Vehicle drive device

Abstract

In a rear transaxle 1, an electric motor 2 is disposed alongside a differential 4 in the axial direction of an output shaft 14. A rotor shaft 15 of the electric motor 2 is formed into a hollow shape. A right output shaft 12 extends from the differential 4 to the opposite side from the electric motor 2, and a left output shaft 13 extends from the differential 4 to the electric motor 2 side and is rotatably inserted into the interior space of the rotor shaft 15. A reduction drive 3 includes a motor drive gear part 21 integrally formed on the outer circumference of the rotor shaft 15. The left output shaft 13 is rotatably supported by a first bearing 41 at the end on the opposite side from the differential 4, while the rotor shaft 15 is rotatably supported by a second bearing 42 at the end on the opposite side from the differential 4 and is also rotatably supported by a fourth bearing 44 at the end on the differential 4 side. A resolver 70 is disposed on the differential 4 side relative to the electric motor 2.

Description

Vehicle drive unit

[0001] The present invention relates to a vehicle drive system.

[0002] Conventionally, there is known a technology relating to a vehicle drive device having a compact configuration in which an electric motor and a differential gear are arranged coaxially and an output shaft connected to one of the drive shafts from the differential gear is rotatably inserted into the internal space of a hollow motor output shaft. For example, Patent Document 1 describes a configuration in which, in a vehicle drive device having the above configuration, a rotation sensor (rotation speed detection sensor) that detects the rotation speed of the output shaft of the electric motor (motor output shaft) is arranged on the opposite side of the electric motor from the differential gear.

[0003] Japanese Patent Application Laid-Open No. 2021-42798

[0004] However, in the area opposite the differential device from the electric motor, a bearing supporting an end of the motor output shaft of the electric motor and a bearing supporting an end of the output shaft that passes through the inside of the motor output shaft and is connected to one of the drive shafts are disposed, so if the rotation speed detection sensor is provided so as not to interfere with these bearings, the axial length of the vehicle drive device may become large.

[0005] The present invention has been made in view of these problems, and its purpose is to reduce the size of a vehicle drive device in which an electric motor and a differential device are arranged coaxially and which is equipped with a rotation speed detection sensor that detects the rotation speed of the electric motor.

[0006] In order to achieve the above object, the vehicle drive device of the present invention includes an electric motor, an output shaft including a first output shaft and a second output shaft that are respectively connected to drive shafts that drive vehicle wheels and are arranged coaxially, a differential device interposed between the first output shaft and the second output shaft, a speed reducer that reduces the output of the electric motor and inputs it to the differential device, a rotation speed detection sensor that detects the rotation speed of the electric motor, and a casing that accommodates the electric motor, the differential device, the speed reducer, and the rotation speed detection sensor, wherein the electric motor is arranged alongside the differential device along the axial direction of the output shaft, and the motor output shaft of the electric motor is The motor output shaft is formed hollow, the first output shaft extends from the differential device to the opposite side of the electric motor, the second output shaft extends from the differential device to the electric motor side and is rotatably inserted into the internal space of the motor output shaft, the reducer includes an input gear portion formed on the outer periphery of the motor output shaft, the second output shaft is supported by a first bearing at the end opposite the differential device, the motor output shaft is supported by a second bearing at the end opposite the differential device and is supported by a third bearing at the end on the differential device side, and the rotation speed detection sensor is arranged on the differential device side with respect to the electric motor.

[0007] According to the vehicle drive device of the present invention, the electric motor and the differential device are arranged coaxially, and the vehicle drive device equipped with a rotation speed detection sensor that detects the rotation speed of the electric motor can be made smaller.

[0008] 5 is a perspective view showing the outer shape of the rear transaxle according to the present embodiment; FIG. 6 is a perspective view showing the internal structure of the rear transaxle according to the present embodiment; FIG. 7 is a cross-sectional view showing the internal structure of the rear transaxle according to the present embodiment; FIG. 8 is a cross-sectional view showing the vicinity of the electric motor of the rear transaxle; FIG. 9 is an enlarged cross-sectional view showing the vicinity of the second bearing; and FIG. 10 is a cross-sectional view of the casing, second snap ring, second bearing, rotor shaft, and left output shaft taken along line A-A in FIG.

