How does variable valve timing work? And what is the structure of the variable timing wheel?

The spiral groove VVT-I controller includes a gear driven by a timing belt, an internal gear rigidly connected with the intake camshaft, and a movable piston located between the internal gear and the external gear. There are spiral splines on the surface of the piston, and the piston moves along the axial direction, which will change the phase of the internal gear and the external gear, thus causing the continuous change of the valve distribution phase. When the oil pressure is applied to the left side of the piston, forcing the piston to move to the right, the intake camshaft will advance by a certain angle relative to the camshaft timing pulley due to the helical spline on the piston. When the oil pressure acts on the stone side of the piston, forcing the piston to move to the left, it will delay the intake camshaft by a certain angle. When the ideal valve timing is obtained, the camshaft timing hydraulic control valve will close the oil passage to balance the pressure on both sides of the piston and the piston will stop moving.

Now all advanced engines have "Engine Control Module" (ECM), which is responsible for ignition, fuel injection, emission control, fault detection and so on. The ECM of Toyota VVT-I engine automatically searches for the optimal valve timing corresponding to engine speed, air intake, throttle position and cooling water temperature under various driving conditions, and controls the camshaft timing hydraulic control valve. The actual valve timing is sensed through the signals of various sensors, and then feedback control is carried out to compensate the system error and reach the optimal valve timing position, thus effectively improving the power and performance of the automobile and minimizing the fuel consumption and exhaust emissions.