Patent Description:
A turbine engine, for example a gas turbine engine, is engaged in regular operation to an air starter. Air starters are typically mounted to the turbine engine through a gearbox or other transmission assembly. The transmission transfers power from the starter to the turbine engine to assist in starting the turbine engine. The internal components of both the turbine engine and the air starter spin together such that the air starter can be used to start the turbine engine.

<CIT> relates to an engine starting system for starting a gas turbine power plant comprises two turbine rotor units mechanically interconnected and arranged to be driven from different sources of motive fluid, means being provided whereby the inlet and outlet of one of the turbine rotors are connected to spaces at substantially the same pressure so that this rotor will act as a compressor to provide a braking effect to prevent overspeeding when the second turbine rotor is being driven. <CIT> relates to an advancing mechanism for the jaw means of an engine starter including a screw shaft driven by power means, a travel nut threadedly engaged upon the screw shaft and operatively connected to the starter jaw means so that the latter is advanced axially by axial movement of the nut and is adapted to rotate therewith and a device for imposing a drag upon the jaw means as the latter is rotated by the screw shaft, the device includes a heavy member connected to the travel nut by means including helical splines and movable axially relatively to the nut when the latter is initially rotated to engage a fixed member and exert a restraining torque on the nut whereby the latter is caused to move axially along the screw shaft. <CIT> discloses a starter for starting an internal combustion engine, and more particularly a starter of the turbine type in which gases under pressure generated by igniting a cartridge containing an explosive mixture or a stored fluid are used as the motive power for the turbine.

Aspects and advantages of the disclosure will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the disclosure.

In one aspect, the present disclosure generally relates to an air starter according to claim <NUM> that includes a housing defining an interior having a primary inlet and a primary outlet to define a primary air flow path from the primary inlet to the primary outlet. A turbine is located in the interior of the housing, where the turbine includes a rotor with a plurality of circumferentially spaced blades. A drive shaft extends from the rotor to a gear train located in a gear box in the interior. An output shaft couples to the gear train. A spline connection, located upstream of the rotor or between the rotor and the gear train, includes a first spline interface provided on the drive shaft and a second spline interface, enmeshed with the first spline interface, provided on the output shaft. At least one pilot guide, located between the rotor and the gear train, includes a first pilot element provided on the drive shaft and a second pilot element provided on the output shaft, wherein the first pilot element axially overlaps, at least in part, the second pilot element.

In another aspect, the present disclosure generally relates to an air starter that includes a housing defining an interior having a primary inlet and a primary outlet to define a primary air flow path from the primary inlet to the primary outlet. A gear box, located in the interior, includes a gear train and a sun gear shaft wherein the gear train is rotatably coupled the sun gear shaft. A turbine, located in the interior, includes a rotor with a plurality of circumferentially spaced blades. A drive shaft extends from the rotor wherein the drive shaft includes at least one sleeve receiving at least a portion of the sun gear shaft. A spline connection, located upstream of the rotor or between the rotor and the gear train, includes a first spline interface provided on the drive shaft and a second spline interface, enmeshed with the first spline interface, provided on the sun gear shaft. At least one pilot guide, located between the rotor and the gear train, axially spaced from the spline connection, includes a first pilot element provided on the drive shaft and a second pilot element provided on the sun gear shaft, wherein the first pilot element overlaps at least a portion of the second pilot element.

These and other features, aspects and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.

A full and enabling disclosure of the present disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended FIGs, in which:.

Aspects of the disclosure described herein are directed to a turbine engine with a starter that includes a spline interface axially spaced from a pilot interface that couple a sleeve of a turbine and an output shaft.

Typically, an air starter includes a turbine coupled to a drive shaft, where the turbine and drive shaft rotate about an axis of rotation. The traditional coupling of the turbine to the drive shaft occurs at or near the intersection of the axis of rotation and a radial centerline of the rotor or blades of the turbine. Connection at this point can decrease the operating life of the turbine.

One known adaptation is to uniformly form the turbine and drive shaft. However, the material used for the uniformly formed turbine and drive shaft must have an outer sleeve adaptor made of a different material in order to couple to a sun gear of a gear train. The sleeve adapter circumscribes the drive shaft, which increases the inner diameter of the required sun gear, resulting in an increase in the overall size of the air starter.

For purposes of illustration, the present disclosure will be described with respect to an air starter for an aircraft turbine engine. For example, the disclosure can have applicability in other vehicles or engines, and can be used to provide benefits in industrial, commercial, and residential applications as further described in <FIG>.

As used herein, the term "upstream" refers to a direction that is opposite the fluid flow direction, and the term "downstream" refers to a direction that is in the same direction as the fluid flow. The term "fore" or "forward" means in front of something and "aft" or "rearward" means behind something. For example, when used in terms of fluid flow, fore/forward can mean upstream and aft/rearward can mean downstream.

Additionally, as used herein, the terms "radial" or "radially" refer to a direction away from a common center. For example, in the overall context of a turbine engine, radial refers to a direction along a ray extending between a center longitudinal axis of the engine and an outer engine circumference. Furthermore, as used herein, the term "set" or a "set" of elements can be any number of elements, including only one.