[0009] An embodiment of a vehicle drive system embodying the present invention will now be described. FIG. 1 is a perspective view showing the exterior of a rear transaxle 1, which is a vehicle drive system according to one embodiment of the present invention. FIG. 2 is a perspective view showing the internal structure of the rear transaxle 1. FIG. 3 is a cross-sectional view showing the internal structure of the rear transaxle 1. Note that the rear transaxle 1 will be described below with reference to the vehicle direction when mounted on a vehicle.

[0010] 1 and 2, rear transaxle 1 is disposed between the left and right rear wheels of a vehicle and includes an electric motor 2, a reduction gear 3, and a differential 4. A right drive shaft 7 (drive shaft) that drives the right wheel of the vehicle and a left drive shaft 8 (drive shaft) that drives the left wheel of the vehicle are connected to rear transaxle 1. Rear transaxle 1 transmits driving force from electric motor 2 to the right and left rear wheels via right and left drive shafts 7 and 8, while allowing differential rotation between the right and left rear wheels.

[0011] The rear transaxle 1 is also equipped with an inverter 10 that controls the drive of the electric motor 2. The inverter 10 is disposed adjacent to the electric motor 2. The rear transaxle 1 is configured in the shape of a rectangular box, integrating the electric motor 2, the reduction gear 3, the differential device 4, and the inverter 10. As shown in FIG. 3 , the rear transaxle 1 is configured with the electric motor 2, the reduction gear 3, the differential device 4, and the inverter 10 housed within a casing 11.

[0012] The rear transaxle 1 includes an output shaft 14 that includes a right output shaft 12 (first output shaft) extending rightward from the differential 4 and a left output shaft 13 (second output shaft) extending leftward from the differential. One end (left end) of the right output shaft 12 is connected to the differential 4, and the other end (right end) is connected to the right drive shaft 7. One end (right end) of the left output shaft 13 is connected to the differential 4, and the other end (left end) is connected to the left drive shaft 8. The right output shaft 12 and the left output shaft 13 are arranged coaxially side by side. The rear transaxle 1 also includes a countershaft 20 that is parallel to and spaced apart from the left output shaft 13 in the radial direction (hereinafter simply referred to as the "radial direction"). That is, as shown in FIG. 2 , the countershaft 20 is arranged parallel to and spaced apart from the output shaft 14 and the rotor shaft 15 in the vehicle front-rear and up-down directions. The countershaft 20 extends in the left-right direction so as to overlap the right end of the left output shaft 13 and the differential device 4 in the axial direction.

[0013] The electric motor 2 includes a rotor 2r as a rotor and a stator 2s as a stator, and is arranged side by side on the left side of the differential device 4 along the axial direction of the differential device 4 and the output shaft 14 (hereinafter simply referred to as the "axial direction"). The rotor shaft 15 (motor output shaft), which is the output shaft of the electric motor 2, is formed hollow, and the left output shaft 13 is inserted therein so that they can rotate relative to each other. A motor drive gear portion 21 (input gear portion), which is, for example, a helical gear, is formed on the right end of the rotor shaft 15.

[0014] A counter driven gear unit 22 that meshes with the motor drive gear unit 21 is fixed to the left end of the counter shaft 20. In this embodiment, a parking gear 27 that is included in the vehicle's parking lock mechanism is integrally provided with the counter driven gear unit 22. A counter drive gear unit 23, which is, for example, a helical gear or a spur gear, is formed at the right end of the counter shaft 20. The counter drive gear unit 23 is configured to mesh with a final driven gear unit 25 that is fixed to a differential case 24, which is a power input portion of the differential device 4. The counter shaft 20, the motor drive gear unit 21, the counter driven gear unit 22, the counter drive gear unit 23, and the final driven gear unit 25 form the reducer 3. The output of the electric motor 2 is transmitted from the rotor shaft 15 to the motor drive gear section 21, the counter driven gear section 22, the counter shaft 20, the counter drive gear section 23, and the final driven gear section 25 in that order, and is input to the reducer 3, and is then output to the right output shaft 12 and the left output shaft 13 via the differential device 4.

