Patent Description:
Aircraft engines are designed to provide many years of operation, and as part of that it is necessary to provide them with periodic servicing and occasional repairs. Sometimes it is necessary to strip down the engine and then rebuild it as part of these processes. Stripping and rebuilding an engine is a complex and time-consuming process, especially when accessing components deep within the engine structure. Because many components within the engine are designed to rotate freely, it is often necessary to immobilise parts of the engine before they, or pieces they are attached to, can be removed.

It would be beneficial to simplify and/or speed up the process for stripping or rebuilding and engine, as saving time and resources required to perform this task also means saving money for the operator.

United States patent <CIT> relates to a device dedicated to securing a machine shaft on a bearing support. The device comprises i) a locknut provided with a stop, comprising a front face, a thread intended to interact with a thread of the bearing support, and first coupling means, ii) an extraction nut comprising a thread intended to interact with a thread of the shaft, inverted in relation to the thread of the bearing support, two coupling means and a stop provided with a front face, intended to be supported on a rear face of a stop of the bearing support, and a rear face on which butts the front face of the locknut stop when it is located in an immobilisation position, and iii) a nut lock provided with third and fourth coupling means, designed so as to interact respectively with the first and second coupling means, in order to couple in rotation the extraction nut and the locknut once they have been located in an immobilisation position.

United States patent<CIT> relates to a retaining arrangement for retaining a bearing around a stub shaft having a machined cavity and which includes a ring forming a stop for the bearing nut and a locking piece.

In a first aspect there is provided a tool for immobilising a first shaft of a gas turbine engine in relation to a second shaft of a gas turbine engine, as set out in claim <NUM>. Optional features are included in the dependent claims. Such a tool is advantageous in the servicing of gas turbine engines, as it reduces the number of parts that need to be removed in order to access certain interior components within the engine, saving time and money for the operator.

The tool may further comprise a backstop on the exterior surface of the cylindrical body to limit longitudinal movement of the tool in one direction with relation to the second shaft. The backstop can be useful in providing consistent positioning of the tool in relation to the shafts. The backstop may be integral with the exterior protrusions.

Optionally, the interior protrusions of the tool may be at the first end of the cylindrical body. Optionally, the exterior protrusions may be at the second end of the cylindrical body. The arrangement of the protrusions can be adjusted dependent upon the configuration of the shafts being immobilised.

Optionally, the tool may comprise stainless steel.

The tool may further comprise a securing device configured to receive a second section of the first shaft and to create an interference fit with the cylindrical body so as to fix the cylindrical body axially with respect to the first and second shaft. Such a securing device may be helpful in providing consistent positioning of the tool in relation to the shafts, and preventing the tool from becoming prematurely uncoupled from either shaft. The securing device may be a threaded nut.

In a second aspect of the present invention, there is disclosed a method for removing a first component from a gas turbine engine as set forth in claim <NUM>. Such a method is advantageous in the servicing of gas turbine engines, as it reduces the number of parts that need to be removed in order to access certain interior components within the engine, saving time and money for the operator.

The first shaft can be an intermediate-pressure shaft, and the first component can be an intermediate pressure compressor module. The second shaft can be a low-pressure turbine shaft, and the second component can be a low-pressure turbine.

As noted elsewhere herein, the present invention may relate to a gas turbine engine.

For example, the gas turbine engine may have at least two shafts that connect turbines and compressors.

The planet carrier <NUM> constrains the planet gears <NUM> to process around the sun gear <NUM> in synchronicity whilst enabling each planet gear <NUM> to rotate about its own axis.

It will be appreciated that the arrangement shown in <FIG> and <FIG> is by way of example only, and various alternatives are within the scope of the present invention.

By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the invention is not limited to the exemplary arrangement of <FIG>.

Accordingly, the present invention extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

Other gas turbine engines to which the present invention may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in <FIG> has a split flow nozzle <NUM>, <NUM> meaning that the flow through the bypass duct <NUM> has its own nozzle <NUM> that is separate to and radially outside the core exhaust nozzle <NUM>. However, this is not limiting, and any aspect of the present invention may also apply to engines in which the flow through the bypass duct <NUM> and the flow through the core <NUM> are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the invention may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine <NUM> may not comprise a gearbox <NUM>.

