A transaxle includes a transaxle casing, a bi-directional overrunning clutch in the transaxle casing, a friction mechanism, and a clutch-off biasing mechanism. The bi-directional overrunning clutch includes coaxial input and output members journalled by the transaxle casing, and includes a cage disposed between the input member and the output member. Rollers carried by the cage are rotatable to follow rotation of the output member. The cage is rotatable relative to the input member according to the rotation of the rollers following the output member until the rollers contact the input member to engage the bi-directional overrunning clutch. The friction mechanism applies a friction resistance to the cage to rotate the cage relative to the input member. The clutch-off biasing mechanism biases the cage to the initial position. The friction mechanism and the clutch-off biasing mechanism are distributed in the transaxle casing at first and second end portions of the cage.

BACKGROUND

Field of the Invention

At least an embodiment of the present invention relates to a transaxle including a bi-directional overrunning clutch.

As disclosed by U.S. Pat. No. 8,857,294 B, there is a well-known four-wheel drive vehicle including main and auxiliary transaxles configured so that power is transmitted from the main (rear-wheel) transaxle to the auxiliary (front-wheel) transaxle. In the four-wheel drive vehicle, the auxiliary transaxle adopts a bi-directional overrunning clutch, and is provided with a clutch-engagement control unit for temporarily canceling the engagement of the bi-directional overrunning clutch. The clutch-engagement control unit includes an electrically controlled electromechanical device, such as a coil or a solenoid.

The bi-directional overrunning clutch also includes an armature plate. The armature plate includes a plurality of tabs. The armature plate is engaged to a roll cage via the tabs so that the armature plate rotates together with the roll cage. When the electromechanical device is energized, the armature plate is controlled in location so as to apply a dragging torque to the roll cage, thereby actuating the bi-directional overrunning clutch. Therefore, the bi-directional overrunning clutch is engaged to drive the auxiliary transaxle when a rotary speed of its driven side relative to its drive side reaches a predetermined rotary speed. Once the electromechanical device is unenergized, the dragging torque is no further applied to the roll cage, thereby inactivating the bi-directional overrunning clutch. Therefore, even if the rotary speed of the driven side relative to the drive side reaches the predetermined rotary speed, the bi-directional overrunning clutch is still disengaged, whereby rotation of the auxiliary transaxle is still free from the driving force.

Further, the clutch-engagement control unit includes a torsion spring biasing the roll cage to its neutral position so as to center rollers on a cam surface of a clutch housing. During engagement of the bi-directional overrunning clutch, when the roll cage rotates in any direction to rotate relative to the clutch housing, the torsion spring is deflected. The spring force of the torsion spring acts against the relative rotation of the clutch housing and the roll cage, so that, when a speed of the relative rotation becomes less than the predetermined rotary speed, the roll cage is forcibly restored to the initial neutral position. Due to such a construction, the engagement of the bi-directional overrunning clutch is quickly and smoothly canceled, thereby preventing the auxiliary transaxle from being still driven even while the electromechanical device is unenergized.

U.S. Pat. No. 8,857,294 B discloses another embodiment of a clutch-engagement control unit including an adapter connected to the torsion spring and the roll cage. The adapter serving as a spring retainer is attached along the clutch housing. A pin is provided on a side surface of the clutch housing.

The adapter includes projections outward from another side surface opposite the surface with the pin. The projections are engaged into slits formed in the armature plate when the armature plate is placed on the adapter. Due to the engagement of the armature plate to the adapter, the adapter is connected to the roll cage. In other words, similar to the above-mentioned embodiment, the roll cage is connected to the armature plate via tabs. The torsion spring is connected to the adapter via the pin. Similar to the above-mentioned embodiment, the torsion spring biases the roll cage to the neutral position.

However, in each of the embodiments, the clutch-engagement control unit is disposed adjacent to the armature plate and the electromechanical device. In other words, the clutch-engagement control unit including the torsion spring, the electromechanical device, and the armature plate are assembled eccentrically in one side of the transaxle including the bi-directional overrunning clutch. As a result, the clutch housing and the roll cage have respective end portions at the one side complicated in shape so as to complicate their assembling. Also, the complicatedly shaped end portions of the clutch housing and the roll cage at the one side may have cutout portions increased so as to reduce their strengths.

SUMMARY

At least an embodiment of the present application provides a transaxle including a bi-directional overrunning clutch prevented from being unexpectedly wedged-like engaged while ensuring its capacity of being capable of canceling its engagement quickly and smoothly. The transaxle is designed so that its assembling is not complicated, and a clutch housing and a cage have respective end portions from reduction of their strengths concentrated at one side thereof.

To achieve the above, a transaxle comprises a transaxle casing, a bi-directional overrunning clutch, a friction mechanism, and a clutch-off biasing mechanism. The bi-directional overrunning clutch is disposed in the transaxle casing. The bi-directional overrunning clutch includes an input member, an output member, a cylindrical cage, and a plurality of rollers. The input member is journalled by the transaxle casing. The output member is journalled by the transaxle casing and coaxially surrounded by the input member. The input member and the output member have an annular space between an inner circumferential surface of the input member and an outer circumferential surface of the output member. The inner circumferential surface of the input member includes a plurality of wedge portions aligned in the circumferential direction of the input member, and includes a plurality of radially expanded portions which are diametrically larger than the wedge portions. The cage is disposed coaxially to the input member and the output member in the annular space. The cage has first and second end portions opposite each other in the axial direction of the output member. The plurality of rollers are carried by the cage and contact the outer circumferential surface of the output member rotatably following rotation of the output member.

The bi-directional overrunning clutch is automatically shifted between its disengagement state where the rollers are disposed at the respective radially expanded portions of the input member and are separated from the respective wedge portions, and its engagement state where the rollers contact the respective wedge portions. The shift of the bi-directional overrunning clutch depends on change of rotary speed difference between the input member and the output member.

The friction mechanism applies a frictional force to the cage so as to enable the cage to rotate relative to the input member according to the rotation of the rollers following the output member. The clutch-off biasing mechanism biases the cage in a direction to disengage the bi-directional overrunning clutch. The friction mechanism and the clutch-off biasing mechanism are distributed so that the friction mechanism is disposed at the first end portion of the cage, and the clutch-off biasing mechanism is disposed at the second end portion of the cage.

Preferably, the clutch-off biasing mechanism includes a spring interposed between the input member and the cage so as to be elastically transformable according to the rotation of the cage relative to the input member, thereby biasing the cage to the initial rotational position relative to the input member.

Further preferably, the input member is provided with first and second engagement members that are rotatable integrally with the input member. The cage is provided with third and fourth engagement members that are rotatable integrally with the cage. The spring is a compression spring, including an elastic looped portion that is able to expand and contract in the radial direction thereof, and including first and second end portions extended in the same radial direction from the looped portion, the first and second end portions of the spring being disposed between the first and second engagement members and between the third and fourth engagement members. When the cage is disposed at its initial rotational position relative to the input member to disengage the bi-directional overrunning clutch, the third and fourth engagement members are aligned with the respective first and second engagement members on respective radial lines, when viewed in the axial direction of the input member and the cage, so that the first end portion of the spring is engaged to the first and third engagement portions, and the second end portion of the spring is engaged to the second and fourth engagement portions. During rotation of the cage relative to the input member from the initial rotational position until the bi-directional overrunning clutch is engaged, the third and fourth engagement members are offset from the first and second engagement members in the circumferential direction of the input member and the cage so that one of the first and second end potions of the spring is engaged to either the first or second engagement member, and the other of the first and second end portions of the spring is engaged to either the third or fourth engagement portion.

Further preferably, the cage is provided with a spring holder supporting the elastic looped portion of the spring between the first and second end portions of the spring. The spring holder includes the third and fourth engagement members. The spring holder is engaged to the second end portion of the cage rotatably integrally with the cage.

Alternatively, preferably, the input member is provided with first and second surfaces that are rotatable integrally with the input member. The cage is provided with third and fourth surfaces that are rotatable integrally with the cage. The spring is a torsion spring such that a pair of end portions of the spring are pulled to cross over each other and have the first, second, third and fourth surfaces therebetween. When the cage is disposed at its initial rotational position relative to the input member to disengage the bi-directional overrunning clutch, the third and fourth surfaces are aligned with the respective first and second surfaces on respective radial lines, when viewed in the axial direction of the input member and the cage, so that the first end portion of the spring contacts the first and third surfaces, and the second end portion of the spring contacts the second and fourth surfaces. During rotation of the cage relative to the input member from the initial rotational position until the bi-directional overrunning clutch is engaged, the third and fourth surfaces are offset from the first and second surfaces in the circumferential direction of the input member and the cage so that one of the first and second end potions of the spring is engaged to either the first or second surface, and the other of the first and second end portions of the spring is engaged to either the third or fourth surface.

Alternatively, preferably, the input member clutch housing is provided with a first engagement member that is rotatable integrally with the input member. The cage is provided with a second engagement member that is rotatable integrally with the cage. The spring is a torsion spring such that a pair of end portions of the spring are pulled to cross over each other and have both the first and second engagement members therebetween. When the cage is disposed at the initial rotational position relative to the input member to disengage the bi-directional overrunning clutch, the first and second engagement members are disposed on one radial line, when viewed in the axial direction of the input member and the cage, so as to engage to both of the end portions of the spring respectively. During rotation of the cage relative to the input member from the initial rotational position until the bi-directional overrunning clutch is engaged, the first and second engagement members are offset from each other in the circumferential direction of the input member and the cage so that first engagement member engages to one of the end portions of the spring, and the second engagement member engages to the other of the end portions of the spring.

Further preferably, the cage is provided with a spring holder supporting an elastic looped portion of the spring between the end portions of the spring. The spring holder includes the second engagement member. The spring holder is engaged to the second end portion of the cage rotatably integrally with the cage.

Alternatively, preferably, one end portion of the spring is engaged to the cage so as to be rotatable integrally with the cage. Another end portion of the spring is engaged to the input member so as to be rotatable integrally with the input member. An elastic portion of the spring between the end portions is disposed in a space between the cage and the input member so as to be allowed to elastically transform according to the rotation of the cage relative to the input member.

Alternatively, preferably, a pair of end portions of the spring are engaged to the input member rotatably integrally with the input member so as to have a constant gap therebetween. An intermediate portion of the spring is engaged to the cage rotatably integrally with the cage. The spring includes a pair of elastic portions between the respective end portions and the intermediate portion, such that the elastic portions of the spring are disposed in a space between the cage and the input member so as to be allowed to elastically transform according to the rotation of the cage relative to the input member.

Therefore, due to the distribution of the friction mechanism and the clutch-off biasing mechanism at the first and second end portions of the cage opposite each other in the axial direction of the output member, the transaxle is advantageous in simplifying each of the friction mechanism and the clutch-off biasing mechanism so as to reduce labors for assembling the transaxle, in comparison with the case where the friction mechanism and the clutch-off biasing mechanism are complicatedly assembled with each other and are concentrated at one end portion of the cage in the axial direction of the output member.

Further, due to the distribution of the friction mechanism and the clutch-off biasing mechanism at the first and second end portions of the cage opposite each other in the axial direction of the output member, the transaxle is advantageous in lightening respective portions of the transaxle around the first and second end portions of the cage in the transaxle casing so as to economically ensure durability of the transaxle, in comparison with a case where the friction mechanism and the clutch-off biasing mechanism are concentrated at one end portion of the cage in the axial direction of the output member so as to stress a portion of the transaxle at the side of the cage and so as to require costs for strengthening the portion of the transaxle to ensure required durability of the transaxle.

These and other features and advantages will appear more fully from the following detailed description of the invention with reference to attached drawings.

DETAILED DESCRIPTION

Referring toFIG. 1, a vehicle100equipped with an auxiliary transaxle1serving as a transaxle including a bi-directional overrunning clutch CL will be described.

Vehicle100includes a vehicle body frame101to which an engine102and a main transaxle104are mounted. Main transaxle104serves as a rear transaxle of vehicle100for driving rear wheels18R and18L. Vehicle100is provided with a cargo (not shown) on a rear portion thereof so as to serve as a load-carrying vehicle, such as a truck or a utility vehicle. However, any kind of vehicle may serve as vehicle100if only a transaxle including bi-directional overrunning clutch CL is adaptable thereto.

A continuously variable belt transmission (CVT)103is interposed between an input shaft of main transaxle104and an output shaft of engine102. As usual, main transaxle104is installed therein with a gear transmission mechanism105, a differential gear unit106and a power take-off unit107.

Main transaxle104journals right and left rear output shafts16R and16L. Axles18aof respective right and left rear wheels18L and18R are elastically suspended from respective right and left output shafts16R and16L via respective propeller shafts17with respective universal joints.

Auxiliary transaxle1is supported by a front portion of vehicle body frame101so as to serve as a front transaxle of vehicle100for driving right and left front wheels10R and10L. Auxiliary transaxle1includes a transaxle casing2incorporating a later-discussed bi-directional overrunning clutch CL. Transaxle casing2journals right and left output shafts8R and8L (collectively referred to as “output shafts8”).

Axles10aare elastically suspended from distal end portions of right and left output shafts8R and8L via universal joints so as to be drivingly connected to right and left output shafts8R and8L, respectively. Right and left front wheels10R and10L are steerable wheels, which are integrated with respective axles10aand are steerably supported by vehicle body frame101as usual.

An input shaft12of auxiliary transaxle1projects at a rear end portion thereof outward from the rear portion of transaxle casing2. On the other hand, a power take-off (PTO) shaft15projects forward from power take-off unit107of main transaxle104. The rear end portion of input shaft12is drivingly connected to PTO shaft15via propeller shafts14and13with a coupling and universal joints.

In main transaxle104, gear transmission mechanism105receives power from engine102via CVT103. Gear transmission mechanism105distributes the power between differential gear unit106and power take-off unit106. Differential gear unit106distributes the power between right and left output shafts16R and16L for driving rear wheels18R and18L. Power take-off unit107transmits the power to input shaft12of auxiliary transaxle1via PTO shaft15and propeller shafts14and13.

Bi-directional overrunning clutch CL of auxiliary transaxle1includes a clutch housing4, a cylindrical cage5, right rollers6R and left rollers6L (collectively referred to as “rollers6”), and a right hub7R and a left hub7L (collectively referred to as “hubs7”). Clutch housing4serves as an input member of bi-directional overrunning clutch CL, and hubs7serve as an output member of bi-directional overrunning clutch CL.

