Reduction of turbocharger core unbalance with centering device

A method for balancing a rotating assembly, the rotating assembly comprising a shaft (52) with a turbine end and a threaded compressor end (56), a turbine wheel (51) rigidly connected to the turbine end of the shaft, a compressor nut (30, 34, 36, 37, 38, 39), and a compressor wheel (20) with a nose end face (21) and a hub end face (22), and held in position on the compressor end of the shaft by the clamp load from the compressor nut (30, 34, 36, 37, 38, 39) threaded onto said threaded end of the shaft, wherein said rotating assembly rotates about a centerline, and wherein the nut (30, 34, 36, 37, 38, 39) and the compressor wheel nose end face are provided with complementary engaging surfaces such that tightening of the nut against the compressor wheel causes said compressor wheel to center relative to the centerline of the rotating assembly, the method comprising:

• (a) introducing the compressor wheel (20) onto the shaft,
• (b) threading the nut onto the threaded end of the shaft and tightening the nut (30, 34, 36, 37, 38, 39) against the compressor wheel (20) causing the compressor wheel to align on a centerline generated by the cylindricity of the zones (74 and 75) of the shaft and wheel acted upon by the journal bearings, and
• (c) measuring the imbalance of the rotating assembly, and if the imbalance is greater than a predetermined value, subjecting, said rotating assembly to a balancing step, and repeating step (c1) until the rotating assembly imbalance is below the predetermined threshold.