Patent Description:
In one aspect, the present disclosure relates to an air turbine starter according to claim <NUM>.

In yet another aspect, the present disclosure relates to a method for operating an air turbine starter, according to claim <NUM>.

The present invention is related to a driving mechanism generating kinetic motion in the form of a rotating shaft coupled with a piece of rotating equipment. One non-limiting example of a driving mechanism can include a gas turbine engine rotationally driving a piece of rotating equipment, such as a starter. The starter has various applications including starting a gas turbine engine and generating electrical power when the gas turbine engine is in operation. While the exemplary embodiment described herein is directed to application of a gas turbine engine and a starter, embodiments of the disclosure can be applied to any implementation of a driving mechanism that generates rotational motion at a driving output, and provides the rotational motion to another piece of rotating equipment.

Referring to <FIG>, a starter motor or air turbine starter <NUM> including an accessory gear box (AGB) <NUM>, also known as a transmission housing, are schematically illustrated as being mounted to a gas turbine engine <NUM>. This assembly is commonly referred to as an Integrated Starter/Generator Gearbox (ISGB), or simply an air turbine starter <NUM>. The gas turbine engine <NUM> comprises an air intake with a fan <NUM> that supplies air to a high pressure compression region <NUM>. The air intake with a fan <NUM> and the high pressure compression region collectively are known as the 'cold section' of the gas turbine engine upstream of the combustion. The high pressure compression region <NUM> provides the combustion chamber <NUM> with high pressure air. In the combustion chamber, the high pressure air is mixed with fuel and combusted. The hot and pressurized combusted gas passes through a high pressure turbine region <NUM> and a low pressure turbine region <NUM> before exhausting from the gas turbine engine. As the pressurized gases pass through the high pressure turbine (not shown) of the high pressure turbine region <NUM> and the low pressure turbine (not shown) of the low pressure turbine region <NUM>, the turbines extract rotational energy from the flow of the gases passing through the gas turbine engine <NUM>. The high pressure turbine of the high pressure turbine region <NUM> can be coupled to the compression mechanism (not shown) of the high pressure compression region <NUM> by way of a shaft to power the compression mechanism. The low pressure turbine can be coupled to the fan <NUM> of the air intake by way of a shaft to power the fan <NUM>.

The gas turbine engine can be a turbofan engine, such as a General Electric GEnx or CF6 series engine, commonly used in modern commercial and military aviation or it could be a variety of other known gas turbine engines such as a turboprop or turboshaft. The gas turbine engine can also have an afterburner that burns an additional amount of fuel downstream of the low pressure turbine region <NUM> to increase the velocity of the exhausted gases, and thereby increasing thrust.

The AGB <NUM> is coupled to a turbine shaft of the gas turbine engine <NUM>, either to the low pressure or high pressure turbine by way of a mechanical power take-off <NUM>. The mechanical power take off <NUM> contains multiple gears and means for mechanical coupling of the AGB <NUM> to the gas turbine engine <NUM>. The assembly <NUM> can be mounted on the outside of either the air intake region containing the fan <NUM> or on the core near the high pressure compression region <NUM>.

Referring now to <FIG>, the air turbine starter <NUM> is shown in greater detail. Generally, the air turbine starter <NUM> includes a housing <NUM> defining an inlet <NUM>, an outlet <NUM>, and a flow path <NUM> extending between the inlet <NUM> and outlet <NUM> for communicating a flow of gas there through. The air turbine starter <NUM> includes a turbine member <NUM> journaled within the housing <NUM> and disposed within the flow path <NUM> for rotatably extracting mechanical power from the flow of gas along the flow path <NUM>. Further, a gear train <NUM>, disposed within the gear box <NUM> and drivingly coupled with the turbine member <NUM>, can be caused to rotate.

The gear train <NUM> includes a ring gear <NUM> and can further comprise any gear assembly including for example but not limited to a planetary gear assembly or a pinion gear assembly. A turbine shaft <NUM> couples the gear train <NUM> to the turbine member <NUM> allowing for the transfer of mechanical power. The turbine shaft <NUM> is rotatably mounted to the gear train <NUM> and supported by a pair of turbine bearings <NUM> while the gear train <NUM> is supported by a pair of carrier bearings <NUM>.

A gear box interior <NUM> can contain oil to provide lubrication and cooling to mechanical parts contained therein such as the gear train <NUM>, ring gear <NUM>, and bearings <NUM>, <NUM>.

