Patent Description:
Conventionally, vehicles such as lawn mowing vehicles equipped with lawn mower blades, in which the wheels can be driven by an electric motor to travel, have been known. <CIT> and <CIT> disclose a lawn mowing vehicle in which left and right wheels are driven by the same electric motor. <CIT> discloses a lawn mowing vehicle in which the left and right wheels can be driven by motors independently of each other, with the left wheel driven by a left electric motor and the right wheel driven by a right electric motor.

In the above disclosures, the vehicles in which the left and right wheels are driven by one or two motors use a power transmission unit to transmit driving power of the motor(s) to the wheels. In the power transmission unit disclosed in <CIT>, it is suggested that a motor case in which a motor is enclosed is fixed to a transmission case enclosing a gear mechanism to transmit driving power from an input shaft to an output shaft. However, since the motor case has a complicated shape, there is a room for improvement to reduce the manufacturing cost of the entire power transmission unit.

Furthermore, when fixing the motor case to the transmission case, if misalignment exists between a center axis of an inner circumferential surface formed in the motor case, to which a stator core of the motor is fixed, and a center axis of a hole formed in the transmission case, through which a motor shaft of the motor passes, it becomes difficult to assemble the motor case to the transmission case. There is also a room for improvement to reduce the manufacturing cost of the power transmission unit. If the center axis of the inner circumferential surface is misaligned with the center axis of the hole, noise and vibration increase.

<CIT> discloses a power transmission unit including a motor and a transmission case as well as a gear mechanism.

An object of the present invention is to reduce a manufacturing cost of a power transmission unit in which a motor case is fixed to a transmission case.

According to the invention, a power transmission unit includes: a motor; and a transmission case to enclose an input shaft, an output shaft, and a gear mechanism that transmits driving power between the input shaft and the output shaft, wherein a motor case is attached to the transmission case on a side opposite the gear mechanism of the transmission case, the motor case has a cylindrical shape whose cross section is constant throughout a direction orthogonal to an axial direction of the motor case, and the motor is placed inside the motor case.

Furthermore, the power transmission unit according to the invention includes a cover fixed to the motor case to block an opening at an outer end in the axial direction of the motor case, wherein the motor case is directly coupled to the transmission case and wherein a support to secure a bearing that supports a rotor shaft of the motor is provided on a side of the transmission case. A further aspect of the invention is disclosed in the dependent claim.

Embodiment(s) of the present invention will be described based on the following figures, wherein:.

Embodiments of the present disclosure will be described below in detail with reference to the drawings. In the following, a power transmission unit mounted on an lawn mowing vehicle as a working vehicle is described, but the vehicle mounting the power transmission unit of the present disclosure is not limited thereto, and may be a work vehicle equipped with a work machine capable of performing at least one task including snow removal, excavation, civil engineering, and agricultural work, or an off-road type utility vehicle having a cargo bed and traveling on uneven terrain (Utility Vehicle), or an all-terrain vehicle (ATV) called a buggy, or a Recreational Vehicle (RV), or a Recreational Off-highway Vehicle (ROV). In the following, the electric vehicle, in which two rear wheels are driven with two motors, respectively, is described as an example, but it may be configured so that two front wheels are driven with two motors, respectively. Also in the following, a left-right lever-type operator with left and right operating levers is described as only an example, but the present disclosure is not limited thereto; a steering handle may be used as a steering device and an accelerator pedal provided in front of a seat may be used as an accelerator device. In the following description, the same elements are denoted by identical reference numerals throughout all the drawings.

<FIG> and <FIG> show a first embodiment of the present disclosure. In the drawings referred to below, a front-and-rear direction, a right-and-left direction, and a vertical direction are indicated by X, Y, and Z, respectively. In the drawings referred to below, a side indicated by Fr and a side indicated by Lh are defined as the front side and the left side, respectively. X, Y, and Z are orthogonal to each other.

First, the general configuration of a lawn mowing vehicle <NUM> is described, and then power transmission units 41a, 71a (see <FIG> and <FIG>) mounted on a lawn mowing vehicle <NUM> are described in detail. The lawn mowing vehicle <NUM>, which is of the riding type on which no engine is mounted, includes a main frame <NUM> comprising a body, two caster wheels <NUM>, <NUM> constituting left and right front wheels, two wheels <NUM> constituting left and right rear wheels, a lawn mower <NUM> as the working machine, left and right two operation levers <NUM>, <NUM>, and a power source unit <NUM> including a battery. In <FIG>, the left rear wheel, which is hidden by the body, is invisible.

A driver's seat <NUM> disposed on the upper side of the body is fixed to the main frame <NUM> at the middle point in the front-and-rear direction. The left and right caster wheels <NUM>, <NUM> are supported on the front side of the main frame <NUM>. As each of the caster wheels <NUM>, <NUM> is freely rotatable around a vertical axis, the vehicle can turn more than <NUM> degrees on horizontal terrain. The left and right rear wheels <NUM> are supported on the rear side of the main frame <NUM>. The left and right rear wheels <NUM> are main driving wheels and are driven by left and right electric motors <NUM> for traveling, respectively, as described below (see <FIG>).

Instead of the two caster wheels <NUM>, <NUM>, only one caster wheel, or three or more caster wheels may be attached to the lawn mowing vehicle <NUM>. The caster wheels and the driving wheels may be switched in position; i.e., the front-and-rear direction.

The lawn mower <NUM> is supported by the main frame <NUM> under the body at the middle point in the front-and-rear direction. The lawn mower <NUM> includes a mower deck <NUM> and three lawn mower blades (not shown) as a mowing rotary tool, each of which is rotatable around a vertical axis inside the mower deck <NUM>. The rotation of the lawn mower blades makes it possible to break up and mow grass, etc. Each of the lawn mower blades is driven by a motor <NUM> for the mower.

The rotation of the lawn mower blades makes it possible to mow the lawn, and the mowed grass is discharged from the inside of the mower deck <NUM> to one of the outside thereof in the left-and-right direction.

