Vehicle drive device

Abstract

A rear transaxle 1 comprises: an electric motor 2; a right output shaft and a left output shaft which are respectively connected to right and left drive shafts 7, 8 of a vehicle and are coaxially disposed; a differential device 2 interposed between the right output shaft and the left output shaft; a speed reducer 3 which decelerates the output of the electric motor 2 and inputs the decelerated output to the differential device; an inverter 10 which drives and controls the electric motor 2; and a casing 11 which houses the inverter 10, the differential device 2, and the speed reducer 3. The output shaft of the electric motor 2 is formed in a hollow shape, and the left output shaft is rotatably disposed in the internal space of said output shaft. The electric motor 2 is arranged with the differential device 4 in the axial direction of a second output shaft with the speed reducer 3 interposed therebetween. The speed reducer 3 projects more rearward than the electric motor 2 in the radial direction of the second output shaft. The inverter 10 is disposed so as to be adjacent to the projection of the speed reducer 3 and overlapped with the electric motor 2 in the axial direction.

Description

Vehicle drive unit

[0001] The present invention relates to a drive unit for driving a vehicle equipped with a differential gear.

[0002] As a drive unit for driving the left and right wheels of a vehicle, a drive source such as a motor, a reduction gear, and a differential gear have been developed as a unit. For example, in the drive unit described in Patent Document 1, an electric motor is built into the rear transaxle of a vehicle that has a differential gear. The electric motor is disposed adjacent to the differential gear on one side of the left drive shaft, and the output shaft of the electric motor and the left drive shaft are disposed coaxially.

[0003] The rear transaxle is equipped with a countershaft (intermediate shaft) parallel to the driveshaft, and a pair of gears is provided between the motor output shaft and the countershaft, and between the countershaft and the differential case (differential case). The differential case is driven by a reduction in speed from the electric motor output shaft via the countershaft through two sets of gears. This structure allows for a single electric motor to transmit driving force while allowing differential movement between the left and right driveshafts. This drive system has a compact configuration because the electric motor is located adjacent to the differential and coaxially with the driveshaft.

[0004] JP 2014-101959 A

[0005] An inverter is required to drive and control an electric motor that drives a vehicle. The inverter is often located adjacent to, for example, the top of the electric motor. However, for high-output motors such as drive motors, the inverter tends to be large. If a large inverter is located above the electric motor, the drive unit including the inverter becomes large, particularly in vertical height, which impairs mountability on the vehicle. The present invention was made in light of these problems, and its purpose is to provide a drive unit including a compact electric motor and inverter.

[0006] In order to achieve the above object, the vehicle drive device of the present invention is a vehicle drive device comprising: 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 the wheels of the vehicle and arranged on the same axis; a differential device interposed between the first output shaft and the second output shaft; a reducer that reduces the output of the electric motor and inputs it to the differential device; an inverter that drives and controls the electric motor; and a casing that incorporates at least the inverter, wherein the motor output shaft, which is the output shaft of the electric motor, is formed hollow and the second output shaft is arranged inside so as to be rotatable relative to the motor output shaft; the motor is arranged side by side with the differential device and the output shaft in the axial direction, with the reducer between them; the reducer has a portion that protrudes radially beyond the motor in the output shaft direction; and the inverter is arranged adjacent to the protruding portion of the reducer and is arranged so that the axial positions of the motor and the output shaft overlap.

[0007] In the vehicle drive device of the present invention, the inverter is positioned adjacent to the protruding portion of the reducer so that the axial positions of the electric motor and the second output shaft overlap, so that the vehicle drive device can be configured compactly together with the inverter.

[0008] Fig. 1 is a perspective view showing the outer shape of the rear transaxle according to the present embodiment; Fig. 2 is a perspective view showing the internal structure of the rear transaxle according to the present embodiment; Fig. 3 is a cross-sectional view showing the internal structure of the rear transaxle according to the present embodiment; Fig. 4 is an explanatory diagram showing a method of installing an inverter; Fig. 5 is a rear view of the rear transaxle with the side cover open.

[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 wheels of the vehicle and a left drive shaft 8 (drive shaft) that drives the left wheels 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, respectively, while allowing differential rotation between the right and left rear wheels.

[0011] The rear transaxle 1 is also provided 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, with the electric motor 2, the reduction gear 3, the differential device 4, and the inverter 10 all assembled together.

[0012] The rear transaxle 1 includes output shafts including 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. The right output shaft 12 is formed integrally with the right drive shaft 7, and one end (left end) is connected to the differential 4. The left output shaft 13 has one end (right end) connected to the differential 4 and the other end (left end) 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 (intermediate shaft) parallel to the left output shaft 13 and spaced apart in the radial direction (hereinafter simply referred to as the "radial direction"). The countershaft 20 extends left-right so that its axial position overlaps with the right end of the left output shaft 13 and the differential 4.