There is an aperture <NUM> through which the turbine shaft <NUM> extends and meshes with a carrier shaft <NUM> to which a clutch <NUM> is mounted and supported by a pair of spaced bearings <NUM>. A drive shaft <NUM> extends from a portion of the gear box <NUM> and is coupled to the clutch <NUM> and additionally supported by the pair of spaced bearings <NUM>. The drive shaft <NUM> is driven by the gear train <NUM> and coupled to the power take-off <NUM> of the gas turbine engine <NUM>, such that operation of the engine <NUM> provides a driving motion to the gear box <NUM>.

The clutch <NUM> can be any type of shaft interface portion that forms a single rotatable shaft <NUM> including the turbine shaft <NUM>, the carrier shaft <NUM>, and the drive shaft <NUM>. The shaft interface portion can be by any known method of coupling including, but not limited to, gears, splines, a clutch mechanism, or combinations thereof. An example of a shaft interface portion <NUM> is disclosed in <CIT>.

The gear box <NUM> and the starter <NUM> can be formed by any known materials and methods, including, but not limited to, die-casting of high strength and lightweight metals such as aluminum, stainless steel, iron, or titanium. The housing for the gear box <NUM> and starter <NUM> can be formed with a thickness sufficient to provide adequate mechanical rigidity without adding unnecessary weight to the assembly <NUM> and, therefore, the aircraft.

The rotatable shaft <NUM> can be constructed by any known materials and methods, including, but not limited to extrusion or machining of high strength metal alloys such as those containing aluminum, iron, nickel, chromium, titanium, tungsten, vanadium, or molybdenum. The diameter of the turbine shaft <NUM>, carrier shaft <NUM>, and drive shaft <NUM> can be fixed or vary along the length of the rotatable shaft <NUM>. The diameter can vary to accommodate different sizes, as well as rotor to stator spacing.

As described herein, either the gear box <NUM> or the starter <NUM> can be a driving mechanism for driving the rotation of the rotating shafts <NUM>, <NUM>, <NUM>. For example, during starting operations, the starter <NUM> can be the driving mechanism for rotation of the rotating shafts <NUM>, <NUM>, <NUM>. Alternatively, during normal gas turbine engine <NUM> operation, the gear box <NUM> can be the driving mechanism for rotation of the rotating shafts <NUM>, <NUM>, <NUM>. The non-driving mechanism, that is, the equipment being driven by the driving mechanism, can be understood as rotating equipment utilizing the rotational movement of the rotating shafts <NUM>, <NUM>, <NUM>, for example to generate electricity in the starter <NUM>.

The drive shaft <NUM> is further coupled to a decoupler assembly <NUM> including a backdrive decoupler <NUM> having an output shaft <NUM>, configured to be operably coupled to and rotate with the engine <NUM>, and a tensile fuse <NUM>. The tensile fuse <NUM> is selectively receivable and axially moveable within an internal threaded portion <NUM>, that can be for example a helical female thread, of the output shaft <NUM>. All joining parts can be formed from steel or like materials.

<FIG> illustrates an exploded perspective view of one exemplary embodiment of the decoupler assembly <NUM> including the backdrive decoupler <NUM> and the drive shaft <NUM>. The drive shaft <NUM> can include a circular depression <NUM> and an orthogonal depressions <NUM>. The circular depression <NUM> is surrounded by the orthogonal depression <NUM>. A central opening <NUM> is bound by a circular lip <NUM>. Circumscribing the circular lip <NUM> are a plurality of stops <NUM>.

A thread insert <NUM> is included in the decoupler assembly <NUM> and is illustrated as including a complementary circular protrusion <NUM> and orthogonal portion <NUM> formed to fit into the circular and orthogonal shaped depressions <NUM>, <NUM> of the drive shaft <NUM>. The thread insert <NUM> further includes an internal helical threaded portion <NUM> which can be for example but not limited to a three helical female thread.

The decoupler assembly <NUM> can also include a compression spring <NUM> and a ring spring <NUM>.

The output shaft <NUM> includes a first end <NUM> having an exteriorly threaded portion <NUM>. The exteriorly threaded portion <NUM> can include, but is not limited to, a helical male thread, with a proximal end including complementary stops <NUM>. A second end <NUM> is configured to be operably coupled to and rotate with the engine <NUM>.

The tensile fuse <NUM> includes a cylindrical first end <NUM>. A second end <NUM> of the tensile fuse <NUM> includes a head <NUM> and a threaded portion <NUM> that can be, for example, a helical male thread, disposed beneath the head <NUM>. The tensile fuse <NUM> further includes a neck portion <NUM> having a reduced diameter between the first end <NUM> and the threaded portion <NUM>.

The cylindrical first end <NUM> is received in the central opening <NUM> where a retainer pin <NUM> retains the first end <NUM> of the tensile fuse <NUM> within the drive shaft <NUM> operably coupling the tensile fuse <NUM> to the drive shaft <NUM>. At assembly the tensile fuse <NUM> can be drilled and pinned with the retainer pin <NUM>. The threaded portion <NUM> disposed beneath the head <NUM> is received within the internal threaded portion <NUM> of the output shaft <NUM>.

