Patent Publication Number: US-9850768-B2

Title: Turbine wheel including a turbine disk, turbine blades, and seal plates

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2014-51865 filed Mar. 14, 2014 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a turbine wheel comprising a turbine disk including a plurality of groove portions which are formed in its outer periphery; a plurality of turbine blades respectively including protrusions which are formed on their base ends, and fixed to the turbine disk by fitting the protrusions into the groove portions in an axial direction; and seal plates for sealing gaps between the groove portions and the protrusions by being fixed to respective one axial end surfaces of the turbine blades and the turbine disk. 
     Description of the Related Art 
     One such turbine wheel has been publicly known in Japanese Patent Application Laid-open No. 2005-163732. The seal plates of this turbine wheel are designed as follows. Each seal plate is formed from a curved elastic plate member that is fixed with a radially outer end portion of the elastic plate member in engagement with an outer annular groove which is formed in the one axial end surface of the turbine blade and opened inward in a radial direction, and with a radially inner end portion of the elastic plate member in engagement with an inner annular groove which is formed in the one axial end surface of the turbine disk and opened outward in the radial direction. Attachment of the seal plate is achieved by: elastically deforming the seal plate by pressing protrusions formed on the elastic plate member in a way that the seal plate comes into intimate contact with the one axial end surface of the turbine blade or the one axial end surface of the turbine disk; and with the seal plate thus kept elastically deformed, bringing the radially outer end portion of the seal plate into engagement with the outer annular groove of the turbine blade by moving the seal plate outward in the radial direction. 
     The above-mentioned conventional turbine wheel, however, involves the likelihood that: when the protrusions are pressed for the purpose of attaching the seal plate to the turbine blades and the turbine disk, the seal plate formed from the elastic plate member is excessively deformed and thus plastically deformed; and the seal plate resultantly loses its elasticity, and comes out of the outer annular grooves and the inner annular groove. 
     SUMMARY OF THE INVENTION 
     The present invention has been made with the foregoing situation taken into consideration. An object of the present invention is to preclude the seal plate from coming off the turbine wheel by inhibiting the seal plate from being excessively deformed while the seal plate is being attached. 
     In order to achieve the object, according to a first feature of the present invention, there is provided a turbine wheel comprising: a turbine disk including a plurality of groove portions which are formed in its outer periphery; a plurality of turbine blades respectively including protrusions which are formed on their base ends, and fixed to the turbine disk by fitting the protrusions into the groove portions in an axial direction; outer annular grooves each formed in one axial end surface of the corresponding turbine blade, and each opened inward in a radial direction; an inner annular groove formed in one axial end surface of the turbine disk, and opened outward in the radial direction; and seal plates for sealing gaps between the groove portions and the protrusions by being fixed to the respective one axial end surfaces of the turbine blades and the turbine disk with a radially outer end portion of each of the seal plates in contact with a groove bottom of the corresponding outer annular groove, and with a radially inner end portion of each seal plate in engagement with a step portion in the inner annular groove, wherein each seal plate is formed from an elastic plate member whose radially intermediate portion is curved projecting toward the one axial end surfaces, and the seal plate includes an assembly recessed portion, which is recessed in a direction getting closer to the one axial end surfaces, in a position near a radially outer end of the seal plate, and a disassembly protrusion, which projects in a direction getting away from the one axial end surfaces, in a position near a radially inner end of the seal plate. 
     According to the first feature of the present invention, the turbine wheel including: the turbine disk including the multiple groove portions which are formed in its outer periphery; the multiple turbine blades respectively including the protrusions which are formed on their base ends, and fixed to the turbine disk by fitting the protrusions into the groove portions in the axial direction; the outer annular grooves each formed in the one axial end surface of the corresponding turbine blade, and each opened inward in the radial direction; the inner annular groove formed in the one axial end surface of the turbine disk, and opened outward in the radial direction; and the seal plates for sealing the gaps between the groove portions and the protrusions by being fixed to the respective one axial end surfaces of the turbine blades and the turbine disk with the radially outer end portion of each of the seal plates in contact with the groove bottom of the corresponding outer annular groove, and with the radially inner end portion of each seal plate in engagement with the step portion in the inner annular groove. 
