JP2012241770A - Electric vehicle reduction differential gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric vehicle reduction differential gear including an electric motor, and a planetary gear type reduction gear and a differential gear, for improving the durability of constant velocity joints by shortening the distance between the motor side and differential side constant velocity joints disposed coaxially on both sides of the gear to reduce the mounting angles of the constant velocity joints.SOLUTION: An axial bearing hole 19 is provided in a stem 17b of a differential side outer ring 17 included in the differential side constant velocity joint, and an output shaft supporting bearing 22 exists between the end of an output shaft 15 inserted into the bearing hole 19 and the inner diameter face of the bearing hole 19.

Description

The present invention relates to a reduction gear differential for an electric vehicle using a motor as a drive source, and in particular, by reducing the length in the axial direction, the restriction on the layout of the vehicle is reduced, and the mounting angle of the constant velocity joint is reduced. By doing so, the durability of the constant velocity joint is improved.

  A conventionally known deceleration differential device for an electric vehicle is composed of a combination of an electric motor, a planetary gear type reduction device, and a planetary gear type differential device (Patent Documents 1 and 2). The speed reducer includes an input shaft integrated with a motor shaft of the electric motor, and the differential device receives a speed reduction output of the speed reducer as an input.

  In the differential device, the output is differentially distributed to the two distribution members of the sun gear and the carrier constituting the planetary gear mechanism, and one of the distribution members (the sun gear in the case of Patent Document 1 and the carrier in the case of Patent Document 2). The output shaft inserted and coupled to the center of the shaft passes through the inside of the reduction gear input shaft and the motor shaft integrated therewith in a coaxial state. The outer ring of the motor side constant velocity joint is connected to the tip of the output shaft. The outer ring of the differential side constant velocity joint is connected to the center of the other distribution member (the carrier in Patent Document 1 and the sun gear in Patent Document 2).

  Each of the outer rings is on the driving side of the left and right constant velocity joints, and a fixed mounting angle is provided between the inner ring and the inner member on the driven side. As for the mounting angle, if the distance from each joint to the corresponding wheel is constant, the distance between the motor-side and differential-side joints arranged on the left and right sides of the speed-reducing differential device becomes short. By reducing the joint attachment angle, the load load per joint rotation applied to each contact portion inside the joint is reduced, and the joint life is improved.

JP-A-8-42656 JP-A-6-323404

  However, in the case of Patent Document 1, in the differential side constant velocity joint, a bearing that supports the output shaft (the bearing 8D in FIG. 1 of Patent Document 1) and a bearing that supports the carrier (the bearing 8A in FIG. 1 also). Since there is a certain axial distance between the two, the distance is a factor that increases the axial distance between the constant velocity joints.

  In the case of Patent Document 2, the carrier of the differential device is coupled to the output shaft, and the sun gear is coupled to the differential side constant velocity joint. The sun gear is provided with a boss extending in the axial direction, and the boss has an extending portion extending further in the axial direction than the sun gear in order to ensure a certain length necessary for inserting the stem of the constant velocity joint. Provided. The stem of the constant velocity joint is inserted into the inner diameter surface of the extended portion and integrated. Therefore, the axial distance between the constant velocity joints is increased by the axial length of the extending portion.

  Therefore, the present invention improves the support structure of the constant velocity joint outer ring and further reduces the distance between the left and right constant velocity joints to reduce the mounting angle of each constant velocity joint, thereby An object is to improve durability.

  In order to solve the above-described problems, the present invention provides an electric motor, a planetary gear type reduction gear and a planetary gear type differential device arranged in a coaxial state, a casing housing each member, an output shaft, It consists of a combination of the outer ring of the motor side constant velocity joint and the outer ring of the differential side constant velocity joint arranged separately on the electric motor side and the differential device side, and the output shaft is arranged through the motor shaft of the electric motor Both ends thereof are supported by the casing via output shaft support bearings, the power of the electric motor is decelerated by the speed reducer and output to the differential device, and the decelerated driving force is loaded by the differential device. Is distributed to the two distribution members according to the size of the motor, and one distribution member is connected to the motor-side constant velocity joint via the output shaft. In the electric vehicle deceleration differential device, the other distribution member is connected to the outer ring of the differential side constant velocity joint, and an axial bearing hole is formed in the stem of the outer ring of the differential side constant velocity joint. The output shaft support bearing is interposed between an end portion of the output shaft inserted into the bearing hole and an inner diameter surface of the bearing hole.

