Kohei Nakashima

Development of Air-Cooled Cylinder by Utilizing Natural Convection

An air-cooled engine with a finned cylinder may have residual heat between the fins. Residual heat decreases heat release from the cylinder when cooling air is not forced over the engine. In order to induce natural convection in the cylinder, cooling ports were drilled in the fins parallel to the cylinder axis to determine if residual heat could be decreased and additional cylinder cooling could be developed. The effects of the fin configurations on air-cooling were investigated to utilize the cooling ports for a stationary engine and a non-moving motorbike engine. The experimental cylinder design permitted variation in the number of fins and fin pitch. Numbers of fins that had various port sizes and port positions were investigated; in addition, the temperature inside of the cylinder and in the space between the fins was measured. Results indicated that heat release from the cylinder was increased by utilizing the fins with ports as compared to the fins without ports. It was also found that fin pitch, number of fins, port size, port position, and number of ports have significant effects on cylinder temperature. These results can be utilized to improve the design of an air-cooled cylinder by utilizing natural convection.

DEVELOPMENT OF A SIMPLIFIED METHOD FOR MEASURING ENGINE MOTORING FRICTION AND ITS APPLICATION TO VALVE TRAIN FRICTION MEASUREMENT

We developed a simpler and less expensive method for measuring friction. Our equipment floats the double-end shaft motor by supporting both sides of the motor shaft with bearings, allowing the stator within the motor case to swing on the rotor with the shaft. Two arms were installed in the motor case; one is attached to a load meter; the other to a balance weight. The motor shaft is connected to the engine shaft, and when the engine is operated by the motor, torque is exerted on the stator with the motor case in the direction opposite to the motor shaft rotation, with engine friction acting as the reaction force. Torque is calculated by multiplying the arm length by the load as measured by the load meter in the arm. As an application of our new motoring friction test method, we measured valve train friction. The cylinder head of a single cylinder gasoline engine was clamped on a test bed, and its camshaft was connected to our friction measuring equipment. Utilizing various follower configurations of the rocker arms, we investigated the friction loss between the rocker arms and the cam. We thus clarified the effect of the valve-opening period and the valve lift on friction loss under various camshaft rotation speeds, and understood the lubricating conditions between the rocker arms and the cam.