Variable-vane assembly having unison ring guided radially by rollers and fixed members, and restrained axially by one or more fixed axial stops

1. A variable-vane assembly for a turbocharger, comprising:

a nozzle ring encircling an axis and having an axial thickness defined between opposite first and second faces of the nozzle ring, the nozzle ring having a plurality of circumferentially spaced-apart first apertures each extending axially into the first face and a plurality of circumferentially spaced-apart second apertures that are circumferentially spaced from the first apertures and each of which extends axially from the first face to the second face;

a plurality of vanes each having an axle extending from one end thereof, the axles being received respectively into the second apertures from the second face of the nozzle ring and being rotatable in the second apertures such that the vanes are rotatable about respective axes defined by the axles, a distal end of each axle projecting out from the respective second aperture beyond the first face;

a plurality of vane arms respectively affixed rigidly to the distal ends of the axles, each vane arm having a free end;

a unison ring positioned coaxially with the nozzle ring adjacent the first face thereof, the unison ring having a first side that faces the first face of the nozzle ring and having an opposite second side, the unison ring having a radially inner edge defining a plurality of recesses therein respectively receiving the free ends of the vane arms, the unison ring being rotatable about the axis of the nozzle ring so as to pivot the vane arms, thereby pivoting the vanes in unison;

a plurality of radial guide rollers for the unison ring, the radial guide rollers each being supported on a pin that is received in a respective one of the first apertures in the nozzle ring and is rigidly affixed therein such that the radial guide rollers are secured to the nozzle ring and positioned such that the radially inner edge of the unison ring is restrained by the radial guide rollers against excessive movement in radial directions;

a fixed axial stop for the unison ring, the axial stop having an affixing portion that is received in another of the first apertures in the nozzle ring and is rigidly affixed therein, and a stop portion projecting out from the first aperture, a part of the stop portion overhanging and opposing the second side of the unison ring so as to prevent excessive axial movement of the unison ring away from the nozzle ring, the axial stop providing restraint of the unison ring in the axial direction but not in the radial direction; and

a plurality of axial-radial guide pins respectively inserted into first apertures of the nozzle ring circumferentially spaced apart about the nozzle ring and rigidly affixed therein such that each of the axial-radial guide pins is non-rotatably secured to the nozzle ring with a guide portion of the axial-radial guide pin projecting axially from the first face of the nozzle ring, the guide portion of each axial-radial guide pin having a radial guide surface confronting the radially inner edge of the unison ring and an axial guide surface confronting the second side of the unison ring, such that the unison ring is restrained by the axial-radial guide pins against excessive radial and axial movements,

wherein the radial guide rollers are all located on one side of an imaginary line that divides the nozzle ring into two half-circular ring halves, and the axial-radial guide pins are located on an opposite side of the imaginary line, and wherein the axial stop is located on said one side of the imaginary line.

2. The variable-vane assembly of claim 1 , further comprising a vane arm stop affixed to the nozzle ring and positioned both to function as a hard stop for one of the vane arms and to restrain the unison ring against excessive movement in a radial direction.