The exteriorly threaded portion <NUM> of the output shaft <NUM> and the internal threaded portion <NUM> of the tensile fuse <NUM> are formed so that the tensile fuse <NUM> is threaded into the output shaft <NUM> with an opposite hand turn compared to when the output shaft <NUM> is threaded into the thread insert <NUM>. The stops <NUM> and complementary stops <NUM> decrease axial loads along the threaded portions, <NUM>, <NUM>, <NUM>, <NUM> when the output shaft <NUM> is fully threaded into the thread insert <NUM> of the drive shaft <NUM>.

<FIG> illustrates the decoupler assembly <NUM> mounted with the drive shaft <NUM>. Because the drive shaft <NUM> and the thread insert <NUM> have corresponding circular depression <NUM>, orthogonal depressions <NUM> and circular protrusion <NUM> and orthogonal portions <NUM>, respectively, they can be operably coupled. Likewise, the complementary shapes of the stop <NUM> and <NUM> operably couple the drive shaft <NUM> to the output shaft <NUM>. It should be understood that the shapes of the depressions and corresponding receiving portions depicted as orthogonal and circular and the shapes of the complementary stops are for illustrative purposes and not meant to be limiting.

A biasing mechanism can be included between the thread insert <NUM> and the drive shaft <NUM>. In the illustrated example, the biasing mechanism is the compression spring <NUM>.

A load path can go through mating stop features including the stops <NUM>, <NUM> and transmit a driving torque. Under normal operating conditions the driving torque is transmitted from the drive shaft <NUM> of the clutch <NUM> to the output shaft <NUM> to drive the engine <NUM> by the mating stop features <NUM>, <NUM>. The load path leaves the threaded portions, <NUM>, <NUM>, <NUM>, <NUM>, the tensile fuse <NUM>, and the retainer pin <NUM> unloaded.

A top view of the thread insert <NUM> in <FIG> illustrates the ring spring <NUM>. Under normal operating conditions the threads of the exteriorly threaded portion <NUM> push the ring spring <NUM> outward into an inner portion <NUM> of the thread insert <NUM> in an expanded position.

When the clutch <NUM> becomes disengaged and the engine <NUM> transmits an overrunning torque, having a magnitude below a certain level, to the air turbine starter <NUM> the mating stop features <NUM>, <NUM> become unloaded while the threaded portions, <NUM>, <NUM>, <NUM>, <NUM>, the tensile fuse <NUM>, and retainer pin <NUM> become partially loaded.

Turning to <FIG>, in the event of a backdrive which can occur when the clutch <NUM> fails, the air turbine starter <NUM> decouples its load path so that components of the gear box <NUM> and starter <NUM> are disconnected from the engine <NUM>. The failing clutch <NUM> becomes engaged or locked while the engine <NUM> transmits an overrunning torque, with a magnitude of torque at or above the certain level, to the air turbine starter <NUM>. This can also be considered a back driving torque.

In the case of the locked clutch, the backdrive decoupler <NUM> would be exposed to enough drag torque that the output shaft <NUM> would unwind from the drive shaft <NUM>, and to simultaneously unwind the tensile fuse <NUM> from the output shaft <NUM>. The thread ratios between the internal threaded portion <NUM> and the threaded portion <NUM> for the tensile fuse <NUM> compared to those between the internal threaded portion <NUM> and the threaded portion <NUM> for the output shaft <NUM> allow for the tensile fuse <NUM> to translate two times the translation distance of the output shaft <NUM>, contributing to a high strain on the neck portion <NUM>, causing it to shear and creating a sheared portion <NUM> and a base <NUM>. The sheared portion <NUM> of the tensile fuse <NUM> is unwound from the output shaft <NUM> leaving the base <NUM> retained by the retainer pin <NUM>.

The unwinding of the output shaft <NUM> is further aided by the compressive spring <NUM>. When the output shaft <NUM> begins to unwind, the compressive spring <NUM> is configured to expand and bias the output shaft <NUM> away from the drive shaft <NUM>. It will be understood that any suitable biasing mechanism can be utilized and that the compressive spring is one illustrated example.

A top view of the thread insert <NUM> in <FIG> illustrates the movement of the ring spring <NUM> in the event of a back drive. Because the output shaft <NUM> has translated, the threads of the exteriorly threaded portion <NUM> are no longer pushing the ring spring <NUM> outward. This allows the ring spring <NUM> to compress to a retracted position where the ring spring <NUM> overlies a portion of the thread insert <NUM> preventing rethreading of the first end <NUM> of the output shaft <NUM> and the thread insert <NUM>. In this manner, the ring spring <NUM> is configured to secure the output shaft <NUM> in a decoupled and separate position from the drive shaft <NUM>.

