Toroidal continuously variable transmission

In a toroidal continuously variable transmission, a roller-and-cage bearing assembly is interleaved between a power-roller outer ring and a trunnion power-roller accommodating portion to permit a parallel translation of a power roller in an axial direction of input and output disks. A cage of the roller-and-cage bearing assembly is formed with an oval slotted hole. A disk-shaped member is attached to the trunnion power-roller accommodating portion. The slotted hole and the disk-shaped member are fitted to each other to define a predetermined clearance that limits a displacement of the roller-and-cage bearing assembly in a direction perpendicular to both a rotation axis of the power roller and a trunnion axis to a set displacement.

FIELD OF THE INVENTION

The present invention relates to a toroidal continuously variable transmission, and specifically to a support for a power roller interposed between input and output disks of a toroidal continuously variable transmission.

DESCRIPTION OF THE RELATED ART

In recent years, to meet demands for increased shift comfort, improved driveability, and reduced fuel consumption and exhaust emissions, there have been proposed and developed various continuously variable transmissions, such as a segmented metal belt-drive continuously variable transmission and a toroidal continuously variable transmission often abbreviated to “toroidal CVT”, in which a transmission ratio is steplessly variable within limits. Toroidal CVTs in which engine power (torque) is transmitted from an input disk to an output disk via a traction oil film formed between a power roller and each of the input and output disks, using a shearing force in the traction oil film at high contact pressure, are superior to belt-drive CVTs, in a higher torque capacity, and faster transmission-ratio changes. Such toroidal CVTs went into mass production. Toroidal CVTs are generally classified into a full-toroidal CVT and a half-toroidal CVT. From the viewpoint of reduced spin loss, the half-toroidal CVT model is superior to the full-toroidal CVT model. The half-toroidal CVT has a power roller interposed between input and output disks and being in contact with a torus surface of each of the input and output disks under preload, and a trunnion serving as a power roller support. During transmission-ratio changing, in order to obtain a desired transmission ratio determined based on the magnitude of a gyration angle of the power roller, first of all, the power roller is offset from the center of rotation of the disks by slightly shifting the trunnion in a direction of a trunnion axis perpendicular to a rotation axis of the power roller. By virtue of a side slip force occurring in a very limited contact zone between the power roller and the input and output disks due to the slight offset (the slight vertical displacement), the power roller is tilted or inclined. When the gyration angle corresponding to the desired transmission ratio has been reached, the vertical displacement of the trunnion is returned to zero, so as to stop the inclining motion of power roller. During ratio changing with inclining motion of the power roller, to keep the power roller and the respective disk in contact with each other, the input disk is forced axially against the output disk by means of a loading cam device. Generally, the output disk is axially stationary, whereas the input disk is axially moveable. On the other hand, a trunnion rod itself is not moveable in the axial direction of the disks. To keep the power roller and the respective disk in contact with each other regardless of changes in a relative distance of the input disk to the output disk under axial preload of the loading cam device, the power roller itself has to be shifted in the axial direction of the disks. Owing to deformation of the input and output disks during power transmission, or in presence of a slight misalignment after installation, there is a slight error in relative position between the power roller and the respective disk. To absorb such a slight error, in the same manner as the axial preload of the loading cam device, it is necessary to create a displacement of the power roller in the axial direction of the disks, that is, a horizontal displacement of the power roller. As a power-roller support that permits the horizontal displacement of the power roller, an eccentric pivot whose axis is eccentric to the rotation axis of the power roller is often used. In this case, oscillating motion of the eccentric pivot causes the horizontal displacement of the power roller. At the same time, the oscillating motion of the eccentric pivot also causes an undesirable vertical displacement of the power roller. Thus, the undesirable vertical displacement results in a slight offset of the power roller from the center of rotation of the disks. This causes undesirable transmission-ratio changing.

