Patent Description:
Centrifugal compressors in a gas turbine engine include an impeller and a diffuser downstream from the impeller. At the compressor exit, the compressed air may be used, in addition to providing compressor air to the engine core for combustion, to pressurize an engine air system as well as pressurize nearby air-oil interfaces such as those sealing bearing cavities.

Typically, an impeller baffle is disposed downstream of a rear face of the impeller, to limit losses and restrict air which may otherwise escape around the rear face of the impeller. Such impeller baffles are typically add-on parts that require some form of attachment to a mating part. These add-on baffles may be complicated to assemble, afford minimal dynamic tuning options, and their attachment means may loosen or require service over time.

<CIT> discloses a prior art gas turbine engine according to the preamble of claim <NUM>.

<CIT> discloses a turbocharger comprising a centrifugal compressor having an impeller, a bearing casing including bearings rotationally supporting the impeller, and an intermediate wall separating the compressor casing from the bearing casing, the intermediate wall comprising a plurality of stiffening elements.

<CIT> discloses a gas turbine engine comprising a centrifugal compressor having an impeller and a lubrication sump that includes sump walls that define a bearing compartment in which a bearing is located. Hot compressor discharge air flows radially inward along the backface of the impeller and through a high pressure cavity of the lubrication sump.

In one aspect, there is provided a gas turbine engine according to claim <NUM>.

In certain embodiments, the front baffle face is shaped to follow the profile of the rear face of the impeller.

In certain embodiments, the plurality of stiffening elements include one or more of ribs, webs or struts.

In certain embodiments, the plurality of stiffening elements are hollow.

In certain embodiments, the plurality of stiffening elements are evenly spaced about the circumference of the annular collar.

In certain embodiments, the baffle includes a varying thickness between the front baffle face and the rear baffle face.

In certain embodiments, the thickness of the baffle varies in a radial or circumferential direction.

In certain embodiments, upon mounting the flange to the exterior surface of the bearing housing, the plurality of air passages are in fluid communication with an interior chamber of the bearing housing.

In certain embodiments, the flange includes a plurality of bolt holes for mounting to the exterior surface of the bearing housing.

In certain embodiments, the bearing housing cover is mounted to an upstream end of the bearing housing.

In certain embodiments, the gas turbine engine further includes a second bearing housing cover mounted to a downstream end of the bearing housing, the second bearing housing cover including a plurality of air passages in fluid communication with the plurality of air passages in the bearing housing cover mounted to the upstream end of the bearing housing.

In certain embodiments, the central baffle opening in the bearing housing cover includes an inner ring having a lip extending radially inwardly adjacent an outer surface of the bearing housing to define an air gap leading to the interior chamber of the bearing housing.

In another aspect, there is provided a method of manufacturing a gas turbine engine according to claim <NUM>.

<FIG> illustrates an exemplary gas turbine engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a centrifugal compressor <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine <NUM> for extracting energy from the combustion gases. A main engine shaft <NUM> along longitudinal axis <NUM> interconnects the fan <NUM>, the centrifugal compressor <NUM> and the turbine <NUM>. In use, pressurized air provided by the centrifugal compressor <NUM> through a diffuser <NUM> enters the combustor <NUM> for combustion. While <FIG> shows gas turbine engine <NUM> to be a turbofan gas turbine engine, it is understood that the present disclosure is applicable to other types of gas turbine engines as well.

<FIG> shows an enhanced view of the engine <NUM> proximate the combustor <NUM> and diffuser <NUM>. A centrifugal compressor <NUM> as in <FIG>, which may include multiple axial stage rotors, is followed by an impeller <NUM> and a coverplate <NUM>. The centrifugal compressor <NUM> supplies pressurized air to the combustor <NUM>, the hot gases from which drive a turbine <NUM> as in <FIG>. The impeller <NUM> has a rear face <NUM> behind which the air swirls at high velocity due to the rotation of the impeller <NUM>. This swirling, high-velocity air tends to lower the pressure of the "rear face air", i.e. the airflow F immediately behind (i.e. downstream of) the impeller rear face <NUM>.

As further shown in <FIG>, a bearing housing <NUM>, located downstream from the impeller <NUM>, houses a bearing <NUM> which rotationally supports the main engine shaft <NUM>, upon which the centrifugal compressor <NUM> and turbine <NUM> are mounted for example. The bearing <NUM>, housed within an interior chamber of the bearing housing <NUM>, is lubricated and cooled with oil circulated by a lubrication system within the gas turbine engine <NUM>. A front carbon seal <NUM> as well as a rear carbon seal <NUM> are mounted to the bearing housing <NUM> to ensure that oil is sealed within the bearing housing <NUM>. The front carbon seal <NUM>, which may be a controlled-gap seal, is pressurized to prevent oil from leaking out of the bearing housing <NUM>. Other seals may be contemplated as well.

