Drive force distributing apparatus

A drive force distributing device includes first and second rollers rotatable jointly with main a drive wheel system and a subordinate drive wheel system, respectively. Control of the drive force distribution between the main drive wheels and the subordinate drive wheels is performed by adjusting an inter-roller pressing force. A structural body suppresses turning of one of the first and second rollers at a predetermined position. A reference position setting mechanism turns either one of the first and second rollers to turn in one direction, detects a position at which the turn is suppressed by the structural body, and sets a reference position based on the detected position. A turning amount of one of the first and second rollers is detected with respect to the reference position set by the reference position setting mechanism and the control of drive force distributing is performed based on the detected turning amount.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2012-167929 filed Jul. 30, 2012. The entire disclosure of Japanese Patent Application No. 2012-167929 is incorporated herein by reference.

BACKGROUND

The present invention generally relates to a vehicle drive force distributing apparatus suitable for a transfer case of a four-wheel drive vehicle.

2. Related Art

A drive force distributing apparatus including a first roller mechanically coupled to a transmission system of a pair of main drive wheels and a second roller mechanically coupled to a drive system of a pair of sub-drive or subordinate wheels is disclosed. The system becomes engaged when first and second rollers are mechanically pressed so as to make contact with each other at their outer peripheral surfaces. As such, a mechanical torque can be distributed between the main drive wheels and subordinate drive wheels such that a percentage allocated to the main drive wheels vs. the percentage allocated to the subordinate drive wheels is continuously selectable. Accordingly, a torque transmission capacity between the rollers can be controlled by adjusting a radial pressing force between the first roller and the second roller so as to adjust the distribution of the drive force between the main drive wheels and the sub-drive wheels.

An example mechanism for performing this drive force distribution control is disclosed in the Japanese Laid-open Patent Publication No. 2011-11560 (and corresponding U.S. Patent Application Publication No. 2012/0100955 A1). In this example a second roller is supported in an eccentric shaft portion of a crankshaft and the rotation axis of the second roller revolves or turns about the eccentric axis by operating the crankshaft to rotate. By displacing the position of the rotation axis of the second roller (by an angular amount along a curve) the second roller becomes displaced toward the first roller. Thus, the radial pressing force between the first roller and the second roller may be controlled. To perform this control, it is necessary to detect the rotation angle of the crankshaft. The rotation angle of the crankshaft corresponds to the angular position of the eccentric axis of the second roller and is obtainable as an amount of angular movement with respect to a reference position.

The reference point is set as follows. The crankshaft is turned and the axis of the second roller is therefore displaced toward the first roller. Meanwhile the first roller is turned to one direction at a constant torque while the second roller is turned in the reverse direction at the same magnitude of constant torque. As the first and second rollers are pressed with increasing force toward one another (by turning the crank shaft) eventually the second roller stops turning due to the torque imposed by the first roller. The angular position of the crankshaft at which the second roller stops it taken as a reference point. This reference point corresponds to the situation in which the two rollers are pressed together with sufficient force so prevent slippage between the rollers and thus represents the point at which drive force distribution system is beginning to be engaged for transferring torque. By increasing the crankshaft rotation angle beyond this reference point allows torque to be increasingly diverted from the main drive wheels to the sub-drive wheels.

The above described system, however, suffers from the drawback that, generally, a time delay is associated with the detection of the rotation angle of the crankshaft.

SUMMARY OF THE INVENTION

The disclosed embodiments overcome the above problems and provide a drive force distributing apparatus that can more quickly detect the rotation angle of the crankshaft.

According to an embodiment, a drive force distributing device includes first and second rollers rotatable jointly with a main drive wheel system and a subordinate drive wheel system, respectively. Control of the drive force distribution between the main drive wheels and the subordinate drive wheels is performed by adjusting an inter-roller pressing force. A structural body suppresses turning of one of the first and second rollers at a predetermined position. A reference position setting mechanism turns either one of the first and second rollers to turn in one direction, detects a position at which the turn is suppressed by the structural body, and sets a reference position based on the detected position. A turning amount of one of the first and second rollers is detected with respect to the reference position set by the reference position setting mechanism and the control of drive force distributing is performed based on the detected turning amount.

It is to be appreciated that any additional disclosure found in the Figures is meant to be exemplary and not limiting to any of the features shown in the Figures and described in the specification below.

