Oil supply unit for a running power transmission

There is provided an oil supply unit for a running power transmission of a vehicle. The oil supply unit includes a housing, a hydraulic pump of a variable displacement type, a detecting mechanism and a control mechanism. The detecting mechanism is constructed to monitor a driven state of an engine. The control mechanism is constructed to operate an output adjusting member of the hydraulic pump to thereby regulate the discharge quantity against the suction quantity of the hydraulic pump based on the driven state of the engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oil supply unit for a running power transmission of a vehicle. The oil supply unit includes a hydraulic pump which is operatively connected to an engine and which supplies discharged oil to a power transmission portion in a power transmission mechanism.

2. Related Art

An oil supply unit including a hydraulic pump operatively connected to an engine is conventionally utilized in various fields such as a working vehicle.

For example, the oil supply unit is formed so as to supply discharged oil from the hydraulic pump as hydraulic fluid and lubricating oil for a hydraulic actuator such as a forward/reverse switching device and/or a PTO clutch and, also, to supply the discharged oil as lubricating oil for a member to be lubricated such as a mechanical transmission which requires lubrication.

However, there is a problem of large power loss in the conventional oil supply unit, because a discharge quantity of the hydraulic pump is merely proportional to an engine speed.

In other words, in the conventional oil supply unit, the hydraulic pump is of a fixed displacement type; therefore, a discharged oil quantity of the hydraulic pump is simply proportional to the engine speed. In short, the discharge quantity of the hydraulic pump is the smallest when the engine is at idle and increases as the rotation speed increases from idle.

The oil quantity discharged from the hydraulic pump is set according to use of the discharged oil.

For example, an assumption is made that the discharged oil is utilized as hydraulic fluid for the hydraulic actuator such as the forward/reverse switching device and the PTO clutch and is also utilized as lubricating oil for the members to be lubricated such as the hydraulic actuator and the mechanical transmission.

In this case, if an amount of hydraulic fluid required by the hydraulic actuator is X1m3/s and an amount of lubricating oil required by the members to be lubricated is X2m3/s, the hydraulic pump is set to be able to discharge oil of X1m3/s+X2m3/s when the engine is at idle.

Because the discharge quantity of the hydraulic pump is proportional to the engine speed in the conventional oil supply unit as described above, the hydraulic pump discharges oil more than the required discharged amount X1m3/s+X2m3/s when the engine speed is increased. The surplus discharged oil merely circulates through an oil hydraulic circuit and is not used advantageously.

Because the hydraulic pump of the fixed displacement type is set to discharge the required amount of oil when the engine is at idle in the conventional oil supply unit as described above, if the engine speed is increased, useless oil according to the increase is discharged, which causes the power loss.

It has conventionally been proposed to utilize a housing for accommodating the power transmission mechanism as an oil source of the hydraulic pump.

With this structure, the housing is also used as an oil reservoir to thereby save space and reduce costs by using the member in two ways.

However, the oil stored in the housing causes stirring resistance to the power transmission housed in the housing, which results in further power loss in the above structure.

The present invention has been accomplished with the above conventional art in view and it is an object of the invention to reduce power loss in an oil supply unit formed to use discharged oil from a hydraulic pump operatively connected to an engine as hydraulic fluid and/or lubricating oil.

It is another object of the invention to prevent running out of oil and to reduce power loss when a housing for accommodating a power transmission mechanism is used as an oil source of the hydraulic pump.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an oil supply unit that includes a housing, a hydraulic pump of a variable displacement type, a detecting mechanism and a control mechanism.

The housing is constructed to accommodate a power transmission mechanism which has a power transmission portion and an output portion and in which a driving force from the engine is transmitted to the output portion through the power transmission portion. The housing is also constructed so that at least a part of an inside space of the housing is an oil reservoir space.

The hydraulic pump of a variable displacement type is constructed to be operatively connected to the engine and include a suction port fluid-connected to the oil reservoir space, a discharge port fluid-connected to the power transmission portion and an output adjusting member. The discharge quantity against a suction quantity of the pump is variable based on operation of the output adjusting member.

The detecting mechanism is constructed to monitor a driven state of the engine.

The control mechanism is constructed to operate the output adjusting member to thereby regulate the discharge quantity against the suction quantity of the hydraulic pump of the variable displacement type based on the driven state of the engine.

