1 axis, the rotational speed of the second sun gear 22 on the S2 axis, and the rotational speed of the carrier 24 on the C axis. The relationship between the rotational speeds of the first sun gear 20, the second sun gear 22, and the carrier 24 is represented by a straight line intersecting the S1 axis, the S2 axis, and the C axis. In other words, the rotational speeds of the first sun gear 20, the second sun gear 22, and the carrier 24 are represented as the intersections of this straight line with the S1 axis, the S2 axis, and the C axis. The values ​​a and b shown in FIG. 2 are determined by the number of teeth of the first sun gear 20 and the second sun gear 22.

[0021] FIG. 2 shows that the first sun gear 20, the second sun gear 22 and the carrier 24 each rotate at a rotation speed of N S1 ,N S2 ,NC The torques on the first sun gear 20, the second sun gear 22, and the carrier 24 are respectively T S1 ,T S2 ,T C The input torque T S1 ,T S2 The sum of these is the output torque T C So, T S1 +T S2 =T C (1) Also, from the balance of torque, aT S1 -bT S2 =0 (2) It is.

[0022] 3 is a diagram showing the torque characteristics of the synchronous motor 12 and the induction motor 14. The horizontal axis represents the frequency f INV (Hereinafter, the driving frequency f INV The rotation frequency f of the synchronous motor 12 is expressed as M1 , the rotation frequency of the induction motor f M2 3, the line indicated by A represents the torque characteristics of the synchronous motor 12, and the line indicated by B represents the torque characteristics of the induction motor 14.

[0023] The rotation frequency f of the synchronous motor 12 M1 is the driving frequency f INV Since it is synchronized with, the frequency ratio is 1(f M1 / f INV = 1), only the torque increases or decreases. In the induction motor 14, the rotor lags behind the rotating magnetic field, that is, slip occurs, and thus torque is generated. In other words, when the rotation frequency f M2 is the driving frequency f INV When it matches (f M2 / f INV = 1), the torque is 0 and the rotational frequency f M2 is the driving frequency f INV When the rotation frequency f becomes smaller than M2 Drive frequency f INVThe torque increases as the delay relative to the rotational speed, i.e., the slip, increases, but when the slip exceeds a certain value, the torque decreases. Usually, the induction motor 14 is controlled so that the slip is in the range from a value that gives the maximum torque to zero.

[0024] When power is supplied to the synchronous motor 12 and the induction motor 14 by one inverter 42, it is possible to control the torque of the induction motor 14 by controlling the rotation speed of the synchronous motor 12 to cause slip in the induction motor 14. Of the three elements of the planetary gear mechanism 16, the rotation speed of the remaining element is determined when the rotation speeds of two of the elements are determined. Since the rotation speed of the carrier 24 is determined by the running speed of the vehicle, the rotation speed of the induction motor 14 can be determined by determining the rotation speed of the synchronous motor 12. If the rotation speed of the induction motor 14 at this time is made slower than the drive frequency, that is, the rotation speed of the rotating magnetic field generated by the power supply, and slip is caused, the induction motor 14 will output torque.

[0025] 3 and 4 to 7 described above, the control of the induction motor 14, particularly the control of increasing the output from a no-load state, will be described. For ease of explanation, a and b in FIG. 2 are set equal (a=b), and the gear ratio of the first input gear pair 30 and the second input gear pair 32 is set to 1. The number of teeth of the first sun gear 20 and the second sun gear 22 is set equal to a=b. This is achieved by making the revolution radii of the outer pinion 26 and the inner pinion 28 equal, displacing them in the direction of the rotation axis so that they overlap, meshing with each other at the overlapping portions, and meshing with the first sun gear 20 and the second sun gear 22 at the non-overlapping portions on both sides. In addition, by setting the gear ratio of the first and second input gear pairs 30, 32 to 1, the rotation speeds of the first sun gear 20 and the synchronous motor 12 become equal, and the rotation speeds of the second sun gear 22 and the induction motor 14 become equal. Therefore, the S1 axis is the M1 axis representing the rotation speed of the synchronous motor 12, and the S2 axis is the M2 axis representing the rotation speed of the induction motor 14. In addition, the torque T S1 and the output torque T of the synchronous motor 12 M1 becomes equal (T S1 =T M1) Torque T on the second sun gear 22 S2 and the torque T of the induction motor 14 M2 become equal (T S2 = T M2 ). Further, since a = b, from the above formula (2), T S1 = T S2 , T M1 = T M2 is obtained.

