What is the function of valve timing?
1 Answers
The function of valve timing is to coordinate with the operation of the piston and cylinder liner, regularly opening and closing the intake and exhaust valves. Valve timing refers to the opening and closing moments of the intake and exhaust valves and their duration, expressed in terms of crankshaft rotation angles. It is typically represented by a circular diagram. In a four-stroke engine, the intake valve opens when the crank is at top dead center and closes when the crank reaches bottom dead center; the exhaust valve opens when the crank is at bottom dead center and closes when it reaches top dead center. The intake and exhaust durations each occupy 180 degrees of crankshaft rotation. The purpose of advancing the intake valve opening is to ensure that the intake valve is fully open when the intake stroke begins, allowing fresh air to smoothly fill the cylinder. When the piston reaches bottom dead center, the pressure inside the cylinder is still lower than atmospheric pressure. During the initial stage of the compression stroke, when the piston moves upward at a slower speed, the inertia of the airflow and the pressure difference can still be utilized to continue the intake process. Therefore, delaying the closing of the intake valve slightly is beneficial for improving cylinder charging.
