Abstract:
A balance weight for a rotor includes: (a) an arcuate body including a front wall and a rear wall interconnected by an end wall, the front, rear, and end walls collectively defining a generally U-shaped cross-sectional shape; and (b) a projection extending outwardly from the rear wall, the projection being adapted to engage an aperture extending through a flange of the rotor.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the balancing of turbine rotors in gas turbine engines, and, more particularly, to boltless balance weights for rotor disks of such engines. 
     Gas turbine engines include one or more rotors comprising a disk carrying a plurality of airfoil-shaped turbine blades which extract energy from combustion gases. Because of the high rotational speeds of the disks and the large disk and blade masses, proper balancing of the rotors of the turbine is important. Unbalance may, in some cases, seriously affect the rotating assembly bearings and engine operation. 
     One known method of balancing a rotor disk is to provide the disk with dedicated balance planes incorporating extra material. These can be selectively ground away as needed. However, this process is difficult to implement efficiently and with repeatable results. 
     Another known method for balancing turbine disks is to add washers or other weights to select bolted joints of the rotors. The number, position, and mass of the weighted washers needed to balance the disk is dependent on the balance characteristics of each turbine disk being balanced. These balance characteristics are determined by a balance test on each rotor. After finding the unbalance of a turbine rotor, the weighted washers are added to designated bolted joints until the rotor is balanced. While this method works well for turbine rotors with bolted joints, not all turbine rotors have such joints. 
     BRIEF SUMMARY OF THE INVENTION 
     These and other shortcomings of the prior art are addressed by the present invention, which provides a boltless balance weight for use with turbine rotors. 
     According to one aspect of the invention, a balance weight for a rotor includes: (a) an arcuate body including a front wall and a rear wall interconnected by an end wall, the front, rear, and end walls collectively defining a generally U-shaped cross-sectional shape; and (b) a projection extending outwardly from the rear wall, the projection being adapted to engage an aperture extending through a flange of the rotor. 
     According to another aspect of the invention, a turbine rotor assembly includes: (a) a rotatable disk adapted to carry a plurality of turbine blades at its rim; (b) a flange arm extending axially from a surface of the disk; (c) a radially-extending flange disposed at a distal end of the flange arm, the flange having a plurality of apertures extending therethrough; and (d) a balance weight disposed in a slot cooperatively defined by the disk, the flange arm, and the flange, the balance weight having: (i) an arcuate body including a front wall and a rear wall interconnected by an end wall, the front, rear, and end walls collectively defining a generally U-shaped cross-sectional shape; and (ii) a projection extending outwardly from the rear wall, the projection engaging one of the apertures of the turbine rotor, so as to secure the balance weight to the turbine rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
         FIG. 1  is a cross-sectional view of a portion of a gas turbine engine including two turbine rotor stages constructed according to an aspect of the present invention; 
         FIG. 2  is a front perspective view of a balance weight for use with a gas turbine rotor; 
         FIG. 3  is a rear perspective view of the balance weight of  FIG. 2 ; 
         FIG. 4  is a partial perspective view of a disk with the balance weight of  FIG. 2  installed therein; 
         FIG. 5  is a rear perspective view of a balance weight for use with a turbine rotor; 
         FIG. 6  is a front view of the balance weight of  FIG. 5 ; 
         FIG. 7  is a side view of the balance weight of  FIG. 5 ; and 
         FIG. 8  is a partial perspective view of a disk with the balance weight of  FIG. 5  installed therein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  depicts a portion of a gas generator turbine  10 , which is part of a gas turbine engine of a known type. The function of the gas generator turbine  10  is to extract energy from high-temperature, pressurized combustion gases from an upstream combustor (not shown) and to convert the energy to mechanical work, in a known manner. The gas generator turbine  10  drives an upstream compressor (not shown) through a shaft so as to supply pressurized air to a combustor. 
     In the illustrated example, the engine is a turboshaft engine and a work turbine (not shown) would be located downstream of the gas generator turbine  10  and coupled to an output shaft. This is merely one example of a possible turbine configuration, and the principles described herein are equally applicable to rotors of similar or different configuration used in turbofan and turbojet engines, as well as turbine engines used for other vehicles or in stationary applications, as well as rotors that require balancing in other types of machinery. 
     The gas generator turbine  10  includes a first stage nozzle  12  which comprises a plurality of circumferentially spaced airfoil-shaped hollow first stage vanes  14  that are supported between an arcuate, segmented first stage outer band  16  and an arcuate, segmented first stage inner band  18 . The first stage vanes  14 , first stage outer band  16  and first stage inner band  18  are arranged into a plurality of circumferentially adjoining nozzle segments that collectively form a complete 360° assembly. The first stage outer and inner bands  16  and  18  define the outer and inner radial flowpath boundaries, respectively, for the hot gas stream flowing through the first stage nozzle  12 . The first stage vanes  14  are configured so as to optimally direct the combustion gases to a first stage rotor  20 . 
     The first stage rotor  20  includes a array of airfoil-shaped first stage turbine blades  22  extending outwardly from a first stage disk  24  that rotates about the centerline axis of the engine. A segmented, arcuate first stage shroud  26  is arranged so as to closely surround the first stage turbine blades  22  and thereby define the outer radial flowpath boundary for the hot gas stream flowing through the first stage rotor  20 . 
     A second stage nozzle  28  is positioned downstream of the first stage rotor  20 , and comprises a plurality of circumferentially spaced airfoil-shaped hollow second stage vanes  30  that are supported between an arcuate, segmented second stage outer band  32  and an arcuate, segmented second stage inner band  34 . The second stage vanes  30 , second stage outer band  32  and second stage inner band  34  are arranged into a plurality of circumferentially adjoining nozzle segments that collectively form a complete 360° assembly. The second stage outer and inner bands  32  and  34  define the outer and inner radial flowpath boundaries, respectively, for the hot gas stream flowing through the second stage turbine nozzle  28 . The second stage vanes  30  are configured so as to optimally direct the combustion gases to a second stage rotor  38 . 
