Mounting for ceramic scroll

Abstract: A mounting for a ceramic scroll (42) on a metal engine block of a gas turbine engine includes a first ceramic ring (60) and a pair of cross-key connections (66-70) between the first ceramic ring (60), the ceramic scroll (42), and the engine block. The cross-key connections (66-70) support the scroll (42) on the engine block independent of relative radial thermal growth and for bodily movement towards an annular mounting shoulder (28) on the engine. The scroll (42) has an uninterrupted annular shoulder (70) facing the mounting shoulder (28) on the engine block. A second ceramic ring (62) is captured between the mounting shoulder (28) and the uninterrupted shoulder (70) on the scroll (42) when the latter is bodily shifted towards the mounting shoulder (28) to form a gas seal between the scroll (42) and the engine block.

Description: This invention relates to a scroll mounting for a ceramic scroll on a metal engine block of a gas turbine engine. In hot sections of gas turbine engines where temperatures may exceed 1370°C (2500°F), ceramics are preferable to alloy metals because the former do not require air cooling for acceptable durability, while alloy metals do. A scroll forming, for example, a transition from tangential discharge of a combustor to an axial annular nozzle is an ideal candidate for substitution of ceramic for alloy metal. Mounting a ceramic scroll on a metal engine block, however, is challenging because of the different physical properties, including thermal expansion characteristics, of the two materials. EP-A-0,487,125 describes a mounting for a ceramic scroll on a metal engine block of a gas turbine engine. The present invention seeks to provide an improved scroll mounting. According to an aspect of the present invention, there is provided a scroll mounting for use in a gas turbine engine as specified in claim 1. The present invention can provide a relatively simple and effective connection between a ceramic scroll and a metal engine block in a gas turbine engine. In a preferred embodiment, the scroll has a ceramic shell forming a volute chamber with an annular discharge nozzle defined between concentric inner and outer cylindrical wall segments of the shell. A first ceramic ring of the mounting of this embodiment is connected by a first set of cross-keys to the inner ceramic wall segment and by a second set of cross-keys to a steel spider bolted to the engine block. The cross-key connections support the scroll on the engine block for bodily shiftable movement towards an annular mounting shoulder on the engine block and accommodate effectively relative radial thermal growth between the scroll and the engine block to foreclose thermal growth induced stress concentrations. The inner cylindrical wall segment has a first annular shoulder facing the mounting shoulder on the engine block. A second ceramic ring of the mounting of this embodiment is disposed between the first annular shoulder and the mounting shoulder on the engine block and has a second annular shoulder facing the first annular shoulder. A retaining plate outside the first ceramic ring clamps the second ceramic ring against the mounting shoulder on the engine block by clamping the first annular shoulder on the scroll against the second annular shoulder on the second ceramic ring. An embodiment of the present invention is described below, by way of illustration only, with reference to the accompanying drawings, in which: Figure 1 is a fragmentary elevational view of a hot section of a gas turbine engine incorporating an embodiment of ceramic scroll mounting; Figure 2 is a cross-sectional view of the engine of Figure 1 taken along line 2-2 of Figure 1; Figure 3 is a cross-sectional view of the engine of Figure 1 taken along line 3-3 of Figure 2; and Figure 4 is a fragmentary, exploded perspective view of the ceramic scroll mounting of Figure 1. Referring to Figure 1, a partially illustrated hot section 10 of a gas turbine engine includes a single stage turbine rotor 12 of the type described in US-A-4,639,194. The turbine rotor 12 includes a ceramic turbine wheel 14 and an alloy steel shaft 16. A tubular end 18 of the alloy steel shaft is attached to a tubular stem 20 of the turbine wheel. The turbine wheel 14 has a plurality of turbine blades 22 around its circumference. The engine block is made of alloy metal and has a structurally rigid cylindrical wall 24 aligned on a primary axis 26 of the engine block. The cylindrical wall terminates at an annular mounting shoulder 28 in a plane perpendicular to the primary axis. A generally tubular, metallic seal carrier 30 is disposed in the cylindrical wall 24 with a radial annular flange 32 of the carrier being seated against the annular mounting shoulder 28. Bearings, not shown, support the turbine rotor on the engine block for rotation about the primary axis 26. A pair of high temperature seal rings 34A-B are disposed between the carrier 30 and the tubular end 18 of the alloy steel shaft 16 and are separated by a spacer sleeve 36. Cooling air is supplied to the seal rings 34A-B through