Abstract
Some studies to reduce the friction of valve train mechanism have been conducted in order to prevent the global warming by improving the fuel economy for internal combustion engines. In the case of the contact between the cam and the shim offset on the valve lifter for the direct-type valve train, the characteristics of friction diagrams measured with the cam / slipper follower friction tester were examined and also the oil film thickness between the valve lifter and the shim was predicted by the hydrodynamic lubrication theory so that the followings have been summarized, (1) The friction of rolling contact between cam and follower becomes considerably small because the shim offset on the valve lifter rotates under the contact of cam. (2) The thickness of oil film with the round side face or the flat bottom face of the shim is enough to make the shim to rotate on the vale lifter.
