Bearing outer race retention during high load events

The present subject matter relates generally to a bearing in a gas turbine engine, or more particularly to an apparatus for retention of the outer race of the bearing.

A gas turbine engine generally includes a fan and a core arranged in flow communication with one another with the core disposed downstream of the fan in the direction of the flow through the gas turbine. The core of the gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section and is confined within an outer casing. With multi-shaft gas turbine engines, the compressor section can include a high pressure compressor (HP compressor) disposed downstream of a low pressure compressor (LP compressor), and the turbine section can similarly include a low pressure turbine (LP turbine) disposed downstream of a high pressure turbine (HP turbine). With such a configuration, the HP compressor is coupled with the HP turbine via a high pressure shaft (HP shaft), which also is known as the high pressure spool (HP spool). Similarly, the LP compressor is coupled with the LP turbine via a low pressure shaft (LP shaft), which also is known as the low pressure spool (LP spool).

In operation, at least a portion of air over the fan is provided to an inlet of the core. Such portion of the air is progressively compressed by the LP compressor and then by the HP compressor until the compressed air reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section through the HP turbine and then through the LP turbine. The flow of combustion gasses through the turbine section drives the HP turbine and the LP turbine, each of which in turn drives a respective one of the HP compressor and the LP compressor via the HP shaft (aka HP spool) and the LP shaft (aka LP spool). The combustion gases are then routed through the exhaust section, e.g., to atmosphere.

During normal engine operation, a ball bearing assembly can be provided to act along with the interface shell, which is non-rotatably coupled to the outer casing of the engine, to retain the axial position of the HP shaft (aka HP spool), and a roller bearing assembly can be provided to provide radial damping of the fan/rotor system. A traditional design approach consisting of an axial spring finger housing combined with a radial squeeze film oil damper can be provided to protect the bearings against damage during relatively small unbalance load situations. During these normal operating conditions, the squeeze film damper bearing requires clearance in all directions around the bearing (radial, tangential & axial) for dynamic operation. However, such an axial spring finger housing contains relatively long axial spring fingers for retention of the ball bearing housing, and the long spring fingers take up space in the engine housing, add weight to the engine, have limited torsional load capability and are complicated for manufacture.

Moreover, in a failure mode that results from a liberated fan blade, or a liberated compressor blade or a liberated turbine blade, very high radial loads combined with very high torsional windup provide significant design challenges to the bearings and to the spring finger housing for the ball bearing. The radial load closes the damper gap and the radial bumper gap and creates a harmonic drive effect that loads the spring fingers in torsion. This torsion load on the bearing and its retention housing structure results in an opposing sinusoidal load distribution that twists the spring fingers enough so that the spring fingers develop cracks, which are very undesirable.

<patcit id="pcit0001" dnum="US20120213629A1"><text>US 2012/0213629 A1</text></patcit> relates to a device for centering and guiding the rotation of a turbomachine shaft. <patcit id="pcit0002" dnum="EP2479406A2"><text>EP 2 479 406 A2</text></patcit> relates to a bearing system for a gas turbine engine. <patcit id="pcit0003" dnum="US20150098826A1"><text>US 2015/0098826 A1</text></patcit> relates to an apparatus and method for assembling a damper bearing assembly. <patcit id="pcit0004" dnum="EP1626188A2"><text>EP 1 626 188 A2</text></patcit> relates to a bearing assembly for a gas turbine engine with resilient support.

Various aspects and advantages of the invention will be set forth in part in the following description, or may be clear from the description, or may be learned through practice of the invention.

A retention housing for the outer race of a ball bearing for a high pressure spool of a gas turbine engine is provided in accordance with the appended claims.

In one example of the present disclosure, a housing structure for retention of the outer race of a ball bearing that acts to retain the axial position of the HP shaft has spring fingers that are flat and short. The retention housing includes a spring finger housing connected to a ball bearing housing that is disposed radially inwardly from the spring finger housing. The forward end of the spring finger housing is connected to the forward end of the ball bearing housing via a connecting web, and the spring finger housing includes a plurality of spring fingers.

The aft end of the ball bearing housing includes a plurality of blind bores that extend radially into the ball bearing housing with an open end that is facing toward the spring finger housing. Each one of a plurality of radially extending dowel pins is received in a respective one of the blind bores to connect the aft end of the ball bearing housing to the interface shell, which is non-rotatably coupled to the outer casing of the engine, and defines a respective plurality of through bores. A respective one of the through bores is defined radially through the interface shell and is aligned with a respective one of the blind bores of the ball bearing housing to define an aligned pair of bores that receives a respective one of the dowel pins and thereby limits the circumferential deflections of the spring fingers and self-arrests the distortion of the spring finger structure. One end of each dowel pin is non-rotatably fixed within a respective one of the through bores and projects radially out of the respective through bore and defines a free end that extends into a respective blind bore and is spaced apart from the blind end of the blind bore and thereby limits the radial deflections of the retention housing.