[0015] The casing 11 of the rear transaxle 1 has a four-part structure, consisting of, lined up in the axial direction from the left side, a first casing 31, a second casing 32, a third casing 33, and a fourth casing 34. The first casing 31 is shaped like a lid that covers the left side of the electric motor 2, the second casing 32 houses the electric motor 2, the motor drive gear unit 21, and the counter driven gear unit 22, the third casing 33 houses the counter drive gear unit 23 and the final driven gear unit 25, and the fourth casing 34 houses the reducer 3 and also serves as the right side wall of the casing 11.

[0016] The second casing 32 is provided with a first partition wall 37 that partitions the internal space of the casing 11 between the electric motor 2 and the motor drive gear unit 21 and between the inverter 10 and the counter driven gear unit 22. The third casing 33 is provided with a second partition wall 38 (center plate) that partitions the internal space of the casing 11 between the motor drive gear unit 21 and the counter driven gear unit 22 and between the counter drive gear unit 23 and the final driven gear unit 25. The second partition wall 38 is provided with a through hole through which the left output shaft 13 passes.

[0017] A first bearing 41 (first bearing) that rotatably supports the left end portion of the left output shaft 13 and a second bearing 42 (second bearing) that rotatably supports the left end portion of the rotor shaft 15 are fixed to the first casing 31. The first bearing 41 and the second bearing 42 are arranged adjacent to each other in the axial direction. A third bearing 43 that rotatably supports the left end portion of the countershaft 20 is fixed to the first partition wall 37 of the second casing 32. A fourth bearing 44 (third bearing) that rotatably supports the right end portion of the rotor shaft 15 and a fifth bearing 45 that rotatably supports the left end portion of the differential case 24 are fixed to the second partition wall 38 of the third casing 33. The fourth bearing 44 is arranged on the left side of the second partition wall 38. The fifth bearing 45 is arranged on the right side of the second partition wall 38. A sixth bearing 46 that rotatably supports the right end of the countershaft 20 and a seventh bearing 47 that rotatably supports the right end of the differential case 24 are fixed to the fourth casing 34.

[0018] Next, a configuration for achieving a compact rear transaxle 1 according to this embodiment will be described. Fig. 4 is a cross-sectional view showing the vicinity of the electric motor 2 of the rear transaxle 1, Fig. 5 is an enlarged cross-sectional view showing the vicinity of the second bearing 42, and Fig. 6 is a cross-sectional view of the casing 11, second snap ring 62, second bearing 42, rotor shaft 15, and left output shaft 13 taken along line A-A in Fig. 5. Note that the stator 2s of the electric motor 2 is not shown in Fig. 5.

[0019] As shown in FIG. 4 , the inner circumferential surface of the second bearing 42, which supports the left end of the rotor shaft 15, is fitted into a step formed on the left end of the rotor shaft 15, and its lower end abuts against a first snap ring 61 attached to the rotor shaft 15. This positions the second bearing 42 in the axial direction relative to the rotor shaft 15. Meanwhile, a cylindrical support portion 50 is formed on the casing 11 (first casing 31), and the outer circumferential edge of the second bearing 42 is fitted into this support portion 50. A groove 52 into which a second snap ring 62 (snap ring) is fitted is formed on the inner circumferential surface of the support portion 50. The second snap ring 62 is fitted into the groove formed on the outer circumferential edge of the second bearing 42, thereby positioning the second bearing 42 in the axial direction relative to the casing 11. This eliminates the need for a fixing member 80 to determine the axial position of the second bearing 42 relative to the casing 11, as shown by the two-dot chain line in FIG. 5 , for example. Therefore, the number of parts can be reduced, and there is no need to shift the electric motor 2 to the right in the drawing by the amount of the fixing member 80, so the axial length of the rear transaxle 1 can be shortened.

