Experimental Study on Lubricating Characteristics at a Small End Bearing of a Connecting Rod in Reciprocating Compressors

In this study we experimentally investigate lubricating characteristics or metallic contact characteristics at a small end bearing of a connecting rod in reciprocating compressors for household refrigerators. In practical operation of the compressor, a periodically changing load acts on the small end bearing and a piston pin rotates periodically in the bearing bore during one revolution of the shaft, which makes formation of oil film at that bearing difficult. In order to observe the condition of metallic contact at the bearing, electrodes were mounted on the sliding surface at the bearing and variations of the contact resistance were measured using a simple electric circuit. Combinations of refrigerant and refrigeration oil used in this study were HFC-134a/ester oil and CFC-12/mineral oil, and the measurement was performed under different operating pressures, temperatures and rotational speed of the compressor. It was concluded, from the observation of electric signals from the electrodes, that there occurs partial metallic contact at the small end bearing during one revolution of the compressor, there exists a correlation between the metallic contact rate and the value of U/Fc (ratio of sliding velocity to load) as the metallic contact increases with decreasing U/Fc, there is no significant difference in lubricating characteristics between HFC-l34a/ester oil and CFC-12/mineral oil.