DETAILED DESCRIPTION

First Embodiment

FIG. 1is a schematic top down view of a power train of a four-wheel drive vehicle equipped with a drive force distributing apparatus1according to a first disclosed embodiment. The basic structure is as disclosed in U.S. Patent Application Publication No. 2011/0319223 A1, which is incorporated by reference herein in its entirety.

The four-wheel drive vehicle is based on a rear wheel drive configuration in which torque from an engine2is multiplied by a transmission3and is transferred through a rear propeller shaft4and a rear final drive unit5to left6L and right6R rear wheels. The vehicle can operate in a four-wheel drive manner by using the drive force distributing apparatus1to divert a portion of the torque being provided to the left6L and right6R rear wheels (main drive wheels) through a front propeller shaft7and a front final drive unit8to transmit torque to left9L and right9R front wheels (subordinate drive wheels).

The drive force distributing apparatus1thus determines a drive force distribution ratio between the left6L and right6R rear wheels (main drive wheels) and the left9L and right9R front wheels (subordinate drive wheels). In this embodiment, the drive force distributing apparatus1can be configured as shown inFIG. 2.

As shown inFIG. 2, the apparatus includes a housing11. An input shaft12and an output shaft13are arranged to span across an inside of the housing11diagonally with respect to each other such that a rotational axis O1of the input shaft12and a rotational axis O2of the output shaft13intersect each other. The input shaft12is rotatably supported in the housing11on ball bearings14and15located at both ends of the input shaft12. Furthermore, both ends of the input shaft12protrude from the housing11and are sealed in a liquid-tight fashion or a substantially liquid-tight fashion by seal rings25and26. In this arrangement, one end of the input shaft12shown at the left side ofFIG. 2is coupled to an output shaft of the transmission3(seeFIG. 1). Also, the other end of the input shaft2at the right side ofFIG. 2is coupled to the rear final drive unit5through the rear propeller shaft4(seeFIG. 1)

A pair of bearing supports16and17are provided between the input shaft12and the output shaft13in positions near the ends of the input shaft12and the output shaft13. The bearing supports16and17are fastened to axially opposite internal walls of the housing11with fastening bolts (not shown), at approximate middle portions of the bearing supports16and17. Bearing support16,17, is provided with an input shaft through bore16a,17a, output shaft through bore16c,17c, for passing through the output shaft13and crankshaft51L,51R, and a vertical wall16b,17b, connecting between the input shaft through bore16a,17a, and output shaft through bore16c,17c, and is generally shaped in the axial direction front view. Roller bearings21,22, are arranged between the bearing supports16,17, and input shaft12for supporting the input shaft12freely or rotatably relative to bearing supports16,17, so that input shaft12is supported inside the housing11rotatably through the bearing supports16,17.

A first roller31is formed integrally and coaxially with the input shaft12in an axially intermediate position located between the bearing supports16and17, that is, between the roller bearings21and22. A second roller32is formed integrally and coaxially with the output shaft13in an axially intermediate position such that the second roller32can make frictional contact via working oil (lubricating oil) with the first roller31in a power transmittable way. The outer circumferential surfaces of the first roller31and the second roller32are conically tapered in accordance with the diagonal relationship of the input shaft12and the output shaft13such that the outer circumferential surfaces can line contact each other (i.e., make contact along a line) without or substantially without a gap between the surfaces.

The output shaft13is rotatably supported with respect to the bearings supports16and17at positions near both ends of the output shaft13. Thus, the output shaft13is rotatably supported inside the housing11through the bearing supports16and17. A support structure used to support the output shaft13rotatably with respect to the bearing supports16and17is realized by an eccentric support structure as will now be explained.

As shown inFIG. 2, a crankshaft51L configured as a hollow outer shaft is moveably fitted between the output shaft13and the bearing support16. Also, a crankshaft51R configured as a hollow outer shaft is moveably fitted between the output shaft13and the bearing support17. These crankshafts51L,51R are used as a roller turning drive members. The crankshaft51L and the output shaft13protrude from the housing11as shown on the left side ofFIG. 2. At the protruding portion, a seal ring27is installed between the housing11and the crankshaft51L. Also, a seal ring28is installed between the crankshaft51L and the output shaft13. The seal rings27and28serve to seal the portions where the crankshaft51L and the output shaft13protrude from the housing11in a liquid-tight or substantially liquid-tight fashion.