All directional references (e.g., radial, axial, proximal, distal, upper, lower, upward, downward, left, right, lateral, front, back, top, bottom, above, below, vertical, horizontal, clockwise, counterclockwise, upstream, downstream, forward, aft, etc.) are only used for identification purposes to aid the reader's understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of aspects of the disclosure described herein. Connection references (e.g., attached, coupled, secured, fastened, 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 one another. 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.

Referring to <FIG>, a starter motor or air starter <NUM> is coupled to an accessory gear box (AGB) <NUM>, also known as a transmission housing, and together are schematically illustrated as being mounted to a turbine engine <NUM> such as a gas turbine engine. The 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 turbine engine <NUM> upstream of the combustion. The high pressure compression region <NUM> provides a 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 turbine engine <NUM>. 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 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 the shaft to power the fan <NUM>. The turbine engine <NUM> can be a turbofan engine or it could be a variety of other known turbine engines such as a turboprop or turboshaft.

The AGB <NUM> is coupled to the turbine engine <NUM> at either the high pressure or low pressure turbine region <NUM>, <NUM> 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 turbine engine <NUM>. Under normal operating conditions, the mechanical power take-off <NUM> translates power from the turbine engine <NUM> to the AGB <NUM> to power accessories of the aircraft or vehicle. For example, power accessories can include, but are not limited to, fuel pumps, electrical systems, and cabin environment controls. The air starter <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>. Optionally, an air intake conduit <NUM> can couple to the air starter <NUM>. The air intake conduit <NUM> can supply the air starter <NUM> with pressurized air.

Referring now to <FIG>, an example of an air starter <NUM> is shown. Generally, the air starter <NUM> includes a housing <NUM> defining an interior <NUM> having a primary inlet <NUM> and a primary outlet <NUM>. A primary air flow path <NUM>, illustrated schematically with an arrow, extends between the primary inlet <NUM> and the primary outlet <NUM> for communicating a flow of fluid, including, but not limited to gas, compressed air, or the like, there through. The primary outlet <NUM> can include a plurality of circumferentially arranged openings <NUM> in a peripheral wall of the housing <NUM>. In this configuration, the primary inlet <NUM> is an axial inlet and the primary outlet <NUM> is a radial or circumferential outlet alone the periphery of the housing <NUM>.

The housing <NUM> can be made up of two or more parts that are combined together or can be integrally formed as a single piece. In the depicted aspects of the disclosure, the housing <NUM> of the air starter <NUM> generally defines, in an axial series arrangement, an inlet assembly <NUM>, a turbine section <NUM>, a gear box <NUM>, and a drive section <NUM>. The air starter <NUM> can be formed by any materials and methods, including, but not limited to, additive manufacturing or die-casting of high strength and lightweight metals such as aluminum, stainless steel, iron, or titanium. The housing <NUM> and the gear box <NUM> can be formed with a thickness sufficient to provide adequate mechanical rigidity without adding unnecessary weight to the air starter <NUM>.

<FIG> is a schematic cross section of the air starter <NUM> of <FIG> which shows the inlet assembly <NUM>, the turbine section <NUM>, and the gear box <NUM> in greater detail. The turbine section <NUM> can include a turbine <NUM> located within the housing <NUM>. The turbine <NUM> can include a rotor <NUM> and a plurality of circumferentially spaced blades <NUM>. The rotor <NUM> can be mounted to the housing in a manner for rotation, for example, the rotor <NUM> can be journaled within the housing <NUM>. The plurality of circumferentially spaced blades <NUM> can be disposed in the primary air flow path <NUM> for rotatably extracting mechanical power from the flow of gas from the primary inlet <NUM> to the primary outlet <NUM>. The turbine <NUM>, the rotor <NUM>, and the plurality of circumferentially spaced blades <NUM> can rotate about an axis of rotation <NUM>. A rotor width <NUM> can be defined as the axial width of the rotor <NUM> of the turbine <NUM>.

The inlet assembly <NUM> can include a stator <NUM> to guide the air flow in the primary air flow path <NUM>. By way of non-limiting example, the stator <NUM> can define at least a portion of the primary air flow path <NUM> from the primary inlet <NUM> to the rotor <NUM>. The stator <NUM> can include a permeable portion <NUM>, where air in the primary air flow path <NUM> can pass through the stator <NUM>. The permeable portion <NUM> can be at least one airfoil, nozzle, vent, or any other structure used to direct or allow the through flow of air.

A rotor centerline <NUM> can pass through a center point <NUM> of the turbine <NUM>. Further, the rotor centerline <NUM> can be generally perpendicular to the axis of rotation <NUM>. Generally perpendicular in this context means that the angle between the rotor centerline <NUM> and the axis of rotation <NUM> can be between or includes <NUM> degrees to <NUM> degrees.

A drive shaft <NUM> can extend in an axial direction from the rotor <NUM> of the turbine <NUM> where the axial direction is defined in the axial direction of the axis of rotation <NUM>. As illustrated, by way of non-limiting example, the drive shaft <NUM> can include a sleeve portion <NUM> having an inner surface <NUM> that defines a hollow interior <NUM>. The hollow interior <NUM> can receive at least a portion of a sun gear shaft or output shaft <NUM>. That is, at least a portion of the drive shaft <NUM> can be tubular, where the output shaft <NUM> can be received in the hollow interior <NUM> of the drive shaft <NUM>. The sleeve portion <NUM> can extend from the rotor <NUM> a sleeve distance <NUM>.

