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Effects of high temperature sintering on mechanical properties of sintered low alloy steels were investigated. With regard to sintering temperature dependence of mechanical properties, as-sintered steels are classified into two groups. High temperature sintering increased strength of the group1 steels and ductility of the group2 steels, while it did not affect ductility of the group1 steels and strength of the group2 steels. When these steels were heat treated after sintering, both strength and ductility of the steels obtained by high temperature sintering were superior to those of the steels of a conventional sintering process.

We have developed high efficiency oil pump rotors with a new tooth profile. This profile design is designated intelligent profile rotor (IPR). Its features are: 1. high efficiency by equalized flow rate, 2. reduced sliding which yields less frictional (torque) loss, and 3. lower noise by decreasing the working clearance to 1/3 or less of standard design. We have also improved the dimensional accuracy of sintered rotors, reducing or eliminating machining.

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.

Variable valve timing (VVT) unit, which is able to decrease environmental load and improve fuel economy is loaded onto many automobiles recently. This unit consists mainly of sprocket, housing and rotor. These parts are requested different properties according to environment. We produce sintered parts for variable valve timing unit by selecting compact, sinter process and special treatment according to demanded properties. In this paper, demanded properties of sintered parts for variable valve timing unit and adopted technique to satisfy them are presented.

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.

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.

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.