Lubrication Characteristics Between Bush And Blade Of Swing Compressor

This paper presents the lubrication characteristics between a bush and a blade of a swing compressor that was developed for a new type of compressor for an air conditioner using alternative refrigerants. The mixed lubrication analysis that simultaneously solved the motion equations of the bush and the blade, the lubrication equation and the rough surface contact equation was performed. Moreover, to confirm the validity of the analytical results, the oil film condition between the bush and the blade was measured by using the electrical resistance method and the electrostatic capacity method. NOMENCLATURE a: width of blade, m Mc: moment of viscosity friction between shaft and piston, N·m x1: coordinate, m Cb: clearance of bush, m Mg: moment of refrigerant gas, N·m x2: coordinate, m Cp: clearance of shaft, m O: center point of cylinder y: coordinate, m E: equivalent Young’s module, Pa Ob: center point of rolling bush y1: coordinate, m e: eccentricity (=Rc-Ro), m Op: center point of piston y2: coordinate, m F1: contact force of upper edge of bush in suction side, N P0: fluid pressure between bush in suction side and cylinder, Pa α: attitude angle of piston, rad F2: contact force of lower edge of bush in suction side, N P1: fluid pressure between bush in suction side and blade, Pa γ1: constant for direction of friction between bush and blade F3: contact force of upper edge of bush in discharge side, N P2: fluid pressure between bush in discharge side and blade, Pa γ 2: constant for direction of friction between bush and cylinder F4: contact force of lower edge of bush in discharge side, N P3: fluid pressure between bush in discharge side and cylinder, Pa ε: eccentricity ratio Fbd: contact force between bush in discharge side and cylinder, N Pbs: contact pressure between bush in suction side and cylinder, Pa η: viscosity, Pa·s h: film thickness between bush in suction side and blade, m Pc: compression chamber pressure, Pa θ: rotational angle of shaft, rad h0: film thickness of lower edge of bush in suction side, m Pm: back pressure (=discharge pressure), Pa μc: friction coefficient between bush and cylinder h1: film thickness of upper edge of bush in suction side, m Ps: suction pressure, Pa μp: friction coefficient between bush and blade k: slope between bush in suction side pc: contact pressure, Pa σ: composite RMS roughness, m and blade kc: constant Rb: radius of bush, m φ1: angle, rad L: length of sliding surface of blade, m Rc: radius of cylinder, m φ2: angle, rad L0: length between O and Ob, m Ri: inner radius of piston, m φ3: angle, rad Lc: width of cylinder slot, m Ro: outer radius of piston, m φ4: angle, rad Lg: length of blade in cylinder, m t: time φ5: angle, rad Ll: length of lower half of bush, m W: load carrying capacity, N φ6: angle, rad Lp: width of piston, m Wx: load carrying capacity in direction of x2 axis, N ∆u1: sliding velocity between bush and blade, m/s Lu: length of upper half of bush, m Wy: load carrying capacity in direction of y1 axis, N ∆u2: sliding velocity between bush and cylinder, m/s Lv: length of bush, m x: coordinate, m ω: angular velocity of shaft, rad/s INTRODUCTION The swing compressor was developed for a new type of compressor for an air conditioner using alternative refrigerants such as HFC. This compressor consists of the blade combined rigidly with a roller and oscillatory motion bushes and they form a compression chamber in a cylinder. The swing compressor aims at improving the lubrication condition of the sliding part by getting rid of the sliding part between the roller and the blade of a rolling piston type of rotary compressor. However, the quantitative predominance in the lubrication characteristic of the sliding part between the blade and the bushes of the swing compressor is not clear yet. This paper shows the mixed lubrication analysis method between the bush and the blade of the swing compressor and compares the calculated lubrication characteristics of the swing compressor with that of the rotary compressor [1]. In addition, the measured results of the oil film condition between the bush and the blade were shown to compare the calculated results [2]. ANALYSIS METHOD Figures 1 and 2 show an analytical model of the swing compressor and the enlarged view of the bush respectively. In this analysis, the following assumptions are made: (1) The inertial forces and the viscosity forces that affect the bush and the piston can be neglected. (2) The distribution of fluid pressure between the bush and the cylinder and between the blade and the bush in the discharge side are the proportion distribution of the refrigerant gas pressure. (3) The friction of solid contact part follows the Coulomb's law. Motion Equations of Bush and Blade The balance equations of the forces acting on the bush and the blade are shown as follows: (1) The moments acting on the piston: ( ) ( ) ( ) ( ) ( ) ( ) 0 2 2