The output shaft <NUM> can extend through at least a portion of the inlet assembly <NUM>, the turbine section <NUM>, and the gear box <NUM>. By way of non-limiting example, a retaining element <NUM> can couple to the drive shaft <NUM> on a forward side <NUM> of the rotor <NUM>. The drive shaft <NUM> can extend through the retaining element <NUM>, the rotor <NUM>, the drive shaft <NUM>, one or more gears or clutch assemblies such as a gear train <NUM> in the gear box <NUM>. The output shaft <NUM> can rotatably couple to the gear train <NUM>, so that the output shaft <NUM> provides a rotational output from the turbine <NUM> or rotor <NUM> to the gear train <NUM>. That is, the output shaft <NUM> allows for the transfer of energy from air in the primary air flow path <NUM> to rotational mechanical power.

A spline connection <NUM> can be used to couple the drive shaft <NUM> to the output shaft <NUM>. The spline connection <NUM> provides an interface between the drive shaft <NUM> and the output shaft <NUM>, so that the output shaft <NUM>, the drive shaft <NUM>, and the turbine <NUM> have generally the same angular velocity. That is, the rotor <NUM> rotationally drives the output shaft <NUM> that is coupled to the sleeve portion <NUM> of the drive shaft <NUM> that extends axially from the rotor <NUM>.

The spline connection <NUM> is illustrated, by way of non-limiting example, as located axially between the rotor <NUM> and the gear train <NUM>, however, the spline connection <NUM> can be located upstream of the rotor <NUM>, as further illustrated in <FIG>.

A spline distance <NUM> can be defined by the axial distance from the rotor centerline <NUM> to the spline connection <NUM>. By way of non-limiting example, the spline distance <NUM> is illustrated as the distance between the rotor centerline <NUM> and the forward side <NUM> of the spline connection <NUM>. The spline distance <NUM> is greater than or equal to half the rotor width <NUM>. In other words, the spline connection <NUM> is offset from the turbine <NUM>, therefore the spline connection <NUM> is an example of an offset interface.

At least one pilot guide <NUM> can be located between the rotor <NUM> and the gear train <NUM> and axially spaced from the spline connection <NUM>. The at least one pilot guide <NUM> can axially locate the output shaft <NUM> relative to the drive shaft <NUM>.

A pilot distance <NUM> can be defined by the axial distance from the rotor centerline <NUM> to the at least one pilot guide <NUM>. By way of non-limiting example, the pilot distance <NUM> is illustrated as the distance between the rotor centerline <NUM> and the forward side <NUM> of the at least one pilot guide <NUM>. While the pilot distance <NUM> is illustrated as smaller or less than the spline distance <NUM>, it is contemplated that the pilot distance <NUM> can be greater than the spline distance <NUM>.

The pilot distance <NUM> is greater than or equal to half the rotor width <NUM>. In other words, the at least one pilot guide <NUM> is offset from the turbine <NUM>, therefore the at least one pilot guide <NUM> is another example of an offset interface.

At least one bearing assembly, such as a thrust bearing, can be configured to rotatably support the drive shaft <NUM>. While the at least one bearing assembly is illustrated as a first bearing assembly 98a and a second bearing assembly 98b, any number of bearings or thrust bearings are contemplated. The first bearing assembly 98a and the second bearing assembly 98b can rotatably support the drive shaft <NUM> at a location that is on a rear side <NUM> of the turbine <NUM> and the forward side <NUM> of the gear train <NUM>. The first bearing assembly 98a can be radially adjacent the at least one pilot guide <NUM>. The second bearing assembly 98b can be radially adjacent the spline connection <NUM>. However, any location in relationship to the drive shaft <NUM> of the first and second bearing assembly 98a, 98b is contemplated.

The first bearing assembly 98a or the second bearing assembly 98b can be located in a wet portion <NUM> of the housing <NUM>. That is, the first bearing assembly 98a or the second bearing assembly 98b can be lubricated with a grease or oil in the wet portion <NUM> of the housing <NUM>. The wet portion <NUM> is a cavity or portion in the housing <NUM> that is exposed to grease, oil, or other know coolants or liquids, whereas a dry portion can be a cavity or portion that is not exposed to liquid. By way of non-limiting example of contrast, the forward side of the turbine <NUM> is a dry portion of the housing <NUM>.

<FIG> is an exploded view of the turbine <NUM>, retaining element <NUM>, and output shaft <NUM>. A first spline interface <NUM> is provided on the drive shaft <NUM>. The first spline interface <NUM> can be defined by a portion of the inner surface <NUM> of the sleeve portion <NUM> of the drive shaft <NUM>. The first spline interface <NUM> can be notched or serrated so that portions of the first spline interface <NUM> extend radially into the hollow interior <NUM> of the drive shaft <NUM>. The first spline interface <NUM> can have a first spline radius <NUM> measured from the axis of rotation <NUM> to a recess in the first spline interface <NUM>.

