Patent Description:
In a conventional work vehicle, a seal is provided so that oil inside a housing of a power transmission device does not leak out from a gap between the housing and a rotating shaft. The power transmission device is, for example, a transmission or an axle. The rotating shaft is, for example, an output shaft or an input shaft rotatably supported by the housing.

In <CIT>, a seal is proposed that has a labyrinth structure configured by inserting together a plurality of fixed-side ring elements attached to the housing and a plurality of rotation-side ring elements attached to the output shaft.

However, it is important to quickly detect the occurrence of an oil leakage because it is difficult to completely prevent an oil leak from a gap between a housing and a rotating shaft.

An object of the present disclosure is to provide a power transmission device with which the occurrence of an oil leak can be detected quickly.

A power transmission device according to the present invention comprises a rotating shaft, a housing that rotatably supports the rotating shaft, an oil seal disposed in a gap between the rotating shaft and the housing, and an oil leak detection device disposed outside of the oil seal in an axial direction parallel to an axial center of the rotating shaft. The oil leak detection device has a pair of permanent magnets with an N-pole and an S-pole facing each other, a plurality of commutators, a coil, a pair of brushes, and a current sensor. The pair of permanent magnets are attached to the housing. The plurality of commutators are attached to the rotating shaft. The coil is wound onto the rotating shaft on an inside of the pair of permanent magnets in a radial direction centered on the axial center of the rotating shaft, and is electrically connected to the plurality of commutators. The pair of brushes are attached to the housing and are capable of coming into contact with each of the plurality of commutators, wherein the pair of brushes are attached to the housing through an insulative oil absorbing material. The current sensor is configured to detect an induction current flowing between the pair of brushes and the housing.

In a preferred embodiment, the pair of brushes include a first brush connected to the housing, and a second brush separated from the housing, and the second brush has a brush body and a terminal part that extends from the brush body toward the housing.

In a further preferred embodiment, the first brush is disposed above the rotating shaft, and the second brush is disposed below the rotating shaft.

In a further preferred embodiment, the current sensor has a sensor body disposed outside of the housing and a terminal part that extends from the sensor body to the gap.

In a further preferred embodiment, the current sensor is activated by the induction current.

In a further preferred embodiment, the current sensor wirelessly notifies a controller that the induction current has been detected.

In a further preferred embodiment, the oil leak detection device has a dummy commutator disposed in a gap between the plurality of commutators in a circumferential direction centered on the axial center.

According to the present invention, there can be provided a power transmission device with which the occurrence of an oil leak can be detected quickly.

<FIG> is a side view of a wheel loader <NUM> according to the present embodiment. A power transmission system of the wheel loader <NUM> is illustrated schematically in <FIG>. In the following discussion, "front" and "rear" are the same as "front" and "rear" as seen by an operator seated in the driver's seat.

The wheel loader <NUM> comprises a vehicle body <NUM>, a bucket <NUM>, a work implement drive mechanism <NUM>, and a cab <NUM>. The vehicle body <NUM> has a front vehicle body and a rear vehicle body. The bucket <NUM> used for excavating and loading is attached to the front of the vehicle body <NUM> via the hydraulic work implement drive mechanism <NUM>. The work implement drive mechanism <NUM> is configured by a boom, a bell crank, a coupling link, a bucket cylinder, a boom cylinder, and the like.

The box-like cab <NUM> in which the operator rides is disposed on the vehicle body <NUM>. An engine room <NUM> is provided to a rear end section of the vehicle body <NUM>. An engine <NUM> that is a power source is accommodated inside the engine room <NUM>. In the present embodiment, a crankshaft (not illustrated) of the engine <NUM> is disposed in the front-back direction.

Power of the engine <NUM> is transmitted to a transmission <NUM> via a propeller shaft <NUM>. A portion of the power outputted by the transmission <NUM> is transmitted to a rear drive shaft <NUM> via an output shaft <NUM>. The power transmitted to the rear drive shaft <NUM> is transmitted to the rear wheels via a rear axle <NUM>. A portion of the power outputted by the transmission <NUM> is transmitted to a front drive shaft <NUM> via the output shaft <NUM>. The power transmitted to the front drive shaft <NUM> is transmitted to the front wheels via a front axle <NUM>.

In the present embodiment, the transmission <NUM>, the output shaft <NUM>, the rear drive shaft <NUM>, the rear axle <NUM>, the front drive shaft <NUM>, and the front axle <NUM> configure the "power transmission device" according to the present embodiment.

