Power roller bearing for toroidal-type continuously variable transmission

A power roller bearing for rotatably supporting a power roller of a toroidal-type continuously variable transmission, having: an inner ring; an outer ring; a plurality of balls respectively interposed between the inner and outer rings; and, a retainer for holding the balls therein, wherein the retainer includes a plurality of pockets for storing the balls therein at equi-distant positions in the peripheral direction of the retainer, and the inner peripheral portions of the pockets are respectively formed of elastic material that, when the power roller rotates, allows the balls to shift from the equi-distant positions.

BACKGROUND OF THE INVENTION

The present invention relates to a power roller bearing for a toroidal-type continuously variable transmission for use, for example, in a power transmission system of a vehicle.

A half-toroidal-type continuously variable transmission, as shown partially inFIGS. 9 and 10, comprises a power roller13between an input disk11and an output disk12. The power roller13rotates about a displacement shaft15which is disposed on a trunnion14. The trunnion14is supported by a pair of trunnion shafts16so as to be swung with respect to a support body17. Between the trunnion14and power roller13, there is interposed a power roller bearing18.

The power roller bearing18comprises an inner ring20composed of a portion of the power roller13, an outer ring21disposed to be opposed to the inner ring20, a plurality of balls22respectively interposed between a raceway21aformed in the outer ring21and a raceway20aformed in the inner ring20, a ring-shaped retainer24for holding the respective balls22in a freely rotatable manner, and a thrust bearing25interposed between the outer ring21and trunnion14. The respective balls22are rotatably stored in their associated pockets26formed in the retainer24. These pockets26are disposed at an equal pitch, that is, at equally distant (equi-distant) positions in the peripheral direction of the retainer24.

When the toroidal-type continuously variable transmission is in operation, as shown inFIG. 9, the power roller bearing18and disks11,12are contacted with each other at two contact points C1, C2, thereby providing a so called two-point pressing state. InFIG. 9, θ designates the contact angle. Therefore, the power roller bearing18receives the thrust component of a pressing force P at the contact points C1, C2and, at the same time, it generates the radial-direction component at the mutually 180° opposed position on the circumference of the power roller13. Thus, the circular-ring-shaped power roller bearing18is compressed in the radial direction and, due to this compression force, the inner ring20tends to deform into an elliptical shape.

As a result of this, the load distribution on the circumference of the power roller13is caused to vary. The balls22rotate at high speeds while they are receiving such variable loads and, therefore, the rolling portions of the balls22generate a lot of heat. That is, the power roller bearing18is used under the severer conditions than an ordinary bearing.

Also, when the toroidal-type continuously variable transmission is in operation, at the traction contact points C1, C2for transmission of power between the power roller13and the respective disks11,12, there are generated such tangential-direction forces Ft as shown inFIGS. 10 and 11. A force 2Ft, which is the sum of two forces Ft respectively generated at the two contact points C1, C2, provides a force Fr (which is shown inFIG. 10) going in a direction to fall down the power roller bearing18, thereby causing the above-mentioned compression force to unbalance in magnitude.

The orbital speed of the balls22of the power roller bearing18used under the above conditions provide such distribution as shown by arrow marks inFIG. 12. That is, in case where the rotation direction of the retainer24is shown by the arrow mark R, the orbital speeds R1of the respective balls22situated on the 2Ft side are slower than the orbital speeds R2of the balls22situated on the anti-2Ft side.

In this manner, when the power roller13rotates, since there are produced orbital speed differences between the respective balls22, as shown by the line L1inFIG. 13, the balls22are going to roll in such a manner that they are shifted from the above-mentioned their respective equi-distant positions. However, in fact, because the movements of the balls22are restricted by the retainer24, as shown inFIG. 14, the contact loads between the balls22and retainer24vary according to the positions of the balls22.

That is, the contact loads P2of the balls22situated on the anti-2Ft side act on the balls22so as to push the retainer24in the rotation direction R. On the other hand, the contact loads P1of the balls22situated on the 2Ft side act on the balls22so as to push the retainer24in the opposite direction to the rotation direction R. Due to this, the inner peripheral surfaces of the pockets26of the retainer24and balls22are contacted with each other, which results in the lowered durability of the retainer24.