The lawn mower may be configured to comprise a lawn mowing reel as a rotary tool for mowing the lawn, which has a spiral blade, for example, arranged on a cylinder with a rotation axis parallel to the ground surface, functions to pinch and mow the lawn, etc., and is driven by a deck motor.

The left and right operation levers <NUM> and <NUM> are provided on respective sides of the driver's seat <NUM> to be able to pivot around a horizontal axis along the right-and-left direction and swing toward the front-and-rear direction. When each of the operation levers <NUM>, <NUM> is in a normally upright state, the motor <NUM> for traveling stops rotating. When each of the operation levers is operated to swing, instructions are issued such that a direction and speed of rotation of the motor <NUM> on the corresponding side are to be changed according to a direction and amount of swinging.

The swinging position of the operation levers <NUM>, <NUM> in the front-and-rear direction is detected with a lever sensor (not shown). The detected signal of the lever sensor is input to a control unit (not shown) installed in the vehicle as a signal indicating a rotation instruction of the motor <NUM> for traveling, and the control unit causes the motor <NUM> to rotate in a direction following the instruction. Driving power of the motor <NUM> is transmitted to the left and right rear wheels <NUM> through a gear mechanism <NUM> of the power transmission units 41a, 71a (see <FIG> and <FIG>) described below. This allows the vehicle to travel in the front-and-rear direction depending on the operation of the operation levers <NUM>, <NUM>. In addition, a difference in a rotation speed between the left and right rear wheels <NUM> is caused by varying an amount of a swinging operation between the left and right operation levers <NUM>, <NUM>, so that the vehicle can turn. Furthermore, by tilting one and the other of the two operation levers <NUM>, <NUM> to the front side and the rear side, respectively, the left and right rear wheels <NUM> rotate in opposite directions, so that the turning radius decreases to cause the vehicle to turn quickly.

Furthermore, the two operation levers <NUM>, <NUM> are configured to be able to tilt from the normal upright state toward the outside of the vehicle in the vehicle-width direction so that the tilted position becomes a parking brake position. The two operation levers <NUM>, <NUM> can instruct activation of the parking brake by being moved to the parking brake position. The upper side of the vehicle is provided with a T-shaped guide hole <NUM> to guide the movement of the operation levers <NUM>, <NUM>, so that the two operation levers <NUM>, <NUM> can respectively be only tilted from the upright state thereof toward the outside of the vehicle in the vehicle-width direction. The lower end portions of the operation levers <NUM>, <NUM> and a brake device <NUM> (described below) of the power transmission units 41a, 71a are coupled with a linkage mechanism, so that when the operation levers <NUM>, <NUM> are tilted toward the outside of the vehicle, the brake device <NUM> can be activated to brake a corresponding wheel <NUM>.

The general configuration of the lawn mowing vehicle <NUM> is described above. Next, the power transmission unit 41a (see <FIG>) mounted on the lawn mowing vehicle <NUM> is described below. The right power transmission unit 41a is connected to the right rear wheel <NUM>, and the left power transmission unit 71a (<FIG>) is connected to the left rear wheel. In the following, although the structure of the right power transmission unit 41a is mainly described, the structure of the right power transmission unit 41a and the structure of the left power transmission unit 71a are symmetrical with respect to the center line of the body orthogonal to the right-and-left direction.

<FIG> is a cross sectional view of the power transmission unit 41a for the right rear wheel <NUM>, which is taken along a plane orthogonal to the vertical direction. <FIG> is a partially enlarged diagram illustrating a rear part of FIG. <FIG> is a cross sectional view taken along line G-G of <FIG>. <FIG> and <FIG> correspond to cross sectional views taken along line H-H of <FIG>. The power transmission unit 41a includes a transmission case 42a (see <FIG> and <FIG>), a motor case <NUM>, an output shaft <NUM>, the motor <NUM> for traveling, and the gear mechanism <NUM>, which are integrally combined to form the power transmission unit 41a.

The transmission case 42a encloses an input shaft <NUM>, the output shaft <NUM>, and the gear mechanism <NUM>. The gear mechanism <NUM> transmits driving power from the input shaft <NUM> to the output shaft <NUM> while reducing speed. The input shaft <NUM> and the output shaft <NUM> are arranged in parallel. The input shaft <NUM> is also a motor shaft of the motor <NUM> described below. Namely, the input shaft <NUM> functions as the motor shaft. The transmission case 42a is integrated by connecting with a plurality of bolts <NUM> a first case <NUM> forming an inner side (left side) in the vehicle-width direction of one side in an axial direction thereof and a second case <NUM> forming an outer side (right side) in the vehicle-width direction of the other side in the axial direction thereof. Here, the axial direction of the power transmission unit 41a indicates a direction parallel to the input shaft <NUM> and output shaft <NUM>, and aligns with the vehicle-width direction.

The first case <NUM> has a gear case part <NUM> having an opening which extends toward the outside thereof in the vehicle-width direction, and an intermediate wall <NUM> to partition between the motor <NUM> side and the gear mechanism <NUM> side at a position in the middle of a rear portion thereof in the axial direction.

The intermediate wall <NUM> has a boss part 48a as a cylindrical portion extending in the axial direction, inside which there is provided a hole <NUM> through which the input shaft <NUM> as the rotor shaft of the motor <NUM> passes. A bearing <NUM> and a seal <NUM> which protects a gear chamber from invasion of a circulating oil into the motor chamber are fixed on the inner circumferential surface of the hole <NUM>. The input shaft <NUM> is rotatably supported by the bearing <NUM> on the inner circumferential surface of the hole <NUM>. The boss part 48a corresponds to a support to secure the bearing <NUM> which supports the input shaft <NUM>.

An input shaft gear part <NUM>, with which an intermediate gear <NUM> of the gear mechanism <NUM> meshes, is directly formed on the gear mechanism <NUM> side of the input shaft <NUM>.