The left end of the output shaft13protruding from the housing11inFIG. 2is coupled to the front wheels9L and9R through the front propeller shaft7(seeFIG. 1) and the front final drive unit8. A roller bearing52L is arranged between a center hole or bore51La (radius Ri) of the crankshaft51L and a corresponding end portion of the output shaft13. Also, a roller bearing52R is arranged between a center hole51Ra (radius Ri) of the crankshaft51R and a corresponding end portion of the output shaft13. Thus, the output shaft13is supported such that the output shaft13can rotate freely about the center axis O2inside the center holes51La and51Ra of the crankshaft51L and51R

As shown inFIG. 3, the crankshaft51L has an outer circumferential portion51Lb (center shaft axis O3, radius Ro) that is eccentric with respect to the center hole51La. Also, the crankshaft51R has an outer circumferential portion51Rb (center shaft axis O3, radius Ro) that is eccentric with respect to the center hole51Ra. The eccentric outer circumferential portions51Lb and51Rb are offset from the center axis (rotational axis) O2of the center holes51La and51Ra by an eccentric amount E. The eccentric outer circumferential portion51Lb of the crankshaft51L is rotatably supported inside the corresponding bearing support16through a roller bearing53L. The eccentric outer circumferential portion51Rb of the crankshaft51R is rotatably supported inside the corresponding bearing support17through a roller bearing53R. In addition, the roller side contact portions51Ld,51Rd, of crankshafts51L,51R, are freely and rotatably supported on thrust bearings32cL,32cR. Further, thrust bearings54L,54R, are provided axially outside with respect to thrust bearings32cL,32cR. These thrust bearings54L,54R, contact spacers60L,60R rotatably and also contact ring gears51Lc,51Rc rotatably to thereby support crankshaft51L and51R rotatably fee.

Crankshafts51L,51R, are respectively formed integrally with ring gears51Lc,51Rc, which face each other and provided at respective end of the associated crankshaft. These ring gears51Lc,51Rc, are each meshed with a common crankshaft drive pinion55such that the crankshaft pinion is coupled to pinion shaft56. The ring gears51Lc and51Rc are meshed with the crankshaft drive pinion55such that the eccentric outer circumferential portions51Lb and51Rb of the crankshafts51L and51R are aligned with each other in a circumferential direction. That is, the rotational positions of the eccentric outer circumferential portions51Lb and51Rb are in phase with each other.

The pinion shaft56is rotatably supported with respect to the housing11by bearings56aand56barranged at both ends of the pinion shaft56. A right end of the pinion shaft56passes through the housing11as shown on the right-hand side ofFIG. 2. An exposed end portion of the pinion shaft56is operably coupled to an output shaft35aof an inter-roller radial pressing force control motor35through serration coupling and the like. Therefore, rotational position control can be executed with respect to the crankshafts51L and51R by driving the crankshafts51L and51R with the inter-roller radial pressing force control motor35through the pinions55and the ring gears51Lc and51Rc. When this occurs, the output shaft13and the rotation axis O2of the second roller32turn about the center axis (rotational axis) O3so as to revolve along a circular path α indicated with a broken line inFIG. 3.

In the present embodiment a reference position for detection of a rotation angle of crankshaft51L,51R is set as described below, and the crankshaft rotation angle θ at that reference position is set=0°, while the rotational amount from the reference position is defined as a crankshaft rotation angle θ. Until the setting process for the reference point is described (below), for convenience of explanation, the reference rotation angle of crankshaft is assumed to be top dead center for further description.

As described below, by shifting the rotation shaft axis O2(second roller32) along a circular path α as shown inFIG. 3, the second roller32approaches the first roller31in the radial direction as shown inFIGS. 4A to 4C. Thus, by increasing the rotation angle θ of crankshafts51L,51R, the roller center distance L1between the first roller31and the second roller32may be decreased to be less than the sum of the radius of the first roller31and the radius of the second roller32. Thus, the radial pressing force of the second roller32on the first roller31(inter-roller transmission torque capacity; traction transmission capacity) increases. Therefore, in response to the decrease in the inter-roller center distance L1, the inter-roller radial depressing force (inter-roller transmission torque capacity; traction transmission capacity) may be variably controlled to freely adjust the drive force distribution ratio (i.e., the ratio of torque going to front and back wheels).

