Methods for detection of lubrication failure applied to a swashplate compressor

Understanding lubrication failures at the shoe/swashplate contact of automotive swashplate compressors will greatly enhance the reliability of the air conditioning system. Maintaining proper lubrication is not always possible during transient conditions. Therefore, a method for detection of lubricant loss is of great interest to the automotive industry. Three methods for detecting lubrication loss were examined: contact resistance, acoustic emission, and dynamic pressure oscillations. A mobile air conditioning test stand capable of recording many system parameters was used. Oil return to the compressor was monitored using an oil separator and a refrigerant/oil concentration sensor. Data were taken during steady oil return rates and after oil shut off. The electrical contact resistance between the shoe and swashplate was used to indicate changes in the lubrication conditions at this critical interface. Measurements were taken at two oil return rates during steady oil return tests. Preliminary results show that the minimum contact resistance is independent of the steady oil flow rates tested. In addition to the contact resistance, an acoustic emission (AE) sensor and a dynamic pressure transducer (DPX) were used to monitor oil film breakdown after oil shut off. Preliminary data indicate that the DPX may be an early indicator of low oil circulation. Even after several hours of operation after oil shut off, the magnitude of the contact resistance indicated no oil film breakdown had occurred. It was determined that the AE sensor is probably not an adequate indicator of lubrication breakdown.