The second case <NUM> has a cylinder part <NUM> extending along the axial direction toward the outside in the vehicle-width direction, inside which an opening extends in the vehicle-width direction. The output shaft <NUM> passes through the cylinder part <NUM>. The transmission case 42a is formed by connecting the first case <NUM> and the second case <NUM> so that the outer peripheries of both cases are abutted to each other in the vehicle-width direction. A gear chamber S1 is formed inside the transmission case 42a.

There are arranged in the gear chamber S1 a gear mechanism <NUM> side portion of the input shaft <NUM>, the gear mechanism <NUM>, and the output shaft <NUM>. An outer end portion of the output shaft <NUM> in the vehicle-width direction protrudes from the tip of the cylinder part <NUM>, and a hub <NUM> is fixed to the protruding outer end portion. The right rear wheel <NUM> is fixed to the hub <NUM>.

The gear mechanism <NUM> includes the input shaft gear part <NUM> formed on the input shaft <NUM>, an intermediate shaft <NUM>, which is located between the input shaft <NUM> and the output shaft <NUM> and whose outer circumferential surface fixes the intermediate gear <NUM>, and an output gear <NUM> fixed to the output shaft <NUM>, so that the intermediate gear <NUM> meshes with the input shaft gear part <NUM> and the output gear <NUM> meshes with an intermediate shaft gear part <NUM> formed directly on the outer circumferential surface of the intermediate shaft <NUM>. The number of teeth of the output gear <NUM> is greater than that of the intermediate shaft gear part <NUM>, and the number of teeth of the intermediate gear <NUM> is greater than that of the input shaft gear part <NUM>. This allows the rotation speed of the input shaft <NUM> to be reduced by the gear mechanism <NUM> and transmitted to the output shaft <NUM>. Therefore, the gear mechanism <NUM> can transmit driving power from the input shaft <NUM> to the output shaft <NUM> with the rotation speed of the input shaft being reduced.

The input shaft <NUM>, the intermediate shaft <NUM>, and the output shaft <NUM> are rotatably supported by a plurality of bearings <NUM>, <NUM>, <NUM>, and <NUM> provided in the transmission case 42a, respectively.

In addition, a brake rotor <NUM>, which constitutes the brake device <NUM> as described below, is mounted on the intermediate shaft <NUM> so as to be nonrotatable. By pressing the brake rotor <NUM> with a brake shoe <NUM> (see <FIG>) and a brake pad <NUM> (see <FIG>) from both sides in the axial direction, braking torque is applied to the brake rotor <NUM> to stop the intermediate shaft <NUM> from rotating. The brake shoe <NUM> and the brake pad <NUM> together correspond to a pressing part.

The first case <NUM> and the second case <NUM> of the transmission case 42a may be made of metal such as iron, aluminum alloy, or the like. By making each of cases <NUM>, <NUM> of aluminum alloy, it is possible to make the transmission case 42a lightweight. The gear chamber S1 of the transmission case 42a is capable of encapsulating oil to lubricate the gear mechanism <NUM>.

An outer periphery of the motor case <NUM> is abutted and fixed to an inner periphery of the first case <NUM> of the transmission case 42a in the vehicle-width direction. The motor case <NUM> has a cylindrical shape whose cross-section is constant throughout a direction orthogonal to the axial direction, and the motor <NUM> for traveling is placed on the inside thereof. Specifically, as shown in <FIG>, the motor case <NUM> has a cylinder part <NUM>, connecting ribs <NUM> with a semi-circular cross section, which protrude from a plurality of circumferential positions of the cylinder part <NUM> and extend in the axial direction, and reinforcing ribs <NUM>, <NUM>, which protrude from a plurality of circumferential positions of the cylinder part <NUM> and extend in the axial direction, with width along the circumference smaller than width along the circumference of the connecting ribs <NUM>. The connecting ribs <NUM> and reinforcing ribs <NUM>, <NUM> are formed over the entire axial length of the motor case <NUM> in the axial direction. Circular bolt holes <NUM>, into which bolts <NUM> are inserted, are formed at a plurality of positions along the circumference of the motor case <NUM> so as to pass through the connecting ribs <NUM> while a portion of each of the holes enters into the cylinder part <NUM>.

<FIG> is an exploded cross sectional view just before assembly into the state shown in <FIG>. Threaded holes <NUM> are formed at a plurality of positions on the end surface of the first case <NUM> facing the motor case <NUM>, which align with the respective bolt holes <NUM> of the motor case <NUM>. The first case <NUM> is fixed to the motor case <NUM> and a cover <NUM> by screwing the threaded parts of the bolts <NUM>, which pass through the cover <NUM> and the bolt holes <NUM>, with the threaded holes <NUM>. The motor case <NUM> may be made of a metal or alloy whose main component is aluminum or copper. This allows the motor case <NUM> to have higher thermal conductivity. Furthermore, when the motor case <NUM> is made of a metal or alloy whose main component is aluminum, the motor case <NUM> can be made lightweight. The motor case <NUM> may be made of other metals such as iron or the like. When the motor case <NUM> is made of metal, the motor case <NUM> is formed by extrusion molding or pultrusion molding.

Since the motor case <NUM> has a cylindrical shape whose cross-section is constant throughout a direction orthogonal to the axial direction, the motor case <NUM> can be formed by extrusion molding or pultrusion molding with high productivity. This allows a reduction in the manufacturing cost of the motor case <NUM>. Furthermore, when the motor case <NUM> is made of metal with high thermal conductivity, since a larger heat dissipation member allows the heat of the motor <NUM> located inside the motor case to be efficiently transferred from the motor case <NUM> to the transmission case <NUM>, the cooling performance of the motor <NUM> can be improved. Furthermore, since a structure in which the motor <NUM> is assembled inside the motor case <NUM> can be used as a subassembly, it is possible to facilitate assembly work when manufacturing the power transmission unit 41a.

The motor case <NUM> may be made of resin. Also in this case, since the motor case <NUM> has a cylindrical shape whose cross-section is constant throughout a direction orthogonal to the axial direction as well as the shape is simple, a manufacturing die for the motor case <NUM> can be formed easily. This allows a reduction in the manufacturing cost of the motor case <NUM>.