Between the inner diametrical face of the interface shell that opposes the outer diametrical face of the aft end of the ball bearing housing, there is defined a radial gap that acts to retain the spring finger housing in a radial direction.

The number, placement and dimensions of the dowel pins and the aforementioned radial gap are controlled according to the anticipated load in consideration of the retention housing structure's size and material composition.

The resulting design of the retention housing integrates the structural components such that they become capable of withstanding the torsional windup and high radial loads that occur with the sudden increase in load that accompanies a blade failure, whether a fan blade, a compressor blade or a turbine blade.

Moreover, due to the unique tapered and short spring finger design, the amount of axial and radial space needed for the retention housing is reduced along with a concomitant reduction in the weight of the retention housing structure while affording a very high torsional load capability to the retention housing structure.

In another exemplary embodiment of the present disclosure, a gas turbine engine includes a compressor section having at least one compressor and a turbine section located downstream of the compressor section and including at least one turbine. The compressor section can include a low pressure compressor and a high pressure compressor downstream of the low pressure compressor. The turbine section includes a high pressure (HP) turbine and a low pressure (LP) turbine downstream of the HP turbine. The gas turbine engine also includes a high pressure shaft mechanically coupling the high pressure compressor to the high pressure turbine via a ball bearing and which includes a retention housing for the outer race of the ball bearing as described summarily above and in greater detail below. Moreover, embodiments of the retention housing as summarily described above and in more detail hereinafter with various alternative embodiments also can be applied to systems with a low pressure shaft that need to address similar challenges with ball bearing components.

These and other features, aspects and advantages of the present invention 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 embodiments of the invention and, together with the description, serve to explain the principles of the invention.

In the drawings: <ul id="ul0001" list-style="none"><li><figref idref="f0001">FIG. 1</figref> is a schematic cross-sectional view of an exemplary gas turbine engine according to various embodiments of the present disclosure.</li><li><figref idref="f0002">FIG. 2</figref> is an exploded, schematic cross-sectional view of components within the dashed outline of the box designated <figref idref="f0002">FIG. 2</figref> in <figref idref="f0001">FIG. 1</figref>.</li><li><figref idref="f0003">FIG. 3</figref> is a perspective view of an exemplary embodiment of the retention housing component schematically depicted in <figref idref="f0002">FIG. 2</figref> and taken from the forward end of the retention housing.</li><li><figref idref="f0004">FIG. 4</figref> is a perspective view taken from the aft end of the embodiment of the retention housing shown in <figref idref="f0003">FIG. 3</figref> and with a portion of the aft end of the interface shell cut away to reveal components of interest for purposes of facilitating explanation of aspects of the invention.</li><li><figref idref="f0005">FIG. 5</figref> is a view partly in perspective and partly in cross-section of the region identified by the arrows designated 5 - - 5 in <figref idref="f0004">FIG. 4</figref> of the exemplary embodiment of the retention housing component depicted in <figref idref="f0002 f0003 f0004">FIGs. 2 - 4</figref>.</li><li><figref idref="f0005">FIG. 6</figref> is an enlarged, schematic cross-sectional view of the section within the dashed outline of the balloon designated <figref idref="f0005">FIG. 6</figref> in <figref idref="f0005">FIG. 5</figref> of the exemplary embodiment of the retention housing component depicted in <figref idref="f0005">FIG. 5</figref>.</li></ul>

Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of any claims and their equivalents. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention, and identical numerals indicate the same elements throughout the drawings. As used herein, the terms "first", "second", and "third" may be used interchangeably to distinguish one component from another and are not intended to signify location or relative importance of the individual components.

It is to be understood that the ranges and limits mentioned herein include all sub-ranges located within the prescribed limits, inclusive of the limits themselves unless otherwise stated. For instance, a range from 100 to 200 also includes all possible sub-ranges, examples of which are from 100 to 150, 170 to 190, 153 to 162, 145.3 to 149.6, and 187 to 200. Further, a limit of up to 7 also includes a limit of up to 5, up to 3, and up to 4.5, as well as all sub-ranges within the limit, such as from about 0 to 5, which includes 0 and includes 5 and from 5.2 to 7, which includes 5.2 and includes 7.

