So how should the principle and function of the valve device be understood?
Date of release:2018-10-26 Author:Tiansheng Click:
When the two are effectively combined, the variable valve lift technology can match the appropriate valve lift at different engine speeds, making the torque high at low speeds and strong at high speeds. At low speeds, the system uses a small valve lift, which is beneficial to increase the turbulence in the cylinder to increase the combustion speed and increase the low speed torque of the engine. At high speeds, the use of a larger valve lift can significantly increase the intake air amount. Increase the power output at high speeds.
We all know that the engine's valve timing mechanism is responsible for supplying the cylinder with fresh air necessary for gasoline combustion and exhausting the burned exhaust gas. This set of actions can be regarded as the process of inhaling and exhaling the human body. From the working principle, the main function of the valve phase mechanism is to open and close the intake and exhaust valves of each cylinder according to a certain time limit, thereby realizing the whole process of engine cylinder ventilation and replenishment.
So how should the principle and function of the valve be understood? We can compare the engine's valve to a door. The size and length of the door opening determines the flow of people entering and leaving. The larger the angle at which the door is opened, the longer the opening time, and the greater the flow of people entering and leaving, and vice versa. The same principle applies to the engine, which creates the concept of valve lift and timing. The valve lift is like the angle at which the door opens. The valve timing is like the time when the door is open. Looking at the problem from a three-dimensional perspective, the angle plus time is the size of a space, which also determines the amount of intake and exhaust in a unit of time.
The so-called valve clearance means that when the engine is in a cold state, a certain gap is left in the valve transmission mechanism. To compensate for the amount of expansion of the valve and transmission after heating.
When the engine is running, the valve will expand due to the temperature rise. If there is no gap or the clearance is too small between the valve and its transmission member in the cold state, in the hot state, the thermal expansion of the valve and its transmission member will automatically open the valve and cause the valve to be closed tightly, resulting in the engine being The air leakage in the compression and work strokes causes the power to drop, and in severe cases, the engine is not even easy to start. In order to eliminate the above phenomenon, usually, in the cold assembly of the engine, an appropriate gap is left in the valve and its transmission mechanism to compensate for the amount of expansion of the valve after being heated.
The valve clearance depends on the overall structural form of the valve train, and this clearance can also be adjusted. The size of the valve clearance is generally determined by the engine manufacturer according to the test. Usually in the cold state, the clearance of the intake valve is 0.25~0.30mm, and the clearance of the exhaust valve is 0.3~0.35mm. If the clearance is too small, the engine may leak in the hot state, causing the valve to burn out when the power is seriously degraded. If the gap is too large, impact and noise will be generated between the transmission parts and between the valve and the valve seat, and the wear will be accelerated, and the duration of the valve opening will be shortened.
The engine with hydraulic tappet can automatically change the length of the tappet and compensate the thermal expansion of the valve at any time, so there is no need to reserve the valve clearance. For example, FAW Audi and Santana cars do not need to reserve valve clearance.
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