Patent Description:
In an in-wheel motor drive device, a speed reducer is used for downsizing of a motor, thereby being capable of achieving downsizing and reduction in weight of the in-wheel motor drive device as a whole and reduction in unsprung weight. This is because of the following reason. Output torque of the motor is proportional to a size and a weight of the motor. Thus, in order to generate torque which is required for drive of a vehicle solely by a motor, a motor having a large size is required. However, the weight and volume of the motor which are reduced through use of the speed reducer exceed those of the speed reducer.

For example, in Patent Literature <NUM> described below, there is disclosed an in-wheel motor drive device including a two-shaft one-stage parallel shaft gear speed reducer. This speed reducer includes an input gear and an output gear. The input gear rotates integrally with a rotation shaft of a motor. The output gear meshes with the input gear and rotates integrally with a rotation ring of a wheel bearing.

Moreover, in Patent Literature <NUM> described below, there is disclosed an in-wheel motor drive device including a three-shaft two-stage parallel shaft gear speed reducer. This speed reducer includes an intermediate shaft. The intermediate shaft is arranged between an input gear and an output gear, and includes a first counter gear and a second counter gear. The input gear and the first counter gear form a gear train on an input side, and the output gear and the second counter gear form a gear train on an output side. Rotation of the motor is reduced in speed through intermediation of those gear trains in two stages. Patent Literature <NUM> discloses the preamble of claim <NUM>.

In the two-shaft one-stage parallel shaft gear speed reducer disclosed in Patent Literature <NUM> described above, in order to increase a speed reduction ratio thereof, it is required that a pitch circle diameter of the output gear be set larger than a pitch circle diameter of the input gear. When the pitch circle diameter of the output gear is set larger as described above, the input gear meshing with the output gear is arranged with large offset with respect to a wheel center. As a result, a stator portion of the motor arranged coaxially with the input gear protrudes on a radially outer side with respect to a space on an inner periphery of the wheel (hereinafter referred to as "wheel inner space"), and there is a fear in that the in-wheel motor drive device interferes with a vehicle body or suspension parts. Moreover, a lower arm ball joint configured to mount the in-wheel motor drive device to the vehicle body is generally mounted to a lower part of the in-wheel motor drive device. However, when the output gear becomes larger, a housing configured to accommodate the speed reducer also becomes larger. Therefore, a space below the housing becomes narrower, with the result that it becomes more difficult to provide a mounting point for the lower arm ball joint.

As a result, in order to avoid interference of the in-wheel motor drive device with the vehicle body or the suspension parts, the motor cannot be increased in size, and hence there is a fear in that motive power becomes insufficient. Moreover, in order to avoid the interference described above, limitation is added to the shapes of the suspension parts. As a result, there is a fear in that defects such as increase in weight and degradation in strength of the suspension parts or decrease in minimum ground clearance occur. Further, in order to avoid the interference described above, design change on the vehicle body side may be required. As a result, there is a fear in that the motion performance of the vehicle is degraded or standardization of the vehicle body is hindered.

Meanwhile, in the three-shaft two-stage parallel shaft gear speed reducer disclosed in Patent Literature <NUM> described above, the counter gear is interposed between the input gear and the output gear, thereby being capable of increasing the speed reduction ratio while suppressing the pitch circle diameter of the output gear. However, in some cases, there is a difficulty in sufficiently suppressing the pitch circle diameter of the output gear while achieving a high speed reduction ratio by simply increasing the number of gear trains of the parallel shaft gear speed reducer.

Therefore, the present invention has an object to prevent interference of an in-wheel motor drive device with a vehicle body or suspension parts by compactizing the in-wheel motor drive device through sufficient suppression of a pitch circle diameter of an output gear while achieving a high speed reduction ratio.

According to the present invention, which has been devised to achieve the above-mentioned object, there is provided an in-wheel motor drive device as defined in claim <NUM>.

Through the interposition of the intermediate gear between the input gear and the output gear as described above, a pitch circle diameter of the output gear can be suppressed while maintaining a large speed reduction ratio. Therefore, an amount of offset of the motor with respect to a wheel center is suppressed, thereby being capable of reducing the size of the in-wheel motor drive device in a direction orthogonal to the axial direction. Further, according to the present invention, the circumscribed circle of the large-diameter intermediate gear is increased in diameter to such an extent that the circumscribed circle is superimposed with the pitch circle of the plurality of rolling elements of the wheel bearing, when viewed in the axial direction. With this, a speed reduction ratio of a gear train comprising the large-diameter intermediate gear increases, thereby being capable of further suppressing the pitch circle diameter of the output gear while maintaining the large speed reduction ratio of the speed reducer as a whole.

