Trunnion supporting structure of a toroidal continuously variable transmission

Abstract: Plural trunnions (5) of a toroidal continuously variable transmission are joined by a link (7) so as to synchronize the axial displacement of the trunnions. A needle bearing (9) and a spherical joint (8) are interposed between the trunnions and link to permit rotation of the trunnions and inclination within a small range thereof. A wire (11) and pulleys (10) synchronize rotation of the trunnions. If the needle bearing were inclined with respect to the trunnion, an axial force would act on the trunnion as it rotates. The pulleys (10) prevent the relative inclination and axial displacement of the trunnion and spherical joint and thus prevent such an axial force from acting on the trunnion.

Description: FIELD OF THE INVENTION This invention relates to a trunnion support for supporting a power roller of a toroidal continuously variable transmission. BACKGROUND OF THE INVENTION In a toroidal continuously variable transmission, power rollers are supported by trunnions as disclosed for example by Tokkal Sho 57-47060 (& US-A-4 453 427) published by the Japanese Patent Office in 1982. The preamble of claim 1 was based on this document. A piston is fixed to these trunnions respectively. When a piston is driven hydraulically and the trunnions are displaced at right angles to a rotation shaft of an input disk and output disk. the gyration angle of the power roller varies, and a rotation ratio (drive ratio) of the input disk and output disk holding the power rollers varies. The upper ends and lower ends of these trunnions are respectively fitted to a link so that they can displace in synchronism. Each trunnion is joined to the link via a needle bearing and a spherical joint so as to permit it to rotate freely and incline through a very small range. When the power roller is inclined, a load acts on the trunnion in a direction other than the axial direction. This load is absorbed by the relative displacement of the spherical joint and a link. Since there is a small clearance between the needle bearing and the trunnion and between the needles, some needles may incline relative to the trunnion in this case. The inclined needles, however, exert an axial force on the trunnion when it rotates. According to an analysis, about 10% of the force of a radial load supported by the needle bearing acts on the trunnion in the axial direction. As a result, there is an excess or deficiency of the drive force exerted by the piston on the trunnion, and this results in scatter of torque transmitted by the power rollers. SUMMARY OF THE INVENTION It is therefore an object of this invention to prevent the inclined needles from exerting an external force on the trunnion. This object is achieved by a trunnion supporting structure having the features of claim 1. The subclaims contain preferred embodiments of the invention. In order to achieve the above object, this invention provides a trunnion supporting structure of a continuously variable transmission. The transmission comprises an input disk and output disk arranged facing each other on a rotation axis, power rollers for transmitting a torque between the disks, trunnions supporting the power rollers, a link connecting the trunnions, a wire for synchronizing the rotation of the plural trunnions and a pulley supported by the trunnion around which the wire is looped wherein a gyration angle of the power rollers is varied by driving the trunnions along a trunnion axis at right angles to the rotation axis. Further, the supporting structure comprises a needle bearing, and a spherical joint the needle bearing comprises plural rolling parts which roll along a circular path. So as to allow relative rotation between the trunnion disposed inside said circutor path and said spherical joint disposed outside said circular path. Furthermore, the trunnion comprises a shoulder part extending at right angles to the trunnion axis, wherein the spherical joint is fitted between the shoulder part and the pulley such that a displacement of the spherical joint in a direction of the trunnion axis is limited by the shoulder part and the pulley. The supporting structure further comprises a spring pushing the pulley towards the spherical joint. It is further preferable that the supporting structure further comprises a spacer filling a gap between the shoulder part and the spherical joint. In this case. it is further preferable that a contact area between the spacer and the shoulder part is set larger than a contact area between the spacer and the spherical joint. It is also preferable that the pulley is fixed to the trunnion by a nut, and the supporting structure further comprises a thrust needle bearing interposed between the spherical joint and the shoulder part, and a thrust needle bearing interposed between the spherical joint and the pulley. The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical cross-sectional view of a prior art toroidal continuously