Cage5carries right rollers6R at a right half portion thereof, and carries left rollers6L at a left half portion thereof. Cage5carrying rollers6, clutch housing4, right and left hubs7R and7L are disposed in transaxle casing2. Right and left hubs7R and7L are disposed coaxially to each other. Cage5is disposed coaxially around right and left hubs7R and7L. Clutch housing4is coaxially disposed around cage5. In other words, cylindrical clutch housing4is disposed coaxially around hubs7so that clutch housing4and hubs7have an annular space between an inner circumferential surface of clutch housing4and outer circumferential surfaces of hubs7, and cylindrical cage5carrying rollers6is disposed in the annular space.

A proximal (left) end portion of right output shaft8R is fixedly inserted into right hub7R, and a proximal (right) end portion of output shaft8L is fixedly inserted into left hub7L. Bi-directional overrunning clutch CL is configured so as to allow differential rotation of right and left hubs7R and7L, thereby allowing differential rotation of right and left output shafts8R and8L (collectively referred to as “output shafts8”).

In transaxle casing2, a bevel ring gear3is connected to clutch housing4rotatably integrally with clutch housing4. A front end portion of an input shaft12is journalled by a rear portion of transaxle casing2. A bevel gear12ais fixedly provided (or formed) on a front end of input shaft12. Bevel ring gear3and bevel gear12amesh with each other in transaxle casing2.

Therefore, in auxiliary transaxle1, clutch housing4serving as the input member of bi-directional overrunning clutch CL drivingly connected to input shaft12is rotated integrally with input shaft12receiving power from power take-off unit107of main transaxle104, as long as gear transmission mechanism105in main transaxle104receives power from engine102via CVT103.

An engagement (or clutch-on) state of bi-directional overrunning clutch CL is defined so that rollers6abut against clutch housing4so as to transmit the rotary power of clutch housing4to hubs7and output shafts8via cage5carrying rollers6. A disengagement (or clutch-off) state of bi-directional overrunning clutch CL is defined so that rollers6are separated from clutch housing4so as to isolate hubs7and output shafts8from the rotary power of clutch housing4, i.e., so as to make hubs7and output shafts8rotatable freely from the rotary force of clutch housing4.

In a later-discussed ondemand mode, once a rotary speed of clutch housing4exceeds that of output shafts8R and8L, bi-directional overrunning clutch CL of auxiliary transaxle1is engaged so that the rotary power of clutch housing4is transmitted via bi-directional overrunning clutch CL to output shafts8R and8L, and to front wheels10R and10L. In this case, vehicle100travels in a four-wheel drive mode where all the four wheels18R,18L,10R and10L are driven.

On the other hand, once the rotary speed of output shafts8R and8L exceeds that of clutch housing4, bi-directional overrunning clutch CL of auxiliary transaxle1is disengaged so that the rotary power of clutch housing4is not transmitted to front wheels10R and10L, whereby vehicle100travels in a two-wheel drive mode where only rear wheels18R and18L are driven.

Clutch housing4is rotated by receiving power from main transaxle104regardless of what mode is set. Under the ondemand mode, the rotary speed of front wheels10R and10L and output shafts8R and8L rotated by receiving a force from the ground according to movement of vehicle100is set to slightly exceed the rotary speed of clutch housing4. Bi-directional overrunning clutch CL is disengaged as long as the rotary speed of output shafts8R and8L exceeds the rotary speed of clutch housing4. Therefore, vehicle100travels normally in the two-wheel drive mode, thereby ensuring smooth turning ability and high fuel efficiency.

On the other hand, during traveling on rough roads or in such a case, bi-directional overrunning clutch CL is engaged when the rotary speed of clutch housing4becomes lower than that of output shafts8R and8L based on the movement of vehicle100. In other words, at this time, vehicle100travels in the automatically set four-wheel drive mode. Therefore, the traction of vehicle100is increased so that vehicle100can quickly escape from the slipping condition.

Further, due to bi-directional overrunning clutch CL of auxiliary transaxle1, during either forward or backward traveling, vehicle100set in the ondemand mode travels by the two-wheel drive, except that it travels by the four-wheel drive when rear wheel18R or18L slips or is stuck.

Referring toFIG. 2, auxiliary transaxle1includes an actuator50that is shiftable between an ondemand-off position P1and an ondemand position P2. When actuator50is set at ondemand-off position P1, auxiliary transaxle1is set in an ondemand-off mode to cancel the function of bi-directional overrunning clutch CL (to constantly disengage bi-directional overrunning clutch CL). When actuator50is set at ondemand position P2, auxiliary transaxle1is set in the ondemand mode where bi-directional overrunning clutch CL can be disengaged in response to the above-mentioned traveling conditions.

Actuator50is an assembly including a solenoid51and a spool52. Spool52can be thrust or withdrawn in transaxle casing2depending on whether solenoid51is excited or not. Spool52penetrates a vertex wall of transaxle casing2perpendicularly to an axis of right output shaft8R. A tip of spool52projects into a space Sa in transaxle casing2.

Solenoid51is attached on an outside of the vertex wall of transaxle casing2, and is electrically connected to an unshown controller. In this regard, vehicle100is provided with a mode-selection switch (not shown) adjacent to an operator's seat. The mode-selection switch is optionally operated by an operator on vehicle100so as to select either the ondemand mode or the ondemand-off mode of auxiliary transaxle1.

Actuator50for selecting either the ondemand mode or the ondemand-off mode may be a hydraulic actuator (not shown) that selectively has either fluid supply or discharge via an electromagnetic valve so as to be telescopically thrust out or contracted.

Referring toFIGS. 2 and 4, transaxle casing2includes a main housing2aand a side cover2b. Main housing2ajournals right output shaft8R (serving as one output shaft in this embodiment), and side cover2bjournals left output shaft8L (serving as the other output shaft in this embodiment). Further, transaxle casing2includes an unshown input shaft cover journaling input shaft12.

Hereinafter, fore-and-aft and right-and-left directions of auxiliary transaxle1are defined on an assumption that auxiliary transaxle1is located in vehicle100so as to place main housing2arightward, side cover2bleftward, and the input shaft cover rearward.

Referring toFIG. 4, clutch housing4is a substantially circularly cylindrical member having axial right and left open ends. Clutch housing4is journalled by transaxle casing2via a right bearing33R and a left bearing33L. More specifically, left bearing33L is fitted on a left end outer circumferential surface of clutch housing4so as to journal a left end portion of clutch housing4by side cover2bserving as the left part of transaxle casing2. Right bearing33R is fitted on a right end outer circumferential surface of clutch housing4so as to journal a right end portion of clutch housing4by main housing2aserving as the right part of transaxle casing2.

Clutch housing4is formed with a splined outer circumferential portion4gextended rightward from left bearing33L. Bevel ring gear3is spline-fitted at an inner circumferential portion thereof onto splined outer circumferential portion4gof clutch housing4, so that bevel ring gear3is fitted on clutch housing4unrotatably relative to clutch housing4.

Incidentally, a left end of bevel ring gear3abuts against a right end of left bearing33L so as to prevent bevel ring gear3from moving further axially leftward. A right end of bevel ring gear3is retained by a step formed (or a spacer fitted (seeFIG. 8)) on splined outer circumferential portion4gof clutch housing4so as to prevent bevel ring gear3from moving further axially rightward.

Referring toFIGS. 2, 4, 5, 6A and 7A, bi-directional overrunning clutch CL will be described in detail. Cage5is disposed substantially coaxially to clutch housing4in a space defined surrounded by an inner wall surface4aof clutch housing4and outer wall surfaces of hubs7. Cage5is made of plastic, for example. Cage5has a substantially circular cylindrical shape, having right and left distal ends, and has an axial length between the right and left distal ends, which is substantially equal to that of clutch housing4.

Right and left half portions of cage5are formed with respective roller holes5aaligned along a circumferential direction of cage5at regular intervals. In this embodiment, seven right roller holes5aand seven left roller holes5aare formed symmetrically with respect to an axial center portion of cage5.

Each roller hole5apenetrates cage5radially between outer and inner circumferential surfaces of cage5achroller hole5ais formed to have a rectangular opening at each of the outer and inner circumferential surfaces of cage5. The rectangular shape of the opening of roller hole5ahas proximal and distal ends extended circumferentially of cage5, and a pair of parallel axially extended edges between the proximal and distal ends thereof.

The proximal end of roller hole5ais defined as being closer to the axial center of cage5between right roller holes5aand left roller holes5a. The distal end of roller hole5ais defined as being closer to either the right or left distal end of cage5. Therefore, each of right roller holes5ahas a left end as the proximal end thereof, and a right end as the distal end thereof. Each of left roller holes5ahas a right end as the proximal end thereof, and a left end as the distal end thereof.

Referring toFIGS. 2, 4 and 5, cage5includes a cylindrical main part5pand a pair of end rings5qfixed at opposite end sides of main part5p. Roller holes5aare formed in main part5pof cage5. In this regard, as shown inFIG. 5, main part5pis formed integrally with an axially center ring portion5p1, and with right and left bridge portions5p2, which are extended axially rightward and leftward from axially center ring portion5p1and are aligned along the circumferential direction of main part5p. Bridge portions5p2have respective proximal ends joined to axially center ring portion5p1, and have distal ends defined as right and left ends of main part5p.

Right and left end rings5qare fixed to respective right and left ends of main part5p, so that the distal ends of respective bridge portions5p2are joined to respective end rings5q. A distal end surface of each end ring5qopposite main part5pis defined as each of the right and left distal ends of cage5. Outer and inner circumferential surfaces of end rings5qcontinue to the outer and inner circumferential surfaces of main part5p, which are defined as outer and inner circumferential surfaces of axially center ring portion5p1and all bridges5p2.

Therefore, right and left end surfaces of axially center ring portion5p1of main part5pdefine proximal ends of respective right and left roller holes5a. Proximal end surfaces of right and left end rings5qdefine the distal ends of respective right and left roller holes5a. Right and left bridge portions5p2of main part5pextended rightward and leftward from axially center ring portion5p1define the parallel axially extended edges of respective right and left roller holes5a.

Each of end rings5qis formed with grooves5baligned along the circumferential direction at regular intervals. Each groove5bis open radially outward at the outer circumferential surface of end ring5q, and is open axially outward at the distal end of end ring5q. In the circumferential direction of cage5, each groove5bis disposed between adjoining roller holes5a. Therefore, in this embodiment, end ring5qis provided with seven grooves5bcorresponding to seven roller holes5aaligned in the circumferential direction of cage5.

Referring toFIGS. 4, 6A and 7A, left rollers6L are held in respective left roller holes5aformed in the left half portion of cage5, and right rollers6R in respective right roller holes5aformed in the right half portion of cage5. In each roller hole5a, a pair of spring plates20are disposed on the parallel axially extended edges of roller hole5a. Each spring plate20is compressed between an outer circumferential surface of each roller6and each edge surface of roller hole5a. The pair of spring plates20bias each roller6so as to locate roller6at the center of roller hole5ain the circumferential direction of cage5.

Incidentally,FIGS. 6A and 7Aillustrate sectional views of the left half portion of clutch housing4and the left half portion of cage5, carrying left rollers6L and fitted on left hub7L and left output shaft8L. They are representative of the right and left half portions of clutch housing4and the right and left half portions of cage5, carrying right and left rollers6R and6L and fitted on right and left hubs7R and7L and output shafts8R and8L.

Each circular columnar roller6has a diameter that is larger than a radial thickness of cage5between the outer and inner circumferential surfaces thereof. Therefore, rollers6project inward and outward in radial directions of cage5from inner and outer circumferential surfaces of (main part5pof) cage5. The portions of right rollers6R projecting radially inward from the inner circumferential surface of the right half portion of cage5to contact an outer circumferential surface of right hub7R. The portions of left rollers6L projecting radially inward from the inner circumferential surface of the left half portion of cage5to contact an outer circumferential surface of left hub7L.

Referring toFIGS. 6A and 7A, the inner circumferential portion of each of the right and left half portions of clutch housing4is formed with minimum diametric portions4aand recesses4baligned alternately at regular intervals along the circumferential direction of clutch housing4.

Each minimum diametric portion4ais disposed between every pair of recesses4badjoining each other, so that every pair of minimum diametric portions4aadjoining each other define opposite ends4eof each recess4btherebetween. A radially inward end surface of each minimum diametric portion4adefines the minimum inner diameter of cylindrical clutch housing4, and is disposed close to the outer circumferential surface of each of right and left hubs7R and7L.

Recesses4bare arranged to accommodate the portions of respective rollers6projecting radially outward from the outer circumferential surface of cage5(i.e., main part5p). Each recess4bbecomes deepest in the radially outward direction thereof at the circumferential center portion thereof. The deepest portion of recess4bis referred to as deepest center portion4c. Each deepest center portion4cof recess4bdefines the maximum inner diameter of cylindrical clutch housing4.

Minimum diametric portions4aand recesses4bat each of the right and left half portions of clutch housing4correspond in number to rollers6aligned in the circumferential direction of cage5in each of the right and left half portions of cage5. Therefore, in this embodiment, seven minimum diametric portions4aand seven recesses4bare formed on the inner circumferential portion of each of the right and left half portions of clutch housing4.

Incidentally, referring toFIG. 4, in this embodiment, each minimum diametric portion4aat the right half portion of clutch housing4and each minimum diametric portion4aat the left half portion of clutch housing4are joined to each other so as to be formed as a single minimum diametric portion4aextended between right and left ends of clutch housing4to be placed close to the outer circumferential surface of cage5. Also, each recess4bat the right half portion of clutch housing4and each recess4bat the left half portion of clutch housing4are joined to each other so as to be formed as a single recess4aextended between right and left ends of cage5(i.e., main part5p) to accommodate each right roller6R in the right portion thereof, and each left roller6L in the left portion thereof. In other words, in this embodiment, clutch housing4is formed at the axial center portion thereof with no partition between right minimum diametric portions4aand recesses4band left minimum diametric portions4aand recesses4b.

Alternatively, as shown in later-discussed alternative embodiments, clutch housing4may be formed to have right minimum diametric portions4aand recess4band left minimum diametric portions4aand recesses4bpartitioned from each other by the axial center portion thereof.

Each recess4bis formed with a pair of sloped surfaces4dextended from deepest center portion4cto circumferentially opposite ends4ebounding on minimum diametric portions4a. In this regard, when bi-directional overrunning clutch CL is viewed in the axial direction of output shafts8, in each recess4b, one of the pair of sloped surfaces4dis extended circumferentially clockwise from deepest center portion4cso as to correspond to rotation of cage5relative to clutch housing4during a normal rotation of clutch housing4(when rear wheels18R and18L rotate forward), and the other of the pair of sloped surfaces4dis extended circumferentially counterclockwise from deepest center portion4cso as to correspond to rotation of cage5relative to clutch housing4during a reverse rotation of clutch housing3(when rear wheels18R and18L rotate backward). Therefore, bi-directional overrunning clutch CL is available regardless of whether vehicle100travels forward or backward.