To avoid this, Japanese Patent Provisional Publication No. 7-198014 teaches the use of a linear bearing that is disposed between an inner peripheral wall of a power roller accommodating portion of a trunnion and a power roller, in such a manner as to permit parallel translation of the power roller in the right-and-left direction (horizontal direction) relative to the trunnion by means of the linear bearing. During power transmission, slight errors in relative position between the power roller and the respective disk repeatedly occur owing to deformation of the input and output disks, thereby resulting in reciprocating motion of the linear bearing itself in the axial direction of the disks. A horizontal displacement of the linear bearing obtained when the power roller pushes the linear bearing is somewhat different from that obtained when an external force applied to the power roller is released. After the reciprocating motion, there is an increased tendency that the linear bearing does not return to its initial set position. Due to the reciprocating motion of the linear bearing, arising from the parallel translation of the power roller, and undesired slight misalignment after assembling, there is an increased tendency for the linear bearing to be excessively protruded out of the trunnion power-roller accommodating portion. In the presence of the excessive protrusion of the linear bearing out of the trunnion power-roller accommodating portion, in other words, an excessive offset of the linear bearing from the initial set position, it is impossible to adequately support or bear the load acting on the power roller. Owing to the excessive offset of the linear bearing from the initial set position, there is a possibility for the linear bearing to be brought into contact with either the input disk or the output disk.

To avoid this, Japanese Patent Provisional Publication No. 2001-165265 teaches the use of a stopper for a roller-and-cage bearing assembly (substantially corresponding to the linear bearing discussed above) for the purpose of limitation on horizontal displacement of the roller-and-cage bearing assembly relative to a trunnion. The stopper is comprised of two parts, namely a protruded stopper portion and a grooved stopper portion. The protruded stopper portion is provided on the inner peripheral wall of the trunnion power-roller accommodating portion. This causes increased man-hour and manufacturing costs.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a toroidal continuously variable transmission having a simple and inexpensive power roller support structure, which is capable of properly restricting or limiting a horizontal displacement of a roller-and-cage bearing assembly relative to a trunnion power-roller accommodating portion, realizing low manufacturing costs, and of reliably supporting the load acting on the power roller, and of certainly preventing the roller-and-cage bearing assembly to be brought into contact with either an input disk or an output disk during power transmission.

In another aspect, the present invention provides a toroidal continuously variable transmission that includes input and output disks coaxially arranged and opposing each other, a power roller interposed between the input and output disks under axial preload; the power roller comprising a power-roller inner ring kept in contact with the input and output disks, a power-roller outer ring receiving a contact pressure transferred from the input and output disks to the power-roller inner ring under the axial preload, and a power-roller bearing interleaved between the power-roller inner and outer rings, a power-roller support comprising a trunnion having a power-roller accommodating portion that supports the power roller to permit a tilting motion of the power roller about a trunnion axis perpendicular to a rotation axis of the power roller, a roller-and-cage bearing assembly interleaved between the power-roller outer ring and the power-roller accommodating portion to permit a parallel translation of the power roller in an axial direction of the input and output disks, the roller-and-cage bearing assembly comprising a cage formed with a plurality of roller holes, and a plurality of rollers mounted in the plurality of roller holes, the cage having a portion defining a slotted hole, a protruded portion attached to the power-roller accommodating portion so that the protruded portion extends from the power-roller accommodating portion toward the cage in a direction of the rotation axis of the power roller, the slotted hole and the protruded portion being loosely fitted to each other to define a predetermined clearance that limits a displacement of the roller-and-cage bearing assembly in a direction perpendicular to both the rotation axis of the power roller and the trunnion axis to a set displacement.

According to another aspect of the invention, a toroidal continuously variable transmission includes input and output disks coaxially arranged and opposed to each other, a power roller interposed between the input and output disks under axial preload; the power roller comprising a power-roller inner ring kept in contact with the input and output disks, a power-roller outer ring receiving a contact pressure transferred from the input and output disks to the power-roller inner ring under the axial preload, and a power-roller bearing interleaved between the power-roller inner and outer rings, a power-roller support comprising a trunnion having a power-roller accommodating portion that supports the power roller to permit a tilting motion of the power roller about a trunnion axis perpendicular to a rotation axis of the power roller, the power-roller accommodating portion comprising a power-roller support base surface, a pair of upper and lower inner wall surfaces, and a pair of sloped surfaces each interconnecting the power-roller support base surface and either of the upper and lower inner wall surfaces, a roller-and-cage bearing assembly interleaved between the power-roller outer ring and the power-roller accommodating portion to permit a parallel translation of the power roller in an axial direction of the input and output disks, the roller-and-cage bearing assembly comprising a cage formed with a first group of roller holes that is closely juxtaposed to each other in a direction perpendicular to both the rotation axis of the power roller and the trunnion axis and facing a first sloped surface of the pair of sloped surfaces and a second group of roller holes that is closely juxtaposed to each other in a direction perpendicular to both the rotation axis of the power roller and the trunnion axis and facing a second sloped surface of the pair of sloped surfaces, and a first group of rollers mounted in the first group of roller holes and a second group of rollers mounted in the second group of roller holes to receive both a force component acting on the power roller in a direction of the rotation axis of the power roller and a force component transmitted from each of the input and output disks to the power roller and acting in a direction of the trunnion axis, the cage having a portion defining a slotted hole, a protruded portion attached to the power-roller support base surface of the power-roller accommodating portion so that the protruded portion extends from the power-roller support base surface toward the cage in the direction of the rotation axis of the power roller, the slotted hole and the protruded portion being loosely fitted to each other to define a predetermined clearance that limits a displacement of the roller-and-cage bearing assembly in the direction perpendicular to both the rotation axis of the power roller and the trunnion axis to a set displacement, while defining a less clearance along the trunnion axis.

