Abstract:
A method for performing maintenance on a gas turbine engine assembly includes unplugging a first connector from a first socket, the first connector electrically coupled to the engine control unit, the first socket electrically coupled to the hydromechanical unit, plugging a second connector into the first socket, the second connector electrically coupled to a driver simulator, cranking the engine core to a low speed value, and operating the driver simulator to reposition at least one of the variable stator vane assembly and the variable bypass valve from a first operational position to a second operational position that is different than the first operational position.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application relates generally to gas turbine engines and, more particularly, to a method and apparatus for performing gas turbine engine maintenance.  
         [0002]     Gas turbine engines generally include, in serial flow arrangement, a high-pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high temperature gas stream, and a high pressure turbine. The high-pressure compressor, combustor and high-pressure turbine are sometimes collectively referred to as the core engine. Such gas turbine engines also may include a low-pressure compressor, or booster, for supplying compressed air to the high pressure compressor.  
         [0003]     At least some known gas turbine engines also include at least one variable stator vane (VSV) assembly that is utilized to control the quantity of air flowing through the high-pressure compressor to facilitate optimizing the performance of the high-pressure compressor. The variable stator vane assembly includes a plurality of variable stator vanes which extend between adjacent rotor blades. The variable stator vanes are rotatable about an axis such that the stator vanes are positionable in a plurality of orientations to direct air flow through the high-pressure compressor. Moreover, at least some known gas turbine engines include a variable bypass valve (VBV) that is configured to bypass a portion of the pressurized air generated by a booster stage, i.e. the low pressure compressor, around the high-pressure compressor to facilitate matching the output of the booster stage to the input requirements of the high-pressure compressor.  
         [0004]     To facilitate operating the VSV&#39;s and the VBV, at least one known gas turbine engine includes a fuel system that is configured to channel fuel to an actuator that is actuated utilizing an engine control system. More specifically, as the gas turbine engine is operated, the engine control system electrically actuates the actuator such that fuel supplied by the fuel pump, is channeled to either the VSV&#39;s and/or the VBV to facilitate repositioning either the VSV&#39;s and/or the VBV.  
         [0005]     When the gas turbine engine receives a shutdown command, the engine control system, based on at least one predetermined engine operating parameter, ceases to provide the actuator any operational commands such that the VSV&#39;s and the VBV will “drift” to a failsafe operating position.  
         [0006]     Accordingly, to service the gas turbine engine, maintenance personnel must reposition the VSV&#39;s and/or the VBV to a desired position. For example, to borescope the gas turbine engine, the maintenance personnel will reposition the VSV&#39;s to a fully open position, and reposition the VBV to a fully closed position. To reposition either the VSV&#39;s and/or the VBV, the maintenance personnel disconnect the fuel line between the fuel pump and the engine control system, and install a hand pump to facilitate channeling fuel to either the VSV&#39;s and/or the VBV. More specifically, the handpump is operated to either open and/or close at least one the VSV&#39;s and the VBV when the gas turbine engine is not operating.  
         [0007]     However, utilizing a handpump to reposition either the VSV&#39;s and/or the VBV increases the time and thus the cost of maintaining the gas turbine engine. Moreover, when the fuel line between the fuel pump and the engine control system is reconnected, the gas turbine engine must be operated in a test configuration to verify that the fuel system is not leaking. Accordingly, utilizing a hand pump to reposition either the VSV&#39;s and/or the VBV increases the time and thus the cost to perform maintenance on the gas turbine engine.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0008]     In one aspect, a method for performing maintenance on a gas turbine engine assembly is provided. The method includes unplugging a first connector from a first socket, the first connector electrically coupled to the engine control unit, the first socket electrically coupled to the hydromechanical unit, plugging a second connector into the first socket, the second connector electrically coupled to a driver simulator, and operating the driver simulator to reposition at least one of the variable stator vane assembly and the variable bypass valve from a first operational position to a second operational position that is different than the first operational position.  