Deepest center portion4cof each recess4bhas a radial distance from the outer circumferential surface of hub7, which is larger than the diameter of roller6. Each roller6is biased by its spring plates20to be located at deepest center portion4cof corresponding recess4b.

Referring toFIG. 6A, each roller6located at deepest center portion4cis separated from clutch housing4, so that cage5carrying rollers6contacting hubs7fixed on output shafts8is isolated from the rotary power of clutch housing4driven via bevel ring gear3by input shaft12receiving power from PTO shaft15in vehicle100, thereby isolating output shafts8from the rotary power of clutch housing4.

The state such as shown inFIG. 6Ais defined as the clutch-off (disengagement) state of bi-directional overrunning clutch CL where bi-directional overrunning clutch CL is disengaged. As mentioned above, when actuator50is set at ondemand position P2, as far as the rotary speed of output shafts8exceeds the rotary speed of clutch housing4, bi-directional overrunning clutch CL is disengaged.

Each recess4bhas a radial distance at sloped surface4dfrom the outer circumferential surface of hub7, which is reduced as it goes from deepest center portion4cto end4ealong sloped surface4d. The radial distance of each recess4bat end4efrom the outer circumferential surface of hub7is smaller than the diameter of roller6. Therefore, referring toFIG. 7A, each sloped surface4dhas a circumferentially intermediate portion, serving as a wedge portion4d1, whose radial distance from the outer circumferential surface of hub7is equal to the diameter of roller6. Therefore, in each recess4b, deepest center portion4cand the portions of opposite sloped surfaces4dhaving deepest center portion4ctherebetween and between opposite wedge portions4d1are defined as a radially expanded portion of clutch housing4, which has an inner diameter that is greater than an inner diameter of wedge portion4d1.

When the rotary speed of either right output shaft8R or left output shaft8L is reduced to become less than the rotary speed of clutch housing4, cage5having frictional resistance from friction mechanism FM follows the speed reduction of hubs7fixed on output shafts8so as to rotate relative to clutch housing4. When the rotation degree of cage5relative to clutch housing4reaches an angle R, roller6comes to abut against wedge portion4d1of sloped surface4d, thereby drivingly connecting hubs7and output shafts8to clutch housing4via rollers6carried by cage5. The state such as shown inFIG. 7Ais defined as the clutch-on state (engagement) of bi-directional overrunning clutch CL where bi-directional overrunning clutch CL is engaged.

Cage5receiving the friction resistance from friction mechanism FM to rotate relative to clutch housing4has a toque in the rotation direction relative to clutch housing4. Therefore, rollers6abutting against wedge portions4d1of clutch housing4tend to rotate further in the rotation direction of cage5relative to clutch housing4, thereby being pressed and nipped between sloped surfaces4dof clutch housing4and the outer circumferential surface of hub7, so that rollers6are hard to be released from wedge portions4d1of clutch housing4. Accordingly, cage5becomes unrotatable further in the rotation direction relative to clutch housing4, and is hard to rotate in the opposite direction so as to return to its initial position relative to clutch housing4. Such a state where rollers6are engaged to clutch housing4and are hard to be released from clutch housing4is defined as a wedge-like engagement state of bi-directional overrunning clutch CL.

Bi-directional overrunning clutch CL is provided with a later-discussed clutch-off biasing mechanism CM1to release bi-directional overrunning clutch CL from the wedge-like engagement state, i.e., to forcibly separate rollers5from clutch housing4so as to return bi-directional overrunning clutch CL to the clutch-off (disengagement) state of bi-directional overrunning clutch CL where cage5is rotatable relative to clutch housing4.

A proximal left end portion of right output shaft8R and right hub7R spline-fitted on the proximal left end portion of right output shaft8R are inserted into cage5through the right end opening of cage5. A proximal right end portion of left output shaft8L and left hub7L spline-fitted on the proximal right end portion of left output shaft8L are inserted into cage5through the left end opening of cage5.

Therefore, in transaxle casing2, right and left output shafts8R and8L are disposed coaxially to each other, right and left hubs7R and7L fixed on respective right and left output shafts8R and8L are disposed coaxially to each other, cage5is disposed coaxially around right and left hubs7R and7L so that right and left rollers6R and6L carried by cage5are disposed along the respective outer circumferential surfaces of right and left hubs7R and7L, and clutch housing4is disposed coaxially around cage5so as to accommodate right and left rollers6R and6L in respective recesses4bon the inner circumferential portion thereof.

In cage5, cylindrical hubs7R and7L are spigot-and-socket joined at proximal end portions thereof to each other, so as to have substantially constant outer and inner diameters (i.e., maximum outer diameter and minimum inner diameter of hubs7) in the substantially whole range thereof surrounded by cage5. More specifically, the proximal end portion of one of right and left hubs7R and7L (in this embodiment, the right end portion of left hub7L) is formed as a spigot portion7bhaving a smaller outer diameter than the maximum outer diameter of hubs7, and the proximal end portion of the other of right and left hubs7R and7L (in this embodiment, the left end portion of right hub7R) is formed as a socket portion7chaving a larger inner diameter than the minimum inner diameter of hubs7.

Spigot portion7bis fitted into socket portion7cso as to allow differential rotation of right and left hubs7R and7L. In this regard, a needle bearing45is fitted in a radial gap between an outer circumferential surface of spigot portion7band an inner circumferential end of socket portion7c. A washer46is fitted in an axial gap between a distal stepped end of spigot portion7band a proximal end of socket portion7c. Therefore, right and left hubs7R and7L spigot-and-socket joined to each other are allowed to rotate differentially, thereby allowing right and left output shafts8R and8L to rotate differentially.

Spigot and socket portions7band7cof hubs7R and7L project further axially proximally from proximal ends of right and left output shafts8R and8L. Therefore, right and left hubs7R and7L spigot-and-socket like joined to each other has a space Sb therein surrounded by the inner circumferential surface of spigot portion7bbetween the proximal ends of right and left output shafts8R and8L. Space Sb is filled with lubricating fluid so as to surely lubricate splines on outer circumferential surfaces of right and left output shafts8R and8L and the corresponding splines on the inner circumferential surfaces of right and left hubs7R and7L.

A distal right end portion of right hub7R projects rightward from the right end of cage5and is journalled by main housing2aserving as the right part of transaxle casing2via a bearing34R. A distal left end portion of left hub7L projects leftward from the left end of cage5and is journalled by side cover2bserving as the left part of transaxle casing2via a bearing34L.

A distal right portion of right output shaft8R projects rightward from the right end of right hub7R so as to be journalled by a right end portion of main housing2aand projects rightward from the right end portion of main housing2aso as to be formed with a coupling portion to be coupled to propeller shaft17R via the universal joint. A distal left portion of left output shaft8L projects leftward from the left end of left hub7L so as to be journalled by a left end portion of side cover2band projects leftward from the left end portion of side cover2bso as to be formed with a coupling portion to be coupled to propeller shaft17L via the universal joint.

A right end of bearing33R, the right end of clutch housing4, and the right end of cage5substantially coincide to one another in location in the axial direction of clutch housing4. Therefore, bearing34R fitted circumferentially on the right end portion of right hub7R has an outer diameter, which is smaller than that of bearing33R fitted circumferentially on the right end portion of clutch housing4, and is disposed rightward from bearing33R, thereby ensuring space Sa for arranging friction mechanism FM between bearings33R and34R in main housing2arightward from the right end portion of cage5and around the right end portion of hub7R.

A left end of bearing33L and the left end of clutch housing4substantially coincide to each other in location in the axial direction of clutch housing4, and left end ring5qof cage5serving as the left end portion of cage5projects leftward from the left end of clutch housing4. Therefore, bearing34L fitted circumferentially on the left end portion of left hub7L projecting leftward from the left end of cage5has an outer diameter, which is smaller than that of bearing33L fitted circumferentially on the left end portion of clutch housing4, and is disposed leftward from bearing33L, thereby ensuring a later-discussed space Sc for arranging a later-discussed clutch-off biasing mechanism CM1between bearings33L and341in side cover2bleftward from the left end of clutch housing4and around left end ring5qof cage5.

Friction mechanism FM provided in space Sa in transaxle casing2will now be described with reference toFIGS. 2, 3 and 4. Friction mechanism FM includes a spacer36, a rotary-side friction plates26, a fixed-side friction plates27, at least one waved washer110, a retaining plate112, a retaining ring113, and a needle bearing111. Needle bearing111is substantially circularly cylindrical.

Spacer36includes a horizontally axial sleeve portion36aand a vertical disc portion36b. Sleeve portion36ais fitted at an inner circumferential surface thereof on the distal right portion of right hub7R projecting rightward from the right end (i.e., right end ring5q) of cage5so that spacer36is disposed around the distal right portion of right hub7R rotatably relative to right hub7R. Vertical disc portion36bis formed as a flange extended radially outward from a proximal left end of horizontal sleeve portion36a.

Sleeve portion36ais formed with a step36dand an annular groove36e. Step36dis formed radially on an axially intermediate outer circumferential portion of sleeve portion36aso that a distal right portion of sleeve portion36aextended distally rightward from step36dhas an outer diameter which is smaller than that of a proximal left portion of sleeve portion36aextended proximally leftward from step36d. Annular groove36eis formed on an outer circumferential portion of the distal right portion of the distal right portion sleeve portion36aextended distally rightward from step36d.

Sleeve portion36ais cut off by a slit36faxially extended from the distal right end of sleeve portion36ato approach the proximal left end portion of sleeve portion36aformed with vertical disc portion36b. Vertical disc portion36bis formed with at least one through hole36c. In this embodiment, seven through holes36care formed at regular intervals along the circumferential direction of vertical disc portion36b.

Rotary-side friction plate26includes a substantially annular disc portion26sand at least one engagement pawl26a. In this embodiment, rotary-side friction plate26is formed with seven engagement pawls26a. Each engagement pawl26ais extended radially inward from an inner circumferential edge of disc portion26s, and is bent at a substantially right angle so as to extend along the axial direction.

Each engagement pawl26ais extended leftward so as to be passed through each through hole36cformed in vertical disc portion36bof spacer36at the proximal left end of spacer36, and is fitted into each of grooves5bformed in end ring5qdisposed at the right end of cage5, so that rotary-side friction plate26is unrotatable relative to cage5, and is restricted in rotatability relative to spacer36, thereby restricting the rotatability of spacer36relative to cage5. In this state, disc portion26sof rotary-side friction plate26contacts vertical disc portion36bof spacer36. Spacer36does not contact bearing33R and clutch housing4.

Fixed-side friction plate27includes a substantially annular disc27sand at least one stopper pawl27a. In this embodiment, fixed-side friction plate27is formed with four stopper pawls27a. Each stopper pawl27ais extended radially outward from an outer circumferential edge of disc portion27s, and is bent at a substantially right angle so as to extend along the axial direction. Disc portions26sand27scontact each other so that engagement pawls26aof rotary-side friction plate26and stopper pawls27aof fixed-side friction plate27are extended axially opposite each other. Therefore, in transaxle casing2, fixed-side friction plate27is disposed on the distal right side of rotary-side friction plate26so as to extend stopper pawls27adistally rightward.

Rotary-side friction plate26and fixed-side friction plate27are disposed around the proximal left portion of sleeve portion36aof spacer36extended leftward from step36d. In this regard, the inner circumferential edge of fixed-side friction plate27is diametrically smaller than the rotary-side friction plate26. Therefore, an inner circumferential edge of fixed-side friction plate27contacts an outer circumferential surface of horizontal sleeve portion36a, while the inner circumferential edge of rotary-side friction plate26does not contact the outer circumferential surface of horizontal sleeve portion36a.

Waved washer110is attached on the outer circumferential surface of the proximal left portion of sleeve portion36arightward from fixed-side friction plate27. Waved washer110presses fixed-side friction plate27against vertical disc portion36bin the condition that rotary-side friction plate26is disposed between vertical disc portion36band fixed-side friction plate27. Therefore, rotary-side friction plate26and fixed-side friction plate27are pressed against vertical disc portion36b.

Annular retaining plate112includes a knob112pprojecting radially inward from an inner circumferential edge thereof. Retaining plate112adjoins waved washer110on the distal right side of wave washer110and is attached at the inner circumferential edge thereof on the outer circumferential surface of the distal right portion of sleeve portion36arightward from step36dso as to fit knob112pinto slit36f. Accordingly, retaining plate112is unrotatable relative to spacer36. Retaining plate112does not contact vertical disc portion36bbut is leaned against step36dof sleeve portion36abecause the inner circumferential edge of retaining plate112is diametrically smaller than the respective inner circumferential edges of rotary-side friction plate26and fixed-side friction plate27.

Retaining ring113is disposed on the distal right side of retaining plate112, and is fitted at an inner circumferential edge thereof into groove36eso as to fix the axial position of retaining plate112on sleeve portion36a.

When solenoid51is unexcited, the tip of spool52is disposed at a position P1outside of a rotation locus of stopper pawls27aof fixed-side friction plate27. Position P1is defined as ondemand-off position P1of actuator50for setting bi-directional overrunning clutch CL in an ondemand-off mode. In bi-directional overrunning clutch CL set in the ondemand-off mode, during rotation of cage5according to rotation of clutch housing4and hubs7, fixed-side plate27pressed against rotary-side friction plate26by wave washer110is rotatable together with rotary-side friction plate26retained by cage5without frictionally resisting rotary-side friction plate26. Therefore, cage5does not receive the frictional resistance generated by friction mechanism FM. Therefore, rollers6are free from the wedged-like engagement so that rollers6are movable along normal and reverse rotation directions in respective recesses4a. Therefore, bi-directional overrunning clutch CL of auxiliary transaxle1is out of its clutch-function, i.e., bi-directional overrunning clutch CL is constantly disengaged.

When solenoid51is excited, spool52is thrust so that the tip of spool52is disposed at a position P2as shown inFIG. 2, where the tip of spool52is entered into a space between any two stopper pawls27aadjoining each other along the circumferential direction of fixed-side friction plate27. Position P2is defined as ondemand position P2of actuator50for setting bi-directional overrunning clutch CL in an ondemand mode.

Once any one of stopper pawls27aof fixed-side friction plate27rotating to follow the rotation of rotary-side friction plate26becomes to abut against spool52entered in the space between adjoining two stopper pawls27a, fixed-side friction plate27is hindered by spool52from further rotating to follow the rotation of rotary-side friction plate26. In other words, spool52at ondemand position P2keeps fixed-side friction plate27stationary in transaxle casing2. Since fixed-side friction plate27whose disc portion27sis pressed against disc portion26sof rotary-side friction plate26by wave washer110is kept stationary, disc portion27sof fixed-side friction plate27frictionally resists disc portion26sof rotary-side friction plate26rotating together with cage5.