a passage 38 in the cylindrical wall 24 of the engine block and through a plurality of circumferentially spaced holes 41 in the carrier 30. A ceramic scroll 42 of the gas turbine engine has a ceramic shell 44 forming a volute chamber 46 around the primary axis 26 and around the cylindrical wall 24 of the engine block. The shell 44 has a generally cylindrical outer wall segment 48 and a concentric generally cylindrical inner wall segment 50. The outer wall segment 48 extends over the turbine blades 22 and cooperates with the inner wall segment 50 to form therebetween a bladed annular nozzle 52 through which hot gas is discharged from volute chamber 46 in the direction of the axis 26 towards the turbine blades 22. A seal 54 between the outer wall segment 48 and a wall 56 of the engine block minimizes hot gas leakage. The ceramic scroll 42 is connected to the engine block by a mounting 58. The mounting 58 includes a first axially outboard ceramic ring 60, a second or axially inboard ceramic ring 62, and a steel spider 64. The first ceramic ring 60 is connected to the inner wall segment 50 of the shell 44 by a first set of cross-keys including a plurality of radial lugs 66 on the first ceramic ring and a corresponding plurality of longitudinal slots 68 in an annular end face 70 of the inner wall segment 50 of the scroll. Each of the slots 68 has a bottom wall 72 in a common first plane perpendicular to the primary axis 26. The spider 64 is disposed inside the first ceramic ring 60 and is connected to the latter by a second set of cross-keys including a plurality of radial lugs 74 on a ring portion 76 of the spider 64 and a corresponding plurality of radial slots 78 in the first ceramic ring. The spider 64 further includes a plurality of tubular spacers 80 integral with the ring portion 76. The spacers 80 bear against the annular flange 32 on the carrier 30 and are aligned with respective ones of a plurality of holes in the flange 32 and threaded holes in the cylindrical wall 24 of the engine block, only a representative hole 82 in the flange and a representative threaded hole 84 in the engine block being visible in Figure 3. As seen best in Figures 1,3 and 4, the cylindrical inner wall segment 50 of the shell 44 flares radially outwardly adjacent the nozzle 52. A cylindrical counterbore 86 in the inner wall segment 50 terminates at a first uninterrupted annular shoulder 88 on the inner wall segment in a second plane perpendicular to the primary axis 26 and facing the mounting shoulder 28 on the engine block. The second plane is separated by an amount D1, Figures 1 and 4, from the aforesaid first plane in which the bottoms 72 of the slots 68 are located. The second ceramic ring 62 is disposed inside the counterbore 86 and has a second uninterrupted annular shoulder 90 thereon facing the first annular shoulder 88 on the inner wall segment. The second shoulder 90 is set-back from an annular face 92 of the second ceramic ring by an amount D2, Figure 4. An annular metal plate 94 and a annular porous element 96 are stacked between an annular face 98 of the second ceramic ring 62 and the flange 32 on the carrier 30. The metal plate 94 has a thermal barrier ceramic coating 100 and a heat-shielding edge 102 shrouding the outside diameter of the porous element 96. The porous element 96 is made of high temperature resistant material, for example of the type available commercially from Union Carbide Corporation under the tradename Grafoil, and is permanently deformable or compressible in the direction of the primary axis 26. The metal plate and the porous element are perforated to provide clearance around the tubular spacers 80 of the spider. As seen best in Figures 2 and 3, the tubular spacers 80 of the spider 64 receive respective ones of a plurality of threaded rods 104 which project through the spacers and the aligned holes 82 in the flange 32 on the carrier and are screwed into the holes 84 in the cylindrical wall of the engine block. A perforated annular retainer plate 106 is received over the ends of the rods 104 within the inner cylindrical wall segment 50 of the scroll and rests against the axially outboard ends of the spacers 80 and against an axially outboard face 108 of the first ceramic ring 60. The retainer plate has a ceramic thermal barrier coating 110 on one side thereof. A plurality of nuts 112 are secured onto the rods 104 axially outboard of the retainer plate 106 and are concealed by a heat shield 114 tack welded to the retainer plate. The first and second sets of cross-key connections support the scroll 42 on the engine block such that relative radial thermal growth between the engine block and the scroll is accommodated by radial sliding movement between the lugs 66,74 and their respective slots 68,78. In addition, the first and second sets of cross-key connections support the scroll on the engine block for limited shifting movement in the direction of the primary axis 26 towards the mounting shoulder 28 on the engine block, for sealing the scroll against the engine block. More particularly, as the nuts 112 are tightened on the