The principle of the engine valve train is to open and close the intake and exhaust valves of each cylinder in a timely manner according to the working cycle and ignition sequence requirements of the engine, allowing fresh air to be drawn into the cylinder and exhaust gases to be expelled after combustion. Below is a detailed explanation: 1. When the working cycle of the cylinder requires the valves to open for gas exchange, the crankshaft drives the camshaft to rotate through the transmission mechanism. The raised part of the cam on the camshaft pushes the rocker arm to swing via the tappet, push rod, and adjusting screw. The other end of the rocker arm then pushes the valve downward, further compressing the spring. Once the peak of the cam's raised part passes the tappet, the thrust on the tappet gradually decreases. The valve's opening gradually reduces under the tension of the spring until it finally closes. 2. The valve train often uses overhead valves and is categorized into underhead, mid-head, and overhead types based on the camshaft's position. The valve train consists of two main parts: the valve drive group and the valve group. The valve drive group includes the crankshaft timing gear, camshaft timing gear, camshaft, tappet, push rod, rocker arm, valve clearance adjusting screw, lock nut, and rocker arm shaft. The valve group includes the valve, valve guide, valve spring, valve spring seat, valve oil seal, and valve seat. 3. When the maximum raised part of the cam contacts the tappet, the valve reaches its maximum opening. Subsequently, the raised surface of the cam in contact with the tappet gradually decreases, and the valve begins to close under the action of the valve spring, reversely pushing the rocker arm and other transmission components, causing the tappet to move downward to maintain contact with the cam. When the raised part of the cam leaves the tappet, the valve fully closes.