The frictional resistance is applied to cage5via rotary-side friction plate26. Therefore, if the rotation of hub7becomes slower than the rotation of clutch housing4(because of slipping of any of right and left rear wheels18R and18L, for example), cage5becomes slow to follow hub7so as to rotate relative to clutch housing4until rollers6abut against wedge portions4d1of clutch housing4, thereby engaging bi-directional overrunning clutch CL of auxiliary transaxle1.

From this state, if the rotary speed of hub7increases to exceed the rotary speed of clutch housing4, later-discussed clutch-off biasing mechanism CM1functions to quickly and smoothly cancel the wedged-like engagement of bi-directional overrunning clutch CL, whereby hub7becomes rotatable freely from the rotational force of clutch housing4.

Referring toFIGS. 4, 5, 6A, 6B, 7A and 7B, clutch-off biasing mechanism CM1of auxiliary transaxle1will be described. In auxiliary transaxle1, clutch-off biasing mechanism CM1is disposed opposite friction mechanism FM with respect to bevel ring gear3disposed at the axially intermediate portion of bi-directional overrunning clutch CL. On the above-mentioned assumption that friction mechanism FM is disposed rightward of bi-directional overrunning clutch CL, clutch-off biasing mechanism CM1is disposed leftward of bi-directional overrunning clutch CL.

Clutch-off biasing mechanism CM1includes clutch housing4, cage5, left hub7L, a spring holder57, and a wire spring clip66. Wire spring clip66is interposed via spring holder57between clutch housing4and cage5. Substantially discoid spring holder57is detachably attached to the left end portion of cage5. A left side of spring holder57facing bearing34L is defined as a distal side of spring holder57axially opposite bearing33L, clutch housing4and cage5, and a right side of spring holder57is defined as a proximal side of spring holder57facing bearing33L, clutch housing4and cage5.

Clutch housing4is formed with a left end portion4fextended leftward from splined outer circumferential portion4g. Left end portion4fis inserted through bearing33L, and is formed at an utmost left end thereof with a vertical end surface4ft. Left end surface4ftsubstantially coincides to a left end of bearing33L in location in the axial direction of output shafts8, or may be disposed rather proximally rightward from the left end of bearing33L.

As mentioned above, side cover2bserving as the left part of transaxle casing2supports bearing33L journaling left end portion4fof clutch housing4and bearing34L journaling the left portion of left hub7L. Bearings33L and34L have an axial gap therebetween in the axial direction of output shafts8, and have a radial gap therebetween in the radial direction of output shafts8. In correspondence to the axial and radial gaps between bearings33L and34L, side cover2bis formed to ensure a space Sc around left hub7L and leftward from clutch housing4.

Space Sc is sufficiently large for arranging left end ring5qof cage5, spring holder57and wire spring clip66to constitute clutch-off biasing mechanism CM1. In this regard, the left end of main part5pof cage5, defining left ends of left rollers6L in respective left roller holes5a, is disposed to substantially coincide to left end surface4ftof clutch housing4in location in the axial direction of output shafts8. Therefore, left end ring5qof cage5projects distally leftward from left end surface4ftof clutch housing4so as to be disposed between bearing34L and the left end of main part5pof cage5.

A pair of housing pins40aand40bproject axially leftward from left end surface4ftof clutch housing4. Housing pins40aand40bhave a gap g1therebetween. Housing pins40aand40bare columnar projections formed integrally with clutch housing4. Alternatively, housing pins40aand40bmay be individual members separated from clutch housing4and may be fixed to clutch housing4.

Referring toFIG. 5, spring holder57is ring-shaped so as to have an outer circumferential edge and an inner circumferential edge. Spring holder57is formed along the outer circumferential edge thereof with guide pawls57a(in this embodiment, five guide pawls57a). Guide pawls57aare extended radially outward from the outer circumferential edge of spring holder57, and are bent to project proximally rightward so as to abut against bearing33L, thereby ensuring a sufficient axial width of space Sc for arranging wire spring clip66along guide pawls57awhile keeping spring holder57rotatable relative to clutch housing4.

Spring holder57is also formed along the inner circumferential edge thereof with engagement pawls57b(in this embodiment, six inner engagement pawls57b). Engagement pawls57bare extended radially inward from the inner circumferential edge of spring holder57, and are bent to project proximally rightward so as to be fitted into corresponding grooves5bformed in left end ring5qof cage5.

In this regard, right and left end rings5q, each of which is formed with seven grooves5b, are disposed at the right and left ends of cage5. As mentioned above, seven engagement pawls26aof rotary-side friction plate26in friction mechanism FM are fitted into respective grooves5bformed on end ring5qdisposed at the right end of cage5. In other words, common end ring5qmay serve as either right end ring5qto engage with rotary-side friction plate26of friction mechanism FM or left end ring5qto engage with spring holder57of clutch-off biasing mechanism CM1, thereby promoting standardization of a component member of cage5.

Further, spring holder57is formed with a pair of crosscut edges57cand57d, which are formed by cutting off the ring-shape of spring holder57along a chord-like line extended between opposite points on the outer circumferential edge of spring holder57through two adjoining points on the inner circumferential edge of spring holder57. Crosscut edges57cand57dhave respective ends57c1and57d1corresponding to the two adjoining points on the inner circumferential edge of spring holder57, so as to have a gap g2between ends57c1and57d1.

As mentioned above, six engagement pawls57bare fitted into six grooves5b. Remaining one groove5bhas engagement pawls57babsent therefrom. Gap g2between ends57c1and57d1of crosscut edges57cand57dof spring holder57corresponds to the absence of engagement pawl57bfrom groove5b.

Spring holder57is formed on respective ends57c1and57d1of crosscut edges57cand57dwith a pair of pressure pawls57eand57f. Pressure pawls57eand57fare extended radially outward from respective ends57c1and57d1of crosscut edges57cand57d, and are bent to project proximally rightward toward the left end of cage5. Gap g2between pressure pawls57eand57fon ends57c1and57d1of crosscut edges57cand57dis as wide as gap g1between housing pins40aand40b.

Wire spring clip66is a wire made of elastic material, such as steel. The wire serving as wire spring clip66is circularly looped so that wire spring clip66has a circularly looped portion66a, which has a centrifugal spring force when it is compressed centripetally. Wire spring clip66is bent at equal lengths from both ends of the wire serving as wire spring clip66, defined as ends of circularly looped portion66a, so as to form a pair of radial end portions66band66cfacing each other. Radial end portions66band66care extended radially inward from the respective ends of circularly looped portion66aand parallel to each other.

Wire spring clip66is further bent at respective radially inward ends of radial end portions66band66cso as to form a pair of tangent end portions66dand66eextended tangentially away from each other to the respective ends of the wire serving as wire spring clip66.

In space Sc around left end ring5qof cage5, spring holder57is located so that guide pawls57aof spring holder57abut at right ends thereof against bearing33L so as to allow spring holder57to rotate relative to clutch housing4, and so that engagement pawls57bof spring holder57are fitted into corresponding grooves5bof left end ring5qof cage5so as to engage spring holder57to cage5unrotatably relative to cage5.

In the state where spring holder57is disposed in space Sc so as to be associated with clutch housing4and cage5as mentioned above, wire spring clip66is disposed in space Sc so that guide pawls57aof spring holder57are aligned along circularly looped portion66aof wire spring clip66. Housing pin40ais located at an angle space between one end of circularly looped portion66aand radial end portion66b, and housing pin40bis located at an angle space between the other end of circularly looped portion66aand radial end portion66c. Pressure pawl57eof spring holder57is located at an angle space between radial end portion66band tangent end portion66dof wire spring clip66, and pressure pawl57fof spring holder57is located at an angle space between radial end portion66cand tangent end portion66eof wire spring clip66.

Therefore, the pair of radial end portions66band66care disposed between housing pin40aand pressure pawl57eat one end57c1of crosscut edge57cand housing pin40band pressure pawl57fat the other end57d1of crosscut edge57d. Tangent end portions66dand66eare disposed between respective pressure pawls57eand57fof spring holder57and the outer circumferential surface of left end ring5qof cage5, so as to extend tangentially with respect to cage5.

As a result, circularly looped portion66aof wire spring clip66is pressed centrifugally against guide pawls57aof spring holder57aligned therealong, radial end portion66bof wire spring clip66is pressed against both housing pin40aand pressure pawl57eof spring holder57, and radial end portion66cof wire spring clip66is pressed against both housing pin40band pressure pawl57fof spring holder57, so that wire spring clip66is compressed so as to have a gap g3between radial end portions66band66cof wire spring clip66. Gap g3is narrower than an essential gap between radial end portions66band66cwhen wire spring clip66is free from the compression by spring holder57. In other words, in the initial state of wire spring clip66fitted to spring holder57, wire spring clip66functions as a compression spring.

Therefore, compressed wire spring clip66has tangent end portions66dand66eabutting against the outer circumferential surface of left end ring5qof cage5so as to bias cage5centripetally against the relative rotation of clutch housing4and cage5. In this way, wire spring clip66serves as a spring interposed between clutch housing4and cage5so as to be elastically transformable according to rotation of cage5relative to clutch housing4.

During traveling of vehicle100, regardless of whether it travels forward or backward, as far as the rotary speed of right and left front wheels10R and10L rotated to follow rotation of rear wheels18R and18L is kept sufficient to keep the rotation speed of hubs7exceeding to the rotary speed of clutch housing4, bi-directional overrunning clutch CL is disengaged (i.e., clutched off) as shown inFIG. 6A. During the clutch-off state of bi-directional overrunning clutch CL such as shown inFIG. 6, where rollers6are located at their initial positions defined by respective deepest center portions4cof recesses4bof clutch housing4, regardless of whether clutch housing4(together with bevel ring gear3and input shaft12) is rotated normally or reversely, the position of spring holder57fixedly engaged to cage5relative to clutch housing4is kept so as to keep pressure pawl57eof spring holder57at the angle between radial end portion66band tangent end portion66dof wire spring clip66, and so as to keep pressure pawl57fof spring holder57at the angle between radial end portion66cand tangent end portion66eof wire spring clip66, thereby keeping the initially set maximum width of gap g3, as shown inFIG. 6B.

This state of clutch-off biasing mechanism CM1corresponding to the clutch-off state of bi-directional overrunning clutch CL, where rollers6are disposed at their initial positions defined by deepest center portions4cof clutch housing4, is defined as an initial state of clutch-off biasing mechanism CM1. In the initial state of clutch-off biasing mechanism CM1, crosscut edges57cand57dof spring holder57are disposed substantially perpendicular to radial end portions66band66cof wire spring clip66.

As either right or left front wheel10R or10L is loaded to reduce its rotary speed, cage5receiving a frictional resistance from friction mechanism FM follows the speed reduction of hub7R or7L corresponding to loaded front wheel10R or10L via rollers6L or6R so as to rotate relative to clutch housing4. As cage5rotates relative to clutch housing4, spring holder57engaged to cage5via engagement pawls57brotates together with cage5so as to incline crosscut edges57cand57dfrom the initial position where they are extended perpendicular to radial end portions66band66cof wire spring clip66, while constant gap g2between pressure pawls57eand57fat ends57c1and57d1of crosscut edges57cand57dis kept. The inclination of crosscut edges57cand57dcauses one of pressure pawls57eand57fto push corresponding radial end portion66bor66cso as to generate a biasing force to return cage5to its initial position relative to clutch housing4. However, until the rotation degree of cage5relative to clutch housing4reaches angle R (seeFIG. 7A), rollers6are separated from sloped surfaces4dof recesses4bof clutch housing4, thereby keeping the clutch-off state of bi-directional overrunning clutch CL.

Referring toFIG. 7A, as mentioned above, when the rotation degree of cage5relative to clutch housing4reaches angle R, bi-directional overrunning clutch CL is clutched on. In the clutch-on state of bi-directional overrunning clutch CL, rollers6are wedged-like engaged to clutch housing4. Wedge-like engaged rollers6are pressed between clutch housing4and hub7by a torque in one of opposite rotational directions caused by the relative rotation of cage5to clutch housing4. Therefore, a force to push rollers6in the other of the opposite rotational directions against the torque is required to smoothly release rollers6from the wedged-like engagement as soon as loaded front wheel10R or10L is unloaded.

In this regard, when bi-directional overrunning clutch CL is clutched on as shown inFIG. 7A, clutch-off biasing mechanism CM1is set in a clutch-off biasing state as shown inFIG. 7B. In clutch-off biasing mechanism CM1set in the clutch-off biasing state, one of pressure pawls57eand57fpushes corresponding radial end portion66bor66caway from corresponding housing pin40aor40b. Which of pressure pawls57eand57fpushes corresponding radial end portion66bor66cdepends on whether cage5rotates clockwise or counterclockwise relative to clutch housing4, i.e., whether clutch housing4is rotated in the normal direction or the reverse direction.

Here, pressure pawl57fis assumed to push radial end portion66c, as shown inFIG. 7B. While pressure pawl57fpushes radial end portion66caway from housing pin40b, radial end portion66bis held at its initial position by housing pin40a. Incidentally, pressure pawl57emoves away from radial end portion66cas pressure pawl57fpushes radial end portion66d. The movement of pressure pawl57edoes not influence radial end portion66cheld by housing pin40a. Therefore, radial end portion66cpushed by pressure pawl57fapproaches radial end portion66bheld by housing pin40aso as to narrow gap g3, i.e., so as to reduce the width of gap g3between radial end portions66band66c.

Wire spring clip66having narrowed gap g3has been further compressed to bias spring holder57to the initial position of spring holder57relative to clutch housing4. Therefore, once bi-directional overrunning clutch CL is released from the load causing the torque that has wedged-like engaged rollers6to clutch housing4, clutch-off biasing mechanism CM1functions to quickly disengage bi-directional overrunning clutch CL by the biasing force of wire spring clip66applied to cage5via spring holder57.

As mentioned above, auxiliary transaxle1comprises transaxle casing2, bi-directional overrunning clutch CL, friction mechanism FM, and clutch-off biasing mechanism CM1. Bi-directional overrunning clutch CL is disposed in transaxle casing2. Bi-directional overrunning clutch CL includes clutch housing4serving as the input member, hubs7serving as the output member, cylindrical cage5, and rollers6. Clutch housing4is journalled by transaxle casing2. Hubs7are journalled by transaxle casing2and coaxially surrounded by clutch housing4. Clutch housing4and hubs7have the annular space between the inner circumferential surface of clutch housing4, including sloped surfaces4dof recesses4band radially inward ends of minimum diametric portions4a, and the outer circumferential surfaces of hubs7. The inner circumferential surface of clutch housing4includes wedge portions4d1aligned in the circumferential direction of clutch housing4, and includes recesses4bwhose center portions including deepest center portions4cbetween wedge portions4d1serve as radially expanded portions that are diametrically larger than wedge portions4d1. Cage5is disposed coaxially to clutch housing4and hubs7in the annular space. Cage5has right and left end portions opposite each other in the axial direction of hubs7. Rollers6are carried by cage5and contact the outer circumferential surface of hub7rotatably following rotation of hubs7.