<FIG> is a cross-sectional view of a configuration of the entire transmission <NUM> according to the present embodiment. <FIG> is an enlarged view of a portion of <FIG>.

The transmission <NUM> comprises a housing <NUM>, an input shaft <NUM>, a torque converter <NUM>, a first middle shaft <NUM>, a second middle shaft <NUM>, a third middle shaft <NUM>, and the output shaft <NUM>. The input shaft <NUM>, the torque converter <NUM>, the first middle shaft <NUM>, the second middle shaft <NUM>, the third middle shaft <NUM>, and the output shaft <NUM> transmit the power from the engine <NUM>.

The housing <NUM> accommodates the input shaft <NUM>, the torque converter <NUM>, the first middle shaft <NUM>, the second middle shaft <NUM>, the third middle shaft <NUM>, and the output shaft <NUM>. The inside of the housing <NUM> has formed therein an internal space 20R that accommodates the input shaft <NUM>, the torque converter <NUM>, the first middle shaft <NUM>, the second middle shaft <NUM>, the third middle shaft <NUM>, and the output shaft <NUM>. Oil for lubrication is sealed inside the internal space 20R. The housing <NUM> is configured by a conductive material such as a metal. The housing <NUM> is an example of the "housing" according to the present embodiment. The output shaft <NUM> is an example of the "rotating shaft" according to the present embodiment.

Power from the engine <NUM> is inputted to the input shaft <NUM> via the torque converter <NUM>. An F-clutch <NUM> and a first clutch <NUM> are provided to the first middle shaft <NUM>. An R-clutch <NUM> and a second clutch <NUM> are provided to the second middle shaft <NUM>. A third clutch <NUM> and a fourth clutch <NUM> are provided to the third middle shaft <NUM>. A transfer shaft <NUM> is coupled to a front end section of the third middle shaft <NUM>. A transfer gear <NUM> is provided to the transfer shaft <NUM>.

Power from the transfer shaft <NUM> is transmitted to the output shaft <NUM>. An output gear <NUM> that meshes with the transfer gear <NUM>, and a parking brake <NUM> are provided to the output shaft <NUM>.

The output shaft <NUM> is disposed in the front-back direction. A rear end section of the output shaft <NUM> protrudes from the housing <NUM> toward the rear. A front end section of the output shaft <NUM> protrudes from the housing <NUM> toward the front. As illustrated in <FIG>, the output shaft <NUM> is supported by the housing <NUM>. The output shaft <NUM> is rotatable about an axial center AX.

As illustrated in <FIG>, the output shaft <NUM> has a rear coupling section 10a and a front coupling section 10b. The rear coupling section 10a is connected to a front end section of the rear drive shaft <NUM>. The front coupling section 10b is connected to a rear end section of the front drive shaft <NUM>.

As illustrated in <FIG>, the housing <NUM> has a housing body 20a, a rearward protruding section 20b, and a forward protruding section 20c (example of a "protruding section"). The housing body 20a accommodates an axial direction center section of the output shaft <NUM>. The axial direction is a direction parallel to the axial center AX of the output shaft <NUM>. The rearward protruding section 20b protrudes to the rear from the housing body 20a. The rearward protruding section 20b is formed in an annular shape centered on the axial center AX. The forward protruding section 20c protrudes to the front from the housing body 20a. The forward protruding section 20c is formed in an annular shape centered on the axial center AX.

A rearward oil seal <NUM> and a rearward dust seal <NUM> are disposed in a gap between the rear coupling section 10a of the output shaft <NUM> and the rearward protruding section 20b of the housing <NUM>.

The rearward oil seal <NUM> seals oil inside the housing <NUM>. The rearward oil seal <NUM> is in contact with a surface 10T of the rear coupling section 10a of the rotating shaft <NUM> and a surface 20T of the rearward protruding section 20b of the housing <NUM>. The rearward oil seal <NUM> is fixed to the surface 20T of the housing <NUM>. The rearward oil seal <NUM> may be fixed also to the surface 10T of the rotating shaft <NUM>. The rearward oil seal <NUM> is disposed on the axial outward side of the housing <NUM>. The rearward oil seal <NUM> is formed in an annular shape centered on the axial center AX. A well-known oil seal may be used for the rearward oil seal <NUM>.