As shown inFIG. 4A, in the present embodiment, the inter-roller center distance L1in a state of bottom dead center (in which the rotation shaft axis O2is located directly below the rotation axis O3of crankshaft and the inter-roller distance between first roller31and second roller32becomes maximum) is configured to be larger than the sum of the radius of first roller31and the radius of the second roller32. Thus, at the bottom dead center configuration with crankshaft rotation angle=0°, the first roller31and the second roller32are prevented from being pressed against each other in the radial direction. In this configuration, no traction transmission occurs between rollers31,32takes place (i.e., traction transmission capacity=0). Therefore, traction capacity may be continuously set to a value anywhere between θ=0° at the bottom dead center and the maximum value obtainable at the top dead center as shown inFIG. 4C(i.e., θ=180°). In the present embodiment, a rotation angle reference of crankshaft51L,51R, at the bottom dead center (i.e., crankshaft rotation angle θ=0°) is set.

Operation of Drive Force Distribution Apparatus

With reference toFIGS. 1 to 4, the operation of the drive force distribution apparatus is now described. An output torque from the transmission3(shown inFIG. 1) is imparted to input shaft12of drive force distribution apparatus1. The torque can be further transmitted directly from the input shaft12to the left6L and right6R rear wheels (main drive wheels) through the rear propeller shaft4and the rear final drive unit5(both being shown inFIG. 1).

When the inter-roller distance L1(shown inFIG. 4) is set less than the sum of the radius of first roller31and the radius of second roller32in response to the rotation position control of crankshafts51L,51R, by motor35through pinion55and ring gears51Lc,51Rc, the drive force distribution transfer apparatus1acquires an inter-roller transmission torque capacity in accordance with the radial pressing force between first roller31and second roller32. Depending on this torque capacity, drive force distribution apparatus1can divert a portion of the torque from the left and right rear wheels6L and6R (main drive wheels) toward the output shaft13(FIG. 2) by passing torque from the first roller31to the second roller32. A torque reaching the output shaft13is therefore transmitted to drive the left9L and right9R front wheels (subordinate drive wheels). The vehicle can therefore be operated in a four-wheel drive mode in which the left6L and right6R rear wheels (main drive wheels) and the left9L and right9R front wheels (subordinate drive wheels) are driven.

The traction drive system described above conveys the force in the tangential direction (direction of roller rotation) due to the shear stress of a working fluid that is confined in the elastically deformable contact portion produced by radially pressing a pair of smooth roller elements (i.e. first roller31and second roller32). Thus, it is preferable to use a hydraulic fluid with a large limit shear stress (e.g., naphthenic oil).

During travel in the four-wheel drive mode, when the rotation angle θ of crankshaft51L,51R is set at a reference position of θ=90° (FIG. 4B), the first roller31and second roller32are pressed against each other for frictional contact at a radial pressing force corresponding to an offset amount OS. As such, the amount of torque transmission given to left9L and right9R front wheels (subordinate drive wheels) occurs in accordance with the offset value OS between the two rollers.

As the rotation angle θ of crankshaft51L,51R, increases from the reference position shown inFIG. 4Btoward the top dead center (θ=180°) as shown inFIG. 4C, the inter-roller center distance L1further decreases to increase the overlap amount OL between first roller31and second roller32.

Consequently the radial pressing force between first roller31and second roller32will be increased to thereby increase the traction transmission capacity between these rollers. When crankshafts51L,51R, have reached the position of top dead center (θ=180°,FIG. 4C), first roller31and second roller32are pressed at the maximum radial pressing force corresponding to the maximum overlap amount OL. As such, the traction transmission capacity between the two is maximized. The maximum overlap amount OL is obtained by adding the eccentric amount ε0between the second roller rotation axis O2and crankshaft rotation axis O3to the offset amount OS described with reference toFIG. 4B.

As will be appreciated from the description above, by operating crankshafts51L,51R, to rotate from the position of θ=0° to the position of θ=180°, an inter-roller traction transmission capacity may be varied continuously from the minimum (i.e., zero) to the maximum. Conversely, by operating crankshafts51L,51R to rotate from the position of θ=180° to the position of θ=0°, the inter-roller traction transmission capacity may be varied continuously from its maximum to its minimum (i.e. zero). Thus, the inter-roller traction transmission capacity may be controlled freely by the rotational operation of crankshafts51L,51R.