[0026] Figure 4 shows a state where the vehicle is traveling at a speed where the rotational speed N C of the carrier 24 is N0, and the synchronous motor 12 and the induction motor 14 are in a no-load state. The rotational speeds of the first and second sun gears 20, 22 and the synchronous motor 12 and the induction motor 14 are also N0. The frequency of the power supplied to the synchronous motor 12 and the induction motor 14 (driving frequency f INV ) is set to 100 Hz. The rotational frequencies f M1 , f M2 of the synchronous motor 12 and the induction motor 14 are also 100 Hz, and the difference ΔN in rotational speed is 0. This state shows the state at the position P1 shown in Figure 3.

[0027] From the state of Figure 4, as shown in Figure 5, when the torque T M1 of the synchronous motor 12 is increased to torque T1 by torque control (P2 in Figure 3), the synchronous motor 12 and the first sun gear 20 accelerate (N M1 = N1 > N0). The rotational speed N C of the carrier 24 hardly changes because of the large inertia of the vehicle (N C = N0). Therefore, the induction motor 14 decelerates (N M2 = N2 < N0) (P3). As the induction motor 14 decelerates, that is, as the rotational frequency f M2 of the induction motor 14 decreases, the rotational frequency f INV of the induction motor 14 lags behind the driving frequency f M2 , and slip occurs (P4). Since a common drive current is supplied to the synchronous motor 12 and the induction motor 14, the slip of the induction motor 14 is the difference ΔN in the rotational speeds of the synchronous motor 12 and the induction motor 14 (ΔN = N M1-N M2 ) where ΔN is hereinafter referred to as slip. In response to the slip ΔN, the induction motor 14 generates torque (P5), and the torque T M2 is the torque T of the synchronous motor 12. M1 (=T1) is balanced with (T M1 =T M2 =T1) and (P6), the steady state shown in FIG. 6 is reached. In this steady state, the slip frequency is 4 Hz. The torque T of the synchronous motor 12 M1 If we further increase it to T2, as shown in Figure 7, the slip ΔN increases and the T C increases (P7).

[0028] As described above, it is possible to control the output torque of the induction motor 14 by controlling the slip. Furthermore, the output torque of the induction motor 14 can also be controlled by controlling the drive voltage. The synchronous motor 12 can maintain its output torque even if the drive voltage is changed, and it is possible to control the output torque of the induction motor 14 independently of the drive torque of the synchronous motor 12.

[0029] The following describes how the drive voltage from the inverter 42 can be changed without changing the output torque of the synchronous motor 12. The magnetization direction of the rotor of the synchronous motor 12 is taken as the d-axis, and the q-axis is taken in the direction of an electrical angle of 90° to the d-axis.

