The key points of the working principle of the camshaft of an aviation piston engine are as follows:

First, the basic function of the camshaft

The camshaft is a key component of the valve train in an aviation piston engine, and its main function is to precisely control the opening and closing of the valves. Through the rotational movement of the camshaft, the opening and closing of the valves are precisely controlled, thus ensuring that the engine can complete the cycle of four strokes: intake, compression, power generation and exhaust.

Second, the structural features of the camshaft

Main structure

The main body of the camshaft is a cylindrical rod, which is approximately the same length as the cylinder set.

One end of the camshaft is the bearing support point, and the other end is connected to the drive wheel. It is usually driven by the crankshaft through a transmission device such as a chain, toothed belt or gear.

CAM design

The camshaft is equipped with multiple cams designed in a specific shape. The sides of the cams are usually egg-shaped (or called egg-shaped, peach-shaped), and their design purpose is to ensure adequate intake and exhaust of the cylinder.

The shape and position of the CAM determine the lift of the valve (i.e., the maximum distance the valve opens) and the duration of opening and closing.

Third, the working principle of the camshaft

Drive mode

The camshaft is driven to rotate by the crankshaft through a transmission device. The types of transmission devices include gear transmission, chain transmission and toothed belt transmission, etc., which depend on the design requirements of the engine.

Valve control

When the camshaft rotates, the CAM periodically contacts and pushes the valve stem (or directly through the rocker arm mechanism) to move up and down.

This up-and-down movement is immediately transformed into the opening and closing actions of the valves, thereby controlling the timing and duration of air intake and exhaust in the cylinder.

Performance optimization

By adjusting the contour shape and height position of the CAM, the lift of the valve and the duration of its opening and closing can be precisely controlled.

This adjustment is of great significance for improving the intake efficiency of the engine, reducing exhaust resistance, enhancing low-speed torque and high-speed power output, etc.

Fourth, the working conditions and requirements of camshafts

Working conditions

During operation, the camshaft is subjected to periodic impact loads, and the contact stress with the CAM tongs is significant, resulting in a relatively high sliding speed.

Material requirements

The working surfaces of the camshaft journal and CAM need to have high dimensional accuracy, small surface roughness and sufficient rigidity.

Meanwhile, these surfaces also need to have high wear resistance and good lubricity to reduce wear and extend service life.

Fifth, the types and layout forms of camshafts

Type:

According to the number and position of cams on the camshaft, it can be classified into different types such as single overhead camshaft (SOHC) and double overhead camshaft (DOHC).

Layout form

There are three types of camshaft arrangements: bottom-mounted, mid-mounted and top-mounted. The camshaft of the bottom-mounted valve train is located inside the crankcase, that of the mid-mounted valve train is on the upper part of the engine block, and that of the top-mounted valve train is on the cylinder head.

Nowadays, most mass-produced vehicles are equipped with overhead camshafts in their engines. This is because overhead camshafts have a compact structure, a short transmission chain, and greater rigidity of the entire mechanism, allowing the camshaft to be closer to the valves and reducing the waste of reciprocating kinetic energy caused by the larger distance between the camshaft and the valves in bottom-mounted camshafts.

Sixth, maintenance and care of camshafts

Regular inspection

Regularly inspect the working condition of the camshaft, including the wear of the CAM and the tightness of the transmission device, etc.

Lubrication and Cooling

Ensure that the camshaft is well lubricated and cooled to extend its service life.

Fault handling

When a camshaft malfunctions, it should be repaired or replaced promptly to ensure the normal operation of the engine.

In summary, the key points of the working principle of the camshaft in an aviation piston engine involve multiple aspects such as its basic function, structural features, working principle, working conditions and requirements, types and layout forms, as well as maintenance and upkeep. By gaining a thorough understanding of the working principle and characteristics of the camshaft, one can better understand the valve train of the engine, providing strong support for the maintenance and upkeep of the engine.