Modeling Of Scroll Compressor Chamber And Investigation On Strength Of Scroll Wrap

Working characteristics of scroll compressor are investigated. The scroll wrap's essential parameteres are determined and scroll chamber's geometrical model is established based on general profile theory. Using the model, the scroll compressor chamber that in form of aircle involute is analysised and simulated. The distribution of loadinging, stress and deformation of scroll wrap are analysised by theoretical studying and finite element method. Based on loadinging, stress and deformation, failure types of scroll wrap are investigated. Scroll wrap's strength is investigated and strength model is established by synthesizing failure types, the prototype scroll machines and their testing. At the same time, the basic design criterions are ditermined and a current approaches for strength calculation is propsed. Modeling of scroll compressor chambers and investigation on strength of scroll wrap could provied the foundations in theory for scroll machine researches on geometry, kinematics, dynamics, thermodynamics, strength, reliability and parameterized design. It could also provide a direction for obtaining outstanding performances scroll machine and has important significance to the scroll machine's stdudy and application.In general, scroll machine mainly constructed with scroll wrap plane, anti-rotation mechanism, axial and radial compliance mechanism, sealing and lubrication mechanism. The scroll wrap's pitch lines are defined as a-type and b-type. A-type pitch line forms orbitting scroll's outer-line and fixed scroll's inner-line. B-type pitch line forms orbitting scroll's inner-line and fixed scroll's outer-line. Corresponding to scroll wrap middle line's normal angle, the normal wrap thickness is defined as the normal component diffence between outer-line and inner-line and the all wrap thickness is defined as the distence between two point that one point on outer-line and other on inner-line. Considering the characteristics of scroll profile and scroll machine, the orbitting radious, the maximum tangent component of general profile, the wrap thickness coefficient, and the scroll wrap height can be regarded as the essential parameters of scroll wrap.The scroll compressor chambers are classified as a-type and b-type by its types of pitch line. The geometrical model that synthesized the profile, form, deformation, lifecycle and the living numbers of scroll compressor chambers is established. Using established geometrical model, all of geometric characteristics of scroll compressor chambers can be overall analyzed. For scroll compressor chamber that in form of aircle involute, its length and volume can serve as the basic geometric characteristics and it is found that its deformation characteristics are more steady and deformation efficiency is higher. Consequently, the profile which based on aircle involute profile is well adopted in practice, such as PMP profile.The loadinging model that synthesized the inner-pressure loadinging and stable conditions temperature fluid is established. The scroll's inner-pressure loading is correspond to 71-involute angle region inner- pressure loadinging which have an interval ofπangle, the value of inner-pressure loadinging is the pressure difference between inner-side and outer-side of scroll wrap. The inner-pressure loadinging is discontinuous. When the crank angle equal to discharge angle, the inner pressure's value is not only maximal but also the acting region of the maximum inner pressure loading is farthest off the center part of scroll. For small parameter scroll wrap, the scroll wrap's temperature can be substituted by its middle area's temperature .In the centre partion of scoll wrap, scroll wrap's temprature equal to discharge temperature, the other's temperature decrease Vs. normal-angle nearly linearly and equal suction temperature at the end of scroll wrap.It is more reasonable to select equivalent stress analysis in alaysising stress of scroll wrap. The axial deformation and radial deformation can be mainly object in deformation analsys. To the scroll wrap acted various inner-pressure,π-involute angle region inner pressure, stable temperature fluid, and thieir coupling loading, the results simulated by finite element method shows that distribution of the equivalent stress of scroll wrap with various parameter is same basically, distribution of the deformation is also. The stress and deformatiom mainly result from the inner-pressure loading and stable tempreature fluid. The stress and deformation result from the inner-pressure loading change periodicity with duty cycle but the stress and deformation result from stable tempreature fluid have nearly no changes. In all scroll wrap, the maxmum equivalent stress occurs on root of scroll wrap at the same point of involute angle.The value of axidial deformation of scroll wrap is samller than the axidial deformation,but it influence on compressor's performance more gravely. The satble tempreature fluid results in stress and deformation quantity is much than inner-pressure's. Although the satble tempreature fluid and the inner-pressure's inflowence on stress and deformation is reverse, their value of stress and deformation could not add up simply. The stress and deformation scroll wrap acted coupling loading are controled by the satble tempreature fluid. The inner-pressure can obviously weaken the stress and deformation of acroll wrap and make changes of stress and deformation more steadily. The equivalent stress at root of scroll wrap with various inner-pressure or 71-involute angle region inner pressure, the deformation of scroll height with stable temperature fluid loading cab be calculatated by simplified formula. All of the calculated examples prove that the calculated results are well agree with the simulated results using finite element method, simplified calxulation can meet requirement of practices.In general, the breakage failure, surface failure and excessive deformation failure are the basic type of scroll wrap failure. The bending fatigue failure,surface pitting,axial wear-out failure, Scuffing and excessive deformation failure are critical failures. The strength model is constructed from the strength of scroll root (including static strength and bending fatigue strength) and axial rigidity. The bending fatigue strength criterion for scroll root is ascertained as basic design criterion and the axial rigidity have to be examined. The stress resulted from inner-pressure loadinging as stress amplitude and stress resulted from coupling loading as mean stress ,the bending fatigue strength for scroll root could be calculated using safety factor. If the scroll wrap is machined by steel, the concentration coefficient of synthetic stress for scroll wrap root could be simplfied calculation must be considered.The scroll wrap's stength calculation and design based on its strength could be carried out by same approaches. To enhance axial sealing performanc and wear-out strength,the scroll height's dimensional tolerance must be modified base on the deformation of scroll wrap height based on stable temperature field.Synthesizing theoretical research and experiences in engineering, an important direction for obtaining outstanding performances scroll machine cab be proposed as follow:(1) Using geometrical model of compressor chamber to select optimized profile and better stability chamber;(2) Using strength model to select scroll wrap's material and reasonable parameters and forecast the scroll machine's basic performances;(3) Adoptting not only reasonable rotor-bearing system, anti-rotation mechanism, axial and radial compliance mechanism, Sealing and Lubrication mechanism, bu also carrying out modification to the scroll height's dimensional tolerance based on the deformation of scroll wrap height based on stable temperature field.