Abstract:
A protocol for assembling a fuel shut off pin valve assembly for a gas turbine engine. The protocol outlines a specific sequence of events in order to ensure failsafe incorporation of a fuel shut off valve assembly within the low pressure turbine area and specifically within the engine casing of the gas turbine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Division of Applicant&#39;s U.S. patent application Ser. No. 11/560,067 filed on Nov. 15, 2006. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to a fuel shut off valve and method of assembling the valve. 
       BACKGROUND OF THE ART 
       [0003]    Gas turbine engines typically include a fuel shut-off mechanism to be triggered in the unlikely event of a shaft shear event. The clearance between the trigger of the fuel shut-off mechanism and the triggering component must be very accurately controlled so that the shut-off mechanism performs predictably and as required. Often, the trigger clearance is small—the clearance accuracy required is often within the range of the tolerance stack-up on the engine, and therefore the trigger is typically intentionally oversized, and must undergo a custom grinding operation during assembly to ensure the required triggering clearance, which introduces delay into assembly processes. Any grinding error further delays engine assembly. Customization and rework add unwanted cost and time to assembly. Accordingly, there is a need to provide improvements in gas turbine fuel shut-off mechanisms. 
       SUMMARY OF THE INVENTION 
       [0004]    It is therefore an object of this invention to provide a method for adjusting an axial gap between a low pressure turbine and a pin valve fuel shut off assembly in a gas turbine engine, comprising; measuring said axial gap; rotating said pin valve within a support therefore to adjust said pin to a predetermined position; and securing said pin into said predetermined position. 
         [0005]    In another aspect of the present invention, there is provided a method of mounting a fuel shut-off valve assembly in a gas turbine engine, the engine having an exhaust case support member, comprising: providing a fuel shut-off assembly having a seal means, pin means, support means, lever means and cable means mounted within an exhaust case; determining a proper height for the pin means when the assembly is mounted to the engine to ensure function of the fuel shut off assembly; determining seating of the pin means within the support means; and mounting the exhaust case to the engine. 
         [0006]    Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0007]    Reference is now made to the accompanying figures depicting aspects of the present invention, in which: 
           [0008]      FIG. 1  is a schematic cross-sectional view of a turbo fan bypass gas turbine engine, showing an exemplary application of the present invention; 
           [0009]      FIG. 2  is a partially cut away exploded view of an engine casing from a turbo fan engine illustrating a fuel supply shut off assembly; 
           [0010]      FIG. 3A  is a side elevational view of the exhaust casing illustrating the fuel supply shut off lever in situ; 
           [0011]      FIG. 3B  is an enlarged view of the section indicated in  FIG. 3A ; 
           [0012]      FIG. 3C  is a view of the assembly in the direction of arrow “A” shown in  FIG. 3A ; 
           [0013]      FIG. 4A  is a view similar to  FIG. 3A  with the actuation cable connected to the lever; 
           [0014]      FIG. 4B  is a view similar to  FIG. 3B  showing an enlarged area and the position of the cable relative to the lever; 
           [0015]      FIG. 4C  is a view in the direction A of  FIG. 3A ; 
           [0016]      FIG. 4D  is an enlarged view of the area denoted in  FIG. 4A ; 
           [0017]      FIG. 5  is a perspective of a partially cut away view of the exhaust casing illustrating some of the components in their respective positions; 
           [0018]      FIG. 5A  is a partially cut away view illustrating the positioning of the fuel shut off arrangement in position amongst the wiring and other components associated with the exhaust casing; 
           [0019]      FIG. 6  is a partially cut away cross section of the engine casing of the present invention; 
           [0020]      FIG. 7  is an enlarged section of the circled section in  FIG. 6 ; 
           [0021]      FIG. 8  is a side cross sectional view of the engine casing illustrating further details concerning the fuel shut-off pin assembly. 
           [0022]      FIG. 9  is an enlarged view of the area circled in  FIG. 8 ; 
           [0023]      FIG. 10  is a further view of the engine casing; and 
           [0024]      FIG. 11  is a view taken from the direction of the arrow in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Referring to  FIG. 1 , a turbo fan gas turbine engine incorporating an embodiment of the present invention is presented as an example of the application of the present invention, and includes a housing  10 ′, a core casing  13 ′, a low pressure spool assembly seen generally at  12 ′ which includes a shaft  15 ′ interconnecting a fan assembly  14 ′, a low pressure compressor  16 ′ and a low pressure turbine assembly  18 ′, and a high pressure spool assembly seen generally at  20 ′ which includes a shaft at  25 ′ interconnecting a high pressure compressor assembly  22 ′ and a high pressure turbine assembly  24 ′. The core casing  13 ′ surrounds the low and high pressure spool assemblies  12 ′ and  20 ′ in order to define a main fluid path (not indicated) therethrough. In the main fluid path there are provided a combustion section  26 ′ having a combustor  28 ′ therein. Pressurized air provided by the high pressure compressor assembly  22 ′ through a diffuser  30 ′ enters the combustion section  26 ′ for combustion taking place in the combustor  28 ′. Numeral  10  generally denotes the location for the arrangement of the present invention. 
