Patent Description:
In Patent Document <NUM> to Patent Document <NUM>, disclosed is a power transmission device.

<CIT> discloses a transmission device comprising a single, stepped planetary gear set having a plurality of stepped planetary gears, and differential having bevel gears.

<CIT> discloses a power transmission device according to the preamble of claim <NUM>.

The power transmission device of Patent Document <NUM> has three rotation axes that are involved in rotation transmission aligned in parallel, and the size easily increases in the vertical direction (gravity direction) (hereafter called the "<NUM>-axis type").

In the power transmission device of Patent Document <NUM>, a rotor of a motor is a hollow shaft, and a drive shaft penetrates the interior of this hollow shaft. For that reason, compared to the <NUM>-axis type, it is possible to reduce the size in the vertical direction, but due to placement of a large counter gear, it ends up increasing in size in the vertical direction (hereafter called the "<NUM>-axis type").

In the power transmission device of Patent Document <NUM>, rather than the counter gear, a planetary reduction gear having a stepped pinion is used, and compared to the <NUM>-axis type, it is possible to reduce the size in the vertical direction (hereafter called the "<NUM>-axis type").

With the <NUM>-axis type, a planetary reduction gear is used, so there is a tendency for the reduction ratio to be smaller than with the <NUM>-axis type and the <NUM>-axis type.

For that reason, in the <NUM>-axis type power transmission device, there is a demand to increase the reduction ratio, and also to increase the stability of support of the differential gear.

The present invention is a power transmission device according to claim <NUM>.

The elements that rotate in the same way as the differential gear of the second planetary reduction gear and the differential case are integrated with high rigidity. For that reason, when a configuration is adopted in which the elements integrated with the differential gear of the second planetary reduction gear are supported by a case member that is a fixed side member with a bearing that is provided at the first planetary reduction gear side of the second planetary reduction gear interposed, it is possible to increase the reduction ratio, and to increase the stability of support of the differential gear.

Following, an example that does not fall within the scope of the invention, as defined in claim <NUM>, and an embodiment that does fall within the scope of the invention, as defined in claim <NUM>, are explained.

<FIG> is a drawing for explaining a power transmission device <NUM> of said example.

<FIG> is an enlarged view around a reduction mechanism <NUM> (first planetary reduction gear <NUM>, second planetary reduction gear <NUM>) of the power transmission device <NUM>, shown in <FIG>.

The power transmission device <NUM> has: a motor <NUM>; the reduction mechanism <NUM> (first planetary reduction gear <NUM>, second planetary reduction gear <NUM>) that reduces output rotation of the motor <NUM> and inputs that to the differential device <NUM>; and drive shafts <NUM> (8A, 8B).

With the power transmission device <NUM>, the reduction mechanism <NUM> (first planetary reduction gear <NUM>, second planetary reduction gear <NUM>), the differential device <NUM>, and the drive shafts <NUM> (8A, 8B) are provided along the transmission route of the output rotation of the motor <NUM>.

The output rotation of the motor <NUM> is reduced by the reduction mechanism <NUM>, and after being inputted to the differential device <NUM>, is transmitted via the drive shafts <NUM> (8A, 8B) to drive wheels (not illustrated) at left and right of a vehicle in which the power transmission device <NUM> is mounted. In <FIG>, the drive shaft 8A is connected so that rotation can be transmitted to the left wheel of the vehicle in which the power transmission device <NUM> is mounted, and the drive shaft 8B is connected to be able to transmit rotation to the right wheel.

Here, the first planetary reduction gear <NUM> is connected downstream of the motor <NUM>, and the second planetary reduction gear <NUM> is connected downstream of the first planetary reduction gear <NUM>. The differential device <NUM> is connected downstream of the second planetary reduction gear <NUM>, and the drive shafts <NUM> (8A, 8B) are connected downstream of the differential device <NUM>.

The motor <NUM> has: a cylindrical motor shaft <NUM>; a cylindrical rotor core <NUM> externally fitted on the motor shaft <NUM>; and a stator core <NUM> that surrounds the outer circumference of the rotor core <NUM> with a prescribed gap.

The motor shaft <NUM> is provided to be able to rotate relatively with respect to the drive shaft 8B in a state externally fitted on the drive shaft 8B.

With the motor shaft <NUM>, bearings B1, B1 are externally fitted and fixed to the outer circumference of one end 20a side and another end 20b side in the longitudinal direction.

The one end 20a side of the motor shaft <NUM> is supported to be able to rotate by a cylindrical motor support unit <NUM> of an intermediate case <NUM> with the bearing B1 interposed.

The other end 20b side of the motor shaft <NUM> is supported to be able to rotate by a cylindrical motor support unit <NUM> of a cover <NUM> with the bearing B1 interposed.

The motor <NUM> has a motor housing <NUM> that surrounds the outer circumference of the rotor core <NUM> with a prescribed gap. With the related example, the intermediate case <NUM> is joined to one end 10a of the motor housing <NUM>, and the cover <NUM> is joined to the other end 10b of the motor housing <NUM>.

Seal rings S, S are provided on the one end 10a and the other end 10b of the motor housing <NUM>. The one end 10a of the motor housing <NUM> is joined without a gap to a ring-shaped base <NUM> of the intermediate case <NUM> by the seal ring S provided on that one end 10a.

The other end 10b of the motor housing <NUM> is joined without a gap to a ring-shaped junction part <NUM> of the cover <NUM> by the seal ring S provided on that other end 10b.

With the intermediate case <NUM>, the base <NUM> and the motor support unit <NUM> are provided with the positions displaced in the rotation axis X direction.

With the related example, when the intermediate case <NUM> is fixed to the one end 10a of the motor housing <NUM>, the motor support unit <NUM> is made to be inserted inside the motor housing <NUM>.

In this state, the motor support unit <NUM> is arranged facing a one end part 21a of the rotor core <NUM> with a gap being formed in the rotation axis X direction at the inner diameter side of a coil end 253a noted later (see <FIG>).

Also, as shown in <FIG>, a connecting part <NUM> that connects the base <NUM> and the motor support unit <NUM> is provided avoiding contact with the coil end 253a and a side plate <NUM> described later.

A bearing retainer <NUM> is fixed to an end surface 121a of the rotor core <NUM> side of the motor support unit <NUM>.

The bearing retainer <NUM> has a ring shape when seen from the rotation axis X direction. The inner diameter side of the bearing retainer <NUM> abuts the side surface of an outer race B1b of the bearing B1 supported by the motor support unit <NUM> from the rotation axis X direction. The bearing retainer <NUM> prevents falling off of the bearing B1 from the motor support unit <NUM>.

As shown in <FIG>, with the cover <NUM>, the junction part <NUM> and the motor support unit <NUM> are provided with the positions displaced in the rotation axis X direction.

