Gas turbine impeller alignment tool and method

An apparatus and method for centering a shaft (for an impeller or other rotating component) in a gas turbine engine, such as that used in aircraft or other vehicles. The apparatus includes a base, at least one arm and an actuator. The arm is connected to the base and the actuator is located on a predetermined axis and aligns the impeller shaft to that axis. The actuator also applies a force to the actuator to simulate actual operational forces in the engine so that proper tolerances can be measured. The method includes steps of coupling the apparatus to a locator surface, impeller shaft with the actuator and moving the actuator such that an axial load is provided on the shaft.

FIELD OF THE INVENTION

The present invention relates to gas turbine engine repair tools and, more particularly, to a device used to align the impeller of a gas turbine engine, such as those found on aircraft and other vehicles.

BACKGROUND OF THE INVENTION

Jet engines (also called gas turbine engines) are generally designed and built robustly and safely. Nonetheless, these well-designed engines may need to undergo periodic maintenance and/or repair. Such maintenance and repair operations may include partial or complete disassembly of the engine, and removal, repair, or replacement, of one or more components within the engine. Some of the components may be installed in the engine according to relatively tight tolerances. Although these same components may be manufactured to within design specification tolerances, manufacturing variations may still exist. Thus, engine re-assembly following maintenance and/or repair may include instances in which these variations are accounted for by using, for example, mechanical shims.

For example, in the compressor section of a jet engine, it is desirable that the axial clearance between the compressor impeller and the shroud, which surrounds a portion of the impeller, is minimized for efficient impeller operation. Generally, this is because the centrifugal compression increases as the shroud axial clearance decreases, which may result in an engine that runs more efficiently. Conversely, as this axial clearance increases, engine efficiency may decrease. To obtain the appropriate clearance following maintenance or repair, the impeller shaft may be manually centered, and a feeler gauge may be used to check the clearance between the impeller vanes and the shroud. The impeller and shaft may be manually adjusted and mechanical shims may then be fitted between the shroud and another portion of the engine to obtain the appropriate clearance.

The above-described method of centering the impeller shaft and determining and adjusting the impeller to the appropriate clearance may present certain drawbacks. For example, the shaft may not be appropriately centered and may lead to shaft imbalance when the engine is placed back into operation. Additionally, the high pressure case and high pressure shaft bearings that rotationally support the high pressure impeller shaft may have some radial and axial play, which may lead to further inconsistencies in measuring and setting the clearance between the impeller and the shroud. Moreover, during normal operation of the engine, the impeller and shaft will experience an axial force generally not present during the re-assembly of the engine. Because the bearings rotationally supporting the shaft may have some axial play, the clearance between the impeller and shroud may decrease beyond what was previously set when the engine was re-assembled. This decreased clearance may result in less than optimum engine performance and, in some cases, may result in the impeller physically contacting the shroud.

Therefore, there is a need for an apparatus and method that addresses one or more of the above-noted drawbacks. Namely, an apparatus and method that allows accurate centering of the impeller shaft within a jet engine, and/or allows accurate measurement and adjustment of clearances between the impeller and other components within the engine, and/or allows operational axial loads to be imposed during the measurement and adjustment of such clearances. The present invention addresses one or more of these needs.

SUMMARY OF THE INVENTION

The present tool and method of using the tool substantially removes or minimizes variation in the clearance measurement and adjustment process during jet engine maintenance and/or repair. The present tool provides centering of the high pressure shaft of an engine supported by any number of bearings and minimization of any radial and axial bearing play. The present tool further provides axially loading of the shaft to simulate normal engine operation, and provides improved measurement accuracy during assembly, repair and/or overhaul of the engine.

In one embodiment, and by way of example only, a method for centering the shaft and determining a clearance between the impeller and the shroud, for a jet engine including at least a compressor module having an impeller mounted on a shaft and a shroud positioned proximate to the impeller is provided. The method includes the steps of obtaining a shaft centering tool having a base adapted for coupling the tool to a locator surface, at least one arm having a first end coupled to the base and a second end separated from the locator surface, and an actuator mounted on the arm and aligned on a predetermined axis to engage the impeller shaft, apply force thereto and align the shaft with the predetermined axis, coupling the tool to the locator surface, moving the actuator into engagement with an end of the shaft to place a predetermined force on the shaft, and measuring the clearance between the impeller and the shroud.

In another embodiment a tool for centering an impeller shaft in a jet engine in reference to a locator surface is provided, where the tool includes a base, at least one arm, and an actuator. The base is adapted for coupling the tool to the locator surface. The at least one arm includes a first end coupled to the base and a second end separated from the locator surface. The actuator is mounted on the arm and aligned on a predetermined axis to engage the impeller shaft, apply force thereto and align the shaft with the predetermined axis.

In yet another embodiment, a tool for centering an impeller shaft in a jet engine with reference to a locator surface is provided. The tool includes a base, a hub, at least one arm and a threaded rod. The base is adapted for coupling the tool to the locator surface. The hub includes a threaded inner surface defining an opening. The at least one arm has a first end mounted to the base and a second end mounted to the hub to locate the hub along a predetermined axis. The threaded rod is engaged with the threaded inner surface of the hub and has at least a first end adapted to engage the shaft and a second end adapted to engage a nut, and an outer surface that includes threads with the predetermined thread pitch.