rods 104, the retaining plate 106 seats the lugs 66 on the first ceramic ring against the bottoms 72 of the slots 68 in the inner cylindrical wall segment 50. Thereafter, continued tightening of the nuts 112 shifts the scroll towards the mounting shoulder 28 on the engine block until the first annular shoulder 88 engages the second annular shoulder 90 on the second ceramic ring 62. Continued tightening of the nuts 112 clamps the second ceramic ring against the annular mounting shoulder 28 with the flange 32, the porous element 96 and the metal plate 94 located therebetween. The porous element 96 permanently deforms or collapses in the direction of the primary axis 26 as the nuts are tightened to limit compression forces on the second ceramic ring, the scroll, and the lugs 66 on the first ceramic ring. The spacers 80 on the spider 64, bearing directly against the flange 32, limit ultimate compression of the ceramic rings by limiting the inward travel of the nuts 112 on the rods 104. When the nuts 112 are fully tightened, a gas seal is formed between the metal plate 94 and the end face 98 of the second ceramic ring 62 and between the first and second annular shoulders 88,90 on the second ceramic ring and on the inner wall segment of the scroll. The set-back position D2, of the second annular shoulder 90 from the end face 92 of the second ceramic ring 62 slightly exceeds the dimension D1 to prevent deflection of the lugs 66 on the first ceramic ring 60. The disclosures in United States patent application No.854,103, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

Claims: A scroll mounting for use in a gas turbine engine which comprises a metal engine block including a substantially cylindrical wall (24) aligned on a primary axis (26) of the engine block and terminating at an annular mounting shoulder (28) in a plane substantially perpendicular to the primary axis, and a ceramic scroll (42) disposed around the wall and including an annular nozzle (52) formed between a generally cylindrical inner wall segment (50) of the scroll and a generally cylindrical outer wall segment (48) of the scroll, each aligned on the primary axis; the scroll mounting being characterized by a first ring (60) of ceramic material; a first cross-key connection (66-70) in use located between the first ring and an inner wall segment of a scroll and a second cross-key connection in use located between the first ring and the wall (24) of an engine block, whereby in use the scroll is supported on the engine block substantially independent of relative radial thermal growth between the engine block and the scroll and in a manner as to be movable along the primary axis towards a mounting shoulder of the engine block; a ring (62) of ceramic material in use located between the mounting shoulder and the first ring and including a substantially uninterrupted annular shoulder (90) for engagement with a shoulder of the inner wall segment of the scroll when the scroll is moved along the primary axis towards the mounting shoulder; a seal (94) for forming a gas seal between the mounting shoulder and the second ring when the second ring is clamped against the mounting shoulder; and a clamp (,104,112) operative to clamp the second ring against the mounting shoulder with the seal therebetween by moving the scroll towards the mounting shoulder and effecting engagement of the annular shoulder of the second ring against the inner wall segment of the scroll. A scroll mounting according to claim 1, wherein the first cross-key connection (66-70) and the second cross-key connection (64,74-78) include a plurality of first radial lugs (66) on the first ring (60) adapted to be slidably received in corresponding axially extending slots (68) in the inner wall segment of the scroll; a plurality of slots (78) in the first ring; a steel spider (64) rigidly attachable to the mounting shoulder of an engine block inside the first ring; and a plurality of second radial lugs (74) on the steel spider adapted to be slidably received in corresponding slots in the first ring. A scroll mounting according to claim 2, wherein the clamp (96,104,112) includes an annular retaining plate (106) engageable on the first ring; and mounting means (28) for mounting the retaining ring on an engine block in a manner as to allow movement of the retaining ring and of the first ring along the primary axis towards the annular mounting shoulder of the engine block; each axially extending slot (68) of the scroll terminating at a base wall in the inner wall segment of the scroll, each base wall lying in a plane substantially perpendicular to the primary axis, and limiting movement of a corresponding lug (66) in the associated slot. A scroll mounting according to claim 1, 2 or 3, wherein the seal (94) includes an annular metal plate (94) and an annular porous element (96), each disposed in use between the second ring and the annular mounting shoulder of an engine block.

Inventors: PETTY JACK DWANE, PETTY, JACK DWANE
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1993
Main classification: F01D9
IPC codes: F02C7, F01D25, F01D9