Power transmission device

An oil leak detection device includes a pair of permanent magnets, a plurality of commutators, a coil, a pair of brushes, and a current sensor. An N-pole and an S-pole of the pair of permanent magnets face each other. The plurality of commutators are attached to an output shaft. The coil is wound onto the output shaft inside the pair of permanent magnets in the radial direction of the output shaft. The coil is electrically connected to the plurality of commutators. The pair of brushes are attached to a housing and are capable of coming into contact with each of the plurality of commutators. The current sensor detects an induction current flowing between the pair of brushes and the housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2021/000265, filed on Jan. 7, 2021. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2020-037676, filed in Japan on Mar. 5, 2020, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure relates to a power transmission device.

BACKGROUND INFORMATION

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 Laid-Open Utility Specification No. 63-128320, a seal 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.

SUMMARY

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 disclosure 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. The current sensor is configured to detect an induction current flowing between the pair of brushes and the housing.

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

DESCRIPTION OF EMBODIMENTS

(Configuration of Wheel Loader1)

FIG.1is a side view of a wheel loader1according to the present embodiment. A power transmission system of the wheel loader1is illustrated schematically inFIG.1. 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 loader1comprises a vehicle body2, a bucket3, a work implement drive mechanism4, and a cab5. The vehicle body2has a front vehicle body and a rear vehicle body. The bucket3used for excavating and loading is attached to the front of the vehicle body2via the hydraulic work implement drive mechanism4. The work implement drive mechanism4is configured by a boom, a bell crank, a coupling link, a bucket cylinder, a boom cylinder, and the like.

The box-like cab5in which the operator rides is disposed on the vehicle body2. An engine room6is provided to a rear end section of the vehicle body2. An engine7that is a power source is accommodated inside the engine room6. In the present embodiment, a crankshaft (not illustrated) of the engine7is disposed in the front-back direction.

Power of the engine7is transmitted to a transmission9via a propeller shaft8. A portion of the power outputted by the transmission9is transmitted to a rear drive shaft11via an output shaft10. The power transmitted to the rear drive shaft11is transmitted to the rear wheels via a rear axle12. A portion of the power outputted by the transmission9is transmitted to a front drive shaft14via the output shaft10. The power transmitted to the front drive shaft14is transmitted to the front wheels via a front axle15.

In the present embodiment, the transmission9, the output shaft10, the rear drive shaft11, the rear axle12, the front drive shaft14, and the front axle15configure the “power transmission device” according to the present embodiment.

FIG.2is a cross-sectional view of a configuration of the entire transmission9according to the present embodiment.FIG.3is an enlarged view of a portion ofFIG.2.

The transmission9comprises a housing20, an input shaft21, a torque converter22, a first middle shaft23, a second middle shaft24, a third middle shaft25, and the output shaft10. The input shaft21, the torque converter22, the first middle shaft23, the second middle shaft24, the third middle shaft25, and the output shaft10transmit the power from the engine7.

The housing20accommodates the input shaft21, the torque converter22, the first middle shaft23, the second middle shaft24, the third middle shaft25, and the output shaft10. The inside of the housing20has formed therein an internal space20R that accommodates the input shaft21, the torque converter22, the first middle shaft23, the second middle shaft24, the third middle shaft25, and the output shaft10. Oil for lubrication is sealed inside the internal space20R. The housing20is configured by a conductive material such as a metal. The housing20is an example of the “housing” according to the present embodiment. The output shaft10is an example of the “rotating shaft” according to the present embodiment.

Power from the engine7is inputted to the input shaft21via the torque converter22. An F-clutch27and a first clutch28are provided to the first middle shaft23. An R-clutch29and a second clutch30are provided to the second middle shaft24. A third clutch31and a fourth clutch32are provided to the third middle shaft25. A transfer shaft33is coupled to a front end section of the third middle shaft25. A transfer gear33gis provided to the transfer shaft33.

Power from the transfer shaft33is transmitted to the output shaft10. An output gear10gthat meshes with the transfer gear33g, and a parking brake34are provided to the output shaft10.

The output shaft10is disposed in the front-back direction. A rear end section of the output shaft10protrudes from the housing20toward the rear. A front end section of the output shaft10protrudes from the housing20toward the front. As illustrated inFIG.3, the output shaft10is supported by the housing20. The output shaft10is rotatable about an axial center AX.

As illustrated inFIG.3, the output shaft10has a rear coupling section10aand a front coupling section10b. The rear coupling section10ais connected to a front end section of the rear drive shaft11. The front coupling section10bis connected to a rear end section of the front drive shaft14.

