By using VVL, the engine can obtain the required valve lift in both high-speed and low-speed regions. Thereby improve that high-speed power and low-speed torque of the engine.
The principle of engine Variable Valve Timing technology (VVT is the abbreviation of English variable valve timing) is to adjust the intake (exhaust), valve opening and closing time and angle according to the operation of the engine. So as to optimize the intake air quantity and improve the combustion efficiency. Advantages are fuel saving and large power boost ratio; The disadvantage is that the mid-end speed and torque are insufficient.
VVT variable valve timing system. The system adjusts the phase of the engine cam through the equipped control and execution system, so that the opening and closing time of the valve changes with the change of the engine speed, thus improving the charging efficiency and increasing the engine power.
In the engine with VVL technology, the valve stroke can change with the change of engine speed. At high speed, long stroke is used to improve the intake efficiency and make the engine breathe more smoothly. At low speed, the short stroke can generate greater intake negative pressure and more vortex, so that air and fuel can be fully mixed, thus improving the torque output at low speed.
Because of the high cost and high reliability of VVL technology, the design of engine cylinder head is difficult and the cost performance is not as good as that of VVT. At present, only BYD is using this technology in domestic independent brand engines.