With the related example, when the junction part <NUM> of the cover <NUM> is fixed to the other end 10b of the motor housing <NUM>, the motor support unit <NUM> is made to be inserted inside the motor housing <NUM>.

In this state, the motor support unit <NUM> is arranged facing an other end part 21b of the rotor core <NUM> with a gap being formed in the rotation axis X direction at the inner diameter side of a coil end 253b described later.

A connecting part <NUM> that connects the junction part <NUM> and a side wall part <NUM> of the cover <NUM> is provided while avoiding contact with the coil end 253b and a support cylinder <NUM> described later.

Inside the motor housing <NUM>, the rotor core <NUM> is arranged between the motor support unit <NUM> of the cover <NUM> side, and the motor support unit <NUM> of the intermediate case <NUM> side.

The rotor core <NUM> is formed by laminating a plurality of silicon steel sheets, and each of the silicon steel sheets is externally fitted on the motor shaft <NUM> in a state where relative rotation with the motor shaft <NUM> is regulated.

Seen from the rotation axis X direction of the motor shaft <NUM>, the silicon steel sheet has a ring shape, and at the outer peripheral side of the silicon steel sheet, N pole and S pole magnets (not illustrated) are provided alternately in the circumferential direction around the rotation axis X.

The one end part 21a of the rotor core <NUM> in the rotation axis X direction is positioned using a large diameter part <NUM> of the motor shaft <NUM>. The other end part 21b of the rotor core <NUM> is positioned using a stopper <NUM> press fitted in the motor shaft <NUM>.

The stator core <NUM> is formed by laminating a plurality of electromagnetic steel sheets, and each of the electromagnetic steel sheets has a ring-shaped yoke part <NUM> fixed to the inner circumference of the motor housing <NUM>, and a teeth part <NUM> projecting to the rotor core <NUM> side from the inner circumference of the yoke part <NUM>.

With the related example, the stator core <NUM> having a configuration in which a winding <NUM> is distributed and wound across a plurality of teeth parts <NUM> is adopted, and the stator core <NUM> has a longer length in the rotation axis direction than the rotor core <NUM> by the amount of the coil ends 253a, 253b projecting in the rotation axis X direction.

It is also possible to adopt the stator core of a configuration in which the windings are concentrically wound on each of the plurality of teeth parts <NUM> projecting to the rotor core <NUM> side.

With the motor shaft <NUM>, the bearing B1 is press-fitted further to the outer circumference of the area of the one end 20a side than the large diameter part <NUM>.

As shown in <FIG>, with an inner race B1a of the bearing B1, one side surface of the rotation axis X direction abuts a step part <NUM> provided on the outer circumference of the motor shaft <NUM>. With the inner race B1a, a ring-shaped stopper <NUM> that is press-fitted in the outer circumference of the motor shaft <NUM> abuts the other side surface.

With the bearing B1, the inner race B1a is positioned by the stopper <NUM> at a position abutting the step part <NUM>.

The one end 20a of the motor shaft <NUM> is positioned more to the differential device <NUM> side (left side in the drawing) than the stopper <NUM>. In the rotation axis X direction, the one end 20a faces a side surface 41a of a sun gear <NUM> of the first planetary reduction gear <NUM> with a gap being formed therebetween.

At the one end 20a side of the motor shaft <NUM>, a cylinder wall <NUM> is positioned radially outward of the motor shaft <NUM>.

The cylinder wall <NUM> projects to the differential device <NUM> side from the motor support unit <NUM>, and a tip 122a of the cylinder wall <NUM> faces the side surface 41a of the sun gear <NUM> of the first planetary reduction gear <NUM> with a gap being formed therebetween.

The cylinder wall <NUM> surrounds the outer circumference of the motor shaft <NUM> with a prescribed gap, and a lip seal RS is arranged between the cylinder wall <NUM> and the motor shaft <NUM>.

The lip seal RS is provided to partition a space Sa (see <FIG>) of the inner diameter side of the motor housing <NUM> and a space Sb (see <FIG>) of the inner diameter side of the intermediate case <NUM>.

The space Sb of the inner diameter side of the intermediate case <NUM> is linked with a space Sc inside a case <NUM> that houses the differential device <NUM> described later. Lubricating oil of the differential device <NUM> is sealed within the space Sb. The lip seal RS is provided to block inflow of lubricating oil to the space Sa of the inner diameter side of the motor housing <NUM>.

With the related example, a body case <NUM> of the power transmission device <NUM> is constituted by the motor housing <NUM>, the cover <NUM>, the intermediate case <NUM>, the case <NUM>, and an intermediate cover <NUM> described later.

The intemal space of the body case <NUM> uses the intermediate case <NUM> as a boundary, and the space Sa of the motor housing <NUM> side serves as a motor chamber that houses the motor <NUM>. Spaces Sb, Sc of the case <NUM> side serve as gear chambers that house the reduction mechanism <NUM> (first planetary reduction gear <NUM>, second planetary reduction gear <NUM>).

Also, the gear chambers are partitioned by the intermediate cover <NUM> described later into the space Sb that houses the first planetary reduction gear <NUM>, and the space Sc that houses the second planetary reduction gear <NUM> and the differential case <NUM>.

As shown in <FIG>, an area <NUM> of the one end 20a side of the motor shaft <NUM> is formed with a larger inner diameter than an area <NUM> on which the rotor core <NUM> is externally fitted.

A cylindrical linking part <NUM> of the sun gear <NUM> is inserted inside the area <NUM> of this one end 20a side. In this state, the area <NUM> of the one end 20a side of the motor shaft <NUM> and the linking part <NUM> of the sun gear <NUM> are spline fitted without being able to rotate relatively.

For this reason, the output rotation of the motor <NUM> is inputted to the sun gear <NUM> of the first planetary reduction gear <NUM> via the motor shaft <NUM>, and the sun gear <NUM> rotates around the rotation axis X by the rotational drive power of the motor <NUM>.

The sun gear <NUM> has the linking part <NUM> extending in the rotation axis X direction from the side surface 41a of the inner diameter side. The linking part <NUM> is formed integrally with the sun gear <NUM>, and a through hole <NUM> is formed straddling the inner diameter side of the sun gear <NUM> and the inner diameter side of the linking part <NUM>.

The sun gear <NUM> is supported to be able to rotate on the outer circumference of the drive shaft 8B penetrating the through hole <NUM>.

A ring gear <NUM> fixed to the inner circumference of the base <NUM> of the intermediate case <NUM> is positioned at the outer diameter side of the sun gear <NUM> in the radial direction of the rotation axis X. In the radial direction of the rotation axis X, between the sun gear <NUM> and the ring gear <NUM>, a pinion gear <NUM> that is supported to be able to rotate on a pinion shaft <NUM> is engaged with the outer circumference of the sun gear <NUM> and the inner circumference of the ring gear <NUM>.

