The camshaft is a component in a piston engine. 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. Camshafts have high requirements on strength and support, and their materials are generally high-quality alloy steel or alloy steel. 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.
There are three types of camshafts: lower, middle, and upper. The camshaft of the lower-mounted valve mechanism is located in the crankcase, the camshaft of the central-mounted valve mechanism is located at the upper part of the body, and the camshaft of the upper-type valve mechanism is located on the cylinder head.
Common transmission methods between camshaft and crankshaft include gear transmission, chain transmission and toothed belt transmission. Most of the transmission between the lower camshaft and the middle camshaft and the crankshaft use cylindrical timing gears. Generally, only a pair of gears are required from the crankshaft to the camshaft. If the transmission gear diameter is too large, an additional middle Idler. In order to smooth the meshing and reduce the working noise, most of the timing gears use helical gears.
Cam bearings are subject to periodic shock loads. The contact stress between the cam and the tappet is very large, and the relative sliding speed is also high, so the working surface of the cam is relatively worn. In view of this situation, in addition to the higher dimensional accuracy, smaller surface roughness and sufficient rigidity, the camshaft journal and cam working surface should also have higher wear resistance and good lubrication.
Camshafts are usually forged from high-quality carbon steel or alloy steel, and can also be cast from alloy cast iron or ductile iron. The journal and cam working surface are polished after heat treatment.