A valvetrain, or valve train, is part of an internal combustion engine that controls the operation of the intake and exhaust valves. There is an intake valve that allows the air-fuel mixture into the combustion. The exhaust valve allows the exhaust gases to exit the combustion chamber once the process is complete.
The valvetrain opens and closes the intake and exhaust valves, allowing air and fuel mixes to enter and exit the combustion chamber as gases. It consists of all the components responsible for transferring the rotational movement of the camshaft into the opening and closing of the intake and exhaust valves.
In this reading, we’ll explore what a valvetrain is, its components, diagram, and how it works.
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What Is A ValveTrain?
A valve train is a component that is designed to open and close the intake and exhaust valves so that air and fuel mixtures can enter and leave the combustion chamber as gases. Nowadays, engines are designed with overhead cam assemblies, which are known as overhead camshafts. It is located near the top of the engine.
The primary functions of the valvetrain are to control the opening and closing of the valves. The valvetrain also controls the flow of air and fuel that enter the combustion chamber and leave as exhaust gases. In the working of a valvetrain, the camshaft plays a very important role, as its rotational movement aids the opening and closing of the valves using the cam lobes.
Components Of A Valvetrain
The valvetrain is a key part of an internal combustion engine, responsible for controlling the opening and closing of the engine’s intake and exhaust valves. It ensures proper timing and function of the valve operation to regulate air and fuel flow into the cylinders and expel exhaust gases. The main components of a valvetrain include:
Camshaft
The function of the camshaft is to control the timing and lift the profile of the valve opening. This is achieved with the cam lobe on the rotating shaft. In the case of a four-stroke engine, the crankshaft rotates at half the speed of the camshaft. The crankshaft transfers motion to the camshaft using a metal timing chain or mostly a rubber timing belt. A set of gears can also be used.
Pushrod
A pushrod is a long, slender metal rod that is used in overhead valve engines. It’s also used to transfer motion from the camshaft in the engine block to the valves in the cylinder head. There is a lifter on the bottom end of a pushrod that gets in contact with the camshaft. The camshaft lobe moves the lifter upwards, which moves the pushrod. The top end of the lifter further pushes on the rocker arm, which opens the valve.
Rocker Arm/Bucket Tappet
The engine design determines the ways the valve will be actuated, either by a rocker arm, finger, or bucket tappet. In overhead camshaft engines, bucket tappets or fingers are used, upon which the cam lobes contact. Overhead valve engines, which use rocker arms and a pushrod to operate, pivot on a shaft. It can also be pivoted on individual ball studs, which will help to actuate the valves.
Valves
The valve used in most modern engines is called a poppet valve. Some valves, like sleeve valves, slide valves, and rotary valves, are also considered at times. Typically, the camshaft lobe or rocker arm opens poppet valves. A valve spring, which is a coil spring, closes it.
Related: What Is A Camshaft? Its Parts and How It Works
Diagram Of a Valvetrain
How Does A Valvetrain Work?
There are two types of valves: intake and exhaust. Intake valves allow a mixture of air and fuel to enter the engine’s combustion chambers. The cylinder creates a vacuum when the piston moves down on its intake stroke.
After opening at the correct time, the intake valve draws an air-fuel mixture from the intake manifold. The camshaft is responsible for the precise control of the timing and length of the valve opening. .
After the power stroke, exhaust valves, on the other hand, make it easier to remove burned gases from the combustion chamber. On the exhaust stroke, the piston moves up, pushing the exhaust gases out of the cylinder and into the exhaust manifold.
The exhaust valve opens at the appropriate time, releasing the gases into the exhaust system. The timing and duration of the exhaust valves are also accurately synced with the engine’s camshaft, just like the intake valves.