The Camshaft is mainly composed of a journal, CAM, timing Gear or sprocket mounting parts. The journal is the support part of the camshaft, usually distributed in different positions of the camshaft, and the bearing seat on the engine block to ensure that the camshaft can rotate smoothly. The cams are the key characteristic parts of the camshaft, and they are distributed along the journal according to certain rules. Each CAM corresponds to a valve, its profile shape is carefully designed, different profiles determine the valve opening time, lift and duration. The surface of the CAM has been subjected to special heat treatment and processing technology, with high hardness and good wear resistance, to withstand frequent friction and high load pressure between the tappet or Rocker Arm during engine operation. The timing gear or sprocket installation part is located at one end of the camshaft, which is used to connect with the timing gear or sprocket on the crankshaft through the chain, tooth belt and other transmission devices to ensure that the precise transmission ratio between the camshaft and the crankshaft is maintained, so that the four strokes of the engine intake, compression, work and exhaust can be orderly.
When the engine is running, the crankshaft rotates the camshaft through the timing transmission. Take the overhead camshaft engine as an example, when the CAM on the camshaft gradually lifts up with the rotation of the shaft, it will push one end of the rocker arm, so that the rocker arm rotates around the fulcrum, and the other end of the rocker arm will press down on the valve rod to overcome the spring of the valve spring and open the valve. As the CAM continues to rotate, the convex part of the CAM gradually leaves the rocker arm, and the rocker arm returns to its original position under the action of the valve spring, and the valve closes. In this process, the contour shape of the CAM determines the speed at which the valve opens and closes, as well as the size of the lift. For example, when the convex part of the CAM has a steep upward slope, the valve will quickly open to a larger lift, which is conducive to realizing a large amount of intake or exhaust air in a short time; When the slope of the convex part of the CAM is slow, the valve closing process will be relatively stable, reducing the impact force when the valve is seated. In the top rod engine, the CAM first pushes the tappet, the tappet then pushes the push rod, the push rod transfers the force to the rocker arm, and finally realizes the valve opening and closing, the working principle is basically similar, only more tappet and push rod these two intermediate transmission components.