     The second stage rotor  38  includes a radial array of airfoil-shaped second stage turbine blades  40  extending radially outwardly from a second stage disk  42  that rotates about the centerline axis of the engine. A segmented arcuate second stage shroud  44  is arranged so as to closely surround the second stage turbine blades  40  and thereby define the outer radial flowpath boundary for the hot gas stream flowing through the second stage rotor  38 . 
     The first stage disk  24  includes a radially-extending annular flange  46 . The flange  46  is supported by a flange arm  48  that extends axially from the aft side  50  of the first stage disk  24 . Collectively, the first stage disk  24 , flange arm  48 , and flange  46  define an annular slot  52 . The flange  46  has an annular array of apertures  54  formed therethrough (see  FIG. 4 ). The second stage disk  42  is similar in configuration to the first stage disk  24  and includes an annular flange  56 , flange arm  58 , and slot  60 . 
       FIGS. 2 and 3  illustrate an exemplary balance weight  62  for use with the disks  24  and  42 . The balance weight  62  is generally U-shaped in cross-section and includes spaced-apart front and rear walls  64  and  66  interconnected by an end wall  68 . The balance weight  62  is made from a suitable alloy and may be formed by methods such as casting, stamping, or machining. The balance weight  62  is slightly resilient, such that the front and rear walls  64  and  66  can be compressed towards each other for installation but will spring back to their original shape. 
     The rear wall  66  of the balance weight  62  includes a dimple  70  protruding outwardly therefrom. In the illustrated example, the front wall  64  includes a cutout  72  which is aligned with the lateral and radial position of the dimple  70 , to allow the dimple  70  to be formed in the rear wall  66  using a forming die or other similar tooling. Depending on the method of manufacture, the cutout  72  may be eliminated. The overall dimensions, material thickness, and specific cross-sectional profile of the balance weight  62  may be varied in size to increase or decrease its mass as required for a particular application. 
       FIG. 4  illustrates how the balance weight  62  is installed. It will be understood that the installation process is identical for the first and second disks  24  and  42 , and therefore will only be discussed with respect to disk  24 . The balance weight  62  is positioned in the slot  52  by compressing the balance weight  62  such that it slides between the aft side  50  of the first stage disk  24  and the flange  46 . The balance weight  62  is positioned such that the dimple  70  is aligned with one the apertures  54  in the flange  46 . Once the dimple  70  is aligned with the aperture  54 , the balance weight  62  is released to allow it to expand in the slot  52 , forcing the dimple  70  into the aperture  54  and thereby securing the balance weight  62 . 
     At a static condition, the balance weight  62  will be retained by the dimple engagement and friction forces. During operation of the turbine  10 , the balance weight  62  is further secured within the slot  52  by rotational forces caused by the rotation of the first stage disk  24 . In particular, there is a small space between the end wall  68  of the balance weight  62  and the inner diameter of the flange arm  48 . During engine operation, this allows the balance weight  62  to rotate aft with a “hammer head” effect under centrifugal force, urging the dimple  70  into the aperture  54 , thus providing redundant retention in the first stage disk  24 . 
       FIGS. 5-7  illustrate an alternative balance weight  162  which is similar in construction to the balance weight  162  and includes spaced-apart front and rear walls  164  and  166  interconnected by an end wall  168 . The balance weight  162  is made from a suitable alloy and may be formed by methods such as casting, stamping, or machining. The balance weight  162  is slightly resilient, such that the front and rear walls  164  and  166  can be compressed towards each other for installation but will spring back to their original shape. 
     The rear wall  166  includes a pin  170  protruding outwardly therefrom. The pin  170  may be a separate element which is attached to the rear wall  166  by brazing or welding, or it may be integrally formed with the rear wall  166 . As shown, an aft face  172  of the pin  170  is angled or sloped radially outward to ease installation of the balance weight  162 ; however, it should be appreciated that the aft face  172  may also be flat or have any other suitable geometry. 
     A lip  174  extends axially aft from a radially inner edge of the rear wall  166 . The lip  174  may be sized according to the amount of mass needed for balancing, and may also provide additional stability when the balance weight  162  is installed. The overall dimensions, material thickness, and specific cross-sectional profile of the balance weight  162  may be varied in size to increase or decrease its mass as required for a particular application. 
       FIG. 8  illustrates how the balance weight  162  is installed. As with the balance weight  62 , it will be understood that the installation process is identical for the first and second stage disks  24  and  42 , and therefore will only be discussed with respect to disk  24 . The balance weight  162  is positioned in the slot  52  by compressing it such that it slides between the aft side  50  of the first stage disk  24  and the flange  46 . The balance weight  162  is positioned such that the pin  170  is aligned with one the apertures  54  in the flange  46 . Once the pin  170  is aligned with the aperture  76 , the balance weight  162  is released to allow it to expand in the slot  52 , forcing the pin  170  into the aperture  54  and thereby securing the balance weight  162 . 
     At a static condition, the balance weight  162  will be retained by the pin engagement and friction forces. During operation of the turbine  10 , the balance weight  162  is further secured within the slot  52  by rotational forces caused by the rotation of the first stage disk  24 . In particular, there is a small space between the end wall  168  of the balance weight  162  and the inner diameter of the flange arm  48 . During engine operation, this allows the balance weight  162  to rotate aft with a “hammer head” effect under centrifugal force, urging the pin  170  into the aperture  54 , thus providing redundant retention in the disk. 
     The foregoing has described a balance weight for a turbine rotor. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.