It is preferred that the speed reducer comprise gear trains each formed of gears in mesh with each other and the gear trains each have a speed reduction ratio of equal to or larger than <NUM> and equal to or smaller than <NUM>. When the speed reduction ratio of any one of the gear trains is less than <NUM>, a desired speed reduction ratio cannot be achieved, or a pitch circle diameter of a driven gear of another gear train becomes excessively larger. Moreover, when the speed reduction ratio of any one of the gear trains exceeds <NUM>, an undercut is liable to occur in a gear of the gear train on a pinion side, and there arises a problem such as degradation in strength of the gear or vibrations caused thereby.

According to the invention, the large-diameter intermediate gear has a pitch circle diameter which is smaller than a pitch circle diameter of the output gear, the interference between the large-diameter intermediate gear and the speed reducer output shaft can be more easily avoided.

In the in-wheel motor drive device described above, it is preferred that the speed reducer input shaft and the speed reducer output shaft be arranged close to each other. According to the invention, the speed reducer is formed of a three-shaft two-stage parallel shaft gear speed reducer comprising the large-diameter intermediate gear and the input gear in mesh with each other. It is preferred that an angle formed between a line connecting a center of the speed reducer input shaft and a center of the intermediate shaft and a line connecting a center of the speed reducer output shaft and the center of the intermediate shaft be equal to or smaller than <NUM>°. With this, an amount of offset of the speed reducer input shaft with respect to the speed reducer output shaft, that is, the amount of offset of the motor with respect to the wheel center is suppressed, thereby being capable of more easily accommodating the motor in a radial region of a wheel inner space.

The wheel bearing may be, for example, a wheel bearing of an inner-ring rotation type.

As described above , according to the in-wheel motor drive device of the present invention, the in-wheel motor drive device can be compactized through sufficient suppression of the pitch circle diameter of the output gear while achieving the high speed reduction ratio. Therefore, interference of the in-wheel motor drive device with the vehicle body or suspension parts can be prevented.

An in-wheel motor drive device according to one embodiment of the present invention is described in detail with reference to the drawings.

As illustrated in <FIG>, an electric vehicle <NUM> comprises a chassis <NUM>, front wheels <NUM> serving as steered wheels, rear wheels <NUM> serving as driving wheels, and in-wheel motor drive devices <NUM> configured to transmit driving force to the rear wheels <NUM>. As illustrated in <FIG>, each rear wheel <NUM> and each in-wheel motor drive device <NUM> are accommodated inside a wheel housing <NUM> of the chassis <NUM> and fixed below the chassis <NUM> via a suspension device (suspension) <NUM>.

In the suspension device <NUM>, horizontally extending suspension arms are configured to support the rear wheels <NUM>, and a strut comprising a coil spring and a shock absorber is configured to absorb vibrations that each rear wheel <NUM> receives from the ground to suppress the vibrations of the chassis <NUM>. In addition, a stabilizer configured to suppress tilting of a vehicle body during turning and other operations is provided at connecting portions of the right and left suspension arms. In order to improve a property of following irregularities of a road surface to transmit the driving force of the rear wheels <NUM> to the road surface efficiently, the suspension device <NUM> is an independent suspension type capable of independently moving the right and left wheels up and down.

The electric vehicle <NUM> does not need to comprise a motor, a drive shaft, a differential gear mechanism, and other components on the chassis <NUM> because the in-wheel motor drive devices <NUM> configured to drive the right and left rear wheels <NUM>, respectively, are arranged inside the wheel housings <NUM>. Accordingly, the electric vehicle <NUM> has advantages in that a large passenger compartment space can be provided and that rotation of the right and left rear wheels <NUM> can be controlled, respectively.

Prior to the description of a characteristic configuration of this embodiment, an overall configuration of the in-wheel motor drive device <NUM> is described with reference to <FIG>. In the following description, under a state in which the in-wheel motor drive device <NUM> is mounted to the vehicle body, a side closer to an outer side of the vehicle body is referred to as "out-board side" (left side in <FIG>), and a side closer to a center of the vehicle body is referred to as "in-board side" (right side in <FIG>).

