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Austempered ductile iron (ADI) is a material having excellent mechanical properties and damping capacity. However practical mass production of ADI gears has not been possible due to ADI's poor machinability and distortion during the austempering heat treatment. With a new process method of carrying out hobbing before austempering when the material is in its soft condition, then austempering it and lastly, conducting the shave finishing process, we have diminished the above defects and developed practical ADI gears. These new gears generate less noise than ordinary nitrocarburized steel gears and are superior in pitting resistance.

We have developed a tappet with a cam lobe contacting tip made of a hard sintered material whose base material is cobalt, which adheres less to the steel of camshafts, and which also contains fine particles of tungsten carbide and chrome carbide. We have established a new evaluation method to access wear resistance performance of the tappet. It enables us to measure directly the friction force generated between the cam lobe and tappet and to evaluate anti-scuffing performance with high accuracy because we can clarify the time, load and cam angle at which scuffing occures.

In recent year, higher strength for truck and bus transmission gear has become necessary. For the transmission gears, carburized gears have generally been used. We have examined the effects of shot peening and grinding using a CBN grindstone on the pitting strength and the bending fatigue strength of a carburized gear, and further evaluated a material which reduces the structual anomalies produced during carburization. As a result, it has been found that shot peening or CBN grinding is more effective for improving both pitting strength and bending fatigue strength than improving the material composition. Therefore, it is evident that residual compressive stress caused by shot peening or CBN grinding suppresses the propagation of cracks.

The authors developed, for use in diesel engines, ceramic tappets cast in aluminum alloy that drastically improved wear resistance and valve train dynamics. The ceramic tappets consist of two parts: a ceramic head, which contacts the cam and push rod, and a tappet body made of aluminum alloy. Concerning the ceramic, silicon nitride was the best material of the three ceramics evaluated in the tests and the sliding surface, in contact with the cam and push rod, was left unground. As for the aluminum alloy, hyper-eutectic aluminum-silicon alloy with a controlled pro-eutectic silicon size was selected. A reliability analysis using the finite-element method (FEM) was also made on the structure of the ceramic tappet for enhanced durability and reliability. The combination of this tappet and a cam made of hardened ductile cast iron, hardened steel, or chilled cast iron, respectively exhibits excellent wear resistance.

Applying micro-alloyed steel as a cost-effective method of forging engine parts eliminates quench and temper processes and saves energy. We have expanded this application to timing gears and crankshafts by changing the connecting rod material to carbon steel and vanadium, applied at the outset. Then, micro-alloyed steel treated with a soft nitriding process was used. Our recent studies have been focused on materials which exhibit both higher tensile strength and better machinability. This paper describes the results of applying different types of micro-alloyed steel to those engine parts.