In the present embodiment, the axial outward side signifies the rearward protruding section 20b side or the forward protruding section 20c side with respect to the internal space 20R of the housing <NUM> in the axial direction. Additionally, in the present embodiment, the axial inward side signifies the internal space 20R side of the housing <NUM> with respect to the rearward protruding section 20b side or the forward protruding section 20c side in the axial direction.

The rearward dust seal <NUM> limits the intrusion to the rearward oil seal <NUM> side of foreign matter that has intruded into the gap between the output shaft <NUM> and the rearward protruding section 20b of the housing <NUM> from the outside. The rearward dust seal <NUM> is in contact with the surface 10T of the rear coupling section 10a of the rotating shaft <NUM> and the surface 20T of the rearward protruding section 20b of the housing <NUM>. The rearward dust seal <NUM> is disposed on the axial outward side of the rearward oil seal <NUM>. The rearward dust seal <NUM> is formed in an annular shape centered on the axial center AX. A well-known dust seal may be used for the rearward dust seal <NUM>.

An annular seal cover <NUM> for covering the axial outward side of the rearward dust seal <NUM> is attached to the output shaft <NUM>. The seal cover <NUM> limits the intrusion of earth and sand or muddy water or the like (referred to below as "foreign matter") into the gap between the output shaft <NUM> and the rearward protruding section 20b of the housing <NUM>.

A forward oil seal <NUM> and an oil leak detection device <NUM> are disposed in the gap between the front coupling section 10b of the output shaft <NUM> and the forward protruding section 20c of the housing <NUM>.

The forward oil seal <NUM> seals oil inside the housing <NUM>. The forward oil seal <NUM> is in contact with a surface <NUM> of the front coupling section 10b of the rotating shaft <NUM> and a surface <NUM> of the forward protruding section 20c of the housing <NUM>. The forward oil seal <NUM> is fixed to the surface <NUM> of the housing <NUM>. The forward oil seal <NUM> may be fixed also to the surface <NUM> of the rotating shaft <NUM>. The forward oil seal <NUM> is disposed on the axial outward side of the housing <NUM>. The forward oil seal <NUM> is formed in an annular shape centered on the axial center AX. A well-known oil seal may be used for the forward oil seal <NUM>.

The oil leak detection device <NUM> detects an oil leak from the forward oil seal <NUM>. The oil leak detection device <NUM> is disposed on the axial outward side of the forward oil seal <NUM>. A configuration of the oil leak detection device <NUM> is explained below.

An annular seal cover <NUM> for covering the axial outward side of the oil leak detection device <NUM> is attached to the output shaft <NUM>. The seal cover <NUM> limits the intrusion of foreign matter into the gap between the output shaft <NUM> and the forward protruding section 20c of the housing <NUM>.

<FIG> is an enlarged view of a portion of <FIG>. The forward oil seal <NUM> and the oil leak detection device <NUM> are mainly illustrated in <FIG>. <FIG> is cross-sectional view along line A-A in <FIG>. <FIG> is a cross-sectional view along line B-B in <FIG>. <FIG> is a schematic view corresponding to <FIG> and illustrates a state in which an oil leak from the forward oil seal <NUM> has occurred.

The oil leak detection device <NUM> has: a pair of permanent magnets <NUM>, <NUM>; a plurality of commutators <NUM>, <NUM>; a coil <NUM>; a pair of brushes <NUM>, <NUM>; an oil absorbing material <NUM>; dummy commutators <NUM>, <NUM>; a current sensor <NUM>; and a controller <NUM>.

The pair of permanent magnets <NUM>, <NUM> are attached to the surface <NUM> of the forward protruding section 20c within the housing <NUM>. The pair of permanent magnets <NUM>, <NUM> are disposed so that an N-pole and an S-pole face each other. Specifically, the pair of permanent magnets <NUM>, <NUM> include an N-pole magnet <NUM> and an S-pole magnet <NUM> that face each other with the output shaft <NUM> interposed therebetween. The N-pole magnet <NUM> and the S-pole magnet <NUM> are separated from each other in the circumferential direction centered on the axial center AX.

In the present embodiment, the pair of permanent magnets <NUM>, <NUM> are disposed on the axial inward side of the plurality of commutators <NUM>, <NUM>; however, the pair of permanent magnets <NUM>, <NUM> may be disposed on the axial outward side of the plurality of commutators <NUM>, <NUM>.