A second spline interface <NUM> is provided on the output shaft <NUM>. The second spline interface <NUM> can be located on an outer surface <NUM> of a portion of the output shaft <NUM> received by the drive shaft <NUM>. The second spline interface <NUM> can be notched or serrated so that portions of the second spline interface <NUM> extend radially outward from the output shaft <NUM>.

The first spline interface <NUM> is enmeshed with the second spline interface <NUM> to form the spline connection <NUM> when the output shaft <NUM> is received by the drive shaft <NUM> as illustrated in <FIG>. Further, when enmeshed, the first spline interface <NUM> circumscribes at least part of the second spline interface <NUM>.

A first pilot element <NUM> is provided on the drive shaft <NUM>. The first pilot element <NUM> can be defined by a portion of the inner surface <NUM> axially spaced from the first spline interface <NUM>. The first pilot element <NUM> is illustrated as being a smooth surface, however, it is contemplated that the first pilot element <NUM> can be notched or serrated. The first pilot element <NUM> can have a first pilot radius <NUM> measured from the axis of rotation <NUM> to the portion of the inner surface <NUM> that defines the first pilot element <NUM>. While the first pilot radius <NUM> is illustrated as less than the first spline radius <NUM>, it is contemplated that the first pilot radius <NUM> can be greater than the first spline radius <NUM>.

A second pilot element <NUM> is provided on the output shaft <NUM>. The second pilot element <NUM> can be located on the outer surface <NUM> of a portion of the output shaft <NUM> received by the drive shaft <NUM> and axially spaced from the second spline interface <NUM>. The second pilot element <NUM> illustrated as being a smooth surface, however, it is contemplated that the second pilot element <NUM> can be notched or serrated to compliment the first pilot element <NUM>. The second pilot element <NUM> can have a second pilot radius <NUM> measured from the axis of rotation <NUM> to the outer surface <NUM> that defines the second pilot element <NUM>.

The first pilot element <NUM> and the second pilot element <NUM> can form the at least one pilot guide <NUM>, where the first pilot element <NUM> circumscribes at least a portion of the second pilot element <NUM>. (<FIG>) A diametric fit or tight fit between the first pilot element <NUM> and the second pilot element <NUM> can secure the radial and axial location of the output shaft <NUM>. The first pilot radius <NUM> can be between <NUM>% and <NUM>% larger than the second pilot radius <NUM>, defining the tight fit between the first and second pilot elements <NUM>, <NUM>. The tight fit can provide clearance needed to accommodate movement of one or more components or to accommodate thermal expiation or contraction or one or more components.

The output shaft <NUM> can further include a threaded portion <NUM> used to position the retaining element <NUM>. Further, the output shaft <NUM> includes a sun gear <NUM> that can rotatably connect with the gear train <NUM>.

In operation, a fluid, for example air, is supplied to the air starter <NUM>. The air enters the primary air flow path <NUM> through the primary inlet <NUM>. The energy from the air is transformed to mechanical energy by the of the turbine <NUM>, which rotates in response to the air flow through the plurality of circumferentially spaced blades <NUM>. The turbine <NUM> includes the drive shaft <NUM>, which extends axially from the rotor <NUM>. The drive shaft <NUM> circumscribes the forward side <NUM> portion of the output shaft <NUM>. The drive shaft <NUM> and output shaft <NUM> are coupled by the spline connection <NUM>, so that they rotate at generally the same angular velocity. The at least one pilot guide <NUM> helps to position the output shaft <NUM> within the drive shaft <NUM>. The at least one pilot guide <NUM> provides support to the axial position of the output shaft <NUM>. Further, the at least one pilot guide <NUM> can also provide radial alignment of the output shaft <NUM>.

The rear side <NUM> portion of the output shaft <NUM> is rotatably coupled to the gear train <NUM>, which can transfer the mechanical power to the turbine engine <NUM>. The first and second bearings 98a, 98b rotatably support the drive shaft <NUM>. The retaining element <NUM> can be threaded to the output shaft <NUM> on the forward side <NUM> of the rotor <NUM> to further axially locate the output shaft <NUM>.

The offset of the spline connection <NUM> from the center point <NUM> of the rotor <NUM> reduces forces on the rotor <NUM>. The offset interferences, that is, the spline connection <NUM> and the at least one pilot guide <NUM>, allow for an increase in contact area between the turbine <NUM> and the output shaft <NUM> which can further reduce stress on the turbine <NUM>.

The offset of the spline connection <NUM> further enables the turbine <NUM> and the output shaft <NUM> to be made of different materials. By way of non-limiting example, the turbine <NUM> can be made of titanium which is a lighter weight and durable material, while the output shaft <NUM> can be made of steel or another metal better suited to interface with the gear train <NUM>. Having the transition from titanium to steel outside the gear box <NUM> or gear train <NUM> allows the sun gear <NUM> portion of the output shaft <NUM> to have a smaller. The smaller diameter of the sun gear <NUM> can result in the air starter <NUM> being more compact.