[0030] 8 is a diagram showing the relationship between the current i and voltage v supplied to the synchronous motor 12 and the generated magnetic flux Φ on a plane defined by the d-axis and q-axis. The parameters indicated by the symbols used in the diagram are as follows: Armature flux linkage: Φ a d-axis inductance: L d q-axis inductance: L q Rotor angular speed: ω Armature coil resistance: r d-axis and q-axis components of armature current: i d ,i q Drive current: ia Total flux linkage: Φ O Driving voltage (terminal voltage): V a Number of pole pairs (constant): p=1 Rotor driving torque: τ=-pi a ×Φ O

[0031] In current vector control, the rotor drive torque τ (output torque) is calculated by the drive current i a and the total interlinkage flux Φ O It is determined by the product of

[0032] Fig. 9 shows the relationship between the rotor drive torque τ and the drive voltage v a The graph shows the vector representation of each parameter when the driving voltage is small (v a =v a1 ), (b) when the driving voltage is large (v a =v a2 >v a1 ) is shown in Fig. 10. a , drive current i a and the total flux linkage Φ O This figure shows the changes in the d-axis current i d Decrease (i d1 >i d2 ), q-axis current i q Increase (i q1 q2 ) to obtain the driving current i a The action of reducing (i a1 >i a2 ) and the total interlinkage flux Φ O Increases the effect of (Φ O1 <Φ O2 ) to maintain the rotor drive torque τ while decreasing the drive voltage v a Increase (v a1 <v a2 ​) can be obtained. It can therefore be seen that the output torque of the induction motor 14 can be controlled independently of the output torque of the synchronous motor 12. The torque control of the induction motor 14 can be achieved by this torque control based on the drive voltage and the torque control based on slip utilizing the differential action of the planetary gear mechanism 16 described above.

[0033] Figure 11 is a nomographic diagram when a synchronous motor and an induction motor with different outputs are combined. Generally, the larger the output of a synchronous motor, that is, the more permanent magnets are used, and the more expensive it becomes. Induction motors, on the other hand, are inexpensive. By combining a synchronous motor with an induction motor with a larger output than the synchronous motor, a high-output drive unit can be realized at low cost.

[0034] The drive device represented by the collinear diagram in FIG. 11 is a device equipped with a synchronous motor 62 having a maximum output of 50 kW and a maximum rotation speed of 6000 rpm, and an induction motor 64 having a maximum output of 150 kW and a maximum rotation speed of 12000 rpm. The maximum torque of the synchronous motor 62 is 100 Nm, and the maximum torque of the induction motor 64 is 300 Nm. The drive frequency at the maximum rotation speed is 200 Hz for both. The planetary gear mechanism is a compound type planetary gear mechanism equipped with two sun gears, similar to the planetary gear mechanism 16 described above. The rotation speed of the synchronous motor 62 and the sun gear connected thereto is equal, and the rotation speed of the induction motor 64 and the sun gear connected thereto is also equal. The gear ratio of the two sun gears is the reciprocal of the ratio of the maximum torque of the synchronous motor 62 and the induction motor 64, that is, 3:1. This allows the synchronous motor 62 and the induction motor 64 to operate simultaneously at maximum torque. Furthermore, by making the drive frequencies at the maximum rotation speed the same, the synchronous motor 62 and the induction motor 64 can be operated at the maximum rotation speed simultaneously.

[0035] 12 is a diagram showing the output characteristics of the synchronous motor 62 and the induction motor 64. In the diagram, curve A shows the output characteristics of the synchronous motor 62, and curve B shows the output characteristics of the induction motor 64. Also shown are an operating point C of the synchronous motor 62 and an operating point D of the induction motor 64 when the drive frequency is 100 Hz and the slip ΔN of the induction motor 64 is 5 Hz. The synchronous motor 62 operates at a rotation speed of 3000 rpm and an output torque of 50 Nm, and the induction motor 64 operates at a rotation speed of 5700 rpm and an output torque of 150 Nm. The rotation speed of the carrier 24 at this time is 5025 rpm.

[0036] The above-mentioned planetary gear mechanism 16 has been described as a compound type planetary gear mechanism having two planetary gear trains, but other types of planetary gear mechanisms can also be used. Also, a differential mechanism other than a planetary gear mechanism, that is, a mechanism in which three elements rotate relative to one another and the speed of the remaining one is determined when the speeds of two elements are fixed, can be used. For example, a differential device that distributes power to the left and right drive wheels in an automobile can be used as the differential mechanism instead of the planetary gear mechanism.