The terms "upstream" and "downstream" refer to the relative direction with respect to fluid flow in a fluid pathway. For example, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows. As used herein, the fluid can be a gas such as air or a liquid such as a lubricant or liquid fuel. With respect to a device through which fluid is flowing, unless otherwise stated or apparent from the context, assuming the device is stationary or moving toward the fluid, then the fluid flows from the forward end of the device toward the aft end of the device.

Referring now to the drawings, <figref idref="f0001">FIG. 1</figref> is a schematic cross-sectional view of a gas turbine engine that provides a typical environment in which one expects to find exemplary embodiments of the present disclosure. More particularly, for the embodiment of <figref idref="f0001">FIG. 1</figref>, the gas turbine engine is a high-bypass turbofan jet engine 10, referred to herein as "turbofan engine 10." Such engines typically embody a cylindrical symmetry. As shown in <figref idref="f0001">FIG. 1</figref>, the turbofan engine 10 defines an axial direction A (extending parallel to a longitudinal centerline 12 provided for reference) and a radial direction R that is normal to the axial direction A. As schematically shown in <figref idref="f0003">FIG. 3</figref> for example, the circumferential direction C revolves 360° around the axial direction A. As generally depicted in <figref idref="f0001">FIG. 1</figref>, the turbofan 10 includes a fan section 14 and a core turbine engine 16 disposed downstream from the fan section 14.

The exemplary core turbine engine 16 depicted generally includes a substantially tubular outer casing 18 that defines an annular inlet 20. As schematically shown in <figref idref="f0001">FIG. 1</figref>, the outer casing 18 encases, in serial flow relationship, a compressor section including a booster or low pressure (LP) compressor 22 followed downstream by a high pressure (HP) compressor 24; a combustion section 26; a turbine section including a high pressure (HP) turbine 28 followed downstream by a low pressure (LP) turbine 30; and a jet exhaust nozzle section 32. A high pressure (HP) shaft or spool 34 drivingly connects the HP turbine 28 to the HP compressor 24 to rotate them in unison concentrically with respect to the longitudinal centerline 12. A low pressure (LP) shaft or spool 36 drivingly connects the LP turbine 30 to the LP compressor 22 to rotate them in unison concentrically with respect to the longitudinal centerline 12. The compressor section, combustion section 26, turbine section, and nozzle section 32 together define a core air flowpath.

For the embodiment depicted in <figref idref="f0001">FIG. 1</figref>, the fan section 14 includes a variable pitch fan 38 having a plurality of fan blades 40 coupled to a disk 42 in a spaced apart manner. As depicted in <figref idref="f0001">FIG. 1</figref>, the fan blades 40 extend outwardly from the disk 42 generally along the radial direction R. Each fan blade 40 is rotatable relative to the disk 42 about a pitch axis P by virtue of the fan blades 40 being operatively coupled to a suitable actuation member 44 configured to collectively vary the pitch of the fan blades 40 in unison. The fan blades 40, disk 42, and actuation member 44 are together rotatable about the longitudinal axis 12 via a fan shaft 45 that is powered by the LP shaft 36 across a power gear box 46. The power gear box 46 includes a plurality of gears for adjusting the rotational speed of the fan shaft 45 and thus the fan 38 relative to the LP shaft 36 to a more efficient rotational fan speed.

Referring still to the exemplary embodiment of <figref idref="f0001">FIG. 1</figref>, the disk 42 is covered by a rotatable front hub 48 aerodynamically contoured to promote an airflow through the plurality of fan blades 40. Additionally, the exemplary fan section 14 includes an annular fan casing or outer nacelle 50 that circumferentially surrounds the fan 38 and/or at least a portion of the core turbine engine 16. It should be appreciated that the nacelle 50 may be configured to be supported relative to the core turbine engine 16 by a plurality of circumferentially-spaced outlet guide vanes 52. Alternatively, the nacelle 50 also may be supported by struts of a structural fan frame. Moreover, a downstream section 54 of the nacelle 50 may extend over an outer portion of the core turbine engine 16 so as to define a bypass airflow groove 56 therebetween.