The toroidal continuously variable transmission may further comprise a first lubricating oil supply port formed in the power-roller support base surface, a second lubricating oil supply port formed in a back face of the power-roller outer ring, a lubricating oil supply pipe intercommunicating the first and second lubricating oil supply ports, a disk-shaped member mounted on the lubricating oil supply pipe to prevent lubricating oil leakage, and an escape hole formed in the cage for escaping and protruding the disk-shaped member toward the back face of the power-roller outer ring, and wherein the predetermined clearance is a clearance defined between the disk-shaped member and the escape hole in the direction perpendicular to both the rotation axis of the power roller and the trunnion axis.

The other features of this invention will become understood from the following description with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, particularly toFIG. 1, a toroidal continuously variable transmission10of the embodiment is combined with a lock-up torque converter12. As seen from the left-hand side ofFIG. 1, engine torque (driving torque) is transmitted via lock-up torque converter12to an input shaft14of toroidal CVT10. Lock-up torque converter12is comprised of a pump impeller12a, a turbine runner12b, a stator12c, a lock-up clutch12d, an apply-pressure chamber12e, a release-pressure chamber12f, and the like. Transmission input shaft14is rotatably located at the center of lock-up torque converter12d. Input shaft14is connected to a forward and reverse changeover mechanism36. Forward and reverse changeover mechanism36is comprised of a planetary gearset42, a forward clutch44, and a reverse brake46. Planetary gearset42consists of a pinion carrier42awith two planet pinions, a ring gear42bbeing in meshed-engagement with these planet pinions, and a sun gear42c. Pinion carrier42ais connected to a torque-transmission shaft16. A first toroidal CVT mechanism (or a first variator unit)18and a second toroidal CVT mechanism (or a second variator unit)20are set in tandem and arranged in the interior space of a transmission casing22. Such an arrangement of the two variators is often called as a “dual cavity type toroidal CVT”. A valve body of a CVT control system is laid out within a base denoted by reference sign64. First and second toroidal CVT mechanisms18and20have the same construction. First toroidal CVT mechanism18is comprised of a pair of input and output disks18aand18bcoaxially arranged and opposing each other, a pair of power rollers18cand18d, a power roller support or a trunnion (described later in reference toFIG. 2), and a servo piston serving as a hydraulic actuator (described later in reference toFIG. 2). Each of input and output disks18aand18bhas a torus surface. Power rollers18cand18dare interposed between input and output disks18aand18bsuch that power rollers18cand18dare in contact with the torus surfaces of the input and output disks under axial preload. Power rollers18cand18dare symmetrically arranged to each other with respect to torque transmission shaft16.