With this structure, it is possible to effectively prevent the hydraulic pump from discharging an unnecessary surplus quantity of oil to thereby reduce power loss.

In one embodiment of the present invention, the power transmission portion has a drive-side member positioned on the engine side and a driven-side member positioned on the output portion side. The detecting mechanism is formed to directly or indirectly detect an engine speed. The control mechanism operates the output adjusting member so as to reduce the discharge quantity against the suction quantity of the hydraulic pump when the speed detected by the detecting mechanism exceeds a predetermined value.

Alternatively, the detecting mechanism may be formed to detect a load applied on the engine. In this embodiment, the control mechanism operates the output adjusting member so as to increase the discharge quantity against the suction quantity of the hydraulic pump when the load detected by the detecting mechanism exceeds a predetermined value.

Preferably, the oil reservoir space is divided into a first reservoir portion in which the power transmission portion is accommodated and a second reservoir portion in which the portion transmission portion is not accommodated. The housing is formed to be able to send oil from the first reservoir portion to the second reservoir portion by utilizing rotational motion of the power transmission mechanism.

With this preferred structure, it is possible to effectively reduce power loss caused by stirring of stored oil by the power transmission mechanism.

More preferably, the second reservoir portion is disposed substantially at a center in a longitudinal direction of a vehicle. The suction port of the hydraulic pump is fluid-connected to the second reservoir portion.

With this structure, it is further possible to effectively prevent cavitation due to drawing in of air by the hydraulic pump even when the vehicle is inclined in traveling on slopes and the like.

According to the present invention, there is further provided an oil supply unit that includes a hydraulic pump operatively connected to an engine.

The hydraulic pump is formed to be able to supply hydraulic fluid and/or lubricating oil to a power transmission portion of a power transmission mechanism constructed to output a driving force from the engine through the power transmission portion. The hydraulic pump is also formed to be of a variable displacement type in which a discharge quantity against a suction quantity is variable based on operation of an output adjusting member, and the discharge quantity against the suction quantity is varied based on a driven state of the engine.

With this structure, it is possible to effectively prevent the hydraulic pump from discharging an unnecessary surplus quantity of oil to thereby reduce power loss.

For example, the oil supply unit may further includes a detecting mechanism for directly or indirectly detecting an engine speed; and a control mechanism for operating the output adjusting member based on a detection result of the detecting mechanism.

The control mechanism is formed to position the output adjusting member in a predetermined slanting position when the engine at idle and to slant the output adjusting member from the predetermined slanting position toward a neutral position according to an increase in the engine speed when the engine is rotated at a speed exceeding an idle speed.

Alternatively, the oil supply unit may further includes a detecting mechanism for directly or indirectly detecting a load on an engine and a control mechanism for operating the output adjusting member based on a detection result of the detecting mechanism. The control mechanism is formed to position the output adjusting member in a predetermined slanting position when the load on the engine is equal to or less than a predetermined value and to slant the output adjusting member from the predetermined slanting position toward a maximum slanting position according to an increase in the load when the load on the engine exceeds the predetermined value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the invention will be described below with reference to the accompanying drawings.FIG. 1is a vertical sectional view of a transmission100to which an oil supply unit1according to the present embodiment is applied.FIG. 2is an oil hydraulic circuit diagram of the oil supply unit.

The transmission100includes a power transmission mechanism200for transmitting a driving force from an engine101(seeFIG. 2), and a housing300for housing the power transmission mechanism200.

The power transmission mechanism200includes a power transmission portion having a drive-side member operatively connected to the engine101and a driven-side member selectively engaged with the drive-side member, and an output portion operatively connected to the driven-side member of the power transmission portion.

In this embodiment, the power transmission mechanism200includes a traveling power transmission mechanism210for transmitting the driving force from the engine to main drive axles, and a PTO power transmission mechanism260for outputting the driving force from the engine toward an external device such as a work machine.

In this embodiment, the traveling power transmission mechanism210includes a drive shaft211operatively connected to the engine through a flywheel110, a traveling shaft212disposed in parallel with the drive shaft211, a forward/reverse switching device220for switching a power transmission direction from the drive shaft211to the traveling shaft212, a traveling power transmission shaft213coupled to the traveling shaft212so as not to be rotatable with respect to the traveling shaft212about an axis, a traveling drive shaft214coupled to the traveling power transmission shaft213so as not to be rotatable with respect to the traveling power transmission shaft213about the axis, a traveling driven shaft215disposed in parallel with the traveling drive shaft214, a mechanical transmission230for changing a speed of and transmitting power from the traveling drive shaft214to the traveling driven shaft215, a pair of main drive axles250(a pair of rear axles in this embodiment), and a differential gear240for differential transmission from the traveling driven shaft215to the pair of main drive axles250.

