Such as the intake valve: the top dead center before -3 degrees open, to 37 degrees, then it should be closed from 37 or 38 degrees, why is it after the bottom point of 71 degrees?
Modern automobile production, the law of gas into and out of the movement of a more realistic theoretical research and analysis, only to draw the conclusion.
As the current number of revolutions is relatively high, before the crankshaft rotation 70 °, the corresponding piston stroke is small, 70 ° after the piston stroke was significantly increased, then 70 ° will be significantly smaller, the intake valve point after 71 ° It is closed, is that the valve from the open to the amenorrhea 3 + 180 +71 = 254 °
According to this theory, the automobile industry to produce the medium-term, basically into the exhaust valve opening time ahead of time, closing time delay, so that the top deadline and the bottom deadline + -4 ° range, the intake valve and exhaust Door at the same time open the phenomenon, called the valve phase.
Early car engine into the exhaust valve opening and closing time are at the top deadline.
Later, it was found that the valve in the top dead center 0 ° open, due to the inertia of the late role, the actual amount of gas into the cylinder is insufficient.
In order to increase the intake volume, the valve will be better to open the effect in advance.