The pinion gear <NUM> is supported to be able to rotate at the outer circumference of the pinion shaft <NUM> via a needle bearing NB. The pinion shaft <NUM> penetrates the pinion gear <NUM> in the axis line X1 direction along the rotation axis X. One end and the other end of the longitudinal direction of the pinion shaft <NUM> is supported by a pair of side plates <NUM>, <NUM> of a carrier <NUM>.

The side plates <NUM>, <NUM> are provided in parallel with each other with a gap being formed in the rotation axis X direction.

Between the side plates <NUM>, <NUM>, the plurality of pinion gears <NUM> are provided in a plurality (four, for example) at a prescribed interval in the circumferential direction around the rotation axis X.

A cylindrical linking part <NUM> is provided on the side plate <NUM> positioned at the differential device <NUM> side.

The linking part <NUM> in the side plate <NUM> is arranged concentrically with respect to the rotation axis X, and projects in the direction approaching the differential device <NUM> (leftward in the drawing) along the rotation axis X.

Viewed from the intermediate case <NUM>, the ring shaped intermediate cover <NUM> is positioned at the differential device <NUM> side. With the intermediate cover <NUM>, a ring shaped base <NUM> of the outer diameter side is provided in a state sandwiched between the intermediate case <NUM> and the case <NUM>.

With the related example, the intermediate cover <NUM> is positioned between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> aligned in the rotation axis X direction.

The intermediate cover <NUM> has a wall part <NUM> extending to the inner diameter side from the ring shaped base <NUM>. The wall part <NUM> is provided oriented orthogonally to the rotation axis X. The inner diameter side of the wall part <NUM> is inserted from the radial direction of the rotation axis X between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> aligned in the rotation axis X direction.

At the inner diameter side of the wall part <NUM>, an opening <NUM> is provided penetrating the wall part <NUM> in the thickness direction (rotation axis X direction).

The outer circumference of the opening <NUM> is provided at a position intersecting the axis line X1 that passes through the center of the pinion shaft <NUM> of the first planetary reduction gear <NUM>.

The linking part <NUM> provided on the inner diameter side of the side plate <NUM> of the first planetary reduction gear <NUM> penetrates the opening <NUM> at the center of the intermediate cover <NUM> (wall part <NUM>) to the left of the differential device <NUM> side from the motor <NUM> side.

The tip 453a of the linking part <NUM> is positioned inside the case <NUM> attached to the intermediate cover <NUM>. The tip 453a of the linking part <NUM> in the rotation axis X direction faces a side surface 51a of a sun gear <NUM> of the second planetary reduction gear <NUM> with a gap being formed.

A cylindrical linking part <NUM> extending from the sun gear <NUM> is inserted inside the linking part <NUM> and spline fitted, and the linking part <NUM> of the first planetary reduction gear <NUM> side and the linking part <NUM> of the second planetary reduction gear <NUM> side are linked without being able to rotate relatively at the inner diameter side of the intermediate cover <NUM>.

The sun gear <NUM> has the linking part <NUM> extending in the rotation axis X direction from the side surface 51a of the inner diameter side. The linking part <NUM> is formed integrally with the sun gear <NUM>, and a through hole <NUM> is formed straddling the inner diameter side of the sun gear <NUM> and the inner diameter side of the linking part <NUM>.

A side surface 51b of the differential device <NUM> side of the sun gear <NUM> faces a cylindrical support unit <NUM> of the differential case <NUM> described later with a gap being formed in the rotation axis X direction, and the needle bearing NB is interposed between the side surface 51b and the support unit <NUM>.

The sun gear <NUM> engages with a large diameter gear part <NUM> of a stepped pinion gear <NUM> on an extension of the abovementioned linking part <NUM> of the first planetary reduction gear <NUM> side.

The stepped pinion gear <NUM> has the large diameter gear part <NUM> that engages with the sun gear <NUM>, and a small diameter gear part <NUM> having a smaller diameter than the large diameter gear part <NUM>.

The stepped pinion gear <NUM> is a gear component in which the large diameter gear part <NUM> and the small diameter gear part <NUM> are provided integrally, aligned in an axis line X2 direction that is parallel to the rotation axis X.

The stepped pinion gear <NUM> has a through hole <NUM> penetrating the inner diameter side of the large diameter gear part <NUM> and the small diameter gear part <NUM> in the axis line X2 direction.

The stepped pinion gear <NUM> is supported to be able to rotate on the outer circumference of a pinion shaft <NUM> penetrating the through hole <NUM> with the needle bearing NB interposed.

One end and the other end in the longitudinal direction of the pinion shaft <NUM> are supported by a side plate <NUM> integrally formed with the differential case <NUM>, and a side plate <NUM> arranged with a gap being formed on this side plate <NUM>.

Between the side plates <NUM>, <NUM>, the plurality of stepped pinion gears <NUM> are provided in a plurality (three, for example) at a prescribed interval in the circumferential direction around the rotation axis X.

Each of the small diameter gear parts <NUM> is engaged with the inner circumference of the ring gear <NUM>. The ring gear <NUM> is spline fitted with the inner circumference of the case <NUM>, and relative rotation of the ring gear <NUM> with the case <NUM> is regulated.

At the inner diameter side of the side plate <NUM>, a cylindrical part <NUM> is provided extending to the first planetary reduction gear <NUM> side. The cylindrical part <NUM> penetrates the opening <NUM> at the center of the intermediate cover <NUM> (wall part <NUM>) at the motor <NUM> side (right side in the drawing) from the differential device <NUM> side. A tip 552a of the cylindrical part <NUM> faces the side plate <NUM> of the carrier <NUM> of the first planetary reduction gear <NUM> in the rotation axis X direction with a gap being formed.

The cylindrical part <NUM> is positioned radially outward of the engaging part between the linking part <NUM> of the first planetary reduction gear <NUM> side, and the linking part <NUM> of the second planetary reduction gear <NUM> side. A bearing B2 fixed to the opening <NUM> of the intermediate cover <NUM> (wall part <NUM>) is in contact with the outer circumference of the cylindrical part <NUM>. The cylindrical part <NUM> of the side plate <NUM> is supported to be able to rotate on the intermediate cover <NUM> with the bearing B2 interposed.

With the second planetary reduction gear <NUM>, one side plate <NUM> of the side plate <NUM> and the side plate <NUM> constituting the carrier <NUM> is formed integrally with the differential case <NUM> of the differential device <NUM>.

For that reason, the carrier <NUM> (side plates <NUM>, <NUM>, pinion shaft <NUM>) of the second planetary reduction gear <NUM> is substantially formed integrally with the differential case <NUM>.