On the other hand, the PTO power transmission mechanism260includes the drive shaft211, a PTO power transmission shaft261coupled to the drive shaft211so as not to be rotatable with respect to the drive shaft211about an axis, a PTO drive shaft262coupled to the PTO power transmission shaft261so as not to be rotatable with respect to the PTO power transmission shaft261, a PTO driven shaft263disposed so as to be rotatable with respect to the PTO drive shaft262, a PTO clutch270for selectively transmitting power from the PTO drive shaft262to the PTO driven shaft263, a PTO gear unit280operatively connected to the PTO driven shaft263, and a PTO shaft265which is coupled to the PTO gear unit280and from which power can be taken out from outside.

In this embodiment, the PTO shaft265includes a rear PTO shaft265R and a middle PTO shaft265M (seeFIG. 8which will be described later).

In the power transmission mechanism200having the above structure, the forward/reverse switching device220, the mechanical transmission230, and the PTO clutch270form the power transmission portion, and the main drive axles250and the PTO shaft265form the output portion.

The housing300houses the power transmission mechanism and is formed so that at least a part of an inside space of the housing300is used as the oil source of the oil supply unit1.

In this embodiment, the housing300has a front housing310, a middle housing330and a rear housing350coupled to each other in series along a longitudinal direction of a vehicle.

The front housing310is in a hollow shape open at its longitudinal opposite end portions and is formed to house the flywheel110and the forward/reverse switching device220.

Specifically, the housing300further has a reverser case320housing the forward/reverse switching device220and coupled to a front end face of the middle housing330so as to be positioned in the front housing310.

The middle housing330is similarly in a hollow shape open at its longitudinal opposite end portions and is coupled to the front housing310with opposed end faces of the front and middle housings310and330in contact with each other.

Into the middle housing330, the traveling power transmission shaft213and the PTO power transmission shaft261are inserted. In other words, the power transmission portion of the power transmission mechanism200is not positioned in the middle housing330.

The rear housing350is open on its front, upper and rear sides.

The rear housing350is coupled to the middle housing330with a support plate340sandwiched therebetween.

The rear opening and the upper opening of the rear housing350are respectively closed with a rear plate360and an upper plate370.

Specifically, an inside space of the rear housing350is partitioned into a front chamber350F, a middle chamber350M and a rear chamber350R along a back and forth direction of the vehicle with integrally formed first and second partitions351and352.

The mechanical transmission230is housed in the front chamber350F, and the PTO clutch270and the differential gear240are housed in the middle chamber350M. The PTO gear unit280is housed in the rear chamber350R.

In the housing300, in addition to the inside spaces of the middle housing330and the rear housing350, an inside space of the reverser case320is an oil reservoir space in which oil can be stored, and an inside space of the front housing310excluding the reverser case320is a dry chamber.

In the figure, a reference numeral216denotes a four-wheel drive power transmission shaft for transmitting the driving force to axles (front axles in this embodiment) other than the main drive axles250(rear axles in this embodiment) in synchronization with the main drive axles.

Next, the oil supply unit1according to this embodiment will be described.

The oil supply unit1has a hydraulic pump10of a variable displacement type.

The hydraulic pump10has an output adjusting member15, and a discharge quantity is changed by operating the output adjusting member15based on outside operation.

The hydraulic pump10is always and operatively connected to the engine and is formed so that the rotation number of a pump shaft11increases and reduces according to the engine speed.

FIG. 3is a vertical sectional side view of a vicinity of the hydraulic pump10.

More specifically, the hydraulic pump10includes the pump shaft11interlocked with and coupled to the engine, a piston unit12for rotating about an axis of the pump shaft11as the pump shaft11rotates and, also, for reciprocating in synchronization with the rotation, a cylinder block13for supporting the piston unit12in a reciprocatable manner, a plate14for supporting the cylinder block13in a rotatable manner, an output adjusting member15for determining a stroke length of the piston unit12by a slanting position to change drawn/discharged oil quantities by the piston unit12, a control shaft16for regulating the slanting position of the output adjusting member15, and a pump case17coupled to the plate14so as to surround the piston unit12, the cylinder block13and the output adjusting member15, as shown inFIG. 3.