variable transmission to which this invention is applied. Fig. 2 is a vertical cross-sectional view of a trunnion support unit, not forming part of this invention. Fig. 3 is similar to Fig. 2, but showing a trunnion support unit according to the invention. Fig. 4 is similar to Fig. 2, but showing a trunnion support unit, not forming part of the invention. Fig. 5 is a vertical cross-sectional view of a trunnion support unit according to the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1 of the drawings, a toroidal type continuously variable transmission is provided with an input disk 2 and output disk which face each other across an axis O 1 in a transmission case 1. The output disk is not shown in the diagram. Two power rollers 3 are gripped between these disks. Each power roller 3 is supported by a trunnion 5 via a pivot shaft 4. The power roller 3 comes in contact with the input disk 2 and output disk. Due to the frictional force generated between the power roller 3 and these disks, a rotation torque is transmitted from the input disk 2 to the output disk while the power roller rotates about the axis O 2 . When the trunnion 5 is displaced by a servo-piston 6 in an upwards direction from a neutral point shown in the figure at which the axes O 2 and O 1 intersect, the input disk 2 and the output disk exert a rotation load on the power roller 3 so as to rotate it about a trunnion shaft O 3 , and as a result, the trunnion 5 rotates about the axis O 3 . In this way, the gyration angle of the power roller 3 varies, and the rotation ratio of the input disk 2 and output disk is made to vary continuously by varying the contact radius with each disk. Such a structure is indicated, for example, by SAE Technical Paper No. 901761. The upper ends of the trunnions 5 are interconnected by a link 7. The lower ends of the trunnion 5 are interconnected by a different link 7. In this way, the up/down displacements of the trunnions 5 are synchronized. A pulley 10 is fixed to each trunnion 5 and a synchronizing wire 11 is looped between the pulleys 10 so that the rotational displacement angles of the trunnion 5, that is the inclination angles of the power roller 3, are equal. The join between the trunnion 5 and link 7 comprises a spherical joint 8 and needle bearing 9. The spherical joint 8 fits into a throughole in the link 7, and is supported free to incline relative to the link 7 within a predetermined small range. The needle bearing 9 is interposed between the spherical joint 8 and trunnion 5, the trunnion 5 being thereby supported free to rotate relative to the spherical joint 8. According to this Invention, the relative displacement in the up/down direction of the spherical joint 8 and trunnion 5 is prevented by a construction such as is shown in Fig. 3. In the prior art, the spherical joint 8 and needle bearing 9 were for example inclined relative to the trunnion 5 within a clearance A between the needle bearing 9 and trunnion 5 as shown in Fig. 5. In other words, the trunnion 5 and the needle bearing 9 could axially displace with each other within the distance B. Within this distance B. the axial force generated by the inclined needles when trunnion 5 rotates, causes the relative displacement of the trunnion 5 and needle bearing 9 without much resistance. However, after it comes to the state shown in Fig. 5, the relative displacement of the trunnion 5 and needle bearing 9 is locked. If a further axial force is exerted on the trunnion 5 in this state, since the spherical joint 8 can not incline any further, a slip may occur between the spherical joint 8 and link 7 so as to enable the further axial displacement of the trunnion 5. Since these parts are not designed to cause slip. much frictional resistance acts on the trunnion 5 as an external force. This invention prevents this external force from exerting on the trunnion 5. by preventing the relative displacement of the needle bearing 9 and the trunnion 5 in the direction of the axis 03 by a supporting structure shown in Fig. 3. With this prevention, the axial force generated by the inclined needles is supported by this supporting structure and does not bring an external force to the trunnion 5. The prevention of the relative displacement of the needle bearing 9 and the trunnion 5 is realized by preventing the relative displacement of the trunnion 5 and the spherical joint 8 which holds the needle bearing 9. An embodiment of a trunnion support unit, not forming part of this invention will be described referring to Fig. 2. This diagram shows the supporting structure of spherical joint 8 engaged with the lower end of the trunnion 5. Herein, the shoulder unit 5B of the trunnion 5 is located above the spherical joint 8. The lower end 8D of the spherical joint 8 is supported by the pulley 10. The pulley 10 is fixed to the trunnion 5 together with the servo piston 6 and a washer 17 by a nut 16 which screws into a screw part 15 of the lower end of the trunnion 5. The spacer 12 is interposed between the upper