INTERNAL COMBUSTION ENGINE

PROBLEM TO BE SOLVED: To provide a four-stroke internal combustion engine capable of suppressing fluctuation of output torque.SOLUTION: A four-stroke internal combustion engine in which movement of one time between dead points of a piston is regarded as one stroke, and continuous four strokes are successively assigned to an intake stroke, a compression stroke, an expansion stroke and an exhaust stroke, includes a crank shaft 3 rotated by 1/2 in the movement of one stroke of the piston, an output shaft 4, and a speed conversion mechanism 6 disposed between the crank shaft 3 and the output shaft 4, and rotating the crank shaft 3 and the output shaft 4 in an interlocked manner while changing a rotating speed ratio (Vc/Vo) between both shafts as a ratio of the rotating speed (Vc) of the crank shaft 3 to the rotating speed (Vo) of the output shaft 4. The rotating speed ratio in the expansion stroke is smaller than rotating speed ratios of any of the other strokes excluding the expansion stroke, by the speed conversion mechanism 6.SELECTED DRAWING: Figure 2 【課題】出力トルクの変動を抑制可能な４ストロークの内燃機関を提供する。【解決手段】ピストンの死点間の１回の移動を１行程とし、連続する４行程を吸気行程と圧縮行程と膨張行程と排気行程とに順次割り当てる４ストロークの内燃機関であって、ピストンの１行程の移動で１／２回転するクランク軸３と、出力軸４と、クランク軸３と出力軸４との間に介在し、出力軸４の回転速度（Ｖｏ）に対するクランク軸３の回転速度（Ｖｃ）の比である両軸間の回転速度比（Ｖｃ／Ｖｏ）を変化させながら、クランク軸３と出力軸４とを連動回転させる速度変換機構６とを備え、速度変換機構６によって、膨張行程の回転速度比は、膨張行程以外の他の全行程のいずれの回転速度比よりも小さくなる。【選択図】 図２