Wear characterisation of small PM rotors and oil pump bearings

The mechanical, micro and physical properties exhibited by PM rotors and journal bearing employed in oil pumps of automobiles, decides life of the pump. In this work, the factors that markedly characterise wear are featured. Tip clearance between the driving and driven gears influences the volumetric efficiency of the pump. When the tip clearance exceeds 0.20 mm (0.007 in.), and the face clearance exceeds 0.1 mm (0.004 in.) the discharge drops below the desired volumetric efficiency of 70%. Relationships between microstructure, micro-hardness, surface roughness, tip clearance of fresh and worn out parts are investigated. PM bearing bushings are finding increasing use in automobiles and consumer durable products owing to favorable size to weight ratio and cost advantages. Superior life and torque characteristics of PM bearings are related to density, size and geometry. Bushings at 6.8 g/cc with a 0.8 μm bearing clearance were determined to give improved life. Apart from the conventional wear test practices in industries, the concept of accelerated wear test (AWT) is employed to simulate equivalent wear on rotors and bearings; the results obtained are compared with the actual field samples. An empirical data on wear behavior is arrived from experimental studies, which can be used for simulated endurance test of these parts. Possible remedies applicable to achieve optimum life are identified. By optimising the material properties, higher wear resistant PM rotors and bearings could be manufactured economically.