The plurality of commutators <NUM>, <NUM> are attached to the surface <NUM> of the rotating shaft <NUM>. The plurality of commutators <NUM>, <NUM> face each other with the output shaft <NUM> interposed therebetween. The plurality of commutators <NUM>, <NUM> are separated from each other in the circumferential direction centered on the axial center AX. The plurality of commutators <NUM>, <NUM> rotate with the rotating shaft <NUM> around the axial center AX. The plurality of commutators <NUM>, <NUM> that rotate are periodically in contact with the pair of brushes <NUM>, <NUM>.

The coil <NUM> is electrically connected to the plurality of commutators <NUM>, <NUM>. In the present embodiment, both ends of the coil <NUM> are respectively connected to the plurality of commutators <NUM>, <NUM>. The coil <NUM> is disposed on the inside of the pair of permanent magnets <NUM>, <NUM> in the radial direction centered on the axial center AX. The coil <NUM> is wound onto the rotating shaft <NUM> on the inside of the pair of permanent magnets <NUM>, <NUM>. The number of windings of the coil <NUM> may be one or more.

The coil <NUM> rotates with the rotating shaft <NUM> around the axial center AX between the pair of permanent magnets <NUM>, <NUM>. An induced voltage is produced by electromagnetic induction on the rotating coil <NUM>. However, while the induced voltage is produced constantly if the coil <NUM> is rotating, as explained below, a loop circuit in which the induction current flows is not formed so long as there is no oil leak.

In the present embodiment, because the pair of permanent magnets <NUM>, <NUM> are disposed on the axial inward side of the plurality of commutators <NUM>, <NUM>, the coil <NUM> is also disposed on the axial inward side of the plurality of commutators <NUM>, <NUM>. However, when the pair of permanent magnets <NUM>, <NUM> are disposed on the axial outward side of the plurality of commutators <NUM>, <NUM>, the coil <NUM> is also disposed on the axial outward side of the plurality of commutators <NUM>, <NUM>.

The pair of brushes <NUM>, <NUM> are attached to the surface <NUM> of the housing <NUM>. The pair of brushes <NUM>, <NUM> face each other with the output shaft <NUM> interposed therebetween. The pair of brushes <NUM>, <NUM> are separated from each other in the circumferential direction centered on the axial center AX. The pair of brushes <NUM>, <NUM> include a first brush <NUM> connected to the housing <NUM> and a second brush <NUM> separated from the housing <NUM>. The first brush <NUM> is disposed above the rotating shaft <NUM>. The second brush <NUM> is disposed below the rotating shaft <NUM>. The first brush <NUM> is disposed above the axial center AX. The second brush <NUM> is disposed below the axial center AX. The pair of brushes <NUM>, <NUM> are periodically in contact with the plurality of commutators <NUM>, <NUM> that rotate.

In the present embodiment, the pair of brushes <NUM>, <NUM> are supported by the oil absorbing material <NUM>. Therefore, the pair of brushes <NUM>, <NUM> are attached to the surface <NUM> of the housing <NUM> through the oil absorbing material <NUM>.

In the present embodiment, the first brush <NUM> has a brush body a1 and a conductor a2. The brush body a1 is attached to the oil absorbing material <NUM>. The conductor a2 is connected to the brush body a1 and the housing <NUM>. The conductor a2 is configured by an electrically conductive material. The conductor a2 is electrically connected to the brush body a1 and the housing <NUM>.

In the present embodiment, the second brush <NUM> has a brush body a3 and a terminal part a4. The brush body a3 is attached to the oil absorbing material <NUM>. The terminal part a4 extends from the brush body a3 toward the surface <NUM> of the housing <NUM>. The tip end of the terminal part a4 preferably extends close to the surface <NUM> of the housing <NUM>. The tip end of the terminal part a4 preferably extends close to the tip end of a belowmentioned terminal part b2 of the current sensor <NUM>.

The oil absorbing material <NUM> is attached to the surface <NUM> of the housing <NUM>. The oil absorbing material <NUM> is disposed in a gap between the surface <NUM> of the housing <NUM> and the plurality of commutators <NUM>, <NUM>. The oil absorbing material <NUM> absorbs oil that has leaked from the forward oil seal <NUM>. The oil absorbing material <NUM> is configured by a material that has oil absorbency and insulative properties. For example, felt (non-woven fabric) is suitable for such a material.

In the present embodiment, the oil absorbing material <NUM> functions as a supporting member of the pair of brushes <NUM>, <NUM>. In addition, the oil absorbing material <NUM> functions as a dust seal. Specifically, the oil absorbing material <NUM> limits the intrusion, toward the forward oil seal <NUM>, of foreign matter that has intruded into the gap between the rear coupling section 10a of the output shaft <NUM> and the forward protruding section 20c of the housing <NUM>.