     Each seal plate is formed from the elastic plate member whose radially intermediate portion is curved projecting toward the one axial end surfaces. The seal plate includes: the assembly recessed portion, which is recessed in the direction getting closer to the one axial end surfaces, in the position near the radially outer end of the seal plate; and the disassembly protrusion, which projects in the direction getting away from the one axial end surfaces, in the position near the radially inner end of the seal plate. For these reasons, the seal plate can be attached to the turbine wheel by: putting the radially outer end portion of the seal plate opposite the outer annular groove by pressing the assembly recessed portion with the radially inner end portion of the seal plate in contact with the groove bottom of the inner annular groove; and bringing the radially outer end portion of the seal plate into contact with the groove bottom of the outer annular groove, and concurrently bringing the radially inner end portion of the seal plate into engagement with the step portion in the inner annular groove, by moving the seal plate outward in the radial direction. In addition, the seal plate can be detached from the turbine wheel by: releasing the radially inner end portion of the seal plate from its engagement with the step portion by pressing the disassembly protrusion of the attached seal plate; bringing the radially inner end portion of the seal plate into contact with the groove bottom of the inner annular groove by moving the seal plate inward in the radial direction; and thereby making the radially outer end portion of the seal plate come out of the outer annular groove. 
     When the assembly recessed portion is pressed for the purpose of attaching the seal plate, a tip end of the assembly recessed portion comes into contact with the one axial end surface of each turbine blade or the turbine disk, and the seal plate is accordingly inhibited from being excessively deformed. For this reason, the seal plate formed from the elastic plate member is blocked from being plastically deformed, and is precluded from coming off the turbine wheel. 
     According to a second feature of the present invention, in addition to the first feature, the assembly recessed portion is formed from a groove extending in a peripheral direction of the seal plate, and a section of the assembly recessed portion is arcuate. 
     According to the second feature of the present invention, the assembly recessed portion is formed from the groove extending in the peripheral direction of the seal plate, and the section of the assembly recessed portion is arcuate. The section not only makes it easier to control a thickness of the assembly recessed portion and secures strength of the assembly recessed portion more reliably, while the seal plate is being manufactured. But also, the section makes stress less likely to concentrate on the assembly recessed portion when the assembly recessed portion is pressed for the purpose of fitting the seal plate into the outer annular grooves of the turbine blades, and makes the tip end of the assembly recessed portion come into contact with the one axial end surface of each turbine blade or the turbine disk with a wider area. This makes it possible to prevent the plastic deformation of the seal plate more securely. 
     The above and other objects, characteristics and advantages of the present invention will be clear from detailed descriptions of the preferred embodiment which will be provided below while referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing an overall structure of a twin-spool turbofan engine. 
         FIG. 2  is a view showing a main part of a low-pressure turbine in a direction indicated with an arrow  2  in  FIG. 1 . 
         FIG. 3  is a view of a part shown in a direction indicated with an arrow  3  in  FIG. 2 , corresponding to a condition in which a seal plate is removed from the part. 
         FIG. 4  is a perspective view of the seal plate. 
         FIGS. 5A to 5C  are views for explaining a procedure for attaching the seal plate. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Descriptions will be hereinbelow provided for an embodiment of the present invention on the basis of  FIGS. 1 to 5C . 
     As shown in  FIG. 1 , a twin-spool turbofan engine for an aircraft to which the present invention is applied includes an outer casing  11  and an inner casing  12 . Front and rear portions of a low-pressure system shaft  15  are rotatably supported by an inside of the inner casing  12  via front and rear first bearings  13 ,  14 , respectively. A tubular high-pressure system shaft  16  is fitted to an outer periphery of an axial-direction intermediate portion of the low-pressure system shaft  15  in a relatively rotatable manner. A front portion of the high-pressure system shaft  16  is rotatably supported by the inner casing  12  via a front second bearing  17 , while a rear portion of the high-pressure system shaft  16  is supported by the low-pressure system shaft  15  in a relatively rotatable manner via a rear second bearing  18 . 
     A front fan  19  having blade ends which face an inner surface of the outer casing  11  is fixed to a front end of the low-pressure system shaft  15 . Part of air sucked by the front fan  19  passes through stator vanes  20  disposed between the outer casing  11  and the inner casing  12 . Part of the air having passed through the stator vanes  20  thereafter passes through an annular bypass duct  21  formed between the outer casing  11  and the inner casing  12 , and is jetted rearward. Other part of the air is supplied to an axial low-pressure compressor  22  and a centrifugal high-pressure compressor  23  which are disposed inside the inner casing  12 . 
     The low-pressure compressor  22  includes: stator vanes  24  fixed to the inside of the inner casing  12 ; and a low-pressure compressor wheel  25  having compressor blades on its outer periphery, and fixed to the low-pressure system shaft  15 . The high-pressure compressor  23  includes stator vanes  26  fixed to the inside of the inner casing  12 ; and a high-pressure compressor wheel  27  having compressor blades on its outer periphery, and fixed to the high-pressure system shaft  16 . 
     A reverse-flow combustion chamber  29  is disposed in a rear of a diffuser  28  connected to an outer periphery of the high-pressure compressor wheel  27 . Fuel injection nozzles  30  inject fuel into the reverse-flow combustion chamber  29 . The fuel and the air are mixed together and combusted inside the reverse-flow combustion chamber  29 . The generated combustion gas is supplied to a high-pressure turbine  31  and a low-pressure turbine  32 . 