In this embodiment, the hydraulic pump10is disposed at the upper plate370and the driving force of the engine is transmitted from the PTO drive shaft262to the pump shaft11through a proper gear train20.

A suction port of the hydraulic pump10with the above structure is fluid-connected to the oil source, and a discharge port is fluid-connected to the power transmission portion in the power transmission mechanism200(seeFIG. 2).

In other words, the oil supply unit1according to this embodiment is formed to draw oil from the suction port of the hydraulic pump10fluid-connected to the oil source and to supply the drawn oil from the discharge port to the power transmission portion through a proper oil path.

Specifically, as shown inFIG. 2, the suction port is fluid-connected to the housing300, which is also used as the oil source in this embodiment.

The discharge port of the hydraulic pump10is fluid-connected to a reverser hydraulic fluid supply line25for supplying hydraulic fluid to the forward/reverse switching device220, a PTO clutch hydraulic fluid supply line26for supplying hydraulic fluid to the PTO clutch270, and a lubricating oil line27for respectively supplying lubricating oil to the forward/reverse switching device220, the PTO clutch270and the mechanical transmission230.

A rate of the discharged oil quantity to the drawn (or suction) oil quantity of the hydraulic pump10changes based on an engine driven state.

Concretely, the oil supply unit1includes a detecting mechanism30for monitoring the driven state of the engine, and a control mechanism50for operating the output adjusting member15based on a result of monitoring by the detecting mechanism30.

As shown inFIG. 3, in this embodiment, the detecting mechanism30includes a reference shaft31always and operatively connected to the engine, a base member32supported on the reference shaft31so as not to be rotatable with respect to the reference shaft31and so as not to be able to slide in an axial direction, weight members34each supported by the base member32so as to be able to swing about a pivot shaft33orthogonal to the reference shaft31and so as to be able to swing about the pivot shaft33according to a centrifugal force due to the axial rotation of the reference shaft31, a slider member35supported on the reference shaft31so as to be able to swing and so as to be pushed in the axial direction of the reference shaft31from an initial position by the weight members34each swinging about the pivot shaft33, and a biasing member36for biasing the slider member35toward the initial position.

As shown inFIG. 3, in this embodiment, the reference shaft31is the PTO drive shaft262.

As the reference shaft31, various shafts can be used as long as they rotate according to the engine speed.

Each of the weight members34is in an L shape in a vertical sectional side view, the shape having a contact portion34aextending radially inward from the pivot shaft33with respect to the axis (reference axis) of the reference shaft31and a weight portion34bpositioned radially outside the contact portion34awith respect to the reference axis.

When the weight member34rotates about the reference axis as the reference shaft31rotates, the weight portion34bswings due to the centrifugal force about the pivot shaft33so as to move radially outward and, as a result, the contact portion34apushes the slider member35.

The control mechanism50includes a pivot shaft51disposed to be orthogonal to the reference axis, a pushing arm52having a base end portion not rotatable with respect to the pivot shaft51and a free end portion engaged with the slider member35, a coupling arm53having a base end portion not rotatable with respect to the pivot shaft51, an operating arm54having a base end portion not rotatable with respect to the control shaft16, and a connecting rod55for interlocking and linking the free end portion of the coupling arm53and a free end portion of the operating arm54with and to each other.

The control mechanism50is formed to position the output adjusting member15in an initial slanting position (e.g., maximum slanting position) when the engine is at idle and to cause the output adjusting member15to approach a neutral position from the initial slanting position as the engine speed increases.

With the oil supply unit1having the above structure, the following effects can be obtained.

FIG. 4shows a relationship between the engine speed and the discharge quantity of the hydraulic pump. InFIG. 4, portions A, B and C respectively denote an oil quantity to be used as the hydraulic fluid for the power transmission portion, an oil quantity to be used as the lubricating oil for the members to be lubricated and a surplus oil quantity.

In the conventional structure in which the hydraulic pump is of the fixed displacement type and the rotation number of the pump shaft of the pump of the fixed displacement type increases and reduces merely in proportion to the engine speed, the surplus discharge quantity (the portion C inFIG. 4) increases as the engine speed increases.

