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This paper presents several methods for reducing engine weight primarily through substitution with light-weight materials. The efficiency and performance of the engine were reviewed using a light-weight experimental engine (hereinafter called “weight-reduced engine”) constructed by the authors in order to investigate the possibility of practical use of the proposed weight reduction measures. The weight-reduced engine is based on an in-line 4-cylinder, 2.0 liter, gasoline engine with the base engine weight of 162 kg excluding engine oil and coolant and was reduced by 37 kg by applying alternative light-weight materiaLs and new manufacturing techniques. This corresponds to 23 % weight reduction. The materials used in the weight-reduced engine are 53 % steel, 33 % aluminum, 7 % plastics and 7 % other light-weight materials. It was found that by application of light-weight materials, the engine performance of the weight-reduced engine could be improved.

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.

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.