The power of the chain saw is a two-stroke, single-cylinder, forced-air-cooled gasoline engine. The gasoline engine outputs mechanical power to drive the saw chain to stop high-speed operation along the guide plate to generate cutting force, and then complete various sawing tasks.

1. Structure of chain saw The main components of chain saw are crank connecting rod mechanism, crankcase and cylinder, ignition system, fuel supply system, intake and exhaust system, lubrication system, cooling system, starting device, etc. The cylinder includes the inner wall, radiating fins, extinguishing chamber, etc. There are three holes on the cylinder, namely the intake hole, the exhaust hole and the ventilation hole. These three holes are identified by the piston at a certain time. The complete sealing of the cylinder is a necessary condition for the chain saw to continue to run and generate power. The cylinder is mounted on the crankcase. The piston can reciprocate in the cylinder and block the cylinder from the lower part of the cylinder to form a sealed space. The fuel is extinguished in the sealed space, and the generated power pushes the piston to move. The reciprocating motion of the piston pushes the crankshaft to rotate through the connecting rod, and the crankshaft then outputs power from the flywheel end. The crank connecting rod mechanism is composed of piston group, connecting rod, crankshaft and flywheel, which is the main part of the power transmission of the chain saw. The piston group is composed of pistons, piston rings, piston pins, etc. The piston is cylindrical, with a piston ring underneath, which seals the cylinder when the piston reciprocates to avoid gas leakage in the cylinder. The piston pin is cylindrical, and it penetrates into the pin hole on the piston and the small end of the connecting rod to connect the piston and the connecting rod. The connecting rod is divided into three parts: a big end, a small end and a shaft. The big end is connected with the crank pin of the crankshaft, and the small end is connected with the piston pin. In the connecting rod task, the small head end reciprocates with the piston, the big head end rotates around the crankshaft axis with the crank pin, and the shaft makes a complex swing motion. The function of the crankshaft is to convert the reciprocating motion of the piston into a rotary motion, and transfer the work done by the contraction stroke through the flywheel installed on the rear end of the crankshaft. The flywheel can store energy so that the other strokes of the piston can work normally and the crankshaft rotates evenly. The intake and exhaust system usually consists of an air cleaner, an intake pipe, an exhaust pipe and a muffler. In order to supply fuel into the cylinder, the chain saw is equipped with a fuel supply system. The air and fuel are mixed at a certain concentration through a carburetor installed at the inlet end of the intake pipe, and then fed into the cylinder through the intake pipe, and the electric spark controlled by the chain saw ignition system is regularly extinguished. When the fuel in the cylinder of the chain saw is extinguished, the piston, cylinder and other parts are heated, and their temperature rises. In order to ensure the normal operation of the chain saw and prevent the piston, cylinder and other parts from being damaged by overheating, a cooling system must be provided. The flywheel blades and the wind channel formed by the starter cover, housing and other parts form the cooling system of the chain saw. The chain saw cannot be turned from the parking state to the running state by itself, and the crankshaft must be turned by an external force to start it. This kind of device that generates external force is called the starting device.

2. The task principle of the chain saw To continue the task of the chain saw, the piston must return to its original position after pushing the crankshaft in order to push the crankshaft again, which requires the piston to reciprocate in the cylinder. The movement of the piston from one end of the cylinder to the other end of the cylinder is called a stroke. The task cycle of the chain saw consists of processes such as air intake, compression, extinguishing and contraction, and exhaust. First stroke: the piston moves upward from bottom dead center, the air intake, exhaust and ventilation holes on the cylinder are closed at the same time, and the mixed gas entering the cylinder is compressed; the piston continues to move upward, further compressing the mixed gas, and intake The hole will be exposed as the piston moves up, and the combustible mixture flows into the crankcase through the underside of the piston. Second stroke: When the piston is compressed to the vicinity of the top dead center, the spark plug just jumps to fire to extinguish the combustible mixture, and the gas shrinks to push the piston down to do work. As the piston moves down, the intake hole is closed, and the combustible mixture enclosed in the crankcase is compressed; when the piston approaches bottom dead center, the exhaust hole opens, and the exhaust gas rushes out due to weak pressure; then the ventilation hole opens, The pre-compressed combustible mixture rushes into the cylinder through the air exchange channel to drive off the exhaust gas and stop the air exchange process. The exhaust process and intake process of the chain saw are collectively referred to as the ventilation process. The role of the ventilation is to clean the exhaust gas of the previous cycle, so that the current cycle is supplied with fresh gas, so that as much fuel as possible is completely extinguished in the cylinder , So that the chain saw reaches greater power. The quality of the ventilation process directly affects the use of the chain saw. We should reduce the movement resistance of the intake and exhaust systems, so we need to clear the carbon deposit in the channel and clean the air filter on a regular basis.