As shown in <FIG> and <FIG>, the motor <NUM> is a three-phase permanent magnet motor, for example. The motor <NUM> includes a rotor <NUM> fixed on an outer circumferential surface of the input shaft <NUM> inside the motor case <NUM>, a stator core <NUM> facing an outer circumferential surface of the rotor <NUM>, and a three-phase wound stator coil <NUM> arranged on the stator core <NUM>. The rotor <NUM> has permanent magnets arranged at a plurality of positions along a circumference of the rotor core, for example. The stator core <NUM> is fixed to the inside of the motor case <NUM>. By supplying three-phase AC power to the stator coil <NUM>, which is converted from DC power from the battery, the interaction between a rotating magnetic field generated in the stator core <NUM> and the magnetic field generated by the motor rotor <NUM> causes the input shaft <NUM> of a motor shaft to rotate.

Since the motor case <NUM> has a cylindrical shape whose cross-section is constant throughout a direction orthogonal to the axial direction, when assembling the stator core <NUM> inside the motor case <NUM>, an axial position to be fixed of the stator core <NUM> can be determined by using a jig (not shown) with an outer diameter slightly smaller than an outer diameter of the stator core <NUM> and a predetermined thickness in the axial direction. Namely, the stator core <NUM> is overlaid and press-fitted into the motor case <NUM> with the jig, so that the stator core <NUM> can be positioned and fixed inside the motor case <NUM> by the thickness of the jig.

The cover <NUM>, which closes an opening at an inner end in the vehicle-width direction of an axially inner end of the motor case <NUM>, is fixed to the motor case <NUM> by a plurality of bolts (not shown). The cover <NUM> may be made of metal such as iron, aluminum alloy, or the like. A cylindrical portion <NUM> extending in the axial direction is formed on the axially inner side of the cover <NUM>, and a bearing <NUM> rotatably supporting the axially inner end of the input shaft <NUM> is fixed inside the cylindrical portion <NUM>. A recess <NUM> is formed on the outer side of the cover <NUM> in the vehicle width direction, and a cap <NUM>, which is made by resin or metal, etc. and has a plate-like shape, is fixed to a periphery of an opening end of the recess <NUM>. This allows the recess <NUM> to be protected from a foreign-matter intrusion from the outside.

A rotation speed detecting device <NUM> is provided in the recess <NUM> to detect the rotation speed of the input shaft <NUM>. In place of the rotation speed detecting device <NUM>, an angle detecting device may be provided to detect the rotation angle of the input shaft <NUM>. A detected signal of the rotation speed detecting device <NUM> or the angle detecting device is output to the control unit via a cable 69a. The detected signal from the rotation speed detecting device <NUM> is used by the control unit to control the output of the motor <NUM>, etc. When the detected signal from the angle detecting device is output to the control unit, the control unit calculates the rotation speed of the input shaft <NUM> based on the detected signal. The rotation speed detecting device <NUM> and the angle detecting device include a resolver, for example.

In the following, the input shaft <NUM> is described in more detail. The input shaft <NUM> has a structure in which the motor shaft and the input shaft of the gear mechanism <NUM> are integrated. As shown in <FIG> and <FIG>, a key protrusion 74a is formed on the inner circumferential surface of the rotor <NUM>, and a key groove 72a is formed on the outer circumferential surface of the input shaft <NUM> on the side of the motor <NUM>. By engaging the key protrusion 74a to the key groove 72a, rotation of the rotor <NUM> relative to the input shaft <NUM> is prevented. The input shaft gear part <NUM> is formed directly on the outer circumferential surface on the gear mechanism <NUM> side of the input shaft <NUM>.

<FIG> is a perspective view illustrating an example of the motor case <NUM> according to the embodiment. As shown in <FIG>, the motor case <NUM> has a plurality of ribs 130a, 130b protruding at a plurality of positions along the circumference on the outer circumferential surface, for example. The ribs 130a and 130b are provided over the entire axial length of the motor case <NUM> in the axial direction, and the cross-sectional shape of each of the ribs 130a and 130b in a direction orthogonal to the axial direction is constant over the entire axial length. Some of the plurality of ribs 130a among the plurality of ribs 130a and 130b have the bolt holes <NUM> through which the bolts <NUM> (see <FIG>) pass. The plurality of bolt holes <NUM> are formed in parallel with the central axis O1 of the motor case at a plurality of positions along the circumference of the motor case <NUM>.

<FIG> is a partially enlarged cross sectional view of the two rear wheels <NUM> corresponding to a cross sectional view taken along line I-I of <FIG>. <FIG> is a perspective view with some parts omitted illustrating the power transmission unit 41a for the right rear wheel <NUM> of the vehicle <NUM> according to the embodiment. A braking force generator <NUM> applies braking force to the brake rotor <NUM>. The braking force generator <NUM> includes a cam shaft <NUM> located upside the first case <NUM> along the vertical direction, the brake shoe <NUM>, the brake pad <NUM>, and a brake arm <NUM>.

Specifically, a multi-disc brake rotor <NUM> fits with the intermediate shaft <NUM> constituting the gear mechanism <NUM> in such a manner that relative rotation is impossible. A brake device 90a includes the brake rotor <NUM> and the braking force generator <NUM>. More specifically, as shown in <FIG>, <FIG>, and <FIG>, a female spline part 111a formed in the central hole of a plurality of rotor plates <NUM> which form the brake rotor <NUM> meshes with the intermediate shaft gear part <NUM> formed directly on the outer circumferential surface of the intermediate shaft <NUM> in such a manner that relative rotation is impossible. The rotor plate <NUM> is capable of axially sliding slightly relative to the intermediate shaft gear part <NUM>. This allows the brake rotor <NUM> to be mounted on the intermediate shaft <NUM> in such a manner that relative rotation is impossible. A fixed side plate <NUM>, which is supported by the transmission case 42a in such a manner as to be movable in the axial direction, is located between the plurality of rotor plates <NUM>. For the sake of simplicity, <FIG> shows only one rotor plate <NUM> and one fixed side plate <NUM>.

