Noise Reduction Analysis on Inverter Driven Two-Cylinder Rotary Compressor

Sanyo has originally introduced 6HP two-cylinder rotary compressors for packaged airconditioners in I 985. The concept of two-cylinder rotary compressor has been recently applied to room airconditioners(RACs) for the purpose of reducing vibration and noise of the unit. However. RACs are demanded to decrease the noise by lowering levels of the compressor noise. SanYo has newly developed the quieter !HP two-cylinder rotary compressor for major RACs with inverter system. This paper describes generating mechanisms of established by analysis using signal processing engineering(CAEJ. In addition, concrete countermeasures noise reduction of the two-cylinder rotary compressor. INTRODUCTION Sanyo two-cylinder rotary compressor the comPressor noise and computer aided are presented for the The construction of Sanyo's IHP two-cYlinder rotary compressor is shown in l'ig. 1. This constrution was originally developed for the two-cylinder compressor in 1985. In the process of the develoPment. an investigation was made to determine specifications as shown in Fig. 2 for the decision of the basic construction of the two-cylinder rotary compressor. Finally, Spec. 3 was selected because the span of jounals is much shorter and the whole of pump is much compacter. However. strains of the cYlinder according to this specification increased. Therefore. the cYlinder configuration was optimized to solve the problem by tacked welding and fitting the cylinder on the shrinkage case. The pump of this compressor is constructed with 1st and 2nd cylinders, upper and lower journals. one middle plate. discharge mufflers. one shaft. two rollers and two vanes. This pump is fixed between the 1st cylinder and the case by tacked welding. The assembling of the pump is an important technique for setting the sweep clearance. The process is as follows: After setting the 1st cylinder. the pump assembly machine memorize the relative location of the cylinder and roller. and de-assemble parts. Next. after setting the 2nd cylinder as well as 1st cylinder. the machine reassemble the rest of parts according to the memory. Two-cylinder rotary compressor noise levels in low frequency band considerably low because compression torque ripple of two-cylinder compressors is 1/3 that of one-cylinder. Fig. 3 gives the comoarison of operating circumference vibration levels between the twoand one-cylinder rotary compressors. On the other hand. 600Hz-1.5KHz levels increase being influenced by the interference with gas from each cylinder. Outline of the rotary compressor nois~ 1 . Noise based an frequency domain ( I J Less then 500Hz a. The fluctuation of the shaft speed is generated by that of the gas compression torque during one cycle. The noise is caused by the compressor vibration from this phenomenon. The advantage of two-cylinder compressor is that the 1st order of the electro-source frequency is almost eliminated. b. The electromagnetic noise of motor is generated by the eccentricity of the rotor and ununiformity of magnetisms. Further, the beat noise is affected by the difference between the operating source frequency and shaft revolution. c. The whole compressor is vibrated as a result of reaction by inertia force which is generated by unbalanced mass. (2) 500Hz-2KHz a. Gas resonance noises are generated in the case. mufflers and the accumlator. This noise has clear directivity and goes through the compressor case and unit oanels. h. Counter wei!lhters are placed on the rotor in order to adjust static balance for revolution. However. the shaft is dynamically deformed by the centrifugal force and the electromagnetic force through the rotor and balancers, thus the _noise aaaeared by revolving like a wooden pestle movement. The two;-cYIInder CO!IJDressor has advantage for this noise because of no counter weuU!ters requtred. c. The noise is generated as a results of up-down moving of the rotor and