Optical measurement of discharge valve modal parameters for a rolling piston refrigeration compressor

Abstract

In this paper we describe the methodology and results of an experiment to measure the fundamental undamped natural frequency and damping ratio for the discharge reed valve in a rolling piston rotary compressor. The small size and extreme flexibility of the valve assembly required the use of a non-contacting measurement technique; thus, an optical displacement follower was chosen as the primary transducer. The measurement system also incorporated a strain gage load cell and PC-based signal processing software. The sensitivity of the system modal parameters to design variables such as valve preload geometry, lubricant viscosity, and retaining screw torque was investigated. Eventually, the measured stiffness, fundamental natural frequency and equivalent viscous damping ratio were incorporated as valve model parameters in a comprehensive computer simulation program for the compressor. Results show that this reed valve design is lightly damped, and that the fundamental natural frequency is a strong function of preload geometry. Lubricant viscosity and retaining screw torque had little effect on the modal parameters.