Other independent features and advantages of the preferred apparatus and method will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Before proceeding with a detailed description of the various embodiments, it is to be appreciated that the shaft centering device described below may be used in conjunction with various types of gas turbine engines, such as an aircraft turbofan jet engine, that include one or more rotating shafts. The skilled artisan will appreciate that the below description, when referring to a turbofan jet engine, encompasses either single stage or multistage jet engine architectures. Thus, although the present invention is, for convenience of explanation, depicted and described as being implemented with a two-stage turbofan jet engine, it will be appreciated that it can be implemented with other engine designs.

Turning now to the description, and with reference first toFIG. 1, a partial cross-section side of a turbofan jet engine, with which the novel impeller alignment tool400may be used, is depicted. As this figure illustrates, a turbofan jet engine100includes at least four major modules. These major modules include a fan module110, a compressor module120, a combustor and turbine module130and an exhaust module140.

The fan module110is positioned at the front, or “inlet” section of the engine100, and includes a fan108that induces air from the surrounding environment into the engine100. The fan module110accelerates a fraction of this air toward the compressor module120, and the remaining fraction is accelerated into and through a bypass112, and out the exhaust module140. The compressor module120raises the pressure of the air it receives to a relatively high level.

This high-pressure compressed air then enters the combustor and turbine module130, where a ring of fuel nozzles114(only one illustrated) injects a steady stream of fuel. The injected fuel is ignited by a burner (not shown), which significantly increases the energy of the high-pressure compressed air. This high-energy compressed air then flows first into a high pressure turbine115and then a low pressure turbine116, causing rotationally mounted turbine blades118on each turbine115,116to turn and generate energy. The energy generated in the turbines115,116is used to power other portions of the engine100, such as the fan module110and the compressor module120. The air exiting the combustor and turbine module130then leaves the engine100via the exhaust module140. The energy remaining in the exhaust air aids the thrust generated by the air flowing through the bypass112.

With reference now toFIGS. 2 and 3, a more detailed description of the compressor module120will be provided. As shown, the compressor module120includes a low pressure section150and a high pressure section160. The low pressure section150includes four stages155a-d, each of which includes four rotors170and four stators175. Each of the rotors170has a plurality of blades177and is surrounded by a shroud180. As shown more clearly inFIGS. 2 and 3, each of the rotors170is rotationally mounted on a low pressure shaft190, which is driven by the low pressure turbine116. As the rotors170rotate, the blades177force air through each of the stators175in subsequent sections. Each stator175also includes a plurality of vanes185. As the air from the rotors170travels across the vanes185, it is forced to travel at a substantially optimum angle to the next stage, thereby increasing the air pressure as the air travels from stage to stage.

The high pressure section160includes a high pressure diffuser case210, a shroud215, and a high pressure impeller220. The high pressure diffuser case210couples the low pressure section150to the high pressure section160and directs the air exhausted from the fourth stage155dof the low pressure section150at the appropriate angle into high pressure impeller220. The shroud215is mounted to the diffuser case210and surrounds a portion of the high pressure impeller220. The high pressure impeller220has a plurality of vanes222, and is mounted on a impeller shaft195. The impeller shaft195, as shown more clearly inFIG. 1, is rotationally supported by a first set of bearings123and a second set of bearings125. The impeller shaft195surrounds the low pressure shaft190, and is driven by the high pressure turbine115. Thus, the impeller shaft195rotates independently of the low pressure shaft190. As shown more clearly inFIG. 2, the shroud215and the vanes222flare radially outwardly. The clearance between the shroud215and the vanes222, as was previously noted, is set to a predetermined magnitude to obtain substantially optimum engine performance.

During assembly, or following engine maintenance, repair and/or overhaul of the engine100, the impeller shaft195and impeller220may need to be centered, and the clearance between the impeller vanes222and the shroud215checked and adjusted to obtain substantially optimal engine performance. To do so, a shaft alignment and loading tool400may be used. A particular preferred embodiment of the tool400is depicted inFIGS. 4,5, and6, and will now be described in detail. The tool400includes a base420, three arms430, and an actuator500. The base420is used to couple the tool400to a locator surface. The locator surface may be the collar212of the high pressure diffuser case210(see FIG.2). Thus, the base420may include holes580that line up with threaded holes in the high pressure diffuser case collar212(see FIG.6). As may be appreciated by one skilled in the art, the locator surface may be other sections of the engine100, or may be some surface that is not part of the engine at all. By way of non-limiting example, the base420could completely surround the high pressure compressor section and be coupled to a floor, table, cart, or any one of numerous other surfaces. Additionally, although in the depicted embodiment, the base420is substantially circular in shape, it should be appreciated that the base420could be made into any one of numerous other shapes.