As illustrated inFIG.3, the housing20has a housing body20a, a rearward protruding section20b, and a forward protruding section20c(example of a “protruding section”). The housing body20aaccommodates an axial direction center section of the output shaft10. The axial direction is a direction parallel to the axial center AX of the output shaft10. The rearward protruding section20bprotrudes to the rear from the housing body20a. The rearward protruding section20bis formed in an annular shape centered on the axial center AX. The forward protruding section20cprotrudes to the front from the housing body20a. The forward protruding section20cis formed in an annular shape centered on the axial center AX.

A rearward oil seal35and a rearward dust seal36are disposed in a gap between the rear coupling section10aof the output shaft10and the rearward protruding section20bof the housing20.

The rearward oil seal35seals oil inside the housing20. The rearward oil seal35is in contact with a surface10T of the rear coupling section10aof the rotating shaft10and a surface20T of the rearward protruding section20bof the housing20. The rearward oil seal35is fixed to the surface20T of the housing20. The rearward oil seal35may be fixed also to the surface10T of the rotating shaft10. The rearward oil seal35is disposed on the axial outward side of the housing20. The rearward oil seal35is formed in an annular shape centered on the axial center AX. A well-known oil seal may be used for the rearward oil seal35.

In the present embodiment, the axial outward side signifies the rearward protruding section20bside or the forward protruding section20cside with respect to the internal space20R of the housing20in the axial direction. Additionally, in the present embodiment, the axial inward side signifies the internal space20R side of the housing20with respect to the rearward protruding section20bside or the forward protruding section20cside in the axial direction.

The rearward dust seal36limits the intrusion to the rearward oil seal35side of foreign matter that has intruded into the gap between the output shaft10and the rearward protruding section20bof the housing20from the outside. The rearward dust seal36is in contact with the surface10T of the rear coupling section10aof the rotating shaft10and the surface20T of the rearward protruding section20bof the housing20. The rearward dust seal36is disposed on the axial outward side of the rearward oil seal35. The rearward dust seal36is formed in an annular shape centered on the axial center AX. A well-known dust seal may be used for the rearward dust seal36.

An annular seal cover37for covering the axial outward side of the rearward dust seal36is attached to the output shaft10. The seal cover37limits the intrusion of earth and sand or muddy water or the like (referred to below as “foreign matter”) into the gap between the output shaft10and the rearward protruding section20bof the housing20.

A forward oil seal38and an oil leak detection device39are disposed in the gap between the front coupling section10bof the output shaft10and the forward protruding section20cof the housing20.

The forward oil seal38seals oil inside the housing20. The forward oil seal38is in contact with a surface10S of the front coupling section10bof the rotating shaft10and a surface20S of the forward protruding section20cof the housing20. The forward oil seal38is fixed to the surface20S of the housing20. The forward oil seal38may be fixed also to the surface10S of the rotating shaft10. The forward oil seal38is disposed on the axial outward side of the housing20. The forward oil seal38is formed in an annular shape centered on the axial center AX. A well-known oil seal may be used for the forward oil seal38.

The oil leak detection device39detects an oil leak from the forward oil seal38. The oil leak detection device39is disposed on the axial outward side of the forward oil seal38. A configuration of the oil leak detection device39is explained below.

An annular seal cover40for covering the axial outward side of the oil leak detection device39is attached to the output shaft10. The seal cover40limits the intrusion of foreign matter into the gap between the output shaft10and the forward protruding section20cof the housing20.

FIG.4is an enlarged view of a portion ofFIG.3. The forward oil seal38and the oil leak detection device39are mainly illustrated inFIG.4.FIG.5is cross-sectional view along line A-A inFIG.4.FIG.6is a cross-sectional view along line B-B inFIG.4.FIG.7is a schematic view corresponding toFIG.4and illustrates a state in which an oil leak from the forward oil seal38has occurred.

The oil leak detection device39has: a pair of permanent magnets51,52; a plurality of commutators53,54; a coil55; a pair of brushes56,57; an oil absorbing material58; dummy commutators59,60; a current sensor61; and a controller62.

The pair of permanent magnets51,52are attached to the surface20S of the forward protruding section20cwithin the housing20. The pair of permanent magnets51,52are disposed so that an N-pole and an S-pole face each other. Specifically, the pair of permanent magnets51,52include an N-pole magnet51and an S-pole magnet52that face each other with the output shaft10interposed therebetween. The N-pole magnet51and the S-pole magnet52are separated from each other in the circumferential direction centered on the axial center AX.

