Rocker arms open and close valves in internal combustion engines. They can be made from stamped steel or heavier materials, and are operated by camshaft lobes or lifter-driven pushrods. Seesaw designs have improved over time, with variations in design affecting efficiency and wear resistance. Material strength and weight are important considerations in their construction.
A rocker arm is a valve train component in internal combustion engines. When the camshaft lobe acts on the arm, it opens an intake or exhaust valve. This allows fuel and air to enter the combustion chamber during the intake stroke or exhaust gases to be expelled during the exhaust stroke. Seesaws were first invented in the 19th century and have changed little in function since then. However, improvements have been made both in the efficiency of the operation and in the construction materials. Many modern rockers are made from stamped steel, although some applications may use heavier materials.
In many internal combustion engines, rotational motion is induced in the crankshaft as the pistons cause it to turn. This rotation is transferred to the camshaft through a belt or chain. In turn, the camshaft lobes are used to open the valves through rocker arms. This can be accomplished through direct contact between a camshaft lobe and rocker arm or indirectly through contact with a lifter-driven pushrod. Overhead cam engines have lobes on the camshaft that contact each rocker arm directly, while overhead valve engines use lifters and pushrods. In overhead cam engines, the camshaft may be located in the head, while overhead valve engines have the camshaft in the block. Both varieties are seen in the United States, but the regulations have contributed to the decline in overhead valve applications in other parts of the world.
Throughout the history of the seesaw, its function has been studied and improved. These improvements have resulted in arms that are more efficient and more resistant to wear. Some designs may use two rocker arms per valve, while others use a “rundle” roller bearing to press the valve. These variations in design can result in swing arms that look physically different from one another, even though each arm still performs the same basic function.
Since energy is required to move a rocker and depress a valve, your weight can be an important consideration. If a seesaw is excessively heavy, it may require too much energy to move. This can prevent the motor from reaching the desired rotational speed. The strength of the material can also be a consideration, as weak material can be stressed or worn too quickly. Many automotive applications use stamped steel for these reasons, as this material can provide a balance between weight and durability. Some applications, particularly diesel engines, may make use of heavier materials. Motors like these can run at higher torques and lower rotational speeds, allowing the use of materials such as cast iron or forged carbon steel.
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