Power transmission unit for electric vehicles

Abstract

To provide a power transmission unit for an electric vehicle for driving left and right wheels with one electric motor which enables a case for housing an axle and a gear mechanism to be molded by casting and achieves downsizing.SOLUTION: A power transmission unit 41 includes: a motor case 50 that is provided on the same side as a second axle 19 with respect to a center between a first axle 18 and the second axle 19, separated to right and left, in a right-left direction and that houses an electric motor 70; a first axle case 43 housing a reduction gear mechanism 78, a differential gear mechanism 118, and the first axle 18; and a second axle case 130 that is fixed to the first axle case 43 in a separable manner and houses the second axle 19.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a power transmission unit for an electric vehicle. [Background technology]

[0002] It has been known for some time that vehicles such as lawnmowers equipped with lawnmowers have wheels driven by electric motors to enable the vehicle to travel. Patent Document 1 describes a lawnmower as an electric vehicle in which one electric motor drives both left and right wheels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-154375 Summary of the Invention [Problem to be solved by the invention]

[0004] As in the configuration described in Patent Document 1, an electric vehicle in which one electric motor drives both left and right wheels uses a power transmission unit that transmits the power of the electric motor to the wheels. In this power transmission unit, an axle case portion that supports the left and right axles is integrally provided with a gear cover portion that constitutes a gear case that houses a gear mechanism for power transmission.

[0005] On the other hand, in order to reduce the size of the power transmission unit, it is possible to place the electric motor close to one of the axles. However, when forming the unit case by casting, such as die casting, it is difficult to configure a mold that can form the fixing surface of the motor case while ensuring the strength of the connection between the axle case and the gear cover. For this reason, it is difficult to achieve miniaturization when forming the case by casting.

[0006] The object of the present invention is to achieve miniaturization of a power transmission unit for an electric vehicle that drives left and right wheels with a single electric motor, while enabling the case that houses the axle and gear mechanism to be molded by casting. [Means for solving the problem]

[0007] The power transmission unit for an electric vehicle according to the present invention is a power transmission unit for an electric vehicle in which the power of an electric motor is transmitted to each of a first axle and a second axle separated into left and right axles via a reduction gear mechanism and a differential gear mechanism, and comprises: a motor case that houses the electric motor and is arranged on the same side as the second axle in the left-right direction with respect to the center between the first axle and the second axle; a first axle case that houses the reduction gear mechanism, the differential gear mechanism, and the first axle; and a second axle case that is fixed so as to be separable from the first axle case and houses the second axle. [Effects of the Invention]

[0008] In the power transmission unit for an electric vehicle according to the present invention, in a configuration in which one electric motor drives left and right wheels, the second axle case, which houses the second axle on the same side as the electric motor with respect to the center between the axles, is separably fixed to the first axle case, which houses the reduction gear mechanism, differential gear mechanism, and first axle. This eliminates the need to form a connection between the case portion housing the second axle and the gear cover portion in a single casting. Therefore, even if the electric motor is located close to the second axle, the fixing surface for the motor case can be formed on the first axle case while ensuring the necessary mold configuration. This enables the case housing the axle and gear mechanism to be molded by casting, while also achieving a compact power transmission unit.

[0009] In the above power transmission unit for an electric vehicle, the first axle case may be configured by fixing an inner case element on the electric motor side and an outer case element on the opposite side from the electric motor by screws.

[0010] According to the above configuration, even if the first axle case has a complex shape, the inner and outer case elements can be easily formed by casting, so the first axle case can be easily formed.

[0011] In the above configuration, the outer case element may be configured such that an axle case portion that houses the first axle and a cover portion that covers one axial end of the reduction gear mechanism are integrally molded.

[0012] According to the above configuration, the number of parts is reduced, thereby reducing manufacturing costs.

[0013] In the above-described power transmission unit for an electric vehicle, the electric motor may have a motor shaft extending in a vehicle left-right direction parallel to an extension direction of the first axle and the second axle, and the reduction gear mechanism may include an input gear provided on the motor shaft or an input shaft arranged on the same axis as the motor shaft and unable to rotate relative to the motor shaft, an intermediate gear shaft on which an intermediate gear meshing with the input gear is provided, and an intermediate gear portion provided on the intermediate gear shaft and meshing with a ring gear provided on the outer periphery of the differential gear mechanism, wherein the motor shaft is arranged at different positions in a first direction perpendicular to the vehicle left-right direction and at the same position in a second direction perpendicular to the vehicle left-right direction and the first direction, and the intermediate gear shaft is arranged at a different position in the second direction relative to the first axle, the second axle, and the motor shaft.

[0014] According to the above configuration, even when an intermediate gear shaft having an intermediate gear is provided between the input gear of the reduction mechanism and the differential gear mechanism, the unit can be made smaller.

[0015] In the above power transmission unit for an electric vehicle, a recess may be formed in a portion of the second axle case that faces the motor case, and a portion of the motor case may fit into the recess.

[0016] According to the above configuration, the electric motor and the second axle can be placed closer to each other, which allows the unit to be made even more compact.

[0017] In the above-described power transmission unit for an electric vehicle, a thrust washer may be disposed between a side bevel gear that is non-rotatably combined with the second axle and a first axle case, the thrust washer having a harder hardness than the first axle case, and rotation may be prevented by a rib formed on the first axle case.

[0018] With the above configuration, even if an axial thrust force is applied to the side bevel gear, the thrust force can be received by the high-hardness thrust washer, preventing the side bevel gear from coming into direct sliding contact with the first axle case. This makes it possible to form the first axle case from a low-hardness material such as aluminum or an aluminum alloy, while preventing the first axle case from being scraped by the side bevel gear. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a cross-sectional view showing the overall configuration of an electric vehicle equipped with a power transmission unit for an electric vehicle according to an embodiment of the present invention. [Figure 2] 1 is an exploded perspective view of a power transmission unit for an electric vehicle according to an embodiment; [Figure 3] 1 is a diagram showing a power transmission unit for an electric vehicle according to an embodiment, viewed from above and partially in cross section; [Figure 4] 4 is an enlarged view of the portion of the axle case shown in FIG. 3 that houses the reduction gear mechanism. [Figure 5] 4 is a cross-sectional view taken along the line AA in FIG. 3. [Figure 6] BB cross-sectional view of FIG. 3. [Figure 7] 4 is a cross-sectional view taken along CC in FIG. 3. [Figure 8] 7 is an enlarged view of the front half of FIG. 6, showing the first axle case without the brake holder. [Figure 9] FIG. 5 is a cross-sectional view taken along the line DD in FIG. 4. [Figure 10] 10 is a cross-sectional view of FIG. 9 taken along line E-E. [Figure 11] FIG. 4 is an enlarged cross-sectional view of the differential gear mechanism and its vicinity in FIG. 3. [Figure 12] FIG. 10 is a perspective view showing the state immediately before the second axle case is attached to the inner case element of the first axle case. [Figure 13] FIG. 10 is a perspective view showing a state immediately before a thrust washer is attached to the inside of an outer case element of the first axle case and a retaining ring is locked to the first axle. [Figure 14] 3 is an enlarged view of the right side portion of FIG. 2, showing the state immediately before the motor case is attached to the first axle case. [Figure 15] 3 is a perspective view, partially separated, showing how a power transmission unit for a left wheel of another vehicle is formed using some of the components that make up the power transmission unit of FIG. 2. FIG. [Figure 16] FIG. 16 is a cross-sectional view of the power transmission unit for the left wheel shown in FIG. [Figure 17] 3 is a perspective view, with some parts omitted, showing how a power transmission unit for a right wheel of another vehicle is formed using some of the components that make up the power transmission unit of FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present invention will be described in detail below with reference to the drawings. The following description will focus on a case where the power transmission unit for an electric vehicle is mounted on a lawnmower, which is a work vehicle. However, the electric vehicle on which the power transmission unit is mounted is not limited to this. It may also be another work vehicle equipped with a work implement for performing one or more of the following tasks: snow removal, excavation, civil engineering, or agricultural work; an off-road utility vehicle (UTV) with a loading platform that travels on rough terrain; an all-terrain vehicle (ATV), also known as a buggy; a recreational vehicle (RV); or a recreational off-highway vehicle (ROV), all of which are electric motor-driven vehicles. The following description will primarily focus on a case where the electric vehicle has two rear wheels driven by a single electric motor; however, the vehicle may also have two front wheels driven by a single electric motor. In the following description, like elements will be designated by the same reference numerals throughout the drawings.

[0021] An embodiment of a power transmission unit for an electric vehicle will be described using Figures 1 to 14. In the drawings described below, the vehicle longitudinal direction is indicated by X, the vehicle lateral direction is indicated by Y, and the vehicle vertical direction is indicated by Z. Hereinafter, the vehicle longitudinal direction, vehicle lateral direction, and vehicle vertical direction will simply be referred to as the longitudinal direction, lateral direction, and vertical direction. Furthermore, the front side is indicated by Fr, the left side is indicated by Lh, and the upper side is indicated by Up. X, Y, and Z are perpendicular to each other. The lateral direction coincides with the vehicle width direction.

