Drive device for vehicle

Abstract

A rear transaxle 1 includes, in a casing 11, right and left output shafts respectively connected to right and left drive shafts 7, 8 of a vehicle and arranged on the same axis, a differential gear 4 interposed between the right output shaft and the left output shaft, a reduction gear 3 for decelerating output of the electric motor 2 and inputting the output to the differential gear 4, an inverter 10 for driving and controlling the electric motor 2, and an oil cooler 95 for cooling lubricating oil for cooling the electric motor 2 by introducing cooling water. An output shaft of the electric motor 2 is disposed coaxially with the left output shaft. The reduction gear 3 projects more rearward than the electric motor 2. The inverter 10 is disposed adjacent to a protruding portion of the reduction gear 3 so as to overlap the electric motor 2 in the axial direction, and has a cooling water supply pipe 96 extending from the outside along the casing 11 to connect to the oil cooler 95, and a cooling water discharge pipe 97 extending from the oil cooler 95 to the outside of the casing 11 along the casing 11.

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 motor is arranged coaxially on one of the left and right output shafts.

[0003] The reducer is provided with a countershaft arranged parallel to the left and right output shafts, and a pair of gears between the motor output shaft and countershaft, and between the countershaft and the differential case. With this configuration, the motor output shaft is reduced by two sets of gears via the countershaft to drive the differential case. This allows a single motor to transmit driving force while allowing differential movement between the left and right output shafts. With this drive unit, the motor is arranged coaxially with the output shaft, resulting in a compact configuration.

[0004] Furthermore, Patent Document 2 discloses a cooling structure for an electric motor in a drive unit in which an electric motor, a reduction gear, and a differential gear are built into a casing. In Patent Document 2, cooling oil is introduced into the casing from the outside to cool the electric motor and also to lubricate the reduction gear and the electric motor with the oil.

[0005] JP 2014-101959 A JP 2021-116865 A

[0006] An inverter is required to drive and control an electric motor, and drive units with an inverter installed adjacent to the electric motor have been developed. In such drive units equipped with an inverter and an electric motor, cooling is required for both the electric motor and the inverter. Furthermore, the drive unit is required to be equipped with an oil pump to circulate oil for lubrication and cooling of the reducer, etc.

[0007] The provision of cooling oil pumps and other auxiliary equipment in drive systems increases the size of the drive system, which reduces its mountability in a vehicle. Furthermore, drive systems mounted on vehicles are also required to stably cool the electric motor and other components for long periods of time.

[0008] The present invention has been made in view of the above problems, and its object is to provide a vehicle drive device that effectively and stably cools an inverter and an electric motor and is compactly configured.

[0009] In order to achieve the above object, a vehicle drive device of the present invention is a vehicle drive device including, within a casing, an electric motor, output shafts including a first output shaft and a second output shaft connected to drive shafts that drive vehicle wheels and arranged on the same axis, 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 an oil cooler that introduces cooling water to cool the electric motor and the inverter and cool oil that lubricates the speed reducer, wherein the output shaft of the electric motor is arranged coaxially with the second output shaft, and the speed reducer is The casing has a portion that protrudes more radially from the output shaft than the electric motor, the inverter is positioned adjacent to the protruding portion of the reducer so that the electric motor and the second output shaft are overlapping in the axial direction, the oil cooler is positioned in a portion of the casing that covers the reducer and has a cooling water inlet that introduces cooling water between the casing and the oil cooler to cool the inverter, and has a cooling water supply pipe that extends from the outside along the casing outside the casing, passes through the cooling water inlet and is connected to the oil cooler, and a cooling water discharge pipe that extends from the oil cooler along the casing outside the casing.

[0010] In the vehicle drive system of the present invention, the inverter is cooled by passing coolant through the coolant inlet, and the oil that cools the electric motor is cooled by introducing coolant into the oil cooler, thereby effectively and stably cooling the electric motor and the inverter. Furthermore, by arranging the coolant supply pipe and the coolant discharge pipe to extend outside the casing along the casing, the casing can be made smaller, and the vehicle drive system can be configured compactly.

[0011] Fig. 1 is a perspective view showing the exterior of a rear transaxle according to this embodiment; Fig. 2 is a perspective view showing the internal structure of a rear transaxle according to this embodiment; Fig. 3 is a cross-sectional view showing the internal structure of a rear transaxle according to this embodiment; Fig. 4 is a perspective view of the exterior of a rear transaxle unit showing the structure of a cooling water channel;

[0012] 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.

[0013] 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.

[0014] 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.