Similarly to the first toroidal CVT mechanism18, the second toroidal CVT mechanism20is comprised of a pair of axially opposing input and output disks20aand20b, a pair of power rollers20cand20d, a power roller support or a trunnion (described later in reference toFIG. 2), and a servo piston serving as a hydraulic actuator (described later in reference toFIG. 2). First and second CVT mechanisms18and20are arranged in reverse to each other on torque transmission shaft16such that output disk18bincluded in first toroidal CVT mechanism18and output disk20bincluded in second toroidal CVT mechanism20are opposed to each other with respect to an output gear28. Of input disks18aand20a, input disk18aof first toroidal CVT mechanism18is preloaded axially rightwards (viewingFIG. 1) by means of a loading cam device34. Loading cam device34is designed to produce a magnitude of the axial preload substantially proportional to input torque transmitted from lock-up torque converter12to input shaft14. Loading cam device34has a slide bearing38, and a loading cam34asupported on torque transmission shaft16via slide bearing38. On the other hand, input disk20aof second toroidal CVT mechanism20is permanently biased axially leftwards (viewingFIG. 1) by means of a coned disc spring40. Each of input disks18aand20ais supported on torque transmission shaft16by way of ball-spline-engagement (ball splines24and26), so as to permit each of input disks18aand20ato axially move relative to the torque transmission shaft, and to rotate about the torque transmission shaft.

During ratio changing, each of power rollers18c,18d,20c, and20dis tilted or inclined so that the magnitude of a gyration angle based on a desired transmission ratio is attain. In accordance with a continuous change in the gyration angle, driving torque is transmitted to each of output disks18band20bwhile steplessly varying an input speed of each of input disks18aand20a. Output disks18band20bare connected to output gear28by way of spline-engagement. In contrast to input disks18aand20a, each of output disks18band20bis axially stationary. Output gear28is fitted to torque transmission shaft16so that the output gear is rotatable relative to the torque transmission shaft. The driving torque is further transmitted from the output disks through output gear28to a gear30afixedly connected to a countershaft30. Output gear28and gear30aform a first torque transmission mechanism32. The driving torque transmitted to countershaft30is further transmitted from a gear52through an idler gear54and a gear56to a transmission output shaft50coupled to a propeller shaft60. Gear52is fixedly connected to countershaft30, while gear56is fixedly connected to output shaft50. Idler gear54is in meshed-engagement with both the gears52and56. Gears52,56, and idler gear54construct a second torque transmission mechanism48.

Referring now toFIG. 2, there is shown the system block diagram of the CVT control system used to tilt each of power rollers18c,18d,20c, and20din order to obtain a gyration angle corresponding to a transmission ratio. As shown inFIG. 2, each of power rollers18c,18d,20c, and20dis supported on one end of each of trunnions17a,17b,27a, and27b. Power rollers18c,18d,20c, and20dare rotatable about the respective power-roller rotation axes15a,15b,25a, and25b. As described later, the four power rollers are supported by the respective trunnions17a,17b,27a,27b, in such a manner as to permit parallel translation of each of the power rollers in the right-and-left direction (also referred to as being in the horizontal direction or in the axial direction of the input and output disks) relative to the associated trunnion. More precisely, the right-and-left direction is defined as a direction perpendicular to both the rotation axis of the power roller and a trunnion axis (described later).

Each of servo pistons70a,70b,72a, and72bis provided on the other end of each of trunnions17a,17b,27a, and27b, so as to tilt each of the power rollers by shifting trunnions17aand17bof first toroidal CVT mechanism18in opposite directions of their trunnion axes perpendicular to the power-roller rotation axes and by shifting trunnions27aand27bof second toroidal CVT mechanism20in opposite directions of their trunnion axes perpendicular to the power-roller rotation axes. The hydraulic control system that controls the respective servo pistons70a,70b,72a, and72b, includes a high-pressure oil passage74communicating a high-pressure chamber, a low-pressure oil passage76communicating a low-pressure chamber, and a ratio change control valve78having a port78aconnected to high-pressure oil passage74, a port78bconnected to low-pressure oil passage76, a line-pressure port78c, and a ratio change control spool78d. Line pressure is produced by a hydraulic pressure source containing an oil pump80and a pressure relief valve82. The line pressure is supplied into line-pressure port78cof ratio change control valve78. Ratio change control spool78dis mechanically linked via a lever84to a precision cam86.

The precision cam86serves to detect a vertical displacement of trunnion17aalong its trunnion rod (trunnion axis) and a tilting motion of trunnion17a(or a gyration angle of power roller18c), for feeding a change in the vertical displacement of trunnion17aand a change in the tilting motion of trunnion17aback to the ratio change control valve. A ratio change control sleeve78eis also provided in ratio change control valve78. Ratio change control sleeve78ecan be moved axially by means of a stepping motor88whose angular steps are electromagnetically controlled by a CVT controller110.