end 8C of the spherical joint 8 and the shoulder 5B. By selecting the thickness of this spacer 12, the maximum up/down displacement due to inclination of the spherical joint 8 can be minimized, i.e., at least less than B, and the needle bearing 9 is prevented form exerting an external force in the axial direction on the trunnion 5 when it rotates. According to this embodiment. the spherical joint 8 is gripped by the pulley 10 and shoulder unit 5B, so a retainer and snap ring are unnecessary, therefore the cost can be reduced by a corresponding amount. Fig. 3 shows the trunnion support unit of this invention wherein a plate spring 19 is added between the pulley 10 and washer 17 of the aforesaid embodiment. In this embodiment, frictional wear is absorbed. In the aforesaid embodiments, it is preferable that the external diameter of the spacer 12 is set larger than the external diameter of the end of the spherical joint 8 with which the spacer 12 is in contact, and smaller than the maximum diameter of the spherical joint 8. This is in order to make the contact area between the spacer 12 and shoulder unit 5B greater than the contact area between the spacer 12 and spherical joint 8. Due to this setting, relative rotation of the spacer 12 and shoulder unit 5B is prevented, and friction frictional wear of the shoulder unit 5B is prevented. In this case, the spacer 12 and spherical joint 8 rotate relative to each other due to the rotation of the trunnion 5, and if these parts are constructed of the same hard materials. frictional wear of the spacer 12 and spherical joint 8 due to the relative rotation therebetween is limited to the absolute minimum. Fig. 4 shows a further embodiment of a trunnion support unit, not forming part of this invention wherein a thrust needle bearing 21 is applied to the spherical joint 8 which engages with the lower end of the trunnion 5. Herein, the spherical joint 8 is gripped via the thrust needle bearing 21 by the shoulder unit 5B of the trunnion 5 and pulley 10. The washer 22 forming a slip surface of the bearing 21 is interposed between the upper thrust needle bearing 21 and shoulder unit 5B. The pulley 10 is tightened towards the spherical joint 8 by the nut 16. An up/down clearance alpha is however left between the trunnion 5 and the pulley 10. Due to this clearance alpha, the spherical joint 8 is supported without leaving a gap between the shoulder unit 5B and pulley 10. According to this embodiment, prevention of the inclination of the spherical joint 8 and needle bearing 9 can be enhanced.

Claims: A trunnion supporting structure of a continuously variable transmission, said transmission comprising an input disk (2) and output disk arranged facing each other on a rotation axis (O1), power rollers (3) for transmitting a torque between said disks, trunnions (5) supporting said power rollers (3), a link (7) connecting said trunnions (5), a wire (11) for synchronizing the rotation of said plural trunnions (5), and a pulley (10) supported by said trunnion (5) around which said wire (11) is looped, wherein a gyration angle of the power rollers (3) is varied by driving the trunnions (5) along a trunnion axis (03) at right angles to said rotation axis (01), said trunnion supporting structure comprising a needle bearing (9) and a spherical joint (8), said needle bearing (9) comprising plural rolling parts which roll along a circular path so as to allow relative rotation between said trunnion (5) disposed inside said circular path and said spherical joint (8) disposed outside said circular path, and a shoulder part (5B) extending from said trunnion (5) at right angles to said trunnion axis (03), wherein the spherical joint (8) is interposed between said shoulder part (5B) and said pulley (10) such that said shoulder part (5B) and said pulley (10) prevent said spherical joint (8) from displacing in a direction of said trunnion axis (03), characterized in that said supporting structure further comprises a spring (19) pushing said pulley (10) towards said spherical joint (8). A supporting structure as defined in Claim 1, wherein said supporting structure further comprises a spacer (12) filling a gap between said shoulder part (5B) and said spherical joint (8). A supporting structure as defined in Claim 2, wherein a contact area between said spacer (12) and said shoulder part (5B) is set larger than a contact area between said spacer (12) and said spherical joint (8). A supporting structure as defined in any of Claims 1 through 3, wherein said pulley (10) is fixed to said trunnion (5) by a nut (16), and said supporting structure further comprises a thrust needle bearing (21) interposed between said spherical joint (8) and said shoulder part (5B), and a thrust needle bearing (21) interposed between said spherical joint (8) and said pulley (10).

Inventors: OSHIDARI TOSHIKAZU, OSHIDARI, TOSHIKAZU
Applicants: NISSAN MOTOR, NISSAN MOTOR CO., LTD.
Application year: 1998
Main classification: F16H15
IPC codes: F16H15, F16C35, F16C19