Mathematical Simulation of Lubrication Conditions in Rotary Vane Compressors

I N T R 0 D U C T I 0 N In recent years, the application of double-flow rotary vane compressor in automotive air-conditioning systems has been increased because of its multiple cylinder characteristic. A certain problem is its high friction loss at higher speeds. The greatest amount of the friction is caused by the lubrication systems between the vane tip and the cylinder wall and between vane 461 side face and rotor groove. For improving the compressor performance a minimizing of this friction is an important step. Some work has been done in the past that included one or both of the above-mentioned losses /3 7/. In this paper, the model to determine the friction loss between vane tip and cylinder wall bases on hydrodynamic lubrication theory. For the calculation of the lubrication conditions an exact knowlegde of the geometry of the clearance between both sliding parts is necessary. The description of the geometry of the clearance is complicated because the following sizes change during the rotation : the length of the vane outside the rotor the inclining angle between vane and cylinder wall -the curvature of the cylinder wall -the location of the minimum oil film thickness between vane tip and cylinder wall across the vane thickness. In the following, a new model to determine friction losses is presented. CALCULATION OF LUBRICATION CONDITIONS For the mathematical simulation of the lubrication conditions between vane tip and cylinder wall, the following modified Reynolds' equation was used ( 1) Equation 1 describes the instationary case including variable velocities between the two surfaces, the squeeze effect and the influence of the acceleration forces /8/. This equation can be solved using by finite difference equations. For the frictional forces between vane side face and rotor groove Coulomb's law was applied because of the low friction power as compared to the vane tip friction power 1 oss. S L I D I N G GEOMETRY The calculation of the lubrication pressure profile postulates a mathematical description of the geometry of the clearance. All numerical calculations concerning the lubrication gap are carried out in the complex plane by vector loops /9/. The cylinder shape contour of this double flow rotary vane compressor is given as a hypertrochoid of second order.