[0037] <Additional Notes> [1] A synchronous motor; An induction motor; a differential transmission mechanism having a first input element connected to the synchronous motor, a second input element connected to the induction motor, and an output element connected to drive wheels; a single inverter that supplies power to the synchronous motor and the induction motor; A drive device for an electric vehicle. [2] A drive device for an electric vehicle according to the above item [1], The differential transmission mechanism is configured such that an absolute value of a ratio of a relative speed of the synchronous motor with respect to the output element and a relative speed of the induction motor with respect to the output element is a ratio of a maximum torque of the induction motor and a maximum torque of the synchronous motor. A drive unit for an electric vehicle. [3] The drive device for an electric vehicle according to the above item [1] or [2], wherein a maximum torque of the induction motor is greater than a maximum torque of the synchronous motor. [4] The drive device for an electric vehicle according to any one of the above items [1] to [3], wherein the differential transmission mechanism includes a planetary gear mechanism, and three elements of the planetary gear mechanism that move relative to each other are the first input element, the second input element, and the output element. [5] A drive device for an electric vehicle according to any one of the above items [1] to [4], wherein a slip is generated in the induction motor by changing the rotation speed of the synchronous motor, and the induction motor outputs a torque according to the slip. [6] A drive device for an electric vehicle according to any one of the above items [1] to [4], the drive device of the electric vehicle includes a control device that controls the synchronous motor and the induction motor via the inverter, The control device drives the synchronous motor by torque control, and generates slip in the induction motor by changing the rotation speed of the synchronous motor, thereby causing the induction motor to output torque. A drive unit for an electric vehicle. [Explanation of symbols]

[0038] 10 Drive device, 12, 62 Synchronous motor, 14, 64 Induction motor, 16 Planetary gear mechanism (differential transmission mechanism), 18 Drive wheel, 20 First sun gear, 22 Second sun gear, 24 Planetary carrier, 26 Outer pinion, 28 Inner pinion, 30 First input gear pair, 32 Second input gear pair, 34 Output gear, 42 Inverter, 44 Battery, 46 Synchronous motor current sensor, 48 Synchronous motor rotation speed sensor, 50 Induction motor current sensor, 52 Induction motor rotation speed sensor, 54 Control device, N M1 Rotational speed of a synchronous motor, N M2 Rotational speed of induction motor, N C Rotational speed of the planetary carrier, T M1Output torque of a synchronous motor, T M2 Output torque of induction motor, T C Planetary carrier output torque, f INV Driving frequency, f M1 Rotational frequency of a synchronous motor, f M2 The rotational frequency of an induction motor.

Claims

1. A synchronous motor; An induction motor; a differential transmission mechanism having a first input element connected to the synchronous motor, a second input element connected to the induction motor, and an output element connected to drive wheels; a single inverter that supplies power to the synchronous motor and the induction motor; A drive device for an electric vehicle.

2. The drive device for an electric vehicle according to claim 1, The differential transmission mechanism is configured such that an absolute value of a ratio of a relative speed of the synchronous motor with respect to the output element and a relative speed of the induction motor with respect to the output element is a ratio of a maximum torque of the induction motor and a maximum torque of the synchronous motor. A drive unit for an electric vehicle.

3. 3. The drive device for an electric vehicle according to claim 2, wherein a maximum torque of the induction motor is greater than a maximum torque of the synchronous motor.

4. 4. The drive device for an electric vehicle according to claim 3, wherein the differential transmission mechanism includes a planetary gear mechanism, and three elements of the planetary gear mechanism that move relative to one another are the first input element, the second input element, and the output element.

5. 5. The drive device for an electric vehicle according to claim 1, wherein a slip is generated in the induction motor by changing the rotation speed of the synchronous motor, and the induction motor outputs a torque according to the slip.

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