ANALYSIS OF TORSIONAL VIBRATION SYSTEM CONSISTING OF CROSS-FLOW FAN AND FAN MOTOR.

The requirements for noise reduction of split-type air conditioners are becoming more and more strict, and many air conditioners in today's market are achieving an indoor noise level below 30 dB(A) at low fan speed operation. During such low noise level operation, the noise problem of air conditioners is usually produced by the electric vibration of the motor, rather than by the ventilating function of the blower fan. In particular, the vibration of a doubled power supply frequency (double-frequency vibration), which is produced by the rotating axis system of the motor, is the main cause of the noise problem in many cases. In order to solve such noise problems caused by double-frequency vibration, an analysis study has been conducted with the following suppositions: 1) The fan (cross-flow fan) is an elastic bar; 2) The fan and rotor of the motor jointly form a torsional vibration system. When characteristic constants of certain elements of the torsional vibration system are measured, it is possible to predict the response characteristics of double-frequency vibration on the system. Then, it is possible to solve the air conditioner noise problem effectively.