Also, when the balls22are contacted with the retainer24, they receive a reactive force from the retainer24. Due to this, the actual shifting amounts of the balls22, as shown by the line L2inFIG. 13, become smaller by aM than their ideal shifting amounts (line L1). That is, the respective balls22are caused to slide on the rolling surface by the amount ofM, which reduces the efficiency of the toroidal-type continuously variable transmission.

In JP-A-2001-4003, there is disclosed a technique in which, in order to reduce phase differences to be generated between balls, pockets are made slightly longer in the peripheral direction of a retainer (that is, the pockets are respectively formed as elongated pockets) to thereby widen a clearance between the balls and the inner peripheral surfaces of the pockets. According to this conventional technique, in a high load area, the balls are able to shift in the longitudinal direction of the pockets and, therefore, the orbital speed differences of the balls can be absorbed. However, in a low load area, since the phase differences between the balls are small, the balls tend to stay in the vicinity of the centers of the pockets; and, because the above-mentioned clearance is relatively large, there is a possibility that the retainer can be vibrated in the peripheral direction thereof.

SUMMARY OF THE INVENTION

In view of the above circumstances of the related art, it is an object of the invention to provide a power roller bearing which can restrict the slippage between balls and rolling surfaces to thereby be able to prevent the efficiency of the power roller bearing from being lowered.

In attaining the above object, according to the invention, there is provided a power roller bearing for rotatably supporting a power roller of a toroidal-type continuously variable transmission, comprising: an inner ring; an outer ring; a plurality of balls interposed between the inner and outer rings; and, a retainer for holding the balls therein, wherein the retainer includes a plurality of pockets for storing the balls therein at equi-distant positions in the peripheral direction of the retainer, and the inner peripheral portions of the pockets are respectively formed of such elastic material that, when the power roller rotates, allows the balls to shift from the equi-distant positions.

According to the above construction of the invention, it is preferable that the inside diameter of each of the pockets is larger than the outside diameter of each of the balls, the inside diameter of the opening of the pocket is smaller than the outside diameter of the ball, and the opening has such elasticity that allows the opening to spread out to a size equal to or larger than the outside diameter of the ball.

Since, when the power roller rotates, for the above-mentioned reason, there are produced the orbital speed differences between the balls, the balls are going to roll shifted from their respective equi-distant positions. The retainer, which is used in the power roller bearing according to the invention, due to its elasticity, allows the balls to roll shifted from their respective equi-distant positions. Thus, the reactive forces, which are given to the balls from the retainer when they are contacted with each other, are small. Therefore, the shifting amounts of the balls can be made to approach the ideal shifting amounts, thereby being able to restrict slippage between the balls and rolling surfaces.

In the present invention, preferably, the inside diameter of each of the pockets may be larger than the outside diameter of each of the balls, the inside diameter of the opening of each pocket may be smaller than the outside diameter of each ball, and the retainer may have such elasticity that allows the opening to spread more than the outside diameter of the ball. In this case, the balls can be easily inserted into their associated pockets. This makes it possible to prevent the balls incorporated into the retainer from slipping out of the retainer.

Also, according to the invention, there is provided a power roller bearing for rotatably supporting a power roller of a toroidal-type continuously variable transmission, comprising: an inner ring; an outer ring; a plurality of balls interposed between the inner and outer rings; and, a retainer for holding the balls therein, wherein the retainer includes a plurality of pockets for storing the balls there in at equi-distant positions in the peripheral direction of the retainer and, in the inner peripheral portion of each of the pockets, there are disposed a pair of suspension mechanisms which, when the power roller rotates, allow the balls to shift from the equi-distant positions.

According to the above construction of the invention, it is preferable that a pair of suspension mechanisms are disposed in the interior of their associated pocket so as to be opposed to each other with their associated ball between them.

According to the above construction of the invention, it is preferable that each of the balls can be inserted into and removed from the associated pocket and, in a state where the associated ball is inserted in the associated pocket, the ball is held by the pair of suspension mechanisms.

