Dynamic Behavior of a Variable Displacement Wobble Plate Compressor for Automotive Air Conditioners

The present study examines the dynamic behavior of a variable displacement wobble plate compressor which makes it possible to control the cooling capacity continuously. The continuous cooling capacity control Is achieved by the complicated motion of the piston, the piston rod, the wobble plate, the rotating journal and the drive shaft. In order to analyze the complicated motion of each moving element, the inertial forces and moments of the moving elements are calculated first. Subsequently, the constraint force at each pair of compressor elements and the frictional forces given by Coulomb's Jaw of friction are calculated. The unknown frictional coefficient was determined on the basis of experimental data on the cylinder pressure and the driving power. It can be concluded that the inertial an:d frictional forces have a significant effect upon the feasibility to control the cooUng capacity, and upon the quiet operation and durability of compressor parts at high operating speeds. INTRODUCTION Variable displacement wobble plate compressors have brought on a revolution in automobile air conditioning since commercial production [sec Ref. 1]. The refrigerant flow rate discharged from the compressor is controlled by continuously changing the piston displacement, thus resulting in wide-range continuous control of the cooling capacity and in high efficiency. The variable displacement wobble plate compressors are now widely considered to be the best choice for automobile air conditioning with its stringent requirements for comfort and reduced energy consumption. The continuous control of the cooling capacity is achieved, however, by the complicated motion of many compressor clements, such as the piston, the piston rod, the wobble plate, the rotating journal and the drive shaft. Subsequently, questions concerning the quiet operation and durability of these parts at high operating speeds arise. Tbe complicated motion of variable displacement wobble plate compressors and the dynamic balancing of the rotating shaft have been treated in several previous studies [ 2, 3] from the kinematics viewpoint. However, the inertial forces and moments of the moving elements and also the frictional force at each pair of compressor elements have not been taken into account. As the operating speed of the compressor increases, the effects of the inertial and frictional forces become increasingly significant. The present study examines the dynamic behavior of a 6-cylinder variable displacement wobble plate compressor. The complicated motion of each moving element of the compressor is precisely analyzed, from both the kinematics and dynamics viewpoints, and thus the inertial forces and moments of the moving elements and the frictional forces acting on the clement pairs are calculated. Based on the calculated results, the effects of the inertial and frictional forces upon the feasibility to control the cooling ~apacity, and upon th_e quiet operation and durability of compressor parts at high operatmg speeds, arc exammcd. Furthermore, the power losses due to friction are examined and design criteria for quiet operation and high speed durability of compressor parts are obtained.