On the other hand, in the oil supply unit1according to this embodiment, the output adjusting member15is set to be able to obtain the necessary discharged oil quantity (the portion A+the portion B inFIG. 4) when the engine is at idle, and the output adjusting member15is moved to the neutral position when the engine speed exceeds an idle speed as described above.

Therefore, the discharge quantity of the hydraulic pump10can approach the necessary oil quantity irrespective of the engine speed and the surplus discharge quantity (the portion C inFIG. 4) can be reduced or eliminated, to thereby reduce horsepower loss.

Further, the following structure is employed in the oil supply unit1according to this embodiment so as to reduce stirring loss caused by the power transmission mechanism and to effectively prevent running out of oil of the oil source of the hydraulic pump.

In other words, as described above, the housing300for housing the power transmission mechanism200is used as the oil source of the hydraulic pump10in this embodiment.

In this form, if an amount of oil stored in the housing300is increased, the stirring resistance to the power transmission mechanism200increases. On the other hand, if the amount of oil stored in the housing300is reduced, the oil for the hydraulic pump10may run out.

In this respect, in this embodiment, the oil reservoir space in the housing300is divided into a first reservoir portion in which the power transmission portion is housed and a second reservoir portion in which the power transmission portion is not housed, and oil is sent from the first reservoir portion to the second reservoir portion by utilizing rotational motion of the power transmission mechanism200.

Specifically, in the housing300, an inside space of the reverser case320positioned in the front housing310is used as the oil reservoir space in addition to the inside space of the middle housing330and the inside space of the rear housing350.

The forward/reverse switching device220forming the power transmission portion is housed in the reverser case320, the mechanical transmission230forming the power transmission portion is housed in the rear housing350, and the middle housing330in which the power transmission portion is not housed is positioned in the center between the reverser case320and the rear housing350in the longitudinal direction of the vehicle.

The housing is formed so that the stored oil in the reverser case320and the stored oil in the rear housing350are respectively sent to the middle housing330by utilizing the rotational motion of the forward/reverse switching device220and the mechanical transmission230.

In other words, in this embodiment, the reverser case320and the rear housing350form the first reservoir portion of the oil reservoir space, and the middle housing330forms the second reservoir portion.

Concretely, the oil is sent from the first reservoir portion to the second reservoir portion by the following structure.

As shown inFIG. 5, the reverser case320has a conduit member321for receiving oil raked up by a rotor221in the forward/reverse switching device220and guiding the received oil into the middle housing330.

Similarly, as shown inFIG. 7, the rear housing350has conduit members351for receiving oil raked up by a rotor231in the mechanical transmission230and guiding the received oil into the middle housing330.

The support plate340is provided with holes341for allowing oil to flow from the conduit members351into the middle housing330(seeFIG. 6).

The conduit members351provided to the rear housing350has a forward conduit member351F for receiving the oil raked up when the rotor231rotates in a forward direction and a rear conduit member351R for receiving oil raked up when the rotor231rotates in a reverse direction.

Moreover, in the oil supply unit1according to this embodiment, the hydraulic pump10is formed to draw oil from the second reservoir portion.

FIG. 8is a sectional view taken along line VIII—VIII inFIG. 1.FIG. 9is a sectional view taken along line IX—IX inFIG. 8.

As shown inFIGS. 8 and 9, the rear housing350has an oil taking-out space350S below the front chamber350F, the space350S communicating with the inside space of the middle housing330and being separated from the other portion of the rear housing350in a liquid-tight manner.

In this embodiment, the hydraulic pump10is formed to draw oil from the oil taking-out space350S through a line filter40.

A reference numeral41inFIGS. 8 and 9denotes an oil heater for heating the stored oil drawn through the line filter40to a proper temperature.

As described above, in this embodiment, the oil reservoir space in the housing300is divided into the first reservoir portion in which the power transmission portion in the power transmission mechanism is housed and the second reservoir portion in which the power transmission portion is not housed, the oil is sent from the first reservoir portion to the second reservoir portion, and the oil is drawn from the second reservoir portion.

As a result, while effectively preventing power loss due to stirring loss of the power transmission mechanism, running out of the oil is prevented.

Further, in this embodiment, the middle housing330positioned substantially at a center in the longitudinal direction of the vehicle forms the second reservoir portion.

In this form, it is possible to suppress variation in an oil level in the second reservoir portion when the vehicle travels on slopes such as upward and downward slopes.