  One of the two distribution members of the differential device is a differential sun gear constituting a differential planetary gear mechanism, and the other distribution member is connected to the pinion shaft of the planetary gear mechanism. It may be a carrier, and one end of the output shaft may be connected to the differential sun gear.

  In addition, the boss of the differential carrier is fitted and integrated with the stem outer diameter surface of the portion provided with the bearing hole, and the boss of the differential carrier and the stem are fitted and integrated by serration coupling. A configuration in which a differential-side carrier support bearing is interposed between the outer diameter surface of the boss of the differential-side carrier and the casing can be employed.

  As described above, according to the present invention, the output shaft support bearing on the differential side constant velocity joint side includes the output shaft end portion and the inner diameter surface of the bearing hole provided in the stem of the outer ring of the constant velocity joint. Since the structure is interposed, the distance between the left and right constant velocity joints can be shortened. As a result, the mounting angle of the constant velocity joint is reduced, and the durability of the constant velocity joint is improved.

  Further, by adopting a configuration in which the boss of the differential side carrier is fitted and integrated with the stem outer diameter surface of the portion provided with the bearing hole, the distance is further shortened, and the durability of the constant velocity joint is improved. Improvements can be made.

FIG. 1 is a cross-sectional view of the first embodiment. FIG. 2 is a partially enlarged sectional view of the above. 3 is a cross-sectional view taken along line X1-X1 of FIG. 4 is a cross-sectional view taken along line X2-X2 of FIG. FIG. 5 is a partially enlarged perspective view of the gear of the planetary gear mechanism.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
[Embodiment 1]

  As shown in FIGS. 1 and 2, the electric vehicle deceleration differential device according to the first embodiment includes an electric motor 11, a planetary gear type reduction device 12, and a planetary gear type differential device arranged in a coaxial state. 13, a casing 14 in which each member is housed, an output shaft 15, an outer ring 16 (hereinafter referred to as a motor-side outer ring 16) of a motor-side constant velocity joint disposed on the electric motor 11 side, and a differential device 13. The outer ring 17 (hereinafter referred to as the differential-side outer ring 17) of the differential-side constant velocity joint disposed on the side is formed.

  The motor-side outer ring 16 and the differential-side outer ring 17 have cups 16a and 17a and stems 16b and 17b, respectively, and the cups 16a and 17a and the stems 16b and 17b are separated by cup bottom plates 16c and 17c, respectively. The stem 16b is provided with a serration hole 18 penetrating in the axial direction, and the stem 17b is provided with a bearing hole 19 penetrating in the axial direction.

  The output shaft 15 is disposed through the hollow motor shaft 21 of the electric motor 11, and the end of the output shaft 15 on the electric motor 11 side is inserted into the serration hole 18 of the stem 16 b of the motor-side outer ring 16, They are connected together by serration coupling. The end of the output shaft 15 on the differential device 13 side is inserted into the bearing hole 19 of the stem 17 b of the differential outer ring 17. An output shaft support bearing 22 formed of a needle roller bearing is interposed between the insertion end of the output shaft 15 and the inner diameter surface of the stem 17b.

  The casing 14 is a combination of a motor casing 14 a that houses the electric motor 11, a reduction differential casing 14 b that houses the reduction gear 12 and the differential device 13, and a casing lid 14 c on the differential device 13 side.

The motor casing 14a and the deceleration differential casing 14b are each closed at one end and opened at the other end. The closed end of the speed reduction differential casing 14b is closely contacted and coupled to the open end of the motor casing 14a, and the casing lid 14c is closely contacted and coupled to the open end of the speed reduction differential casing 14b.
Note that the structure of the casing 14 is merely an example, and is not limited thereto, and may be a further divided structure.

  A shaft hole 23 is provided at the center of the closed end portion of the motor casing 14 a, and a boss 24 protruding in the axial direction is provided inside the shaft hole 23. One end of the motor shaft 21 is inserted into the inner diameter surface of the inner end of the boss 24, and a motor shaft support bearing 25 made of a deep groove ball bearing is interposed therebetween.

  A stem 16 b of the motor-side outer ring 16 is inserted into the outer open end of the boss 24, and an output shaft support shaft 26 formed of a deep groove ball bearing is interposed between the stem 16 b and the boss 24. An oil seal 27 is mounted between the stem 16b and the boss 24 along the outside of the output shaft support bearing 26 to seal the lubricating oil in the motor casing 14a.