The present actuator500includes a hub440, and a rod450. However, the actuator500is not limited to a hub440and rod450structure, and may alternately be a structure located at the end of each arm that can mechanically, electrically, pneumatically or hydraulically apply force to the impeller shaft195. In the present actuator500, that includes the hub440, and the rod450, the hub440, as shown more particularly inFIG. 5, includes a top surface470, a bottom surface480, forming an inner surface500. In the depicted embodiment, a sleeve510is inserted into the hub440and is coupled to the hub inner surface500. The sleeve510includes an inner surface405and, as will be discussed more fully below, in a preferred embodiment the sleeve inner surface504is threaded. It will be appreciated that the sleeve510may be omitted and that the hub inner surface500may instead by threaded.

Each of the arms430is coupled between the base420and the hub440. In the depicted embodiment, the arms430are coupled to the hub side surface490, though it will be appreciated that the tool400is not limited to this configuration. For example, the arms430could be coupled to any one or more of the outer surfaces, including the hub top surface470or the hub bottom surface480. The arms430may be coupled to the base420and hub440by, among other things, a welding process. Alternately, the arms430may be integrally formed as part of the base420and/or the hub440. In the depicted embodiment, three arms430are depicted. However, it will be appreciated that other embodiments of the tool400may include one or two arms. And yet other embodiments of the tool400may include more than three arms. Although three arms are depicted, any suitable connecting structure can be used between the hub and base. In a preferred embodiment, the arms430are shown to be formed into a substantially arch-like shape. However, the skilled artisan will appreciate that the arms430can be fashioned in any one of numerous shapes including, but not limited to straight, linear, or angular. Additionally, the skilled artisan will appreciate that the length of the arms430may vary depending on the desired distance between the hub440and the base420. It will also be appreciated that the base420, the arms430, and the hub440may be made out of any one of numerous materials. In a preferred embodiment however, each is made of an aluminum alloy.

The rod450is inserted into and through the hub opening495and the sleeve510, if it is installed. The rod450is adjustably movable axially within the hub440. That is, the rod450may be moved axially within the hub440, and substantially fixed in a particular position. In a preferred embodiment, the rod450is threaded with the same thread pitch as the sleeve510to provide this adjustable axial movement. In the depicted embodiment, an adjustment nut460is coupled to a first end540of the rod450. The adjustment nut460allows a tool, such as a wrench, to be used to rotate the rod450and thereby axially move the rod450. The nut460may be threaded onto the rod first end540and then welded in place, it may additionally be formed integral therewith, welded or brazed in place, or coupled via fasteners.

A shaft engagement piece, or pilot cone410, is coupled to a second end550of the rod. As shown more particularly inFIG. 7, the pilot cone410, in a preferred embodiment, includes at least a top surface560, a bottom surface570, and a side surface580. The bottom surface570, as will be described more fully below, is used to contact an end of the impeller shaft195. In some jet engines, the end of the impeller shaft195may have a beveled surface on the inside diameter thereof (beveled surface not illustrated). For these impeller shaft configurations, the pilot cone bottom surface570may be beveled with the same bevel angle as the beveled surface in the impeller shaft195. Similar to the adjustment nut460, the pilot cone410may also be threaded onto the rod second end550, formed integrally therewith, welded or brazed in place, or coupled via fasteners.

Turning now toFIG. 8, the use of the tool400for assembly, maintenance, or repair of the engine100will now be described. AsFIG. 8illustrates, in the depicted embodiment, the tool400is placed on the turbofan jet engine100and, more particularly, on the high pressure160compressor section. The low pressure section150is disassembled from the high pressure section160, such that the low pressure shaft190is disassembled from the impeller shaft195. Resultingly, the impeller shaft195, impeller215, shroud220and high pressure diffuser case210are exposed.

Thereafter, a stretch tool (not illustrated) or any other tool which may stretch the impeller shaft195, may be installed to stretch the impeller shaft195to a desired pre-determined value. Once the impeller shaft195is stretched, the stretch tool is removed. In the preferred embodiment, the tool400is installed by being coupled to the high pressure diffuser case collar212. The holes580located on the base420of the tool400are lined up with threaded holes in the high pressure diffuser case collar212. Screws are then threaded through the holes580on the base420and the holes in the high pressure diffuser case collar212. Once the tool400is secured to the collar212, a torque wrench, set at a predetermined torque, is then applied to the adjustment nut530. The adjustment nut530thereby axially moves the rod450, until the desired torque is achieved. A feeler gauge, or any one of other numerous tools that measure clearance, may then be inserted between the impeller215and shroud220to determine whether the clearance between the impeller215and the shroud220meets a predetermined value. If the distance between the impeller215and shroud220does not meet the predetermined value, the adjustment nut530is disengaged from the rod250and mechanical shims may be fitted or removed from between the shroud and engine to obtain the appropriate clearance.

The tool400can be used for centering the impeller shaft195in relation to the other high pressure portion160components for an engine where the high pressure shaft is supported by any number of bearings. Variation of the tool400can be used to align other engine shafts as well. The present invention is useful for removing variation from the shim process and can remove the radial play from the bearings. Further, the tool400loads the high pressure shaft and impeller against the bearings in an axial manner to simulate operational forces and thus how the impeller may react in the engine during operation. The tool400improves measurement accuracy for the mechanic during assembly, aftermarket, repair and/or overhaul of the engine.