The in-wheel motor drive device <NUM> comprises a drive section A configured to generate driving force, a speed reduction section B configured to reduce a speed of rotation of the drive section A to output the rotation, and a bearing section C configured to transmit the output from the speed reduction section B to the wheels serving as driving wheels. The drive section A, the speed reduction section B, and the bearing section C are accommodated in a housing <NUM>. The housing <NUM> may have a unified structure as illustrated in <FIG>, or may have a dividable structure.

The drive section A is a radial gap type electric motor <NUM> comprising a stator <NUM> fixed to the housing <NUM>, a rotor <NUM> arranged on a radially inner side of the stator <NUM> at an opposed position with a gap, and a motor rotation shaft <NUM>, which is arranged on a radially inner side of the rotor <NUM> so as to rotate integrally with the rotor <NUM>. The motor rotation shaft <NUM> is rotatable at high speed of ten thousand rotations or more per minute. The stator <NUM> is formed by winding a coil around an outer periphery of a magnetic core, and the rotor <NUM> is formed of a magnetic body such as a permanent magnet. The motor rotation shaft <NUM> is supported at its in-board-side end portion by a rolling bearing <NUM> and at its out-board-side end portion by a rolling bearing <NUM> so as to be freely rotatable with respect to the housing <NUM>.

The speed reduction section B is formed of a three-shaft two-stage parallel shaft gear speed reducer <NUM> comprising a speed reducer input shaft Sin, an intermediate shaft Sm, and a speed reducer output shaft Sout. The speed reducer input shaft Sin integrally comprises an input gear <NUM>. The intermediate shaft Sm integrally comprises a large-diameter intermediate gear <NUM> and a small-diameter intermediate gear <NUM>. The speed reducer output shaft Sout integrally comprises an output gear <NUM>. The large-diameter intermediate gear <NUM> and the small-diameter intermediate gear <NUM> are provided integrally and coaxially with each other. The input gear <NUM> and the large-diameter intermediate gear <NUM> mesh with each other to form a gear train G1 on the input side. The input gear <NUM> is a drive gear of the gear train G1 on the input side. The input gear <NUM> has a pitch circle diameter smaller than that of the large-diameter intermediate gear <NUM>, and has the smaller number of teeth. Moreover, the small-diameter intermediate gear <NUM> and the output gear <NUM> mesh with each other to form a gear train G2 on the output side. The small-diameter intermediate gear <NUM> is a drive gear of the gear train G2 on the output side. The small-diameter intermediate gear <NUM> has a pitch circle diameter smaller than that of the output gear <NUM>, and has the smaller number of teeth. The gear trains G1 and G2 each have a speed reduction ratio of equal to or larger than <NUM> and equal to or smaller than <NUM>. Values of the speed reduction ratios of the gear trains G1 and G2 are set relatively close to each other. For example, a ratio of the speed reduction ratios of the gear trains G1 and G2 is set to equal to or larger than <NUM> and equal to or smaller than <NUM>, preferably, equal to or larger than <NUM> and equal to or smaller than <NUM>. Through intermediation of the gear trains G1 and G2 in two stages, a rotary motion of the motor rotation shaft <NUM> is reduced in speed with a predetermined speed reduction ratio.

The speed reducer input shaft Sin is coaxially mounted to the motor rotation shaft <NUM> on the out-board side by spline fitting. The speed reducer input shaft Sin is supported at its both ends by rolling bearings <NUM> and <NUM> on both sides of the input gear <NUM> in the axial direction. In the illustrated example, the in-board-side end portion of the speed reducer input shaft Sin is supported on the housing <NUM> by the rolling bearing <NUM> so as to be freely rotatable, and the out-board-side end portion of the speed reducer input shaft Sin is supported on the housing <NUM> by the rolling bearing <NUM> so as to be freely rotatable. The speed reducer input shaft Sin may be formed integrally with the motor rotation shaft <NUM>. In this case, any one of the bearing <NUM> configured to support the out-board-side end portion of the motor rotation shaft <NUM> and the bearing <NUM> configured to support the in-board-side end portion of the speed reducer input shaft Sin may be omitted.

The intermediate shaft Sm is supported at its in-board-side end portion on the housing <NUM> by a rolling bearing <NUM> so as to be freely rotatable, and is supported at its out-board-side end portion on the housing <NUM> by a rolling bearing <NUM> so as to be freely rotatable.