Bi-directional overrunning clutch CL is automatically shifted between its disengagement state where rollers6are disposed at the respective radially expanded portions of clutch housing4and are separated from respective wedge portions4d1, and its engagement state where rollers6contact respective wedge portions4d1. The shift of the bi-directional overrunning clutch CL depends on change of rotary speed difference between clutch housing4and hubs7.

Friction mechanism FM applies a frictional force to cage5so as to enable cage5to rotate relative to clutch housing4according to the rotation of rollers6following hub7. Clutch-off biasing mechanism CM1biases cage5in the direction to disengage bi-directional overrunning clutch CL. Friction mechanism FM and clutch-off biasing mechanism CM1are distributed so that friction mechanism FM is disposed at one (in this embodiment, right) of the right and left end portions of cage5, and clutch-off biasing mechanism CM1is disposed at the other (in this embodiment, left) of the right and left end portions of cage5.

Therefore, due to the distribution of friction mechanism FM and clutch-off biasing mechanism CM1at the right and left end portions of cage5opposite each other in the axial direction of hubs7, auxiliary transaxle1is advantageous in simplifying each of friction mechanism FM and clutch-off biasing mechanism CM1so as to reduce labors for assembling auxiliary transaxle1, in comparison with an imaginary case where friction mechanism FM and clutch-off biasing mechanism CM1are complicatedly assembled with each other and are concentrated at one end portion of cage5in the axial direction of hubs7(seeFIGS. 24 and 25).

Further, due to the distribution of friction mechanism FM and clutch-off biasing mechanism CM1at the right and left end portions of cage5opposite each other in the axial direction of hubs7, auxiliary transaxle1is advantageous in lightening respective portions of auxiliary transaxle1at the right and left sides in transaxle casing2(i.e., main housing2aand side cover2b) so as to economically ensure durability of the transaxle, in comparison with an imaginary case where friction mechanism FM and clutch-off biasing mechanism CM1are concentrated at one end portion of cage5in the axial direction of hubs7so as to stress a portion of auxiliary transaxle1around the end portion of cage5and so as to require costs for strengthening the portion of auxiliary transaxle1to ensure required durability of auxiliary transaxle1(seeFIGS. 24 and 25).

Clutch-off biasing mechanism CM1includes wire spring clip66, serving as a spring, interposed between clutch housing4, serving as the input member, and cage5so as to be elastically transformable according to the rotation of cage5relative to clutch housing4, thereby biasing cage5to the initial rotational position relative to clutch housing4.

Clutch housing4is provided with housing pins40aand40bserving as engagement members that are rotatable integrally with clutch housing4. Cage5is provided with engagement pawls57eand57fthat are rotatable integrally with cage5. Wire spring clip66is a compression spring, including elastic looped portion66athat is able to expand and contract in the radial direction thereof, and including radial end portions66band66cextended in the same radial direction, i.e., radially inward, from looped portion66a. Radial end portions66band66cof wire spring clip66are disposed between housing pins40aand40band between engagement pawls57eand57f. When cage5is disposed at its initial rotational position relative to clutch housing4to disengage bi-directional overrunning clutch CL, engagement pawls57eand57fare aligned with respective housing pins40aand40bon respective radial lines, when viewed in the axial direction of clutch housing4and cage5, so that end portion66bof wire spring clip66is engaged to housing pin40aand engagement pawl57e, and radial end portion66cof wire spring clip66is engaged to housing pin40band engagement pawl57f. During rotation of cage5relative to clutch housing4from the initial rotational position until bi-directional overrunning clutch CL is engaged, engagement pawls57eand57fare offset from housing pins40aand40bin the circumferential direction of clutch housing4and cage5so that one of radial end potions66band66cof wire spring slip66is engaged to either housing pin40aor40b, and the other of end portions66band66cof wire spring clip66is engaged to either engagement pawl57eor57f.

In auxiliary transaxle1, cage5is provided with spring holder57supporting elastic looped portion66aof wire spring clip66between radial end portions66band66cof wire spring clip66. Spring holder57includes engagement pawls57eand57fto engage to radial end portions66band66cof wire spring clip66. Spring holder57is engaged to the left end portion of cage5rotatably integrally with cage5.

Therefore, due to auxiliary transaxle1including clutch-off biasing mechanism CM1, the wedged-like engagement can be quickly and smoothly canceled so as to quickly and smoothly shift bi-directional overrunning clutch CL from the clutch-on state to the clutch-off state. Therefore, vehicle100equipped with auxiliary transaxle1can be quickly and smoothly returned from the four-wheel drive state to the two-wheel drive state.

Further, since wire spring clip66has been already compressed slightly in the initial state of clutch-off biasing mechanism CM1when cage5is disposed at its initial position relative to clutch housing4, wire spring clip66starts to be elastically transformed to bias cage5to the initial position as soon as cage5starts to rotate relative to clutch housing4from the initial position, thereby preventing unexpected wedged-like engagement or the like. In other words, bi-directional overrunning clutch CL is prevented from being unexpectedly wedged-like engaged in the ondemand-off mode, i.e., is prevented from being accidentally engaged.

An alternative auxiliary transaxle1A including bi-directional overrunning clutch CL provided with an alternative clutch-off biasing mechanism CM2will be described with reference toFIGS. 8, 9 and 10. Hereinafter, structures functioning similar to those of auxiliary transaxle1will be designated by the same reference numerals, and description of the structures will be omitted. The same thing is adapted to later description of auxiliary transaxles1B,1C,1D,1E and1F such as shown inFIGS. 11 to 25.

Auxiliary transaxle1A includes clutch-off biasing mechanism CM2disposed leftward in transaxle casing2opposite friction mechanism FM with respect to bi-directional overrunning clutch CL. Clutch-off biasing mechanism CM2includes clutch housing4, an alternative cage5A, left hub7L and a torsion spring61.

In auxiliary transaxle1A, left end portion4fprojecting leftward from splined outer circumferential portion4gof clutch housing4is notched with two radial grooves4fsand4rsdistant from each other at a predetermined angle along a circumferential direction thereof. Left end portion4fof clutch housing4projects leftward from the left end of bearing33L so that end surface4ftas the left end of left end portion4fis disposed in space Sc between bearings33L and34L in side cover2b. Radial grooves4fsand4rsare open distally leftward on end surface4ftof clutch housing4and radially inward and outward at inner and outer circumferential surfaces of left end portion4fof clutch housing4.

Bi-directional overrunning clutch CL of auxiliary transaxle1A uses an alternative cage5A. Cage5A includes main part5psimilar to that of cage5for auxiliary transaxle1. End ring5qformed with grooves5bcorresponding to engagement pawls26aof rotary-side friction plate26is fixed to the right end of main part5pof cage5A, similar to that of cage5for auxiliary transaxle1. An alternative left end ring5slof cage5A is notched by two radial grooves5fsand5rsdistant from each other at a predetermined angle along the circumferential direction of cage5A. Each of grooves5fsand5rsis open distally leftward at a left end surface of left end ring5sof cage5A, and is open radially outward and inward at outer and inner circumferential surfaces of left end ring5sof cage5A.

A center angle at the axis of cage5A between grooves5fsand5rsis not more than 90 degrees, desirably, or 50 degrees, more desirably. The center angle between grooves5fsand5rssubstantially coincides to a center angle at an axis of clutch housing4between notched grooves4fsand4rs. Grooves5fsand5rsof cage5A correspond to respective grooves4fsand4rsof clutch housing4in location along the circumferential direction thereof. Grooves5fsand5rsserving as two steps of cage5A and grooves4fsand4rsserving as two steps of clutch housing4are aligned along respective radial lines.

Alternatively, left end ring5sof cage5A and clutch housing4may be configured so that the center angle at the axis of cage5A between grooves5fsand5rsand the center angle at the axis of clutch housing4between grooves4fsand4rsexceed 90 degrees and are substantially equal to 180 degrees.

Left hub7L is radially stepped on an outer circumferential surface thereof so as to be formed with an annular vertical surface7Ls. A left end portion7Lv of left hub7L extended leftward from annular vertical surface7Ls has a diametrically smaller outer circumferential surface than the outer circumferential surface of the main part of left hub7L extended rightward from annular vertical surface7Ls to constitute bi-directional overrunning clutch CL.

A left half portion of the outer circumferential surface of left end portion7Lv is fitted to the inner circumferential surface of bearing34L, and a right half portion of the outer circumferential surface of left end portion7Lv faces an inner circumferential surface of left end ring5sof cage5A, thereby ensuring a gap space C1between the outer circumferential surface of left end portion7Lv of left hub7L and the inner circumferential surface of left end ring5sof cage5A and between bearing34L and annular vertical surface7Ls of left hub7L.

Torsion spring61is made of elastic material such as steel, and includes a coiled portion61cand two arm portions61aand61b. Arm portions61aand61bare pulled to cross over each other and are bent radially outward from coiled portion61c. Torsion spring61is interposed between clutch housing4and cage5. More specifically, coiled portion61cis relatively rotatably coiled along the outer circumferential surface of left end portion7Lv of left hub7L in gap space C1. One arm portion61ais passed through groove5fsin left end ring5sof cage5A, and is fitted at an utmost end portion thereof into groove4fsin left end portion4fof clutch housing4. The other arm portion61bis passed through groove5rsin left end ring5sof cage5A, and is fitted at an utmost end portion thereof into groove4rsI left end portion4fof clutch housing4.

In the circumferential direction of clutch housing4, radial groove4fshas opposite end surfaces4f1and4f2, and radial groove4rshas opposite end surfaces4r1and4r2. End surface4f1of radial groove4fsis closer to radial groove4rsthan end surface4f2of radial groove4fs. End surface4r1of radial groove4rsis closer to radial groove4fsthan end surface4r2of radial groove4rs. A circumferential gap between end surfaces4f1and4f2in radial groove4fsand a circumferential gap between end surface4r1and4r2in radial groove4rsare sufficient to ensure the rotatability of cage5A relative clutch housing4in the respective opposite directions until rollers6abuts against wedge portions4d1of clutch housing4.

In the circumferential direction of cage5A, radial groove5fshas opposite end surfaces5f1and5f2, and radial groove5rshas opposite end surfaces5r1and5r2. End surface5f1of radial groove5fsis closer to radial groove5rsthan end surface5f2of radial groove5fs. End surface5r1of radial groove5rsis closer to radial groove5fsthan end surface5r2of radial groove5rs. A circumferential gap between end surfaces5f1and5f2in radial groove5fsand a circumferential gap between end surface5r1and5r2in radial groove5rsare sufficient to ensure the rotatability of cage5A relative clutch housing4in the respective opposite directions until rollers6abuts against wedge portions4d1of clutch housing4.

The center angle at the axis of clutch housing4between end surface4f1of radial groove4fsand end surface4r1of radial groove4rs, and the center angle at the axis of cage5A between end surface5f1of radial groove5fsand end surface5r1of radial groove5rs, are slightly larger than a center angle of an axis of coiled portion61cof torsion spring61between arm portions61aand61bwhen torsion spring61is free from either tension or compression force. Therefore, torsion spring61fitted to cage5A and clutch housing4as mentioned above is slightly expanded to make the circumferential gap between arm portions61aand61btherebetween larger than the essential gap between arm portions61aand61bwhen torsion spring61is free from either tension or compression force.

Accordingly, in an initial state of clutch-off biasing mechanism CM2, torsion spring61serves as a tension spring having arm portions61aand61bslightly expanded to increase the gap therebetween so that arm portion61ais pressed against end surface5f1of radial groove5fsand end surface4f1of radial groove4fs, and arm portion61bis pressed against end surface5r1of radial groove5rsand end surface4r1of radial groove4rs. Therefore, torsion spring61starts to be elastically transformed to bias cage5A to its initial position relative to clutch housing4as soon as a slight torque occurs to rotate cage5A relative to clutch housing4.

As cage5A rotates relative to clutch housing4from its initial position relative to clutch housing4until rollers6abuts against wedge portions4d1of clutch housing4, one arm portion61aor61bof torsion spring61is pushed away from end surface4f1or4r1of corresponding radial groove4fsor4rsby cage5A, i.e., end surface5f1or5r1of corresponding radial groove5fsor5rs, while the other arm portion61aor61bof torsion spring61is still pressed against end surface4f1or4r1of corresponding radial groove4fsor4rs. Therefore, torsion spring66is elastically transformed so that the circumferential gap between arm portions61aand61bof torsion spring61is increased to increase the spring force of torsion spring61to bias cage5A to its initial position relative to clutch housing4.

Which of arm portions61aand61bis pushed by cage5A depends on whether cage5A rotates clockwise or counterclockwise relative to clutch housing4, i.e., whether the rotation direction of clutch housing4receiving power from PTO shaft15via input shaft12and bevel ring gear3is normal or reverse.

As mentioned above, in auxiliary transaxle1A, friction mechanism FM and clutch-off biasing mechanism CM2are distributed so that friction mechanism FM is disposed at one (in this embodiment, right) end portion of cage5A, and clutch-off biasing mechanism CM2is disposed at the other (in this embodiment, left) end portion of cage5A.

Therefore, auxiliary transaxle1A including clutch-off biasing mechanism CM2brings the effects similar to those of auxiliary transaxle1.

Clutch-off biasing mechanism CM2includes torsion spring61interposed between clutch housing4and cage5A so as to be elastically transformable according to the rotation of cage5A relative to clutch housing4, thereby biasing cage5A to the initial rotational position relative to clutch housing4.

In clutch-off biasing mechanism CM2, clutch housing4is provided with end surfaces4f1and4r1that are rotatable integrally with clutch housing4. Cage5A is provided with end surfaces5f1and5r1that are rotatable integrally with cage5A. Arm portions61aand61bserving as end portions of torsion spring61are pulled to cross over each other and have end surfaces5f1,5r1,4f1and4r1therebetween. When cage5A is disposed at its initial rotational position relative to clutch housing4to disengage bi-directional overrunning clutch CL, end surfaces5f1and5r1are aligned with respective end surfaces4f1and4r1on respective radial lines, when viewed in the axial direction of clutch housing4and cage5A, so that arm portion61aof torsion spring61contacts end surfaces5f1and4f1, and arm portion61bof torsion spring61contacts end surfaces5r1and4r1. During rotation of cage5A relative to clutch housing4from the initial rotational position until bi-directional overrunning clutch CL is engaged, end surfaces5f1and5r1are offset from end surfaces4f1and4r1in the circumferential direction of clutch housing4and cage5A so that one of arm potions61aand61bof torsion spring61is engaged to either end surface4f1or4r1, and the other of arm portions61aand61bof torsion spring61is engaged to either end surface5f1or5r1.