  The electric motor 11 accommodated in the motor casing 14a includes a stator 28 fixed to the inner peripheral surface of the motor casing 14a and a rotor 29 integrally attached to the motor shaft 21 on the inner diameter side thereof. One end of the motor shaft 21 is supported by the motor shaft support bearing 25, and the other end is supported by a motor shaft support bearing 31 formed of a deep groove ball bearing interposed between the reduction differential casing 14b. An end portion of the motor shaft 21 protruding from the motor shaft support bearing 31 toward the reduction gear 12 is a reduction gear input shaft 30.

  In the reduction differential casing 14b, the reduction gear 12 and the differential device 13 are accommodated in a coaxial state sequentially from the closed end.

  The speed reducer 12 includes a speed reducing sun gear 35 (see FIGS. 2 and 3) integrally provided on the outer peripheral surface of the tip of the speed reducer input shaft 30, and an outer diameter side of the speed reducer 12 on the inner diameter surface of the speed reducing differential casing 14b. A reduction-side ring gear 36 fixed in a coaxial state, a reduction-side pinion gear 37 and a reduction-side carrier 38 (see FIG. 1 and FIG. 2) that are interposed at three equal intervals in the circumferential direction between the sun gear 35 and the ring gear 36. ). In this case, it is a type using three pinion gears 37, that is, a three-pinion type, but the number is not limited.

The reduction side pinion gear 37 meshes with the sun gear 35 and the ring gear 36. Also,
The pinion gear 37 is supported by a reduction-side pinion shaft 41 via a deep groove ball bearing 39 (see FIGS. 2 and 3). The pinion shaft 41 is provided with an oil passage hole 42 penetrating in the axial direction.

  As shown in FIG. 2, both end portions of the reduction side pinion shaft 41 are respectively supported by a reduction side carrier 38 and a disk portion 44 a of a differential side ring gear 44 described later.

  As shown in FIG. 2, the speed reducing carrier 38 is fitted between the closed end of the speed reducing differential casing 14 b and the speed reducing pinion gear 37 with a radial clearance around the speed reducer input shaft 30. Combined. A thrust bearing 43 is interposed between the deceleration side carrier 38 and the closed end.

  A plurality of coupling pieces 40 (see FIGS. 1 and 3) bent toward the differential device 13 are provided at a plurality of locations in the circumferential direction of the outer periphery of the deceleration side carrier 38. By inserting and fixing the coupling piece 40 into the ring gear disc portion 44a of the differential side ring gear 44, the reduction side carrier 38 and the differential side ring gear 44 are coupled and integrated.

  As shown in FIGS. 1, 2, and 4, the differential device 13 includes a differential side ring gear 44, a differential side sun gear 45 provided coaxially on the inner diameter side thereof, and the ring gear 44 and the sun gear 45. Double-pinion type differential-side pinion gears 46a, 46b that are interleaved with each other, differential-side pinion shafts 47a, 47b that support these pinion gears 46a, 46b, and differential-side that support these pinion shafts 47a, 47b It is constituted by a carrier 48.

  The differential side ring gear 44 is formed on a disk part 44a, a peripheral part 44b formed by bending the outer peripheral edge of the disk part 44a outward (toward the casing lid 14c), and an inner diameter surface of the peripheral part 44b. It is comprised by the made gear part 44c. The disc portion 44a is fitted and arranged in a coaxial state on the outer periphery of the output shaft 15 with a radial gap (see FIG. 2). A thrust bearing 63 is interposed between the disc portion 44 a and the differential-side sun gear 45.

The differential-side sun gear 45 is integrated with the output shaft 15 by serration coupling, with the output shaft 15 being inserted into a serration hole 50 provided at the center thereof. The distal end portion of the output shaft 15 protruding outward from the serration coupling portion is inserted into the stem 17b of the differential side outer ring 17. An output shaft support bearing 22 formed of a needle roller bearing is interposed between the distal end portion of the output shaft 15 and the inner diameter surface of the stem 17b. The portion of the stem 17b is supported by the casing lid 14c via a differential side carrier support bearing 54 described later. The differential-side sun gear 45 is provided with an axial oil passage hole 62.
The serration coupling part may be a spline coupling.

