Patent Description:
In Patent Document <NUM> to Patent Document <NUM>, disclosed is a power transmission device. A power transmission device according to the preamble of claim <NUM> is disclosed in <CIT>.

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").

In a <NUM>-axis type power transmission device, there is a demand to make the reduction ratio greater while suppressing an increase in size.

<CIT> discloses a power transmission device which, in the opinion of the examining division of the European patent office, falls within the wording of the precharacterizing portion of claim <NUM>.

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

According to the present invention, it is possible to make the reduction ratio greater while suppressing an increase in size.

Following, embodiments of the present invention are explained.

<FIG> is a drawing for explaining a power transmission device <NUM> of the present embodiment.

<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>.

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>, <NUM> 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 present embodiment, 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 present embodiment, 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, a connecting part <NUM> that connects the base <NUM> and the motor support unit <NUM> (see <FIG>) 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 present embodiment, 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 along the rotation axis X 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 present embodiment, 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 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, and lubricating oil of the differential device <NUM> is sealed within. 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>.

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>, a ring shaped intermediate cover <NUM> is positioned at the differential device <NUM> side. The intermediate cover <NUM> is provided in a state sandwiched between the intermediate case <NUM> and the case <NUM>.

The linking part <NUM> provided on the inner diameter side of the side plate <NUM> penetrates an opening <NUM> at the center of the intermediate cover <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.

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 a 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 on this side plate with a gap being formed.

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> 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 inner circumference of the opening <NUM> of the intermediate cover <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>.

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 R2 of the small diameter gear part <NUM> is smaller than an outer diameter R1 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, 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>.

An inner race B2a of the bearing B2 is press fitted on the outer circumference of a support unit <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 rotation axis X direction.

Two side gears 63A, 63B are provided with a gap being formed in the rotation axis X direction 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.

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>.

As shown in <FIG>, 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>.

The output unit (carrier <NUM>) of the first planetary reduction gear <NUM> is linked with the input unit (sun gear <NUM>) of the second planetary reduction gear <NUM> without having another member such as a clutch, a shifting mechanism, etc., interposed.

Specifically, the output unit (carrier <NUM>) of the first planetary reduction gear <NUM>, and the input unit (sun gear <NUM>) of the second planetary reduction gear <NUM> rotate integrally (normally rotate integrally).

Thus, it is possible to make the distance between the first planetary reduction gear <NUM> and the second planetary reduction gear <NUM> closer by the amount that the other member is not on the power transmission route, so this contributes to shortening in the axial direction.

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 R2 of the small diameter gear part <NUM> is smaller than the outer diameter R1 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.

Then, the rotation inputted to the differential case <NUM> is transmitted via the drive shafts <NUM> (8A, 8B) to the left and right drive wheels (not illustrated) of the vehicle in which the power transmission device <NUM> is mounted.

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.

As described above, the power transmission device <NUM> of the present embodiment 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 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 gear.

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 second planetary reduction gear <NUM> is provided at a position 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 first 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 easy to take space in the periphery compared to 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.

The power transmission device <NUM> of the present embodiment has the following configuration.

(<NUM>) With the first planetary reduction gear <NUM>, the sun gear <NUM> is an input element of the output rotation of the motor <NUM>, the carrier <NUM> is an output element of the rotation outputted from the first planetary reduction gear <NUM>, and the ring gear <NUM> is a fixed element.

The ring gear <NUM> that has a ring shape when viewed from the rotation axis X direction is a member positioned at the outermost diameter side in the first planetary reduction gear <NUM>, and is arranged near the inner circumference of the intermediate case <NUM> (base <NUM>) that is a fixed side member.

When the ring gear <NUM> is a fixed element, the ring gear <NUM> merely has to be fixed to the fixed side member arranged in the periphery of that ring gear <NUM>.

When not having the ring gear <NUM> be a fixed element, in the periphery of the ring gear <NUM>, it is necessary to have space for placing components for inputting and outputting rotation with respect to the ring gear <NUM>, but by having the ring gear <NUM> be a fixed element, that space is not necessary. Specifically, in the power transmission device <NUM>, it is possible to reduce wasted space in the periphery of the ring gear.

