Theoretical Investigation Of Wrap Meshing Profile For Multi-wraps Scroll Compressor

As a new efficient positive displacement device, scroll compressor, which has been widely used in the area of air conditioning and refrigeration, has a unique advantage compared with other types of compressor. With the development of scroll compressor to bigger displacement and bigger power gradually, the advantages of scroll compressor employing twin-wraps or multi-wraps, such as increasing the displacement and reducing the diameter of scroll plate, have been got increasingly approbation. However, the meshing profile of multi-wraps, as the technique key of multi-wraps scroll compressor, has received few research. According to the requirement of the Doctorate Foundation of Ministry of Education (Investigation of Profile Meshing Theory for Multi-wraps), the mathematic model of meshing profile for multi-wraps is established, and this mathematic model is taken as the theoretical foundation to study the problems such as meshing profile, wrap profile modification methods and their geometric theories for single wrap and multi-wraps with random wrap number. The theory system of meshing profile for multi-wraps including single wrap is set up, and the twin-wraps scroll compressor is designed and developed by using the proposed theory.Through presenting the orbiting central position model, three aspects of the movement relationship between orbiting scroll and fixed scroll, generation law of two multi-wraps and solving conjugate profile are connected together closely, and the mathematic model of meshing profile for multi-wraps is established. The position of final meshing point is determined, and the conditions of circular arc, circle involute and line segment using as meshing profile for single wrap and multi-wraps are obtained. The proposed mathematic model is taken as theoretical foundation and the proof of realizing perfect meshing for forming many meshing profiles for multi-wraps in this paper.The analytical design method of wrap profile modification using twin-circular arcs is made perfect, due to derive the precise calculation formulas of every working chambers with random value of modified wrap parameters and random crankshaft rotation angle, and compressor ratio with random discharge angle for modified wrap. The law and condition of modified wrap using twin-circular arc is revealed;the type- II modified wrap using twin-circular arcs is proposed, and the modified wraps with extreme limit of modified wrapparameters when modification angle and modification expanding angle are minimal respectively are proposed, too. The twin-circular arcs profile modification theory is made perfect. Aiming at the disadvantage of modified wrap using twin-circular arcs that there is only one independent wrap parameter and it is difficult to improve pressure ratio and wrap head strength at same time, the two wrap profile modification methods using multi-circular arcs and circle involute which comprehensive performance is higher than profile modification method using twin-circular arcs are proposed, and their geometric theories are established.A profile modification method using twin-circular arcs for twin-wraps, which can form perfect meshing profile, as well as its geometric theories, are established. The equations of modification circular arcs, an accurate expression for calculating axial projective area of modified wrap as well as the calculation of compression chamber volume in different angular positions of crankshaft are given. The influence of every modification parameters on performance of modified scroll wrap such as compression ratio and strength, etc., is also analyzed. The profile modification method using twin-circular arc is expanded to 3-wraps and 4-wraps, and the general generation method as well as common characteristics of the twin-circular arcs modified multi-wraps with random wrap number are summed up. The profile modification theory of multi-wraps using twin-circular arcs is made perfect.The 7 types of meshing profiles such as regular polygon involute, Archimedes curve, etc., are used as multi-wrap meshing profile, and usable condition or profile equation are given. The 10 type of symmetric and asymmetric wrap profile modification methods for multi-wraps such as using twin-circular arc, circle involute, etc., which can realize perfect meshing are presented, and the performances of modified wrap are compared. Through giving the general involute type profile modified wrap, the profile modification is suitable for circle involute, polygon involute, etc., the involute type profile. The theory system of meshing profile for multi-wraps including single wrap is established.According to the law of designing discharge port, the maximal allowable design regions of discharge hole for twin-wraps and 3-wraps are obtained, and the usable shape of discharge port is given. The influences of multi-wraps with different wrap number on displacement and compressor ratio of scroll compressor are analyzed. The different characteristics between single wrap and twin-wraps scroll compressor in working process are analyzed from many aspects such as the forming law of working chambers, the leakage and heat exchange between gases in immediate working chambers, the gas discharge velocity and the gas force acting on the scroll plate, etc.A twin-wraps scroll compressor is designed and developed by using the proposed meshing profile theory of multi-wraps, and its performance is tested. Two experiments, whichare the influences of axial clearance of orbiting scroll on performances, and amount control of lubricating oil in gas respectively, were carried out. The accuracy of the proposed theory is tested by the experiment and sets up the foundation of the design of multi-wraps scroll compressor.