Like the human respiratory system, the engine has different requirements for the air entering the cylinder under different working conditions. in case
If only one intake and exhaust mode is maintained, then the engine will not be able to have a good output in all situations.
Therefore, not only can not show the corresponding power, but also can not achieve the effect of low fuel consumption. The valve variable timing system will
This bondage has changed into the past. So how is this technology developed?
Although everyone knows the working principle of the four-stroke engine, the intake and exhaust system of the cylinder is
not simple. In the history of valve development, we have used piston valves, sleeve valves, rotary valves, but most
At the end of the day, we still use the most flexible and practical cam valve system, because this form is the most in controlling the valve opening and closing.
Effective, the force on the valve is relatively simple.
However, with the further improvement in engine performance requirements, people began to study the addition of gas in addition to the intake and exhaust strokes.
Beyond the door, there is no better way to mix oil and gas. In order to increase the amount of intake air, the designer hopes to live
The plug does not close the intake valve when it reaches the bottom dead center, that is, as long as the inhalation stroke still exists, let the air intake
The valve continues to open. Therefore, the intake valve is closed after the piston has reached the bottom and is running at a crank angle of approximately 60 degrees.
By the same token, we can also let the exhaust valve open earlier, that is, when the piston reaches the bottom dead center.
The exhaust valve is opened before the crank angle of 60 degrees, because at this time, the pressure in the exhaust manifold has already been compared with the pressure of the exhaust gas in the cylinder.
The power is almost the same.
Although opening the exhaust valve early will damage certain useful energy, at the same time, excessive back pressure will affect the vehicle's sex.
Can perform (this is why there is enough energy in the exhaust to drive the worm gear). And the piston finished fourth
After the stroke, the engineers still do not let the exhaust valve close, so that the piston continues to rotate 15-20 degrees crankshaft.
Close after the corner. At the same time, the intake valve opens at 10-20 degrees before the first stroke is again, allowing more oil and gas mixture to enter the cylinder. Thus, about 30-40 degrees of crankshaft rotation is the same as the intake and exhaust valves.
It is turned on.
This phase of opening the intake and exhaust valves together is called the overlap phase. Through this design, you can further mention
High engine performance, especially for some high speed engines, the angle of the overlap phase can even reach 80 degrees
about. Therefore, from the above principles, we can understand that “compromise” is the most important for valve timing technology.
A design that performs well under low turns may not be effective at high turns, while an engine design with more overlaps is at low turn.
The performance of the torque output is not good, and the engine with less overlap is replaced by the engine at the expense of the power performance.
Uniform and high torque. Therefore, it is necessary to optimize the launch at the time of design, taking full account of the cam shape and timing design.
Therefore, for a long period of time, the design of the engine has been relatively moderate, no machine can
Guarantee the effectiveness of the high turn, and ensure the high torque of low turn. However, in the early 1970s, it was opened for emission reduction purposes.
The variable cam timing technology has given an important inspiration to the engine design community. Apply valve timing adjustment during the overlap phase
The exhaust gas can be used to reduce the temperature and thus reduce NOx emissions.
Therefore, in the 1970s, exhaust gas external circulation (EGR) technology has been widely used to reduce NOx.
It is generally accepted, but if the inner loop can be formed, the design of the engine will be simpler. So, people apply later
A longer overlap time allows some of the exhaust gas to enter the cylinder during the intake stroke. However, although this problem gets
Solved, however, the effects of idle and low speed were affected and the engine could not pass the exhaust in the initial stage.
The high temperature to activate the catalyst, so people began to use variable cam timing technology.
Note: VVT solenoid factory, oil control valve manufacturer, cam phaser supplier, cam phaser factory.