Control of Traction Transmission Capacity

During four-wheel drive operation (described above), drive force distribution apparatus1outputs and conveys a part of the torque to left6L and right6R rear wheels (main drive wheels) to left9L and right9R front wheels (subordinate drive wheels). Thus, the traction transmission capacity between the first roller31and the second roller32is required to correspond to a target front wheel drive force to be distributed to left and right front wheels (subordinate wheels) that is obtainable based on the drive force to left and right rear wheels (main drive wheels)6L,6R and the distribution ratio of front to rear wheel target drive force. In the present embodiment, in order to perform a required traction transmission capacity control, a transfer controller111is provided shown inFIG. 1to perform control of the rotational position (control of rotation angel θ of crankshaft) of motor35.

Therefore, transfer controller111receives a signal from accelerator pedal opening sensor112to detect the accelerator depressing amount (accelerator pedal opening degree) APO to adjust the output of engine2, a signal from rear wheel speed sensor113to detect the rotational peripheral speed Vwr of left and right rear wheels6L,6R (main drive wheels), a signal of yaw-rate sensor114to detect a yaw-rate φ about the vertical axis passing through the center of gravity of the vehicle, a signal from the crankshaft rotation angle sensor115to detect the rotation angle θ of crankshaft51L,51R, and a signal of an oil temperature sensor116to detect a temperature TEMP of working oil within the transfer1(housing11).

Based on the input information of each sensor described above, transfer controller111controls the traction transmission capacity (front to rear wheel drive force distribution control of four wheel drive vehicle) in the following manner.

Specifically, transfer controller111first determines both a drive force of left and right wheels6L,6R (main drive wheels) and the front to rear target drive force distribution ratio.

Subsequently, transfer controller111determines a target front wheel drive force to be conveyed to left9L and right9R front wheels (subordinate wheels) based on the drive force of left6L and right6R rear wheels (main drive wheels) and the target distribution ratio between front and rear drive force.

Further, transfer controller111determines a target radial inter-roller pressing force (traction transmission capacity) imparted by first roller31and second roller32necessary to transmit the target front drive force, and then determines a target rotation angle θtof crankshaft51L,51R (seeFIGS. 2,3), which is, target rotation angle of second roller axis O2so as to achieve the target radial inter-roller pressing force (traction transmission capacity between first roller31and second roller32).

Then, transfer controller111instructs the inter-roller pressing force control motor35to adjust crankshaft rotation angle θ so as to match the target crankshaft rotation angle θtin accordance with the difference between the crankshaft rotation angle θ detected by sensor115and the target crankshaft rotation angle θt. When the rotation angle θ of crankshaft51L,51R, matches the target value θt, the first roller31and the second roller32are pressed against each other so as to transmit the target front wheel drive force. In this way, the first roller31and second roller32may be controlled to adjust the traction transmission capacity to match the target front to rear wheel drive force distribution.

Detection of Rotation Angle θ

The crankshaft rotation angle θ (rotation of crankshaft51L,51R) detected by the crankshaft rotation angle sensor115merely represents a relative value. Thus, in order to detect an absolute value of crankshaft rotation angle θ, it is necessary to set a reference position and to convert the detection value of the crankshaft rotation angle sensor115to give the rotational amount or rotation angle with respect to the reference position. In this respect, in the present embodiment, a structural body510(FIG. 5) is provided to suppress the turn of the second roller32further than a predetermined position. In addition, the transfer controller111turns the second roller32in one direction and detect the position of suppression (crankshaft rotation angle θ) so as to set the detected position as a reference position (θ=0°).

FIG. 5is a front diagram of crankshaft51L (51R) as viewed in the axial direction, illustrating output shaft13, ring gear51Lc (51Rc), and crankshaft drive pinion55in meshed relationship therewith. The structural body is formed by inserting a filler into a part of teeth of ring gear51Lc (51Rc) of crankshaft51L (51R). In an embodiment, the filling may be fixed by welding. Either the teeth of ring gear51Lc or the teeth of ring gear51Rc may be filled.