[0022] FIG. 1 is a cross-sectional view showing the overall configuration of a lawnmower vehicle 10, which is an electric vehicle equipped with a power transmission unit for an electric vehicle 41 according to an embodiment. First, the overall configuration of the lawnmower vehicle 10 will be described, followed by a detailed description of the power transmission unit for an electric vehicle 41 mounted on the lawnmower vehicle 10. Hereinafter, the power transmission unit for an electric vehicle 41 will be referred to as the power transmission unit 41. The engine-less riding lawnmower vehicle 10 includes a main frame 16 that forms the vehicle body, a left wheel 12 and a right wheel 13 that are two main drive wheels supported on the rear side of the main frame 16, and a left wheel 14 and a right wheel 15 that are two driven wheels supported on the front side. A power transmission unit 41 including an electric motor 70 is connected to the two rear wheels 12, 13. As will be described later, the power transmission unit 41 includes an electric motor 70 housed in a motor case 50 fixed to the axle case 42, and a power transmission mechanism 77 (FIG. 3) that transmits the power of the electric motor 70 to the left and right wheels 12, 13. The power transmission mechanism 77 includes a reduction gear mechanism 78 and a differential gear mechanism 118 (FIG. 3), and the left and right wheels 12, 13 are connected to both the left and right sides of the differential gear mechanism 118 via a first axle 18 or a second axle 19.

[0023] A driver's seat (not shown) is located above the central portion of the main frame 16 in the longitudinal direction, and a steering wheel 20, which serves as a turning command device, and an accelerator pedal (not shown) are located in front of the driver's seat. By operating the steering wheel 20, the left and right front wheels 14, 15 of the vehicle 10 are steered via a steering mechanism 21 on the front side of the vehicle. The steering mechanism 21 may employ a conventionally known structure such as the Ackermann system. In addition, mounting bosses formed on the outer ends of axle cases 42, 130 (described later) of the power transmission unit 41 are screwed to and suspended from the rear lower portion of the main frame 16 in the longitudinal direction.

[0024] The accelerator pedal corresponds to an acceleration command unit that commands the acceleration of the electric motor 70. The accelerator pedal is supported by the main frame 16 so that it can swing about a left-right axis. When the driver steps on the front end of the accelerator pedal, the electric motor 70 accelerates in the forward direction. When the driver steps on the rear end of the accelerator pedal, the electric motor 70 accelerates in the reverse direction. The swing position of the accelerator pedal is detected by a pedal sensor, and the detection signal is sent to a control device (not shown). The control device controls the rotation speed of the electric motor 70 in accordance with the detection signal from the pedal sensor.

[0025] The vehicle 10 also includes a mower 25, which is a work machine, and a power supply unit (not shown) that includes a battery. The mower 25 is supported on the lower side of the main frame 16 in the middle in the front-to-rear direction. The mower 25 includes a mower deck 26 and three mower blades 27, which are rotary lawn-mowing tools that are mounted inside the mower deck 26 and can each rotate around a vertical axis. The mower blades 27 rotate to break and mow the grass, etc. Each mower blade 27 is driven by an electric mower motor (not shown).

[0026] The grass can be cut by rotating the lawnmower blade 27, and the cut grass is discharged from the inside of the mower deck 26 through a duct 28 into a grass collection container (not shown) attached to the rear end of the vehicle 10. The cut grass may also be discharged from the mower deck to one side in the width direction of the vehicle.

[0027] The lawn mower may be configured as a rotary lawn mowing tool, with a cylinder having a rotation axis parallel to the ground surface and, for example, a spiral blade arranged on it, which has the function of clamping and mowing grass, etc., and is equipped with a lawn mower reel driven by an electric mower motor.

[0028] The above is the overall configuration of the lawnmower vehicle 10, and next we will explain the power transmission unit 41 that is mounted on this lawnmower vehicle 10. Fig. 2 is an exploded perspective view of the power transmission unit 41. Fig. 3 is a partial cross-sectional view of the power transmission unit 41 as viewed from above. Fig. 4 is an enlarged view of the portion of the axle case 42 in Fig. 3 that houses the reduction gear mechanism 78.

[0029] The power transmission unit 41 is formed by integrally combining an axle case 42, a motor case 50 fixed to the axle case 42, a traveling electric motor 70 housed in the motor case 50, a power transmission mechanism 77 (FIG. 3) housed in the axle case 42, and left and right axles: a first axle 18 and a second axle 19. The second axle 19 is longer than the first axle 18, and as will be described later, the motor case 50 is disposed on the same side as the second axle 19 in the left-right direction with respect to the center between the first axle 18 and the second axle 19. This allows the center of gravity of the power transmission unit 41 to be closer to the left-right center line O1 (FIG. 3) of the vehicle 10.

[0030] 3 and 4, axle case 42 accommodates therein input shaft 60, reduction gear mechanism 78, and differential gear mechanism 118 that constitute power transmission mechanism 77, as well as portions of first axle 18 and second axle 19. Reduction gear mechanism 78 is a mechanism that transmits power between input shaft 60 and a ring gear 119 that is provided on the outer periphery of differential gear mechanism 118, and transmits the power from input shaft 60 to ring gear 119 after reducing the speed. Input shaft 60 is disposed coaxially with motor shaft 72 of electric motor 70 and is coupled so as to be unable to rotate relative to motor shaft 72, i.e., so as to rotate integrally with motor shaft 72.

[0031] The axle case 42 is formed by joining together a first axle case 43, which houses a portion of the first axle 18, the reduction gear mechanism 78, and the differential gear mechanism 118, and a second axle case 130, which houses a portion of the second axle 19, with a plurality of bolts 58 (FIG. 2). The first axle 18 and the second axle 19 are separated into left and right halves, each extending in the left-right direction. The inner ends of the first axle 18 and the second axle 19 are rotatably fitted inside a cylindrical sleeve 120 that forms the differential gear mechanism 118, and the inner ends of the first axle 18 and the second axle 19 face each other inside the sleeve 120.

[0032] The first axle case 43 is formed by fixing together with screws an inner case element 44 on the electric motor 70 side and an outer case element 45 on the opposite side from the electric motor 70. Fig. 5 is a cross-sectional view taken along line AA in Fig. 3, and Fig. 6 is a cross-sectional view taken along line BB in Fig. 3. As shown in Figs. 2 to 5, the inner case element 44 has a front opening 46 and a rear opening 47 (Fig. 2) that are generally circular in cross section on both sides in the front-to-rear direction at the right end, and also has an opening 48 at the left end that extends from the front side to the rear side, as shown in Fig. 6.

[0033] Figure 7 is a cross-sectional view taken along CC in Figure 3. As shown in Figures 3, 4, and 7, the outer case element 45 is formed integrally with a tubular portion 49, which is an axle case portion that houses the first axle 18, and a cover portion 140 that covers one axial end of the reduction gear mechanism 78. As shown in Figure 3 and with reference to Figure 13 described later, two wall portions 141, 142 are joined via ribs to both front-rear direction sides of the outer side of the tubular portion 49, and a plurality of plate portions 143 extending in the front-rear direction are joined to multiple positions on the left and right of the two wall portions 141, 142, thereby reinforcing the tubular portion 49.

[0034] Additionally, outer case element 45 has an opening 144 extending from the front to the rear on the right side of the vehicle. Cylinder portion 49 extends cylindrically from the rear toward the left on the left side, which is the outer side in the vehicle width direction, of outer case element 45. First axle 18 passes through this cylinder portion 49 and is rotatably supported by bushes 145, 146, which are sliding bearings, provided on the inside at two axial positions.

[0035] The inner case element 44 and the outer case element 45 are joined together so that the outer peripheral edges of their left and right ends butt against each other, and an opening 48 at the left end of the inner case element 44 is closed by the outer case element 45. As a result, a gear chamber S1 is formed inside the first axle case 43, in which gears of the reduction gear mechanism 78 and the differential gear mechanism 118 are disposed. Meanwhile, a front opening 46 at the right end of the first axle case 43 is closed by the motor case 50 (described later). The outer case element 45 and the inner case element 44 are formed from a metal material such as an aluminum alloy and formed by die casting, which is a type of casting. After being formed by die casting, the inner case element 44 may be machined to increase the flatness of, for example, a first fixing surface 44a (FIG. 4) against which an end face of the motor case 50 (described later) abuts and fixes the inner case element 44, and a second fixing surface 44b (FIG. 4) against which an end face of the second axle case 130 abuts and fixes the inner case element 44. A recessed groove 44c (FIG. 4) is formed in the vertical direction between the first fixing surface 44a and the second fixing surface 44b to prevent the first and second fixing surfaces 44a, 44b from being directly connected to each other.