  The double pinion type pinion gears 46a and 46b are gears having the same number of teeth and the same size. As shown in FIG. 4, while meshing with each other, one pinion gear 46a has a larger PCD than the other pinion gear 46b, meshes with the ring gear 44, and a pinion gear 46b with a smaller PCD meshes with the sun gear 45. Needle roller bearings 58a and 58b are interposed between the pinion gears 46a and 46b and the pinion shafts 47a and 47b, respectively. Each pinion shaft 47a, 47b is provided with an oil supply hole 66.

  As shown in FIG. 2, the differential side carrier 48 is arranged along the inner surface of the casing lid 14 c, and the differential side carrier auxiliary member 49 is arranged along the disc portion 44 a of the differential side ring gear 44. The both ends of the pinion shafts 47a and 47b are supported between the two. At a plurality of locations on the outer peripheral edge of the differential side carrier 48, coupling protrusions 59 are provided toward the differential side carrier auxiliary member 49 side (see FIGS. 1 and 4), and are provided at the tips of the coupling protrusions 59. The small protrusion 60 is inserted and fixed in the coupling hole 61 of the differential side carrier auxiliary member 49. Thereby, the differential side carrier 48 and the differential side carrier auxiliary member 49 are coupled and integrated.

  The differential carrier 48 has a boss 51 protruding outward around the center hole, and the stem 17 b of the differential outer ring 17 is inserted into the boss 51. Serrations are provided on the outer diameter surface of the stem 17b and the inner diameter surface of the boss 51, respectively, and a serration coupling portion 52 is formed by firmly engaging both serrations so as to achieve integration by so-called mating. A thrust bearing 64 is interposed between the differential carrier 48 and the differential sun gear 45.

  A carrier support bearing 54 formed of a deep groove ball bearing is interposed between the boss 51 of the differential side carrier 48 and the boss 53 of the casing lid 14c, and the differential side carrier 48 and the differential side outer ring 17 are connected to the casing lid 14c. To support.

  The holding ring 55 of the carrier support bearing 54 is fixed to the outer surface of the boss 53 of the casing lid 14c by a bolt 56. An oil seal 57 is mounted between the pressing ring 55 and the stem 17b, and seals the lubricating oil in the deceleration differential casing 14b.

  The electric vehicle deceleration differential apparatus of Embodiment 1 is configured as described above, and the operation thereof will be described next.

  When the electric motor 11 (see FIG. 1) is driven, the motor shaft 21 rotates, and at the same time, the speed reducer input shaft 30 integral with the motor shaft 21 and the reduction-side sun gear 35 integral with the input shaft 30 rotate. . The reduction-side pinion gear 37 engaged with the reduction-side sun gear 35 revolves while rotating. Due to the revolution, the deceleration side carrier 38 is decelerated and rotated, and the decelerated rotation is output to the differential side ring gear 44 on the differential device 13 side.

  As is well known, the reduction ratio is Zs / (Zs + Zr) where the number of teeth of the reduction-side sun gear 35 is Zs and the number of teeth of the reduction-side ring gear 36 is Zr.

  The load on one wheel of the vehicle is applied to the differential sun gear 45 via the motor side constant velocity joint including the motor side outer ring 16 and the output shaft 15, and the load on the other wheel includes the differential side outer ring 17. It is applied to the differential side carrier 48 through the differential side constant velocity joint. When the loads acting on both wheels are equal, the differential sun gear 45, the pinion gears 46a and 46b, and the carrier 48 rotate together with the input rotation of the ring gear 44 and do not rotate relative to each other. . For this reason, the input rotation is evenly distributed to the motor-side outer ring 16 and the differential-side outer ring 17, and the left and right wheels are rotated at the same speed through the respective constant velocity joints.

  On the other hand, when a difference occurs in the load acting on the left and right wheels, the input rotation is caused by the rotation and revolution of the pinion gears 46a and 46b. Is distributed differentially.

That is, when the load acting on the output shaft 15 through the motor-side outer ring 16 becomes relatively large and the rotational speed Ns of the sun gear 45 integrated therewith is smaller than the input rotational speed Nr of the ring gear 44 by ΔN, the carrier 48 The rotational speed Nc of
Nc = Nr + λ / (1-λ) · ΔN
Thus, the speed of the carrier 48 and the differential-side outer ring 17 integrated therewith is increased. Where λ is the gear ratio (= Zs / Zr), Zs is the number of teeth of the sun gear 45, and Zr is the number of teeth of the ring gear 44.