A method <NUM> for operating an air turbine starter <NUM> is outlined in a flow chart in <FIG>. The method <NUM> begins at <NUM> with extracting mechanical power from a flow of gas utilizing a turbine <NUM> and driving the gear train <NUM> and clutch <NUM>, including the drive shaft <NUM>. At <NUM> a driving torque is transmitted from the drive shaft <NUM> to an output shaft <NUM> which is operably coupled to the engine <NUM>.

In the case of back driving at <NUM> the backdrive decoupler <NUM> is activated when the tensile fuse <NUM> that is operably coupled to both the output shaft <NUM> and the drive shaft <NUM> is sheared. The sheared portion <NUM> of the tensile fuse <NUM> is then unwound from the output shaft <NUM> and translated away from the drive shaft <NUM>. The output shaft <NUM> is unwound from the drive shaft <NUM> and translated away from the drive shaft <NUM>.

At <NUM> the output shaft <NUM> is prevented from reengaging the drive shaft <NUM> when the ring spring <NUM> contracts. The contraction of the ring spring <NUM> prevents the output shaft <NUM> from reengaging by blocking the internal helical threaded portion <NUM> from receiving the exteriorly threaded portion <NUM>. The compression spring <NUM> is a secondary mechanism that also prevents reengagement when it has sprung. The springing of the compression spring <NUM> biases the output shaft202 out and away from the drive shaft <NUM>. The air turbine starter <NUM> is therefore disabled after decoupling, which prevents an additional engine start.

All directional references (e.g., radial, upper, lower, upward, downward, left, right, lateral, front, back, top, bottom, above, below, vertical, horizontal, clockwise, counterclockwise) are only used for identification purposes to aid the reader's understanding of the disclosure, and do not create limitations, particularly as to the position, orientation, or use thereof. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and can include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. The exemplary drawings are for purposes of illustration only and the dimensions, positions, order and relative sizes reflected in the drawings attached hereto can vary.

Many other possible embodiments and configurations in addition to that shown in the above figures are contemplated by the present disclosure. Additionally, the design and placement of the various components such as starter, AGB, or components thereof can be rearranged such that a number of different in-line configurations could be realized.

The aspects of the present disclosure provide a decoupler for decoupling a torque load coming from the gear train of an engine to prevent backdriving of the entire air turbine starter. Benefits associated with this decoupling include reducing the risk of spinning a damaged air turbine starter which could cause additional damage to the air turbine starter if not decoupled. Further still, the decoupling results in only the tensile fuse being needed to be replaced instead of more costly parts damaged by the continued backdriving.

Claim 1:
An air turbine starter (<NUM>) for starting an engine (<NUM>), comprising:
a housing (<NUM>) defining an inlet (<NUM>), an outlet (<NUM>), and a flow path (<NUM>) extending between the inlet and the outlet for communicating a flow of gas therethrough;
a turbine member (<NUM>) journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the flow of gas;
a gear train (<NUM>) drivingly coupled with the turbine member;
a clutch (<NUM>) having a drive shaft (<NUM>) operably coupled with the gear train, and a thread insert (<NUM>) operably coupled to the drive shaft (<NUM>), the thread insert (<NUM>) comprising a threaded portion (<NUM>); and
a decoupler (<NUM>), comprising:
a tensile fuse (<NUM>) having a first end (<NUM>) operably coupled to the drive shaft, a threaded portion (<NUM>), and a neck portion (<NUM>) having a reduced diameter located between the first end and the threaded portion; and
an output shaft (<NUM>) having a first end (<NUM>) selectively operably coupled to the drive shaft, a second end (<NUM>) configured to be operably coupled to and rotate with the engine, an exteriorly threaded portion (<NUM>) of the first end (<NUM>), and an internal threaded portion (<NUM>) that receives the threaded portion of the tensile fuse;
wherein the threaded portion (<NUM>) of the thread insert (<NUM>) receives the exteriorly threaded portion (<NUM>) of the first end of the output shaft (<NUM>); and
wherein when a driving torque is transmitted from the drive shaft of the clutch to the output shaft the tensile fuse is not loaded, when an overrunning torque is transmitted below a certain level the tensile fuse is partially loaded and when the overrunning torque reaches a certain level the tensile fuse shears at the neck portion and the threaded portion (<NUM>) of the tensile fuse (<NUM>) is unwound from the internal threaded portion (<NUM>) in a direction away from the drive shaft and the output shaft (<NUM>) is unwound from the thread insert (<NUM>) in a direction away from the drive shaft.