When building a high-performance engine, valve trains are critical components to consider. In an internal combustion engine, a valve train serves as the mechanical system that controls the operation of the intake and exhaust valves. Though the primary function of a valve train is to control the opening and closing of valves, it also controls the flow of air and fuel that enters and leaves the combustion chamber.
In order for a valve train to work, a camshaft is used as it plays an integral role in the rotational movement which aids the opening and closing of valves that use cam lobes. Most heavy-duty diesel engines use four valves in each cylinder. Two valves are required for the intake of the fuel-air mixture and two for exhaust gasses. Furthermore, there is an injector in the middle of the valves that pushes fuel into the cylinder, and it is timed perfectly to ensure that it is working efficiently. Beyond the valves, valve trains consist of numerous other components that allow them to work optimally.
is responsible for controlling the timing and lift of the valve opening. This is achieved with the help of the cam lobe on the rotating shaft. The camshaft is driven by the crankshaft. However, the crankshaft rotates at half the speed than it would for a four-stroke engine. Through the use of a metal timing chain, rubber timing belt, or a set of gears, the crankshaft transfers motion to the camshaft.
In particular, a pushrod is a long, slender metal rod used in overhead valve engines.. Additionally, it is utilized to transfer motion from the camshaft in the engine block to the valves in the cylinder heads. At the bottom end of the pushrod, there is a lifter that gets into contact with the camshaft. The camshaft lobes move the lifter upwards, moving the pushrod as a result. Then, the top end of the lifter pushes on the rocker arm, which opens the valve.
Rocker Arm/Bucket Tappet
Typically, an engine’s design determines how the valve can be actuated. In most cases, a rocker arm, finger, or bucket tappet is used. In overhead camshaft engines, bucket tappets or fingers are utilized. Overhead valve engines, on the other hand, are actuated by a pushrod and pivot on the shaft. It may also be pivoted on individual ball studs which aid in actuating the valves.
In modern engines, poppet valves are most common. However, sleeve valves, slide valves, and rotary valves are also viable options. Usually, poppet valves are opened by the camshaft lobe or rocker arm, and they are closed by a coiled spring called a valve spring.
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