[0013] The electric motor 2 is arranged on the left side of the differential device 4, aligned along the axial direction of the differential device 4 and the left output shaft 13 (hereinafter simply referred to as the "axial direction"). A 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 inside so that they can rotate relative to each other. A motor drive gear portion 21 (first gear group), which is a helical gear, is formed on the right end of the rotor shaft 15.

[0014] A counter driven gear 22 (first gear group), which is a helical gear that meshes with the motor drive gear unit 21, is fixed to the left end of the counter shaft 20. A final drive gear unit 23 (second gear group), which is, for example, a helical gear, is formed at the right end of the counter shaft 20. The final drive gear unit 23 is configured to mesh with a final driven gear 25 (second gear group) that is fixed to a differential case 24, which is a power input portion of the differential device 4. The counter shaft 20, motor drive gear unit 21, counter driven gear 22, final drive gear unit 23, and final driven gear 25 form the reducer 3. The output of the electric motor 2 is transmitted from the rotor shaft 15 through the motor drive gear unit 21, counter driven gear 22, counter shaft 20, final drive gear unit 23, and final driven gear 25 in this order, and is input to the differential device 4 and output to the right output shaft 12 and the left output shaft 13.

[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 22, the third casing 33 houses the final drive gear unit 23 and the final driven gear 25, and the fourth casing 34 houses the differential device 4 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 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 22 and between the final drive gear unit 23 and the final driven gear 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 that rotatably supports the left end portion of the left output shaft 13 and a second bearing 42 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 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 portion of the countershaft 20 and a seventh bearing 47 that rotatably supports the right end portion of the differential case 24 are fixed to the fourth casing 34.

[0018] The rear transaxle 1 is also provided with a parking lock mechanism 51. The parking lock mechanism 51 has a parking gear 52 that is formed integrally with the counter driven gear 22, and sprags 53 that restrict rotation of the parking gear 52 by engaging with the parking gear 52, and by operating the sprags 53 with an electric actuator 56, the parking lock mechanism 51 switches between a locked state that restricts rotation and an unlocked state that does not restrict rotation.

[0019] In this embodiment, the countershaft 20 is provided at a position radially rearwardly spaced apart from the right output shaft 12 and the left output shaft 13, and the countershaft 20 is provided with a counter driven gear 22 and a final drive gear section 23, so that the second casing 32, the third casing 33, and the fourth casing 34, which are parts of the casing 11 that cover these gears, protrude radially (rearwardly) toward the countershaft 20.

[0020] The electric motor 2, which is provided around the left output shaft 13, does not protrude radially beyond the countershaft 20. The inverter 10 is disposed behind the electric motor 2 and forward of the rear ends of the second casing 32 and the third casing 33 that cover the reduction gear 3. In other words, the inverter 10 is disposed in a recess in the electric motor 2 and the reduction gear 3, which are arranged in an L-shape when viewed from above, and the entire rear transaxle 1 including the inverter 10 is configured to be rectangular when viewed from above.

[0021] FIG. 4 is an explanatory diagram showing a method for installing the inverter 10. FIG. 5 is a rear view of the rear transaxle 1 with the side cover 71 (first cover member) open. As shown in FIGS. 1, 3, 4, and 5, the inverter 10 is housed in the casing 11, more specifically, the second casing 32. The rear surface of the second casing 32 is provided with an opening 70 (first opening) for inserting the inverter 10 during assembly of the rear transaxle 1. The second casing 32 is also provided with a side cover 71 (first cover member) that covers the opening 70.

[0022] When assembling the inverter 10 into the second casing 32, first, the inverter 10 is fixed to the side cover 71 with bolts or the like, then the inverter 10 fixed to the side cover 71 is inserted into the second casing 32 through the opening 70, and the side cover 71 is fixed to the second casing 32 with bolts 72a to 72d.

[0023] A terminal block 75 for connecting a power cable is provided on the top of the inverter 10. A window 76 (second opening) is provided on the top surface of the second casing 32 to expose the terminal block 75 of the inverter 10. The window 76 is covered by a top cover 78 (second cover member) that is fixed at its four corners to the second casing 32 by, for example, four bolts 77a, 77b, 77c, and 77d. The left-right length of the top cover 78 is greater than the left-right length of the inverter 10.

[0024] Female threads to which bolts 77a to 77d are fastened are formed on the top surface of second casing 32. Of the four bolts 77a to 77d, the female threads to which left-side bolts 77a and 77b are fastened are formed on a flange-shaped boss 79 provided on the left side wall 32a of second casing 32. The female threads to which right-side bolts 77c and 77d are fastened are formed on bosses 80 provided on second casing 32.

[0025] The boss portion 80 protrudes downward from the upper wall of the second casing 32, but is provided in a position that avoids the upper part of the inverter 10 to the right. The boss portion 79 is located above and to the left of the inverter 10. The lower ends of the boss portions 79 and 80 are located below the upper surface of the inverter 10.