[0015] The rear transaxle 1 is equipped with 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 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.

[0016] 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.

[0017] 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.

[0018] 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 reducer 3 and also serves as the right-side lid of the casing 11.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] In addition, the rear transaxle has oil sealed within the casing 11 for lubricating the reducer 3 and differential device 4, and is structured so that, for example, when driving, the rotation of the gear (final driven gear 25) of the reducer 3 scoops up the oil within the casing 11, thereby lubricating the various gears of the reducer 3.

[0023] The rear transaxle 1 is also provided with an oil passage for circulating oil for cooling the electric motor 2, and an oil pump 85 for circulating the oil through the oil passage.

[0024] The oil pump 85 is disposed next to the right side of the second partition wall 38 and below the electric actuator 56. The electric actuator 56 and the oil pump 85 are disposed on the front side of the differential device 4 so as to be substantially overlapping in the axial direction.

[0025] 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.

[0026] 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.

[0027] The inverter 10 is housed in the second casing 32. An opening for inserting the inverter 10 during assembly is provided on the rear surface of the second casing 32. The second casing 32 also has a side cover 71 (cover member) that covers the opening.

[0028] A space 90 (cooling water inlet) for passing cooling water is formed between the side cover 71 and the inverter 10. The side cover 71 is provided with a cooling water inlet 91 that introduces a portion of the cooling water into the space 90, and a cooling water outlet 92 that discharges the cooling water from the space 90. The space 90 is sealed except for the cooling water inlet 91 and the cooling water outlet 92.

[0029] A side surface (rear surface) 10a of the inverter 10 faces a space 90 between the inverter 10 and the side cover 71. A cooling water inlet 91 is disposed at the bottom of the side cover 71, and a cooling water outlet 92 is disposed at the top of the side cover 71, with the cooling water outlet 92 disposed above the cooling water inlet 91 at a distance. Pipes and hoses (hereinafter referred to as pipes) are connected to the cooling water inlet 91 and the cooling water outlet 92. The cooling water inlet 91 extends to the left, and the cooling water outlet 92 extends to the right, i.e., toward the reducer 3 and the differential device 4.

[0030] An oil cooler 95 is provided on the right side of the casing 11 and above the differential device 4. The oil cooler 95 is provided in the oil circulation path between the oil pump 85 and the electric motor 2, and introduces cooling water to exchange heat with the oil used to cool the electric motor 2. The oil cooler 95 is provided with a cooling water inlet 95a and a cooling water outlet 95b that are aligned in the vertical direction and extend rearward. The cooling water inlet 95a of the oil cooler 95 is located above the cooling water outlet 95b.

[0031] The cooling water outlet 92 of the side cover 71 and the cooling water inlet 95a of the oil cooler 95 are connected by a cooling water supply pipe 96. The cooling water supply pipe 96 extends rightward from the cooling water outlet 92, passes behind the third casing 33, bends forward behind the oil cooler 95, passes above the oil pump 85 (to the right of the electric actuator 56 of the parking lock mechanism 51), extends forward, and is connected to the cooling water inlet 95a of the oil cooler located at the upper front of the right side of the casing 11.

[0032] A cooling water discharge pipe 97 connected to the cooling water outlet 95b of the oil cooler 95 extends from the cooling water outlet 95b substantially parallel to the cooling water supply pipe 96, bends leftward at the rear of the casing 11, extends leftward below the cooling water supply pipe 96, passes between the cooling water inlet 91 and the cooling water outlet 92 of the side cover 71, and extends to the left of the rear transaxle 1. The cooling water supply pipe 96 and the cooling water discharge pipe 97 are arranged outside the casing 11 in close proximity along the outer wall surface of the casing 11.

[0033] Cooling water for cooling the electric motor 2 and the inverter 10 is introduced from a cooling water inlet 91 of the side cover 71 into a space 90 inside the side cover 71 facing the inverter 10, thereby cooling the inverter 10. The cooling water passes from the space 90 through a cooling water supply pipe 96 and is introduced into an oil cooler 95, where it cools the oil used to cool the electric motor 2. The cooling water then passes from the oil cooler 95 through a cooling water discharge pipe 97 and returns to the cooling circuit for the cooling water.

[0034] 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. Therefore, the rear transaxle 1 including the inverter 10 can be configured in a compact rectangular box shape. 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 on a vehicle.

