Process for producing a pulley for a continuously variable belt drive transmission

1. A process for producing a pulley for a continuously variable belt drive transmission including an input pulley, an output pulley and an endless belt disposed between the input and output pulleys, the input and output pulleys having tapered surfaces contacted with the endless belt, respectively, the endless belt including a plurality of metal elements stacked on each other in a thickness direction thereof, the metal elements each having a plurality of microscopic projections and recesses on opposed side faces which are contacted with the tapered surfaces of the input and output pulleys, the tapered surfaces of at least one of the input and output pulleys being formed with microgrooves in the form of concentric grooves or a continuous helical groove, in which a relationship represented by the following expression: W 1 ≧(W 2 +W 3 ), wherein W 1 is a width of each of the microscopic projections on the side faces of the metal elements, W 2 is a width of a top surface of each of microprojections defined between the adjacent microgrooves, and W 3 is a width of each of the microgrooves, is satisfied, the process comprising:

subjecting tapered surfaces of a preform of at least one of the input pulley and the output pulley to surface hardening;

subjecting the surface-hardened tapered surfaces of the preform to hard turning to form the microgrooves radially spaced from one another thereon, between which microprojections are formed; and

reducing a height of the microprojections to thereby provide the at least one of the input pulley and the output pulley having the tapered surfaces with the microgrooves which satisfy said relationship.

2. The process as claimed in claim 1 , wherein the hard turning is conducted to control a pitch of the microgrooves to 30 μm or less.

3. The process as claimed in claim 1 , wherein the hard turning is conducted at least a region of the tapered surfaces of the preform in which a pulley ratio is 1 or more.

4. The process as claimed in claim 1 , wherein the height of the microprojections is reduced by controlling a surface roughness Ra of the surface-hardened tapered surfaces to a range of 0.05-0.25 μm.

5. The process as claimed in claim 1 , wherein the height of the microprojections is reduced by controlling the height of the microprojections to a range of 0.5-2.5 μm.

6. The process as claimed in claim 1 , wherein the height of the microprojections is reduced by undergoing plastic deformation.

7. The process as claimed in claim 6 , wherein the microprojections undergo the plastic deformation using one of a spherical tool and a cylindrical tool.

8. The process as claimed in claim 7 , wherein the plastic deformation of the microprojections is allowed by roller burnishing.

9. The process as claimed in claim 1 , wherein the height of the microprojections is reduced using a formed grindstone.

10. The process as claimed in claim 1 , wherein the height of the microprojections is reduced by film lapping.

11. The process as claimed in claim 1 , wherein the at least one of the input pulley and the output pulley is the input pulley.

12. The process as claimed in claim 1 , comprising producing an input pulley and an output pulley pulley set, wherein the hard turning is conducted at least a region of the tapered surfaces of the preform in which a pulley ratio for the input pulley and the output pulley of the set is 1 or more.

13. A process for producing a pulley for a continuously variable belt drive transmission including an input pulley, an output pulley and an endless belt disposed between the input and output surfaces, the input and output pulleys having tapered surfaces contacted with the endless belt, respectively, the endless belt including a plurality of metal elements stacked on each other in a thickness direction thereof, the metal elements each having a plurality of microscopic projections and recesses on opposed side faces which are contacted with the tapered surfaces of the input and output pulleys, the tapered surfaces of at least one of the input and output pulleys being formed with microgrooves in the form of concentric grooves or a continuous helical groove, in which a relationship represented by the following expression: W 1 ≧(W 2 +W 3 ), wherein W 1 is a width of each of the microscopic projections on the side faces of the metal elements, W 2 is a width of a top surface of each of microprojections defined between the adjacent microgrooves, and W 3 is a width of each of the microgrooves, is satisfied, the process comprising:

subjecting tapered surfaces of a preform of at least one of the input pulley and the output pulley to surface hardening;

subjecting the surface-hardened tapered surfaces of the preform to shot peening; and

subjecting the shot-peened tapered surfaces of the preform to finishing to form the microgrooves thereon and thereby provide the at least one of the input pulley and the output pulley which has the tapered surfaces with the microgrooves which satisfy said relationship.

14. The process as claimed in claim 13 , wherein the shot peening is conducted at least a region of the tapered surfaces of the preform in which a pulley ratio is 1 or more.

15. The process as claimed in claim 13 , wherein the finishing is conducted using a formed grindstone.

16. The process as claimed in claim 13 , wherein the finishing is conducted by film lapping.