In a preferred embodiment of the invention, in the interior of each of the pockets, there are disposed a pair of suspension mechanisms which are opposed to each other with their associated ball between them. Also, in this preferred embodiment of the invention, the balls to be inserted into their respective pockets can be inserted into and removed from such pockets; and, in a state where the balls are respectively inserted into the pockets, the balls are held by their respective suspension mechanisms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, description will be given below of a power roller bearing18A according to a first embodiment of the invention with reference toFIGS. 1 to 4.

As shown inFIG. 1, between a power roller13and a trunnion14, there is interposed a power roller bearing18A. The power roller13, as in the half-toroidal-type continuously variable transmission shown inFIG. 9, is interposed between an input disk and an output disk. The power roller13rotates about a displacement shaft15disposed on the trunnion14. The trunnion14is supported by a pair of trunnion shafts16so as to be swung with respect to a support body17.

The power roller bearing18A comprises an inner ring20composed of a portion of the power roller13, an outer ring21disposed to be opposed to the inner ring20, a plurality of balls22respectively stored between a raceway21aformed in the outer ring21and a raceway20aformed in the inner ring20, a ring-shaped retainer24A for holding the balls22so as to be able to rotate, and a thrust bearing25interposed between the outer ring21and trunnion14. The respective balls22are rotatably stored in their associated pockets26formed in the retainer24A. These pockets26are formed at an equal pitch, that is, at equi-distant positions in the peripheral direction of the retainer24A.

When the power roller13rotates, for the above-mentioned reason, the balls are going to rotate in such a manner that they are shifted from their respective equi-distant positions in accordance with the orbital speed differences between the balls22. The retainer24A is formed of such elastic material30that allows the balls22to rotate shifted from their respective equi-distant positions. As the elastic material30, there can be used elastomer formed of synthetic resin having rubber-like elasticity or sponge (porous elastomer) and synthetic rubber. The term “elastic material30” used in the present specification means material which can flex in the thickness direction thereof and the deforming area (elastic area) of which, within the elastic limit, is larger than metal such as brass.

In the toroidal-type continuously variable transmission, there is used special traction oil for the purpose of power transmission. Due to this, as the elastic material30forming the retainer24A, there may be recommended such material that does not substantially react with the base oil (such as mineral oil, or synthetic oil) of the traction oil; for example, fluorine-system resin or Teflon-system resin.

As shown inFIG. 4A, the inside diameter D1of the pocket26is larger than the outside diameter D2of the ball22. The inside diameter D3of the opening26aof the pocket26is smaller than the outside diameter D2of the ball22. As shown inFIG. 4B, the retainer24A has such elasticity as allows the opening26aof the pocket26to spread up to a size equal to or larger than the outside diameter D2of the ball22. Thanks to this elasticity, the bail22can be inserted into the pocket26, and also the ball22inserted into the pocket26can be taken out of the pocket26.

Since the retainer24A has such elasticity, when assembling the power roller bearing18A, the balls22can be inserted into their associated pockets26easily. And, the retainer24A itself is able to prevent the inserted balls22from slipping out of the pockets26. Therefore, there is eliminated the need to caulk a portion of the retainer after the balls are inserted into their respective pockets, which has been conventionally executed in the case of a metal-made retainer. This can simplify the assembling process of the power roller bearing and thus can reduce the cost of the power roller bearing.

In the power roller bearing18A, when the power roller13rotates, for the above-mentioned reason, in accordance with the orbital speed differences between the balls22, the balls22are going to roll at positions shifted from their respective equi-distant positions in a direction along the raceways20a,21a. When the balls22are going to roll at positions shifted from their respective equi-distant positions, the pockets26of the retainer24A having elasticity are allowed to shift together with the balls22in such a manner as shown exaggeratedly by two-dot chained lines inFIG. 3.

This allows the balls22to shift in position, whereby the balls22roll on their respective rolling surfaces with such ideal shift amounts (line L1) shown inFIG. 13. This can reduce slippage between the balls22and rolling surfaces (raceways20a,21a), thereby being able to enhance the efficiency and durability of the toroidal-type continuously variable transmission.

