Performance Improvement of a Reciprocating Air Microcompressor

A previously developed reciprocating air microcompressor having a 1-mm(0.04 in)-diameter piston, an inlet port that did not have a moving valve, and an outlet port equipped with a miniature reed valve, was capable of a maximum discharge pressure of 80 kPa (gage, 11.6 psig) at a piston frequency of 100 Hz. We have improved on this compressor performance, and have attained a maximum discharge pressure of 100 kPa (gage, 14.5 psig) with a volumetric efficiency of 90% by supplying oil to the cylinder. The amount of the oil needed was as small as one drop per hour. By analyzing the compressor performance while focusing on the effect of leakage, we found that the performance improvement was due to the sealing effect of the oil preventing leakage through the discharge reed valve. INTRODUCTION In recent years many studies have been done on miniaturized fluid machinery and related components[1,3,5]. However, little work has been done on microcompressors. Development of a practical microcompressor is important, though, because it will be a step towards realizing micropneumatic systems and micro-refrigerators. Positive-displacement microcompressors are the most promising because the velocity of working fluid must be low in miniaturized machines. We previously developed a reciprocating air microcompressor having a 1-mm(0.04 in)-diameter piston[2]. However, the volumetric efficiency was significantly lower than that predicted by a numerical simulation. The lower efficiency was probably caused by internal leakage, but, the specific causes were not clear. In this paper, possible causes of the lower efficiency are investigated. As a measure to improve performance, we supplied oil to the cylinder and the effectiveness of this measure is also discussed. DESIGN AND FABRICATION OF THE MICROCOMPRESSOR The compressor used in the present study was designed and fabricated fundamentally as described in our previous paper[2]. We briefly review the main points here. A schematic view of the microcompressor is shown in Fig.l. The piston diameter is 1 mm(0.04 in) and the stroke is 3 mm(0.12 in). The inlet port is located on the cylinder bore near the bottom and does not have a moving valve. The port is closed when the piston covers it and is opened when the piston's top edge is below the top of the port contour. The outlet port is equipped with a miniature reed valve and this port is located at the top of the cylinder . The reed valve is For pressure gage Figure 1 Schematic view of microcompressor