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The function of valve lifter, what is valve lifter


The engine is the power system of a car, and engine failure is also the biggest problem that plagues riders. So how do we respond when the engine fails? This requires a lot of knowledge about the internal components of the engine in daily life. The valve lifter is an important part of the engine. So what is the function of the engine valve lifter? Let us understand together.

The role of valve lifters

In order to ensure that the valve closes tightly, there is a proper gap between the end of the valve rod and the valve driver (rocker arm, tappet or cam), which is called valve clearance. The valve clearance is relatively small when the car is hot, and larger when the car is cold. This is because when the engine is running, the valve stem expands and stretches due to the increase in temperature, which causes the gap to shrink.

If the valve clearance is not adjusted properly, the engine will operate abnormally. If the valve clearance is too large, it will affect the opening of the valve. The reduced valve lift will cause insufficient intake and incomplete exhaust. If the valve clearance is too small, the valve will not close tightly and cause air leakage, resulting in a decrease in power. . In order to avoid the trouble caused by improper valve clearance adjustment, hydraulic lifters that can adjust the valve clearance are generally used on high-speed engines.

One end of the tappet is in contact with the cam, and the other end is in contact with the valve. Its function is to transmit the thrust of the cam to the valve. The tappet on the old engine is equipped with an adjustment screw and a lock nut at one end to adjust the valve clearance, while the hydraulic tappet omits the adjustment screw and the lock nut, and hydraulic adjustment replaces the role of these rigid parts.

The hydraulic tappet is always in contact with the camshaft and runs without gaps. The inside of the tappet uses hydraulic power to adjust the gap. The hydraulic tappet is mainly composed of a plunger, a one-way valve and a one-way valve spring, etc., using the function of the one-way valve to store or release oil, and the working length of the hydraulic tappet can be changed by changing the oil pressure in the tappet body cavity , So as to automatically adjust the valve clearance.

When the engine is working, when the valve is closed, the oil enters the plunger cavity through the tappet body and the orifice of the plunger, pushes the one-way valve straight into the tappet body cavity, and the plunger rises under the action of the oil pressure of the tappet body cavity and the spring. Tighten the valve push rod. At this time, the rising force of the plunger is not enough to overcome the tension of the valve spring, and the valve will not be opened but only eliminates the gap in the entire valve mechanism. At this time, the tappet body cavity is full of oil, and the one-way valve is closed under the action of oil pressure and spring, cutting off the oil path.

When the cam turns to the working surface, the tappet rises, the valve spring tension acts on the plunger through the valve push rod, but at this time the one-way valve is closed so that the oil cannot overflow, and the incompressibility of the oil makes the tappet like The whole body pushes the valve to open. During this process, due to the high oil pressure in the tappet body cavity, a little oil leaks out through the gap between the tappet body and the plunger, which "shortens" the working length of the tappet. When the cam turns over the working surface, the tappet descends, the valve closes, and the oil pressure in the tappet body cavity also drops, so the oil in the main oil passage opens the one-way valve again and injects it into the tappet body cavity to replenish oil, repeat Cycle the above actions.

Through the oil leakage and replenishment in the tappet body cavity, the working length of the tappet is continuously and automatically adjusted to keep the valve working normally without gaps in the entire mechanism, reducing the impact and noise between parts, and eliminating the old engine valve The ills of the gap. At the same time, the use of hydraulic tappets can make the camshaft profile a bit more slender, making the valve opening and closing faster, and more in line with the requirements of modern high-speed engines.

The above is the sorted out about the related problems of the valve lifter of the car engine. Every component of the car engine is very important. We need to know more about the related problems of the engine components in our daily life. When the car encounters an engine failure We are not at a loss. We can solve some small problems ourselves.