[0036] As will be described in detail later, the reduction gear mechanism 78 includes a first helical gear 79 which is an input gear provided on the input shaft 60, and an intermediate gear shaft 82 on which a second helical gear 81 which is an intermediate gear that meshes with the first helical gear 79 is provided. Furthermore, an intermediate gear portion 83 (FIG. 10) provided on the intermediate gear shaft 82 meshes with a ring gear 119 provided on the outer periphery of a differential gear mechanism 118 which will be described later.

[0037] Meanwhile, the second axle case 130 is fitted inside the rear opening 47 at the right end of the first axle case 43, and the end face of the second axle case 130 abuts against the second fixing surface 44b on the periphery of the rear opening 47 on the right side of the first axle case 43.

[0038] As shown in Figures 2, 3, and 12 (described later), the second axle case 130 includes a cylindrical tube portion 131 and two wall portions 132, 133 connected via ribs on both front-rear direction outer sides of the tube portion 131. Furthermore, a plurality of plate portions 134 extending in the front-rear direction are connected to multiple positions on the left and right of the two wall portions 132, 133 to reinforce the tube portion 131. A cylindrical portion 135 is formed at the left end of the second axle case 130 to fit into the inside of the rear opening 47 of the first axle case 43. The second axle 19 passes through the inside of the tube portion 131 of the second axle case 130 and is rotatably supported by bushings 147, 148 provided at two axial positions.

[0039] The second axle case 130 is made of a metal such as an aluminum alloy and is formed by die-casting. In this state, as shown in FIGS. 2 and 5, a substantially rectangular flange 136 whose vertical length is longer than its longitudinal length is formed at the inner end, which is the left end, of the second axle case 130. The second axle case 130 is fixed to the first axle case 43 with a plurality of bolts 58 that pass through the flange 136. In this manner, the axle case 42 is formed. The fixing surface of the second axle case 130 that abuts against the second fixing surface 44b of the inner case element 44 for fixing may be machined to increase flatness.

[0040] Furthermore, recesses 137 recessed toward the tubular portion 131 are formed in the left-right middle portion of each of the walls 132, 133 of the second axle case 130. The cross-sectional shape of each recess 137 perpendicular to the up-down direction is substantially the same over the entire length in the up-down direction. As a result, the recesses 137 are formed in the portion of the second axle case 130 that faces the motor case 50. When the motor case 50 is combined with the first axle case 43, a portion of the motor case 50 fits into the recesses 137.

[0041] Furthermore, the second axle case 130 is fixed to the first axle case 43 in a manner that allows it to be separated from the first axle case 43. The outer end of the tubular portion 49 of the first axle case 43 and the outer end of the second axle case 130 are fixed to fixing members 17a, 17b that constitute the main frame 16 of the vehicle. The tubular portion 49 of the first axle case 43 and the second axle case 130 may also be fixed directly to the main frame 16. The outer end of the first axle 18 in the vehicle width direction protrudes from the tip of the tubular portion 49 of the outer case element 45, and a hub for securing a left wheel is fixed to this protruding portion. On the other hand, the outer end of the second axle 19 in the vehicle width direction protrudes from the tip of the second axle case 130, and a hub for securing a right wheel is fixed to this protruding portion.

[0042] 11 , which will be described later, the differential gear mechanism 118 includes a differential case 121 supported within the first axle case 43 so as to be disposed coaxially with the axles 18, 19, a ring gear 119 fixed to the outer circumferential surface of the differential case 121 and meshing with the intermediate gear portion 83 of the reduction gear mechanism 78, a pinion shaft 122 disposed orthogonal to the axles 18, 19 within the differential case 121 and rotating integrally with the differential case 121, a pinion 123 which is a bevel gear rotatably supported on the pinion shaft 122, and a side bevel gear 124 fixed to the inner end of each axle 18, 19 and meshing with the pinion 123. This differentially connects the first axle 18 and the second axle 19. The power of the electric motor 70 is transmitted from the motor shaft 72 to the input shaft 60, reduced in speed by the reduction gear mechanism 78, and then differentially transmitted to the first axle 18 and the second axle 19 by the differential gear mechanism 118. As a result, the first axle 18 and the second axle 19 are driven differentially. In FIG. 2, a cover member 180 is shown in parentheses. As will be described later, by combining the cover member 180 with the first axle case 43 in place of the second axle 19 and the second axle case 130, power transmission units 41a, 41b for the left and right wheels of another example vehicle shown in FIGS. 15 to 17 described later are formed.

[0043] FIG. 8 is an enlarged view of the front half of FIG. 6 , showing the first axle case 43 without the brake holder. FIG. 9 is a DD cross-sectional view of FIG. 4 . As shown in FIGS. 4 , 8 , and 9 , the brake rotor 76 and the brake holder 102 are disposed inside the first axle case 43, and a brake chamber S2 is formed that includes one end of the input shaft 60 and one end of the motor shaft 72 facing the input shaft 60, and includes a position where the two shafts 60, 72 face each other. The input shaft 60 is rotatably supported in the first axle case 43 by two bearings 51, 52. Of the two bearings 51, 52, the bearing 51 is held by a partition wall 150 that extends from the peripheral wall of the inner case element 44 toward the inside of the case, and the bearing 52 is held by the inner surface of a standing wall 151 of the outer case element 45.

[0044] The gear chamber S1 provided in the first axle case 43 accommodates the input shaft 60, the reduction gear mechanism 78, and the differential gear mechanism 118. An appropriate amount of oil is filled inside the first axle case 43, and an oil level is formed at the boundary with the air layer. As will be described later, oil is allowed to flow freely between the gear chamber S1 and the brake chamber S2, and the oil is contained below both chambers S1 and S2. As a result, the gear chamber S1 lubricates the gear mechanisms 80 and 118, and the brake chamber S2 cools the brake rotor 76, which will be described later. In Figures 5 to 8 and 10, which will be described later, the oil level is indicated by a solid line La. An air layer is formed above each of the chambers S1 and S2.

[0045] On the other hand, a motor shaft 72 of an electric motor 70 is connected to one end of the input shaft 60, which is the inner end in the vehicle width direction, by a coupling member 74 serving as a joint. In this way, the power of the motor 70 is transmitted from the motor shaft 72 to the input shaft 60.

[0046] The motor case 50 houses the motor 70 inside and is connected and fixed to the inner case element 44 of the axle case 42 with bolts 59 (FIG. 2), thereby closing the front opening 46 of the axle case 42 and extending to the right. As a result, the motor case 50 is located on the same side as the second axle 19 in the left-right direction with respect to the center between the first axle 18 and the second axle 19. Also, as shown in FIG. 3, a portion of the motor case 50, specifically the portion that protrudes rearward from the right end, fits into a recess 137 formed in a wall 132 of the second axle case 130 on the electric motor 70 side. As will be described later, this allows the electric motor 70 and the second axle 19 to be closer together, thereby enabling the power transmission unit 41 to be further reduced in size.

[0047] The motor case 50 is formed by closing the right opening of a cylindrical case body 50a with a bottom and a cover 55. The bottom of the case body 50a has a cylindrical fitting portion 50b that protrudes axially from the inner periphery of the inner end surface of the cylindrical body portion, and a stepped cylindrical cover portion 50c that closes the inner end opening of the cylindrical fitting portion 50b. A motor shaft 72 of the electric motor 70 penetrates inside a small-diameter cylindrical portion formed in the center of the cover portion 50c. The cylindrical fitting portion 50b is fitted into the front opening 46 of the inner case element 44. A bearing 53 and a seal 54 are fixed to the inner periphery of the small-diameter cylindrical portion to prevent oil from the axle case 42 from entering the motor case 50. The motor shaft 72 is rotatably supported inside the small-diameter cylindrical portion by the bearing 53. As a result, the motor shaft 72 of the electric motor 70 extends in the left-right direction parallel to the extension direction of the first axle 18 and the second axle 19. Furthermore, the motor shaft 72 is disposed at different positions in the front-rear direction, which is a first direction perpendicular to the left-right direction, and at the same position in the up-down direction, which is a second direction perpendicular to the left-right direction and the front-rear direction. On the other hand, as shown in FIGS. 5 to 9 , the intermediate gear shaft 82 of the reduction gear mechanism 78 is disposed at a different position in the up-down direction relative to the first axle 18, the second axle 19, and the motor shaft 72. Specifically, the intermediate gear shaft 82 is disposed below the first axle 18, the second axle 19, and the motor shaft 72. This makes it possible to reduce the size of the power transmission unit 41 even when the intermediate gear shaft 82 having the second helical gear 81, which is an intermediate gear, is provided between the first helical gear 79, which is the input gear of the reduction gear mechanism 78, and the differential gear mechanism 118.