The dummy commutators <NUM>, <NUM> are each disposed in a gap between the plurality of commutators <NUM>, <NUM> in the circumferential direction centered on the axial center AX. The dummy commutators <NUM>, <NUM> limit the intrusion of foreign matter on the axial inward side of the oil leak detection device <NUM>. The dummy commutators <NUM>, <NUM> face each other with the output shaft <NUM> interposed therebetween. The dummy commutators <NUM>, <NUM> are separated from each other in the circumferential direction centered on the axial center AX. The dummy commutators <NUM>, <NUM> are configured by a material having an insulative property. For example, rubber or felt may be used as such a material. When the dummy commutators <NUM>, <NUM> are configured by felt, the dummy commutators <NUM>, <NUM> may be integrated with the oil absorbing material <NUM>.

The current sensor <NUM> detects an induction current flowing between the pair of brushes <NUM>, <NUM> and the forward protruding section 20c of the housing <NUM> as indicated below. Firstly, as illustrated in <FIG>, when an oil leak occurs from the forward oil seal <NUM> and oil becomes interposed between the second brush <NUM> and the housing <NUM>, the second brush <NUM> and the housing <NUM> are electrically connected by the oil. As a result, a loop circuit is formed by the plurality of commutators <NUM>, <NUM>, the coil <NUM>, the pair of brushes <NUM>, <NUM>, and the housing <NUM> and an induction current caused by the induced voltage occurring in the coil <NUM> flows through the loop circuit. The current sensor <NUM> is activated by the induction current flowing through the loop circuit and detects that an induction current is flowing. The current sensor <NUM> wirelessly notifies the controller <NUM> that an induction current has been detected.

In the present embodiment, the current sensor <NUM> has a sensor body b1 and the terminal part b2. The sensor body b1 is disposed outside the housing <NUM>. The terminal part b2 passes through the housing <NUM> and extends from the sensor body b1 to the gap between the output shaft <NUM> and the housing <NUM>. The tip end of the terminal part b2 preferably extends close to the surface <NUM> of the housing <NUM>. The tip end of the terminal part b2 preferably close to the tip end of the terminal part a4 of the second brush <NUM>.

The controller <NUM> is disposed, for example, in the cab <NUM>. The controller <NUM> issues a warning (warning sound, warning display, etc.) to a worker upon receiving the notification from the current sensor <NUM> indicating that an induction current has been detected.

In the above embodiment, the transmission <NUM> comprises the output shaft <NUM>, the housing <NUM>, the forward oil seal <NUM>, and the oil leak detection device <NUM>. The housing <NUM> rotatably supports the output shaft <NUM>. The forward oil seal <NUM> is disposed in a gap between the output shaft <NUM> and the housing <NUM>. The oil leak detection device <NUM> is disposed on the axial outward side of the forward oil seal <NUM>. The oil leak detection device <NUM> has: the pair of permanent magnets <NUM>, <NUM>; the plurality of commutators <NUM>, <NUM>; the coil <NUM>; the pair of brushes <NUM>, <NUM>; and the current sensor <NUM>. The N-pole and the S-pole of the pair of permanent magnets <NUM>, <NUM> face each other. The plurality of commutators <NUM>, <NUM> are attached to the output shaft <NUM>. The coil <NUM> is wound around the output shaft <NUM> inside the pair of permanent magnets <NUM>, <NUM> in the radial direction of the output shaft <NUM>. The coil <NUM> is electrically connected to the plurality of commutators <NUM>, <NUM>. The pair of brushes <NUM>, <NUM> are attached to the housing <NUM> and are able to come into contact with each of the plurality of commutators <NUM>, <NUM>. The current sensor <NUM> detects an induction current flowing between the pair of brushes <NUM>, <NUM> and the housing <NUM>.

Therefore, the current sensor <NUM> detects the induction current flowing through the loop circuit formed by the plurality of commutators <NUM>, <NUM>, the coil <NUM>, the pair of brushes <NUM>, <NUM>, and the housing <NUM> when an oil leak from the forward oil seal <NUM> occurs and the second brush <NUM> and the housing <NUM> are electrically connected by the oil. Accordingly, the occurrence of the oil leak can be detected quickly.