The CVT controller110generally comprises a microcomputer. The CVT controller includes an input/output interface (I/O), memories (RAM, ROM), and a microprocessor or a central processing unit (CPU). The input/output interface (I/O) of CVT controller110receives input information from various engine/vehicle sensors, namely a throttle opening sensor112, an engine speed sensor114, a transmission input shaft speed sensor (simply, a transmission input speed sensor)116, and a transmission output shaft speed sensor (simply, a transmission output speed sensor)118. A vehicle speed sensor is often used as the transmission output speed sensor. Within CVT controller110, the central processing unit (CPU) allows the access by the I/O interface of input informational data signals from the previously-discussed engine/vehicle sensors112,114,116, and118. The CPU of CVT controller110is responsible for carrying the stepping motor control program stored in memories and is capable of performing necessary arithmetic and logic operations containing a toroidal-CVT ratio control management processing (not shown). Computational results (arithmetic calculation results), that is, a calculated output signal is relayed via the output interface circuitry of the CVT controller to the stepping motor.

Supports of four power rollers18c,18d,20c, and20dare the same. Therefore, only the support structure of power roller18cis hereunder described in detail in reference toFIG. 3.

Trunnion17ais formed at its one end with a recessed power-roller accommodating portion91. Power-roller accommodating portion91has a substantially C shape in cross section. As can be seen inFIG. 3, power-roller accommodating portion91is formed with a flat power-roller support base surface91a, a pair of vertically opposing upper and lower flat inner wall surfaces91band91c, an upper sloped surface91dinterconnecting support base surface91aand upper flat inner wall surface91b, and a lower sloped surface91einterconnecting support base surface91aand lower flat inner wall surface91c. Power roller18cis accommodated in the power-roller accommodating portion91and supported by trunnion17ain such a manner as to permit parallel translation of power roller18cin the right-and-left direction (in the horizontal direction). Trunnion17ais provided to tilt or incline about its trunnion axis (an axis of tilting motion)19aperpendicular to the rotation axis15aof power roller18c, supporting power roller18c. Power roller18cis comprised of a power-roller ball bearing92, a power-roller inner ring93, a power-roller outer ring94, and a roller bearing95. Power-roller inner ring93is kept in contact with input and output disks18aand18b. Power-roller outer ring94has a central shaft portion94aon which power-roller inner ring93is rotatably supported via roller bearing95. Power-roller outer ring94is supported on the previously-discussed power-roller support base surface91aso that the rotation axis of the power roller is perpendicular to a flat plane of power-roller support base surface91a. Power-roller ball bearing92is interleaved between power-roller inner and outer rings93and94. Under axial preload produced by loading cam device34, a contact pressure transferred from input and output disks18aand18bto power-roller inner ring93is received by power-roller outer ring94through power-roller ball bearing92.

A roller-and-cage bearing assembly96is interposed between power-roller outer ring94and power-roller accommodating portion91of trunnion17a, for supporting power roller18c, while permitting the parallel translation of power roller18cin the axial direction of input and output disks18aand18b. Upper and lower roller bearing portions of roller-and-cage bearing assembly96are located on the respective sloped surfaces91dand91e. The upper and lower roller bearing portions, located on the respective sloped surfaces91dand91e, receive a force component acting on power roller18cin a direction of power-roller rotation axis15a(or in the fore-and-aft direction inFIG. 3), and a force component transmitted from each of input and output disks18aand18bto power roller18cand acting in a direction of trunnion axis19a(in the vertical direction inFIG. 3). To more effectively receive these force components, the upper and lower roller bearing portions of the roller-and-cage bearing assembly are symmetrical with respect to the rotation axis of the power roller.