[0048] As shown in FIG. 3, motor 70 is, for example, a permanent magnet three-phase motor. Motor 70 has a motor rotor fixed to the outer circumferential surface of motor shaft 72, a stator core facing the outer circumferential surface of the motor rotor, and three-phase stator coils wound around the stator core. The motor rotor has, for example, permanent magnets arranged at multiple positions around the rotor core. The stator core is fixed inside motor case 50. The right end of motor shaft 72 is rotatably supported by a bearing (not shown) in motor case 50. When three-phase AC power is supplied from a battery to the stator coil, the motor shaft 72 rotates due to the interaction between a rotating magnetic field generated in the stator core and a magnetic field generated by the motor rotor.

[0049] The motor shaft 72 is arranged coaxially with the input shaft 60 of the gear mechanism 80, and the motor shaft 72 and the input shaft 60 are connected by a connecting member 74 with their respective distal end surfaces spaced apart. Specifically, male splines are formed on the outer peripheral surface of one end of the motor shaft 72 and the outer peripheral surface of one end of the input shaft 60, respectively. Axial ends of a cylindrical portion 75 of the connecting member 74 are fitted to the outside of one end of the motor shaft 72 and the outside of one end of the input shaft 60, respectively. Female splines are formed on the inner circumference of the cylindrical portion 75 along the axial length and engage with the male splines on the outer peripheral surfaces of one end of the motor shaft 72 and one end of the input shaft 60, respectively. This prevents the motor shaft 72 and the input shaft 60 from rotating relative to each other, i.e., they rotate integrally, while allowing the connecting member 74 and the input shaft 60 to move axially relative to the motor shaft 72. Note that the motor shaft 72 and the input shaft 60 can be connected to the cylindrical portion 75 using a key instead of the spline, providing the same functionality.

[0050] Furthermore, a brake rotor 76 is integrally formed on the outer periphery of one end of the cylindrical portion 75 of the connecting member 74. This makes it possible to prevent the power transmission unit 41 from becoming larger in size in a configuration in which the brake rotor 76 is provided around the input shaft 60.

[0051] The reduction gear mechanism 78 includes a first helical gear 79 that is formed directly on the input shaft 60 and is therefore attached to the input shaft 60, and an intermediate gear shaft 82 to which a second helical gear 81 is engaged on its outer periphery.

[0052] As shown in Fig. 10, the intermediate gear shaft 82 has an inner shaft 82a fixed to the axle case 42 and an outer shaft 82b fitted onto the outer periphery of the inner shaft 82a, with the outer shaft 82b supported so as to be rotatable relative to the inner shaft 82a. An intermediate gear portion 83 that is axially wide and shaped like a spur gear is formed on the outer periphery of the outer shaft 82b, and a ring gear 119 (Fig. 11) meshes with the teeth on the right side, which is one side, of the intermediate gear portion 83. Internal teeth formed on the inner periphery of the second helical gear 81 mesh with the teeth on the left side, which is the other side, of the intermediate gear portion 83, and they are engaged so as not to rotate relative to each other.

[0053] To allow the second helical gear 81 to move axially relative to the intermediate gear portion 83, no protrusions or snap rings are provided on the outer periphery of the intermediate gear portion 83. Instead, the axial displacement of the second helical gear 81 is limited by a pair of thrust bearing members 152, 153 ( FIG. 6 ). FIG. 10 shows only one thrust bearing member 152 of the pair of thrust bearing members 152, 153. The hardness of each thrust bearing member 152, 153 is higher than the hardness of each case element 44, 45. This prevents the second helical gear 81 from coming into direct sliding contact with the case elements 44, 45, as will be described later, and prevents the second helical gear 81 from abrading members with which it comes into sliding contact. The intermediate gear portion 83 is made of sintered material, which allows for mass production at low cost, but since its outer periphery does not have the stepped portion described above, the density distribution of the sintered material can be made uniform, and manufacturing quality such as hardness and strength can be maintained.

[0054] The second helical gear 81 forms a helical gear mechanism by meshing with the first helical gear 79. The number of teeth of the ring gear 119 is greater than the number of teeth of the intermediate gear portion 83, and the number of teeth of the second helical gear 81 is greater than the number of teeth of the first helical gear 79. As a result, the rotation of the input shaft 60 is reduced in two stages by the reduction gear mechanism 78 and transmitted to the ring gear 119 as an output gear.

[0055] The left end, which is one end of the inner shaft 82a of the intermediate gear shaft 82, is fitted into a recess 151a formed in the standing wall 151 of the outer case element 45. The right end, which is the other end of the inner shaft 82a, is inserted non-rotatably into a through hole 84 formed in the wall of the inner case element 44. The right tip of the inner shaft 82a is machined to form a flat portion on its outer circumferential surface, and when fitted into the flat portion of the through hole 84, the inner shaft 82a is made non-rotatable.

[0056] The first helical gear 79 mounted on the input shaft 60 is sandwiched between the inner rings of the two bearings 51 and 52 on both sides, and when the first helical gear 81 is driven to rotate, a displacement (thrust force) in the axial direction of the input shaft 60 is generated by the inherent backlash of the bearings 51 and 52. However, this axial displacement is absorbed by the relative sliding of the spline engagement points of the connecting member 74 described above, and is not transmitted to the motor shaft 72. Therefore, the motor shaft 72 and the motor rotor are not moved in the axial direction, and there is no risk of detection failures in the various detection sensors (not shown) attached to the motor shaft 72 and the motor rotor, and the accuracy of the electric motor during operation can be maintained at a high level.

[0057] On the other hand, the second helical gear 81 is configured to be able to move axially relative to the intermediate gear shaft 82. In the helical gear mechanism, when the first helical gear 79 and the second helical gear 81 are engaged with each other, a thrust force is applied in the axial direction when the helical gears 79, 81 are driven to rotate. As a result, only the second helical gear 81 moves axially, and the direction of this movement changes depending on the rotation direction of the first helical gear 79, i.e., the rotation direction of the motor shaft 72. The second helical gear 81 is made of a hard material such as iron or steel. On the other hand, the case elements 44, 45 are made of aluminum or an aluminum alloy to reduce weight, and have a lower hardness than the second helical gear 81. For this reason, if the second helical gear 81 moves axially and comes into contact with the axle case 42, causing friction, the axle case 42 may be scraped.

[0058] In this embodiment, to prevent such inconvenience, a pair of thrust bearing members 152, 153 (FIGS. 6, 7, and 10) are provided in the axle case 42 in case portions that face one axial end face and the other axial end face of the second helical gear 81. The pair of thrust bearing members 152, 153 are each supported non-rotatably with respect to the axle case 42.

[0059] Specifically, as shown in FIG. 7 , one thrust receiving member 152 on the outer case element 45 side includes a disk-plate-shaped main body portion 152a, a first arm 152b formed integrally with the main body portion 152a and extending upward, and a fan-shaped second arm 152c formed integrally with the main body portion 152a and extending rearward. A through hole formed in the main body portion 152a is fitted with one end of the intermediate gear shaft 82, and the first arm 152b is interposed between the outer case element 45 and the second helical gear 81. The width of the first arm 152b narrows from the main body portion 152a toward its middle portion and remains constant from the middle portion to its tip. The tip portion, which is the outer end of the first arm 152b in the extension direction, is bent at a substantially right angle toward the outer case element 45, forming a bent portion 152d. As shown in FIG. 10, a circular recess 151b is formed on the inner surface of the standing wall 151 of the outer case element 45, and a bent portion 152d is fitted into the recess 151b, thereby preventing rotation of one thrust receiving member 152.

[0060] Furthermore, the tip of the portion of the second arm 152c that is the outer end in the extension direction where the width is increased and that extends outward from the outer periphery of the second helical gear 81 has a bent portion 152e that is bent at a substantially right angle so as to be parallel to the tooth width of the second helical gear 81. The bent portion 152e faces the outer periphery of the second helical gear 81. This prevents one thrust receiving member 152 from rotating co-rotating when the second helical gear 81 rotates, and also prevents the second helical gear 81 from scooping up oil present on the lower side inside the gear chamber S1 of the axle case 42. This reduces the resistance to agitating the oil, thereby reducing energy loss in the power transmission unit 41.

[0061] 6, the other thrust receiving member 153 is pad-shaped and fits into a recess 154 with a generally rectangular cross section formed in the side surface of the inner case element 44 on the outer case element 45 side, with a portion protruding beyond the open end of the recess 154 toward the outer case element 45 and facing the side surface of the second helical gear 81. This also prevents the second helical gear 81 from abutting and coming into frictional contact with the axle case 42, thereby preventing the axle case 42 from being scraped.

