Automated pressure reducer applied on internal combustion engine with at least one powered cylinder

An automated pressure reducer applied on internal combustion engine with at least one powered cylinder, the cylinder further consisting of at least one combustion room and a valve driven by the rock arm and the cam of the cam shaft to open or shut down the room, mainly comprising a shell body sleeved on the cam shaft and by one side of the exhaust cam, this shell body having a space forward to the exhaust valve and a concave adjacent to the valve on the cam shaft; a positioning element contained in the space being capable of elevating up and down therein to either the first position or the second position, one end of the element being curved to a first segment and a second segment; and a sliding element with a curved body acting on the concave of the cam shaft to lift up the rock arm to open the exhaust valve while the positioning element having arrived at the first position and one side of the sliding element being matching up the first segment, and in converse, while the positioning element having arrived t