| 摘要 |
PURPOSE:To carry out the necessary cooling in simple ways by forming a water head increasing part by extending a part of a water passage communicating to a water jacket in the upper part and setting the water head exerted onto a water pump in a specific relation for the revolution speed of an engine and the discharge pressure of the water pump. CONSTITUTION:When an engine 13 installed in the upper part of a propulsion unit 12 in an outboard motor 10 is driven, a water pump 32 is driven through a driving shaft 14, and the outside water supplied from a water taking-in port 33 is supplied into the water jackets 30 and 31 on the body side and head side through a water supplying passage 34, and cooling is performed. With such constitution, a branched water supply passage 35 communicating to the body side water jacket 30 is extended in the upper part along the outside surface of a cylinder body 17, and the uppermost part is formed into a waterhead increasing part 41. The water head which the water head increasing part 41 exerts onto the water pump 32 is set larger than the discharge pressure of the water pump 32 during the low speed operation of the engine and smaller than the discharge pressure during the intermediate or high speed operation of the engine increased. |
