Its role is to control the opening and closing actions of the valve. Although the speed of the camshaft in a four-stroke engine is half that of the crankshaft (the speed of the camshaft is the same as that of the crankshaft in a two-stroke engine), it usually still has a high speed and needs to withstand a large amount of torque. Camshaft has high requirements on strength and support. Its material is generally special cast iron, and occasionally it uses forgings. Because the valve motion is related to the power and running characteristics of an engine, the camshaft design occupies a very important position in the engine design process.
The main body of the camshaft is a cylindrical rod with the same length as the cylinder group. There are several cams on the top for driving the valves. One end of the camshaft is a bearing support point, and the other end is connected to the driving wheel.
The sides of the cam are egg-shaped. The purpose of its design is to ensure sufficient intake and exhaust of the cylinder, specifically to complete the opening and closing of the valve in the shortest possible time. In addition, considering the durability of the engine and the smoothness of the operation, the valve should not have too much impact due to the acceleration and deceleration during the opening and closing action, otherwise it will cause severe valve wear, increased noise, or other serious consequences. Therefore, the cam and the engine's power, torque output and smooth running are directly related.
Generally, in-line engines, one cam corresponds to one valve, while V-type engines or horizontally opposed engines share one cam for every two valves. Rotor engines and valveless gas engines do not require cams because of their special structure.