On the contrary, when the load acting on the differential-side outer ring 17 becomes relatively large and the rotation speed Nc of the carrier 48 integrated therewith is smaller than the input rotation speed Nr by ΔN, the rotation speed Ns of the sun gear 45 is ,
Ns = Nr + (1-λ) / λ · ΔN
Thus, the output shaft 15 is accelerated.

  Oil bath lubrication is adopted as the lubrication method of the electric vehicle speed-reducing differential gear according to the first embodiment described above. That is, in the casing 14, the lubricating oil common to the motor casing 14a and the deceleration differential casing 14b is stored up to the position indicated by the oil level L. The stator 28 of the electric motor 11 is immersed in the oil level L, but the rotor 29 is prevented from being immersed. In this way, even if the rotor 29 rotates, the lubricant is not stirred by the rotor 29, and loss due to stirring can be reduced.

  In the speed reducer 12, the coupling piece 40 and the speed reduction pinion gear 37 provided on the outer periphery of the speed reduction side carrier 38 pass through the oil below the oil level L of the lubricating oil in the middle of rotation, thereby Performs scraping action. The scraped up lubricating oil is scattered inside the speed reducer 12 and applied to each component. A part thereof passes through the oil passage hole 42 of the deceleration side pinion shaft 41 and moves in the axial direction.

  In the differential device 13, the coupling protrusion 59 provided on the outer peripheral portion of the differential side carrier 48, the differential side pinion gears 46 a and 46 b, and the like perform a scraping action of the lubricating oil. The scraped lubricating oil is scattered inside the differential 13 and applied to each component. A part of the oil passes through an oil passage hole 62 provided in the differential-side sun gear 45 and moves in the axial direction.

  During the operation, the lubricating oil is prevented from leaking out of the casing 14 by the oil seals 27 and 57 at the two left and right positions. Further, inside the casing 14, the lubricating oil accumulated in the motor casing 14a and the reduction differential casing 14b goes back and forth through a communication hole 65 provided in the blocking wall of the reduction differential casing 14b.

  According to the oil bath lubrication described above, not only the lubrication to the bearing portion, but also the meshing portion of various gears, but in order to further improve the lubricity of the gear tooth surface, It is effective to perform such rough surface processing.

  That is, in the gears constituting the planetary gear mechanism of the speed reducer 12 and the differential device 13, as shown in FIG. Innumerable minute depressions 75 are randomly provided on the bottom 74.

  The surface roughness parameters of the tooth surface 71 are set such that Ryni is 2.0 to 5.5 μm, Rymax is 2.5 to 7.0 μm, Rqni is 0.3 to 1.1 μm, and Rsk is 1.6 or less. The

  Since the minute depression 75 becomes an oil reservoir, sufficient durability can be maintained even in the case of oil bath lubrication. As a result, the gear itself can be reduced in size and the entire apparatus can be reduced in size.

  The roughening is preferably performed on the tooth surface of the smallest diameter gear among the planetary gear mechanisms of the speed reducer 12 and the differential unit 13. The sun gear 35 in the speed reducer 12 and the differential-side pinion gears 46a and 46b in the differential device 13 are smaller than the other gears and increase in the number of loads. Is effective. In some cases, it may be better to apply both to the sun gear 35 and the pinion gears 46a and 46b.

  In order to form the minute recesses 75 at random, the tooth surface 71 is smoothed by gyro polishing, barrel polishing, or the like, and then a recess forming means is applied to the smoothed tooth surface. In this case, the recess formation means is performed by a method in which fine hard particles mainly composed of aluminum oxide or the like are collided by shot peening, liquid honing, or the like.

