The piston four-stroke engine is completed by 4 strokes of intake, compression, work and exhaust, and we are concerned with the problem of the valve opening to the engine inlet. The basic principle of cylinder intake is "negative pressure", that is, the gas pressure difference inside and outside the cylinder. In the engine low-speed operation, the valve opening degree must not be too large, so easy to cause the cylinder inside and outside pressure equalization, negative pressure reduction, so that the intake is not sufficient, for the valve work, this "small degree open" need to control the way of short stroke; If the valve is still timid refused to open, the engine inlet must be blocked, so we need a long stroke of the valve lift.
Often, engineers need to take into account the engine in the low-speed zone torque characteristics, but also want to extract the power characteristics of the high-speed zone, can only adopt a "compromise" of the train of thought, the end of the engine high-speed power, low-speed short torque ... So in this case, a device for adjusting the valve lift is needed, which is what we would call "variable valve timing technology". This technology can not only guarantee low speed and high torque, but also get high speed and power, which is a great breakthrough for the engine.