[0062] Next, the connecting member 74 that connects the motor shaft 72 and the input shaft 60 will be described using Figures 4, 8, and 9. As described above, the connecting member 74 has a cylindrical portion 75 with a female spline on its inner circumference. A single-plate brake rotor 76 that protrudes diametrically around the entire circumference is integrally provided on the outer periphery of one end of the cylindrical portion 75. In this example, the brake rotor 76 is fitted to the outside of both the input shaft 60 and the motor shaft 72 via the cylindrical portion 75, preventing the brake rotor 76 from rotating relative to the input shaft 60 and the motor shaft 72.

[0063] The connecting member 74 is molded by sintering to form an integral brake rotor 76. Brake shoes 92 and brake pads 93, which serve as friction materials and are pressing parts that constitute the brake device 90, are arranged facing each other on both axial sides of the brake rotor 76. When the brake shoes 92 and brake pads 93 are pressed against the brake rotor 76 from both axial sides, a braking torque is applied, causing the input shaft 60 and motor shaft 72 to stop rotating.

[0064] Specifically, the brake device 90 includes a braking force generating unit 91 and a brake rotor 76. The brake rotor 76 is disposed in a brake rotor housing section S3 defined within the brake chamber S2. In the brake rotor housing section S3, a circular recess 101 slightly larger than the outer diameter and thickness of the brake rotor 76 is formed in one side wall surface T1 of a partition wall 150 that forms the brake chamber S2, and the brake rotor 76 is disposed therein.

[0065] A braking force is applied to the brake rotor 76 from a braking force generating unit 91. The braking force generating unit 91 includes a brake shaft 94, a brake shoe 92, a brake pad 93, and a brake arm 95 (FIG. 2). The brake pad 93 is held in a pocket on one side wall surface T1 located within the recess 101.

[0066] The brake shaft 94 extends in the vertical direction at the top of the inner case element 44 and is rotatably supported by the axle case 42. The upper portion of the brake shaft 94 protrudes outward from the upper surface of the inner case element 44. For this reason, a through hole 110 into which the brake shaft 94 fits is formed in the upper end of the inner case element 44 at a position that coincides in the front-to-rear direction with a circumferential portion of the brake rotor 76. The upper portion of the through hole 110 has a larger diameter than the lower portion, and an O-ring 98 is provided inside to maintain oil-tightness.

[0067] Meanwhile, a semicircular section with a cam surface 97 (FIG. 4) is formed at the lower portion of the brake shaft 94 that passes through the brake chamber S2 and enters the brake rotor housing S3. Therefore, upper and lower openings 156a and 156b (FIG. 8) for inserting the lower portion of the brake shaft 94 are formed in the side wall surface T1. Each opening 156a and 156b extends in the same direction as the longitudinal direction of the brake shaft 94 and communicates with the recess 101. Of the openings 156a and 156b, only the upper opening 156a passes through the brake shaft 94. When the axle case 42 is used as an axle case for the right wheel of a different vehicle, as described below, the lower opening 156b is turned upside down and used with the opening 156b facing upward. The cam surface 97 faces the brake shoe 92, which is movable in the left-right direction of the axle case 42. The brake shoe 92 is disposed between the brake shaft 94 and the brake rotor 76, with the surface facing the brake rotor 76 serving as the braking surface. The brake shoe 92 has two plate-shaped legs that protrude from both ends of the plate-shaped main body in the front-rear direction on the side opposite the brake rotor 76, and is guided by a brake holder 102, which will be described later.

[0068] The brake pads 93 are attached to the partition wall 150 of the inner case element 44. When the cam surface 97 is arranged parallel to the brake shoes 92, the brake shoes 92 move away from the brake rotor 76 and are in a non-braking state. On the other hand, when the brake shaft 94 rotates and the cam surface 97 is inclined relative to the brake shoes 92, the cam surface 97 is pressed against the brake shoes 92, which are guided by the brake holder 102, and the braking surface protrudes from the brake holder 102. As a result, the brake rotor 76 is pressed against the brake pads 93 and is sandwiched between the brake shoes 92 and the brake pads 93 on both sides, thereby braking the brake rotor 76 and the power transmission system extending from the input shaft 60 to the left and right wheels 12, 13 to which power is transmitted.

[0069] The brake arm 95 is attached and fixed to the upper end of the brake shaft 94 in a direction perpendicular to the brake shaft 94. A brake operating tool (not shown) arranged around the driver's seat is connected to the tip of the brake arm 95 via a link mechanism. A spring 99 ( FIG. 9 ) is arranged between the brake arm 95 and the periphery of the brake shaft 94 on the outer surface of the inner case element 44. Both ends of the spring 99 engage with a first engagement pin (not shown) fixed to the brake arm 95 and protruding downward, and a second engagement pin (not shown) fixed to the inner case element 44 and protruding upward. As a result, the brake shaft 94 is biased in a first rotational direction by the spring 99 via the brake arm 95 so that the cam surface 97 and the brake shoe 92 become parallel and no braking is applied.

[0070] When the vehicle's brake operating tool is operated to the parking brake position, the tip of the brake arm 95 moves against the biasing force of the spring 99, and the brake shaft 94 rotates in a second rotation direction in which the cam surface 97 is inclined relative to the brake shoe 92 and presses the brake shoe 92 against the brake rotor 76. The second rotation direction is opposite to the first rotation direction. This causes the brake device 90 to enter a braking state, stopping the rotation of the brake rotor 76 and the wheel 24 and maintaining that state.

[0071] Meanwhile, a brake holder 102 fixed to the axle case 42 is disposed on the opposite side of the brake shaft 94 from the brake shoe 92. The brake holder 102 is provided to enable the brake shoe 92 and the brake pad 93 to be pressed against the brake rotor 76 more stably, thereby realizing more stable braking.

[0072] The brake holder 102 is made of a metal material such as iron, steel, or aluminum alloy. Approximately in the center of the brake holder 102 is a central opening 102a, which is a through-hole that allows the tubular portion 75 of the connecting member 74 to pass through. A guide surface 103 ( FIG. 9 ) with an arc-shaped cross section, which allows part of the brake shaft 94 to enter from above, is formed in the vertical direction on the surface of the brake holder 102 facing the brake shaft 94 in the thickness direction. Grooves 104 that can engage and hold each leg portion of the brake shoe 92 are also formed in two positions spaced apart in the vertical direction on the guide surface 103.

[0073] The brake holder 102 has a central opening 102a in the center of its front surface for inserting the motor shaft 72 and cylindrical portion 75, and a bolt 111 passing through the front end and one of two extending portions extending upward and downward from the rear end is screwed into a threaded hole formed in the one side wall surface T1, thereby fixing the brake holder 102 to the axle case 42. Furthermore, the brake holder 102 has a guide surface 103 that receives the lower end of the brake shaft 94 and abuts against the semicircular arc surface opposite the cam surface 97, and is configured so that this guide surface 103 receives the reaction force of the brake shaft 94 against the brake shoe 92 when the brakes are applied.

[0074] In order to configure the pressing mechanism of the brake rotor 76 as a durable wet type, the oil in the gear chamber S1 also flows into the brake chamber S2 through the lower first oil circulation port 113 of two elongated first oil circulation ports 113 formed through the partition wall 150 so as to be positioned above and below the oil level La, and the second oil circulation port 114 located below the oil level La. As a result, oil is also contained in the brake chamber S2, the brake rotor 76 is bathed in oil, and heat generated during braking is dissipated through the oil. When the axle case 42 is used as an axle case for the right wheel of a vehicle in another example described below, the upper first oil circulation port 113 is turned upside down for the right wheel so that its vertical position is reversed from that of the lower first oil circulation port 113 and it is positioned below the oil level La.

[0075] When the motor shaft 72 rotates, the brake rotor 76 also rotates, stirring up the oil in the brake chamber S2, which creates agitation resistance and results in energy loss in the power transmission unit 41. Therefore, in this embodiment, the brake holder 102 has its flat back surface abutting against the periphery of the opening of the recess 101 and covering the front of the recess 101, thereby separating the motor-side portion S2a (FIG. 4), which is the portion of the brake chamber S2 other than the brake rotor housing portion S3, from the brake rotor housing portion S3. This limits the oil that comes into contact with the brake rotor 76, thereby reducing the amount of oil that is stirred up. This reduces the oil agitation resistance caused by the brake rotor 76, thereby reducing energy loss in the power transmission unit 41.

[0076] As described above, the recess 101 is open to the motor-side portion S2a of the brake chamber S2 through openings 156a and 156b formed at the top and bottom to allow the lower end of the brake shaft 94 to pass through. As a result, when the brake rotor 76 rotates, the surrounding oil is blown out by centrifugal force from the open position of the brake rotor housing portion S3 into the motor-side portion S2a of the brake chamber S2, for example, in the directions of arrows α1 and α2 in FIG. 5 . The blown-out oil merges with the oil in the motor-side portion S2a. The blown-out oil creates a slight negative pressure in the brake rotor housing portion S3, which draws oil from the motor-side portion S2a into the brake rotor housing portion S3 through the gap between the inner circumferential surface of the central opening 102a and the outer circumferential surface of the connecting member 74, facilitating the circulation of the oil while in contact with the brake rotor 76. This promotes heat dissipation from the brake rotor 76. In this example, when constructing left and right power transmission units 41a, 41b for a vehicle of another example as shown in Figures 15 to 17 described later, openings 156a, 156b are formed on both the upper and lower sides so that the axle case 42 can be turned upside down to be shared, but if sharing is not a consideration, one of the openings 156b may be omitted.

