Drive arrangement for a unison ring of a variable-vane assembly

A variable-vane assembly for a turbocharger, comprising:

• a nozzle ring having opposite first and second faces;
• a plurality of vanes adjacent the second face of the nozzle ring and having respective axles received into apertures in the nozzle ring and being rotatable in the apertures such that the vanes are rotatable about respective vane axes defined by the axles in the apertures, a distal end of each axle projecting out from the respective 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 adjacent the nozzle ring with a first face of the unison ring opposing the first face of the nozzle ring, the unison ring being connected to the free ends of the vane arms, the unison ring being rotatable about a rotation axis so as to pivot the vane arms about the vane axes, thereby pivoting the vanes in unison;
• and
• a crank mechanism for rotatably driving the unison ring to pivot the vanes, the crank mechanism including an external crank assembly positioned radially outward of the unison ring, a non-round drive block disposed in a correspondingly shaped non-round recess in an outer periphery of the unison ring such that the drive block is prevented from rotating relative to the unison ring, and a crank arm having a forked end connected to the drive block and an opposite end connected to the external crank assembly, the forked end defining two legs spaced apart in a direction parallel to the rotation axis of the unison ring, the drive block being disposed between the legs and being pivotally connected to the legs such that the drive block is pivotable relative to the crank arm about a pivot axis that is generally parallel to the rotation axis of the unison ring, the crank mechanism being arranged such that the crank arm is caused to swing through an arc of movement about an axis located at the opposite end of the crank arm, thereby rotating the unison ring.