The speed reducer output shaft Sout comprises a main body portion <NUM> and a connection portion <NUM>. The main body portion <NUM> comprises the output gear <NUM>. The connection portion <NUM> is provided integrally with the main body portion <NUM> on the out-board side. The speed reducer output shaft Sout is supported on the housing <NUM> by rolling bearings <NUM> and <NUM> so as to be freely rotatable. In the illustrated example, both ends of the main body portion <NUM> of the speed reducer output shaft Sout in the axial direction are supported by the rolling bearings <NUM> and <NUM>. With this, the speed reducer output shaft Sout which bears large torque can be supported with a sufficient bearing span while preventing interference of the rolling bearing <NUM> with the large-diameter intermediate gear <NUM>, thereby being capable of obtaining high support rigidity.

In this embodiment, helical gears are used as the gears <NUM> to <NUM> forming the parallel shaft gear speed reducer <NUM>. With the helical gears, the number of teeth which are simultaneously in mesh becomes larger, and teeth contact is dispersed. Therefore, the helical gears are effective in quietness and less torque fluctuation. In consideration of a meshing ratio and a limit rotation number of the gears, it is preferred that modules of the gears be set to from <NUM> to <NUM>.

The bearing section C is formed of a wheel bearing <NUM> of an inner-ring rotation type. The wheel bearing <NUM> is a double-row angular contact ball bearing mainly comprising an outer ring <NUM>, an inner member (rotation ring), a plurality of rolling elements <NUM>, and a retainer. The outer ring <NUM> is fixed to the housing <NUM> and serves as an outer member (fixed ring). The inner member is arranged on an inner periphery of the outer ring <NUM>. The plurality of rolling elements <NUM> are arranged between the inner member and the outer ring <NUM>. The retainer is configured to retain the rolling elements <NUM>. In the illustrated example, the inner member comprises a hub ring <NUM> and an inner ring <NUM> press-fitted to an outer periphery of the hub ring <NUM>. A raceway surface is formed on an outer peripheral surface of each of the hub ring <NUM> and the inner ring <NUM>. Double-row raceway surfaces are formed on an inner peripheral surface of the outer ring <NUM>. The hub ring <NUM> integrally comprises a flange 40a. A brake rotor and a wheel are connected to the flange 40a by hub bolts.

The connection portion <NUM> of the speed reducer output shaft Sout is connected to the rotation ring of the wheel bearing <NUM>. In this embodiment, the connection portion <NUM> of the speed reducer output shaft Sout is inserted along an inner periphery of the hub ring <NUM> of the wheel bearing <NUM> so that the connection portion <NUM> and the hub ring <NUM> of the wheel bearing <NUM> are connected to each other by spline fitting in a torque-transmittable manner. The fitting of the spline fitting portion connecting between the connection portion <NUM> of the speed reducer output shaft Sout and the hub ring <NUM> of the wheel bearing <NUM> is in a state of clearance fitting in which a gap is defined between tooth surfaces opposed to each other and between tooth bottoms and tooth tops opposed to each other so that the hub ring <NUM> and the speed reducer output shaft Sout are slightly movable relative to each other in the radial direction. With this, vibrations that each wheel receives from the ground are absorbed by the gap in the spline fitting portion, thereby being capable of suppressing vibrations received by the parallel shaft gear speed reducer <NUM> and the motor <NUM>.

Grease is interposed between opposed tooth surfaces in the spline fitting portion of the connection portion <NUM> of the speed reducer output shaft Sout and the hub ring <NUM> of the wheel bearing <NUM>. For example, when the grease is applied to one or both of splines of the connection portion <NUM> of the speed reducer output shaft Sout and the hub ring <NUM> and thereafter the connection portion <NUM> of the speed reducer output shaft Sout is inserted along the inner periphery of the hub ring <NUM>, the grease is interposed between the tooth surfaces in the spline fitting portion. Moreover, the grease is interposed also between the raceway surface of the outer ring <NUM> of the wheel bearing <NUM> and the rolling elements <NUM> and between the hub ring <NUM> or the raceway surface of the inner ring <NUM> and the rolling elements <NUM>.

Meanwhile, lubricating oil is sealed inside the housing <NUM>. At the time of drive of the in-wheel motor drive device <NUM>, the lubricating oil in the housing <NUM> is pumped by an oil pump (for example, rotary pump) (not shown), and thus is fed to the bearings and gears. With this, the bearings and gears are cooled and lubricated. The space in which the lubricating oil is sealed and the space in which the grease is sealed, are partitioned by a sealing device (not shown) provided at the out-board-side end portion of the rolling bearing <NUM>.