On the other hand, the cam shaft <NUM>, which constitutes the braking force generator <NUM>, extends in the vertical direction and is rotatably supported by the transmission case 42a, and the upper portion thereof protrudes from the top of the transmission case 42a. Accordingly, a through hole 115a, through which the cam shaft <NUM> passes, is formed at the upper end portion above the intermediate shaft <NUM> of the first case <NUM> in the vertical direction. The upper portion of the through hole 115a has a larger diameter than the lower portion, and two O-rings <NUM> are provided inside thereof to seal between the through hole 115a and the outer circumferential surface of the cam shaft <NUM>. It may be the case that only one O-ring <NUM> is provided. On the other hand, in the gear chamber S1, a portion with semi-circular cross section functioning as a cam surface <NUM> is formed on the lower side of the cam shaft <NUM>. The cam surface <NUM> faces the brake shoe <NUM> which is movable in the axial direction of the transmission case 42a. The brake shoe <NUM> is located between the cam shaft <NUM> and the brake rotor <NUM>.

The brake pads <NUM> are attached on an inner wall of the transmission case 42a. The brake rotor <NUM> is located between the brake shoes <NUM> and the brake pads <NUM>. When the cam surface <NUM> is positioned in parallel to the brake shoes <NUM>, the brake shoes <NUM> move away from the brake rotor <NUM> to be in a non-braking state. On the other hand, when the cam shaft <NUM> rotates so that the cam surface <NUM> inclines with respect to the brake shoes <NUM>, the cam surface <NUM> is pressed against the brake shoes <NUM>. As a result, since the brake rotor <NUM> is sandwiched between the brake pads <NUM> and brake shoes <NUM>, the brake rotor <NUM> and thus the wheel <NUM> to which power is transmitted from the input shaft <NUM> are braked.

The brake arm <NUM> is a long member attached and fixed to the upper end portion of the cam shaft <NUM> in a direction orthogonal to the cam shaft <NUM>. A tip of the brake arm <NUM> is coupled to the lower end portions of the operation levers <NUM>, <NUM> (see <FIG>) via a link mechanism (not shown). A spring <NUM> is disposed between the outer circumferential surface of the transmission case 42a enclosing the cam shaft <NUM> and the brake arm <NUM> in the vertical direction. A first engagement pin <NUM> which is fixed to the brake arm <NUM> and protrudes downward and a second engagement pin <NUM> which is fixed to the transmission case 42a and protrudes upward engage with respective ends of the spring <NUM>. This forces the cam shaft <NUM> to rotate toward a first rotation direction from the spring <NUM> via the brake arm <NUM> so that the cam surface <NUM> becomes parallel to the brake shoes <NUM> to be in a non-braking state. On the other hand, when operating the operation levers <NUM>, <NUM> to assume the parking brake position, the tip of the brake arm <NUM> moves against spring bias of the spring <NUM>. This forces the cam shaft <NUM> to rotate toward a second rotation direction so that the cam surface <NUM> inclines relative to the brake shoes <NUM> to press the brake shoes <NUM> against the brake rotor <NUM>. The second rotation direction is opposed to the first rotation direction. As a result, the brake device 90a comes into the braking state where the rotation of the brake rotor <NUM> and the wheel <NUM> stop, and this state is maintained. The brake rotor may be configured to be mounted on the gear mechanism side of the input shaft instead of the intermediate shaft. In this case, the brake shoes and brake pads press the brake rotor from both sides in the axial direction to stop the input shaft from rotating and brake the wheels.

With respect to the input shaft <NUM> of the first case <NUM>, a lower through hole 115b is formed at the lower end portion which is the opposite side to the upper through hole 115a through which the cam shaft <NUM> passes. The lower through hole 115b is plugged with a plug <NUM>. The two through holes 115a and 115b are identical in shape. When the vertical direction of the transmission case 42a is reversed, the lower through hole 115b in <FIG> becomes the upper through hole to pass through the cam shaft <NUM>, and the upper through hole 115a in <FIG> becomes the lower through hole to be plugged with the plug <NUM>.

<FIG> is a cross sectional view taken along line J-J of <FIG>. In the first case <NUM> of the transmission case 42a, two through holes 115c and 115d, which pass through the first case in the vertical direction, are formed on the upper and lower side of the input shaft <NUM>, respectively. An air breather device <NUM> is installed through the upper through hole 115c. The air breather device <NUM> is provided to prevent entry of liquids such as water, dust, etc. thereinto from the upper side and to allow air inside the gear chamber S1 to be sucked in and out of the transmission case 42a. When the internal pressure of the gear chamber S1 rises, air is discharged outside the transmission case 42a through the air breather device <NUM> to prevent an excessive rise in internal pressure. The lower through hole 115d is plugged with a plug <NUM>. The two through holes 115c and 115d are identical in shape. When the vertical direction of the transmission case 42a is reversed, the lower through hole 115d in <FIG> becomes the upper through hole to attach the air breather device <NUM>, and the upper through hole 115c in <FIG> becomes the lower through hole to be plugged with the plug <NUM>.

According to the above-mentioned power transmission units 41a, 71a, the motor case <NUM>, which is attached to the transmission case 42a on the side opposite to the gear mechanism <NUM> side of the transmission case 42a, has a cylindrical shape whose cross-section is constant throughout a direction orthogonal to the axial direction, and the motor <NUM> is placed inside the same. This allows a reduction in manufacturing cost of a power transmission unit 41a, 71a in which the motor case <NUM> is fixed to the transmission case 42a.