<FIG> is another example of a schematic cross section of an air starter <NUM> which shows an inlet assembly <NUM>, a turbine section <NUM>, and a gear box <NUM> in greater detail. The air starter <NUM> is similar to the air starter <NUM>, therefore, like parts will be identified with like numerals increased by <NUM>, with it being understood that the description of the like parts of the air starter <NUM> applies to the air starter <NUM>, unless otherwise noted.

The turbine section <NUM> can include a turbine <NUM> located within a housing <NUM>. The turbine <NUM> can include a rotor <NUM> and a plurality of circumferentially spaced blades <NUM>. The rotor <NUM> can be mounted to the housing in a manner for rotation, for example, the rotor <NUM> can be journaled within the housing <NUM>. The plurality of circumferentially spaced blades <NUM> can be disposed in a primary air flow path <NUM> for rotatably extracting mechanical power from the flow of gas from a primary inlet <NUM> to a primary outlet <NUM>. The turbine <NUM>, the rotor <NUM>, and the plurality of circumferentially spaced blades <NUM> thereof, can rotate about an axis of rotation <NUM>. A rotor width <NUM> can be defined as the axial width of the rotor <NUM> of the turbine <NUM>.

The inlet assembly <NUM> can include a stator <NUM> to guide the air flow in the primary air flow path <NUM>. By way of non-limiting example, the stator <NUM> can define at least a portion of the primary air flow path <NUM> from the primary inlet <NUM> to the rotor <NUM>. The stator <NUM> can include a permeable portion <NUM>, where air in the primary air flow path <NUM> can pass through the stator <NUM>. The permeable portion <NUM> can be at least one airfoil, nozzle, vent, or any other structure used to direct or allow the flow of air.

A rotor centerline <NUM> can pass through a center point <NUM> of the turbine <NUM>. Further, the rotor centerline <NUM> can be generally perpendicular to the axis of rotation <NUM>. That is, the angle between the rotor centerline <NUM> and the axis of rotation <NUM> can be, and includes, <NUM> degrees to <NUM> degrees.

A drive shaft <NUM> can extend in an axial direction from the rotor <NUM> of the turbine <NUM> where the axial direction is defined in the direction of the axis of rotation <NUM>. As illustrated, by way of non-limiting example, the drive shaft <NUM> can include a sleeve portion <NUM> having an inner surface <NUM> that defines a hollow interior <NUM>. The hollow interior <NUM> can receive at least a portion of a sun gear shaft or output shaft <NUM>. That is, at least a portion of the drive shaft <NUM> can be tubular, where the output shaft <NUM> can be received in the hollow interior <NUM> of the drive shaft <NUM>. The sleeve portion <NUM> can extend from the rotor <NUM> a sleeve distance <NUM>.

At least one pilot guide can be located between the rotor <NUM> and the gear train <NUM> and axially spaced from the spline connection <NUM>. The at least one pilot guide is illustrated, by way of non-limiting example as a first or forward pilot guide 294a and a second or rear pilot guide 294b. The forward and rear pilot guides 294a, 294b can axially or radially locate the output shaft <NUM> relative to the drive shaft <NUM>. Further the forward and rear pilot guides 294a, 294b can be axially spaced from each other and from the spline connection <NUM>.

A first pilot distance 296a can be defined by the axial distance from the rotor centerline <NUM> to the forward pilot guide 294a. By way of non-limiting example, the first pilot distance 296a is illustrated as the distance between the rotor centerline <NUM> and the forward side <NUM> of the forward pilot guide 294a. While the first pilot distance 296a is illustrated as smaller or less than the spline distance <NUM>, it is contemplated that the first pilot distance 296a can be greater than the spline distance <NUM>.

The first pilot distance 296a is greater than or equal to half the rotor width <NUM>. In other words, the forward pilot guide 294a is offset from the turbine <NUM>, therefore the forward pilot guide 294a is another example of an offset interface.

A second pilot distance 296b can be defined by the axial distance from the rotor centerline <NUM> to the rear pilot guide 294b. By way of non-limiting example, the second pilot distance 296b is illustrated as the distance between the rotor centerline <NUM> and the forward side <NUM> of the rear pilot guide 294b. While the second pilot distance 296b is illustrated as larger than the spline distance <NUM>, it is contemplated that the second pilot distance 296b can be less than the spline distance <NUM>.

The second pilot distance 296b is greater than or equal to half the rotor width <NUM>. In other words, the rear pilot guide 294b is offset from the turbine <NUM>, therefore the rear pilot guide 294b is another example of an offset interface.

At least one bearing assembly, such as a thrust bearing, can be configured to rotatably support the drive shaft <NUM>. While the at least one bearing assembly is illustrated as a first bearing assembly 298a and a second bearing assembly 298b, any number of bearing assemblies are contemplated. The first bearing assembly 298a and the second bearing assembly 298b can rotatably support the drive shaft <NUM> at a location that is on a rear side <NUM> of the turbine <NUM> and the forward side <NUM> of the gear train <NUM>. The first bearing assembly 298a can be radially adjacent the forward side <NUM> of the spline connection <NUM>. The second bearing assembly 298b can be radially adjacent the rear side <NUM> of the spline connection <NUM>. However, any location in relationship to the drive shaft <NUM> of the first and second bearing assemblies 298a, 298b is contemplated.