The reference position may be set by the manufacturer or at a later time after the vehicle has been driven a predetermined distance. The structural body510may be positioned so that when crankshafts51L,51R are positioned at top dead center (TDC) no further rotation is permitted.

The reference position setting unit117determines that structural body510is in a position to suppress the turn of the second roller32upon detecting that crankshafts51L,51R, have stopped based on the detection value of crankshaft rotation sensor115. Alternatively, when a current value to be supplied to motor35is automatically set in accordance with a rotation resistance to achieve a predetermined rotation angle of motor35(rotation amount of crankshafts51L,51R), it may be determined as well that the structural body510has suppressed the turn of the second roller32upon detection of the increase in that current value (for example, upon the command current value exceeding a preset threshold).

Subsequently, the stopped position of crankshafts51L,51R, is stored and set as a reference position. Stated another way, the crankshaft rotation angle θ at the reference point or position is set (θ=0°). The detection value of the crankshaft rotation angle sensor115is calculated with reference to the output value of crankshaft rotation angle sensor115at the stored reference position (θ=0°). Thus the detection value is converted to an absolute crankshaft rotation angle θ. The transfer controller, in turn, executes a drive force distributing control based on this (absolute) crankshaft rotation angle θ (equivalent to the turning amount of the second roller32).

Effects of the First Embodiment

According to the present embodiment, as the second roller32is turned in one direction, the angular position at which this turning is stopped by structural body510is set as a reference position. The drive force distribution control is then performed based on the turning amount of the second roller32detected relative to this reference position. Therefore, in setting a reference position of the turning amount of second roller32, it is not necessary for the second roller32to be turned in both directions. This facilitates a quick detection of the turning amount of the second roller32and therefore improves the responsiveness in drive force distribution control as it relates to the radial inter-roller pressing force control.

The above described embodiment stands in contrast to the conventional technique (described in U.S. Patent Application Publication No. 2012/0100955 A1) in which, in order to set a crankshaft rotation angle reference point, the second roller has to be turned in two directions such that it takes time to detect an absolute value of crankshaft rotation angle (or a reference position setting therefore). Further, in the conventional technique, the torque for driving the crankshaft for setting a reference position (torque of motor/actuator) is taken to be the value at which the second roller stops to turn upon start of contact of the periphery of the second roller with the periphery of first roller (i.e., the minimum required torque). Thus, a relatively long time would be required when using this minimum required torque and actuating the crankshaft to rotate in both directions according to the conventional approach. Therefore, the response of the driving force distribution control via pressing force control in the radial direction, according to the conventional approach, is not optimal.

In contrast, according to the present embodiment, there is no need to rotate the crankshafts51L,51R, in both directions to set a reference position of crankshaft rotation angle θ, but rather, it suffices to drive only in one direction. In addition, in the present embodiment, a larger torque value may be used for setting a reference point (i.e., one that is greater than is required to stop second roller32upon contact on the outer periphery31aof the first roller31). In this way, the torque value exceeds the one used in the conventional technique. Therefore, a shorter time is necessary for driving the crankshafts51L,51R for setting the reference position. Therefore, the responsiveness in the drive force distribution control is increased relative to that of the conventional approach.

The friction of bearings supporting crankshaft or second roller (output shaft) depends on the oil temperature and age of the components. Thus, the relationship between the torque for driving the crankshaft and the radial inter-roller pressing force (frictional contact force) depends on these factors. In the conventional technique, an accurate adjustment of torque (motor current) or accurate detection of start of contact between two rollers based on motor current is difficult to set. Such conventional techniques require that the second roller stops to turn when the outer periphery of second roller begins to contact the outer periphery of the first roller causing the crankshaft to stop rotating. In the conventional technique these variations may be overcome to some extent by setting a central position between the stopped positions of the second roller in both directions. However, in the conventional configurations, time is required to set a reference position of the crankshaft rotation angle θ and there is a limit on the ability to accurately set the reference position due to the effects mentioned above.

In contrast, according to the drive force distribution apparatus1of the present embodiment, the position at which turning of second roller32, is stopped by structural body510is mechanically determined and is not affected by changes in friction of the roller bearings52,53etc., resulting from changes in oil temperature or aging. Therefore, the accuracy in drive force distribution control is increased. In addition, since there is no need to drive crankshafts51L,51R, in both directions to offset such effects as in the case of conventional technique, the time required for setting the reference position is shortened.