Furthermore, the input shaft <NUM> is a motor shaft, in which the rotor <NUM> is fixed on the outer circumferential surface thereof. The input shaft gear part <NUM>, with which the intermediate gear <NUM> of the gear mechanism <NUM> meshes, is formed directly on the gear mechanism <NUM> side of the input shaft <NUM>. This makes it possible to shorten the length of the power transmission units 41a, 71a in the axial direction, since it is not necessary to connect the motor shaft and the input shaft as two different members through a joint with each other. Furthermore, differently from the case where the motor shaft and input shaft are two different members, it is possible to reduce the manufacturing cost by decreasing not only the number of parts but also the number of man-hours required to assemble the parts. Furthermore, since the input shaft gear part <NUM> of the input shaft <NUM> can be made smaller in diameter, the power transmission units 41a, 71a can be made smaller as a whole.

<FIG> is a diagram illustrating another example having a different transmission case from the embodiment shown in <FIG>. <FIG> is a partially enlarged diagram illustrating a rear part of <FIG>. <FIG> is a diagram illustrating another example having a different transmission case from the embodiment shown in <FIG>. <FIG> is a diagram illustrating another example having a different transmission case from the embodiment shown in <FIG>.

Another example of a transmission case 42a1 is configured so that the second case <NUM> is connected to a first case 115a1 by bolts <NUM>. A cylinder <NUM> with a cylindrical shape, which protrudes from an axial end surface of the first case 115a1 toward the motor case <NUM>, is formed on the axial end surface on the boss part 48a side having the hole <NUM>, and in which it is overlaid with the motor case <NUM>. The end portion of the transmission case 42a1 side of the motor case <NUM> is fitted to the outside of the outer circumferential surface of the cylinder <NUM> without rattling. The cylinder <NUM> is a centering structure to align a central axis O2 of the hole <NUM> in the transmission case 42a1 with a central axis O1 of the inner circumferential surface in the motor case <NUM>, to which the stator core <NUM> is fixed.

This allows more precise alignment of the central axis O1 of the inner surface of the motor case <NUM> and the center axis O2 of the hole <NUM> formed in the transmission case 42a1, through which the input shaft <NUM> as the motor shaft of the motor <NUM> passes. As a result, since the assembly work of the motor case <NUM> to the transmission case 42a1 is facilitated, the manufacturing cost of the power transmission unit 41a can be reduced. In addition, since central axes of the motor rotor <NUM> and the stator core <NUM> of the motor <NUM> can be aligned more precisely, a rotational fluctuation of the motor <NUM> can be suppressed, thereby suppressing an increase of vibration and noise.

In the configuration shown in <FIG>, the shape of the cylinder <NUM> formed in the first case 115a1 is not limited to the cylinder. For example, it is possible to configure such that top surfaces of three or more protrusions formed on the outer circumferential surface of the cylinder part along the outer circumference can fit to the inner circumferential surface of the motor case <NUM>.

<FIG> is a diagram illustrating another example that is different from the embodiment shown in <FIG>, in that the brake rotor <NUM> is not mounted on an intermediate shaft <NUM> (see <FIG> and <FIG>) but only one brake rotor <NUM> is mounted on the input shaft <NUM>. In the first case <NUM> of the transmission case 42a, the cam shaft <NUM> of the brake device 90a passes through the through hole 115c, which is formed on the upper side of the input shaft <NUM> to pass through the first case in the vertical direction. The brake arm <NUM> is fixed to the upper end portion of the cam shaft <NUM>, similarly to the configuration shown in <FIG>.

On the other hand, a brake rotor <NUM> for the input shaft <NUM>, which constitutes the brake device <NUM>, is mounted on the input shaft gear part <NUM> formed in a portion disposed in the transmission case 42a so as to be nonrotatable. By pressing the brake rotor <NUM> with the brake shoe <NUM> and the brake pad <NUM> from respective sides in the axial direction, braking torque is applied to the brake rotor to stop the input shaft <NUM> from rotating. The brake shoe <NUM> and the brake pad <NUM> together form the pressing part.

Furthermore, the intermediate gear <NUM> (see <FIG>) fixed to the intermediate shaft <NUM> meshes with the input shaft gear part <NUM> at a different position from the brake rotor <NUM> in the axial direction. A braking force generator 92a is constituted to include the cam shaft <NUM>, the brake shoes <NUM>, the brake pads <NUM>, and the brake arm <NUM>. The configuration of the braking force generator 92a is similar to that of the braking force generator <NUM> shown in <FIG> except for parts arrangement position. In the configuration shown in <FIG>, the through hole 115a (see <FIG>), through which the cam shaft passes, is not formed at the upper end portion above the intermediate shaft <NUM> of the transmission case 42a in the vertical direction, or, even when the though hole 115a is formed, it is plugged with the plug.

In the configuration shown in <FIG>, since the brake rotor <NUM> is fixed to the input shaft <NUM> which has the highest rotation speed of the gear mechanism <NUM>, it is possible to decrease braking torque to be applied to the brake rotor <NUM> from the pressing part. This allows a reduction in brake capacity, so that the operating force to activate the brake device 90a can be lowered. As a result, a load that the driver has to exert to operate the brake device 90a with the operation levers <NUM>, <NUM>, etc. can be reduced. In the configuration in which the brake device is activated by an electric actuator, it is possible to make the electric actuator smaller.

<FIG> show another example of a power transmission unit 41b different from the embodiment mentioned above. <FIG> is a diagram illustrating another example of the power transmission unit 41b different from the embodiment shown in <FIG>. <FIG> is a cross sectional view taken along line K-K of <FIG> corresponds to a cross sectional view taken along line L-L in <FIG>. <FIG> is an exploded cross sectional view with some parts omitted just before assembly into the state shown in <FIG>. In this example configuration, differently from the configurations shown in <FIG>, a motor case 120a has a simple cylindrical shape without ribs or reinforcing ribs on the outer circumferential surface. Thereby, as shown in <FIG>, while the motor case 120a is sandwiched between the first case <NUM> and the cover <NUM> to which the cap <NUM> is fixed, by connecting the bolts <NUM> which pass through the cover <NUM> and a space outside the outer circumferential surface of the motor case 120a to the threaded holes <NUM> of the first case <NUM>, the first case <NUM>, the motor case 120a, the cover <NUM>, and the cap <NUM> are fixed together.