During operation of the turbofan engine 10, a volume of air 58 enters the turbofan 10 through an associated inlet 60 of the nacelle 50 and/or fan section 14. As the volume of air 58 passes across the fan blades 40, a first portion of the air 58 as indicated by arrow 62 is directed or routed into the bypass airflow groove 56, and a second portion of the air 58 as indicated by arrow 64 is directed or routed into the upstream section of the core air flowpath, or more specifically into the inlet 20 of the LP compressor 22. The ratio between the first portion of air 62 and the second portion of air 64 is commonly known as a bypass ratio. The pressure of the second portion of air 64 is then increased as it is routed through the high pressure (HP) compressor 24 and into the combustion section 26, where the highly pressurized air is mixed with fuel and burned to provide combustion gases 66.

The combustion gases 66 are routed into and expand through the HP turbine 28 where a portion of thermal and/or kinetic energy from the combustion gases 66 is extracted via sequential stages of HP turbine stator vanes 68 that are coupled to the outer casing 18 and HP turbine rotor blades 70 that are coupled to the HP shaft or spool 34, thus causing the HP shaft or spool 34 to rotate, thereby supporting operation of the HP compressor 24. The combustion gases 66 are then routed into and expand through the LP turbine 30 where a second portion of thermal and kinetic energy is extracted from the combustion gases 66 via sequential stages of LP turbine stator vanes 72 that are coupled to the outer casing 18 and LP turbine rotor blades 74 that are coupled to the LP shaft or spool 36, thus causing the LP shaft or spool 36 to rotate, thereby supporting operation of the LP compressor 22 and rotation of the fan 38 via the power gearbox 46.

The combustion gases 66 are subsequently routed through the jet exhaust nozzle section 32 of the core turbine engine 16 to provide propulsive thrust. Simultaneously, the pressure of the first portion of air 62 is substantially increased as the first portion of air 62 is routed through the bypass airflow groove 56 before it is exhausted from a fan nozzle exhaust section 76 of the turbofan 10, also providing propulsive thrust. The HP turbine 28, the LP turbine 30, and the jet exhaust nozzle section 32 at least partially define a hot gas path 78 for routing the combustion gases 66 through the core turbine engine 16.

It should be appreciated, however, that the exemplary turbofan engine 10 depicted in <figref idref="f0001">FIG. 1</figref> is by way of example only, and that in other exemplary embodiments, the turbofan engine 10 may have any other suitable configuration. For example, in other exemplary embodiments, the fan 38 may be configured in any other suitable manner (e.g., as a fixed pitch fan) and further may be supported using any other suitable fan frame configuration. Moreover, it also should be appreciated that in other exemplary embodiments, any other suitable HP compressor 24 and HP turbine 28 configurations may be utilized. It also should be appreciated, that in still other exemplary embodiments, aspects of the present disclosure may be incorporated into any other suitable gas turbine engine. For example, in other exemplary embodiments, aspects of the present disclosure may be incorporated into, e.g., a turboshaft engine, turboprop engine, turbocore engine, turbojet engine, etc., as well as turbine engines used for other vehicles or in stationary applications.

<figref idref="f0002">FIG. 2</figref> presents an exploded, schematic cross-sectional view of components within the dashed outline of the box designated <figref idref="f0002">FIG. 2</figref> in <figref idref="f0001">FIG. 1</figref>. One end of a stator vane 67 of the HP compressor 24 is mounted to a stationary structural frame 69, while the opposite end of the stator vane 67 is truncated in the view shown in <figref idref="f0002">FIG. 2</figref> but would be held fixed with respect to the outer casing 18. A flange 71 is connected to and depends radially inwardly from the stationary structural frame 69. The inner ring 81 of a roller bearing 80 is non-rotatably coupled to the HP spool 34. The roller bearing 80 includes a cage 82, a plurality of rollers 83 (only one roller 83 being depicted in the view shown in <figref idref="f0002">FIG. 2</figref>) and an outer ring 84. As schematically shown in <figref idref="f0002">FIG. 2</figref>, interface shell 86 non-rotatably couples the outer ring 84 of the roller bearing 80 to the flange 71 of the stationary structural frame 69 via a mechanical fastener such as a bolt 88. It should be appreciated that there will be a plurality of such bolts 88 spaced apart from one another around the entire circumference of the outer ring 84.

The inner ring 91 of a conventional ball bearing 90 is non-rotatably coupled to the HP spool 34. The ball bearing 90 also includes a cage 92, a plurality of rotatable balls 93 (only one ball 93 being shown in the view of <figref idref="f0002">FIG. 2</figref>) and an outer ring 94, which is disposed radially outwardly farther away from the axis of rotation 12 than the disposition of the inner ring 91.