[0077] In this example, the axle case 42 is symmetrical about the vertical center so that it can be used upside down. As a result, as shown in FIG. 9 , a lower through-hole 110a is formed in the inner case element 44 at a lower end position that is vertically aligned with the upper through-hole 110 into which the brake shaft 94 fits, and the lower through-hole 110a is closed with a plug 115. The upper and lower ends of the axle case 42, which have the through-holes 110 and 110a, are also symmetrical about the vertical center. When the axle case 42 is turned upside down, the lower through-hole 110a faces up in FIG. 9 , allowing the brake shaft 94 to be inserted therein, and the upper through-hole 110 faces down in FIG. 9 , allowing the plug 115 to be attached. 6 and 9, the partition wall 150 also has a second oil circulation port 114 open above, symmetrically to the second oil circulation port 114 below the oil level La. The holders for the brake pads 93 and brake shoes 92 are also provided at vertically symmetrical positions on one side wall surface T1 and the brake holder 102, respectively, and are replaced when the axle case 42 is turned upside down.

[0078] 5 and 6, two through holes 84 for inserting the right end of the intermediate gear shaft 82 are formed at positions symmetrical with respect to the center in the vertical direction of the inner case element 44. On the other hand, as shown in FIG. 7, two recesses 151a, 151b for inserting the left end of the intermediate gear shaft 82 are formed at positions symmetrical with respect to the center in the vertical direction of the outer case element 45. Furthermore, as shown in FIG. 6, a recess 154 for mounting the other thrust receiving member 153, which faces one axial surface of the second helical gear 81, is formed at a position symmetrical with respect to the center in the vertical direction in the wall of the inner case element 44. This allows the axle case 42 to be turned upside down to be used in common when configuring a power transmission unit 41b (FIG. 17) for the right wheel of a vehicle of another example described later. 7, of the two recesses 151a and 151b, the recess 151b that is located above the oil level La has the bent portion 152d provided in a part of the thrust receiving member 152 inserted therein, as described above. This allows for effective use of the recess 151b for commonality.

[0079] Furthermore, as shown in FIGS. 9 and 10 , the brake chamber S2 of the inner case element 44 has a circular vertical hole 157 formed vertically at a position where the upper and lower ends, located rearward of the through-hole 110, are aligned in the vertical direction, and are symmetrical about the vertical center. The vertical hole 157 and the elongated horizontal hole 158 are connected to the inner end of the vertical hole 157 and extend toward the electric motor 70. One end of the horizontal hole 158 communicates with the brake chamber S2. An air breather device 117 is inserted into and attached to the outer end opening of the upper vertical hole 157. The air breather device 117 prevents liquids such as water and dust from entering the axle case 42 and allows air to be drawn in and out of the axle case 42. When internal pressure increases due to oil expansion in the axle case 42, air is discharged to the outside of the axle case 42 through the air breather device 117, preventing an excessive increase in internal pressure. The outer end opening of the lower vertical hole 157 is closed by a plug 115a. When the axle case 42 is turned upside down, the lower vertical hole 157 and horizontal hole 158 in Figure 9 become upper sides, and the air breather device 117 can be attached to the upper vertical hole 157, and the upper vertical hole 157 and horizontal hole 158 in Figure 9 become lower sides, and the plug 115a can be attached to the lower vertical hole 157.

[0080] In this example, the lower end of vertical hole 157 is connected to horizontal hole 158 without vertically penetrating axle case 42, which prevents oil in brake chamber S2 from scattering and penetrating deep into vertical hole 157. This ensures the reliability of air breather device 117 over the long term.

[0081] As shown in FIG. 5 , an oil dipstick hole 159 is formed in the wall of the inner case element 44 near the mounting portion of the flange 136 of the second axle case 130, approximately in the vertical center and in a portion not covered by the flange 136. The inner end of the oil dipstick hole 159 is connected to the gear chamber S1. A bolt 160 serving as an oil dipstick plug is threadedly engaged into the oil dipstick hole 159 to close the oil dipstick hole 159. By removing the bolt 160 and confirming that only a small amount of oil is leaking from the axle case 42 or that it is about to leak, it can be confirmed that the oil level La is properly located near the bottom end of the oil dipstick hole 159. The oil dipstick hole 159 can also be used as a hole for pouring oil into the axle case 42. Oil may be poured into the axle case 42 using the vertical hole 157 and horizontal hole 158 for mounting the air breather device 117.

[0082] As shown in Fig. 6, a flat permanent magnet 161 is held in a locking groove 162 in the partition wall 150 of the inner case element 44 at a position below the oil level La in the gear chamber S1 in which the input shaft 60 is disposed. The permanent magnet 161 attracts metal foreign matter such as iron powder in the oil. In order to standardize the axle case in the power transmission unit 41b for the right wheel of the vehicle of another example, another locking groove 162 is formed at a position symmetrical to the above-mentioned locking groove 162 with respect to the center in the vertical direction of the inner case element 44.

[0083] FIG. 11 is an enlarged cross-sectional view of the differential gear mechanism 118 and its vicinity in FIG. 3. FIG. 12 is a perspective view showing the state immediately before the second axle case 130 is attached to the inner case element 44 of the first axle case 43. As shown in FIGS. 11 and 12, the aforementioned bushing 147 is provided between the second axle 19 and a cylindrical portion 135 formed at the inner end of the second axle case 130. A large-diameter cylindrical surface 163, which has a larger diameter than the inner peripheral surface of the axial center of the second axle case 130, is formed on the inner peripheral surface of the cylindrical portion 135 at the axial inner end of the second axle case 130, and the bushing 147 is fitted into the large-diameter cylindrical surface 163. One axial end of the bushing 147 faces a stepped surface 163a formed on the rear side of the large-diameter cylindrical surface 163 of the second axle case 130, thereby restricting axial movement of the bushing 147. As shown in Figure 3, a bushing 148 is provided between the inner peripheral surface of the outer end of the cylindrical portion 131 of the second axle case 130 and the second axle 19, and a sealing member 164 is provided further outside the bushing 148 between the inner peripheral surface of the cylindrical portion 131 and the second axle 19 to prevent oil leakage.

[0084] Of the two bushings 147, 148 provided at both ends of the second axle case 130, the outer diameter of the inner bushing 147 is larger than the outer diameter of the outer bushing 148. Two tapered surfaces 165a, 165b are formed on both sides of the cylindrical portion 131 of the second axle case 130. The inner diameters of the two tapered surfaces 165a, 165b gradually decrease from the inner ends of the bushings 147, 148 toward a position to the right of the axial center of the cylindrical portion 131. Of the two tapered surfaces 165a, 165b, the axial length of the inner tapered surface 165a is longer than the axial length of the outer tapered surface 165b. The tapered surfaces 165a, 165b are provided to facilitate punching during casting of the second axle case 130. This allows the axial length of the second axle case 130 to be increased while using an inexpensive, small-diameter bushing for the outer bushing 148.

[0085] 11 and 12, the portion of the inner end of the second axle 19 that protrudes axially inward beyond the bushing 147 passes through a thrust washer 166 and a generally C-shaped retaining ring 167, and then is spline-fitted into the center hole of the right side bevel gear 124. This prevents the side bevel gear 124 from rotating relative to the second axle 19, i.e., the side bevel gear 124 rotates integrally with the second axle 19. For this reason, the thrust washer 166 is disposed between the side bevel gear 124 and the first axle case 43. The thrust washer 166 is made of iron, steel, or the like, and is harder than the first axle case 43. The thrust washer 166 is prevented from rotating by a retaining boss 168, which is a rib formed on the inner surface of the inner case element 44 of the first axle case 43.

[0086] As shown in FIG. 12 , the retaining boss 168 is formed on the inner surface of the inner case element 44 by a cylindrical portion that protrudes inward from the opening periphery of the rear opening 47, into which the cylindrical portion 135 of the second axle case 130 is fitted. Four locking recesses 169 with a substantially right-angled triangular cross section are formed at four circumferential positions on the inner periphery of the tip surface of the retaining boss 168. The inner ends of the locking recesses 169 do not reach the outer surface of the wall of the inner case element 44. The four locking recesses 169 are shaped to match the four corners of a rectangle. The thrust washer 166 is a metal plate with a substantially U-shaped cross section, with one end of two parallel legs connected by a connecting portion, and protrusions are formed at four positions on the outer surface of both ends of each leg. The four protrusions of the thrust washer are locked in the locking recesses 169 of the retaining boss 168, preventing it from rotating relative to the inner case element 44.

