Ordinary engine valve mechanism, we all know that the valve is driven by the crankshaft of the engine through the camshaft, and the valve timing depends on the rotation angle of the camshaft. When the engine is running, we need to let more fresh air into the combustion chamber, so that the exhaust gas can be discharged from the combustion chamber as much as possible. The best solution is to open the intake valve in advance and let the exhaust valve close later. In this way, between the intake stroke and the exhaust stroke, the intake valve and the exhaust valve will open at the same time, and the overlap between the intake and exhaust valves is called the valve overlap angle. On an ordinary engine, the opening and closing time of the intake valve and the exhaust valve is fixed, and the valve superposition angle is also fixed. cannot be changed. However, the level of engine speed has an impact on intake, exhaust flow and the combustion process in the cylinder. When the speed is high, the intake air flow rate is high and the inertial energy is large, so it is hoped that the intake valve will be opened earlier and closed later, so that fresh gas can be smoothly charged into the cylinder, and as much mixture or air as possible.