With the second planetary reduction gear <NUM>, the output rotation of the motor <NUM> reduced by the first planetary reduction gear <NUM> is inputted to the sun gear <NUM>.

The output rotation inputted to the sun gear <NUM> is inputted to the stepped pinion gears <NUM> via the large diameter gear part <NUM> that engages with the sun gear <NUM>, and the stepped pinion gear <NUM> rotates around the axis line X2.

Having done that, the small diameter gear part <NUM> that is integrally formed with the large diameter gear part <NUM> rotates around the axis line X2 integrally with the large diameter gear part <NUM>.

Here, the small diameter gear part <NUM> engages with the ring gear <NUM> fixed to the inner circumference of the case <NUM>. For that reason, when the small diameter gear part <NUM> rotates around the axis line X2, the stepped pinion gear <NUM> rotates around the rotation axis X while auto-rotating around the axis line X2.

Having done that, the one end of the pinion shaft <NUM> is supported on the side plate <NUM> that is integrally formed with the differential case <NUM>, so in conjunction with the displacement of the stepped pinion gear <NUM> in the circumferential direction around the rotation axis X, the differential case <NUM> rotates around the rotation axis X.

Here, with the stepped pinion gear <NUM>, an outer diameter R<NUM> of the small diameter gear part <NUM> is smaller than an outer diameter R2 of the large diameter gear part <NUM> (see <FIG>).

Also, with the second planetary reduction gear <NUM>, the sun gear <NUM> serves as the input unit of the output rotation of the motor <NUM>, and the carrier <NUM> that supports the stepped pinion gear <NUM> serves as the output unit of the inputted rotation.

Having done that, the rotation inputted to the sun gear <NUM> of the second planetary reduction gear <NUM>, after being significantly reduced by the stepped pinion gear <NUM>, is outputted to the differential case <NUM> with which the side plate <NUM> of the carrier <NUM> is integrally formed.

As shown in <FIG>, the differential case <NUM> is formed to have a hollow shape that internally houses a shaft <NUM>, bevel gears 62A, 62B, and side gears 63A, 63B.

With the differential case <NUM>, cylindrical support units <NUM>, <NUM> are provided at both sides in the rotation axis X direction (lateral direction in the drawing). The support units <NUM>, <NUM> extend along the rotation axis X in the direction away from the shaft <NUM>.

As shown in <FIG>, a connector piece <NUM> that connects the side plate <NUM> and the side plate <NUM> of the carrier <NUM> is provided at the outer diameter side of the support unit <NUM>.

One end of the differential case <NUM> side of the connector piece <NUM> is provided straddling the side plate <NUM> and the outer circumference of the differential case <NUM>, and the other end is connected to the side plate <NUM> from the rotation axis X direction.

The connector piece <NUM> is provided at a position avoiding interference with the stepped pinion gear <NUM> noted above. As described above, the stepped pinion gear <NUM> is provided in a plurality (three, for example) at a prescribed interval in the circumferential direction around the rotation axis X.

The connector pieces <NUM> are provided between adjacent stepped pinion gears <NUM> in the circumferential direction around the rotation axis X.

An inner race B2a of a bearing B2 is press fitted on the outer circumference of the support unit <NUM> of the differential case <NUM>. An outer race B2b of the bearing B2 is held by a ring-shaped support unit <NUM> of the case <NUM>, and the support unit <NUM> of the differential case <NUM> is supported to be able to rotate by the case <NUM> with the bearing B2 interposed.

The drive shaft 8A that penetrates an opening <NUM> of the case <NUM> is inserted from the rotation axis X direction in the support unit <NUM>, and the drive shaft 8A is supported to be able to rotate by the support unit <NUM>.

The lip seal RS is fixed to the inner circumference of the opening <NUM>, and by a lip section (not illustrated) of the lip seal RS being elastically in contact with the outer circumference of the drive shaft 8A, the gap between the outer circumference of the drive shaft 8A and the inner circumference of the opening <NUM> is sealed.

The drive shaft 8B that penetrates an opening <NUM> of the cover <NUM> is inserted in the support unit <NUM> from the rotation axis direction.

The drive shaft 8B is provided crossing the motor shaft <NUM> of the motor <NUM>, the sun gear <NUM> of the first planetary reduction gear <NUM>, and the inner diameter side of the sun gear <NUM> of the second planetary reduction gear <NUM> in the rotation axis X direction, and the tip end side of the drive shaft 8B is supported to be able to rotate by the support unit <NUM>.

The lip seal RS is fixed to the inner circumference of the opening <NUM> of the cover <NUM>, and the gap between the outer circumference of the drive shaft 8B and the inner circumference of the opening <NUM> is sealed by the lip part (not illustrated) of the lip seal RS being elastically in contact with the outer circumference of the drive shaft 8B.

In the interior of the differential case <NUM>, side gears 63A, 63B are spline fitted at the outer circumference of the tip end part of the drive shafts 8A, 8B, and the side gears 63A, 63B and drive shafts <NUM> (8A, 8B) are linked to be able to rotate integrally around the rotation axis X.

Shaft holes 60a, 60b penetrating the differential case <NUM> in the direction orthogonal to the rotation axis X are provided at symmetrical positions sandwiching the rotation axis X.

The shaft holes 60a, 60b are positioned on the axis line Y that is orthogonal to the rotation axis X, and one end 61a side and another end 61b side of the shaft <NUM> are inserted.

The one end 61a side and the other end 61b side of the shaft <NUM> are fixed to the differential case <NUM> by a pin P, and the shaft <NUM> is prohibited from auto-rotating around the axis line Y.

The bottom side of the differential case <NUM> is immersed in the lubricating oil inside the case <NUM>.

With the embodiment, when the one end 61a or the other end 61b of the shaft <NUM> is positioned at the bottommost side, the lubricating oil is pooled inside the case <NUM> at least to a height at which the one end 61a or the other end 61b of the shaft <NUM> is positioned within the lubricating oil.

The shaft <NUM> is arranged along the axis line Y positioned between the side gears 63A, 63B inside the differential case <NUM>.

The bevel gears 62A, 62B are externally fitted on the shaft <NUM> inside the differential case <NUM> and supported to be able to rotate.

Two bevel gears 62A, 62B are provided with a gap being formed in the longitudinal direction of the shaft <NUM> (axial direction of the axis line Y), and the bevel gears 62A, 62B are arranged in a state so that their teeth face each other. In the shaft <NUM>, the bevel gears 62A, 62B are provided with the shaft center of the bevel gears 62A, 62B matched to the shaft center of the shaft <NUM>.

Inside the differential case <NUM>, the side gears 63A, 63B are positioned at both sides of the bevel gears 62A, 62B in the axial direction of the rotation axis X.