[0020] Furthermore, by positioning the second bearing 42 in the axial direction, the second bearing 42 can withstand the axial thrust force acting on the rotor shaft 15. In other words, the right end of the rotor shaft 15 on the differential device 4 side does not need to withstand the thrust force. Therefore, the second bearing 42 is configured as a ball bearing capable of withstanding the thrust force, while the fourth bearing 44 ( FIG. 4 ), which supports the right end of the rotor shaft 15 on the differential device 4 side, is configured as a roller bearing. As a result, the diameter of the fourth bearing 44 can be made smaller than in the case where a ball bearing is used, thereby enabling the radial length of the rear transaxle 1 to be shortened. Note that in this embodiment, the parking gear 27 is integrally formed with the motor drive gear unit 21, utilizing the space created by the smaller diameter of the fourth bearing 44.

[0021] Next, the assembly process of the second bearing 42 into the casing 11 will be described. First, the worker attaches the second snap ring 62 to the groove 52 of the first casing 31. Here, a cutout 54 is formed in the support portion 50 to provide space for the second snap ring 62 assembly. The cutout 54 is formed by cutting out a portion of the axially right side of the support portion 50 along the circumferential direction, including at least a portion that communicates with the groove 52. As shown in FIG. 6 , the second snap ring 62 is positioned so that the claws 62 a are exposed in the cutout 54. Then, the worker inserts the rotor shaft 15, to which the second bearing 42 is attached, into the support portion 50 from the axially right side. Note that in this assembly process, the rotor 2r, rotor shaft 15, and second bearing 42 of the electric motor 2 are assembled into the first casing 31, and assembly of the stator 2s is a separate process. Therefore, as shown in FIG. 5 , the stator 2s is not present here. Therefore, the worker inserts a tool (not shown) into the cutout 54 from above in FIG. 5 and spreads the claws 62a of the second snap ring 62 in the circumferential direction so as to avoid interference between the second snap ring 62 and the outer circumferential edge of the second bearing 42 (see the arrows in FIG. 6 ). Therefore, the groove 52 is formed with a margin for deforming the second snap ring 62 to an extent that enables the above-mentioned interference to be avoided. Then, when the groove of the second bearing 42 and the second snap ring 62 are aligned in the axial direction, the second snap ring 62 fits into the groove, and the worker removes the tool from the claws 62a. This completes the assembly of the second bearing 42 to both the casing 11 and the rotor shaft 15.

[0022] Returning to the explanation of Figure 4, in this embodiment, the motor drive gear unit 21, which is one of the components of the reducer 3, is formed integrally with the outer periphery of the rotor shaft 15. Therefore, compared to when the motor drive gear unit 21 is a gear separate from the rotor shaft 15, a bearing for rotatably supporting the separate gear in the casing 11 is not required, and the number of parts can be reduced. In addition, there is no need to perform spline processing on the rotor shaft 15 to mate with the separate gear, making manufacturing easier.

[0023] The motor drive gear portion 21 and the counter driven gear portion 22 that meshes with the motor drive gear portion 21 are formed by helical gears. As a result, when the electric motor 2 is driving or regenerating, an axial thrust force is generated between the motor drive gear portion 21 and the counter driven gear portion 22. Therefore, when the vehicle is driving or braking, a thrust force acts on the rotor shaft 15 in either the axial direction as a preload force, thereby suppressing vibration of the rotor shaft 15. This eliminates the need to provide a spring member for applying a thrust force as a preload force to the rotor shaft 15, thereby reducing the number of parts and enabling the axial length of the rear transaxle 1 to be shortened.

[0024] As shown in Figure 4, the rear transaxle 1 is also equipped with a resolver 70 (rotation speed detection sensor) for detecting the rotation speed of the electric motor 2. The resolver 70 has a connector and a connection cable (not shown) that extend to the outside of the rear transaxle 1 and are connected to a control device (not shown) that controls the electric motor 2 mounted on the vehicle. The resolver 70 detects the rotation angle and rotation speed of the electric motor 2 and outputs the detected rotation angle and rotation speed to the control device. The resolver 70 may also be another rotation speed detection sensor, such as a rotary encoder.

