Technical principle of variable valve timing

The valve timing system of the traditional engine is a mechanical system, and the valve timing is unchanged, that is, the valve is opened and closed. This valve timing system can't meet the engine's demand for valve timing under various working conditions, and can't meet the engine's demand for strong power output under various speed conditions. Variable valve timing system is an electronic control system that changes the valve opening time or opening size. By matching the vehicle with more reasonable valve opening or closing time at different speeds, the balance of vehicle torque output is enhanced, engine power is improved, and vehicle fuel consumption is reduced.

It can be seen from the valve timing diagram that the intake valve will open ahead of time and close later during the intake process when the piston moves from top dead center to bottom dead center. When the engine does work and the piston moves from bottom dead center to top dead center, the exhaust valve will open ahead of time and close later.

This method of extending the valve opening time will inevitably lead to the moment when the intake valve and the exhaust valve open at the same time. This moment is called "overlapping stage" in the valve distribution phase, which may cause exhaust backflow. This phenomenon is most obvious when the engine speed is only below 1 000 r/min (the "overlapping phase" time at idle speed is 7 times that at medium speed). This will easily lead to unsmooth idle work, excessive vibration, power drop and other phenomena. Especially for four-valve engines, because of the large value of "curtain area", "overlapping stage" is more likely to cause the phenomenon of poor idle running. In order to eliminate this defect, the designer adopted a "variable" valve drive mechanism instead of "variable".

The variable valve drive mechanism is to reduce the valve stroke and curtain value when the engine works quickly, but to increase the valve stroke and curtain value and change the time of "overlapping stage" when the engine works at high speed, so that the engine can provide powerful power at high speed and generate enough torque at low speed, thus improving the working performance of the engine. The variable valve driving mechanism can change the valve timing, valve lift and valve opening duration at any time according to the driving condition of the automobile.