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We developed a quantitative evaluation method based on observation of torque wave due to valve train friction. We evaluated the reduction of energy consumed in one cam drive cycle. The result of torque wave analysis shows the Si3N4 adjusting shim with a mirror-finished surface reduces valve train friction by 25%-30% in some limited range of engine speed. We discussed that by what means the reduction in valve train friction was being achieved and that the oil film parameter Λ, according to the EHL(Elasto-Hydrodynamic Lubrication) theory.

The high reliability silicon nitride sintered body and the mirror finish grinding machining technique have been developed, which improved fuel efficiency by reducing weight and friction loss of the valve systems. This ceramics, consists of finer grains (mean grain size:1-3μm) has high strength (σ 3b=1600MPa) and high Weibull modulus (m>20). In the case of motoring test by using this ceramics as the cam follower of the valve systems, it has a durability of more than 10,000rpm., which is approx. 30% higher than that of conventional silicone nitride, against the impact load to which the cam followers were subjected at occurrence of valve bouncing.