Two side gears 63A, 63B are provided with a gap being formed in the axial direction of the rotation axis X in a state so that their teeth face each other, and the bevel gears 62A, 62B and the side gears 63A, 63B are assembled in a state with the teeth mutually engaged.

As described above, with the power transmission device <NUM>, the differential case <NUM> rotates around the rotation axis X by rotation input via the reduction mechanism <NUM> (first planetary reduction gear <NUM>, second planetary reduction gear <NUM>).

Here, with the differential case <NUM>, of the support units <NUM>, <NUM> provided at both sides of the rotation axis X direction, only the one support unit <NUM> is supported by the case <NUM> with the bearing B2 interposed.

As shown in <FIG>, with the power transmission device <NUM>, the second planetary reduction gear <NUM> (small diameter gear part <NUM> of the stepped pinion gear <NUM>) is positioned at the outer diameter side of the other support unit <NUM>. For that reason, the specification is that it is not possible to provide a member for supporting the differential case <NUM> at the outer diameter side of the support unit <NUM>.

For that reason, the specification is that the support unit <NUM> side of the differential case <NUM> is indirectly supported by the cover <NUM> by the drive shaft 8B that penetrates the support unit <NUM> being supported by the cover <NUM> via the bearing B1.

As described above, with the related example, the carrier <NUM> of the second planetary reduction gear <NUM> positioned at the outer diameter side of the support unit <NUM> is integrally formed with the differential case <NUM>.

For that reason, the carrier <NUM> and the differential case <NUM> are provided integrally having a prescribed rigidity and strength.

Furthermore, the intermediate cover <NUM> that extends to the inner diameter side (rotation axis X side) is provided between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM>, and at the inner diameter side of the other side plate <NUM> of the pair of side plates <NUM>, <NUM> constituting the carrier <NUM>, the cylindrical part <NUM> that crosses the opening <NUM> of the intermediate cover <NUM> (the wall part <NUM>) in the rotation axis X direction is provided.

Also, a bearing B3 fixed to the inner circumference of the opening <NUM> of the intermediate cover <NUM> (wall part <NUM>) is in contact with the outer circumference of the cylindrical part <NUM>, and the cylindrical part <NUM> that extends from the side plate <NUM> of the carrier <NUM> is supported to be able to rotate on the intermediate cover <NUM> with the bearing B3 interposed.

With the related example, the carrier <NUM> is substantially integrally formed with the differential case <NUM>. For that reason, the cylindrical part <NUM> of the carrier <NUM> can be thought of as a portion of the differential case <NUM>.

Thus, between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM>, the cylindrical part <NUM> which is a portion of the differential case <NUM> is supported on the inner circumference of the wall part <NUM> of the intermediate cover <NUM> which is a fixed side member, with the bearing B3 interposed.

In this way, with the support unit <NUM> side (right side in <FIG>) of the differential case <NUM>, the cylindrical part <NUM> of the carrier <NUM> provided integrally with the differential case <NUM> is supported by the wall part <NUM> of the intermediate cover <NUM> with the bearing B3 interposed. The specification is that by doing this, the differential case <NUM> is supported indirectly by the intermediate cover <NUM> via the carrier <NUM> that is integrally formed with that differential case <NUM>.

Here, the support position by the intermediate cover <NUM> is closer to the differential case <NUM> than the support position by the cover <NUM>. For that reason, by providing the intermediate cover <NUM> and having the differential case <NUM> indirectly supported by the intermediate cover <NUM>, the support stability of the differential case <NUM> rotating around the rotation axis X is increased more than when indirectly supported only by the cover <NUM>.

The action of the power transmission device <NUM> of this configuration is explained.

When the rotor core <NUM> rotates around the rotation axis X by the driving of the motor <NUM>, the rotation is inputted to the sun gear <NUM> of the first planetary reduction gear <NUM> via the motor shaft <NUM> that rotates integrally with the rotor core <NUM>.

With the first planetary reduction gear <NUM>, the sun gear <NUM> serves as the input unit of the output rotation of the motor <NUM>, and the carrier <NUM> that supports the pinion gear <NUM> serves as the output unit of the inputted rotation.

When the sun gear <NUM> rotates around the rotation axis X by the output rotation of the motor <NUM>, the pinion gear <NUM> engaged with the outer circumference of the sun gear <NUM> and the inner circumference of the ring gear <NUM> rotates around the axis line X1.

Here, the ring gear <NUM> is spline fitted to the inner circumference of the intermediate case <NUM> (fixed side member), and relative rotation with the intermediate case <NUM> is regulated.

For that reason, the pinion gear <NUM> revolves around the rotation axis X while rotating around the axis line X1. By doing this, the carrier <NUM> (side plates <NUM>, <NUM>) that supports the pinion gear <NUM> rotates around the rotation axis X at a rotation speed lower than the output rotation of the motor <NUM>.

As described above, the linking part <NUM> of the carrier <NUM> is linked to the linking part <NUM> of the sun gear <NUM> of the second planetary reduction gear <NUM> side, and the rotation of the carrier <NUM> (output rotation of the first planetary reduction gear <NUM>) is inputted to the sun gear <NUM> of the second planetary reduction gear <NUM>.

With the second planetary reduction gear <NUM>, the sun gear <NUM> serves as the input unit of the output rotation of the second planetary reduction gear <NUM>, and the carrier <NUM> that supports the stepped pinion gear <NUM> serves as the output unit of the inputted rotation.

When the sun gear <NUM> rotates around the rotation axis X by the inputted rotation, the stepped pinion gear <NUM> (large diameter gear part <NUM>, small diameter gear part <NUM>) rotates around the axis line X2 by the rotation inputted from the sun gear <NUM> side.

Here, the small diameter gear part <NUM> of the stepped pinion gear <NUM> is engaged with the ring gear <NUM> fixed to the inner circumference of the case <NUM>. For that reason, the stepped pinion gear <NUM> rotates around the rotation axis X while auto-rotating around the axis line X2.

By doing this, the carrier <NUM> (side plates <NUM>, <NUM>) that supports the stepped pinion gear <NUM> rotates around the rotation axis X at a rotation speed lower than the rotation inputted from the first planetary reduction gear <NUM> side.

Here, with the stepped pinion gear <NUM>, the outer diameter R1 of the small diameter gear part <NUM> is smaller than the outer diameter R2 of the large diameter gear part <NUM> (see <FIG>).

For that reason, the rotation inputted to the sun gear <NUM> of the second planetary reduction gear <NUM> is more greatly reduced by the stepped pinion gear <NUM> than with the first planetary reduction gear <NUM>, after which it is outputted to the differential case <NUM> (differential device <NUM>) with which the side plate <NUM> of the carrier <NUM> is integrally formed.