The in-wheel motor drive device <NUM> is accommodated inside the wheel housing <NUM> (see <FIG>), and thus becomes unsprung load. Therefore, downsizing and reduction in weight thereof are required. Thus, through combination of the parallel shaft gear speed reducer <NUM> and the motor <NUM>, the small-sized motor <NUM> with low torque and high-speed rotation can be used. For example, in a case in which the parallel shaft gear speed reducer <NUM> having a speed reduction ratio of <NUM> is used, the small-sizedmotor <NUM> with high-speed rotation of about ten and several thousand rotations per minute can be used. As described above, through downsizing of the motor <NUM>, the compact in-wheel motor drive device <NUM> can be achieved. As a result, the unsprung weight is suppressed, thereby being capable of obtaining the electric vehicle <NUM> which is excellent in traveling stability and NVH characteristics.

Next, the characteristic configuration of the in-wheel motor drive device <NUM> according to this embodiment, in particular, arrangement of members forming the parallel shaft gear speed reducer <NUM> is described in detail with reference to <FIG> and <FIG>. The reference symbol M given in <FIG> denotes a radially outer end of the wheel inner space.

As illustrated in <FIG>, the in-wheel motor drive device <NUM> is accommodated in a radial region of the wheel inner space M. The speed reducer input shaft Sin and the speed reducer output shaft Sout of the parallel shaft gear speed reducer <NUM> are arranged with offset in the direction orthogonal to the axial direction. In the illustrated example, the speed reducer input shaft Sin, the intermediate shaft Sm, and the speed reducer output shaft Sout are arranged so as to form a triangular shape when viewed from the axial direction. More specifically, the speed reducer output shaft Sout and the speed reducer input shaft Sin are provided at substantially the same height, and the intermediate shaft Sm is provided above the speed reducer output shaft Sout and the speed reducer input shaft Sin. As described above, when the speed reducer input shaft Sin and the speed reducer output shaft Sout are arranged with offset in the direction orthogonal to the axial direction, at least a part of the speed reducer input shaft Sin in the axial direction can be arranged in an axial region of the speed reducer output shaft Sout (see <FIG>). In the illustrated example, the entire axial region of the speed reducer input shaft Sin is arranged in the axial region of the speed reducer output shaft Sout. Through the superimposition of the axial regions of the speed reducer input shaft Sin and the speed reducer output shaft Sout as described above, an axial dimension of the in-wheel motor drive device <NUM> is reduced, and hence a projection amount of the in-wheel motor drive device <NUM> from the wheel inner space M toward the in-board side can be suppressed, thereby being capable of avoiding interference with the vehicle body and the suspension device.

Moreover, in the three-shaft two-stage parallel shaft gear speed reducer <NUM>, the intermediate shaft Sm comprising the large-diameter intermediate gear <NUM> and the small-diameter intermediate gear <NUM> is provided between the speed reducer input shaft Sin and the speed reducer output shaft Sout. Therefore, the speed reduction ratio can be increased while suppressing a pitch circle diameter (outer diameter) of the output gear <NUM>. Inparticular, in this embodiment, as illustrated in <FIG>, the large-diameter intermediate gear <NUM> is increased in diameter to such a limit that a circumscribed circle (radially outermost portion) of the large-diameter intermediate gear <NUM> is superimposed with a pitch circle P of the rolling elements <NUM> of the wheel bearing <NUM>, that is, a cylindrical plane passing through centers of the rolling elements <NUM> when viewed from the axial direction. With this, the speed reduction ratio of equal to or larger than <NUM> is achieved while suppressing the pitch circle diameter of the output gear <NUM>.

As illustrated in <FIG>, the speed reducer input shaft Sin is arranged with offset with respect to a wheel center <NUM> to avoid the interference with the output gear <NUM>. On this occasion, the pitch circle diameter of the output gear <NUM> is suppressed as described above, thereby being capable of suppressing an amount of offset of a center O1 of the motor <NUM> with respect to the wheel center <NUM>. Thus, the motor <NUM> can easily be accommodated in the radial region of the wheel inner space M, including the stator <NUM> and the housing <NUM> retaining the stator <NUM>.