Therefore, it is possible to effectively prevent cavitation due to drawing in of air by the hydraulic pump10during traveling on the slope.

Another preferred embodiment of the invention will be described below with reference to the accompanying drawings.

FIG. 10is a vertical sectional side view of an oil supply unit2according to this embodiment.

Members similar or corresponding to those in the first embodiment will be denoted by the same reference numerals; therefore, detailed description thereof will not be made herein.

Although the oil supply unit1according to the first embodiment is formed so that the output adjusting member15of the hydraulic pump10is operated according to the engine speed, the oil supply unit2according to this embodiment is formed so that the output adjusting member15of the hydraulic pump10is operated according to a load on the engine.

In other words, the oil supply unit2according to this embodiment has substantially the same structure as that in the first embodiment except that it has a detecting mechanism70and a control mechanism90respectively instead of the detecting mechanism30ad the control mechanism50.

First, the detecting mechanism70will be described.

The detecting mechanism70is formed to monitor the load on the engine between a drive-side member operatively connected to the engine and a driven-side member operatively connected to the output portion to receive power transmission from the drive-side member.

Concretely, the detecting mechanism70includes a slider member72supported on a drive-side reference shaft71(traveling power transmission shaft213in the embodiment shown in the figure) so as not to be rotatable with respect to the drive-side reference shaft71and to be able to slide in an axial direction, the drive-side reference shaft71being operatively connected to the engine, a coupling member74which couples the drive-side reference shaft71to a driven-side reference shaft73(traveling drive shaft214in the form shown in the figure) “forming a power transmission path together with the drive-side reference shaft71” so that the shaft71cannot axially rotate with respect to the shaft73and which cannot axially slide with respect to both the shafts71and73, and a biasing member75for biasing the slider member72toward the coupling member74.

The slider member72is formed at its end face opposed to the coupling member74with a cam groove (not shown) extending in a circumferential direction with respect to the axis of the drive-side reference shaft71. The cam groove includes a deepest portion having the largest depth and slanting portions between which the deepest portion is sandwiched and which have depths reducing toward opposite sides in the circumferential direction.

The coupling member74has a projection to be engaged in the cam groove on an end face of the coupling member74facing the slider member72.

In this embodiment, the coupling member74has a ball locking hole in the end face of the coupling member74facing the slider member72, and balls76are retained in a rollable manner in the ball locking hole. The balls76form the projection to be engaged in the cam groove.

The detecting mechanism70having the above structure operates as follows.

When the load applied on the output portion (main drive axles250in this embodiment) is small, the slider member72and the coupling member74rotate together in a state where the balls76are engaged in the deepest portion of the cam groove. Therefore, the slider member72is kept retained in an initial position by the biasing member75.

On the other hand, when the large load is applied on the output portion, the balls76mount the slanting portions from the deepest portion due to the large load. As a result, the slide member72is pushed in such a direction as to move away from the coupling member74against a biasing force of the biasing member75.

As described above, in the detecting mechanism70, the slider member72is positioned in the initial position when the load applied on the output portion is equal to or less than a predetermined value, and the slider member72is pushed in the axial direction by a distance corresponding to the load when the load applied on the output portion has exceeded the predetermined value.

Next, the control mechanism90will be described.

The control mechanism90is formed to increase the discharge quantity of the hydraulic pump10according to an increase in the load when the load applied on the output portion has exceeded the predetermined value.

In other words, the control mechanism90positions the output adjusting member15of the hydraulic pump10in a predetermined initial slanting position when the slider member72is positioned in the initial position. When the slider member72has been pushed from the initial position, the control mechanism90moves the output adjusting member15of the hydraulic pump10from the initial slanting position toward a maximum slanting position according to a distance by which the slider member72has been pushed.

In the oil supply unit2having the above structure, the oil quantity supplied from the hydraulic pump10to the power transmission portion can be made a minimum necessary quantity when the load applied on the output portion is small, and the oil quantity supplied to the power transmission portion can be increased when the load applied on the output portion has become large.

In other words, the required quantity of oil can efficiently be supplied when necessary to thereby reduce the power loss.

Although mechanical detecting mechanisms are employed as the detecting mechanisms30and70in the first and second embodiments, it is needless to say that various detecting mechanisms such as electric mechanisms may be employed.

This specification is by no means intended to restrict the present invention to the preferred embodiments set forth therein. Various modifications to the oil supply unit may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.