In this example, since the shape of the motor case 120a is much simpler than in the configuration shown in <FIG>, this makes it possible to simplify a manufacturing of the extrusion molding die, and thus the manufacturing cost of the motor case <NUM> can be further reduced. The other configurations and actions of this example are the same as those of the embodiment shown in <FIG> and <FIG>.

<FIG> is a perspective view illustrating another example of the motor case different from the embodiment mentioned above. In the configuration of this example, although the ribs 130b are formed at a plurality of positions on the outer circumferential surface of the motor case 120b along the outer circumference throughout the axial direction, no ribs with bolt holes, through which the bolts <NUM> (see <FIG> and <FIG>) to connect the motor case 120b to the transmission case pass through, are formed. In the configuration of this example, similarly to the configuration shown in <FIG>, while the motor case 120b is sandwiched between the first case <NUM> and the cover <NUM> to which the cap <NUM> is fixed, by connecting the bolts <NUM> which pass through the cover <NUM> and a space outside the outer circumferential surface of the motor case 120b to the threaded holes <NUM> of the first case <NUM>, the first case <NUM>, the motor case 120b, the cover <NUM>, and the cap <NUM> are fixed together. The other configurations and actions of this example are the same as those of the embodiment shown in <FIG>, <FIG>, or <FIG>.

<FIG> is a diagram illustrating another example having a transmission case different from the embodiment shown in <FIG>. <FIG> is a diagram illustrating another example having the transmission case different from the embodiment shown in <FIG>. In the configuration of this example, differently from the configuration shown in <FIG>, the cylinder <NUM> with a cylindrical shape, which protrudes from an axial end surface of the first case 115a1 comprising the transmission case 42a1 toward the motor case 120a, is formed on the axial end surface on the boss part 48a side having the hole <NUM>, and in which it is overlaid with the motor case 120a. The other configurations and actions of this example are the same as those of the embodiment shown in <FIG>, or <FIG>.

<FIG> is a diagram illustrating another example of a power transmission unit 41c different from the embodiment shown in <FIG>. <FIG> is a cross sectional view taken along line M-M of <FIG>. <FIG> is a perspective view of the motor case 120b removed from <FIG>. In the configuration of this example, the centering structure to align the central axis O2 of the hole <NUM> in a transmission case 42b with the central axis O1 of the inner circumferential surface in the motor case 120b, to which the stator core <NUM> of the motor <NUM> is fixed, are formed in both the transmission case 42b and the motor case 120b. In this example, the centering structure is configure to include a plurality of first holes <NUM> formed on a first end surface T1 which is the end surface of a first case 115a2 comprising a transmission case 42b, which faces and is overlaid with the end surface of the motor case 120b, a plurality of second holes <NUM> formed on a second end surface T2 which is the end surface of a motor case 120b and overlaid with the first end surface T1, and a plurality of pins <NUM> simultaneously fitted into both the plurality of first holes <NUM> and the plurality of second holes <NUM>.

The plurality of first holes <NUM> are arranged on the first end surface T1 at two positions whose phases differ by <NUM> degrees or so along the circumference around the central axis O2 of the hole <NUM>, and formed parallel to the central axis O2 of the hole <NUM> as holes with a circular cross section. The plurality of second holes <NUM> are arranged so as to face the plurality of the first holes <NUM> on the second end surface T2 at two positions whose phases differ by <NUM> degrees or so along the circumference of the motor case around the central axis O1 of the inner circumferential surface of the motor case 120b, and formed parallel to the central axis O1 as holes with a circular cross section. At this time, as shown in <FIG> and <FIG>, a circumferential width of ribs 130c formed on the outer surface of the motor case 120b is larger than that of the other ribs 130a and 130b. The bolt hole <NUM> is formed on one side along the circumference of the rib 130c with a larger circumferential width, and the second hole <NUM> is formed on the other side along the circumference thereof. The plurality of pins <NUM> are parallel pins with cylindrical outer surfaces and whose both end portions are simultaneously press-fitted into the first hole <NUM> and the second hole <NUM> so that they are aligned with each other.

Similarly to the configuration shown in <FIG>, this configuration also allows more precise alignment of the central axis O1 of the inner surface of the motor case <NUM> and the center axis O2 of the hole <NUM> formed in the transmission case 42b. The other configurations and actions of this example are the same as those of the embodiment shown in <FIG>, <FIG>, or <FIG>.

<FIG> is a partially enlarged diagram illustrating another example of a power transmission unit 41d different from the embodiment shown in <FIG>. <FIG> is a cross sectional view taken along line P-P of <FIG>. In the configuration of this example, the centering structure to align the central axis of the hole <NUM> in a transmission case 42c with the central axis of the inner circumferential surface in the motor case 120c, to which the stator core <NUM> comprising the motor <NUM> is fixed, are formed in both the transmission case 42c and the motor case 120c. In this example, the centering structure is configured to include a plurality of first circular holes <NUM> formed on the first end surface T1 which is the end surface of a first case 115a3 comprising a transmission case 42c, which faces and is overlaid with the end surface of the motor case 120c, a plurality of second circular holes <NUM> formed on the second end surface T2 which is the end surface of a motor case 120c and overlaid with the first end surface T1, and a plurality of cylinders <NUM>.

The plurality of first circular holes 138a are arranged on the first end surface T1 side associated with two threaded holes <NUM> among a plurality (e.g. three) of threaded holes <NUM> in the first case 115a3 whose central axis is aligned with the central axis of the threaded hole <NUM> and whose inner surface has a larger diameter than the threaded hole <NUM>. The plurality of second circular holes <NUM> are arranged on the second end surface T2 side associated with two bolt holes <NUM> among a plurality (e.g., three) of bolt holes <NUM> each with a circular cross section in the motor case 120c whose central axis is aligned with the central axis of the bolt hole <NUM> and whose inner surface has a larger diameter than the bolt hole <NUM>. The second circular hole <NUM> may be formed by machining after the motor case 120c other than the second circular hole <NUM> is formed by pultrusion molding, for example. The bolt hole <NUM> corresponds to an axial hole. The plurality of cylinders <NUM> are two metal cylindrical pins, which are in parallel with each other and each have a hollow structure, and whose both end portions are simultaneously press-fitted into the first circular hole <NUM> and the second circular hole <NUM> so that they are aligned with each other. The bolt <NUM> passes through the inside of each of the plurality of cylinders <NUM>.