The sun gear <NUM> is a member positioned furthest to the inner diameter side in the first planetary reduction gear <NUM>, and the motor shaft <NUM> that outputs the rotation of the rotor core <NUM> (rotor) of the motor <NUM> is positioned in the inner diameter side of the power transmission device <NUM>.

By having the sun gear <NUM> of the first planetary reduction gear <NUM> be an input element, it is possible to have the output element of the motor <NUM> (motor shaft <NUM>), and the input element of the first planetary reduction gear <NUM> side (sun gear <NUM>) be closer in the rotation axis X direction.

This makes it possible to decrease the size of the <NUM>-axis type power transmission device <NUM> in the rotation axis X direction.

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

The ring gear <NUM> that has a ring shape when viewed from the rotation axis X direction is a member positioned at the outermost diameter side in the second planetary reduction gear <NUM>, and is arranged near the inner circumference of the case <NUM> that is a fixed side member.

The sun gear <NUM> of the second planetary reduction gear <NUM> is a member positioned furthest to the inner diameter side in the second planetary reduction gear <NUM>.

By having the sun gear <NUM> of the second planetary reduction gear <NUM> be an input element, and having the carrier <NUM> of the first planetary reduction gear <NUM> be an output element, it is possible to have the output element of the first planetary reduction gear <NUM>, and the input element of the second planetary reduction gear <NUM> be closer in the rotation axis X direction.

Furthermore, by having the carrier <NUM> of the second planetary reduction gear <NUM> be an output element, it is possible to have the output element of the second planetary reduction gear <NUM>, and the differential device <NUM> (differential gear) be closer in the rotation axis X direction.

This also makes it possible to reduce the size of the <NUM>-axis type power transmission device in the rotation axis X direction.

(<NUM>) The carrier <NUM> of the first planetary reduction gear <NUM> overlaps the sun gear <NUM> of the first planetary reduction gear <NUM> in the rotation axis X axial direction.

The carrier <NUM> of the first planetary reduction gear <NUM> is supported by a part that integrally rotates with the sun gear <NUM> of the first planetary reduction gear <NUM> with a thrust bearing (needle bearing NB) interposed.

When viewed from the rotation axis X direction, when the carrier <NUM> of the first planetary reduction gear <NUM> overlaps the sun gear <NUM> of the first planetary reduction gear <NUM>, it is necessary to prevent interference (contact) of the two.

Here, there is play in the engagement of the gears of each of the constituent elements of the first planetary reduction gear <NUM>. For that reason, to prevent interference of the carrier <NUM> and the sun gear <NUM>, it is necessary to expand the clearance in the rotation axis X direction between the carrier <NUM> side (side plate <NUM>) and the sun gear <NUM> side (side surface 41b).

The thrust bearing (needle bearing NB) can be formed thinly in the rotation axis X direction.

In light of that, the needle bearing NB is interposed between the carrier <NUM> (side plate <NUM>) and the sun gear <NUM> side (side surface 41b), and the carrier side and the sun gear side are supported via the needle bearing NB. Having done that, it is possible to have the carrier <NUM> (side plate <NUM>) and the sun gear <NUM> side (side surface 41b) be as close as possible to each other, and possible to reduce the dimension in the axial length direction of the <NUM>-axis type power transmission device having two planetary reduction gears.

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 (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>), and
a pinion (<NUM>) of the first planetary reduction gear (<NUM>) is a stepless pinion, and a pinion (<NUM>) of the second planetary reduction gear (<NUM>) is a stepped pinion,
characterized in that
the carrier (<NUM>) of the first planetary reduction gear (<NUM>) overlaps with the sun gear (<NUM>) of the first planetary reduction gear (<NUM>) in an axial direction, and
the carrier (<NUM>) of the first planetary reduction gear (<NUM>) is supported by a part that integrally rotates with the sun gear (<NUM>) of the first planetary reduction gear (<NUM>) via a thrust bearing (NB).