Patent ID: 7568883
Filing Date: 2009-08-04
Classification: F04D,F05B

Abstract:
1. A turbocharger, comprising: a turbine wheel disposed in a turbine housing and mounted on one end of a rotatable shaft for rotation about an axis of the shaft, an opposite end of the shaft defining an unthreaded end portion and an externally threaded portion spaced in a first axial direction from the unthreaded end portion; a two-stage compressor comprising a compressor wheel mounted on an opposite end of the shaft and disposed within a compressor housing, the compressor wheel comprising a first-stage impeller and a separately formed second-stage impeller, each impeller having a hub and a plurality of compressor blades extending from the hub, wherein the first-stage and second-stage impellers each has a front side and a back, and the impellers are arranged with the back of the first-stage impeller facing in the first axial direction generally toward the turbine wheel and toward the back of the second-stage impeller; the hub of the second-stage impeller defining a bore extending entirely through the hub for passage of the shaft therethrough, the hub of the first-stage impeller defining an unthreaded pilot hole for receiving the unthreaded end portion of the shaft, the pilot hole defining an inner cylindrical first pilot surface engaging an outer cylindrical surface of the unthreaded end portion of the shaft for establishing a coaxial relationship between the first-stage impeller and the shaft; the hub of the first-stage impeller defining a hollow cylindrical pilot member integrally formed with the first-stage impeller and projecting from the back of the first-stage impeller, the pilot member comprising an inner threaded surface spaced in the first axial direction from the first pilot surface, and an outer cylindrical surface coaxial with the first pilot surface of the pilot hole; the bore of the second-stage impeller comprising a first bore portion defining an inner cylindrical second pilot surface engaging the outer cylindrical surface of the pilot member for establishing a coaxial relationship between the first- and second-stage impellers, and a second bore portion defining an inner cylindrical third pilot surface coaxial with the second pilot surface and engaging an outer cylindrical surface of the shaft for establishing a coaxial relationship between the shaft and the second-stage impeller; and the externally threaded portion of the shaft engaging the inner threaded surface of the pilot member for securing the first- and second-stage impellers to the shaft and to each other and constraining relative axial movement therebetween, wherein the first, second, and third pilot surfaces are non-threaded and serve to coaxially locate the impellers and shaft and constrain relative radial movement therebetween without constraining relative axial movement therebetween.