Therefore, due to auxiliary transaxle1A including clutch-off biasing mechanism CM2, the wedged-like engagement can be quickly and smoothly canceled so as to quickly and smoothly shift bi-directional overrunning clutch CL from the clutch-on state to the clutch-off state. Therefore, vehicle100equipped with auxiliary transaxle1A can be quickly and smoothly returned from the four-wheel drive state to the two-wheel drive state.

Further, since torsion spring61has been already expanded slightly in the initial state of clutch-off biasing mechanism CM2when cage5A is disposed at its initial position relative to clutch housing4, torsion spring61starts to be elastically transformed to bias cage5to the initial position as soon as cage5A starts to rotate relative to clutch housing4, thereby preventing unexpected wedged-like engagement or the like. In other words, bi-directional overrunning clutch CL is prevented from being unexpectedly wedged-like engaged even in the ondemand-off mode, i.e., is prevented from being accidentally engaged.

An auxiliary transaxle1B including bi-directional overrunning clutch CL provided with an alternative clutch-off biasing mechanism CM3will be described with reference toFIGS. 11 to 17.

Torsion spring60made of elastic material such as steel is interposed via a spring holder55A between clutch housing4and cage5B to resist the rotation of cage5B relative to clutch housing4. Substantially discoid spring holder55A is detachably attached around left hub7L between the right end of bearing34L and a left end of cage5B.

Left end surface4ftof clutch housing4and the left end of cage5B substantially coincide to the left end of bearing33L in location in the axial direction of output shafts8, thereby ensuring space Sc between bearings33L and34L around spring holder55A. In space Sc around spring holder55A, a housing pin41projects axially leftward from left end surface4ftof clutch housing4. Housing pin41is formed integrally with clutch housing4. Alternatively, housing pin41may be a pin separated from clutch housing4but fixed to clutch housing4so as to project leftward from left end surface4ftof clutch housing4.

Referring toFIG. 13, cage5B includes main part5pand right end ring5q, similar to those of cage5, and includes an alternative left end ring51placed at the left end of cage5B. Left end ring5tis fixed to main part5pso as to have an outer circumferential surface continuing to the outer circumferential surface of main part5p, and so as to have an inner circumferential surface continuing to the inner circumferential surface of main part5p.

In this regard, left end ring5tis notched by a plurality of recesses5tcaligned along the circumferential surface thereof at regular interval. The number of recesses5tccorresponds to that of roller holes5aaligned circumferentially in the left half portion of main part5p. Therefore, in this embodiment, left end ring5thas seven recesses5tc. Each recess5tcis open distally leftward at the left end surface of left end ring5t, proximally rightward at a right end surface of left end ring5t, and radially outward at the outer circumferential surface of left end ring5t, and is closed by an inner circumferential portion of left end ring5tso as to form a recess-bottom circumferential surfaces having a smaller outer diameter than the maximum outer diameter of the outer circumferential surface of left end ring5t.

Left end ring5tfixed to main part5phas the inner and outer circumferential surfaces continuous to the inner and outer circumferential surfaces of main part5p. In this regard, a left end portion of each of left bridge portions5p2of main part5pis formed as a radially thinned left end portion5u(seeFIGS. 16 and 17). Radially thinned left end portion5uincludes an outer circumferential surface continuous to the outer circumferential surface of the remaining part of main part5p, and includes an inner circumferential surface is radially outwardly stepped to have an inner diameter that is larger than the minimum inner diameter of the inner circumferential surface of the remaining part of main part5p.

Radially thinned left end portions5uof left bridge portions5p2of main part5pare fitted into respective recesses5tcof left end ring5t, so that the inner circumferential surfaces of radially thinned left end portions5uare fitted onto the recess-bottom circumferential surfaces of respective recesses5tc. Therefore, the inner circumferential surfaces of the main portions of left bridge portions5p2(extended rightward from radially thinned left end portion5u) continue to the inner circumferential surface of left end ring5t, and the outer circumferential surface of radially thinned left end portions5uof left bridge portions5p2continue to the outer circumferential surface of left end ring5t.

Further, left end surfaces of radially thinned left end portions5uof left bridge portions5p2fitted in respective recesses5tccontinue to the left end surface of left end ring5t. In other words, the left end surface of left end ring5tfixed to main part5pcoincides to the left end surface of main part5pin the axial direction of cage5B, so that the left end of left end ring5tand the left end of main part5pserve as the left end of cage5B, thereby ensuring the axial width of space Sc around left hub7L between the left end of cage5B and the right end of bearing34L.

Two of left bridge portions5p2of main part5pof cage5B, which are radially opposite each other with respect to the axis of main part5p, are notched at left ends thereof with respective pin grooves5tcopen radially outward and distally leftward at the left end of cage5B.

Referring toFIG. 13, spring holder55A has two vertical end surfaces axially opposite each other, one of the end surfaces is a distal left end surface of spring holder55A, and the other of the end surfaces is a proximal right end surface of spring holder55A. Two fixture pins55care fixed or formed on spring holder55A so as to project axially rightward from the proximal right end surface of spring holder55A. Fixture pins55care spaced from each other at 180 degrees on the circumference, i.e., are opposite each other with respective to an axis of discoid spring holder55A. Fixture pins55care fitted into respective pin grooves5tcof cage5B so that spring holder55A is detachably attached to cage5B. Spring holder55A attached to cage5B is rotatable integrally with cage5and relative to clutch housing4.

Discoid ring-shaped spring holder55A has an outer circumferential edge between the distal left end surface and the proximal right end surface. The outer circumferential edge of spring holder55A is formed circumferentially therealong with a spring groove55s. Referring toFIG. 12, torsion spring60includes a coiled portion60csimilar to coiled portion61cof torsion spring61, and coiled portion60cis fitted into spring groove55s.

A part of the outer circumferential edge of spring holder55A is chord-like cut off so as to form a flat edge surface55vbetween the distal left end surface and the proximal right end surface. After spring holder55A is attached to cage5B, a center portion of flat edge surface55vat the middle point between opposite ends thereof on the outer circumferential edge of spring holder55A substantially coincides to a point on the outer circumferential surface of cage5B in location in the radial direction of spring holder55A and cage5B. In other words, the outer circumferential edge of spring holder55A, except for flat edge surface55v, has a constant outer diameter that is greater than the outer diameter of cage5B. A radial distance of flat edge surface55vfrom the axis of spring holder55A and cage5B is reduced as it goes therealong from each of the opposite ends thereof to the center portion thereof, so that the radial distance becomes equal to the outer radius of cage5B when it reaches the center portion of flat edge surface55v.

On the other hand, an inner diameter of spring holder55A is substantially equal to the inner diameter of cage5B. In other words, spring holder55A has an inner circumferential edge continuous to the inner circumferential surface of cage5B.

Spring holder55A is formed with two parallel slits55dextended radially between flat edge surface55vand the inner circumferential edge of spring holder55A and open on the proximal right end surface thereof. Slits55dmay be replaced with holes closed at the proximal right end surface of spring holder55A (see spring holder56A shown inFIG. 16). The center portion of flat edge surface55v, having a width equal to a diameter of housing pin41, is disposed between open ends of respective slits55dat flat edge surface55v. Therefore, the proximal right end surface of spring holder55A includes a radial linear portion, having the width equal to the diameter of housing pin41, and extended radially inward from the center portion of flat edge surface55vbetween parallel slits55d. The radial linear portion between slits55dis formed as a minimum diametric portion projecting proximally rightward from the axially deepest end of slits55dso as to serve as a spring-pressure portion55p.

Torsion spring60includes two arm portions60aand60b, which are pulled to cross over each other and are bent to extend radially inward from coiled portion60c. Coiled portion60cis fitted into spring groove55sas mentioned above, so that torsion spring60is wound on the outer circumferential edge of spring holder55A. In this state, arm portion60ais disposed axially proximally from arm portion60b. Two arm portions60aand60bare pulled along the circumferential direction of spring holder55A, so as to cross over each other when viewed in the axial direction of spring holder55A, thereby slightly compressing coiled portion60cradially inward.

Arm portions60aand60bcrossing over each other are disposed opposite each other with respect to housing pin41and spring-pressure portion55pin the circumferential direction of spring holder55A, and the radially inward extended portions of respective arm portions60aand60bare disposed in respective slits55d. Arm portions60aand60bhave respective utmost ends60cand60ddisposed in respective slits55d, thereby being prevented from projecting radially inward from the inner circumferential edge of spring holder55A to be interfered with the outer circumferential surface of left hub7L passed through the hole defined by the inner circumferential edge of spring holder55A.

When cage5B is disposed at the initial position relative to clutch housing4, the center portion of flat edge surface55vof spring holder55A approaches closest to housing pin41so as to coincide to housing pin41in location in the circumferential direction of cage5B and clutch housing4. In other words, spring-pressure portion55pdefined by the center portion of flat edge surface55vand housing pin41are aligned on a radial line extended from the axis of spring holder55A. In this state, both arm portions60aand60bare hung at the respective bent portions thereof on housing pin41, and are pressed against opposite surfaces of spring-pressure portion55pin respective slits55dat the respective portions thereof extended radially inward to respective ends60cand60d.

As cage5B rotates relative to clutch housing4from the initial position, one of arm portions60aand60bis pushed by spring-pressure portion55pof spring holder55A fixed to cage5B and is separated from housing pin41, while the other of arm portion60aand60bis retained by housing pin41and is separated from spring-pressure portion55p. Therefore, torsion spring60is elastically transformed so as to expand a gap between arm portions60aand60bin the circumferential direction of spring holder55A, thereby biasing cage5B to the initial position relative to clutch housing4.

As mentioned above, in auxiliary transaxle1B, friction mechanism FM and clutch-off biasing mechanism CM3are distributed in transaxle casing2so that friction mechanism FM is disposed at one (in this embodiment, right) end portion of cage5B, and clutch-off biasing mechanism CM3is disposed at the other (in this embodiment, left) end portion of cage5B.

Therefore, auxiliary transaxle1B including clutch-off biasing mechanism CM3brings the effects similar to those of auxiliary transaxles1and1A.

Referring toFIGS. 14 and 15, an alternative spring holder55B may be detachably attached to cage5B. Spring holder55B attached to cage5B is rotatable integrally with cage5B and relative to clutch housing4. Spring holder55B is detachably attached to cage5B by fitting fixture pins55cinto respective pin grooves5tcof cage5B, similar to spring holder55A. Hereinafter, components similar to the above-mentioned components of spring holder55A are designated by the same reference numerals, and description of the components is omitted.

Referring toFIG. 15, has two vertical end surfaces axially opposite each other, one of the end surfaces is a distal left end surface of spring holder55B, and the other of the end surfaces is a proximal right end surface of spring holder55B. Two fixture pins55cproject axially rightward from the proximal right end surface of spring holder55B, similar to those of spring holder55A.

Discoid ring-shaped spring holder55B has an outer circumferential edge between the distal left end surface and the proximal right end surface. The outer circumferential edge of spring holder55B is formed circumferentially therealong with spring groove55ssimilar to that of spring holder55A. Referring toFIG. 14, coiled portion61cof torsion spring61is fitted into spring groove55s.

A part of the outer circumferential edge of spring holder55B is chord-like cut off so as to form a flat edge surface55ubetween the distal left end surface and the proximal right end surface. A spring-pressure portion55qprojects radially outward from a center portion of flat edge surface55uat the middle point between opposite ends of flat edge surface55uon the outer circumferential edge of spring holder55B. Circumferentially opposite end surfaces of spring-pressure portion55qare extended radially of spring holder55B, so as to have a width therebetween equal to the diameter of housing pin41. Axially opposite end surfaces of spring-pressure portion55qcontinue to the proximal and distal (right and left) end surfaces of spring holder55B, so as to have a width therebetween equal to the width of flat edge surface55ubetween the proximal and distal end surfaces of spring holder55B.

After spring holder55B is fixed to cage5B, a radially utmost end of spring-pressure portion55qsubstantially coincides to a point on the outer circumferential surface of cage5B in location in the radial direction of spring holder55B and cage5B, while the outer circumferential edge of spring holder55B, except for flat edge surface55u, has a constant outer diameter that is greater than the outer diameter of cage5B.

On the other hand, an inner diameter of spring holder55B is substantially equal to the inner diameter of cage5B, so that spring holder55B has an inner circumferential edge continuous to the inner circumferential surface of cage5B. The radially inward end of spring-pressure portion55qdefined as the center portion of flat edge surface55uis disposed close to the inner circumferential edge of spring holder55B, however, it is disposed radially outward from the inner circumferential edge of spring holder55B.

Arm portions60aand60bof torsion spring60wound around spring holder55B are pulled along the circumferential direction of spring holder55B, so as to cross over each other when viewed in the axial direction of spring holder55B, thereby slightly compressing coiled portion60cradially inward. Arm portions60aand60bcrossing over each other are disposed opposite each other with respect to housing pin41and spring-pressure portion55qin the circumferential direction of spring holder55B. Utmost ends60cand60dof respective arm portions60aand60bare disposed radially outward from flat edge surface55u, thereby being prevented from being interfered with flat edge surface55uof spring holder55B and left hub7L passed through the hole defined by the inner circumferential edge of spring holder55B.

When cage5B is disposed at the initial position relative to clutch housing4, the radially utmost end of spring-pressure portion55qapproaches closest to housing pin41so as to coincide to housing pin41in location in the circumferential direction of cage5B and clutch housing4. In other words, spring-pressure portion55qand housing pin41are aligned on a radial line extended from the axis of spring holder55B. In this state, both arm portions60aand60bare hung at respective bent portions thereof on housing pin41, and are pressed against the circumferentially opposite surfaces of spring-pressure portion55qat the respective portions thereof extended radially inward to respective ends60cand60d.

As cage5B rotates relative to clutch housing4from the initial position, one of arm portions60aand60bis pushed by spring-pressure portion55qof spring holder55B fixed to cage5B and is separated from housing pin41, while the other of arm portion60aand60bis retained by housing pin41and is separated from spring-pressure portion55q. Therefore, torsion spring60is elastically transformed so as to expand a gap between arm portions60aand60bin the circumferential direction of spring holder55B, thereby biasing cage5B to the initial position relative to clutch housing4.