         [0009]     In another aspect, a driver simulator for performing maintenance on a gas turbine engine assembly is provided. The gas turbine engine assembly includes a gas turbine engine including at least one variable stator vane assembly, at least one variable bypass valve, a hydromechanical unit that includes a first servo motor coupled to at least one variable stator vane assembly and a second servo motor coupled to at least one variable bypass valve. The driver simulator includes a first system coupled to the hydromechanical unit and configured to reposition the variable stator vane assembly from a first operational position to a second operational position, and a second system coupled to the hydromechanical unit and configured to reposition the variable bypass valve from a first operational position to a second operational position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is schematic illustration of an exemplary gas turbine engine;  
         [0011]      FIG. 2  is a schematic view of a section of the high pressure compressor used with the engine shown in  FIG. 1 ;  
         [0012]      FIG. 3  is a simplified schematic illustration of an exemplary driver simulator that can be utilized with the gas turbine engine shown in  FIG. 1 ;  
         [0013]      FIG. 4  is a simplified schematic illustration of the exemplary driver simulator coupled to the gas turbine engine shown in  FIG. 1 ;  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      FIG. 1  is a schematic illustration of an exemplary gas turbine engine assembly  10  that includes, in serial flow relationship, a low pressure compressor  12 , a high pressure compressor  14 , and a combustor assembly  16 . Engine  10  also includes a high pressure turbine  18 , and a low pressure turbine  20  arranged in a serial, axial flow relationship. Compressor  12  and turbine  20  are coupled by a first shaft  24 , and compressor  14  and turbine  18  are coupled by a second shaft  26 . In one embodiment, engine  10  is an GE90 engine commercially available from General Electric Company, Cincinnati, Ohio.  
         [0015]     In operation, air flows through low pressure compressor  12  from an upstream side  11  of engine  10  and compressed air is supplied from low pressure compressor  12  to high pressure compressor  14 . Compressed air is then delivered to combustor assembly  16  where it is mixed with fuel and ignited. The combustion gases are channeled from combustor  16  to drive turbines  18  and  20 .  
         [0016]     Gas turbine engine  10  also includes at least one variable bypass valve (VBV)  30  that is utilized to control the quantity of air flowing from low-pressure compressor  12  to high pressure compressor  14 . More specifically, VBV  30  facilitates matching the output airflow from low pressure compressor  12  to the input airflow requirements of high pressure compressor  14 . More specifically, gas turbine engine  10  includes a servo motor  32  that is coupled to VBV  30  such then when servo motor  32  is actuated by an engine control unit  34  (ECU), fuel is channeled from a fuel pump  36  to servo motor  32  to facilitate repositioning VBV  30 .  
         [0017]     Gas turbine engine  10  also includes at least one variable stator vane assembly  56  (shown in  FIG. 2 ). More specifically, and in the exemplary embodiment, high pressure compressor  14  includes a plurality of stages  50 , wherein each stage  50  includes a row of rotor blades  52  and a row of variable stator vane assemblies  56 . Rotor blades  52  are typically supported by rotor disks  58 , and are connected to rotor shaft  26 . Each variable stator vane assembly  56  includes a plurality of variable vanes  74  each having a respective vane stem  76 . Vane stem  76  protrudes through an opening  78  in casing  62 . Each variable stator vane assembly  56  also includes a lever arm assembly  80  that extends from each variable stator vane  74 . In the exemplary embodiment, lever arm assembly  80  is utilized to rotate the respective variable stator vanes  74 . Vanes  74  are oriented relative to a flow path through compressor  14  to control air flow therethrough. In addition, at least some vanes  74  are attached to an inner casing  82 . Each variable stator vane assembly is coupled to a lever arm  84  that is configured to move each variable stator vane assembly  56  approximately simultaneously. More specifically, gas turbine engine  10  includes a servo motor  86  that is coupled to lever arm  84  such then when servo motor  86  is actuated by ECU  34 , fuel is channeled from a fuel pump  36  to servo motor  86  to facilitate repositioning variable stator vane assemblies  56 . In the exemplary embodiment, servo motor  32  and servo motor  86  are coupled within a single hydromechanical unit (HMU)  88 . Servo motor as used herein is defined as an electrical device, such as a motor for example, that is coupled to a valve. When the electrical device is activated the valve is moved to facilitate channeling a working fluid therethrough.  
         [0018]     During operation, gas turbine engine  10  is operated such that fuel pump  36  is configured to channel fuel to either servo motor  32  and/or servo motor  86 . More specifically, as gas turbine engine  10  is operated, ECU  34  electrically actuates servo motors  32  and  86  such that fuel supplied by fuel pump  36 , is channeled to either the VSV&#39;s  56  and/or the VBV  30  to facilitate repositioning either VSV&#39;s  56  and/or VBV  30 . As used herein, ECU  34  can be any control unit that is configured to transmit and/or receive signals from gas turbine engine  10  to facilitate operating gas turbine engine  10 . For example, ECU  34  may be either a Full Authority Digital Engine Control (FADEC), or a Modernized Digital Engine Control (MDEC). As used herein, an ECU can be any electronic device that resides on or around gas turbine engine  10  and includes at least one of software and/or hardware that is programmed to control and/or monitor gas turbine engine  10 .  