DESCRIPTION OF SYMBOLS 11 Electric motor 12 Reducer 13 Differential device 14 Casing 14a Motor casing 14b Deceleration differential casing 14c Casing lid 15 Output shaft 16 Motor side outer ring 16a Cup 16b Stem 16c Cup bottom plate 17 Differential side outer ring 17a Cup 17b Stem 17c Cup bottom plate 18 Serration hole 19 Bearing hole 21 Motor shaft 22 Output shaft support bearing 23 Shaft hole 24 Boss 25 Motor shaft support bearing 26 Output shaft support bearing 27 Oil seal 28 Stator 29 Rotor 30 Reducer input shaft 31 Motor shaft support bearing 35 Reduction side sun gear 36 Reduction side ring gear 37 Reduction side pinion gear 38 Reduction side carrier 39 Deep groove ball bearing 40 Connecting piece 41 Reduction side pinion shaft 42 Oil passage hole 43 Thrust bearing 44 differential side ring gear 44a disc part 44b peripheral edge part 44c gear part 45 differential side sun gears 46a, 46b differential side pinion gears 47a, 47b differential side pinion shaft 48 differential side carrier 49 differential side carrier auxiliary member 50 serration hole 51 boss 52 serration coupling portion 53 boss 54 differential side carrier support bearing 55 holding ring 56 bolt 57 oil seal 58a, 58b needle roller bearing 59 coupling projection 60 small projection 61 coupling hole 62 oil passage hole 63 thrust bearing 64 thrust bearing 65 Communication hole 66 Lubrication hole 71 Tooth surface 72 Tooth tip part 73 Tooth part 74 Tooth bottom part 75 Indentation

Claims (11)

  Coaxially arranged electric motor, planetary gear type reduction gear and planetary gear type differential device, casing housing each member, output shaft, electric motor side and differential device side. The outer ring of the motor-side constant velocity joint and the outer ring of the differential-side constant velocity joint, and the output shaft is disposed through the motor shaft of the electric motor, and both ends thereof are arranged via the output shaft support bearing. Supported by the casing, the power of the electric motor is decelerated by the speed reducer and output to the differential device, and the decelerated driving force is differentially distributed according to the size of the load in the differential device. One distribution member is connected to the outer ring of the motor side constant velocity joint via the output shaft, and the other distribution member is output to the differential member. In the reduction differential for an electric vehicle connected to the outer ring of the constant velocity joint, an axial bearing hole is provided in the stem of the outer ring of the differential side constant velocity joint, and the output shaft inserted into the bearing hole The reduction differential for an electric vehicle, wherein the output shaft support bearing is interposed between an end portion and an inner diameter surface of the bearing hole.   One of the two distribution members of the differential device is a differential sun gear constituting a differential planetary gear mechanism, and the other distribution member is connected to the pinion shaft of the planetary gear mechanism. 2. The reduction differential device for an electric vehicle according to claim 1, wherein the output differential shaft is a carrier, and one end of the output shaft is connected to the differential-side sun gear.   3. A reduction differential for an electric vehicle according to claim 1, wherein a boss of the differential carrier is fitted and integrated with a stem outer diameter surface of a portion provided with the bearing hole.   The electric vehicle deceleration differential device according to claim 3, wherein the boss of the differential side carrier and the stem are fitted and integrated by serration coupling.   5. The reduction differential for an electric vehicle according to claim 1, wherein a differential-side carrier support bearing is interposed between an outer diameter surface of a boss of the differential-side carrier and the casing. apparatus.   An axial serration hole is provided in the stem of the outer ring of the motor side constant velocity joint, and the end of the output shaft inserted into the serration hole and the stem are integrated by serration coupling, and the stem and the casing 6. An electric vehicle deceleration differential apparatus according to claim 1, wherein an output shaft support bearing is interposed between the two.   The speed-reduction differential device for an electric vehicle according to claim 6, wherein an oil seal is interposed between the stem and the casing outside in the axial direction of the other output shaft support bearing.   The gear teeth constituting the planetary gear mechanism of the speed reducer and differential gear are randomly provided with an infinite number of minute concave recesses, and the surface roughness parameter of this surface is set to Ryni of 2.0 to 5.5 μm. Rymax is set to 2.5 to 7.0 [mu] m, Rqni is set to 0.3 to 1.1 [mu] m, and Rsk is set to 1.6 or less, The electric vehicle deceleration according to any one of claims 1 to 7 Differential device.   9. The reduction differential for an electric vehicle according to claim 8, wherein the minute concave recess is provided at least on a tooth surface of a gear having the smallest diameter among the planetary gear mechanisms of the reduction gear.   9. The reduction differential for an electric vehicle according to claim 8, wherein the minute concave recess is provided on a tooth surface of a gear having the smallest diameter in at least a planetary gear mechanism of the differential. The tooth surface is smoothed by gyro-polishing, and the innumerable recesses are randomly formed on the smoothed tooth surfaces by a recess forming means for colliding fine hard particles mainly composed of aluminum oxide. The reduction | decrease differential apparatus for electric vehicles of Claim 9 or 10.

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