The tool of the present invention is used during the processes of disassembling or reassembling an engine, for example of any of the types previously described. Indeed, the tool can be used in any gas turbine engine system comprising two or more independently rotating shafts that require immobilising for the purposes of building/disassembling the rotating assembly. This could be for example a <NUM>-shaft or <NUM>-shaft engine design.

The tool of the present invention is designed to immobilise one shaft with respect to another. As such, the tool has a generally cylindrical design so that it can be positioned concentrically between a first and second shaft of the gas turbine engine. <FIG> shows a side-on cut-through view of a tool <NUM> according to the present invention. The tool <NUM> comprises a generally cylindrical body <NUM>, with an outer surface <NUM>, an inner surface <NUM>, a first end <NUM> and a second end <NUM> opposite the first end <NUM>. On the inner surface are a number of interior protrusions <NUM>. In <FIG> only three interior protrusions <NUM> are shown on the half of the tool that is visible, but it is to be understood that any number can be present within the tool, including a single interior protrusion, if it is dimensioned appropriately. The interior protrusions <NUM> are aligned axially within the body <NUM>, so as to form a circle of interior protrusions <NUM> within the tool <NUM>. On the outer surface <NUM> there are a number of exterior protrusions <NUM>. Only two are shown in <FIG>, but it is to be understood that any number can be present on the tool, including a single exterior protrusion, if it is dimensioned appropriately.

In use, the body <NUM> of the tool <NUM> is passed over a section of a first shaft of the engine <NUM>, for example the low-pressure turbine shaft <NUM>. The outer surface of the section of the low-pressure turbine shaft <NUM> comprises a number of slots equal or greater than the number of interior protrusions <NUM> on the tool, and the low-pressure turbine shaft <NUM> and/or tool <NUM> is rotated until each of the interior protrusions <NUM> is aligned with a slot on the outer surface of the low-pressure turbine shaft <NUM>. The interior protrusions <NUM> of the tool are then slotted into the slots on the outer surface of the low-pressure turbine shaft <NUM> such that the tool <NUM> and the low-pressure turbine shaft <NUM> are interlocked, and fixed relative to one another.

Next, or simultaneously, the tool <NUM> is brought into contact with a section of a second shaft <NUM> of the engine <NUM>, for example the interconnecting shaft <NUM>. The inner surface of the section of the interconnecting shaft <NUM> comprises a number of slots equal to or greater than the number of exterior protrusions <NUM>, and the interconnecting shaft <NUM> and/or tool <NUM> is rotated until each of the exterior protrusions <NUM> on the tool is aligned with a slot on the inner surface of the interconnecting shaft <NUM>. The exterior protrusions <NUM> of the tool are then slotted into the slots on the inner surface of the interconnecting shaft <NUM> such that the tool <NUM> and the interconnecting shaft <NUM> are interlocked, and fixed relative to one another.

In an alternative embodiment shown in <FIG>, the exterior protrusions <NUM> can be positioned on one of the first <NUM> or second <NUM> ends of the body <NUM>, such that they protrude axially along the length of the body. In the example shown in <FIG>, the exterior protrusions <NUM> extend from the second end of the body <NUM> of the tool <NUM>. In this case, either the end surface or interior surface of the interconnecting shaft <NUM> comprises a number of slots equal to or greater than the number of exterior protrusions <NUM>, and the interconnecting shaft <NUM> and/or tool <NUM> is rotated until each of the exterior protrusions <NUM> is aligned with a slot on the end surface or interior surface of the interconnecting shaft <NUM>. The exterior protrusions <NUM> of the tool are then slotted into the slots on the end surface or interior surface of the interconnecting shaft <NUM> such that the tool <NUM> and the interconnecting shaft <NUM> are interlocked, and fixed relative to one another.

Where the exterior protrusions <NUM> are located on the outer surface <NUM> of the body <NUM>, the outer surface may additionally comprise a backstop <NUM> such as that shown in <FIG>. The backstop <NUM> provides a surface against which a surface of the interconnecting shaft <NUM> can come to rest once the exterior protrusions <NUM> of the tool <NUM> have been inserted into the corresponding slots of the interconnecting shaft <NUM>. In this way the backstop provides a datum location to ensure consistent placing of the tool each time it is used.

In an alternative embodiment shown in <FIG>, the backstop <NUM> can be integral with the exterior protrusions <NUM>.