         [0019]      FIG. 3  is a simplified schematic illustration of a driver simulator  100  that can be utilized to operate either servo motor  32  and/or servo motor  86  and thus reposition either VBV  30  and/or VSV&#39;s  56 . In the exemplary embodiment, driver simulator  100  is a portable device that is configured to be removably coupled to HMU  88 . In an alternative embodiment, driver simulator  100  is coupled directly to servo motor  32  and/or servo motor  86 .  
         [0020]     In the exemplary embodiment, driver simulator  100  includes a power source  110 . In one embodiment, power source  110  is a DC battery. In an alternative embodiment, power source  110  includes a transformer (not shown) such that standard AC current can be utilized to operate driver simulator  100 . Driver simulator  100  also includes a first system  120  that is configured to either open and/or close VBV  30 , and a second system  122  that is configured to either open and/or close VSV&#39;s  56 . In the exemplary embodiment, first system  120  includes at least one resistive element  130  that is utilized to resist, limit and/or regulate the flow of electrical current from power source  110  to HMU  88 , and at least one current interrupter  132  that is coupled between power source  110  and resistive element  130 . In the exemplary embodiment, current interrupter  132  is a fuse that is configured to interrupt the flow of electrical current from power source  110  to HMU  88  when a predetermined current threshold has been exceeded.  
         [0021]     First system  120  also includes a meter  134  that is configured to sense the output from power source  110  and generate a visual indication to facilitate an operator determining when power source  110  is not operating within predefined limits. First system  120  also includes a multi-position switch  136  to facilitate operating first system  120  in a plurality of different operational modes. In the exemplary embodiment, switch  136  is a three position switch such that first system  120  can be operated in three distinct modes of operation. In the exemplary embodiment, driver simulator  100  also includes a reverse polarity switch  140  that is operable to facilitate connecting the power supply and the load side, i.e. power source  110  and HMU  88 , when both are of contrary polarity, that is, out of phase, with respect to each other such that driver simulator  100  can be utilized on a wide variety of gas turbine engines.  
         [0022]     Driver simulator  100  also includes second system  122 . In the exemplary embodiment, second system  122  is substantially similar to first system  120  and includes at least one resistive element  150  that is utilized to resist, limit and/or regulate the flow of electrical current from power source  110  to HMU  88 , and at least one current interrupter  152  that is coupled between power source  110  and resistive element  150 . In the exemplary embodiment, current interrupter  152  is a fuse that is configured to interrupt the flow of electrical current from power source  110  to HMU  88  when a predetermined current threshold has been exceeded.  
         [0023]     Second system  122  also includes a meter  154  that is configured to sense the output from power source  110  and generate a visual indication to facilitate an operator determining when power source  110  is not operating within predefined limits. Second system  122  also includes a multi-position switch  156  to facilitate operating second system  122  in a plurality of different operational modes. In the exemplary embodiment, switch  156  is a three position switch such that second system  122  can be operated in three distinct modes of operation.  
         [0024]     In the exemplary embodiment, portions of first system  120  and second system  122  are coupled within a container  170 . For example, power source  110 , current interrupters  132  and  134 , resistive elements  130  and  150  are sealed substantially within container  170 . Whereas, portions of switches  136  and  156 , and meters  134  and  154  extend at least partially through container  170  to enable an operator to control driver simulator  100  from outside container  170 . In the exemplary embodiment, container  170  is fabricated utilizing a substantially water proof and shock resistant material. Moreover, container  170  is fabricated utilizing a relatively light weight material such that driver simulator  100  is portable and can be utilized on a wide variety of gas turbine engines located in different locations.  
         [0025]      FIG. 4  is simplified schematic illustration of driver simulator  100  coupled to HMU  88 . To operate driver simulator  100 , driver simulator  100  is first coupled to HMU  88 . More specifically, HMU  88  includes an electrical socket  160  and ECU  34  includes and electrical connector  162  that is configured to plug into socket  160  such that electrical and/or data signals can be transmitted from ECU  34  to HMU  88 . Accordingly, to couple driver simulator  100  to HMU  88 , electrical connector  162  is disconnected from electrical socket  160 . Moreover, in the exemplary embodiment, although ECU  34  may include a plurality of electrical connectors that are coupled to HMU  88 , electrical connector  162  represents the connector that is utilized to transmit information to HMU  88  that is utilized by HMU  88  to reposition at least one of the VSV&#39;s  56  and/or VBV  30 .  