In accordance with an embodiment of the present invention, a retention housing 98 is generally designated by the numeral 98 in <figref idref="f0002">FIGs. 2</figref>, <figref idref="f0003">3</figref>, <figref idref="f0004">4</figref> and <figref idref="f0005">5</figref>. The retention housing 98 is configured and disposed for retaining the ball bearing 90 and absorbing the loads that result from a failure of one or more of a fan blade, a compressor blade or a turbine blade when any such blade suffers any compromise of its structural integrity, e.g., becomes at least partially detached or broken. As shown in <figref idref="f0003">FIG. 3</figref> for example, the retention housing 98 desirably includes a ball bearing housing 100 and a spring finger housing 110. As schematically shown in <figref idref="f0003">FIG. 3</figref> for example, each housing 100, 110 is a cylindrically symmetrical component that is disposed concentrically with respect to a central rotational axis 89 of the retention housing 98.

As schematically shown in <figref idref="f0002">FIG. 2</figref> for example, the retention housing 98 non-rotatably couples to the flange 71 of the stationary structural frame 69, the outer ring 94 of the ball bearing 90 for a high pressure spool 34 of a gas turbine engine 10. The spring finger housing 110 can be fixed with respect to the outer casing 18 as by being mechanically bolted or welded to the flange 71. In one exemplary embodiment, the spring finger housing 110 is rendered stationary by being coupled to the outer casing 18 in a manner that can be performed in any of a number of conventional manners, any one of which being suitable for purposes of illustrating exemplary embodiments of the present disclosure. As shown in <figref idref="f0002">FIG. 2</figref> for example, this can be accomplished via an annular mounting flange 113 that elongates generally in a radial direction from the aft end 112 of the spring finger housing 110. The spring finger housing 110 and the annular mounting flange 113 desirably are formed as a monolithic structure.

As shown in <figref idref="f0003">FIG. 3</figref>, the annular mounting flange 113 is drilled with a plurality of axially extending mounting holes 114 therethrough. These mounting holes 114 are spaced circumferentially apart from one another around the entire circumference of the mounting flange 113. As shown in <figref idref="f0002">FIG. 2</figref> for example, each of the mounting holes 114 through the annular mounting flange 113 of the retention housing 98 desirably is configured to receive a respective mounting bolt 88 (one of which being depicted in cross-section in the view of <figref idref="f0002">FIG. 2</figref>) by which the mounting flange 113 may be attached to the flange 71 of the stationary structural frame 69. As shown in <figref idref="f0002">FIG. 2</figref> for example, the annular mounting flange 113 non-rotatably couples the spring finger housing 110 to the flange 71 of the stationary structural frame 69 via a mechanical fastener such as a bolt 88, which enables the retention housing 98 to be removed from the engine 10 for replacement, maintenance and/or repair.

As schematically shown in <figref idref="f0003">FIGs. 3</figref> and <figref idref="f0005">5</figref> for example, the ball bearing housing 100 defines its own forward end 101, which is disposed axially apart from its own aft end 102. Similarly, as schematically shown in <figref idref="f0003">FIGs. 3</figref> and <figref idref="f0005">5</figref> for example, the spring finger housing 110 defines its own forward end 111, which is disposed axially apart from its own aft end 112.

As shown in <figref idref="f0003">FIGs. 3</figref> and <figref idref="f0005">5</figref> for example, between the forward end 101 and midpoint of the ball bearing housing 100 there is defined a plurality of openings 103, each opening 103 extending radially through the ball bearing housing 100. Each such opening 103 is configured to receive therein an attachment bolt 104 such as depicted in cross-section in <figref idref="f0002">FIG. 2</figref> and which is locked by a retention nut 105. As shown in <figref idref="f0003">FIG. 3</figref> for example, the ball bearing housing 100 includes a retention flange 106, which extends radially inwardly toward the central axis 89 from the aft end 102 of the ball bearing housing 100. As shown in <figref idref="f0002">FIG. 2</figref> for example, the outer ring 94 of the ball bearing 90 is restrained against axial movement by being held between the retention flange 106 of the ball bearing housing 100 and the retention nut 105. Accordingly, under normal operating conditions of the engine 10, the outer ring 94 of the ball bearing 90 becomes restrained against axial movement with respect to the HP spool 34.

