An Experimental Analysis on the Flow Rate in Scroll Compressors

Experimental analysis on the oil supply characteristics of scroll compressor for package air conditioner has been presented based on the experimental apparatus operating at variable speed Scroll compressor has four major lubricating parts : the lower journal bearing, the main journal bearing, the orbiting scroll journal bearing and the thrust bearing between the orbiting scroll and the main frame. And oil is supplied to the lubricating parts by the rotation of the crankshaft. The flow rates were measured with the change of 3 major elements : positive displacement oil pump, mainframe and crankshaft, which have great effects on the oil supply system. The measured results show that the pump efficiency increases as the swept volume of positive displacement oil pump increases, the structure of oil passage in main frame has great effects on the flow rate to the thrust bearing between main frame and orbiting scroll, moreover, the configuration of the inner oil passage in crankshaft has great effects on the pump efficiency. INTRODUCTION Scroll compressor consists of a motor, a shaft, ftxed and orbiting scrolls, and main and lower frames that support the shaft. It is superior to rotary and reciprocating type compressors in efficiency, noise and vibration due to its structural advantages. But it is rather difficult to supply enough oil to the lubricating parts because these parts are located at the upside of compressor. So it is much more important to supply oil properly to these parts for reliability. Oil plays important roles in compressors' reliability, such as the prevention of gas leakage at the compression chamber, the lubrication of the lubricating parts and the cooling of the lubricating parts heated by friction heat. Especially the operating condition of bearings is much severer as adapting inverter technology into scroll compressor . When the operating speed of compressor is high, the PV value becomes so large that the scuffmg phenomena happen from high friction heat. In other hands when the operating speed is low, the Sommerfeld number becomes so low that the metal contacts happen from low minimum film thickness. Therefore it's very important that the oil flow rate should be supplied more than required according to the variable speed. For the satisfaction of above needs to the inverter technology, the positive displacement oil pump is considered. In this study an experimental analysis has been carried out for the design of oil supply system, especially 3 major elements : positive displacement oil pump, main frame and crankshaft. Experimental Apparatus As shown in Fig. I_, scroll compressors have four major lubricating parts: the orbiting scroll journal bearing, the main journal bearing, the main tluust bearing and the lower journal bearing. Out of the oil pumped up through the inner hole of crankshaft from the base reservoir by the centrifugal force and pumping capacity of the rolling piston typed oil pump, some flows out through the upper oil discharge hole of crankshaft by the centrifugal force between