For an air-cooled engine, designers must choose the number of fins required for cooling, then arrange them along the cylinder at a suitable fin pitch. Most motorbikes mount their air-cooled engines at a slant, with their cylinder central axis not perpendicular to the air flow. This study investigated the cooling characteristics of air-cooled experimental cylinders, with various fin pitches and number of fins, mounted at tilt angles between 0° (vertical) and 90° (horizontal), in a wind tunnel at air velocities of 20km/h (5.6m/s) and 60km/h (16.7m/s). Heat transfer rate from the cylinder was measured, air flow between fins was observed using the smoke wire method, and air flow over fin surfaces was observed using the oil film method. Results indicated that, except at 20km/h (5.6m/s) and a pitch of 7.5mm, cylinder cooling increased as tilt angle increased from 0° to 40°, then decreased when the cylinder tilt angle exceeded 40°. Only at 20km/h (5.6m/s) and a pitch of 7.5mm, cylinder cooling increased as tilt angle increased from 0° to 30°, then decreased when the cylinder tilt angle exceeded 30°. Cylinder cooling was maximized with 7 fins pitched at 10mm.

Industrial robots need motors with small size, large torque, and high precision. The electromagnetic motors connected with reducers are generally used, but they often become large. On the other hand, the motors integrated with reducers can output reduced rotation directly and then achieve downsizing. However, driving parts have to receive load torque in the reducer-integrated motors proposed in the past and it is difficult to hold large torque or to gain high stiffness. To solve this problem, a reducer-integrated motor using the principle of a strain wave gearing system is proposed in this research. In the proposed motor, high-stiffness internal gears support the load torque applied to the motor. This paper first explains the structure of the proposed motor and discusses its characteristics. Next, we analyze numerically the tooth tips interference in order to show the structural condition for the proposed motor working properly. The prototype of the proposed motor is developed and an experiment is conducted. The result verifies the fundamental effectiveness of the proposed motor.