[0087] The inner end of the second axle 19 is secured to a retaining ring 167 in a retaining groove provided around the entire outer surface of the portion that passes through the thrust washer 166, thereby preventing the second axle 19 from coming loose from the first axle case 43.

[0088] Furthermore, a radial oil groove 170 that reaches both the inner and outer peripheral surfaces is formed in a circumferential portion of the tip surface of cylindrical portion 135 of second axle case 130, at a position that is below the oil level during use. As shown in Fig. 11, an axial oil groove 171 that extends axially toward the rear side of second axle case 130 is connected to the radially inner end of radial oil groove 170, and the rear end of axial oil groove 171 extends further rearward than stepped surface 163a of second axle case 130 and opens into second axle arrangement space S4, whose both axial ends are blocked by bushings within second axle case 130. When thrust washer 166 is engaged with retaining boss portion 168, the radially outer end of radial oil groove 170 is located in a position that is not covered by thrust washer 166. This allows the oil in the first axle case 43 to flow into the second axle arrangement space S4 through the radial oil grooves 170 and the axial oil grooves 171. Therefore, the oil in the first axle case 43 lubricates the rotation support portion of the second axle 19.

[0089] As described above, the thrust washer 166 is disposed between the side bevel gear 124, which is non-rotatably assembled to the second axle 19, and the inner case element 44, and the thrust washer 166 is prevented from rotating by the retaining boss portion 168. As a result, even when the side bevel gear 124 rotates in conjunction with the rotation of the electric motor 70 and an axial thrust force is applied to the side bevel gear 124, the thrust force of the side bevel gear 124 can be received by the thrust washer 166, which has high hardness. This prevents the side bevel gear 124 from coming into direct sliding contact with the inner case element 44. This allows the inner case element 44 to be formed from a low-hardness material such as aluminum or an aluminum alloy, while preventing the inner case element 44 from being scraped by the side bevel gear 124.

[0090] 6, two sets of radial oil grooves 170 and axial oil grooves 171 are formed at two positions symmetrical in the up-down direction on the tip surface of cylindrical portion 135 of second axle case 130. On the other hand, the upper set of oil grooves 170, 171 of the two sets may be omitted. When two sets of oil grooves 170, 171 are formed, they can be used by being inverted in the up-down direction so that the side on which motor case 50 of power transmission unit 41 is located is reversed in the left-right direction, and in that case, the upper set of oil grooves 170, 171 in FIG. 6 can be positioned below the oil level.

[0091] FIG. 13 is a perspective view showing a state immediately before a thrust washer 166 is attached to the inside of the outer case element 45 of the first axle case 43 and a retaining ring 167 is locked to the first axle 18. As shown in FIGS. 11 and 13, a retaining boss 172 is formed to protrude from the inner surface of the outer case element 45 facing the left side bevel gear 124. The retaining boss 172 has a cylindrical shape with protrusions having L-shaped cross-sectional corners at their tips protruding radially outward from four circumferential positions on the outer periphery. As a result, L-shaped cross-sectional corners protrude axially at four circumferential positions on the tip surface of the retaining boss 172, and locking recesses 173 with a substantially right-angled triangular cross section are formed inside the corners. The four locking recesses 173 are shaped to match the four corners of the rectangle.

[0092] A bushing 145 is provided between the inner peripheral surface of the inner end of the outer case element 45, including the retaining boss portion 172, and the first axle 18. The inner peripheral surface of the inner end of the outer case element 45 has a large-diameter cylindrical surface 174 formed thereon, the diameter of which is larger than that of the inner peripheral surface at the axial center. The bushing 145 is fitted into the large-diameter cylindrical surface 174. One axial end of the bushing 145 faces a stepped surface 174a formed on the inner side of the large-diameter cylindrical surface 174 in the tubular portion 49, thereby restricting axial movement of the bushing 145. As shown in FIG. 3 , two tapered surfaces 175a, 175b whose diameters decrease toward the axial middle are also formed on the inside of the tubular portion 49. Of the two bushings 145, 146 provided at both ends of the tubular portion 49, the outer diameter of the inner bushing 145 is slightly larger than the outer diameter of the outer bushing 146.

[0093] The portion of the inner end of the first axle 18 that protrudes axially inward beyond the bushing 145 passes through a thrust washer 166 and a retaining ring 167, and then is spline-fitted into the center hole of the left side bevel gear 124, thereby combining the first axle 18 with the side bevel gear 124 so that the side bevel gear 124 cannot rotate relative to the first axle 18. This also results in the thrust washer 166 being disposed between the side bevel gear 124 and the outer case element 45. The thrust washer 166 for the first axle 18 is similar to the thrust washer 166 for the second axle 19, and its rotation is prevented by the retaining boss portion 172 described above. The structure that allows oil in the first axle case 43 to flow to the first axle space S5 in the cylindrical portion 49 is similar to the structure on the second axle 19 side. This allows the outer case element 45 to be formed from a low-hardness material such as aluminum or an aluminum alloy, while preventing the outer case element 45 from being scraped by the side bevel gear 124 .

[0094] FIG. 14 is an enlarged view of the right side of FIG. 2 , showing the state immediately before the motor case 50 is attached to the first axle case 43. As shown in FIG. 14 , when attaching the motor case 50 to the first axle case 43, the motor case 50 is placed outside the front opening 46 of the first axle case 43 with the motor shaft 72, located inside the motor case 50, tilted relative to the input shaft 60 to avoid interference between the motor case 50 and the second axle case 130. From this state, the motor case 50 is moved closer to the inside of the front opening 46 while gradually reducing the tilt of the motor shaft 72 relative to the input shaft 60, and the fitting tubular portion 50b at the inner end of the motor case 50 is fitted into the front opening 46. With the motor case 50 fitted into the front opening 46, the motor case 50 is further pushed into the front opening 46 until the stepped surface 50d formed at the rear end of the fitting tubular portion 50b abuts against the first fixing surface 44a of the first axle case 43. Then, multiple bolts 59 (FIG. 2) that pass through the flange of motor case 50 are screwed into threaded holes formed in first axle case 43, thereby fixing motor case 50 to first axle case 43. In this state, part of motor case 50 fits into recess 137 formed in the portion of second axle case 130 that faces motor case 50. This allows electric motor 70 to be positioned closer to second axle 19 as described above, thereby enabling the power transmission unit 41 to be made more compact.

[0095] According to the power transmission unit 41 described above, the second axle case 130, which houses the second axle 19 on the same side as the electric motor 70 with respect to the center between the left and right axles 18, 19, is separably fixed to the first axle case 43, which houses the reduction gear mechanism 78, the differential gear mechanism 118, and the first axle 18. This eliminates the need to form the connecting portion between the axle case portion housing the second axle 19 and the gear cover portion in a single casting, so that even if the electric motor 70 is located close to the second axle 19, the first fixing surface 44a, which is the fixing surface for the motor case 50, can be formed on the first axle case 43 while ensuring the necessary mold configuration. This makes it possible to mold the case elements 44, 45 of the axle case 43, which houses the axles 18, 19 and the gear mechanism, by die casting, and also enables the power transmission unit 41 to be made smaller.

[0096] On the other hand, it is possible to form the connecting portion between the second axle case portion and the gear cover portion of the case in a single casting. In that case, however, strength is usually ensured by forming a curved surface with a large radius of curvature at the connecting portion. However, in this case, the presence of the curved surface makes it difficult to bring the fixing portion of the motor case close to the axle. According to the embodiment, this problem can be prevented.

[0097] Furthermore, first axle case 43 is fixed by screws between inner case element 44 on the electric motor 70 side and outer case element 45 on the opposite side from electric motor 70. As a result, even if first axle case 43 has a complex shape, inner and outer case elements 44, 45 can be easily formed by die casting, making it easy to form first axle case 43.

[0098] Furthermore, the outer case element 45 is integrally formed with a cylindrical portion 49, which is the axle case portion that houses the first axle 18, and a cover portion 140 that covers one axial end of the reduction gear mechanism 78. This reduces the number of parts that make up the axle case 42, thereby reducing the manufacturing cost of the power transmission unit 41.

[0099] Fig. 15 is a perspective view, with some parts separated, showing how a power transmission unit for a left wheel of another vehicle is formed using some of the parts that make up the power transmission unit of Fig. 2. Fig. 16 is a cross-sectional view of the power transmission unit for the left wheel shown in Fig. 15. Fig. 17 is a perspective view, with some parts omitted, showing how a power transmission unit for a right wheel of another vehicle is formed using some of the parts that make up the power transmission unit.