[0026] As described above, the rear transaxle 1 of this embodiment is configured with the inverter 10, electric motor 2, reduction gear 3, and differential 4 housed within the casing 11. The reduction gear 3 protrudes rearward from the right side of the electric motor 2, so that the electric motor 2 and reduction gear 3 are arranged in an L-shape when viewed from above, with the inverter 10 located in the recess. In other words, the electric motor 2 is arranged side by side with the differential 4 and the left output shaft 13 in the axial direction, with the reduction gear 3 sandwiched between them. The reduction gear 3 has a portion that protrudes radially beyond the electric motor 2 in the radial direction of the left output shaft 13, and the inverter 10 is located adjacent to the protruding portion of the reduction gear 3, with the electric motor 2 and the left output shaft 13 overlapping in the axial direction. Therefore, the rear transaxle 1 including the inverter 10 can be configured in a compact rectangular box shape. In particular, by locating the inverter 10 behind the electric motor 2, the overall vertical length of the rear transaxle 1 can be reduced compared to locating the inverter 10 above the electric motor 2, improving mountability in a vehicle. Furthermore, it becomes possible to install a large inverter 10 in a vertical orientation within the casing 11, with a large vertical size.

[0027] Furthermore, the inverter 10 is secured to a side cover member 71 provided on the second casing 32, and then the side cover member 71 is attached to the second casing 32 from the rear, improving the ease of assembly and maintenance of the inverter 10. The second casing 32 is provided with a window 76 above a terminal block 75 above the inverter 10, and a top cover 78 that covers the window 76. The top cover 78 covers the window 76 used when the terminal block 75 connects a power cable, and the window 76 and the top cover 78 only need to be large enough to expose at least the terminal block 75. However, if bosses 79, 80 are provided on the top of the inverter 10, for example, the top cover 78 must be positioned above the bosses 79, 80.

[0028] In contrast, in this embodiment, the top cover 78 is longer in left-right direction than the inverter 10, and the boss portions 79, 80 for the bolts that secure the top cover 78 are positioned so as to avoid the top of the inverter 10 in the left-right direction, i.e., outside the inverter 10 when viewed from above.

[0029] This allows the upper surface of the inverter 10 and the upper cover 78 to be positioned close to each other in the vertical direction, thereby reducing the vertical protrusion of the second casing 32 near the storage section for the inverter 10. This reduces the vertical size of the casing 11 and the entire rear transaxle 1.

[0030] The present invention is not limited to the above embodiment, and can be modified within the scope of the invention. In this embodiment, the present invention is applied to a rear transaxle 1, but it can also be applied to a front transaxle that drives the front wheels of a vehicle.

[0031] DESCRIPTION OF SYMBOLS 1 Rear transaxle (vehicle drive device) 2 Electric motor (motor) 3 Reducer 4 Differential device 7 Right drive shaft (drive shaft) 8 Left drive shaft (drive shaft) 11 Casing 12 Right output shaft (first output shaft) 13 Left output shaft (second output shaft) 15 Rotor shaft (motor output shaft) 20 Countershaft (intermediate shaft) 21 Motor drive gear section (first gear group) 22 Counter driven gear (first gear group) 23 Final drive gear section (second gear group) 25 Final driven gear (second gear group) 70 Opening (first opening) 71 Side cover (first cover member) 75 Terminal block 76 Window section (second opening) 78 Top cover (second cover member) 79, 80 Boss section

Claims

1. A vehicle drive system comprising: an electric motor; an output shaft including a first output shaft and a second output shaft arranged on the same axis and each connected to a drive shaft that drives the vehicle wheels; 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; an inverter that drives and controls the electric motor; and a casing that houses at least the inverter, wherein the motor output shaft, which is the output shaft of the electric motor, is formed hollow and the second output shaft is arranged inside it so as to be rotatable relative to the motor output shaft; the motor is arranged side by side with the differential device and the output shaft in the axial direction, with the speed reducer between them; the speed reducer has a portion that protrudes radially beyond the motor in the output shaft direction; and the inverter is arranged adjacent to the protruding portion of the speed reducer so that the axial positions of the motor and the output shaft overlap.

2. The vehicle drive device described in claim 1, characterized in that the reducer comprises an intermediate shaft arranged parallel to and radially spaced from the output shaft, a pair of first gear groups provided on the motor output shaft and the intermediate shaft, and a pair of second gear groups provided between the intermediate shaft and the differential device, and the inverter is arranged overlapping with the intermediate shaft when viewed in the axial direction of the output shaft.

3. A vehicle drive device according to claim 1 or 2, characterized in that the casing has a first opening into which the inverter can be inserted and a first cover member that covers the first opening, and the inverter is fixed to the first cover member.

4. A vehicle drive device as described in any one of claims 1 to 3, characterized in that a terminal block for connecting an electric cable to the inverter is provided on one side of the inverter, the casing is formed with a second opening for exposing the terminal block at a position adjacent to the one side of the inverter, and a second cover member is provided which is fixed by a bolt to a boss portion provided on the casing and covers the second opening, and the boss portion is positioned outside the inverter when viewed from the one side.

5. The vehicle drive device according to claim 4, wherein the one side surface is a surface facing upward toward the vehicle.

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