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Principle of variable valve timing

Date:Sep 05, 2019

The crankshaft drives the camshaft to rotate via the toothed transmission device, so that the valve has a certain correspondence with the rotation angle of the crankshaft when the valve is opened and closed. The flow of gas will change with the speed of the engine. How can the cylinder achieve good intake efficiency at different speeds? To do this, you must change the time the valve is opened and closed. The camshaft can be additionally rotated at a small angle via a hydraulic device mounted on the front end of the camshaft to allow the intake valve to open early when the speed is increased.


The engine's performance can be improved with a variable valve timing mechanism. Different engine speeds require different timings for valve timing. This is because when the engine speed is changed, since the intake air flow rate and the exhaust gas flow rate during the forced exhaust period also change, the effect of increasing the intake air and promoting the exhaust gas by the inertia of the air flow during the valve late closing period will be different.


For example, when the automobile engine is running at a low speed, the airflow inertia is small. If the timing of the valve is kept constant at this time, part of the intake air will be pushed out of the cylinder by the piston, so that the intake air amount is reduced, and the residual exhaust gas in the cylinder will increase. When the engine is running at high speed, the airflow inertia is large. If the intake delay angle and the valve overlap angle are increased at this time, the intake air amount and the residual exhaust gas amount will be increased, and the engine ventilation process will be perfected.

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