In an alternative embodiment shown in <FIG>, the exterior protrusions <NUM> are all positioned towards a first end of the body <NUM> of the tool <NUM>, while the interior protrusions <NUM> are all positioned towards a second end <NUM> of the body <NUM> of the tool <NUM> opposite to the first end. Such a configuration may be advantageous if the ends of the two shafts the tool is to be fitted between are within a distance of each other for which a tool can be readily constructed.

<FIG> shows in cross-section an example of how the tool embodiment <NUM> of <FIG> can be positioned so as to link two shafts, in this case a first shaft <NUM> and a second shaft <NUM>, so as to immobilise them with respect to one another. The exterior protrusions <NUM> on the body <NUM> of the tool <NUM> engage with the second shaft slots <NUM> formed on the interior surface of the second shaft <NUM>, whilst the interior protrusions <NUM> engage with slots <NUM> formed on the surface of the first shaft <NUM>. With both the shafts <NUM>, <NUM> engaged with the tool <NUM>, immobilisation of one shaft will lead to the immobilisation of both shafts.

It will be readily apparent to the skilled person how the arrangement of protrusions and slots can be altered whilst still achieving the same effect. For example, in <FIG>, the exterior protrusions <NUM> on the body <NUM> of the tool <NUM> are on the end surface and extend axially, as shown on the tool of <FIG>. The axial protrusions are accommodated by having the second shaft slots <NUM> formed on the axially-facing end-surface of the second shaft <NUM>. Alternatively, the second shaft slots <NUM> may be formed in the same position as that shown in <FIG>, i.e. on the interior surface of the second shaft <NUM>, with an axially-facing opening. In a further alternative, the slots of the first <NUM> and second <NUM> shafts may be positioned at the same axial location (i.e. in the same axial plane) relative to one another, such that the interior <NUM> and exterior <NUM> protrusions may also have the same or similar axial location on the body <NUM> of the tool <NUM>, as shown for example in <FIG>.

<FIG> and <FIG> also show an optional securing device <NUM>, which can be used to help keep the body <NUM> of the tool <NUM> fixed once in place. The securing device can be positioned using an interference fit, or could be a threaded nut which is secured to a thread (not shown) on a second section of the exterior surface of the first shaft <NUM>.

<FIG> is a schematic illustration of a method <NUM> for removing an interior component, in this case the intermediate pressure compressor (IPC) module <NUM>, from a gas turbine engine <NUM> according to the prior art. In a first step <NUM> the fan case <NUM> is removed from the front of the engine <NUM>. In the second step <NUM> the fan disc and associated components <NUM> are also removed from the front of the engine. In the third step <NUM> the low-pressure turbine (LPT) module <NUM> is removed from the rear of the engine. Only once the LPT module has been removed can the intermediate-pressure compressor (IPC) module be removed in step four <NUM>. This is because, before the IPC module can be removed, a further component (not shown) must be removed which otherwise will interfere with the IPC module removal process. The further component is directly linked to the intermediate pressure turbine (IPT) rotor, and is secured inside the IPC module by means of a threaded nut (not shown). In order to remove the nut, the further component, and ultimately the IPC module, the IPT rotor must be immobilised. In this known method of the prior art, the IPT rotor can only be accessed to be immobilised once the LPT module <NUM> has been removed. This is usually achieved by fitting an immobilising device (not shown) to the IPT module at the rear of the engine. With the IPT module immobilised, the nut can be removed, followed by the further component, and finally the IPC module.

Claim 1:
A tool (<NUM>) for immobilising a first shaft of a gas turbine engine in relation to a second shaft of the gas turbine engine (<NUM>), the tool comprising:
a cylindrical body (<NUM>) having a first end (<NUM>) and a second end (<NUM>) opposite the first end;
the cylindrical body (<NUM>) having an inner surface (<NUM>) with one or more interior protrusions (<NUM>) formed therein for engaging with the first shaft, and an outer surface (<NUM>) having one or more exterior protrusions (<NUM>) formed thereon for engaging with the second shaft;
the tool being configured to immobilise the first shaft in relation to the second shaft such that at least part of the tool is insertable within and held fixed relative to a first section of the second shaft via the exterior protrusions (<NUM>), and a first section of the first shaft can be inserted within and held fixed relative to the interior of the cylindrical body via the interior protrusions (<NUM>).