The toroidal CVT is equipped with a lubricating system generally composed of a trunnion lubrication system mainly used for lubrication of joints, ball and roller bearings and for lubrication and cooling of the power rollers and the input and output disks, and a rolling contact surface lubrication system used for lubrication of rolling contact surfaces between the power roller and input and output disks. Of these lubrication systems, a former lubrication system is hereunder described in detail in reference toFIG. 3. Trunnion17ais formed with a trunnion lubricating oil passage97. Some of pressure oil discharged from a hydraulic pump (not shown) passes through an oil cooler (not shown) and then the properly-cooled traction oil (called “continuously variable transmission fluid” abbreviated to “CVTF”) is supplied to trunnion lubricating oil passage97for lubricating and cooling the power roller and trunnion. After lubrication, almost all of the traction oil drains back into an oil reservoir (not shown). Power-roller outer ring94is formed with a power-roller outer ring lubricating oil passage98for delivering lubricating oil (traction oil) from trunnion lubricating oil passage97through power-roller outer ring lubricating oil passage98to both ball bearing92and roller bearing95. A lubricating oil supply port97ais formed in power-roller support base surface91a, whereas a lubricating oil supply inlet98ais formed in the back face of power-roller outer ring94. One end of a lubricating oil supply pipe99is fixedly connected to lubricating oil supply port97a, while the other end of lubricating oil supply pipe99is fitted into lubricating oil supply inlet98a, so as to intercommunicate the two lubricating oil supply ports97aand98a. To prevent oil leakage, an axially-protruded, disk-shaped member101and an elastic member (or a restricting member)100are attached onto or provided on the outer periphery of lubricating oil supply pipe99, so that disk-shaped member101is permanently forced toward the back face of power-roller outer ring94by restricting member100, for good sealing.

The horizontal-displacement limiting structure for roller-and-cage bearing assembly96attached to the power-roller support of the toroidal CVT of the embodiment is hereunder described in detail in reference toFIGS. 4A and 4B.

As seen inFIGS. 4A and 4B, roller-and-cage bearing assembly96is comprised of a cage96aand a plurality of rollers96b1(in a first group) and96b2(in a second group). Cage96ais formed with a first group of roller holes96c1(a plurality of upper roller holes) closely juxtaposed and parallel to each other in the right-and-left direction (in the horizontal direction), and a second group of roller holes96c2(a plurality of lower roller holes) closely juxtaposed and parallel to each other in the right-and-left direction. First group of roller holes96c1face the sloped surface91d, while second group of roller holes96c2face the sloped surface91e. Rollers96b1and96b2are mounted in the respective roller-hole groups96c1and96c2, so that the rollers96b1and96b2are rotatable about their axes.

The horizontal-displacement limiting structure for roller-and-cage bearing assembly96is formed by a substantially central, oval slotted hole96dformed in cage96aof roller-and-cage bearing assembly96and the aforesaid disk-shaped member101coaxially arranged on lubricating oil supply pipe99and loosely fitted into oval slotted hole96d. The substantially central, oval slotted hole96dserves as an escape hole through which the disk-shaped member101axially escapes or protrudes toward the back face of power-roller outer ring94. A major axis of oval slotted hole96dextends in the right-and-left direction, while a minor axis of oval slotted hole96dextends in the vertical direction (seeFIG. 4B). Furthermore, as can be seen inFIG. 4B, the oval slotted hole96dhas a flat portion96eat the top and an equal flat portion96fat the bottom while the left side portion96gand the right side portion96hof the oval slotted hole96deach have the shape of opposing elliptical portions.

More specifically, while loosely fitting disk-shaped member101into the oval slotted hole96d, a predetermined clearance (t, t) therebetween is determined in the right-and-left direction. The predetermined clearance (t, t) is defined in a direction of a major axis of the oval slotted hole96dor in the right-and-left direction shown inFIG. 4B. In contrast, there is lesser clearance in the vertical direction (or the direction that is perpendicular to the right-and-left direction inFIG. 4B). The predetermined clearance (t, t) corresponds to a horizontal clearance that acts to restrict or limit the horizontal displacement (i.e., a displacement of roller-and-cage assembly96relative to trunnion17ain the right-and-left direction) to a maximum allowable set displacement. The actual values of the predetermined clearance (t, t) is determined using design considerations that are well within the abilities of those skilled in the art. For example, in one embodiment, the value of the “t” is selected such that the end rollers of the roller-and-cage assembly (for example, either96b1or96b2) do not protrude out and contact the trunnion (for example, trunnion17a) when the cage96ais at its extreme right or left position. In this way, the edge rollers (for example,96b1or96b2) do not contact the trunnion when the cage96ais at its extreme right or left position and the rollers are not scratched or damaged by the trunnion or vice versa. Also, as shown inFIG. 4B, in one embodiment, each of the flat portions96eand96falso have the same dimensions (t, t) corresponding to the predetermined clearances (t, t) on the right and left side between the oval slotted hole96dand the disk-shaped member101. In one embodiment, the flat portions (t, t) are arranged to be symmetrical about the trunnion axis in the right-and-left direction.