In the present embodiment, the pair of permanent magnets51,52are disposed on the axial inward side of the plurality of commutators53,54; however, the pair of permanent magnets51,52may be disposed on the axial outward side of the plurality of commutators53,54.

The plurality of commutators53,54are attached to the surface10S of the rotating shaft10. The plurality of commutators53,54face each other with the output shaft10interposed therebetween. The plurality of commutators53,54are separated from each other in the circumferential direction centered on the axial center AX. The plurality of commutators53,54rotate with the rotating shaft10around the axial center AX. The plurality of commutators53,54that rotate are periodically in contact with the pair of brushes56,57.

The coil55is electrically connected to the plurality of commutators53,54. In the present embodiment, both ends of the coil55are respectively connected to the plurality of commutators53,54. The coil55is disposed on the inside of the pair of permanent magnets51,52in the radial direction centered on the axial center AX. The coil55is wound onto the rotating shaft10on the inside of the pair of permanent magnets51,52. The number of windings of the coil55may be one or more.

The coil55rotates with the rotating shaft10around the axial center AX between the pair of permanent magnets51,52. An induced voltage is produced by electromagnetic induction on the rotating coil55. However, while the induced voltage is produced constantly if the coil55is 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 magnets51,52are disposed on the axial inward side of the plurality of commutators53,54, the coil55is also disposed on the axial inward side of the plurality of commutators53,54. However, when the pair of permanent magnets51,52are disposed on the axial outward side of the plurality of commutators53,54, the coil55is also disposed on the axial outward side of the plurality of commutators53,54.

The pair of brushes56,57are attached to the surface20S of the housing20. The pair of brushes56,57face each other with the output shaft10interposed therebetween. The pair of brushes56,57are separated from each other in the circumferential direction centered on the axial center AX. The pair of brushes56,57include a first brush56connected to the housing20and a second brush57separated from the housing20. The first brush56is disposed above the rotating shaft10. The second brush57is disposed below the rotating shaft10. The first brush56is disposed above the axial center AX. The second brush57is disposed below the axial center AX. The pair of brushes56,57are periodically in contact with the plurality of commutators53,54that rotate.

In the present embodiment, the pair of brushes56,57are supported by the oil absorbing material58. Therefore, the pair of brushes56,57are attached to the surface20S of the housing20through the oil absorbing material58.

In the present embodiment, the first brush56has a brush body a1and a conductor a2. The brush body a1is attached to the oil absorbing material58. The conductor a2is connected to the brush body a1and the housing20. The conductor a2is configured by an electrically conductive material. The conductor a2is electrically connected to the brush body a1and the housing20.

In the present embodiment, the second brush57has a brush body a3and a terminal part a4. The brush body a3is attached to the oil absorbing material58. The terminal part a4extends from the brush body a3toward the surface20S of the housing20. The tip end of the terminal part a4preferably extends close to the surface20S of the housing20. The tip end of the terminal part a4preferably extends close to the tip end of a below-mentioned terminal part b2of the current sensor61.

The oil absorbing material58is attached to the surface20S of the housing20. The oil absorbing material58is disposed in a gap between the surface20S of the housing20and the plurality of commutators53,54. The oil absorbing material58absorbs oil that has leaked from the forward oil seal38. The oil absorbing material58is 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 material58functions as a supporting member of the pair of brushes56,57. In addition, the oil absorbing material58functions as a dust seal. Specifically, the oil absorbing material58limits the intrusion, toward the forward oil seal38, of foreign matter that has intruded into the gap between the rear coupling section10aof the output shaft10and the forward protruding section20cof the housing20.

The dummy commutators59,60are each disposed in a gap between the plurality of commutators53,54in the circumferential direction centered on the axial center AX. The dummy commutators59,60limit the intrusion of foreign matter on the axial inward side of the oil leak detection device39. The dummy commutators59,60face each other with the output shaft10interposed therebetween. The dummy commutators59,60are separated from each other in the circumferential direction centered on the axial center AX. The dummy commutators59,60are configured by a material having an insulative property. For example, rubber or felt may be used as such a material. When the dummy commutators59,60are configured by felt, the dummy commutators59,60may be integrated with the oil absorbing material58.