As schematically shown in <figref idref="f0002">FIGs. 2</figref> and <figref idref="f0003">3</figref>, the ball bearing housing 100 defines a cylindrical inner surface 107 that is disposed equidistantly from the central axis of rotation 89 that extends in an axial direction (A). As shown in <figref idref="f0002">FIG. 2</figref> for example, this inner surface 107 of the ball bearing housing 100 of the retention housing 98 desirably contacts the cylindrically shaped outer surface 95 of the outer ring 94 of the ball bearing 90. As schematically shown in <figref idref="f0001">FIGs. 1</figref> and <figref idref="f0002">2</figref> for example, the radial direction (R) (and thus the diametrical direction) is defined in a direction that is normal to the axial direction (A) and normal to the central axis of rotation 89.

As schematically shown in <figref idref="f0002">FIGs. 2</figref>, <figref idref="f0003">3</figref> and <figref idref="f0005">5</figref> for example, the spring finger housing 110 is disposed radially apart from and radially outwardly from the ball bearing housing 100 and disposed concentrically around the ball bearing housing 100.

As schematically shown in <figref idref="f0002">FIGs. 2</figref>, <figref idref="f0003">3</figref> and <figref idref="f0005">5</figref> for example, each embodiment of the retention housing 98 desirably includes a connecting web 108 disposed at the forward end of the retention housing 98. The connecting web 108 spans between the forward end 111 of the spring finger housing 110 and the forward end 101 of the ball bearing housing 100. The connecting web 108 provides a fulcrum of the retention housing 98 that transitions between the forward end 111 of the spring finger housing 110 and the forward end 101 of the ball bearing housing 100. Each connecting web 108 extends generally in the radial direction (R) between the ball bearing housing 100 and the spring finger housing 110. Desirably, the spring finger housing 110, the connecting web 108 and the ball bearing housing 100 are formed as a monolithic structure.

As schematically shown in the cross - sectional portion of <figref idref="f0005">FIG. 5</figref> in a virtual plane defined by the radial (R) and axial (A) directions, the connecting web 108 takes on a shape that resembles the letter C. As schematically shown in <figref idref="f0002">FIGs. 2</figref> and <figref idref="f0005">5</figref> for example, the connecting web 108 includes a radial section 1080 that extends in the radial direction (R). As shown in <figref idref="f0005">FIG. 5</figref> for example, a first elbow section 1081 connects the radial section 1080 to the forward end 111 of the spring finger housing 110 by a gradual bend over the right angle that exists between the radial (R) and axial (A) directions. A second elbow section 1082 similarly connects the radial section 1080 to the forward end 101 of the ball bearing housing 100. The connecting web 108 functions as a flexure that permits small radial displacements between the aft end 102 of the ball bearing housing 100 and the interface shell 86 and accordingly between the aft end 102 of the ball bearing housing 100 and the aft end 112 of the spring finger housing 110.

As schematically shown in <figref idref="f0002">FIGs. 2</figref>, <figref idref="f0004">4</figref>, <figref idref="f0005">5 and 6</figref> for example, the interface shell 86 includes a plurality of through bores 140 defined radially through the interface shell 86. As schematically shown in <figref idref="f0004">FIG. 4</figref> for example, individual ones of the through bores 140 are spaced apart from one another in the circumferential direction (C) around the entire circumference of the interface shell 86, and desirably this spacing is uniform but need not be. In the embodiment depicted in <figref idref="f0004">FIG. 4</figref> for example, there are eight through bores 140 spaced evenly apart from one another around the entire circumference of the interface shell 86.

As schematically shown in <figref idref="f0002">FIGs. 2</figref>, <figref idref="f0004">4</figref> and <figref idref="f0005">5</figref> for example, a plurality of dowel pins 136 is provided to restrain circumferential movement between the aft end 102 of the ball bearing housing 100 and the interface shell 86, which as described above is non-rotatably coupled to the outer casing 18 of the engine 10 shown in <figref idref="f0001">FIG. 1</figref> for example. One end of each dowel pin 136 is disposed within a respective one of the through bores 140 and is fixed non-rotatably within the respective through bore 140. The one end of each dowel pin 136 can be non-rotatably fixed within a respective through bore 140 by any conventional means of non-rotatable attachment, including for example being press-fit therein, screwed in, welded therein or held by adhesive therein. Thus, each through bore 140 is configured to receive and hold therein one of the plurality of dowel pins 136. The opposite end of each dowel pin 136 projects radially out of the respective through bore 140 and toward the central axis 89 (<figref idref="f0004">FIG. 4</figref>) of the retention housing 98.