[0100] As shown in FIGS. 15 to 17, power transmission units 41a and 41b for left and right wheels of a vehicle according to another embodiment can be configured using some of the components of the power transmission unit 41 shown in FIGS. 1 to 14. In the vehicle according to the another embodiment, two electric motors 70 on the left and right sides independently drive the left and right wheels. In such a vehicle, for example, two control levers, one on each side of the driver's seat, are used as the acceleration command unit and the other on the right and left sides. The left and right control levers are configured to be swingable forward and backward around an axis extending in the left-right direction. By tilting each control lever forward, the corresponding electric motor 70 on the left or right side can be rotated in the forward direction, and by tilting each control lever backward, the corresponding electric motor 70 can be rotated in the reverse direction. By varying the forward swing positions of the left and right control levers, the vehicle can be made to turn.

[0101] 15 and 16, to configure a power transmission unit 41a for the left wheel, the second axle case 130 is removed from the power transmission unit 41 of FIGS. 1 to 14, and instead a cover member 180 is fixed to the first axle case 43 by threaded connection with bolts 59. As a result, the rear opening 47 of the first axle case 43 is closed by the cover member 180.

[0102] As shown in FIG. 16 , the cover member 180 has a cylindrical tubular portion 182 protruding from the inner surface of a rectangular plate-shaped cover main body 181. With the tubular portion 182 fitted into the rear opening 47, the cover main body 181 abuts against the second fixing surface 44b of the inner case element 44, and the cover member 180 is fixed to the inner case element 44 by a plurality of bolts 59 passing through the cover main body 181. The left axle 183 passes through the tubular portion 49 of the outer case element 45, and a wheel-fixing hub 184 is fixed to the portion protruding from the tubular portion 49. The left axle 183 is rotatably supported on the first axle case 43 by a bushing 185 provided on the inside of the outer end of the tubular portion 49 and a bushing 186 supported on the inner circumferential surface of the tubular portion 182 of the cover member 180. An output gear 187 is fixed to a portion of the left axle 183 that is disposed in the gear chamber so as not to rotate relative to the left axle 183. The output gear 187 meshes with the intermediate gear portion of the intermediate gear shaft 82. A reduction gear mechanism 78a is formed by the first bevel gear 79 provided on the input shaft 60, the second bevel gear 81 provided on the intermediate gear shaft 82, and the output gear 187 meshing with the intermediate gear portion. The power of the electric motor 70 is transmitted to the left axle 183 via the reduction gear mechanism 78a, and rotates a wheel fixed to a hub 184.

[0103] On the other hand, when configuring the power transmission unit for the right wheel shown in Fig. 17, the first axle case 43 is turned upside down in the power transmission unit for the left wheel 41a shown in Figs. 15 and 16. Then, the brake shaft, brake arm 95, and air breather device 117 are attached to the upper side of the turned-up first axle case 43. In addition, both ends of the intermediate gear shaft 82 (Fig. 10) are attached to the lower through-hole 84 (Fig. 5) and recess 151b (Fig. 7).

[0104] A right axle 188 for a right wheel is rotatably supported inside the first axle case 43, similar to the left wheel, and a hub 189 for fixing the right wheel is fixed to the portion of the right axle 188 that protrudes from the cylindrical portion 49 of the outer case element 45. Other configurations of the power transmission unit 41b for the right wheel are the same as those of the power transmission unit 41a for the left wheel shown in Figures 15 and 16. As a result, the power of the electric motor is transmitted to the right axle 188 via the motor shaft, input shaft, and reduction gear mechanism, causing the wheel fixed to the hub 189 to rotate.

[0105] In this way, according to the power transmission unit 41 shown in Figures 1 to 14, it is possible to use some of the parts to configure alternative power transmission units 41a, 41b for vehicles in which the left and right wheels can be driven independently by two electric motors 70, thereby reducing the manufacturing costs of the alternative power transmission units 41a, 41b.

[0106] In the above embodiment, the first helical gear 79, which is the input gear of the reduction gear mechanism, is provided on the input shaft 60, which is arranged coaxially with the motor shaft and is unable to rotate relative to it. However, the input shaft may be a shaft member formed integrally with the motor shaft, and the input gear may be provided radially outward of the motor shaft.

[0107] 10 Lawnmower vehicle, 12 Left wheel, 13 Right wheel, 14 Left wheel, 15 Right wheel, 16 Main frame, 17a, 17b Fixing member, 18 First axle, 19 Second axle, 20 Steering wheel, 21 Steering mechanism, 25 Lawnmower, 26 Mower deck, 27 Lawnmower blade, 28 Duct, 41 Power transmission unit for electric vehicle (power transmission unit), 42 Axle case, 43 First axle case, 44 Inner case element, 45 Outer case element, 46 Front opening, 47 Rear opening, 48 Opening, 49 Cylinder portion, 50 Motor case, 51, 52, 53 Bearing, 54 Seal, 55 Cover, 58, 59 Bolt, 60 Input shaft, 63 Hub, 70 Electric motor, 72 Motor shaft, 74 Connecting member, 75 Cylinder portion, 76 Brake rotor, 77 power transmission mechanism, 78, 78a reduction gear mechanism, 79 first helical gear, 81 second helical gear, 82 intermediate gear shaft, 83 intermediate gear portion, 84 through hole, 90 brake device, 91 braking force generating portion, 92 brake shoe, 93 brake pad, 94 brake shaft, 95 brake arm, 98 O-ring, 99 spring, 101 recess, 102 brake holder, 103 guide surface, 104 groove, 110, 110a through hole, 111 bolt, 113 first oil circulation port, 114 second oil circulation port, 115, 115a plug, 117 air breather device, 118 differential gear mechanism, 119 ring gear, 120 sleeve, 130 second axle case, 131 cylindrical portion, 132, 133 wall portion, 134 Plate portion, 135 cylindrical portion, 136 flange, 137 recess, 140 cover portion, 141, 142 wall portion, 143 plate portion, 144 opening, 145 to 148 bushing, 150 partition wall, 151 vertical wall, 152, 153 thrust receiving member, 154, 155 recess, 156a, 156b opening, 157 vertical hole, 158 horizontal hole, 159 oil check hole, 160 bolt, 161 permanent magnet, 162 locking groove, 163 large diameter cylindrical surface, 164 sealing member, 165a, 165b tapered surface, 166 thrust washer, 167 retaining ring, 168 retaining boss portion, 169 locking recess, 170 radial oil groove, 171 axial oil groove, 172 retaining boss portion, 173 Locking recess, 174 large diameter cylindrical surface, 180 cover member, 181 cover body, 182 cylindrical portion, 183 left axle, 184 hub, 185,186 bushing, 187 output gear, 188 right axle, 189 hub.

Claims

1. A power transmission unit for an electric vehicle in which power from an electric motor is transmitted to a first axle and a second axle separated into left and right axles via a reduction gear mechanism and a differential gear mechanism, a motor case that is disposed on the same side as the second axle in the left-right direction with respect to a center between the first axle and the second axle, and that houses the electric motor; a first axle case that accommodates the reduction gear mechanism, the differential gear mechanism, and the first axle; a second axle case detachably fixed to the first axle case and accommodating the second axle; a recess formed in a portion of the second axle case facing the motor case, A part of the motor case is fitted into the recess. Power transmission unit for electric vehicles.

2. 2. The power transmission unit for an electric vehicle according to claim 1, The first axle case is configured by fixing an inner case element on the electric motor side and an outer case element on the opposite side to the electric motor by screws. Power transmission unit for electric vehicles.

3. 3. The power transmission unit for an electric vehicle according to claim 2, The outer case element is formed integrally with an axle case portion in which the first axle is housed and a cover portion that covers one axial end of the reduction gear mechanism. Power transmission unit for electric vehicles.

4. 4. The power transmission unit for an electric vehicle according to claim 1, the electric motor has a motor shaft extending in a vehicle left-right direction parallel to an extension direction of the first axle and the second axle, the reduction gear mechanism includes an input gear provided on the motor shaft or an input shaft arranged coaxially with the motor shaft and unable to rotate relative to the motor shaft; an intermediate gear shaft provided with an intermediate gear that meshes with the input gear; an intermediate gear portion provided on the intermediate gear shaft and meshing with a ring gear provided on the outer periphery of the differential gear mechanism, the motor shaft is disposed at a different position with respect to the first axle and the second axle in a first direction perpendicular to the vehicle left-right direction, and at the same position with respect to a second direction perpendicular to the vehicle left-right direction and the first direction, the intermediate gear shaft is disposed at a different position in the second direction relative to the first axle, the second axle, and the motor shaft; Power transmission unit for electric vehicles.

5. 4. The power transmission unit for an electric vehicle according to claim 1, a thrust washer is disposed between the first axle case and a side bevel gear that is non-rotatably combined with the second axle; The thrust washer has a hardness greater than that of the first axle case, and rotation is prevented by a rib formed on the first axle case. Power transmission unit for electric vehicles.

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