The pair of brushes <NUM>, <NUM> include the first brush <NUM> connected to the housing <NUM> and the second brush <NUM> separated from the housing <NUM>. The second brush <NUM> has the brush body a3 and the terminal part a4 that extends from the brush body a3 toward the housing <NUM>. Accordingly, the loop circuit can be formed quickly by oil that has leaked along the surface <NUM> of the housing <NUM> coming into contact with the second brush <NUM>.

The first brush <NUM> is disposed above the output shaft <NUM> and the second brush <NUM> is disposed below the output shaft <NUM>. Accordingly, the second brush <NUM> is able to quickly make contact with the oil that has leaked along a lower part of the surface <NUM> of the housing <NUM>.

The current sensor <NUM> has the sensor body b1 that is disposed outside of the housing <NUM>, and the terminal part b2 that extends from the sensor body b1 to the inside of the housing <NUM>. Accordingly, the current sensor <NUM> is able to quickly make contact with the oil that has leaked along the surface <NUM> of the housing <NUM>.

The current sensor <NUM> is activated by the induction current flowing between the pair of brushes and the housing. Accordingly, the configuration of the oil leak detection device <NUM> is further simplified because there is no need for a power source for the current sensor <NUM>.

The current sensor <NUM> wirelessly notifies the controller <NUM> that an induction current has been detected. Accordingly, the configuration of the oil leak detection device <NUM> can be further simplified in comparison to when the current sensor <NUM> and the controller <NUM> are connected by wire.

The pair of brushes <NUM>, <NUM> are attached to the housing <NUM> via the insulative oil absorbing material <NUM>. Accordingly, delaying of the oil leak and the intrusion of foreign matter from the outside through the gap between the plurality of commutators <NUM>, <NUM> and the housing <NUM> can be suppressed.

The oil leak detection device <NUM> has the dummy commutators <NUM>, <NUM> that are each disposed in a gap between the plurality of commutators <NUM>, <NUM> in the circumferential direction centered on the axial center AX. Accordingly, the intrusion of foreign matter from the outside through the gap between the plurality of commutators <NUM>, <NUM> can be suppressed.

The present invention is not limited to the above embodiment and various changes and modifications may be made without departing from the scope of the invention as defined in the claims.

While the oil seal and the oil leak detection device according to the present disclosure apply to the gap between the output shaft <NUM> and the housing <NUM> of the transmission <NUM> in the above embodiment, the present disclosure is not limited in this way. The oil seal and the oil leak detection device according to the present disclosure may also be applied to a gap between the input shaft <NUM> and the housing <NUM> of the transmission <NUM>, a gap between the rear drive shaft <NUM> and the housing of the rear axle <NUM>, a gap between the front drive shaft <NUM> and the housing of the front axle <NUM>, and the like.

While the second brush <NUM> has the brush body a3 and the terminal part a4 in the above embodiment, the second brush <NUM> may not have the terminal part a4.

Claim 1:
A power transmission device comprising:
a rotating shaft (<NUM>);
a housing (<NUM>) configured by a conductive material and rotatably supporting the rotating shaft (<NUM>);
an oil seal (<NUM>, <NUM>) disposed in a gap between the rotating shaft (<NUM>) and the housing (<NUM>); and
an oil leak detection device (<NUM>) disposed outside of the oil seal (<NUM>, <NUM>) in an axial direction parallel to an axial center (AX) of the rotating shaft (<NUM>),
wherein the oil leak detection device (<NUM>) has a current sensor (<NUM>) configured to detect a current,
characterized in that the oil leak detection device (<NUM>) further comprises:
a pair of permanent magnets (<NUM>, <NUM>) attached to the housing (<NUM>) and having an N-pole and an S-pole that face each other;
a plurality of commutators (<NUM>, <NUM>) attached to the rotating shaft (<NUM>);
a coil (<NUM>) wound onto the rotating shaft (<NUM>) on an inside of the pair of permanent magnets (<NUM>, <NUM>) in a radial direction centered on the axial center (AX) of the rotating shaft (<NUM>), and electrically connected to the plurality of commutators (<NUM>, <NUM>);
a pair of brushes (<NUM>, <NUM>) that are attached to the housing (<NUM>) and capable of coming into contact with each of the plurality of commutators (<NUM>, <NUM>);
wherein the pair of brushes (<NUM>, <NUM>) are attached to the housing (<NUM>) through an insulative oil absorbing material (<NUM>); and
wherein the current sensor (<NUM>) is configured to detect an induction current flowing between the pair of brushes (<NUM>, <NUM>) and the housing (<NUM>).