As schematically shown in <figref idref="f0002">FIGs. 2</figref>, <figref idref="f0004">4</figref> and <figref idref="f0005">5</figref> for example, the aft end 102 of the ball bearing housing 100 defines a plurality of blind bores 130. As schematically shown in <figref idref="f0005">FIG. 6</figref> for example, each blind bore 130 extends in the radial direction (R) and is defined by an open end 131 that provides an entrance permitting access into the bore 130. Each bore 130 is further defined by a blind end 132 that is spaced apart in the radial direction (R) from the open end 131 of the bore 130. The blind end 132 of each bore 130 is "blind" because it prevents the bore 130 from extending completely through the aft end 102 of the ball bearing housing 100. Thus, the blind end 132 of each bore 130 is a solid wall that closes off the end of each bore 130 that is opposite to the open end 131 of each bore 130. A radially extending side wall 133 defines the part of the blind bore 130 that extends between the open end 131 and the blind end 132. The transverse cross - sectional shape of the blind bore 130 that is defined by the side wall 133 desirably is a circle, but could be a polygon such as a square, a hexagon, and an octagon, etc.

As schematically shown in <figref idref="f0002">FIGs. 2</figref> and <figref idref="f0005">5</figref> for example, the open end 131 of each bore 130 is facing toward the spring finger housing 110. Accordingly, the entrance to each bore 130 is disposed closer to the spring finger housing 110 than is the disposition of the blind end 132 of each bore 130, and thus the blind end 132 faces away from the spring finger housing 110. Each of the plurality of blind bores 130 is disposed so as to be aligned with a respective one of the plurality of through bores 140 defined radially through the interface shell 86 to form a plurality of aligned through bores 140 and blind bores 130. As schematically shown in <figref idref="f0005">FIG. 5</figref> for example, each of these aligned through bores 140 and blind bores 130 forms a pair of bores 130, 140 that receives therethrough one of the plurality of dowel pins 136.

As schematically shown in <figref idref="f0005">FIG. 6</figref> for example, a respective one of the plurality of dowel pins 136 is disposed in a respective one of the plurality of blind bores 130, which is dimensioned to be larger than the dimensions of the dowel pin 136 to afford gaps between the cylindrical surfaces that define the side walls 133 of the blind bores 130 and the cylindrical surfaces that define the peripheral exterior surfaces 138 of the dowel pins 136 to allow relative movement (in both the circumferential C and axial A directions) between the dowel pin 136 and the cylindrical wall surfaces 133 that define the blind bore 130. Because of where the cross - section is taken for the view depicted in <figref idref="f0005">FIG. 6</figref>, the axial gap between the wall surfaces 133 of the blind bore 130 and the exterior surfaces 138 of the dowel pin 136 is what is visibly depicted in <figref idref="f0005">FIG. 6</figref>. However, these gaps will completely surround the peripheral surfaces 138 of the dowel pin 136 and thus exist in both the axial direction (A) and circumferential direction (C). Accordingly, the diameter of the blind bore 130 is dimensioned larger than the diameter of the dowel pin 136 by of the order of 0.508 to 1.27 mm (20 thousandths to 50 thousandths of an inch). In this way, the retention housing 98 permits a certain amount of displacement in the axial direction (A) and the circumferential direction (C) to occur between the aft end 102 of the ball bearing housing 100 and the end of the dowel pin 136 that is projecting from the interface shell 86 before limiting the further axial deflection and circumferential deflection of the retention housing 98 when the peripheral surfaces 138 of the projecting end of the dowel pin 136 come into contact with the cylindrical walls 133 that define the blind bore 130.

Moreover, as schematically shown in <figref idref="f0005">FIG. 6</figref> for example, the blind end 132 of the blind bore 130 is disposed deep enough in the radial direction (R) to allow for a radial gap between the free end 137 of the dowel pin 136 and the blind end 132 of the blind bore 130. This radial gap allows the retention housing 98 to permit a certain amount of displacement in the radial direction (R) to occur between the aft end 102 of the ball bearing housing 100 and the free end 137 of the dowel pin 136 before limiting the further radial deflection of the retention housing 98 when the free end 137 of the dowel pin 136 eliminates the radial gap by coming into contact with the blind end 132 of the blind bore 130. This radial gap desirably will always be larger than either the axial gap or the circumferential gap and accordingly will be larger than 0.508 mm (20 thousandths of an inch) for an axial gap or a circumferential gap of this magnitude, and thus also larger than 1.27 mm (50 thousandths of an inch) for an axial gap or a circumferential gap of this magnitude.