The angular position at which the second roller32stops turning is not necessarily at the top dead center, but may be chosen to be at bottom dead center also.

Irrespective of which position is set as the reference position, the beneficial effects described above may be achieved. In the present embodiment, since the structural body510is provided so as to stop rotation of the second roller32at the position (top dead center) at which the radial inter-roller pressing force represents the maximum, any angular position between bottom dead center and top dead center is possible and is not blocked by the structural body510. Stated another way, turning of second roller32may be stopped at top dead center not only in response to a turn in the direction indicated by arrow inFIG. 5but also in response to a turn in the opposite direction. Therefore, since the control range (upper limit) will not be restricted depending on the direction of turn (direction of rotation of crankshaft51L,51R) from the initial turning position, the control width or controllability of traction transmission capacity is improved.

Further, overshoot beyond the top dead center position (i.e. over-turning of second roller32excessively beyond the top dead center during the drive control of the motor35) is prevented. The accuracy in the traction transmission capacity control is therefore improved. Indeed, when the target crankshaft rotation angle θtis near the top dead center, the torque to drive the crankshaft51L,51R will be large, and the likelihood of overshoot is larger. By stopping the turning of second roller32at the top dead center by the structural body510, (even if current of motor35would have overshot) the situation of over-turn beyond the top dead center will be prevented. Thus the accuracy in the radial inter-roller pressing force in the vicinity of the top dead center (torque transmission capacity) is improved. Also, since no radial inter-roller pressing force is generated at the bottom dead center, the problem of control accuracy (related to overshot) does not arise.

Crankshafts51L,51R, are provided as a roller turning drive member to turn the second roller32. Crankshafts51L,51R, are provided with ring gears51Lc,51Rc, in meshed relationship with teeth (pinion55) formed on the drive shaft (pinion shaft56) rotatably driven by motor35and are disposed rotatably in housing11. A second roller32is rotatably supported at the location eccentrically located from the axis of rotation of crankshafts51L,51R (center axis O3). The structural body510is formed by filling a part of teeth of ring gears51Lc,51Rc. Thus through a simple structure formed by only filling a part of the teeth of existing ring gears51Lc,51Rc, originally provided to drive the roller to rotate, the structural body510for setting reference position provides a simple, compact, cost effective solution.

Second Embodiment

In a second embodiment, a drive force distributing apparatus is provided that has a different configuration from that of the first embodiment with regard to the structure510. The structural body510is provided with both a first protrusion portion511(FIG. 6) formed at the outer periphery of crankshaft51R and a second protrusion portion512(FIG. 7) formed in the inner periphery of housing11opposing the outer periphery of the crankshaft51R such that the rotation of crankshaft51R may be suppressed by engagement between the first protrusion portion511and the second protrusion portion512.

FIG. 6is an axial front view of a crankshaft51R according to the second embodiment. The axial end face of the crankshaft51R opposing or facing the inner periphery of the housing11is provided with a first protrusion511.FIG. 7shows a portion where the axial end surface of the crank shaft51R is opposed to the inner periphery of the housing11in the vertical cross sectional view of the drive force distributing apparatus according to the second embodiment. The inner periphery of the housing11facing the axial end surface of the outer periphery of the crankshaft51R is provided with a second protrusion512. When crankshafts51L,51R (first protruding part511) are rotated from the bottom dead center position (FIG. 6) to near the top dead center, the first protrusion511contacts with the second protrusion portion512, and as shown by the broken lines inFIG. 7. At this position, further rotation of crankshafts51L,51R is restricted.

Problems associated with the first embodiment may be avoided with the second embodiment. With the first embodiment there is a possibility that the entire tooth of crankshaft51R may be deformed. This may lead to generation of noise in the meshing portion of the teeth. In contrast, according to the present second embodiment, no risk of deformation of overall teeth of crankshaft51L,51R is encountered so that these problems may be avoided.

With respect to the location at which the first protrusion511is formed on the crankshaft51R, there is no limitation to the axial end face. Further, the first protrusion may be provided in either outer periphery of the first and second crankshafts51L,51R.

