POWER UNIT

To provide a poWer unit capable of being miniaturized by simplifying a structure by reducing the number of components of a shift drive mechanism, and suppressing enlargement of a transmission unit, and performing quick and smooth gear change by an electric motor.SOLUTION: In a power unit, a driven gear (83) is disposed on a drum rotary shaft portion (81) at one side of a shift drum (80), a case side wall (11Ff) at one side of a crank case (11) journaling the drum rotary shaft portion (81) is covered by an opposed case cover member (50F), a shift motor (61) is disposed on the case cover member (50F) in a manner that a drive gear (62) is projected toward the case side wall (11Ff), and a reduction gear train (75) having a multiple reduction stages for transmitting power between the driving gear (62) and the driven gear (83) is arranged in a manner that both ends of the gear shafts (76, 77) are journaled by the case side wall (11Ff) and the case cover member (50F).SELECTED DRAWING: Figure 5 【課題】変速駆動機構の部品点数を少なくして構造を簡素化し、変速装置の拡大を抑えて小型化を図るとともに、電動モータによるより早くかつ円滑な変速が可能なパワーユニットを低コストで供する。【解決手段】シフトドラム(80)の一方のドラム回動軸部(81)に被動ギア(83)が設けられ、前記ドラム回動軸部(81)を軸支するクランクケース(11)の一方のケース側壁(11Ff)が、対向したケースカバー部材(50F)により覆われ、ケースカバー部材(50F)にシフトモータ(61)が駆動ギア(62)をケース側壁(11Ff)に向けて突出して取り付けられ、駆動ギア(62)と被動ギア(83)との間を動力伝達する多段の減速段を有する減速ギア列(75)が、そのギア軸(76,77)の両端をケース側壁(11Ff)とケースカバー部材(50F)とに軸支されて配列されるパワーユニットである。【選択図】図５