[0025] Here, the first bearing 41 and the second bearing 42 that support the left output shaft 13 are disposed in a region of the electric motor 2 opposite the differential device 4. Meanwhile, since the right end of the left output shaft 13 is connected to the differential device 4, the left end of the left output shaft 13 is supported only by the first bearing at the opposite side of the differential device 4. Furthermore, as described above, a bearing that supports the motor drive gear unit 21 is not required in the configuration of this embodiment. Therefore, the only bearing disposed in the region of the electric motor 2 on the differential device 4 side is the fourth bearing 44 that supports the right end of the rotor shaft 15. In this way, it is easier to secure space near the electric motor 2 in the region of the electric motor 2 on the differential device 4 side than in the region opposite the differential device 4. Therefore, the resolver 70 is disposed in the region on the differential device 4 side of the electric motor 2. More specifically, the resolver 70 is attached to a first partition wall 37 that is provided in the casing 11 so as to surround the outer periphery of the rotor shaft 15. The first partition wall 37 is provided to cover the stator 2s of the electric motor 2 from the axial right side, and has an opening 37b at its tip end 37a for inserting the rotor shaft 15 and the left output shaft 13. A resolver 70 is attached to the surface of the tip end 37a facing the electric motor 2.

[0026] As described above, in the rear transaxle 1 (vehicle drive system) of this embodiment, the electric motor 2 and the differential device 4 are arranged side by side along the axial direction of the output shaft 14. The rotor shaft 15 (motor output shaft) of the electric motor 2 is hollow, and the right output shaft 12 (first output shaft) extends from the differential device 4 toward the opposite side to the electric motor 2, while the left output shaft 13 (second output shaft) extends from the differential device 4 toward the electric motor 2 and is rotatably inserted into the internal space of the rotor shaft 15. The speed reducer 3 includes a motor drive gear portion 21 (input gear portion) formed integrally with the outer periphery of the rotor shaft 15. The left output shaft 13 is rotatably supported by a first bearing 41 at an end opposite to the differential device 4, and the rotor shaft 15 is rotatably supported by a second bearing 42 at an end opposite to the differential device 4 and by a fourth bearing 44 at an end on the differential device 4 side. The resolver 70 (rotation speed detection sensor) is disposed on the differential device 4 side with respect to the electric motor 2 .

[0027] With this configuration, the resolver 70 can be disposed in an area of ​​the electric motor 2 on the differential device 4 side, where space is easier to secure compared to an area on the opposite side of the electric motor 2 from the differential device 4. As a result, there is no need to dispose the resolver 70 so as to avoid the first bearing 41 and the second bearing 42, and the axial length of the rear transaxle 1 can be shortened. Therefore, with the rear transaxle 1 of this embodiment, the electric motor 2 and the differential device 4 are disposed coaxially, and it is possible to reduce the size of a vehicle drive device that includes the resolver 70 that detects the rotation speed of the electric motor 2.

[0028] The casing 11 also includes a first partition wall 37 that defines an internal space surrounding the electric motor 2, and the resolver 70 is attached to the surface of the first partition wall 37 facing the electric motor 2. With this configuration, the resolver 70 can be easily positioned near the electric motor 2 by utilizing the first partition wall 37 that is provided close to the electric motor 2.

[0029] The speed reducer 3 also includes a counter driven gear portion 22 that meshes with the motor drive gear portion 21, and the motor drive gear portion 21 and the counter driven gear portion 22 are helical gears. This configuration eliminates the need for a spring member to apply a thrust force as an axial preload to the rotor shaft 15, thereby enabling the axial length of the rear transaxle 1 to be shortened.

