PROBLEM TO BE SOLVED: To inhibit the breakage of rotary blades on involving stone etc., in mowing lawn.SOLUTION: The power transmission mechanism for transmitting the power from a driving source to the rotary blades is provided by having a transmission gear rotating with the rotary shaft of the rotary blades in one unit and an output gear 54 engaging with the transmission gear. The output gear 54 inserted with the output shaft 39 of the driving source can move along the axial direction of the output shaft 39, and the engaging part 56 of the output gear 54 engages with the projection part 39a of the output shaft 39. When a large burden acts on the rotary blades and driving source, the engagement between the projection part 39a of the output shaft 39 and the engaging part 56 of the output gear 54 is released and the transmission of the power from the driving source to the rotary blades is also released.COPYRIGHT: (C)2012,JPO&INPIT【課題】芝刈時に石等を巻き込んだときに回転刃が破損するのを抑制する。【解決手段】駆動源からの動力を回転刃に伝達する動力伝達機構は、回転刃の回転軸と一体に回転する伝達歯車と、この伝達歯車と係合する出力歯車54とを有する。出力歯車54は、駆動源の出力軸39が挿入されて出力軸39の軸方向に沿って移動可能であり、出力歯車54の係合部56と、出力軸39の凸部39aとが係合する。回転刃と駆動源とに大きな負荷が作用したときには、出力軸39の凸部39aと出力歯車54の係合部56との係合が解除され、駆動源から回転刃への動力の伝達が解除される。【選択図】図7