Third Embodiment

According to a third embodiment, the drive force distributing apparatus is different from the first and second embodiments as it relates to the structural body510. In this embodiment, as illustrated inFIG. 9, the structural body510includes a recess portion513formed on the outer periphery of crankshaft51R, an elastic member (compression coil spring514) disposed in the inner periphery of housing facing the outer periphery of crankshaft51R, and a member with curved shape (ball515) provided on the tip of the elastic member such that the rotation of crankshaft51R may be suppressed by engagement of the spherical member with the recess512.

FIG. 8is an axial front view showing the crank shaft51R according to the third embodiment. At the axial end face of crankshaft51R, the inner periphery of housing11is provided with a recess513.FIG. 9illustrates a portion where the axial end surface of the crank shaft51R is opposed to the inner periphery of the housing11in the vertical cross sectional view of the drive force distributing apparatus. The inner periphery of the housing11facing the axial end surface of the outer periphery of the crankshaft51R is provided with a compression coil spring514as the elastic member and a ball515as a curved body positioned at the tip of the compression coil spring514. The compression coil spring514continuously urges the ball toward the axial end surface of crankshaft51R. When the crankshaft51L,51R (recess portion513) rotates from the bottom dead center shown inFIG. 8to reach the top dead center, the ball515engages with the recess513(shown by dotted line inFIG. 9) such that further rotation of the crankshafts51L,51R is restricted. In other words, structural body510-514suppresses the turning movement of second roller32.

According to the third embodiment, it is possible for ball515to come out of the recess513as a result of the curved shape of ball515in response to compression of the compression coil spring514. This can occur when, after ball515has been engaged with the recess, the current value to be supplied to motor35(i.e. torque of motor35) is increased above a certain magnitude. Thus, instead of complete suppression of rotation of crankshafts51L,51R, by a structural body, the turning position of the second roller32may be restricted through a range of angular positions near the top dead center position. In this way, the width of traction transmission capacity control as well as controllability is improved. The curved member need not be limited to ball515, but a pin may also be employed. Further, an elastic member other than a compression coil spring may be used. Also, the recess portion513may be of arbitrary shape such as hole or groove.

In contrast to the first embodiment, according to the third embodiment there is no risk of deformation of overall teeth of crankshaft51L,51R so that problems associated with noise (discussed above) may be avoided.

Further, in contrast to the first and second embodiments, in the third embodiment, second roller32may be rotated preciously up to the top dead center in both directions with no angular range excluded. Therefore, the reference position may be set at the precise top dead center so that the control range of torque transmission capacity may be maximized to improve both the width of traction transmission capacity control and controllability.

The portion at which the recess portion513is formed in the crankshaft51R is not limited to the axial end. Further, the recess portion may be formed on either outer periphery of the crankshafts51L,51R.

Other Embodiments

In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including,” “having,” and their derivatives. Also, the terms “part,” “section,” “portion,” “member,” or “element,” when used in the singular can have the dual meaning of a single part or a plurality of parts. Also as used herein to describe the above embodiments, the following directional terms “forward,” “rearward,” “above,” “downward,” “vertical,” “horizontal,” “below” and “transverse” as well as any other similar directional terms refer to those directions of a device equipped with the present invention. Accordingly, these terms, as utilized to describe the present invention should be interpreted relative to a device equipped with the present invention. The term “detect” as used herein to describe an operation or function performed by a component, a section, a device or the like includes a component, a section, a device or the like that does not require physical detection, but rather includes determining, measuring, modeling, predicting or computing or the like to perform the operation or function. The term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to perform the desired function. Moreover, terms of degree such as “substantially,” “about,” and “approximately,” as used herein mean an amount of deviation of the modified term such that the end result is not significantly changed.

For example, in respective embodiments, the second roller32is turned by rotation of crankshafts51L,51R. However, such a crankshaft may be provided to turn the first roller31, and, the radial inter-roller pressing force may be adjusted due to turning of the first roller31.

For example, in each embodiment, hollow outer-shaft type of crankshafts51L,51R are employed as the driving member for turning the second roller32. However, other types of driving member may also be employed.

For example, in each embodiment, turning of the second member32is suppressed at the predetermined position by restricting the rotation of crankshafts51L,51R, by the structural member510. However, the turning of second roller32may be directly restricted by a structural member provided to the output shaft13and the like.