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In a motorcycle engine, the tappets convert the rotating motion of the cams to the pitching motion of the valves, and they slide with the cams at a high speed under high pressure. Reducing the friction between the tappets and the cams would increase the power of the engine. We studied a way to reduce the coefficient of friction between tappets and cams by applying a hard thin coating of DLC, MoS2, CrN, or TiN to the tappets. We investigated the adhesion of the coatings with a scratch test and their tribological properties with a ball-on-disk test. We then examined their durability with an engine stand test. We concluded that a tappet coated with DLC effectively reduces friction at the cam and tappet interface and is sufficiently durable to be applied to actual motorcycle engines.

From the viewpoint of applying ERW (Electric Resistance Welded) steel tubes for automotive structural parts by means of hydroforming technology, a series of free-bulge experiments is carried out. Four kinds of mild and high tensile strength steel tubes are provided. Initial stress ratio, αm that represents an axial force level is adopted as an experimental parameter. Expansion limit increases with decrease of αm. The bulge shape and the expansion limit are also affected by the mechanical properties of tubes. The strain hardening property in bulge deformation is approximated by a parabolic equation.

Annual surveys on Octane Number Requirement(ONR) of Japanese model passenger cars have been conducted, and the trend covering the period of 1982-1992 is described as a follow-up of the earlier report-SAE 830510. The ONRs showed a gradual decrease until 1990, but increased in later two years, reaching 91.2 and 95.3 ON at 50% and 90% car satisfaction levels, respectively, in 1992. The ONR at high speed range(80-120 km/hr) tended to increase and its differences from the low speed ONR(30-120 km/hr) have become gradually smaller for 1985-1992. Also, engine speed distribution at the maximum ONR values shifted to higher speed range above 2050rpm. Reflecting the recent increasing use of premium gasoline-spec cars, ONR distribution of these cars was separately measured, and resulted in 97.5 and 100.5 RON at 50% and 90% satisfaction levels respectively, in 1992 year model cars. This value is approximately 5 RON higher than regular gasoline spec cars at 90% satisfaction level.