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The objective of the present study is to clarify the effect of early-closing of an intake-valve on the engine performance in a spark-ignition engine. For the first step of the study, under natural aspirating condition, four sets of expansion ratio pistons of 11, 16, 20 and 22 were prepared for two kinds of camshaft, one is, original and the other is geometrically half early-closing.. The obtained performance data and the indicator pressure records were analyzed. It was shown that up to 7 % of improvement in the thermal efficiency can be realized over a wide range of operating condition. This is considered to be mainly caused by the effect of the increased-expansion cycle. The increased-expansion effect can be estimated to be about 1.4 which almost corresponds to the geometrical inlet-valve closure timing. However, this value is not consistent with the measured volumetric efficiency which was almost half the value associated with original timing.

1 In order to reduce the size and weight of the hybrid motor, improving motor cooling performance is essential. Therefore, we have been working on the development. This paper will explain the development of cooling technology TOYOTA has been working on, specifically the evolution of the hybrid motor cooling system and structure from the 1st generation Prius to the current model.

A new method, in which a piston is formed from thick plate of aluminum-silicon alloy under hot working, has been developed by authors. Namely, in the first process a blank is formed into a shape of piston having a bearing part of a piston-pin by drawing, ironing and bottoming. In the second process a bearing part in the piston is made by means of burring. Finally, the plastically formed piston is finished by machining for grooves of piston rings and an oil ring. In this paper, the forming method of the piston of internal combustion engine is mainly described. Furthermore, each stress distribution of plastically formed piston and die-casting one is examined by strain gage method and simulation of Finite Element Method. As a result of comparing both pistons, there are scarcely problems in practical use for this plastically formed piston.