As schematically shown in <figref idref="f0003">FIGs. 3</figref> and <figref idref="f0005">5</figref> for example, the spring finger housing 110 defines a plurality of axially extending fingers 120. As shown in <figref idref="f0003">FIG. 3</figref> for example, each of the fingers 120 is spaced apart circumferentially from each of its adjacent nearest circumferentially neighboring fingers 120 disposed around the spring finger housing 110, the circumferential direction being schematically indicated by the arrows designated by the letter C. As shown in <figref idref="f0005">FIG. 5</figref> for example, each finger 120 defines a forward end 121 and an aft end 122 disposed axially spaced apart from and opposite to the forward end 121 of each respective finger 120. Desirably, the plurality of forward ends 121 of the fingers 120 and the aft ends 122 of the fingers 120 form a monolithic structure with the spring finger housing 110.

As schematically shown in <figref idref="f0005">FIG. 5</figref> for example, each of the fingers 120 includes an intermediate portion 123 that extends axially between each respective front end 121 and respective aft end 122 of each respective finger 120. Each of these intermediate portions 123 is narrower than each respective front end 121 and respective aft end 122 of each respective finger 120. Each finger 120 undergoes a tapering from each opposite end of each respective finger 120 to a certain degree until the narrowed dimension of that finger 120 is attained at the intermediate portion 123. Each opposite circumferential side and top and bottom surface of each intermediate portion 123 of the finger 120 can be machined to attain the desired tapering. The specific relative dimensions of the intermediate portions 123 with respect to the front ends 121 and aft ends 122 will depend upon the dimensions and composition of the retention housing 98 as well as the anticipated level of stress for which the retention housing 98 is being engineered.

In a typical case, because of this tapering of the fingers 120, the axial lengths of the fingers 120 can be shortened relative to the lengths of conventional fingers. Additionally, the tapering of the fingers 120 results in a reduction in the overall weight of the retention housing 98 when compared to a conventional retention housing.

During normal engine operation, the ball bearing assembly 90 acts to retain the axial position of the HP spool 34, and the associated roller bearing assembly 80 acts to provide radial damping of the fan/rotor system. As schematically shown in the enlarged view of <figref idref="f0005">FIG. 6</figref> for example, a radial bumper gap is defined between the radially outwardly facing surface 1021 of the aft end 102 of the ball bearing housing 100 and the overlying inner surface 87 of the interface shell 86 that is connected to the outer ring 84 of the roller bearing 80 as schematically shown in <figref idref="f0002">FIG. 2</figref> for example. The size of this radial bumper gap is controlled to absorb the anticipated relatively small radial deviations of the HP spool 34 and typically would have dimensions within a range on the order of 5 thousandths of an inch to 20 thousandths of an inch.

However, during a failure mode that results from a liberated fan blade, or a liberated compressor blade or a liberated turbine blade, very high radial loads close the bumper gap in the embodiment depicted in <figref idref="f0005">FIG. 6</figref>. The very high radial loads create a harmonic drive effect that loads the spring fingers 120 in torsion, i.e., in the circumferential direction as schematically indicated in <figref idref="f0003">FIG. 3</figref> by the arrows designated C. This torsion load on the ball bearing 90 and its retention housing 98 results in an opposing sinusoidal load distribution that tends to twist the spring fingers 120. However, as is apparent from the view in <figref idref="f0004">FIG. 4</figref>, this twisting becomes damped by the restraining force exerted by the dowel pins 136 in the circumferential direction (indicated by the arrows designated C in <figref idref="f0003">FIG. 3</figref>) to prevent larger circumferential movement between the ball bearing housing 100 and the spring finger housing 110.

The retention housing 98 described herein with its ball bearing housing 100 pinned to the interference shell 86 has several advantages over the prior art. By employing dowel pins 136 of different sizes and materials as well as different numbers of dowel pins 136 and different circumferential spacings between adjacent dowel pins 136 around the circumference of the retention housing 98 within the respective blind bores 130 of the aft end 102 of the ball bearing housing 100 of the retention housing 98 for the ball bearing 90, damping can be controlled according to the anticipated load in consideration of the size and material composition of the structure of the retention housing 98. The resulting design of the retention housing 98 integrates the structural components such that they become capable of withstanding the torsional windup and high radial loads that occur with the sudden increase in load that accompanies a blade failure, whether a fan blade, a compressor blade or a turbine blade. Moreover, due to the unique tapered and relatively short design of the spring fingers 120, the amount of axial and radial space needed for the retention housing 98 is reduced along with a concomitant reduction in the weight of the retention housing 98 while affording a very high torsional load capability to the retention housing 98.

This written description uses examples to disclose the invention, including the preferred mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the scope of the appended claims. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.