A trunnion of a toroidal continuously variable transmission and manufacturing process thereof

Abstract: A trunnion (3) of a toroidal continuously variable transmission comprises a pulley (38) having a pulley groove (30) and a notch (37) crossing the pulley groove (38). The trunnion (3) rotates in synchronism with another trunnion by looping an endless wire around the pulley groove of each trunnion (3) and by engaging a large diameter part of the endless wire with the notch (37). After the trunnion (3) is formed by die forging, a rotary tool (90) is first aligned with a boundary interface (31'A, 31'B) between the pulley groove (30) and notch (37). The tool (90) is then rotated while it is moved forward in the axial direction of the tool (90), and the boundary interface (31'A, 31'B) is cut to a predetermined position.

Description: The present invention relates to a manufacturing process for a trunnion of a toroidal continuously variable transmission and a trunnion of a toroidal continuously variable transmission, comprising: a support having a hole therethrough and comprising a pulley with a pulley groove and a notch crossing said pulley groove; a first shaft part on a top of said support; and a second shaft part on a bottom of said support that is coaxial with said first shaft part; said notch comprises an arc portion. JP-A-4366049 published by the Japanese Patent Office in 1992 discloses a toroidal continuously variable transmission for vehicles wherein the ratio of the rotation speed of an input disk to the rotation speed of an output disk, i.e., a speed ratio, is continuously varied by varying the gyration angle of a pair of power rollers gripped between the input disk and output disk. The power rollers are respectively supported by trunnions at a position facing each other. These trunnions must be rotated in synchronism. In this context, JP-A-7253145 published by the Japanese Patent Office in 1995, on which the preamble of claim 5 is based, discloses a technique wherein a pulley is formed in the trunnions, and the trunnions are synchronously rotated by looping an endless wire around a pulley groove of the pulley. The slipping of the endless wire in the circumferential direction is prevented by engaging a large diameter part of the endless wire with a notch formed in a pulley groove. Therefore, in order to accurately synchronize the gyration angle of the trunnions, the notch must be formed precisely in the circumferential direction. However, when the trunnions are formed by forging, casting or sintering, the precision of the notch is poor. Therefore, the notch has to be machined after forming, but if the notch is machined by driving a tool in the axial direction while the trunnion is rotated around its rotation axis as the notch runs in a circumferential direction, the number of indexing steps of machining positions and positioning steps increases and the productivity declines. Prior art document US-A-4,694,704 teaches a variable traction roller transmission, wherein a trunnion thereof comprises pivot shafts carrying the respective rollers, wherein grooves are formed in flange areas of the pivot shaft, such that a transmission cable can be disposed in said grooves in order to synchronize the rotation of the several pivot shafts. Said cable is a standard loop steel cable of an appropriate length to fit around the pivot shaft flanges and is provided with crimped-on tube sections of a diameter larger than the cable which tube sections fit in cavities formed in the pivot shaft flanges for operative engagement of the cable with the pivot shaft. It is an objective of the present invention to provide a manufacturing process for a trunnion of a toroidal continuously variable transmission and a trunnion of a continuously variable transmission as indicated above, wherein high precision is ensured. According to the method aspect of the present invention, this objective is solved by a manufacturing process for a trunnion of a toroidal continuously variable transmission according to claim 1. Preferred embodiments are laid down in the dependent claims. According to the apparatus aspect of the present invention, said objective is solved by a trunnion of a toroidal continuously variable transmission according to independent claim 5. Preferred embodiments are laid down in the respective subclaims. The trunnion comprises a support having a hole therethrough comprising a pulley with a pulley groove and a notch crossing the pulley groove, a first shaft part on the top of the support, and a second shaft part on the bottom of the support that is coaxial with the first shaft part, the notch comprising an arc portion and two straight portions, one of the straight portion being formed on one side of the arc portion and the other of the straight portion being formed on the other side of the arc portion. The process comprises forming said pulley groove and said notch by forging, casting or sintering, aligning a rotary tool for machining a flat surface by a blade provided on an end face so as to face one of a boundary interfaces between the pulley groove and notch, and rotating the tool while moving the tool forward in the axial direction of the tool so as to cut the boundary interface to a predetermined position. 