The toroidal CVT of the embodiment having the power-roller support equipped with the horizontal-displacement limiting structure for roller-and-cage bearing assembly96operates as follows.

Power rollers18c,18d,20c, and20dare tilted by slightly shifting trunnions17a,17b,27a, and27bin the respective directions of trunnion axes (a direction of trunnion axis19ain case of trunnion17a) so as to change the transmission ratio.

More specifically, as soon as an axial displacement of ratio change control sleeve occurs by rotating stepping motor88in response to a command signal corresponding to the desired transmission ratio and generated from CVT controller90, working fluid is supplied into a first servo-piston chamber of each of servo pistons70a,70b,72a, and72b. At the same time, working fluid is exhausted from a second servo-piston chamber of each of the servo pistons. As a result of this, each of trunnions17a,17b,27a, and27bis slightly shifted in the direction of its trunnion axis. Thus, the center of rotation of each of power rollers18c,18d,20c, and20dis vertically offset from the center of rotation of the disks. By virtue of a side-slip force occurring in a very limited contact zone between each of power rollers18c,18d,20c, and20dand the associated input and output disks owing to the slight vertical offset (the vertical displacement), power rollers18c,18d,20c, and20dare tilted. The tilting motion (a gyration angle or tilt angle of each power roller) of trunnion17aand the vertical offset (vertical displacement) of trunnion17aare mechanically transmitted via precision cam86and lever84to ratio change control spool78d. By way of feedback action of precision cam86and lever84, ratio change control spool78dis held at a balanced position with respect to ratio change control sleeve78edriven by stepping motor88. In this manner, as soon as the predetermined gyration angle corresponding to the desired transmission ratio has been reached, the vertical displacement of each of the trunnions is returned to zero, in other words, the power-roller rotation axis of each of power rollers18c,18d,20c, and20dis leveled with respect to the center of rotation of the disks, so as to stop the tilting motion of each of the power rollers. As discussed above, the transmission ratio is determined depending on the gyration angle of each of power rollers18c,18d,20c, and20d.

Load Supporting and Sliding Action of Power Roller

Hereunder described in detail is the load supporting and sliding action of power roller18cselected as a representative. This is because the four power rollers exhibit the same load supporting and sliding action.

During power transmission, a contact pressure transferred from input and output disks18aand18bto power-roller inner ring93of power roller18cunder axial preload is received by power-roller outer ring94through power-roller ball bearing92. During power transmission, a force component acting on power roller18cin the direction of power-roller rotation axis15aand a force component transmitted from each of input and output disks18aand18bto power roller18cand acting in the direction of trunnion axis19aare both received by means of roller-and-cage bearing assembly96interposed between power-roller outer ring94and power-roller accommodating portion91. Therefore, during application of the force component transmitted from each of input and output disks18aand18bto power roller18cand acting in the direction of trunnion axis19a, that is, the vertical direction, the vertical force component is reliably received by roller-and-cage bearing assembly96. At this time, assuming that a horizontal force component acts on power roller18c, roller-and-cage bearing assembly96carries or moves power roller18cin the right-and-left direction (in the horizontal direction) by way of a low rolling resistance, with the rollers rolling. That is, the upper and lower roller bearing portions of roller-and-cage bearing assembly96located on the respective sloped surfaces91dand91eact to permit smooth parallel translation of power roller18cin the right-and-left direction (in the horizontal direction), while certainly effectively receiving the vertical force component acting on the power roller during power transmission. Even in the presence of a slight error in relative position between the power roller and the respective disk owing to deformation of the input and output disks during power transmission, or in presence of a slight misalignment after installation, the slight error can be effectively absorbed by way of smooth parallel translation of power roller18crelative to trunnion17a. Due to the smooth parallel translation, it is possible to accurately uniformly balance a pushing force transmitted from input disk18ato power roller18cand a pushing force transmitted from output disk18bto power roller18c. Thus, it is possible to avoid an unbalance between the pushing force transmitted from input disk18ato power roller18cand the pushing force transmitted from output disk18bto power roller18c, thereby suppressing or preventing an undesired slippage from occurring in the very limited contact zone between power roller18cand each of input and output disks18aand18b. Furthermore, the power-roller support structure of the toroidal CVT of the embodiment eliminates the necessity of a fit hole for a conventional eccentric pivot shaft structure used to support a power roller. As a consequence, it is possible to avoid stress concentration around the fit hole, thereby ensuring the increased mechanical strength and rigidity of the trunnion and thus suppressing undesired deformation of the trunnion. For the reasons discussed above, there is less deviation of an actual contact point between power roller18cand each of input and output disks18aand18bfrom a design contact point. This prevents a bearing stress from increasing owing to unbalanced load, and reduces an unintended ratio change, which may occur due to deformation of the input and output disks or deformation of the trunnion.