A lower arm ball joint (not shown) configured to mount the in-wheel motor drive device <NUM> to the suspension device <NUM> is provided below the in-wheel motor drive device <NUM>. In this embodiment, the pitch circle diameter of the output gear <NUM> is suppressed as described above. Therefore, a sufficient space for providing the lower arm ball joint can be secured below the output gear <NUM>.

It is preferred that the speed reducer input shaft Sin and the speed reducer output shaft Sout be arranged as close as possible. In this embodiment, as illustrated in <FIG>, an angle θ between a line connecting the center of the speed reducer input shaft Sin (that is, center <NUM> of the motor) and a center <NUM> of the intermediate shaft Sm and a line connecting the center of the speed reducer output shaft Sout (that is, wheel center <NUM>) and the center <NUM> of the intermediate shaft Sm is equal to or smaller than <NUM>°. In the illustrated example, a center distance D1 between the speed reducer input shaft Sin and the intermediate shaft Sm and a center distance D2 between the speed reducer output shaft Sout and the intermediate shaft Sm is substantially equal to each other, and a ratio between the center distance D1 and the center distance D2 falls within, for example, a range of from <NUM>. <NUM> to <NUM>. With this, the speed reducer input shaft Sin, the intermediate shaft Sm, and the speed reducer output shaft Sout are arranged in a compact manner to form a substantially isosceles triangle or a substantially equilateral triangle as in the illustrated example, when viewed in the axial direction. Therefore, the motor <NUM> can be more easily accommodated in the radial region of the wheel inner space M.

On this occasion, when the speed reducer input shaft Sin and the speed reducer output shaft Sout are arranged excessively close to each other, there is a fear in that the speed reducer input shaft Sin and the output gear <NUM> interfere with each other. Thus, it is required that a distance between the center of the speed reducer input shaft Sin (that is, the center <NUM> of the motor) and the center of the speed reducer output shaft Sout (that is, the wheel center <NUM>) at least be set larger than a sum of a radius of the circumscribed circle of the output gear <NUM> and a radius of the speed reducer input shaft Sin in the axial region of the output gear <NUM> (radius of the cylindrical portion of the input gear <NUM> adjacent to the out-board side), and it is preferred that such distance be set larger than a sum of a radius of the circumscribed circle of the output gear <NUM> and a radius of the circumscribed circle of the input gear <NUM>.

In the parallel shaft gear speed reducer <NUM> described above, as illustrated in <FIG>, a sum of a radius R1 of the circumscribed circle of the large-diameter intermediate gear <NUM> and a radius R2 of an outer peripheral surface of a cylindrical portion 51a of the speed reducer output shaft Sout adjacent to the output gear <NUM> on the in-board side is smaller than the center distance D2 between the intermediate shaft Sm and the speed reducer output shaft Sout (R1+R2<D2). With this, a radially outer end of the large-diameter intermediate gear <NUM> separates from the cylindrical portion 51a of the speed reducer output shaft Sout, and hence interference therebetweenis avoided. In this embodiment, the pitch circle diameter of the large-diameter intermediate gear <NUM> is smaller than the pitch circle diameter of the output gear <NUM>, and hence the dimensional relationship described above can easily be achieved. As long as the dimensional relationship described above can be achieved, the pitch circle diameter of the large-diameter intermediate gear <NUM> may be equal to or larger than the pitch circle diameter of the output gear <NUM>.

In this embodiment, a recess portion 35a having an annular shape is formed in an end surface of the large-diameter intermediate gear <NUM> on the in-board side, and at least a part of the axial region (in the illustrated example, the entirety of the axial region) of the rolling bearing <NUM> is accommodated in the recess portion 35a. Moreover, a recess portion 37a is formed in an end surface of the output gear <NUM> on the out-board side, and at least a part of the axial region (in the illustrated example, the entirety of the axial region) of the rolling bearing <NUM> is accommodated in the recess portion 37a. As described above, when the gears <NUM> and <NUM> and the bearings <NUM> and <NUM> configured to support the gears <NUM> and <NUM> are arranged so as to be superimposed with each other in the direction orthogonal to the axial direction, the axial dimension of the parallel shaft gear speed reducer <NUM> and the axial dimension of the in-wheel motor drive device <NUM> can be reduced.

