Automatic pressure reduction device for diesel engine starting

The utility model relates to an automobile pressure reduction device for diesel engine starting, which comprises a cylinder cap and a pressure reduction shaft. An oil inlet passage is arranged on a cylinder wall of the cylinder cap located on one side of an exhaust rocker arm, one side of the pressure reduction shaft is hermetically connected with the oil inlet passage of the cylinder cap, the other side of the pressure reduction shaft is supported in the cylinder cap through an elastic part, a conical boss on the pressure reduction shaft is connected with the exhaust rocker arm or an air inlet rocker arm, and a small conical surface of the conical boss faces towards one side of the oil inlet passage of the cylinder cap. The automatic pressure reduction device adopts a lubricating system in a diesel engine and adopts lubricating oil as power for controlling axial movement of the pressure reduction shaft, and the conical boss on the pressure reduction shaft is acted onto an exhaust door or an air inlet door th