The first bearing assembly 298a or the second bearing assembly 298b can be located in a wet portion <NUM> of the housing <NUM>. That is, the first bearing assembly 298a or the second bearing assembly 298b can be lubricated with a grease or oil in the wet portion <NUM> of the housing <NUM>. The wet portion <NUM> is a cavity or portion in the housing <NUM> that is exposed to liquid coolant, whereas a dry portion can be a cavity or portion that is not exposed to liquid coolant. By way of non-limiting example of contrast, the forward side of the turbine <NUM> is a dry portion of the housing <NUM>.

A first forward pilot element 310a is provided on the drive shaft <NUM>. The first forward pilot element 310a can be defined by a portion of the inner surface <NUM> axially spaced from the first spline interface <NUM>. The first forward pilot element 310a is illustrated as being a smooth surface, however, it is contemplated that the first forward pilot element 310a can be notched or serrated. The first forward pilot element 310a can have a first forward pilot radius 312a measured from the axis of rotation <NUM> to the portion of the inner surface <NUM> that defines the first forward pilot element 310a. While the first forward pilot radius 312a is illustrated as less than the first spline radius <NUM>, it is contemplated that the first forward pilot radius 312a can be greater than the first spline radius <NUM>.

A second forward pilot element 314a is provided on the output shaft <NUM>. The second forward pilot element 314a can be located on the outer surface <NUM> of a portion of the output shaft <NUM> received by the drive shaft <NUM> and axially spaced from the second spline interface <NUM>. The second forward pilot element 314a illustrated as being a smooth surface, however, it is contemplated that the second forward pilot element 314a can be notched or serrated to compliment the first forward pilot element 310a. The second forward pilot element 314a can have a second forward pilot radius 318a measured from the axis of rotation <NUM> to the outer surface <NUM> that defines the second forward pilot element 314a.

A first rear pilot element 310b is provided on the drive shaft <NUM>. The first rear pilot element 310b can be defined by a portion of the inner surface <NUM> axially spaced from the first spline interface <NUM>. The first rear pilot element 310b is illustrated as being a smooth surface, however, it is contemplated that the first rear pilot element 310b can be notched or serrated. The first rear pilot element 310b can have a first rear pilot radius 312b measured from the axis of rotation <NUM> to the portion of the inner surface <NUM> that defines the first rear pilot element 310b. While the first rear pilot radius 312b is illustrated as greater than the first spline radius <NUM>, it is contemplated that the first rear pilot radius 312b can be less than the first spline radius <NUM>.

A second rear pilot element 314b is provided on the output shaft <NUM>. The second rear pilot element 314b can be located on the outer surface <NUM> of a portion of the output shaft <NUM> received by the drive shaft <NUM> and axially spaced from the second spline interface <NUM>. The second rear pilot element 314b illustrated as being a smooth surface, however, it is contemplated that the second rear pilot element 314b can be notched or serrated to complement the first rear pilot element 310b. The second rear pilot element 314b can have a second rear pilot radius 318b measured from the axis of rotation <NUM> to the outer surface <NUM> that defines the second rear pilot element 314b.

The first forward or rear pilot elements 310a, 310b and the second forward or rear pilot element 314a, 314b can form the forward or rear pilot guides 294a, 294b, where the first forward or rear pilot element 310a, 310b circumscribes at least a portion of the second forward or rear pilot element 314a, 314b. (<FIG>) A diametric fit or tight fit between the first forward or rear pilot element 310a, 310b and the second forward or rear pilot element 314a, 314b can secure the radial and axial location of the output shaft <NUM>. The first forward or rear pilot radius 312a, 312b can be between <NUM>% and <NUM>% larger than the second forward or rear pilot radius 318a, 318b, defining the tight fit between the first and second, forward and rear pilot elements 310a, 310b, 314a, 314b as having negligible or thermal clearance.

The output shaft <NUM> can include a threaded portion <NUM> used to position the retaining element <NUM>. Further, the output shaft <NUM> includes a sun gear <NUM> that can rotatably connect with the gear train <NUM>.

The turbine section <NUM> can include a turbine <NUM> located within a housing <NUM>. The turbine <NUM> can include a rotor <NUM> and a plurality of circumferentially spaced blades <NUM>. The rotor <NUM> can be mounted to the housing in a manner for rotation, for example, the rotor <NUM> can be journaled within the housing <NUM>. The plurality of circumferentially spaced blades <NUM> can be disposed in a primary air flow path <NUM> for rotatably extracting mechanical power from the flow of gas from a primary inlet <NUM> to a primary outlet <NUM>. The turbine <NUM>, the rotor <NUM>, and the plurality of circumferentially spaced blades <NUM> can rotate about an axis of rotation <NUM>. A rotor width <NUM> can be defined as the axial width of the rotor <NUM> of the turbine <NUM>.

A rotor centerline <NUM> can pass through a center point <NUM> of the turbine <NUM>. Further, the rotor centerline <NUM> can be generally perpendicular to the axis of rotation <NUM>. Generally perpendicular in this context means that the angle between the rotor centerline <NUM> and the axis of rotation <NUM> can be, and includes, <NUM> degrees to <NUM> degrees.

