The engine's auxiliary systems contribute to its correct operation. Depending on the engine design, this category includes the valve train, fuel supply system, lubrication system, ignition system (in spark-ignition engines) and starting system, cooling system and exhaust system.
The valve train controls the opening and closing of the intake and exhaust valves at the appropriate points in the engine cycle. Its operation ensures the admission of the air-fuel mixture in spark-ignition (SI) engines, or air in compression-ignition (CI) engines, as well as the discharge of burnt gases.
The main components of the valve train are:
- camshaft: this is the component that controls the opening of the valves. It receives rotational motion from the crankshaft through the timing belt, timing chain or gears, and its cams actuate the mechanism that opens the intake and exhaust valves. It is driven by the crankshaft through the timing belt, chain or gears.
- tappets: their role is to receive motion from the cam on the camshaft and transmit it to the valve operating mechanism, while also reducing wear between the parts in direct contact during operation.
- valves: these are components fitted in the cylinder head, in the intake and exhaust areas, which regulate the admission of the air-fuel mixture or air, as applicable, into the cylinder and the discharge of gases resulting from combustion, in accordance with the engine's operating cycle.
- valve springs: these are coil springs fitted to the valves to return them to the closed position after they have been opened. When the cam actuates the valve, the valve lifts and the spring is compressed. Once the cam stops acting on the valve, the spring returns to its original shape and closes the valve. At high engine speeds, this action is repeated many times within a short period.
Leave a comment