GB820595A - Improvements relating to turbine nozzles - Google Patents

Abstract

820,595. Turbines. GARRETT CORPORATION. May 30, 1957 [May 31, 1956], No. 17210/57. Class 110 (3). In a turbine variable nozzle assembly comprising a ring of nozzle vanes pivoted about axis substantially parallel to that of the turbine, each vane has an operating arm extending away from the turbine axis and affording an engaging surface, the surfaces being engaged by a resilient actuating ring, the radius of the operating arms from the nozzle vane axis to engaging surface differing in such manner that only some of them of maximum radius engage the ring at atmospheric temperature. A centripetal turbine wheel 10 supported in a frame 12 is surrounded by an annular row of pivoted nozzle blades 11 in turn surrounded by a ring of stationary guide vanes 19. The vanes 11 are carried by shafts 14 mounted in bearings 13. Each shaft has a disc-like head 15 with a chordal flat 15a which co-operates with a pin 15b projecting from the frame 12 to limit the extent of rocking movement of the vanes so as to prevent them moving into the path of the wheel 10 in the event of failure of the nozzle actuating mechanism. The aerodynamic loading of the vanes 11 is such that these vanes tend to pivot into the closed position. The shafts 14 are connected by shear pins 22a to arms 22 which extend away from the turbine axis and support a nozzleactuating ring 24. The ring 24 which is of channel-section and resilient, carries pins 27 which engage slots 26 in the arms 22. To alleviate the effects of thermal expansion of the frame 12, the ledges 28 of only four of the arms, distributed uniformly about the circumference, engage the ring 24 under normal ambient temperature conditions. The ledges of the remaining arms have a clearance between them and the ring 24. The ledges 28 at positions midway between the arms which engage the ring have the greatest clearance whilst the remaining ledges are stepped progressively towards the arms which engage the ring. The arrangement is such that when the frame 12 expands during operation of the turbine, the arms 22 which engage the ring 24 deflect the ring and pull the intermediate parts of the ring inwardly towards the ledges 28. At high temperatures, the ring 24 may be forced into close proximity to all of the ledges 28. The ring 24 is actuated by a control-shaft 38 through a crank 36 and link 34 arranged so that when the nozzle vanes are near the closed position a relatively greater movement of the control shaft is required to obtain a comparable angular movement of the vanes 11. The shaft 38 may be actuated by speed, pressure or temperatureresponsive means.