A drive shaft <NUM> can extend in an axial direction from the rotor <NUM> of the turbine <NUM> where the axial direction is defined in the axial direction of the axis of rotation <NUM>. As illustrated, by way of non-limiting example, the drive shaft <NUM> can extend from a forward side <NUM> and a rear side <NUM> of the rotor <NUM>. The drive shaft <NUM> can include a sleeve portion <NUM> having an inner surface <NUM> that defines a hollow interior <NUM>. The hollow interior <NUM> can receive at least a portion of a sun gear shaft or output shaft <NUM>. That is, at least a portion of the drive shaft <NUM> can be tubular, where the output shaft <NUM> can be received in the hollow interior <NUM> of the drive shaft <NUM>.

The output shaft <NUM> can extend through at least a portion of the inlet assembly <NUM>, the turbine section <NUM>, and the gear box <NUM>. By way of non-limiting example, a retaining element <NUM> can couple to the drive shaft <NUM> on the forward side <NUM> of the rotor <NUM>. The drive shaft <NUM> can extend through the retaining element <NUM>, the rotor <NUM>, the drive shaft <NUM>, one or more gears or clutch assemblies such as a gear train <NUM> in the gear box <NUM>. The output shaft <NUM> can rotatably couple to the gear train <NUM>, so that the output shaft <NUM> provides a rotational output from the turbine <NUM> or rotor <NUM> to the gear train <NUM>. That is, the output shaft <NUM> allows for the transfer of energy from air in the primary air flow path <NUM> to rotational mechanical power.

The spline connection <NUM> is illustrated, by way of non-limiting example, as located axially upstream of the rotor <NUM>. The spline connection <NUM> can be located on the forward side <NUM> of the rotor <NUM> and the rear side <NUM> of the retaining element <NUM>. However, it is contemplated that the spline connection <NUM> can be on the rear side <NUM> of the rotor <NUM>.

A spline distance <NUM> can be defined by the axial distance from the rotor centerline <NUM> to the spline connection <NUM>. By way of non-limiting example, the spline distance <NUM> is illustrated as the distance between the rotor centerline <NUM> and the rear side <NUM> of the spline connection <NUM>. The spline distance <NUM> is greater than or equal to half the rotor width <NUM>. In other words, the spline connection <NUM> is not located within the rotor <NUM>. Further the spline connection <NUM> is offset from the rotor <NUM> or the rotor centerline <NUM>, therefore the spline connection <NUM> is an example of an offset interface.

The pilot distance <NUM> is greater than or equal to half the rotor width <NUM>. In other words, the at least one pilot guide <NUM> is offset from the rotor <NUM> or the rotor centerline <NUM>, therefore the at least one pilot guide <NUM> is another example of an offset interface.

At least one bearing assembly, such as a thrust bearing, can be configured to rotatably support the output shaft <NUM>. While the at least one bearing assembly is illustrated as a first bearing assembly 498a and a second bearing assembly 498b, any number of bearings or thrust bearings are contemplated. The first bearing assembly 498a and the second bearing assembly 498b can rotatably support the output shaft <NUM> at a location that is on the rear side <NUM> of the turbine <NUM> and the forward side <NUM> of the gear train <NUM>. The first bearing assembly 498a can be axially downstream of the at least one pilot guide <NUM>. The second bearing assembly 498b radially between the first bearing assembly 498a and the gear train <NUM>. However, any location in relationship to the drive shaft <NUM> or the output shaft <NUM> of the first and second bearing assembly 498a, 498b is contemplated.

The first bearing assembly 498a or the second bearing assembly 498b can be located in a wet portion <NUM> of the housing <NUM>. That is, the first bearing assembly 498a or the second bearing assembly 498b can be lubricated with a grease or oil in the wet portion <NUM> of the housing <NUM>. The wet portion <NUM> is a cavity or portion in the housing <NUM> that is exposed to grease, oil, or other know lubricants, coolants, or liquids, whereas a dry portion can be a cavity or portion that is not exposed to liquid. By way of non-limiting example of contrast, the forward side of the turbine <NUM> is a dry portion of the housing <NUM>.

A first pilot element <NUM> is provided on the drive shaft <NUM>. The first pilot element <NUM> can be defined by a portion of the inner surface <NUM> axially spaced from the first spline interface <NUM>. The first pilot element <NUM> is illustrated as being a smooth surface, however, it is contemplated that the first pilot element <NUM> can be notched or serrated. The first pilot element <NUM> can have a first pilot radius <NUM> measured from the axis of rotation <NUM> to the portion of the inner surface <NUM> that defines the first pilot element <NUM>. While the first pilot radius <NUM> is illustrated as greater than the first spline radius <NUM>, it is contemplated that the first pilot radius <NUM> can be less than the first spline radius <NUM>.

The first pilot element <NUM> and the second pilot element <NUM> can form the at least one pilot guide <NUM>, where the first pilot element <NUM> circumscribes at least a portion of the second pilot element <NUM>. (<FIG>) A diametric fit or tight fit between the first pilot element <NUM> and the second pilot element <NUM> can secure the radial and axial location of the output shaft <NUM>. The first pilot radius <NUM> can be between <NUM>% and <NUM>% larger than the second pilot radius <NUM>, defining the tight fit between the first and second pilot elements <NUM>, <NUM>. The tight fit can provide clearance needed to accommodate movement of one or more components or to accommodate thermal expiation or contraction or one or more components, while maintaining the axial or radial location of the output shaft <NUM>.