Now,FIG. 5shows a portion of a power roller bearing18B according to a second embodiment of the invention. In the case of the present power roller bearing18B, a retainer24B includes an elastic material30forming the inner peripheral portion of a pocket26and a frame member40made of high-rigidity material such as metal. In case where a large force is applied to a retainer as in a toroidal-type continuously variable transmission which provides a high output, such a combination of the elastic material30and frame member40as in the present embodiment can enhance the strength of the retainer24B.

By the way, in the above-mentioned power roller bearings18A,18B, in case where there is formed an oil groove which communicates with the pocket26, supply of the lubricating oil (traction oil) to the pocket26can be facilitated.

Now,FIG. 6shows a portion of a power roller bearing18C according to a third embodiment of the invention. In the present power roller bearing18C, a plurality of pockets26C are formed at equi-distant positions in the peripheral direction of a retainer24C. By the way, inFIG. 6, as the representatives of these pockets26C, there are shown only the two pockets26C formed at two positions which are disposed to be opposed by 180° to each other. Each of the pockets26C is an elongated hole which is slightly longer in the peripheral direction of the retainer24C. In the interior of each pocket26C, there are disposed a pair of suspension mechanisms50which are opposed to each other with a ball22between them.

Each of the suspension mechanisms50includes a member51to be contacted with the ball22and an elastic member52for energizing the member51toward the ball22. As typically shown inFIG. 7, the elastic member52has not only the function of a spring53but also the function of a damper54. By the way, in the present embodiment, the suspension mechanisms50are disposed in the peripheral direction of the retainer24C; however, even in case where the suspension mechanisms50are disposed in the diameter direction of the retainer24C, the suspension mechanisms50are able to perform similar functions.

In case where the elastic member52is made of rubber or a sponge, the suspension mechanism50can be made light in weight and easy to handle. As the material of the elastic member52, preferably, there may be used high molecular material such as fluorine-system material or Teflon-system material which is compatible with the traction oil.

The member51to be contacted with the ball22, preferably, may be formed of wear-resistant material. In case where the whole of the retainer24C is formed of wear-resistant material, it is difficult to machine the retainer24C. However, in case where only the member51to be contacted with the ball22is formed of wear-resistant material, it is possible to facilitate the machining of the retainer24C.

In the present power roller bearing18C, due to the above-mentioned orbital speed differences between the balls22, the balls22are allowed to move in directions shown by the arrow marks Q1, Q2inFIG. 6. The movements of the balls22due to the orbital speed differences are absorbed by the suspension mechanisms50.

As shown inFIG. 8, in the suspension mechanism50, a pair of members51to be contacted with the ball22are structured so as to be able to embrace the ball22between them and, therefore, the ball22can be inserted inside the pair of members51and also can be taken out of them. That is, in a state where the ball22is inserted into the pocket26, the ball22is held by the suspension mechanisms50. Employment of the thus structured suspension mechanisms50not only can enhance the assembling efficiency of the power roller bearing18C but also can omit the caulking step to thereby reduce the cost of the power roller bearing18C.

By the way, in enforcing the invention, of course, the composing elements of the invention, such as the inner ring and outer ring forming the power roller bearing, the shape of the retainer including the pockets, and the concrete examples of the elastic materials can be changed variously without departing from the gist of the invention.

According to the invention, when the power roller rotates, even in case where there are generated orbital speed differences between the respective balls held by the retainer, the respective balls are allowed to roll at positions shifted from their respective equi-distant positions. This can restrict. slippage between the balls and rolling surfaces, which in turn can prevent the efficiency of the toroidal-type continuously variable transmission from being lowered. Also, when compared with the conventional metal-made retainer, the reactive forces that are given to the balls from the present retainer when they are contacted with each other are small and also the contact loads are small, thereby being able to restrict the wear of the retainer and balls.

Also, according to the invention, when assembling the power roller bearing, the balls can be easily inserted into their associated pockets, while the retainer itself is able to prevent the inserted balls from slipping out of the pockets. According to the invention, there is eliminated the need for execution of time-and-labor taking machining operation, such as an operation to caulk a portion of the retainer after the balls are inserted into the pockets, which makes it possible to simplify the assembling process of the power roller bearing.

Further, according to the invention, in the high load area, the orbital speed differences between the balls can be absorbed; and, in the low load area, there can be restricted the vibrations of the retainer that are caused by clearances existing between the balls and pockets.