Referring toFIGS. 16 and 17, auxiliary transaxle1B may use an alternative cage5C so as to constitute clutch-off biasing mechanism CM3. In an embodiment shown inFIG. 16, an alternative spring holder56A having the same function of as spring holder55A also serves as an end ring of cage5C. In an embodiment shown inFIG. 17, an alternative spring holder56B having the same function of spring holder55B also serves as an end ring of cage5C. Hereinafter, structural features similar to above-mentioned structural features of cages5,5A and5B are designated by the same reference numerals, and their description is omitted.

Referring toFIG. 16, spring holder56A includes a discoid ring-shaped spring holder part56ahaving an outer circumferential edge formed with a spring groove56s, into which coiled portion60cof torsion spring60is fitted. Spring holder part56ais formed with a chord-like cut flat edge surface56v, and is formed therein with a pair of radially extended holes56dfor accommodating arm portions60aand60bof torsion spring60. Holes56dhave respective radially outer ends open at flat edge surface56v, and a portion between holes56dserves as a spring-pressure portion56p. Therefore, spring holder part56aof spring holder56A is formed similar to spring holder55A such as shown inFIG. 13so as to have the same function as spring holder55A.

Spring holder56A includes end ring part56tprojecting proximally rightward from the proximal right end surface of spring holder part56a. End ring part56tis formed with recesses56tcaligned along an outer circumferential surface thereof so as to correspond to radially thinned left end portions5uof left bridge portions5p2of main part5p. Therefore, end ring part56tof spring holder56A is formed similar to left end ring5tof cage5B such as shown inFIG. 13so as to have the same function as left end ring5tof cage5B.

Spring holder56A include end ring part56tand spring holder part56aformed integrally with each other. Alternatively, end ring part56tand spring holder part56amay be essentially individual members fixed to each other so as to be configured as spring holder56A.

To constitute clutch-off biasing mechanism CM3including cage5C with spring holder56A, cage5C is completely provided with spring holder part56aif only end ring part56tis fitted to the left end of main part5pby fitting radially thinned left end portions5uof left bridge portions5p2of main part5pinto respective recesses56tcof end ring part56tof spring holder56A. Therefore, labors for constituting clutch-off biasing mechanism CM3are reduced in comparison with the afore embodiment shown inFIGS. 11 to 13, where fixture pins55cof spring holder55A must be inserted into grooves5pcof main part5pof cage5B because spring holder55A is separated from left end ring5tof cage5B.

Referring toFIG. 17, spring holder56B includes a discoid ring-shaped spring holder part56bhaving an outer circumferential edge formed with spring groove56s. Spring holder part56ais formed with a chord-like cut flat edge surface56u, and is formed with a spring-pressure portion56qprojecting radially outward from a center portion of flat edge surface56u. Therefore, spring holder part56bof spring holder56B is formed similar to spring holder55B such as shown inFIG. 15so as to have the same function as spring holder55B.

Spring holder56B includes end ring part56tformed with recesses56tcand projecting proximally rightward from the proximal right end surface of spring holder part56b, similar to end ring part56tof spring holder56A. End ring part56tis formed integrally with spring holder part56b, or may be a member independent of spring holder part56bbut fixed to spring holder part56b. Similar to the advantage of cage5C with spring holder56A, cage5C with spring holder56B is advantageous in reducing labors to constitute clutch-off biasing mechanism CM3including cage5C with spring holder56B.

To constitute clutch-off biasing mechanism CM3including cage5C with spring holder56A, cage5C is completely provided with spring holder part56aif only end ring part56tis fitted to the left end of main part5pby fitting radially thinned left end portions5uof left bridge portions5p2of main part5pinto respective recesses56tcof end ring part56tof spring holder56A. Therefore, labors for constituting clutch-off biasing mechanism CM3are reduced in comparison with the afore embodiment shown inFIGS. 11 to 13, where fixture pins55cof spring holder55A must be inserted into grooves5pcof main part5pof cage5B because spring holder55A is separated from left end ring51of cage5B.

As mentioned above, in clutch-off biasing mechanism CM3, clutch housing4serving as the input member is provided with housing pin41that is rotatable integrally with clutch housing4. Cage5B or5C is provided with spring-pressure portion55p,55q,56por56qthat is rotatable integrally with cage5B or5C. Arm portions60aand60b, serving as a pair of end portions of torsion spring60, are pulled to cross over each other and have both housing pin41and spring-pressure portion55p,55q,56por56qtherebetween. When cage5A or5B is disposed at the initial rotational position relative to clutch housing4to disengage bi-directional overrunning clutch CL, housing pin41and spring-pressure portion55p,55q,56por56qare aligned on one radial line, when viewed in the axial direction of clutch housing4and cage5B or5C, so as to engage to both of arm portions60aand60bof torsion spring60respectively. During rotation of cage5B or5C relative to clutch housing4from the initial rotational position until bi-directional overrunning clutch CL is engaged, housing pin41and spring-pressure portion55p,55q,56por56qare offset from each other in the circumferential direction of clutch housing4and cage5B or5C so that housing pin41engages to one of arm portions60aand60bof torsion spring60, and spring-pressure portion55p,55q,56por56qengages to the other of arm portions60aand60bof torsion spring60.

In auxiliary transaxle1B, cage5B or5C is provided with spring holder55A,55B,56A or56B supporting coiled portion60cserving as an elastic looped portion of torsion spring60between arm portions60aand60b. Spring holder55A,55B,56A or56B includes spring-pressure portion55p,55q,56por56qdisposed between arm portions60aand60bof torsion spring60. Spring holder55A,55B,56A or56B is engaged to the left end portion of cage5B or5C rotatably integrally with cage5B or5C.

Therefore, clutch-off biasing mechanism CM3using either cage5B or5C and any one of spring holders55A,55B,56A and56B brings the effects to overrunning clutch CL in auxiliary transaxle1B similar to the effects of clutch-off biasing mechanism CM1or CM2for overrunning clutch CL.

An auxiliary transaxle1C will now be described with reference toFIGS. 18 and 19.

Auxiliary transaxle1C includes a clutch-off biasing mechanism CM4disposed opposite friction mechanism FM with respect to bi-directional overrunning clutch CL. Clutch-off biasing mechanism CM4includes clutch housing4, cage5, left hub7L and a torsion spring62.

Incidentally, in the foresaid embodiments, each of cages5and5A is defined as having a left end portion extended axially in space Sc between bearings33L and34L so as to have its utmost end surface close to the right and of bearing34L while each of cages5B and5C is defined as being provided with spring holder55A or55B or spring holder part56aor56bbetween the left end thereof and the right end of bearing34L. Auxiliary transaxle1C and later-discussed auxiliary transaxles1D,1E and1F have respective cages carrying rollers6, and each of the cages has its utmost left end surface close to the right end of bearing34L so as to have a left end portion axially extended in space Sc between bearings33L and34L Therefore, a presentative name “cage5” is applied to the cages in auxiliary transaxles1C,1D,1E and1F, although the cages are modified to constitute respective clutch-off biasing mechanisms CM4, CM5, CM6and CM7.

In this regard, inFIGS. 18 and 19, cage5is illustrated as consisting of a single member extended in the whole axial range between the right and left ends thereof to carry right and left rollers6. Further, inFIG. 18, this single member serving as cage5is illustrated as being formed at the right end portion thereof with grooves5binto which engagement pawls26aof rotary-side friction plate26in friction mechanism FM. However, inFIGS. 18 and 19, the illustration of cage5is simplified. Cage5shown inFIGS. 18 and 19may actually include main part5pand right and left end rings attached to the right and left end of main part5p, the right end ring being formed with grooves5b, and the left end ring serving as the left end portion of cage5ndring5qsuch as shown inFIG. 5may serve as the right end ring formed with grooves5b. The same thing is adapted to illustration of later-discussed cages5shown inFIGS. 20 to 25.

To constitute clutch-off biasing mechanism CM4, cage5has a left end surface close to the right end of bearing34L. Also, left end portion4fof clutch housing4is further extended in space Sc leftward from bearing33L so as to have left end surface4ftcoinciding to the left end of cage5in location in the axil direction of clutch housing4and cage5.

Left end portion4fof clutch housing4is radially thinned so as to have an inner circumferential surface having a lager inner diameter than the minimum inner diameter of clutch housing4. Therefore, an annular gap space C2is provided between the inner circumferential surface of left end portion4fof clutch housing4and an outer circumferential surface of a left end portion of cage5, so that a coiled portion62cof torsion spring62is wound around the outer circumferential surface of the left end portion of cage5in gap space C2, in comparison with clutch-off biasing mechanism CM2, in which coiled portion61cof torsion spring61is wound around left hub7L in gap space C1between the outer circumferential surface of left hub7L and the inner circumferential surface of the left end portion of cage5A.

A wire made of elastic material such as steel is formed so as to serve as torsion spring62including coiled portion62cand outer and inner end portions62aand62b. Torsion spring62is interposed between cage5and clutch housing4without any additional member for guiding torsion spring62.

Torsion spring62is bent at one of proximal and distal (right and left) end portions (in this embodiment, a proximal right end portion) of coiled portion62cwound around the left end portion of cage5so as to form outer end portion62aextended radially outward from coiled portion62c. Also, torsion spring62is bent at the other of proximal and distal (right and left) end portions (in this embodiment, a distal left portion) of coiled portion62cwound around the left end portion of cage5so as to form inner end portion62bextended radially inward from coiled portion62c.

Left end portion4fof clutch housing4is notched by a groove4vopen distally leftward at left end surface4ft. Groove4vis open radially inward at the inner circumferential surface of left end portion4fso as to receive outer end portion62aof torsion spring62from the outer circumferential surface of cage5.

At the outer circumferential surface of left end portion4fof clutch housing4surrounded by bearing33L, groove4vis open radially outward, however, an utmost end62dof outer end portion62ais disposed in groove4vso as to be prevented from interfering with bearing33L. Alternatively, groove4vmay be closed at the outer circumferential surface of left end portion4fof clutch housing4.

Groove4vis narrow in the circumferential direction of clutch housing4so as to have a circumferential width that is substantially equal to a diameter of the wire serving as torsion spring62. Therefore, outer end portion62aof torsion spring62is fitted in groove4vso as to be rotatably integral with clutch housing4in the circumferential direction of clutch housing4.

The left end portion of cage5is notched by a groove5vopen distally leftward at the left end surface of cage5. Groove5vis open radially outward at the outer circumferential surface of the left end portion of cage5so as to receive inner end portion62bof torsion spring62from the outer circumferential surface of cage5.

At the inner circumferential surface of cage5facing the outer circumferential surface of left hub7L, groove5vis open radially inward, however, an utmost end62eof inner end portion62bis disposed in groove5vso as to be prevented from interfering with left hub7L. Alternatively, groove5vmay be closed at the inner circumferential surface of the left end portion of cage5.

Groove5vis narrow in the circumferential direction of cage5so as to have a circumferential width that is substantially equal to the diameter of the wire serving as torsion spring62. Therefore, inner end portion62bof torsion spring62is fitted in groove5vrotatably integrally with cage5in the circumferential direction of cage5.

Regarding relative location of grooves4vand5vin the circumferential direction of clutch housing4and cage5, a center angle between grooves4vand5vat the axis of clutch housing4and cage5is optionally determined to correspond to a center angle between outer and inner end portions62aand62bat the axis of coiled portion62cof torsion spring62in its initial state. In this embodiment, the center angle between outer and inner end portions62aand62bof torsion spring62in the initial state is 180 degrees, so that the center angle between grooves4vand5vis set as being 180 degrees when cage5is disposed at the initial position relative to clutch housing4.

As cage5rotates relative to clutch housing4from the initial position relative to clutch housing4, inner end portion62bof torsion spring62fitted in groove5vrotates together with cage5relative to clutch housing4retaining outer end portion62aof torsion spring62fitted in groove4v, so that coiled portion62cof torsion spring62is elastically transformed to generate a spring force to restore torsion spring62to its initial state, thereby biasing cage5to the initial position relative to clutch housing4against the torque for rotation of cage5relative to clutch housing4.

As mentioned above, in auxiliary transaxle1C, friction mechanism FM and clutch-off biasing mechanism CM4are distributed in transaxle casing2so that friction mechanism FM is disposed at one (in this embodiment, right) end portion of cage5, and clutch-off biasing mechanism CM4is disposed at the other (in this embodiment, left) end portion of cage5.

In clutch-off biasing mechanism CM4, outer end portion62aof spring62is engaged to clutch housing4so as to be rotatable integrally with clutch housing4, and inner end portion62bof spring62is engaged to cage5so as to be rotatable integrally with cage5. Elastic coiled portion62cof spring62between outer and inner end portions62aand62bis disposed in gap space C1between cage5and clutch housing4so as to be allowed to elastically transform according to the rotation of cage5relative to clutch housing4.

Therefore, auxiliary transaxle1C including clutch-off biasing mechanism CM4brings an effect similar to those of auxiliary transaxles1,1A and1B.

An auxiliary transaxle1D will now be described with reference toFIGS. 20 and 21.

Auxiliary transaxle1D includes a clutch-off biasing mechanism CM5disposed opposite friction mechanism FM with respect to bi-directional overrunning clutch CL. Clutch-off biasing mechanism CM5includes clutch housing4, cage5, left hub7L and a torsion spring63.

To constitute clutch-off biasing mechanism CM5, a left end surface of cage5is disposed close to the right end of bearing34L. On the other hand, left end portion4fof clutch housing4projects leftward from bearing33L, however, left end surface4ftis disposed rightward from the left end surface of clutch housing4, i.e., in an axially intermediate portion of space Sc between bearings33L and34L.

An annular vertical surface4wsis formed on the outer circumferential portion of cage5surrounded by bearing33L. A left end portion of cage5extended leftward from vertical surface5wsto the left end surface of cage5is formed as a radially thinned left end portion5wwhose outer circumferential surface is radially inward from that of the remaining part of cage5so as to have an outer diameter that is smaller than the maximum outer diameter of the remaining part of cage5. An annular gap space Cx is provided between the outer circumferential surface of radially thinned left end portion5wof groove5E and the inner circumferential surface of left end portion4fof clutch housing4.

Left end portion4fof clutch housing4is notched by a groove4wopen at left end surface4ftand having a certain width along the circumferential direction of clutch housing4. A spring-retainer59is fitted in groove4w. Spring-retainer59contacts a vertical surface4wsat the deepest end of groove4wand is fastened to clutch housing4by a screw or a bolt. In this regard, vertical surface5wsdefining the right end of radially-thinned left end portion5wof cage5is disposed proximally rightward from vertical surface4wsdefining the deepest right end of groove4ws.

A radially inward end of groove4wis open radially inward at the inner circumferential surface of left end portion4fof clutch housing4. Spring-retainer59includes a housing pin59cprojecting radially inward into gap space Cx via the radially inward open end of groove4wtoward the outer circumferential surface of radially thinned left end portion5wof cage5.