The output shaft <NUM> can further include a fitted portion <NUM> that can be received by the retaining element <NUM>. Further, the output shaft <NUM> includes a sun gear <NUM> that can rotatably connect with the gear train <NUM>.

<FIG> is a schematic illustration of the turbine engine <NUM> and starter <NUM> from <FIG>, where the turbine engine <NUM> can be in a vehicle or structure <NUM>. The vehicle or structure <NUM> can be, by way of non-limiting example, a helicopter or other aircraft, a boat or other aquatic vehicle, or a car or other land vehicle. Further, the vehicle or structure <NUM> can be, but is not limited to, a marine power plant, a wind turbine, or a small power plant. It is further considered that the turbine engine <NUM> can be any engine/generator using a turbine with the air starter <NUM> required by the vehicle or structure <NUM>.

Benefits of the aspects of the disclosure include improved axial positioning of the sun gear shaft or output shaft by the at least one pilot guide. Further, the at least one pilot guide also improves the radial positioning of the sun gear shaft or output shaft.

Another benefit is that the sun gear shaft and the turbine can be made of different materials. For example, the turbine can be made of titanium and the sun gear shaft can be made of steel. The titanium is durable and light, but steel is a preferred material for geared or rotatable interfaces. The offset spline connection offers a known and reliable connection between the titanium drive shaft of the turbine and the steel of the sun gear shaft.

Yet another benefit is that the sun gear can have a smaller diameter. The sun gear shaft is received by the drive shaft of the turbine, allowing the sun gear to have a smaller diameter as it can be made from steel. This can result in a smaller air starter. This can also result in a more robust air starter.

Further, the offset interfaces of the spline connection and the at least one pilot interfaces increases the contact area of the drive shaft and the sun gear shaft, reducing overall stress on the turbine. This can allow for greater critical speed.

Claim 1:
An air starter (<NUM>, <NUM>, <NUM>) comprising:
a housing (<NUM>, <NUM>, <NUM>) defining an interior (<NUM>) having a primary inlet (<NUM>, <NUM>, <NUM>) and a primary outlet (<NUM>, <NUM>, <NUM>) to define a primary air flow path (<NUM>, <NUM>, <NUM>) from the primary inlet (<NUM>, <NUM>, <NUM>) to the primary outlet (<NUM>, <NUM>, <NUM>);
a turbine (<NUM>, <NUM>, <NUM>) located in the interior (<NUM>) and including a rotor (<NUM>, <NUM>, <NUM>), with a plurality of circumferentially spaced blades (<NUM>, <NUM>, <NUM>), and a drive shaft (<NUM>, <NUM>, <NUM>) extending from the rotor (<NUM>, <NUM>, <NUM>);
a gear box (<NUM>, <NUM>, <NUM>) located in the interior (<NUM>) and including a gear train (<NUM>, <NUM>, <NUM>) and an output shaft (<NUM>, <NUM>, <NUM>) coupled to the gear train (<NUM>, <NUM>, <NUM>);
a spline connection (<NUM>, <NUM>, <NUM>), located upstream of the rotor (<NUM>, <NUM>, <NUM>) or between the rotor (<NUM>, <NUM>, <NUM>) and the gear train (<NUM>, <NUM>, <NUM>), and comprising a first spline interface (<NUM>, <NUM>, <NUM>) provided on the drive shaft (<NUM>, <NUM>, <NUM>) and a second spline interface (<NUM>, <NUM>, <NUM>), enmeshed with the first spline interface (<NUM>, <NUM>, <NUM>), provided on the output shaft (<NUM>, <NUM>, <NUM>); and
at least one pilot guide (<NUM>, 294a, 294b, <NUM>), axially locating the output shaft relative to the drive shaft, located between the rotor (<NUM>, <NUM>, <NUM>) and the gear train (<NUM>, <NUM>, <NUM>), and comprising a first pilot element (<NUM>, 310a, 310b, <NUM>) provided on the drive shaft (<NUM>, <NUM>, <NUM>) and a second pilot element (<NUM>, 314a, 314b, <NUM>) provided on an outer surface (<NUM>) of the output shaft (<NUM>, <NUM>, <NUM>), wherein the first pilot element (<NUM>, 310a, 310b, <NUM>) axially overlaps, at least in part, the second pilot element (<NUM>, 314a, 314b, <NUM>), wherein the at least one pilot guide (<NUM>, 294a, 294b, <NUM>) is axially spaced from the spline connection (<NUM>, <NUM>, <NUM>), and wherein the turbine (<NUM>, <NUM>, <NUM>) includes a rotor centerline (<NUM>, <NUM>, <NUM>) and has a rotor width (<NUM>, <NUM>, <NUM>), wherein the spline connection (<NUM>, <NUM>, <NUM>) is axially spaced from the rotor centerline (<NUM>, <NUM>, <NUM>) a spline distance (<NUM>, <NUM>, <NUM>) that is greater than or equal to half of the rotor width (<NUM>, <NUM>, <NUM>).