Rocker arm and method of manufacturing the same
A rocker arm 1 made of sheet metal is formed so that Vickers hardness H v of the surface layer portion 9 a of the valve stem receiver 9 is set at H v 650 to 800 and a quantity of the retained austenite γR is set at 25 to 35 vol %.
1. A rocker arm comprising:
a valve stem receiver comprising sheet metal of low carbon steel, said valve stem receiver including a sliding contact face, wherein a valve stem slides and contacts said valve stem receiver,
wherein Vickers hardness of a surface layer portion of said sliding contact face comprises a range of Hv 650 to 800, and a quantity of retained austenite of the surface layer portion of said sliding contact face comprises a range of γR 25 to 35 vol %.
2. The rocker arm according to claim 1 , wherein the quantity of retained austenite of the surface layer portion comprises a range of γR 28 to 32 vol %.
3. The rocker arm of claim 1 , wherein said sliding contact face of said valve stem receiver comprises dimples formed thereon for holding lubricant.
4. The rocker arm of claim 1 , wherein said sheet metal of low carbon steel comprises a carbon content of no greater than 0.4%.
5. The rocker arm of claim 1 , wherein said sliding contact face of said valve stem receiver comprises a convex crown shape.
6. A method of manufacturing a rocker arm comprising sheet metal of low carbon steel, the method comprising:
performing treatment of carburizing, quenching and tempering with respect to a valve stem receiver of the rocker arm such that Vickers hardness of a surface layer portion of a sliding contact face of the valve stem receiver comprises a range of Hv 650 to 800, and a quantity of retained austenite of the surface layer portion of said sliding contact face comprises a range of γR 25 to 35 vol %.
7. The method of manufacturing a rocker arm according to claim 6 , wherein said performing said treatment of quenching sets a quenching temperature at a higher value than a predetermined quenching temperature such that said quantity of said retained austenite to be transformed into martensite is reduced.
8. The method of manufacturing a rocker arm according to claim 6 , wherein performing said treatment of tempering sets a tempering temperature at a value lower than a predetermined tempering temperature such that decomposition of said retained austenite is suppressed such that a quantity of the retained austenite comprises a range of γR 25 to 35 vol %.
9. The method of manufacturing a rocker arm according to claim 6 , further comprising:
shot peening said surface layer portion of said sliding contact face of said valve stem receiver to form dimples thereon for holding lubricant.
10. The method of manufacturing a rocker arm according to claim 6 , wherein said sheet metal of low carbon steel comprises a carbon content of no greater than 0.4%.
11. The method of manufacturing a rocker arm according to claim 6 , further comprising:
forming said sliding contact face of said valve stem receiver into a convex crown shape.
12. A method of manufacturing a rocker arm comprising sheet metal of low carbon steel, the method comprising:
welding a valve stem receiver to said rocker arm; and
performing treatment of carburizing, quenching and tempering to adjust Vickers hardness of a surface layer portion of a sliding contact face of said valve stem receiver to comprise a range of H v 650 to 800, and to adjust a quantity of the retained austenite of the surface layer portion of said valve stem receiver to a range of γR 25 to 35 vol %.
13. The method of manufacturing a rocker arm according to claim 12 , wherein said performing said treatment of quenching sets a quenching temperature at a higher value than a predetermined quenching temperature such that said quantity of said retained austenite to be transformed into martensite is reduced.
14. The method of manufacturing a rocker arm according to claim 12 , wherein said performing said treatment of tempering sets a tempering temperature at a value lower than a predetermined tempering temperature such that decomposition of said retained austenite is suppressed such that a quantity of the retained austenite comprises a range of γR 25 to 35 vol %.
15. The method of manufacturing a rocker arm according to claim 12 , further comprising:
shot peening said surface layer portion of said sliding contact face of said valve stem receiver to form dimples thereon for holding lubricant.
16. The method of manufacturing a rocker arm according to claim 12 , wherein said sheet metal of low carbon steel comprises a carbon content of no greater than 0.4%.
17. The method of manufacturing a rocker arm according to claim 12 , further comprising:
forming said sliding contact face of said valve stem receiver into a convex crown shape.
18. The method of manufacturing a rocker arm according to claim 12 , wherein the quantity of retained austenite of the surface layer portion comprises a range of γR 28 to 32 vol %.
19. The method of manufacturing a rocker arm according to claim 14 , wherein the quantity of retained austenite of the surface layer portion comprises a range of γR 28 to 32 vol %.
20. The method of manufacturing a rocker arm according to claim 12 , wherein said sheet metal of low carbon steel comprises a carbon content of no greater than 0.4%.