Radially thinned left end portion5wof cage5is formed with a recessed groove5cextended from the left end surface of cage5to the inner circumferential surface of radially thinner left end portion5wof cage5. A spring-retainer58is fitted in recessed groove5x, and is fixed to cage5. Spring-retainer58includes a cage pin58cthat projects radially outward into gap space Cx toward the inner circumferential surface of left end portion4fof clutch housing4via a radially extended portion of recessed groove5xalong the left end surface of cage5. Therefore, in gap space Cx, cage pin58cis disposed distally leftward from housing pin59c.

Spring-retainers58and59are made of material, such as metal, having rigidity required to elastically transform torsion spring63against a spring force of torsion spring63.

Torsion spring63includes a coiled portion63cand two end portions63aand63b. Coiled portion63cof torsion spring63is radially duplex-wound around the outer circumferential surface of radially-thinned left end portion5wof cage5between housing pin59cand vertical surface5wsof cage5. The radially outward and inward end portions of coiled portion63care bent to extend leftward in the axial direction of cage5so as to be formed as radially outward end portion63aand radially inward end portion63b. Axially extended end portions63aand63bare pulled to cross over each other so as to compress coiled portion63cradially inward, and are disposed opposite each other in the circumferential direction of cage5with respect to cage pin58cand housing pin59c.

When cage5is disposed at the initial position relative to clutch housing4, each of end portions63aand63bof torsion spring63is pressed against both cage pin58cand housing pin59cso as to keep cage pin58cand housing pin59coverlapping each other on a radial line when viewed in the axial direction of cage5as shown inFIG. 21.

As cage5rotates relative to clutch housing4from the initial position relative to clutch housing4, cage pin58crotates together with cage5relative to housing pin59cfixed to clutch housing4so that one of end portions63aand63bof torsion spring63is pushed by cage pin58cand is separated from housing pin59cwhile the other of end portions63aand63bof torsion spring63is retained by housing pin59cand is separated from cage pin58c, thereby expanding a circumferential gap between end portions63aand63dof torsion spring63, and thereby elastically transforming coiled portion63cof torsion spring63so as to bias cage5to the initial position relative to clutch housing4against the torque for rotation of cage5relative to clutch housing4. Which of end portions63aand63bof torsion spring63is pushed by cage pin58cdepends on whether cage5rotates clockwise or counterclockwise relative to clutch housing4, i.e., whether the rotation direction of clutch housing4drivingly connected to input shaft12via bevel ring gear3is normal or reverse.

As mentioned above, in auxiliary transaxle1D, friction mechanism FM and clutch-off biasing mechanism CM5are distributed so that friction mechanism FM is disposed at one (in this embodiment, right) end portion of cage5, and clutch-off biasing mechanism CM5is disposed at the other (in this embodiment, left) end portion of cage5.

In clutch-off biasing mechanism CM5, clutch housing4serving as the input member is provided with housing pin59cthat is rotatable integrally with clutch housing4. Cage5is provided with cage pin58cthat is rotatable integrally with cage5. End portions63aand63bof torsion spring63are pulled to cross over each other and have both housing pin59cand cage pin58ctherebetween. When cage5is disposed at the initial rotational position relative to clutch housing4to disengage bi-directional overrunning clutch CL, housing pin59cand cage pin58care disposed on one radial line and overlap each other, when viewed in the axial direction of clutch housing4and cage5, so as to engage to both of end portions63aand63bof torsion spring63respectively. During rotation of cage relative to clutch housing4from the initial rotational position until bi-directional overrunning clutch CL is engaged, housing pin59cand cage pin58care offset from each other in the circumferential direction of clutch housing4and cage5so that housing pin59cengages to one of arm portions63aand63bof torsion spring63, and cage pin58cengages to the other of arm portions63aand63bof torsion spring63.

Therefore, auxiliary transaxle1D including clutch-off biasing mechanism CM5brings an effect similar to that of auxiliary transaxles1,1A,1B and1C.

An auxiliary transaxle1E will now be described with reference toFIGS. 22 and 23.

Auxiliary transaxle1E includes a clutch-off biasing mechanism CM6disposed opposite friction mechanism FM with respect to bi-directional overrunning clutch CL. Clutch-off biasing mechanism CM6includes clutch housing4, cage5, left hub7L and a flat spring64.

A long-and-narrow plate made of elastic material, such as steel, is formed as flat spring64including a circularly looped plate portion64cand two end plate portions64aand64b. Opposite end portions of looped plate portion64care bent to extend radially outward from looped plate portion64cso as to be formed as end plate portions64aand64b. In an initial state of flat spring64placed free from cage5and clutch housing4, end plate portions64aand64bhave a gap in the circumferential direction of looped plate portion64c.

Left end portion4fof clutch housing4is notched with a groove4yhaving a certain width along the circumferential direction. In this regard, left end portion4fof clutch housing4is formed with radially extended end surfaces4y1and4y2defining groove4ytherebetween. Groove4yis open leftward at left end surface4ftof clutch housing4, and is open radially inward at the inner circumferential surface of left end portion4fof clutch housing4. The circumferential width of groove4ybetween end surfaces4y1and4y2is slightly smaller than the initial circumferential gap between end plate portions64aand64bof flat spring64placed free from cage5and clutch housing4.

The left end portion of cage5is extended leftward from bearing33L so as to have the left end surface of cage5close to the right end of bearing34L, and is formed on an outer circumferential surface thereof with two V-shaped grooves5dextended in the axial direction so as to have a length that is not less than a width of the long-and-narrow plate serving as flat spring64. Incidentally, only one of grooves5dis shown inFIG. 21. In correspondence to respective grooves5d, looped plate portion64cis bent in V-shape at two circumferentially intermediate portions so as to form radially inwardly projecting projections64f. In the circumferential direction of looped plate portion64c, one projection64fis closer to end plate portion64a, and the other projection64fis closer to end plate portion64a.

Projections64fof flat spring64are fitted into respective grooves5d. Therefore, a portion of looped plate portion64cbetween projections64fis fitted on the outer circumferential surface of cage5. In this state, end plate portions64aand64bare fitted into groove4yso that end plate portion64ais pressed against end surface4y1, and end plate portion64bis pressed against end surface4y2. Therefore, in space C2between the outer circumferential surface of the left end portion of cage5and the inner circumferential surface of left end portion4fof clutch housing4, a portion of looped plate portion64cbetween one projection64fand end plate portion64ais extended between one groove5don the outer circumferential surface of cage5and a radially inward end of end surface4y1of clutch housing4, and another portion of looped plate portion64cbetween the other projection64fand end plate portion64bis extended between the other groove5don the outer circumferential surface of cage5and a radially inward end of end surface4y2of clutch housing4.

While groove4yis open radially outward at the outer circumferential surface of left end portion4fof clutch housing4, end plate portions64aand64bin groove4yhave respective utmost ends64dand64ethat do not project radially outward from the outer circumferential surface of left end portion4fof clutch housing4, thereby being prevented from interfering with bearing33L. Alternatively, groove4ymay be closed at the outer circumferential surface of left end portion4fof clutch housing4.

When cage5is disposed at the initial position relative to clutch housing4, two projections64fare kept to be fitted in respective grooves5dso as to keep the portion of looped plate portion64cbetween projections64ffitted on the outer circumferential surface of cage5. Since the circumferential width of groove4ybetween end surfaces4y1and4y2is slightly smaller than the initial gap of flat spring64between end plate portions64aand64b, end plate portions64aand64bfitted in groove4yare slightly narrowed in the gap therebetween so as to be pressed in opposite directions away from each other against respective end surfaces4y1and4y2, so that plate spring64has a slight spring force in the direction to expand the gap between end plate portions64aand64b. The portions of looped plate portion64cextended in space C2are slightly bent so as to have elasticity such as to correspond to rotation of cage5relative to clutch housing4regardless of whether cage5rotates clockwise or counterclockwise relative clutch housing4.

As cage5rotates relative to clutch housing4from the initial position, one groove5dof cage5circumferentially moves away from corresponding end surface4y1or4y2of clutch housing4, while the other groove5dof cage5circumferentially approaches corresponding end surface4y1or4y2. Therefore, in space C2, one of the portions of looped plate portion64cextended between cage5and clutch housing4is tensioned, and the other of portions of looped plate portion64cextended between cage5and clutch housing4is bent, so that looped plate portion64cof flat spring64is elastically transformed to bias cage5to the initial position relative to clutch housing4.

As mentioned above, in auxiliary transaxle1E, friction mechanism FM and clutch-off biasing mechanism CM6are distributed so that friction mechanism FM is disposed at one (in this embodiment, right) end portion of cage5, and clutch-off biasing mechanism CM6is disposed at the other (in this embodiment, left) end portion of cage5.

In clutch-off biasing mechanism CM6, end plate portions64aand64bof flat spring64are engaged to clutch housing4rotatably integrally with clutch housing4so as to have a constant gap therebetween. Looped portion64cbetween projections64dserving as an intermediate portion of flat spring64is engaged to cage5rotatably integrally with cage5. Flat spring64includes the pair of elastic portions of looped portion64cbetween respective end plate portions64band respective projections64ddefining the portion of looped portion64cserving as the intermediate portion of flat spring64, such that the elastic portions of flat spring64are disposed in space C2between cage5and clutch housing4so as to be allowed to elastically transform according to the rotation of cage5relative to clutch housing4.

Therefore, auxiliary transaxle1E including clutch-off biasing mechanism CM6brings an effect similar to those of auxiliary transaxles1,1A,1B,1C and1D.

An auxiliary transaxle1F will now be described with reference toFIGS. 24 and 25.

Auxiliary transaxle1F includes a clutch-off biasing mechanism CM7disposed together with friction mechanism FM rightward from bi-directional overrunning clutch CL. More specifically, clutch-off biasing mechanism CM7is disposed between the right end portion of bi-directional overrunning clutch CL and friction mechanism FM. Clutch-off biasing mechanism CM7includes clutch housing4, cage5, right hub7R, friction mechanism FM, and a torsion spring65.

In auxiliary transaxle1F, spacer36of friction mechanism FM includes a cylindrical spring cover36hdisposed opposite horizontal sleeve portion36awith respect to vertical disc portion36b. Outer and inner diameters of spring cover36hare greater than the outer diameter of horizontal sleeve portion36a. In friction mechanism FM assembled in axle casing2, a space Sd is formed between vertical disc portion36band a right end surface4htof clutch housing4. Space Sd is surrounded by vertical dis portion36b, spring cover36h, right end surface4htof clutch housing4and the outer circumferential surface of cage5.

A position of a right end surface5htof cage5relative to right end4htof clutch housing4in the present embodiment is different from the position of the right end of cage5relative to the right end of clutch housing4in the foresaid embodiments. More specifically, in the present embodiment, right end surface5htof cage5is disposed rightward from right end surface4htof clutch housing4. A rightward projection degree of right end surface5htof cage5from right end surface4htof clutch housing4substantially coincides to a leftward projection degree of spring cover36hfrom vertical discoid portion36b.

Two housing pins Pn1and Pn2are fixed to (or formed on) clutch housing4so as to project axially distally rightward from right end surface4htof clutch housing4. Spring cover36hof spacer36is located radially outward from housing pins Pn1and Pn2.

A wire made elastic material such as steel is formed as torsion spring65including a coiled portion65cand two end portions65aand65b. Referring toFIG. 24, coiled portion65cis wound along an inner circumferential surface of spring cover36hof spacer36so as to proximal and distal (left and right) end portions. The proximal and distal end portions of coiled portion65care pulled to cross over each other and are bent to extend radially inward from coiled portion65cso as to be formed as proximal (left) end portion65aand distal (right) end portion65bof torsion spring65.

Any pair of adjoining engagement pawls26aare selected from all engagement pawls26aso as to serve as engagement pawls26a1and26a2disposed between end portions65aand65bof torsion spring65. The axially extended portion of each of engagement pawls26a1and26a2fitted in respective grooves5bhas circumferentially opposite end edges. One of the end edges of engagement pawl26a1is more distant from engagement pawl26a2than the other of the end edges of engagement pawl26a1, and is referred to as an end edge26xof engagement pawl26a1. The other of the end edges of engagement pawl26a2is more distant from engagement pawl26a1than the other of the end edges of engagement pawl26a2, and is referred to as an end edge26yof engagement pawl26a2. The circumferential interval between housing pins Pn1and Pn2is set to correspond to a circumferential interval between end edge26xof engagement pawl26a1and end edge26yof engagement pawl26a2.

Housing pins Pn1and Pn2and engagement pawls26a1and26a2are disposed between end portions65aand65bof torsion spring65. When cage5is disposed at the initial position relative to clutch housing4, one of proximal and distal end portions65aand65b(in this embodiment, proximal (left) end portion65a) is hung at a radially outward end portion thereof on housing pin Pn1and is pressed at a radially inward end portion thereof against end edge26xof engagement pawl26a1, and the other of proximal and distal end portions65aand65b(in this embodiment, distal (right) end portion65b) is hung at a radially outward end portion thereof on housing pin Pn2and is pressed at a radially inward end portion thereof against end edge26yof engagement pawl26a2.

As cage5rotates relative to clutch housing4from the neutral position, engagement pawls26a1and26a2rotate together with cage5to move circumferentially relative to housing pins Pn1and Pn2fixed to (or formed on) clutch housing4. Referring toFIG. 25, if cage5rotates clockwise relative to clutch housing4, end portion65bof torsion spring65is pushed by end edge26yof engagement pawl26a2and is separated from housing pin Pn2, while end portion65aof torsion spring65is retained by housing pin Pn1and is separated from end edge26xof engagement pawl26a1. If cage5rotates counterclockwise relative to clutch housing4, end portion65aof torsion spring65is pushed by end edge26xof engagement pawl26a1and is separated from housing pin Pn1, while end portion65bof torsion spring65is retained by housing pin Pn2and is separated from end edge26yof engagement pawl26a2. Therefore, the circumferential gap between end portions65aand65bof torsion spring65is expanded to elastically transform coiled portion65cof torsion spring65so as to bias cage5to the initial position relative to clutch housing4, regardless of whether cage5rotates clockwise or counterclockwise relative to clutch housing4.

Alternatively, only one engagement pawl26aor more than two engagement pawls26amay be disposed between end portions65aand65bof torsion spring65. In such an alternative case, clutch housing4is provided with housing pins Pn1and Pn2having an alternative interval therebetween, and end portions65aand65bof torsion spring65has an alternative gap therebetween, in correspondence to the number of engagement pawls26aplaced between end portions65aand65bof torsion spring65.

It is further understood by those skilled in the art that the foregoing description is a preferred embodiment of the disclosed device and that various changes and modifications may be made in the invention without departing from the scope thereof defined by the following claims.