         [0026]      FIG. 2  illustrates the rear of the turbine exhaust case,  10  with the exhaust cone removed therefrom in order to reveal the parts of the system with reference to the assembly pattern. The pin valve assembly is generally denoted by numeral  12  and includes a pin valve  14 . The pin valve  14  is screwed into a flange head  16  and then unscrewed approximately for five threads. The sub-assembly of  10 ,  14  and flange  16  is then subsequently positioned within support  18 . A seal  20  is inserted into the pin valve  14  up to the point of the back surface of support  18 . The seal  20  is then discarded once positioning has been effected. Once formed, the so formed assembly is inserted in to the turbine exhaust case  10  as is shown in the Figure with parts removed for clarity. 
         [0027]    Within the casing  10 , there is provided mounts  22 , which mounts  22  receive the support  18 . Support  18  is fixedly secured to mounts  22  by fasteners  24 . Antiseize compound is applied to the threads of fasteners  24 . Each fastener then is fixedly secured at a predetermined force, a predetermined torque between 20 pound inches and 26 pound inches in a specific sequence. The sequence involves torquing each fastener alternately in increments of 5 pound inches up to 20-26 pound inches. 
         [0028]    During the installation procedure it is important to ensure that the pin  14  remains movable and to this end, the pin must prevent at least some resistance to movement. This is confirmed by rotating the pin in seal  20  by a quarter of a turn. If no resistance is experienced the pin  14  is removed from support  18  and the seal  20  is replaced. In order to ensure positive engagement, fasteners  24  may also include a locking device, such as locking washers  26 . 
         [0029]    Referring to  FIGS. 3A , B and C, shown are a variety of views of the exhaust case.  FIG. 3A  illustrates a partially cut away side elevational view.  FIG. 3B  illustrates an enlarged view of the circular area noted in  FIG. 3A .  FIG. 3C  is a front view looking in the direction of arrow “A” of  FIG. 3A . In the above mentioned illustrations, a lever  28  is provided and is mounted to support  18  and more specifically, between lateral supports  30  of support  18 . 
         [0030]    A nut and bolt  32 ,  34 , respectively extend through registering apertures within support  18  to receive lever  28 . Antiseize compound is applied to the threads of the bolt and subsequent torquing of the system is performed between 27 and 30 pound inches. Once fastened, lever  28  is checked for free and clear movement without any binding by applying hand force. This also ensures the full seating of pin  14 . 
         [0031]    Referring to the sequence of  FIGS. 4A through 4D , shown are various views similar to those in respect to  FIGS. 3A ,  3 B and  3 C where the actuation device is provided for lever  28 .  FIG. 4A  illustrates the overall arrangement where lever  28  is connected to a shut off cable assembly, globally denoted by numeral  36 . One end of the cable,  38  is fastened adjacent to the terminal end of lever  28 . The fastening may be achieved by a ball connector  40  secured in position by a suitable retainer, an example of which is a cotter pin  42 . The opposed end of cable  38  terminates at a retaining flange  44  generally associated with the turbine exhaust casing  10 . In the mounting procedure, the arrangement includes a washer and nut combination  46 ,  48 . The nut is turned under a predetermined amount of pressure and particularly torqued between 14 and 16 pound inches. 
         [0032]    The cable jacket  50  then extends along the body as is typical in turbo fan engines. 
         [0033]    Referring to  FIGS. 5 and 5A , shown in the first instance is the rear of the turbo fan exhaust casing  10  partially cut away to reveal the disposition of the lever and other components discussed herein previously. The cut away section  FIG. 5A  clearly illustrates the disposition of the lever within the casing once the arrangement is assembled as has been discussed. 
         [0034]    As further steps in the method, once the arrangement is assembled at this stage it is important to ensure that all components are correctly installed and locked. To this end, the cotter pin  42  must be confirmed to be correctly installed and locked into position. It is also at this point that confirmation is made as to whether the nut  32  and bolt  30  of the lever  28  are firmly secured and that the ancillary wiring globally denoted by numeral  52  is securely clamped and secured. 
         [0035]    Finally, once an inspection has been conducted and each of the components is not only functioning properly, but also secured where appropriate and movable where appropriate the sequencing with respect to  FIG. 5  and  FIG. 6  can be effected. 
         [0036]    Referring now to  FIGS. 6 and 7 , the engine  10  is, in a further embodiment of the method according to the present invention rotated to record the dimension indicated in  FIG. 7  by numeral  60 . This dimension is a measurement from the turbine support case flange, globally denoted by numeral  62  to the bearing locator bolt  64 . This measurement is used to then calculate required pin valve  14  height. 
         [0037]    A pulling tool  66  is connected to the pin valve  14  to ensure that the pin is fully seated against its support (numeral designations required for this aspect). 
         [0038]    The valve  14  is adjusted by rotation to the proper height in relation to the exhaust case flange  62 . 
         [0039]    As shown in  FIGS. 10 and 11 , once the pin has been adjusted, it is important to ensure that the pin remains in this position. Accordingly, as shown in  FIG. 11 , a washer lock  68  is positioned on to the support flange  62  and secured there with retaining ring  70  as illustrated in  FIG. 11 . 
         [0040]    The case is then installed on engine in a known manner. 
         [0041]    The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without department from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.