Patent ID: 7469611
Filing Date: 2008-12-30
Classification: F02B,F16H,Y10T

Abstract:
1. A power unit for a vehicle, the power unit comprising: a crankcase, a crankshaft rotatably supported within the crankcase, and a transmission structure, comprising: a main shaft, a countershaft, plural gear sets for selectively connecting the countershaft and the main shaft, wherein said transmission structure is configured to permit selection of one of the plural gear sets, a clutch mechanism for selectively connecting the crankshaft and the main shaft, and a shift drum that drives shift forks in order to select one of the plural gear sets, said shift drum having opposed axial ends, wherein the crankshaft, the main shaft and the countershaft are rotatably supported by the crankcase and have mutually parallel axes, wherein the clutch mechanism is installed at an end of the main shaft at a location outside the crankcase, wherein both axial ends of the shift drum are supported by the crankcase so that the shift drum can rotate about an axis parallel to the axes of the crankshaft, the main shaft and the countershaft, wherein the shift drum is disposed at a location corresponding to the maximum outside diameter of the clutch mechanism when viewed in a plane perpendicular to the axis of the main shaft, and wherein the shift drum is installed in the crankcase from a side of the crankcase to which the clutch mechanism is attached, and the shift drum is situated such that a junction between the shift drum and the crankcase is included in a sealed range of the clutch mechanism.