As described above, when the recess portions 35a and 37a are formed in the end surfaces of the large-diameter intermediate gear <NUM> and the output gear <NUM>, as illustrated in <FIG>, ribs 35b and 37b may be provided in the recess portions 35a and 37a. In the example illustrated in <FIG>, a plurality of ribs 35b and 37b extending in the radial direction are provided in a radial arrangement in the recess portions 35a and 37a of the end surfaces of the first intermediate gear <NUM> and the output gear <NUM>. With this configuration, the strength of the first intermediate gear <NUM> and the output gear <NUM> is enhanced. In this case, the rolling bearings <NUM> and <NUM> are arranged at positions not interfering with the ribs 35b and 37b.

The present invention is not limited to the embodiment described above. For example, as illustrated in <FIG>, the bearing <NUM> configured to support the out-board-side end portion of the speed reducer input shaft Sin may be arranged on the in-board side with respect to the bearing <NUM> configured to support the out-board-side end portion of the intermediate shaft Sm. In the illustrated example, the entirety of the axial region of the bearing <NUM> configured to support the out-board-side end portion of the speed reducer input shaft Sin is arranged in the axial region of the gear train G2 on the output side. With this configuration, the axial length of the speed reducer input shaft Sin can be reduced, thereby being capable of achieving reduction in weight of the speed reducer input shaft Sin and reduction in cost.

In the embodiment described above, description is made of the case in which the wheel bearing <NUM> is of the inner-ring rotation type. However, the present invention is not limited to this. A wheel bearing of an outer-ring rotation type may be used. In this case, the inner ring is a fixed ring fixed to the housing <NUM>, and the outer ring is a rotation ring configured to rotate with respect to the inner ring. The hollow speed reducer output shaft is coupled to the outer peripheral surface of the outer ring by spline fitting in a torque-transmittable manner. The brake rotor and the rear wheel are connected to the flange provided to the outer ring.

Moreover, in the embodiment described above, illustration is given of the motor <NUM> of the radial gap type as the drive section A. However, a motor having a freely selected configuration can be applied. For example, a motor of an axial gap type in which the stator and the rotor are opposed to each other through a gap in the axial direction may be adopted.

Moreover, in the embodiment described above, as illustrated in <FIG>and <FIG>, illustration is given of the electric vehicle <NUM> comprising the rear wheels <NUM> as driving wheels. However, the electric vehicle <NUM> may comprise the front wheels <NUM> as driving wheels, or may be a four-wheel drive vehicle. In Description, the "electric vehicle" encompasses all automobiles which obtain driving force from electric power, and may include, for example, a hybrid car.

Moreover, in the embodiment described above, description is made of the in-wheel motor drive device comprising the three-shaft two-stage parallel shaft gear speed reducer.

Claim 1:
An in-wheel motor drive device (<NUM>), comprising:
a motor (<NUM>);
a wheel bearing (<NUM>) comprising a fixed ring (<NUM>), a rotation ring, and a plurality of rolling elements (<NUM>) arranged between the fixed ring and the rotation ring; and
a speed reducer (<NUM>) configured to connect the motor (<NUM>) and the wheel bearing (<NUM>) to each other, the speed reducer (<NUM>) being formed of a parallel shaft gear speed reducer comprising:
a speed reducer input shaft (Sin), which is configured to rotate integrally with a rotation shaft of the motor (<NUM>), and comprises an input gear (<NUM>);
a speed reducer output shaft (Sout), which is configured to rotate integrally with the rotation ring of the wheel bearing (<NUM>), and comprises an output gear (<NUM>); and
an intermediate shaft (Sm) comprising:
a small-diameter intermediate gear (<NUM>) configured to mesh with the output gear (<NUM>); and
a large-diameter intermediate gear (<NUM>) provided coaxially with the small-diameter intermediate gear (<NUM>),
wherein the speed reducer (<NUM>) is formed of a three-shaft two-stage parallel shaft gear speed reducer comprising the large-diameter intermediate gear (<NUM>) and the input gear (<NUM>) in mesh with each other,
wherein the large-diameter intermediate gear (<NUM>) has a circumscribed circle which is superimposed with a pitch circle of the plurality of rolling elements (<NUM>) of the wheel bearing (<NUM>) when viewed from an axial direction,
wherein the large-diameter intermediate gear (<NUM>) has a pitch circle diameter which is smaller than a pitch circle diameter of the output gear (<NUM>), characterized in that
the speed reducer input shaft (Sin), the intermediate shaft (Sm), and the speed reducer output shaft (Sout) are arranged so as to form a triangular shape when viewed from the axial direction, and
wherein at least a part of the speed reducer input shaft (Sin) in the axial direction is arranged in an axial region of the speed reducer output shaft (Sout).