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. Hereinafter the present invention is illustrated and explained by means of a preferred embodiment in conjunction with the accompanying drawings. In the drawings wherein: Fig. 1 is a sectional view of a trunnion and a power roller of a toroidal continuously variable transmission, Fig. 2 is a front view of the trunnion, Fig. 3 is a side view of the trunnion, Fig. 4 is a base plan view of the trunnion, showing a state before machining, Fig. 5 is a base plan view of the trunnion, showing a state after machining. Referring to Fig. 1 of the drawings, a trunnion 3 comprises a support 3C which supports a power roller 1 such that it is free to rotate, and shaft parts 3A and 3B formed on the top and bottom of the support 3C. The support 3C and shaft parts 3A, 3B are formed in one piece by die forging. A through-hole 34 is formed in the support 3C. One end of a pivot shaft 2 is inserted in the through-hole 34, and the pivot shaft 2 pivots around an axis C. The power roller 1 is supported at the other end of the pivot shaft 2 via a radial bearing 19. An outer ring 18 and ball bearing 16 are interposed between the support 3C and power roller 1, and support a thrust load. When the trunnion 3 displaces in the direction of an axis 3Z, the power roller 1 gyrates between the input disk and output disk, not shown, and the ratio of the rotation speed of the input disk to the rotation speed of the output disk, i.e., the speed ratio, varies continuously. The shaft part 3B is formed in a cylindrical shape, as shown in Fig. 2. A rod 6 of a hydraulic actuator, not shown, is inserted into the shaft part 3B. The rod 6 and trunnion 3 are joined by pressing a pin 36 into a pinhole 33 formed in the support 3C and a pinhole 35 formed in the rod 6 which are formed in the support 3C. A pulley 38 is formed in the lower part of the support 3C, as shown in Fig. 3. The pulley 38 comprises a pulley groove 30 and a notch 37 which crosses the pulley groove 30. An endless wire, not shown, is looped around the pulley groove 30 and notch 37 in order to synchronize the gyration angle of the trunnion 3, and the gyration angle of another trunnion, not shown, which is disposed facing the trunnion 3. The endless wire is provided with a large diameter part having a diameter larger than the wire gage, and this large diameter part engages with the notch 37 so that the endless wire does not slide in a circumferential direction relative to the trunnion 3. The pulley groove 30 and the notch 37 are formed in one piece with the support 3C when the trunnion 3 is formed by die forging. After forging, the angles β formed by the axis C of the pivot shaft 2 and (first) boundary interfaces 31'A, 31'B between the notch 37 and the pulley groove 30 are less than 45 degrees, as shown in Fig. 4. The angles β are for example 39 degrees. Next, machining described later is performed, and the angles between the axis C of the pivot shaft 2 and the (second) boundary interfaces 31A, 31B become α 1 , α 2 as shown in Fig. 5. Here, the angles α 1 , α 2 are 45 degrees. Consequently, the angle of the notch 37 is enlarged from 2β to 90 degrees after forging, and the extension of the boundary interfaces 31A, 31B intersects perpendicularly on the axis 3Z of the trunnion 3. The machining of the boundary interfaces 31A, 31B will now be described further referring to Fig. 4. The rotary tool 90 can machine a flat surface by a blade provided on the tip surface. The tool 90 may be an end mill, for example. First, the boundary interface 31'A on the right-hand side of the figure and the tool 90 are aligned, and the angle between the axis of the tool 90 and the axis C of the pivot shaft 2 is adjusted to a first angle. The first angle is 45 degrees. The tool 90 is then rotated while moving it forward in the axial direction, and cutting of the boundary interface 31'A is started. When the tip of the tool 90 reaches a line L1 which is at an angle of 45 degrees relative to the axis C of the pivot shaft 2, this line extending from the axis 3Z of the trunnion 3, cutting of the boundary interface 31'A is terminated. Next, the tool 90 is retracted in the axial direction to prevent interference with the trunnion, the trunnion 3 is rotated counterclockwise in the figure, and the angle made by the axis of the tool 90 and the axis C of the pivot shaft 2 is adjusted to a second angle. The second angle is -45 degrees. Furthermore, the trunnion 3 is displaced parallel so as to face the tool 90. The tool 90 is then rotated while moving it forward in the axial direction, and cutting of the boundary interface 31'B on the left-hand side of the figure is started. When the tip of the tool 90 reaches a line L2 which makes an angle of 45 degrees relative to the axis C , this line L2 extending from the axis 3Z of the trunnion 3, cutting of the boundary interface 31'B is terminated. Therefore, the angle made by the boundary interfaces 31A, 31B is precisely 90 degrees as shown in Fig. 5 due to the aforesaid double cutting by the tool 90. The shaded portions 32A, 32B in the figure are machining allowances removed by cutting. Accordingly, the shaded portions are removed by cutting straight portions (31'A, 31'B, 31A, 31B). As the relative rotation angle of the trunnion 3 and the tool 90 is 90 degrees, the numerical values used for indexing the cutting position are 45 degrees and 90 degrees, and the work piece can be set easily and quickly. Moreover, since the tool 90 moves only in the axial direction, the setting of a machine tool, not shown, which drives the tool 90 is easy and accurate. If the rotary tool 90 with a large diameter is used and the offset amount from the center of the pulley groove 30 of the tool 90 is made large, no cutting residues remain below the boundary interfaces 31A, 31B as shown in Fig. 3. Hence, it is possible to prevent the endless wire from being caught on the cutting residues when the endless wire is attached, and it is easy to attach it to the notch 37 precisely and rapidly. Further, as the machining allowances 32A, 32B (shaded portions in Fig. 5) are small, the machining time can be reduced. If two of the rotary tools 90 are available, the boundary interfaces 31'A, 31'B can be cut separately at the same time, in which case the machining time may be further reduced. In the above embodiment, the angles α 1 , α 2 formed by the axis C of the pivot shaft 2 and the boundary interfaces 31A, 31B are arranged to be 45 degrees, but these angles may be different values. For example, if the angle α 1 is set to 30 degrees and the angle α 2 is set to 50 degrees, the first and second angles during positioning may be set at respectively 30 degrees and 50 degrees relative to the axis C . In addition, although the trunnion is formed by die forging in the aforesaid embodiment, it may be molded by casting or sintering instead.