     The high-pressure turbine  31  includes: nozzle guide vanes  33  fixed to the inside of the inner casing  12 ; and a high-pressure turbine wheel  34  having turbine blades on its outer periphery, and fixed to the high-pressure system shaft  16 . The low-pressure turbine  32  includes: nozzle guide vanes  35  fixed to the inside of the inner casing  12 ; and low-pressure turbine wheels  36  each having turbine blades on its outer periphery, and fixed to the low-pressure system shaft  15 . 
     For this reason, once the high-pressure system shaft  16  is driven by a starter motor (not illustrated), air sucked by the high-pressure compressor wheel  27  is supplied to the reverse-flow combustion chamber  29 , and mixed with the fuel to be combusted. The generated combustion gas drives the high-pressure turbine wheel  34  and the low-pressure turbine wheels  36 . As a result, the low-pressure system shaft  15  and the high-pressure system shaft  16  rotate. Accordingly, the front fan  19 , the low-pressure compressor wheel  25  and the high-pressure compressor wheel  27  compress air, and supply the compressed air to the reverse-flow combustion chamber  29 . Thereby, even after operation of the starter motor is stopped, the turbofan engine continues its operation. 
     While the turbofan engine is in operation, part of air sucked by the front fan  19  passes through the bypass duct  21 , and is jetted rearward so as to, particularly during low-speed flight, generate main thrust. The remaining part of the air sacked by the front fan  19  is supplied to the reverse-flow combustion chamber  29 , and is mixed with the fuel to be combusted. The combusted gas drives the low-pressure system shaft  15  and the high-pressure system shaft  16 , and is thereafter jetted rearward, generating thrust. 
     As shown in  FIG. 2 , the low-pressure turbine  32  of the embodiment includes the two low-pressure turbine wheels  36 . However, the two low-pressure turbine wheels  36  have substantially the same structure. For this reason, descriptions will be hereinbelow provided for one low-pressure turbine wheel  36 . 
     As shown in  FIGS. 2 and 3 , the low-pressure turbine wheel  36  includes: an annular turbine disk  43  fixed, with bolts  42 , to an outer periphery of a boss  41  which is spline-connected to an outer periphery of the low-pressure system shaft  15 ; and multiple turbine blades  44  radially fixed to an outer periphery of the turbine disk  43 . In order to withstand centrifugal force, the turbine blades  44  are supported by the turbine disk  43  with the assistance of a so-called Christmas-tree structure in which protrusions  44   a  projectingly provided to base end portions of the turbine blades  44  are respectively fitted into groove portions  43   a  formed in the outer periphery of the turbine disk  43  from the rear in the axial direction. Seal plates  45  are attached to a rear surface of the turbine disk  43  in a way that one seal plate  45  is provided to each two turbine blades  44  for the purpose of: preventing the protrusions  44   a  of the turbine blades  44  coming out of the respective groove portions  43   a  in the turbine disk  43  in the axial direction: and sealing gaps between the protrusions  44   a  and the groove portions  43   a  which are fitted to each other. 
     To this end, an inner annular groove  43   b  opened outward in the radial direction is formed in a radially inner portion of the rear surface of the turbine disk  43 , while outer annular grooves  44   b  opened inward in the radial direction are formed in rear surfaces of portions of the turbine blades  44  which face the protrusions  44   a . The outer annular grooves  44   b  have a constant width in a front-rear direction. On the other hand, a step portion  43   c  is formed at a radially intermediate position of the inner annular groove  43   b . The inner annular groove  43   b  is greater in front-rear width at its outer portion beyond the step portion  43   c  in the radial direction. 
     As shown in  FIG. 4 , each seal plate  45  is formed from an elastic metal plate having a substantially rectangular shape. A radially intermediate portion of the seal plate  45  is curved and projects further toward rear end surfaces of the turbine blades  44  and the turbine disk  43  than opposite radial end portions of the seal plate  45 . A groove-shaped assembly recessed portion  45   c  recessed in the axial direction toward the rear end surfaces of the turbine blades  44  and the turbine disk  43  is formed in a peripheral direction along a radially outer end portion  45   a  of the seal plate  45 . In addition, a ridge-shaped disassembly protrusion  45   d  projecting in the axial direction in a way to get away from the rear end surfaces of the turbine blades  44  and the turbine disk  43  is formed in the peripheral direction along a radially inner end portion  45   b.    
     Next, descriptions will be provided for an operation of the embodiment of the present invention including the foregoing configuration. 