[0030] The rear transaxle 1 further includes a second snap ring 62 that positions the second bearing 42 in the axial direction relative to the casing 11. With this configuration, the fourth bearing 44 can be positioned relative to the casing 11 using only the second snap ring 62, eliminating the need for a separate fixing member 80, thereby enabling the axial length of the rear transaxle 1 to be shortened.

[0031] In addition, the casing 11 has a cylindrical support portion 50 that supports the outer peripheral edge of the fourth bearing 44, and the support portion 50 has a groove 52 in which the second snap ring 62 is attached, and a notch portion 54 in which a portion of the circumferential direction is cut out at a position that communicates with the groove 52, and the second snap ring 62 is attached to the groove 52 so that the claw portion 62a for performing the attachment work is exposed in the notch portion 54. With this configuration, the second snap ring 62, the second bearing 42, and the casing 11 can be easily assembled using the notch portion 54.

[0032] Although the description of the embodiment has been completed, the aspects of the present invention are not limited to this embodiment. For example, although the present invention is applied to a rear transaxle in this embodiment, it can also be applied to a front transaxle.

[0033] REFERENCE SIGNS LIST 1 Rear transaxle 2 Electric motor 3 Reducer 4 Differential device 7 Right drive shaft (drive shaft) 8 Left drive shaft (drive shaft) 10 Inverter 11 Casing 12 Right output shaft (first output shaft) 13 Left output shaft (second output shaft) 14 Output shaft 15 Rotor shaft (motor output shaft) 20 Countershaft (intermediate shaft) 21 Motor drive gear section (input gear section) 22 Counter driven gear section 23 Counter drive gear section 24 Differential case 25 Final driven gear section 31 First casing 32 Second casing 33 Third casing 34 Fourth casing 37 First partition wall (partition wall) 37a Tip portion 37b Opening 38 Second partition wall 41 First bearing (first bearing) 42 Second bearing (second bearing) 43 Third bearing 44 Fourth bearing (third bearing) 45 Fifth bearing 46 Sixth bearing 47 Seventh bearing 50 Support portion 52 Groove 61 First snap ring 62 Second snap ring (snap ring) 62a Claw portion 70 Resolver

Claims

1. An electric motor; an output shaft including a first output shaft and a second output shaft, each connected to a drive shaft that drives a vehicle wheel and arranged coaxially; a differential gear interposed between the first output shaft and the second output shaft; a speed reducer that reduces the output of the electric motor and inputs it to the differential gear; a rotation speed detection sensor that detects the rotation speed of the electric motor; and a casing that houses the electric motor, the differential gear, the speed reducer, and the rotation speed detection sensor; wherein the electric motor is arranged side by side along the axial direction of the differential gear and the output shaft; the motor output shaft of the electric motor is formed hollow; the first output shaft extends from the differential gear to the opposite side to the electric motor; the second output shaft extends from the differential gear to the electric motor side and is rotatably inserted in the internal space of the motor output shaft; the speed reducer includes an input gear portion formed on the outer periphery of the motor output shaft; and the second output shaft is supported by a first bearing at the end opposite to the differential gear. the motor output shaft is supported by a second bearing at an end opposite to the differential device and by a third bearing at an end on the differential device side, and the rotation speed detection sensor is disposed on the differential device side with respect to the electric motor.

2. A vehicle drive device according to claim 1, wherein the casing includes a partition wall that defines an internal space surrounding the electric motor, and the rotation speed detection sensor is attached to a surface of the partition wall facing the electric motor.

3. The vehicle drive device according to claim 1, wherein the reducer includes a counter driven gear portion that meshes with the input gear portion, and the input gear portion and the counter driven gear portion are helical gears.

4. The vehicle drive device according to any one of claims 1 to 3, further comprising a snap ring for positioning the second bearing in the axial direction relative to the casing.

5. A vehicle drive device as set forth in claim 4, wherein the casing has a cylindrical support portion that supports the outer peripheral edge of the second bearing, the support portion having a groove in which the snap ring is attached and a notch portion that is cut out in a circumferential direction at a position that communicates with the groove, and the snap ring is attached to the groove so that a claw portion for performing the attachment work is exposed in the notch portion.

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