Claims: Manufacturing process for a trunnion (3) of a toroidal continuously variable transmission, said trunnion (3) comprising a pulley (38) with a pulley groove (30) and a notch (37) crossing said pulley groove (30), in use of said transmission said trunnion (3) rotating in synchronism with another trunnion by looping an endless wire around said pulley groove (30) of each trunnion (3) and by engaging a large diameter part of said endless wire with said notch (37), said process comprises: forming said pulley groove (30) and said notch (37) by forging, casting or sintering; aligning a rotary tool (90) for machining a flat surface by a blade provided on an end face so as to face one of boundary interfaces (31'A, 31'B) between said pulley groove (30) and notch (37); and rotating said tool (90) while moving said tool (90) forward in the axial direction of said tool (90) so as to cut said boundary interface (31'A, 31'B) to a predetermined position. Manufacturing process for a trunnion according to claim 1, characterized in that in use of said transmission said trunnion (3) is provided for supporting a power roller (1) via a pivot shaft (2), said process comprises: aligning said rotary tool (90) for machining the flat surface by said blade so as to face one of the boundary interfaces (31 'A, 31 'B) between said pulley groove (30) and said notch (37); adjusting an angle formed by an axis (C) of said pivot shaft (2) and an axis of said tool (90) to a first angle; rotating said tool (90) while moving said tool (90) forward in the axial direction of said tool (90), and cutting said boundary interface (31'A) to a predetermined position; retracting said tool (90) in the axial direction; rotating and displacing parallel said trunnion (3) so that said tool (90) is facing the other boundary interface (31'B); adjusting an angle formed by said axis (C) of said pivot shaft (2) and said axis of said tool (90); and rotating said tool (90) while moving said tool (90) forward in the axial direction of said tool (90), and cutting said boundary interface (31 'B) to a predetermined position. Manufacturing process for a trunnion according to claim 2, characterized In that during the cutting of said boundary interface (31'A, 31'B), cutting is stopped when a tip of said tool (90) reaches a line (L1, L2) extending from an axis (3Z) of the trunnion (3) at a predetermined angle relative to said axis (C) of said pivot shaft (2). Manufacturing process for a trunnion according to claim 1, characterized by aligning said rotary tool (90) for machining the flat surface by said blade so as to face one of the boundary interfaces (31'A, 31'B) between said pulley groove (30) and said notch (37); adjusting the angle formed by the axis (C) of said pivot shaft (2) and an axis of said first rotary tool (90) to a first angle; rotating said rotary tool (90) while moving said rotary tool (90) forward in the axial direction of said rotary tool (90), and cutting said boundary interface (31'A) to a predetermined position; aligning a second rotary tool (90) for machining the flat surface by a blade so as to face the other one of the boundary interfaces (31'A, 31'B); adjusting the angle formed by said axis (C) of said pivot shaft (2) and an axis of said second rotary tool (90) to a second angle; and rotating said second rotary tool (90) while moving said second rotary tool (90) forward in the axial direction of said second rotary tool (90), and cutting said boundary interface (31'B) to a predetermined position. Trunnion of a toroidal continuously variable transmission, comprising: a support (3C) having a hole (34) therethrough and comprising a pulley (38) with a pulley groove (30) and a notch (37) crossing said pulley groove (30); a first shaft part (3A) on a top of said support (3C); and a second shaft part (3B) on a bottom of said support (3C) that is coaxial with said first shaft part (3A); said notch (37) comprises an arc portion, characterized in that said notch (37) comprises two straight portions (31A, 31B), one of said straight portion (31A) being formed on one side of said arc portion and the other of said straight portion (31B) being formed on the other side of said arc portion, said straight portions (31A, 31B) forming boundary interfaces between said notch (37) and said are portion. Trunnion of a toroidal continuously variable transmission according to claim 5, characterized in that said hole (34) has an axis (C); said axis (C) intersects an imaginary line at a second angle (α) on said sectional plane, said imaginary line (L1, L2) extending from the center (37) of said first shaft part (3A) to one of said boundary interfaces (31A, 31B). Trunnion of a toroidal continuously variable transmission according to claim 6, characterized in that said angle (α) is 45 degrees.

Inventors: NAKANO MASAKI, NAKANO, MASAKI
Applicants: NISSAN MOTOR, NISSAN MOTOR CO., LTD.
Application year: 1999
Main classification: F16H15
IPC codes: F16H15