         [0026]     In the exemplary embodiment, when gas turbine engine  10  is offline, i.e. gas turbine engine  10  is not operating, ECU  34  does not provide an electrical signal to HMU  88  to facilitate repositioning either VSV&#39;s  56  and/or VBV  30 . For example, as described previously herein, when gas turbine engine  10  is stopped, or taken offline, ECU  34  ceases to transmit a control signal to HMU  88  to facilitate controlling either VSV&#39;s  56  and/or VBV  30 . Accordingly, electrical connector  162  is uncoupled, or unplugged, from electrical socket  160  to facilitate providing an electrical access to couple driver simulator  100  to HMU  88 . Therefore, and in the exemplary embodiment, driver simulator  100  is coupled to HMU  88  utilzing a connector  164  that is coupled to, or plugged into, socket  160 .  
         [0027]     After driver simulator  100  is electrically coupled to HMU  88 , driver simulator  100  may be operated in a plurality of modes. More specifically, either switch  136  and/or switch  156  is repositionable such that driver simulator  100  is operable in either a first mode, a second mode, or a third mode to facilitate repositioning either VSV&#39;s  56  and/or VBV  30 , respectively. In the first mode of operation, also referred to herein as the “ON” mode, at least one of switches  136  and/or  156  is positioned in a first position such that power source  110  is electrically coupled to HMU  88 . For example, during operation, when the operator moves at least one of switches  136  and/or  156  to the “ON” position, at least one of VSV&#39;s  56  and/or VBV  30  is repositioned to a desired operating position. More specifically, while switches  136  and/or  156  are maintained in the “ON” position, electrical power is supplied from power source  110  to HMU  88  such that VSV&#39;s  56  and/or VBV  30  are repositionable. Additionally, while simulator  100  is maintained in the “ON” position, gas turbine engine  10  is rotated, either manually or automatically, to facilitate generating sufficient hydraulic pressure such that when either VSV&#39;s  56  actuator and/or VBV  30  actuator is activated utilizing driver simulator  100 , hydraulic fluid is ported through the respective actuators to reposition either VSV&#39;s  56  and/or VBV  30 . Alternatively, when switches  136  and/or  156  are moved from the “ON” position to another position, i.e. the second or third mode of operation, power supplied from power source  110  to HMU  88  is interrupted such that VSV&#39;s  56  and/or VBV  30  cease moving. More specifically, when power supplied from power source  110  to HMU  88  is interrupted driver simulator  100  provides no torque motor current so the torque motor current is approximately 0 mA. Thus VSV&#39;s  56  and/or VBV  30  slew towards the failsafe position as long as a hydraulic force is applied.  
         [0028]     In the second mode of operation, also referred to herein as the “TEST” mode, at least one of switches  136  and/or  156  is positioned in a second position such that power source  110  is electrically coupled to a respective meter  134  and/or  154 , to facilite determining the power discharging from power source  110 . For example, during operation, when the operator moves at least one of switches  136  and/or  156  to the “TEST” position, a respective meter  134  or  154  displays the current supplied by power source  110  such that an operator can confirm that power source  110  is providing the predetermined current to reposition at least one of VSV&#39;s  56  and/or VBV  30 . More specifically, operating driver simulator  100  in the “TEST” position enables an operator to confirm that power source  110  is providing a sufficient current to drive either servo motor  32  and/or servo motor  86  before driver simulator  100  is coupled to HMU  88 .  
         [0029]     In the third mode of operation, also referred to herein as the “OFF” mode, switches  136  and/or  156  are positioned in a third position such that power source  110  is electrically decoupled from HMU  88  to facilite either connecting and/or disconnecting driver simulator  100  from HMU  88 . For example, during operation, when the operator moves switches  136  and/or  156  to the “OFF” position, meters  134  and  154  display approximately zero current such that an operator can safely either connect and/or disconnect driver simulator  100  from HMU  88 .  
         [0030]     The above-described driver simulator includes two systems that are each operable in a plurality of modes to facilitate repositioning at least one of VSV&#39;s  56  and/or VBV  30 . More specifically, when the ECU is deactivated, the driver simulator functions to transmit a signal to at least one of the VSV&#39;s  56  and/or VBV  30 . Accordingly, to borescope the gas turbine engine or perform other maintenance, the maintenance personnel can reposition the VSV&#39;s to a fully open position, and reposition the VBV to a fully closed position without disconnecting the fuel line between the fuel pump and the engine control system. Therefore, the driver simulator described herein facilitates eliminating the requirement to operate the gas turbine engine in a test configuration to verify that the fuel system is not leaking, therefore reducing the time and thus the cost of performing mainentance on the gas turbine engine.  
         [0031]     Exemplary embodiments of a driver simulator are described above in detail. The driver simulator is not limited to the specific embodiments described herein, but rather, components of the system may be utilized independently and separately from other components described herein. Specifically, the driver simulator may be modified to be utilized on any known gas turbine engine.  
         [0032]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.