[0035] Furthermore, a portion of the cooling water cools the inverter 10, and the cooling water after cooling the inverter passes through an oil cooler 95 to cool the oil for cooling the electric motor 2. The oil cooler 95 is provided on the right lid of the casing 11 that covers the protruding portion of the reduction gear 3, and a cooling water supply pipe 96 and a cooling water discharge pipe 97 connected to the oil cooler 95 extend along the outside of the casing 11 rather than inside the casing 11. This allows the casing 11 to be made more compact. Furthermore, in this embodiment, the cooling water supply pipe 96 and the cooling water discharge pipe 97 can be connected between the cooling water inlet position at the left rear of the casing 11 and the oil cooler 95 in the shortest distance, allowing the entire rear transaxle 1, including the cooling water supply pipe 96 and the cooling water discharge pipe 97, to be made more compact.

[0036] In addition, a space 90 is provided between the casing 11 and the oil cooler 95, facing the inverter 10 and into which cooling water is introduced to cool the inverter 10, and the cooling water supply pipe 96 is configured to pass through the space 90, so that cooling water can be introduced into the space 90 over a short distance from the cooling water supply pipe 96 extending along the rear side of the inverter 10, and the length of the cooling water supply pipe 96 can be reduced.

[0037] The cooling water outlet 92 from the space 90 is located above the cooling water inlet 91 to the space 90, so that the cooling water cools the inverter 10 within the space 90, the temperature rises, and the cooling water moves to the upper cooling water outlet 92, allowing the cooling water to pass efficiently within the space 90.

[0038] The cooling water supply pipe 96 is connected to the upper part of the oil cooler 95, and the cooling water discharge pipe 97 is connected to the lower part of the oil cooler 95. As a result, the cooling water supply pipe 96 and the cooling water discharge pipe 97 can be arranged side by side in the vertical direction on the right side surface of the casing 11, and the cooling water supply pipe 96 and the cooling water discharge pipe 97 can be prevented from protruding outside the casing.

[0039] In addition, the casing 11 has an opening into which the inverter 10 can be inserted, and has a side cover 71 that covers the opening, and a space 90 for introducing cooling water is provided between the side cover 71 and the inverter 10, and a cooling water inlet 91 and a cooling water outlet 92 in the space 90 are provided in the side cover 71, so that the space 90 can be formed using the side cover 71 that is used when assembling the inverter 10.

[0040] 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.

[0041] REFERENCE SIGNS LIST 1 Rear transaxle (vehicle drive device) 2 Electric motor 3 Reducer 4 Differential 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) 15 Rotor shaft (motor output shaft) 70 Opening 71 Side cover (cover member) 95 Oil cooler 96 Cooling water supply pipe 97 Cooling water discharge pipe 90 Space (cooling water introduction portion) 91 Cooling water inlet 92 Cooling water outlet

Claims

1. A vehicle drive device comprising: an electric motor; output shafts including a first output shaft and a second output shaft, each connected to a drive shaft that drives a vehicle wheel and arranged on the same axis; 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 an oil cooler that introduces cooling water to cool the electric motor and the inverter and cool oil that lubricates the speed reducer, wherein the output shaft of the electric motor is arranged coaxially with the second output shaft; the speed reducer has a portion that protrudes more radially from the output shaft than the electric motor; the inverter is arranged adjacent to the protruding portion of the speed reducer so that the electric motor and the second output shaft are overlapped in the axial direction; the oil cooler is arranged in a portion of the casing that covers the speed reducer; and a cooling water inlet portion that introduces cooling water between the casing and the oil cooler to cool the inverter, a cooling water supply pipe that extends from the outside of the casing along the outside of the casing, passes through the cooling water inlet portion, and is connected to the oil cooler; and a cooling water discharge pipe that extends from the oil cooler along the outside of the casing.

2. The vehicle drive device according to claim 1, wherein the cooling water outlet from the cooling water introduction section is located above the cooling water inlet to the cooling water introduction section.

3. The vehicle drive device according to claim 2, wherein the cooling water inlet and the cooling water outlet are arranged spaced apart in the vertical direction, and the cooling water discharge pipe passes between the cooling water inlet and the cooling water outlet.

4. A vehicle drive device as described in any one of claims 2 to 3, characterized in that the casing has an opening formed therein through which the inverter can be inserted and has a cover member that covers the opening, the cooling water inlet is provided between the cover member and the inverter, and the cooling water inlet and cooling water outlet of the cooling water inlet are provided in the cover member.

5. A vehicle drive device according to any one of claims 1 to 4, characterized in that the cooling water supply pipe is connected to an upper part of the oil cooler, the cooling water supply pipe is connected to a lower part of the oil cooler, and the cooling water supply pipe and the cooling water supply pipe are arranged side by side in the vertical direction on the side of the casing.

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