By the differential case <NUM> rotating around the rotation axis X by the inputted rotation, the drive shafts <NUM> (8A, 8B) rotate around the rotation axis X, with transmission to the left and right drive wheels (not illustrated) of the vehicle in which the power transmission device <NUM> is mounted.

With the differential case <NUM>, of the support units <NUM>, <NUM> provided at both sides in the rotation axis X direction, the one support unit <NUM> is supported by the case <NUM> via the bearing B2.

With the other support unit <NUM>, though not supported by a fixed side member, the cylindrical part <NUM> of the carrier <NUM> provided integrally with the differential case <NUM> is supported by the intermediate cover <NUM> via the bearing B3, and the differential case <NUM> is indirectly supported by the intermediate cover <NUM> via the bearing B3.

The support positions by these bearings B2, B3 are positioned at both sides sandwiching the position at which the rotation of the differential case <NUM> is inputted from the second planetary reduction gear <NUM> (engagement position of the side plate <NUM> and the pinion shaft <NUM>).

Thus, the support stability of the differential case <NUM> rotating around the rotation axis X by the inputted rotation is increased, and the stability of the differential device <NUM> (differential gear) is increased.

In this way, the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> that constitute the reduction mechanism <NUM> are arranged in series on the transmission route of the output rotation of the motor <NUM>, and one pinion gear of the second planetary reduction gear <NUM> is used as the stepped pinion gear <NUM>.

This makes it possible to make the reduction ratio greater in the reduction mechanism <NUM> than when planetary reduction gears having a normal pinion gear (stepless pinion gear) are simply arranged in series in the <NUM>-axis type power transmission device.

Furthermore, the configuration is such that the intermediate cover <NUM> is provided between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM>, and the cylindrical part <NUM> of the carrier <NUM> provided integrally with the differential case <NUM> is supported by the intermediate cover via the bearing B3.

By doing this, the one side (support unit <NUM>) in the rotation axis X direction of the differential case <NUM> is supported by the case <NUM>, and the other side (support unit <NUM> side) is indirectly supported by the intermediate cover <NUM>, so the support stability of the differential case <NUM> that rotates around the rotation axis X is increased.

By the support stability of the differential case <NUM> being increased, the stability of the differential device <NUM> (differential gear) is also increased.

As described above, the power transmission device <NUM> of the related example has the following configuration.

The drive shaft 8B is arranged penetrating the inner diameter side of the rotor core <NUM> of the motor <NUM> (inner circumference of the rotor), the inner diameter side (inner circumference) of the sun gear <NUM> of the first planetary reduction gear <NUM>, and the inner diameter side (inner circumference) of the sun gear <NUM> of the second planetary reduction gear <NUM>.

The differential device <NUM> has the differential case <NUM> (differential case).

The cylindrical part <NUM> that is a portion of the differential case <NUM>, and is positioned between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> aligned in the rotation axis X direction is supported at the inner circumference side of the intermediate cover <NUM> (case member) via the bearing B3 (bearing).

By configuring in this way, the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> are arranged in series on the transmission route of the output rotation of the motor <NUM>, and by having the planetary reduction gear be two levels, it is possible to increase the reduction ratio.

Here, in the power transmission device <NUM> having two levels of planetary reduction gears (first planetary reduction gear <NUM>, second planetary reduction gear <NUM>), if aiming only for a decrease in size in the rotation axis X direction, it is preferable to shorten the clearance in the rotation axis X direction between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM>.

In such a case, the state is such that the differential case <NUM> arranged downstream of the second planetary reduction gear <NUM> is floating, and the stability of the differential case <NUM> is decreased.

In light of that, to give stability of the differential device <NUM> priority, the cylindrical part <NUM> that is a portion of the differential case <NUM>, and is positioned between the two levels of planetary reduction gears (first planetary reduction gear <NUM>, second planetary reduction gear <NUM>) is supported by the intermediate cover <NUM> via the bearing B3.

This makes it possible for the differential device <NUM> (differential case <NUM>) to rotate stably.

The power transmission device <NUM> of the related example has the following configuration.

(<NUM>) The elements that rotate in the same way as the differential device <NUM> (differential gear) in the second planetary reduction gear <NUM> (carrier <NUM>: including cylindrical part <NUM>), and the differential case <NUM> (differential case) are integrated with high rigidity.

The elements integrated with the differential case <NUM> in the second planetary reduction gear <NUM> (carrier <NUM>, cylindrical part <NUM>) are supported by the intermediate cover <NUM> that is a fixed side member, with the bearing B3 provided on the first planetary reduction gear <NUM> side interposed.

By configuring in this way, the support stability when the differential case <NUM> rotates around the rotation axis X is improved, so it is possible for the differential device <NUM> to rotate stably.

(<NUM>) With the second planetary reduction gear <NUM>, the sun gear <NUM> is an input element, the carrier <NUM> is an output element, and the ring gear <NUM> is a fixed element.

The differential case <NUM> is formed integrally with the carrier <NUM>.

The cylindrical part <NUM> of the carrier <NUM> is supported to be able to rotate with the intermediate cover <NUM> via the bearing B3.

When the differential case <NUM> is formed integrally with the carrier <NUM>, as a result of the rigidity of both the differential case <NUM> and the carrier <NUM> increasing, the stability of the differential case <NUM> increases.

Furthermore, because the differential case <NUM> and the carrier <NUM> are formed integrally, the differential case <NUM> being supported by the intermediate cover <NUM> (wall part) has the same meaning as the carrier <NUM> being supported by the intermediate cover <NUM> (wall part), so the carrier <NUM> can also rotate stably.

(<NUM>) The differential case <NUM> positioned at the side opposite to the second planetary reduction gear <NUM> is supported via the bearing B2 (bearing) by the case <NUM> (case member) that houses the differential case <NUM>.

By being configured in this way, there is a double holding configuration in which the differential case <NUM> is supported at both sides via two bearings B2, B3 (first bearing, second bearing), and with the double holding configuration, the stability of the differential device <NUM> increases.

(<NUM>) At the position of the inner circumference side of the bearing B3 fixed to the inner circumference of the intermediate cover <NUM> (wall part), the linking part <NUM> (output element) of the first planetary reduction gear <NUM> side, and the linking part <NUM> (input element) of the second planetary reduction gear <NUM> are engaged without being able to rotate relatively.

When the linking part <NUM> (output element) of the first planetary reduction gear <NUM> side, and the linking part <NUM> (input element) of the second planetary reduction gear <NUM> side are engaged (spline fitted, etc.), space is needed for engaging.

By using the space of the inner circumference side of the intermediate cover <NUM> as the space for engaging of the output element and the input element, it is possible to reduce the size of the power transmission device <NUM>.

