In this study

the geometry theory of top profile with trigonometric curve was presented based on research on the engaging principle of scroll compressors. General modification equations were given and various modifying patterns were discussed. The equidistant method was employed to calculate the volume of the compression chamber and a general equation was described. Modification parameters that affect the shape of top scroll

volume-reduction ratio

and gas forces were analyzed systematically

and the relations between them were accurately determined. The regularity between variation of modification parameters and that of volume efficiency and leakage loss was summarized. The condition for transformation between trigonometric-curve modification and arc-shape-curve modification was explained. The results can also be applied to modification of top profile in other scroll-type machines.