Honda Motor Co., Ltd.

Shigeo Okui

Kenji Sato

Takeru Hamakawa

Naoto Kodama

Atsushi Nakajima

A spacer covets intermediate portions of respective cylinder bores in a depth direction of a water jacket throughout the entire peripherics of the intermediate portions in the peripheral direction. Accordingly, the intermediate portion of each cylinder bore becomes higher in temperature than any other portion, and is thermally expanded. Thereby, the clearance between the cylinder bore and the corresponding piston increases. Thus, the friction decreases to improve fuel efficiency of an internal combustion engine. Furthermore, the temperature of oil lubricating the intermediate portion of the cylinder bore rises, and the viscosity decreases. Accordingly, the effect of friction reduction is enhanced more. Furthermore, upper and lower portions of the cylinder bores in a cylinder axis direction are sufficiently cooled. Therefore, the cooling performance of a top part and a skirt part of each piston, which tends to become higher in tempera lure, is secured. Accordingly, overheat can be prevented.

Cooling structure for internal combustion engine

A height of a spacer which is arranged inside a water jacket formed to surround peripheries of cylinder bores of a cylinder block of an internal combustion engine is made to be lower by a step in an intermediate portion thereof in a cylinder row line direction. Consequently, among end-portion cylinder bores having a lower temperature and being situated at opposite end portions in the cylinder row line direction and intermediate cylinder bores being other than the end-portion cylinder bores and having a higher temperature, a cooling performance of the intermediate cylinder bores is higher than that of the end-portion cylinder bores. Therefore, all the temperatures of the respective cylinder bores can be made uniform. A similar operation effect can be obtained alternatively by making a thickness of the spacer thinner in portions facing the intermediate cylinder bores and thicker in portions facing the end-portion cylinder bores.

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Wako, Japan

Shigeo Okui