Position Limiting Action for Roller-and-Cage Bearing Assembly

Hereinafter described in detail is the position limiting action for roller-and-cage bearing assembly96in the support structure of power roller18c(selected as a representative) on trunnion17a.

During ratio changing, to keep power roller18cpermanently in contact with input and output disks18aand18birrespective of tilting motion of power roller18c, the input disk is forced toward the output disk by way of axial preload produced by loading cam device34. At this time, only the input disk18ais biased and shifted toward output disk18bby means of loading cam device34. On the other hand, trunnion axis19aof trunnion17ais a fixed axis, which is not moveable in the axial direction of input and output disks18aand18b. Therefore, in order to keeping power roller18cin contact with input and output disks18aand18bby means of loading cam device34, while following slight changes in relative distance between input and output disks18aand18b, power roller18cis supported in a manner so as to permit parallel translation of the power roller18citself in the axial direction of input and output disks18aand18b. Additionally, even when there is a slight error in relative position between the power roller and the respective disk, occurring owing to deformation of input and output disks18aand18bduring power transmission or in presence of a slight misalignment after installation, roller-and-cage bearing assembly96serves to permit the parallel translation of power roller18cin the right-and-left direction to effectively absorb or compensate for the slight error. Assuming that the parallel translation of power roller18crepeatedly takes place owing to the previously-noted factors, there is an increased tendency for roller-and-cage bearing assembly96to be protruded out of power-roller accommodating portion91of trunnion17a. This is because a horizontal displacement of cage96aobtained by pushing cage96aby power roller18cis somewhat different from that obtained when an external force applied to power roller18cis released. However, according to the power-roller support structure of the toroidal CVT of the embodiment, the predetermined clearance (t, t) is defined between oval slotted hole96dformed in cage96aof roller-and-cage bearing assembly96and disk-shaped member101mounted on lubricating oil supply pipe99, such that the horizontal displacement of roller-and-cage bearing assembly96relative to trunnion17ais limited to the maximum allowable set displacement, which is determined by the size of predetermined clearance (t, t). Therefore, the horizontal-displacement limiting structure of the toroidal CVT of the embodiment can reliably prevent roller-and-cage bearing assembly96from being protruded out of power-roller accommodating portion91of trunnion17aor prevent roller-and-cage bearing assembly96from falling out of trunnion17a. In other words, it is possible to maintain roller-and-cage bearing assembly96in a positional range within which the roller-and-cage bearing assembly can provide adequate support for power roller18c.

In addition, the disk-shaped member101, which axially slightly protrudes from flat power-roller support base surface91aof power-roller accommodating portion91of trunnion17atoward the back face of power roller18cand is loosely fitted to substantially central, oval slotted hole96dformed in cage96a, is used as a part of the horizontal-displacement limiting structure of the toroidal CVT of the embodiment. The disk-shaped member101is usually used as a sealing member in the trunnion power-roller support structure. Thus, in the horizontal-displacement limiting structure of the toroidal CVT of the embodiment, it is unnecessary to separately provide a stopper (a protruded stopper) on flat power-roller support base surface91aof power-roller accommodating portion91. Furthermore, the oval slotted hole96dengaged with disk-shaped member101can be easily produced by horizontally enlarging a fit hole (usually formed as a circle) for disk-shaped member101, taking into account the predetermined clearance (t, t), i.e., the maximum allowable set displacement of roller-and-cage bearing assembly96relative to trunnion17a. Such machining is very easy, thus reducing man-hour and manufacturing costs.

The entire contents of Japanese Patent Application No. P2001-035535 (filed Feb. 13, 2001) is incorporated herein by reference.

While the foregoing is a description of the preferred embodiments carried out the invention, it will be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the scope or spirit of this invention as defined by the following claims.