Improvement of Lubrication for Cam and Follower

Abstract

In order to improve the lubrication between cam and follower of internal combustion engines, the influences of materials or oil viscosity and additives on the friction and scuffing characteristics have been examined with a test rig by increasing the contact load at a constant revolution speed. Also the effects of oil supply through the oil-hole of the camshaft on the reduction of friction and the prevention of scuffing have been examined. From the experiments the following results were made obvious.

Firstly, the effect of the material on the reduction of friction or the prevention of scuffing is dependent upon the combination of cam and follower materials. The follower material of hard sintered metal or silicon nitride ceramics is superior in both effects to chilled cast iron when mating with the cam material of hardened S48C steel cam.

Secondly, as the viscosity of base-oil becomes low, the friction increases or decreases depending on oil additives, but the scuffing resistance always becomes small. The organo-molybdenum compounds, MoDTP and MoDTC, decrease the friction and the zinc dialkyl-dithiophosphates are effective in preventing scuffing. In the case of mixed additive with such Molybdenum friction modifiers, primary ZnDTP and secondary ZnDTP enhance the effect to modif' the friction. when mixed with MoDTP, however primary ZnDTP becomes inferior in scuffing resistance to secondary ZnDTP. Specifically the mixed additive of MoDTC and primary ZnDTP improves the lubrication in both respects of the friction and the anti-scuffing.

Lastly, the oil supply from cam surface oil-hole is an effective means of improving the lubrication. The effect becomes largest when the oil-hole is arranged between the flank and shoulder of the cam-lobe corresponding to the valve opening.

Presented as a Sociey of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997

KEY WORDS:

• Internal Combustion Engine
• Valve Train
• Tribology
• Cam
• Follower
• Lubrication
• Friction
• Scuffing Resistance
• Material
• Lubricant
• Oil Additive
• Oil Supply

Notes

Presented as a Sociey of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997