     One seal plate  45  is attached to each two turbine blades  44  in order that with the protrusions  44   a  of the turbine blades  44  fitted into the groove portions  43   a  in the turbine disk  43  in the axial direction, the gaps between the groove portions  43   a  and the turbine blades  44  can be sealed with the seal plate  45 . 
       FIGS. 5A to 5C  show a procedure for attaching the seal plate  45 . As shown in  FIG. 5A , first of all, the radially inner end portion  45   b  of the seal plate  45  is inserted into the inner annular groove  43   b  in the turbine disk  43  with a projecting-portion side of the arc-shaped curving seal plate  45  faced to the rear end surfaces of the turbine blades  44  and the turbine disk  43 . 
     Subsequently, as shown in FIG. SB, with the radially inner end portion  45   b  of the seal plate  45  held in contact with a groove bottom of the inner annular groove  43   b , the assembly recessed portion  45   c  of the seal plate  45  is pressed with a tip end of a tool  46 , and is thereby elastically deformed in a way that its curvature diminishes. By this the radially outer end portion  45   a  is faced to openings of the outer annular grooves  44   b  of the turbine blades  44 . 
     Thereafter, as shown in  FIG. 5C , when the radially outer end portion  45   a  of the seal plate  45  is brought into contact with a groove bottom of the outer annular grooves  44   b  of the turbine blades  44  by moving the tip end of the tool  46  outward in the radial direction, the seal plate  45  starts to return to its original curving shape due to its own elasticity. Thereby, the radially inner end portion  45   b  comes into engagement with the step portion  43   c  in the inner annular groove  43   b  of the turbine disk  43 , and is accordingly prevented from moving inward in the radial direction. Thus, the seal plate  45  is fixed onto the rear end surfaces of the turbine blades  44  and the turbine disk  43 . 
     Detachment of the seal plate  45  is achieved as follows. As indicated with dot-dash lines in  FIG. 5C , the radially inner end portion  45   b  is released from its engagement with the step portion  43   c  in the inner annular groove  43   b  of the turbine disk  43  by pressing a portion of the seal plate  45  outward of the disassembly protrusion  45   d  in the radial direction with the tip end of the tool  46 . Thereafter, the radially inner end portion  45   b  of the seal plate  45  is brought into contact with the groove bottom of the inner annular groove  43   b  of the turbine disk  43  by moving the tip end of the tool  46  inward in the radial direction. Thereby, the radially outer end portion  45   a  of the seal plate  45  comes out of the outer annular grooves  44   b  of the turbine blades  44 . Thus, the seal plate  45  is detached from the turbine blades  44  and the turbine disk  43 . 
     Meanwhile, if the seal plate  45  formed from the elastic plate member would be excessively deformed when as shown in  FIG. 5B , the assembly recessed portion  45   c  is pressed with the tool  46  for the purpose of attaching the seal plate  45 , the seal plate  45  would lose its elasticity due to its plastic deformation. As a result, while in the attached state shown in  FIG. 5C , the radially inner end portion  45   b  may come out of engagement with the step portion  43   c  in the inner annular groove  43   b  of the turbine disk  43  so that the seal plate  45  may accordingly come off. 
     In contrast, according to the embodiment, when the assembly recessed portion  45   c  is pressed with the tool  46 , a tip end of the assembly recessed portion  45   c  comes into contact with the rear end surface of each turbine blade  44  or the turbine disk  43 , and the seal plate  45  is accordingly blocked from being excessively deformed (see  FIG. 5B ). For this reason, the seal plate  45  is prevented from being plastically deformed, and is precluded from coming off the turbine blades  44  and the turbine disk  43 . 
     Furthermore, the assembly recessed portion  45   c  is formed from the groove extending in the peripheral direction of the seal plate  45 , and the section of the assembly recessed portion  45   c  is gently arc-shaped (see  FIG. 4 ). The gently arc-shaped section not only makes it easier to control a thickness of the assembly recessed portion  45   c  and secures strength of the assembly recessed portion  45   c  more reliably while the seal plate  45  is being manufactured than in a case where the assembly recessed portion  45   c  is formed from a protrusion whose section is, for example, quadrangular box-shape. But also, the gently arc-shaped section makes stress less likely to concentrate on the assembly recessed portion  45   c  when the assembly recessed portion  45   e  is pressed for the purpose of fitting the seal plate  45  into the outer annular grooves  44   b  of the turbine blades  44 , and makes the assembly recessed portion  45   c  and its vicinity come into contact with the rear end surface of each turbine blade  44  or the turbine disk  43  with a wider area. This makes it possible to prevent the plastic deformation of the seal plate  45  more securely. 
     The foregoing descriptions have been provided for the embodiment of the present invention. Various design changes, however, can be made to the present invention within the scope not departing from the gist of the present invention. 
     For example, although one seal plate  45  is attached to each two turbine blades  44  in the embodiment, the present invention is not limited to this.