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. When, in the prior art, the needle bearing is inclined with respect to the trunnion, an axial force acts on the trunnion as it rotates. A member (10;13;20;24) is therefore provided which prevents the relative inclination of an inner contact member (5) and an outer contact member (8) of the needle bearing in order to 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 Tokkai Sho JP 57-47060 A published by the Japanese Patent Office in 1982. 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. EP 0 450 495 A, and likewise EP 0 914 573 A, discloses a supporting structure according to the preamble portion of claim 1. EP 914573 A is an Asticle 54(3) document. 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 solved by the features of claim 1. The subclaims contain further 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, and a link connecting the trunnions, 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. The supporting structure comprises a needle bearing, a spherical joint, a trunnion, a sperical joint and a third member. The needle bearing comprises plural rolling parts which roll along a circular path. The trunnion is disposed inside the circular path and the spherical joint is disposed outside the circular path. The needle bearing allows relative rotation between the trunnion and the spherical joint. The third member prevents the relative inclination of the trunnion and the sperical joint. The trunnion comprises a shoulder part extending at right angles to the trunnion axis, the third member is supported by the trunnion, and the spherical joint is fitted between the shoulder part and the third member such that a displacement of the spherical joint in a direction of the trunnion axis is limited by the shoulder part and the third member. The third member comprises an annular retainer supported via a snap ring fitted to the trunnion. It is further preferable that the spherical joint is fitted in a throughole formed in the link. In this case, It is further preferable that the supporting structure further comprises a spacer filling a gap between the shoulder part and the spherical joint. When the spacer is provided, 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 supporting structure further comprises a spring interposed between the snap ring and the retainer. 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 toroidal continuously variable transmission to which this invention is applied. Fig. 2 is a vertical cross-sectional view of a trunnion support unit according to this invention. Fig. 3 is a plan view of the trunnion support unit. Fig. 4 is similar to Fig. 2, but showing a second embodiment of this 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 for example in Figs. 2 and 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 O3 by a supporting structure shown in Fig. 2. 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. Describing this supporting structure, a lower end 8C of the spherical joint 8 is supported via a spacer 12 in a shoulder part 5B of the trunnion 5. An upper end 8D of the spherical joint 8 is supported by the trunnion 5 via a retainer 13 and snap ring 14. By engaging with an annular groove in the trunnion 5 as shown in Fig. 3, the snap ring 14 limits the upward displacement of the annular joint 8 and retainer 13. The thickness of the spacer 12 is set so that a maximum displacement in an up/down direction of the spherical joint 8 is less than the aforementioned distance B. Ideally. the vertical displacement of the spherical joint 8 should be 0, but this is difficult to achieve practically. However, by properly selecting the thickness of the spacer 12, the vertical displacement of the spherical joint 8 can be minimfzed. In any case, it should be less than the distance B. In this way, the up/down displacement of the spherical joint 8 is prevented by the retainer 13 and snap ring 14 and the needle bearing 9 does not exert an external force in the axial direction on the trunnion 5. Fig. 5 shows a second embodiment of this invention wherein a plate spring 18 is added between the snap ring 14 and retainer 13 of the aforesaid first embodiment. The spherical joint 8 is constantly pushed towards the shoulder unit 5B by the plate spring 18, and the up/down clearance between the spherical joint and. other parts is always zero. Therefore, dimensional variations due to frictional wear of parts is absorbed, and the needle bearing 9 is prevented from exerting force on the trunnion 5 for a long period of time. 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. In the first embodiment, it is desirable to provide a stopper between the retainer 13 and snap ring 14 which prevents the relative rotation therebetween. In this way, frictional wear of the snap ring 14 is prevented.

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), and a link (7) connecting said trunnions (5), wherein a gyration angle of the power rollers (3) is varied by driving the trunnions (5) along a trunnion axis (O3) at right angles to said rotation axis (O1), said 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 (O3) said supporting structure further comprising an annular retainer (13), characterized in that said annular retainer is supported via a snap ring (14) fitted to said trunnion (5), said annular retainer (13) in combination with said shoulder part (5B) preventing said spherical joint (8) from displacing in a direction of said trunnion axis (O3). A supporting structure as defined in Claim 1, wherein said spherical joint (8) is fitted in a throughole formed in said link (7). A supporting structure as defined in Claim 1 or 2, 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 3, 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 4, wherein said supporting structure further comprises a spring (18) interposed between said snap ring (14) and said retainer (13).

Inventors: OSHIDARI TOSHIKAZU, OSHIDARI, TOSHIKAZU
Applicants: NISSAN MOTOR, NISSAN MOTOR CO., LTD.
Application year: 1998
Main classification: F16H15
IPC codes: F16H15, F16C35, F16C19, F16C23