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TECHNICAL REPORTS the sliding between the top of the vane and the periph- ery of the rolling piston. We coated the sliding part on the vane with a DLC-Si coating, which resulted in at- taining sliding durability. This is one of the most difficult technologies applied in the development of the CO2 compressor. A detailed explanation of this technology is provided in one of the other reports introduced in this issue; therefore, it will not be discussed in detail here. when using a CO2 refrigerant, indicated faulty sliding within a short time. To solve the problem, we installed a flexible struc- ture in the vane slot in the cylinder, as shown in Fig. 4(b). This flexible structure is slightly bent when the side of the vane is loaded with pressure, thus ex- panding the contact area between the vane and the slot, which reduces contact pressure and eases the sliding condition. There are two points that must be taken into con- sideration for the effective maintenance of this flexible structure. Firstly, the effect of reducing contact stress by expansion of the contact area as the flexible struc- ture bends must be maintained. Secondly, the bend stress caused by the repetitive loading generated dur- ing the compressor’s operation must be kept below the fatigue limit. We then conducted a life test on the flexible struc- ture, depending on several types of specifications. Figure 5 shows the bend stress of the flexible structure, the calculated value of the contact stress during contact with the vane, and the result of the life test with this particular specification. The area where both the bend stress ratio and contact stress ratio of the flexible structure are below one, is the range in which the flexible structure is effec- tive. We determined the specifications of the flexible structure based on the point indicated in the figure. 5. Conclusion As described above, we improved the conventional R410A refrigerant compressor for the characteristics of the CO2 refrigerant and successfully developed a new compressor with sufficiently high performance, oil cir- culation rate and reliability. The reliability of the vane sliding portions, in particular, was achieved by employ- Pressure loading Sliding condition is harsh Intermediate to discharge pressure Discharge pressure Vane Rolling piston Pressure loading Fig. 3 Sliding portions around the vane 5.2 Achievement of sliding durability on the side surface of the vane Figure 4(a) shows the detailed sliding conditions on the vane’s side surface. The vane is inclined slightly due to pressure loading caused by the difference in pressures between the two sides of the vane: thereafter the side surface of the vane touches the corner of the vane slot bore in the cylinder. With the conventional R410A, the existing configuration gave sufficient sliding durability. However, the life test on this configuration, aaa Intermediate to discharge pressure (b) Pressure loading This portion bends slightly. Fig. 4 Improvement in sliding condition of the vane’s side Bend stress ratio Fig. 5 Bend and contact stress at flexible structure Suction pressure Without the flexible structure Sliding-limit contact stress Results of life test Good sliding condition Sign of poor sliding condi- tion Development of faulty slid- ing condition Deformation in flexible structure Specification determination point V ane (a) Pressure loading Vane slot (cylinder) Suction pressure Flexible structure Mitsubishi Electric ADVANCE December 2007 11 The contact area is enlarged. Contact stress ratio Fatigue-limit bend stress Contact portionPDF Image | Heat Pump with Natural Refrigerants 3041
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