At the power output end of the crankshaft, that is, the side connecting the gearbox and the working equipment. The main function of flywheel is to store the energy and inertia outside the power stroke of engine. Four stroke engine only do work one stroke suction, compression, exhaust energy from flywheel storage energy. Correct the balance. The balance of the engine mainly depends on removing the balance weight on the shaft. The single cylinder engine has a special balance shaft.

The flywheel has a large moment of inertia. Because the work of each cylinder of the engine is not continuous, so the engine speed is also changing. When the engine speed increases, the kinetic energy of the flywheel increases and the energy is stored; when the engine speed decreases, the kinetic energy of the flywheel decreases and the energy is released. The flywheel can be used to reduce speed fluctuations during engine operation.

Installed at the rear end of the engine crankshaft, it has rotational inertia. Its function is to store the engine energy, overcome the resistance of other components, and make the crankshaft rotate evenly; connect the engine and the vehicle transmission through the clutch installed on the flywheel; connect with the starter, so as to facilitate the engine starting. It is the integration of crankshaft position sensor and vehicle speed sensor.

In the working stroke, the engine transmits energy to the crankshaft, in addition to the external output, some energy is absorbed by the flywheel, so that the crankshaft speed will not increase a lot. In the three strokes of exhaust, intake and compression, the flywheel releases the energy stored in it to compensate the work consumed in these three strokes, so that the crankshaft speed does not decrease too much.

In addition, the flywheel has the following functions: the flywheel is the driving part of the friction clutch; the flywheel ring gear for starting the engine is inlaid on the flywheel flange; the top dead center mark is engraved on the flywheel to calibrate the ignition timing or injection timing, and adjust the valve clearance.