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Camshaft construction and classification
The main body of the camshaft is a cylindrical rod body of the same length as the cylinder block. Above the set of several cams, used to drive the valve. One end of the camshaft is the bearing support point and the other end is connected to the drive wheel.
The side of the cam is egg-shaped. The purpose of its design is to ensure sufficient intake and exhaust of the cylinder, specifically to complete the valve opening and closing in the shortest possible time. In addition, taking into account the durability of the engine and the smoothness of operation, the valve cannot be excessively impacted due to the acceleration and deceleration processes during the opening and closing operations. Otherwise, it will cause severe valve wear, noise increase, or other serious consequences. Therefore, there is a direct relationship between the cam and the engine's power, torque output, and running smoothness.
In general, in the in-line engine, one cam corresponds to one valve, and the V-type engine or the horizontally-opposed engine shares one cam per two valves. Because of its special structure, the rotary engine and the valveless engine do not need a cam.
According to the number of camshafts, they can be classified into single overhead camshaft (SOHC) and double overhead camshaft (DOHC). There is only one camshaft for a single overhead camshaft and two for a dual overhead camshaft, which is too straightforward to explain.
The single overhead camshaft uses a convex shaft on the cylinder head to directly drive the intake and exhaust valves. It has a simple structure and is suitable for high speed engines. The side camshaft that is generally used in the past, that is, the camshaft is on the side of the cylinder, is directly driven by the timing gear. In order to convert the rotation of the camshaft into the reciprocating motion of the valve, a valve lifter must be used to transmit power. In this way, there are many reciprocating parts, and the inertial mass is large, which is not conducive to the high-speed movement of the engine. Moreover, the slender tappet has a certain degree of elasticity, which easily causes vibration, accelerates the wear of parts, and even makes the valve lose control.
The overhead double camshaft is equipped with two camshafts on the cylinder head, one for driving the intake valve and the other for driving the exhaust valve. The use of dual overhead camshafts does not require high design requirements for camshafts and valve springs. It is particularly suitable for use in V-shaped hemispherical combustion chambers and for use with four-valve gas distribution mechanisms.