Said another way, in the radial direction of the rotation axis X (viewed from the radial direction), the intermediate cover <NUM>, the bearing B2 (bearing), the differential case <NUM>, the linking part <NUM> (output element) of the first planetary reduction gear <NUM>, and the linking part <NUM> (input element) of the second planetary reduction gear <NUM> are overlapping.

(<NUM>) The body case <NUM> (case member) has the wall part <NUM> between the first planetary reduction gear <NUM> and the second planetary reduction gear.

The bearing B3 (bearing) is arranged at the inner circumference of the wall part <NUM>.

The cylindrical part <NUM> which is a portion of the differential case <NUM> is supported at the inner circumference of the wall part <NUM> of the intermediate cover <NUM> with the bearing B3 (bearing) interposed.

By configuring in this way, to emphasize stability of support of the differential case <NUM>, the wall part <NUM> is purposely arranged between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM>, and the cylindrical part <NUM> which is a portion of the differential case <NUM> is supported on the inner circumference of the opening <NUM> of the wall part <NUM> via the bearing B3. This makes it possible to stably support the differential case <NUM> while preventing the outer diameter of the bearing B3 that supports the cylindrical part <NUM> from getting bigger.

The pinion gear <NUM> (pinion) of the first planetary reduction gear <NUM> is a stepless pinion gear, and the pinion gear <NUM> of the second planetary reduction gear <NUM> is a stepped pinion.

In the <NUM>-axis type power transmission device <NUM>, to increase the reduction ratio of the output rotation of the motor <NUM>, it is possible to add a planetary reduction gear (planetary gear mechanism) on the transmission route of the output rotation of the motor <NUM>.

Here, for the pinion gear of the planetary reduction gear, there is the stepped type for which the reduction ratio is easily increased, and the stepless type for which the size is easily made smaller.

If only aiming for the size of the reduction ratio, it is acceptable to have all the planetary reduction gear pinions be stepped types, but in that case, the power transmission device <NUM> becomes larger in the radial direction. Specifically, there is still the problem of increased size.

Here, the first planetary reduction gear <NUM> that is positioned to the downstream side of the motor <NUM> and to the upstream side of the first planetary reduction gear <NUM> is positioned sandwiched by the motor <NUM> and the second planetary reduction gear <NUM>, so it is difficult to take space near the first planetary reduction gear <NUM>.

Also, the second planetary reduction gear <NUM> that is positioned to the downstream side of the second planetary reduction gear <NUM> and to the upstream side of the differential device <NUM> is provided between the first planetary reduction gear <NUM> and the differential case <NUM> of the differential device <NUM>, so it is easier to take space in the periphery than in the case of the first planetary reduction gear <NUM>.

In light of that, while applying the stepless pinion to the first planetary reduction gear <NUM> for which it is difficult to take space in the periphery, by applying the stepped pinion to the second planetary reduction gear <NUM> for which it is comparatively easy to take space in the periphery, in the <NUM>-axis type power transmission device, it is possible to increase the reduction ratio while suppressing an increase in size.

Also, viewing from the radial direction of the rotation axis X, after having the differential case <NUM> and the stepped pinion gear <NUM> overlap, using the bearings B2, B3, the configuration has the differential case <NUM> directly and indirectly supported by the fixed side members (case <NUM>, intermediate cover <NUM>).

This makes it possible to stably support the differential device <NUM> (differential case <NUM>) while suppressing the length in the rotation axis X direction of the power transmission device <NUM>.

<FIG> is an enlarged view around the reduction mechanism <NUM> of a power transmission device 1A of a modification example that is an embodiment of the invention, as defined in claim <NUM>. <FIG> is an enlarged view around a side plate 551A of the second planetary reduction gear <NUM>.

The power transmission device 1A of the embodiment differs from the power transmission device <NUM> described above in that it does not have the intermediate cover <NUM> described above.

With the power transmission device 1A, the side plate 551A of the carrier <NUM> is supported via the bearing B3 on the inner circumference of the intermediate case <NUM>.

The side plate 551A viewed from the rotation axis X direction is a plate member having a ring shape. The side plate 551A is provided oriented orthogonally with respect to the rotation axis X.

The inner diameter side of the side plate 551A extends to the rotation axis X side along the side plate <NUM> of the first planetary reduction gear <NUM> side. An end part 551a of the inner diameter side of the side plate 551A faces the outer circumference of the linking part <NUM> of the first planetary reduction gear <NUM> side with a gap being formed in the radial direction.

With the power transmission device 1A of the embodiment, the linking part <NUM> of the first planetary reduction gear <NUM> side and the linking part <NUM> of the second planetary reduction gear <NUM> side are spline fitted at the inner diameter side of the side plate 551A.

The outer diameter side of the side plate 551A is further to the outer diameter side than the ring gear <NUM> of the first planetary reduction gear <NUM>, and extends to near an outer circumference 531a of the large diameter gear part <NUM> of the second planetary reduction gear <NUM>.

A cylindrical part <NUM> extending to the first planetary reduction gear <NUM> side is provided at the outer diameter side of the side plate 551A.

The cylindrical part <NUM> is inserted from the rotation axis X direction in a recess <NUM> provided in the base <NUM> of the intermediate case <NUM> side. Inside the recess <NUM>, the cylindrical part <NUM> is provided avoiding contact with the base <NUM>.

The recess <NUM> in the base <NUM> is opened at the second planetary reduction gear <NUM> side (left side in <FIG>) at the outer diameter side of the area in which the ring gear <NUM> of the first planetary reduction gear <NUM> is spline fitted.

The recess <NUM> is formed at a depth Dx in the rotation axis X direction that extends to the outer diameter side of the ring gear <NUM>. Viewing from the second planetary reduction gear <NUM> side in the rotation axis X direction, the recess <NUM> has a ring shape.

A step <NUM> that positions the bearing B3 is provided at the outer diameter side of the recess <NUM>.

The bearing B3 is inserted inside the recess <NUM> from the second planetary reduction gear <NUM> side, and an outer race B3b is positioned at a position abutting the step <NUM>.

In this state, the bearing B3 is provided with a gap being formed between it and the large diameter gear part <NUM> of the second planetary reduction gear <NUM> side.

Furthermore, an inner race B3a of the bearing B3 is provided with a gap being formed in the rotation axis X direction between it and the base <NUM>, and the inner race B3a supports the outer circumference of the cylindrical part <NUM> of the second planetary reduction gear <NUM>.

For that reason, the cylindrical part <NUM> of the side plate 551A of the second planetary reduction gear <NUM> is supported to be able to rotate with the intermediate case <NUM> which is a fixed side member with the bearing B3 interposed.

The carrier <NUM> that has the cylindrical part <NUM> is substantially formed integrally with the differential case <NUM>. The cylindrical part <NUM> can be thought of as a portion of the differential case <NUM>.

