| 摘要 |
PROBLEM TO BE SOLVED: To minimize a wheel base by setting the center line of a crankshaft more upwards than the stroke upper limit of a front wheel axle, allowing an upper cylinder to open more widely than a lower cylinder to the horizontal line, and making the axis of the lower cylinder coincide with the contour line of the front wheel at the stroke upper limit position. SOLUTION: The center line C of the crank shaft of a crank case 5 is located rearward at valleys of banks 18 of upper and lower cylinders 16, 17, and the axle 19 of a front wheel 15 and a stroke upper limit position 19a of the axle 19 are positioned downward to the horizontal line L which passes through the center line C. The angle of the upper cylinder 16 is set, for example, to 55 deg. to the horizontal line L which passes through the center line C, and is made to be larger than the angle of the lower cylinder 17 to the horizontal line L which passes through the center line C, for example 45 deg.. A axis L1 of the lower cylinder 17 is almost made to coincide with the tangent L2 direction of the contour line of the front wheel 15 which faces the lower cylinder 17 at the stroke upper position A of the front wheel 15. Therefore, the lower cylinder 17 and the front wheel 15 approach each other, minimizing a wheel base. |
