US Patent 7938634 Self-modulated scroll compressor with optimized built-in volume ratio

A self-modulating scroll compressor includes a built-in volume ratio that is defined as the ratio of a volume of a compression pocket just after completion of suction, i.e. at a beginning of a compression cycle, to the volume of the compression pocket just prior to discharge, i.e. at the end of the compression cycle. The built-in volume ratio can be controlled by the geometry of the scrolls and can be modified by, for example, extending the wrap or adding more turns to the wrap. Because the built-in volume ratio decreases to an effective volume ratio at lower capacity operation, the built-in volume ratio is at least 2.4 in order to optimize overall compressor efficiency.