The current sensor61detects an induction current flowing between the pair of brushes56,57and the forward protruding section20cof the housing20as indicated below. Firstly, as illustrated inFIG.7, when an oil leak occurs from the forward oil seal38and oil becomes interposed between the second brush57and the housing20, the second brush57and the housing20are electrically connected by the oil. As a result, a loop circuit is formed by the plurality of commutators53,54, the coil55, the pair of brushes56,57, and the housing20and an induction current caused by the induced voltage occurring in the coil55flows through the loop circuit. The current sensor61is activated by the induction current flowing through the loop circuit and detects that an induction current is flowing. The current sensor61wirelessly notifies the controller62that an induction current has been detected.

In the present embodiment, the current sensor61has a sensor body b1and the terminal part b2. The sensor body b1is disposed outside the housing20. The terminal part b2passes through the housing20and extends from the sensor body b1to the gap between the output shaft10and the housing20. The tip end of the terminal part b2preferably extends close to the surface20S of the housing20. The tip end of the terminal part b2preferably close to the tip end of the terminal part a4of the second brush57.

The controller62is disposed, for example, in the cab5. The controller62issues a warning (warning sound, warning display, etc.) to a worker upon receiving the notification from the current sensor61indicating that an induction current has been detected.

The transmission9comprises the output shaft10, the housing20, the forward oil seal38, and the oil leak detection device39. The housing20rotatably supports the output shaft10. The forward oil seal38is disposed in a gap between the output shaft10and the housing20. The oil leak detection device39is disposed on the axial outward side of the forward oil seal38. The oil leak detection device39has: the pair of permanent magnets51,52; the plurality of commutators53,54; the coil55; the pair of brushes56,57; and the current sensor61. The N-pole and the S-pole of the pair of permanent magnets51,52face each other. The plurality of commutators53,54are attached to the output shaft10. The coil55is wound around the output shaft10inside the pair of permanent magnets51,52in the radial direction of the output shaft10. The coil55is electrically connected to the plurality of commutators53,54. The pair of brushes56,57are attached to the housing20and are able to come into contact with each of the plurality of commutators53,54. The current sensor61detects an induction current flowing between the pair of brushes56,57and the housing20.

Therefore, the current sensor61detects the induction current flowing through the loop circuit formed by the plurality of commutators53,54, the coil55, the pair of brushes56,57, and the housing20when an oil leak from the forward oil seal38occurs and the second brush57and the housing20are electrically connected by the oil. Accordingly, the occurrence of the oil leak can be detected quickly.

The pair of brushes56,57include the first brush56connected to the housing20and the second brush57separated from the housing20. The second brush57has the brush body a3and the terminal part a4that extends from the brush body a3toward the housing20. Accordingly, the loop circuit can be formed quickly by oil that has leaked along the surface20S of the housing20coming into contact with the second brush57.

The first brush56is disposed above the output shaft10and the second brush57is disposed below the output shaft10. Accordingly, the second brush57is able to quickly make contact with the oil that has leaked along a lower part of the surface20S of the housing20.

The current sensor61has the sensor body b1that is disposed outside of the housing20, and the terminal part b2that extends from the sensor body b1to the inside of the housing20. Accordingly, the current sensor61is able to quickly make contact with the oil that has leaked along the surface20S of the housing20.

The current sensor61is activated by the induction current flowing between the pair of brushes and the housing. Accordingly, the configuration of the oil leak detection device39is further simplified because there is no need for a power source for the current sensor61.

The current sensor61wirelessly notifies the controller62that an induction current has been detected. Accordingly, the configuration of the oil leak detection device39can be further simplified in comparison to when the current sensor61and the controller62are connected by wire.

The pair of brushes56,57are attached to the housing20via the insulative oil absorbing material58. Accordingly, delaying of the oil leak and the intrusion of foreign matter from the outside through the gap between the plurality of commutators53,54and the housing20can be suppressed.

The oil leak detection device39has the dummy commutators59,60that are each disposed in a gap between the plurality of commutators53,54in 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 commutators53,54can be suppressed.

The present invention is not limited to the above embodiment and various changes and modifications may be made without departing from the spirit of the invention.

While the oil seal and the oil leak detection device according to the present disclosure apply to the gap between the output shaft10and the housing20of the transmission9in 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 shaft21and the housing20of the transmission9, a gap between the rear drive shaft11and the housing of the rear axle12, a gap between the front drive shaft14and the housing of the front axle15, and the like.

While the second brush57has the brush body a3and the terminal part a4in the above embodiment, the second brush57may not have the terminal part a4.

While the current sensor61has the sensor body b1and the terminal part b2in the above embodiment, the current sensor61may not have the terminal part b2. Even is such a case, the current sensor61can detect a current flowing through the housing20itself.