The cylindrical part <NUM> which is a portion of the differential case <NUM> is supported by the intermediate case <NUM> via the bearing B3 between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> aligned in the rotation axis X direction.

By doing this, the support unit <NUM> side of the rotation axis X direction of the differential case <NUM> is indirectly supported by the intermediate case <NUM>.

Thus, the support stability of the differential case <NUM> when the differential case <NUM> is rotating around the rotation axis X is increased. Also, by the support stability of the differential case <NUM> being increased, the stability of the differential device <NUM> (differential gear) is also increased.

The power transmission device 1A of the embodiment is not equipped with the intermediate cover <NUM> of the power transmission device <NUM> noted above.

For that reason, a length L1 in the rotation axis X direction of the area in which the linking part <NUM> of the first planetary reduction gear <NUM> side, and the linking part <NUM> of the second planetary reduction gear <NUM> side are spline fitted is shorter than a length L2 of the area in which the linking part <NUM> and the linking part <NUM> of the power transmission device <NUM> are spline fitted.

Furthermore, the cylindrical part <NUM> of the second planetary reduction gear <NUM> side and the bearing B3 supporting the cylindrical part <NUM> are positioned at the outer diameter side of the first planetary reduction gear <NUM>.

For that reason, a portion (the cylindrical part <NUM>) of the second planetary reduction gear <NUM>, and the first planetary reduction gear <NUM> overlap in the rotation axis X direction. Specifically, when viewed from radially outward of the rotation axis X, the cylindrical part <NUM> is provided in a positional relationship to overlap with the first planetary reduction gear <NUM>.

By doing this, the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> are arranged closer than the case of the power transmission device <NUM> noted above. Thus, it is possible to suppress the size of the power transmission device 1A in the rotation axis X direction.

As described above, the power transmission device 1A of the embodiment has the following configuration.

(<NUM>) The power transmission device 1A has:.

The cylindrical part <NUM> of the carrier <NUM> that is a portion of the differential case <NUM>, and is positioned between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> aligned in the rotation axis X direction is supported at the inner circumference side of the intermediate case <NUM> (case member) with the bearing B3 (bearing) interposed.

By configuring in this way, by the cylindrical part <NUM> of the carrier <NUM> being supported by the intermediate case <NUM> via the bearing B3, the support unit <NUM> side of the differential case <NUM> in the rotational axis X direction is indirectly supported by the intermediate case <NUM>.

By doing this, the support stability of the differential case <NUM> when the differential case <NUM> rotates around the rotation axis X is increased. Also, by the support stability of the differential case <NUM> being increased, the stability of the differential device <NUM> (differential gear) is also increased.

The power transmission device 1A of the embodiment has the following configuration.

(<NUM>) The cylindrical part <NUM> of the carrier <NUM> is a portion of the differential case <NUM> positioned between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM>. The cylindrical part <NUM> of the carrier <NUM> is supported at the inner circumference side of the intermediate case <NUM> (case member) with the bearing B3 (bearing) interposed.

By configuring in this way, it is possible to support the cylindrical part <NUM> which is a portion of the differential case <NUM> with the inner circumference of the intermediate case <NUM> which is a fixed side member, without needing the wall part <NUM> arranged between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> in the power transmission device <NUM> noted above.

This makes it possible to omit the intermediate cover <NUM> having the wall part <NUM>, so it is possible to make the length of the power transmission device 1A in the rotation axis X direction shorter than the power transmission device <NUM> noted above by the amount omitted for the intermediate cover <NUM>.

(<NUM>) The bearing B3 (bearing) overlaps with the first planetary reduction gear <NUM> in the radial direction.

When the power transmission device 1A is viewed from the radial direction of the rotation axis X, a portion of the first planetary reduction gear <NUM> is arranged to be hidden at the rotation axis side (inner diameter side) of the bearing B3.

Specifically, in the rotation axis X direction, the bearing B3 and the first planetary reduction gear <NUM> are provided having an overlapping range, so the length of the power transmission device 1A in the rotation axis X direction can be shorter by the amount of the overlapping range.

(<NUM>) The bearing B3 (bearing) overlaps the second planetary reduction gear <NUM> in the rotation axis X direction (axial direction).

By using this kind of configuration, the bearing B3 is provided having a range that overlaps the first planetary reduction gear <NUM> in the rotation axis X direction, and the bearing B3 is arranged further to the inner diameter side than the outer circumference of the second planetary reduction gear <NUM> in the radial direction of the rotation axis X.

The bearing B3 is arranged at the outer diameter side of the first planetary reduction gear <NUM> by using an area of the side of the second planetary reduction gear <NUM> in the rotation axis X direction. The space inside the power transmission device 1A can be utilized more effectively.

Here, the term "connected downstream" in this specification means being in a connection relationship in which the power is transmitted from the components arranged upstream to the components arranged downstream.

For example, in the case of the first planetary reduction gear <NUM> connected downstream of the motor <NUM>, this means that the power is transmitted from the motor <NUM> to the first planetary reduction gear <NUM>.

Claim 1:
A power transmission device (<NUM>) comprising:
a motor (<NUM>);
a first planetary reduction gear (<NUM>) connected downstream of the motor (<NUM>);
a second planetary reduction gear (<NUM>) connected downstream of the first planetary reduction gear (<NUM>);
a differential gear (<NUM>) connected downstream of the second planetary reduction gear (<NUM>); and
a drive shaft (8A,8B) connected downstream of the differential gear (<NUM>), wherein
the drive shaft (8b) is arranged penetrating an inner circumference of a rotor (<NUM>) of the motor (<NUM>), an inner circumference of a sun gear (<NUM>) of the first planetary reduction gear (<NUM>), and an inner circumference of a sun gear (<NUM>) of the second planetary reduction gear (<NUM>),
the differential gear (<NUM>) has a differential case (<NUM>),
the sun gear (<NUM>) of the second planetary reduction gear (<NUM>) is an input element (<NUM>) of the second planetary reduction gear (<NUM>), a carrier (<NUM>) is an output element of the second planetary reduction gear (<NUM>), and a ring gear (<NUM>) of the second planetary reduction gear (<NUM>) is a fixed element, and
the differential case (<NUM>) is integrally formed with the carrier (<NUM>),
characterized in that
a cylindrical part (<NUM>) that is an outer circumference part and a portion of the differential case (<NUM>) positioned between the first planetary reduction gear (<NUM>) and the second planetary reduction gear (<NUM>) is supported at an inner circumference side of a case member (<NUM>) with a first bearing (B3) being interposed,
a side plate (551A) of the carrier (<NUM>) has an outer diameter side further to the outer diameter side than a ring gear (<NUM>) of the first planetary reduction gear (<NUM>), and
the cylindrical part (<NUM>) is provided at the outer diameter side of the side plate (551A), extending to a first planetary reduction gear (<NUM>) side.