Similarly to the configuration shown in <FIG>, this configuration also allows more precise alignment of the central axis of the inner surface of the motor case 120c and the center axis of the hole <NUM> formed in the transmission case 42c. The other configurations and actions of this example are the same as those of the embodiment shown in <FIG>, <FIG>, or <FIG>.

<FIG> is a diagram illustrating another example of a power transmission unit different from the embodiment shown in <FIG>. In the configuration of this example, a bottomed cylindrical cap <NUM> made of metal or the like is screw-fixed to cover the recess <NUM> on the outside of the cover <NUM> in the vehicle-width direction, which is fixed on the side of the motor case 120b opposite to the transmission case 42b. In this example, a substrate <NUM> is fixed to the inner surface of a bottom plate <NUM> of the cap <NUM>, and inverters <NUM> are installed on the substrate <NUM>. This allows the inverters <NUM> to be attached to the cover <NUM>. The inverters <NUM> convert DC power from the battery into three-phase AC power and supply it to the stator coil <NUM>, for example. A plurality of heat-dissipating fins 145a are formed on the outer surface of the bottom plate <NUM> to dissipate the heat generated by the inverters <NUM> to the outside through the substrate <NUM>. In addition, a rotation speed detecting device <NUM> to detect a rotation speed of the input shaft <NUM> may be provided on a portion of a plate part <NUM> fixed to the substrate <NUM> via a cylinder part <NUM> as a spacer for passing through a screw so that it faces a top end surface of the input shaft <NUM>. The other configurations and actions of this example are the same as those of the embodiment shown in <FIG> and <FIG>.

In the above-mentioned embodiments, similarly to the centering structure to perform centering between the transmission case 42a1 and the motor case <NUM> as shown in <FIG>, a cylinder part protruding from the inside surface of the cover <NUM> to the motor case <NUM> side is formed as another centering structure, and the motor case <NUM> is fitted to the outer circumferential surface of the cylinder part. However, the configuration of the centering structure to perform centering between the cover and the motor case is not limited thereto. For example, similarly to the configuration shown in <FIG> or <FIG> and <FIG>, a pin whose both ends are simultaneously fitted into a hole of the cover and a hole of the motor case, or a cylinder part whose both ends are simultaneously fitted into circular holes each with a larger diameter, which are formed on both the cover side end and the motor case side end of the through hole, through which the bolt to connect the cover and the motor case passes, may be employed as the centering structure between the cover and the motor case.

At least one embodiment mentioned above has the first configuration of the power transmission unit of the present disclosure. As a result, a power transmission unit is configured to include: a motor; and a transmission case to enclose an input shaft, an output shaft, and a gear mechanism that transmits driving power between the input shaft and the output shaft, wherein a motor case is attached to the transmission case on a side opposite the gear mechanism of the transmission case, and the motor case has a cylindrical shape whose cross section is constant throughout a direction orthogonal to an axial direction of the motor case, so that the manufacturing cost of the motor case can be reduced. Furthermore, when the motor case is made of metal with high thermal conductivity, since a larger heat dissipation member allows the heat of the motor located inside the motor case to be efficiently transferred from the motor case to the transmission case, the cooling performance of the motor can be improved. Furthermore, since a structure in which the motor is assembled inside the motor case can be used as a subassembly, it is possible to facilitate assembly work when manufacturing the power transmission unit. This enables a reduction in manufacturing cost of a power transmission unit in which the motor case is fixed to the transmission case.

Furthermore, in at least one embodiment mentioned above, a cover is fixed to the motor case to block an opening at an outer end in the axial direction of the motor case, the motor case is directly coupled to the transmission case, and a support to secure a bearing that supports a rotor shaft of the motor is provided on the transmission case side. This makes it possible to omit one of the covers on both sides which are originally required for the motor, thus lowering the cost. In addition, by omitting the motor cover on the transmission case side and coupling the motor case directly to the transmission case, the heat generated by the motor can easily escape to the transmission side, thus improving the cooling performance of the motor.

Furthermore, in at least one embodiment mentioned above, the motor case is made of metal or alloy whose main component is aluminum or copper. Since the motor case is made of metal or alloy whose main component is aluminum, the motor case can be made lightweight. Furthermore, when the motor case is made of metal with high thermal conductivity, since a larger heat dissipation member allows the heat of the motor located inside the motor case to be efficiently transferred from the motor case to the transmission case, the cooling performance of the motor can be improved.

Claim 1:
A power transmission unit (41a, 71a) comprising:
a motor (<NUM>); and
a transmission case (42a) to enclose an input shaft (<NUM>), an output shaft (<NUM>), and a gear mechanism (<NUM>) that transmits driving power between the input shaft (<NUM>) and the output shaft (<NUM>),
wherein a motor case (<NUM>) is attached to the transmission case (42a) on a side opposite the gear mechanism (<NUM>) of the transmission case (42a), the motor case (<NUM>) has a cylindrical shape whose cross section is constant throughout a direction orthogonal to an axial direction of the motor case (<NUM>), and the motor (<NUM>) is placed inside the motor case (<NUM>),
wherein a cover (<NUM>) is fixed to the motor case (<NUM>) to block an opening at an outer end in the axial direction of the motor case (<NUM>), and
wherein the motor case (<NUM>) is directly coupled to the transmission case (42a), the input shaft is a motor shaft of the motor, characterised in that a support to secure a bearing that supports a rotor shaft of the motor (<NUM>, <NUM>) is provided on a side of the transmission case (42a).