Referring additionally to <FIG> and <FIG>, a bearing housing cover <NUM> mountable to the bearing housing <NUM> includes an integrated impeller baffle <NUM>. By "integrated", it is understood that the impeller baffle <NUM> is machined or otherwise formed as a single, unitary or monolithic, piece with the bearing housing cover <NUM>. The bearing housing cover <NUM> includes an annular collar <NUM> having a flange <NUM> mountable to an exterior surface of the bearing housing <NUM>. When mounted, the cover <NUM> at least partially encloses the bearing housing <NUM> and aids in sealing oil within the bearing housing <NUM>. In the shown embodiment, although not necessarily the case in all embodiments, the flange <NUM> includes a plurality of holes <NUM> arranged in a bolt pattern for mounting to the bearing housing <NUM>, illustratively twelve holes <NUM> about the perimeter of the flange <NUM>. The width of the flange <NUM> may vary, for instance based on the structural requirements of the cover <NUM> or the sizing of the exterior surface of the bearing housing <NUM>. The mounting or fastening of the bearing housing cover <NUM> to the bearing housing <NUM> will be discussed in further detail below.

The impeller baffle <NUM> is integrally formed with the annular collar <NUM> and includes a generally annular body with a front baffle face <NUM>, a rear baffle face <NUM> and a central baffle opening <NUM>. Illustratively, a rounded bevel edge <NUM> joins the annular collar <NUM> to the rear baffle face <NUM>, although other transition structures may be contemplated as well. When the bearing housing cover <NUM> is mounted to the bearing housing <NUM>, the front baffle face <NUM> is positioned adjacent the impeller rear face <NUM>. As such, the air pressure leaving the impeller <NUM> drops as it approaches the centerline of the engine <NUM>, i.e. axis <NUM>, and enters the bearing housing <NUM>. This aids in sealing the bearing housing <NUM> and/or provides a cooling flow F within the bearing housing <NUM>, as will be discussed in further detail below. In some cases, the impeller baffle <NUM> may be manufactured to have a complex profile shape based on the engine's <NUM> particular air system requirements. For instance, the front baffle face <NUM> may have a profile that follows that of the impeller rear face <NUM>. Other shapes or profiles for the impeller baffle <NUM> may be contemplated as well.

A plurality of stiffening elements <NUM> extend from the rear baffle face <NUM> to the annular collar <NUM>. The stiffening elements <NUM>, also referred to as reinforcement elements, may be integral with the bearing housing cover <NUM>, i.e. formed from a single piece. In other cases, additional add-on or mountable reinforcement elements may be contemplated as well. In the embodiment shown in <FIG>, these stiffening elements <NUM> are in the form of webs. Other types of stiffening elements may be contemplated as well, as will be discussed in further detail below. As shown, the web base 56a provides support for the web <NUM> at the rear baffle face <NUM>. The web body 56b is shown to be thinner than the web base 56a and slightly curved, although other shapes and sizes may be contemplated as well. The web end 56c where the web <NUM> meets the annular collar <NUM> is reinforced for added support. The number, thickness and spacing of the stiffening elements <NUM>, illustratively the webs <NUM>, may vary, for instance based on the structural requirements of the engine <NUM>. For instance, while the webs <NUM> shown in <FIG> are spaced equally from one another, in other cases the spacing between the webs <NUM> (or other stiffening elements) may vary along the circumference of the bearing housing cover <NUM>. In addition, various parameters of the stiffening elements <NUM> can be adjusted to vary or tune the dynamic response of the impeller baffle <NUM> to reduce vibrations, as will be discussed in further detail below.

Still referring to <FIG> and <FIG>, according to the invention a plurality of air passages <NUM> extend through the bearing housing cover <NUM>. In the shown case, the bearing housing cover <NUM> includes six air passages <NUM>, five of which are visible in <FIG>. Three of the six air passages <NUM> extend at least partially axially through the annular collar <NUM> between air inlets 58a disposed on the front baffle face <NUM> and air outlets 58b disposed on the flange <NUM>. The remaining three air passages <NUM> (two of which are visible in <FIG>) have air inlets 58a within the annular collar <NUM> and outlets 58b disposed on the flange <NUM>. As can be seen in <FIG>, the six air outlets 58b are disposed on the flange <NUM>. Other numbers and pathways for the air passages <NUM> may be contemplated as well. As will be discussed in further detail below, the air passages <NUM> may divert a portion of the airflow F from the impeller rear face <NUM> to the bearing housing <NUM> and/or to components downstream of the bearing housing <NUM> for various engine cooling and sealing requirements. In the shown case, the number of inlets 58a corresponds to the number of outlets 58b. In the shown case, the inlets 58a and outlets 58b are slot-like openings disposed about the circumference of the central baffle opening on the front baffle face <NUM>, within the annular collar <NUM> or on the flange <NUM>. Other shapes, positions and sizes of inlets 58a and/or outlets 58b may be contemplated as well, for instance based on the airflow and/or sealing requirements of the various components of the bearing housing <NUM>.

As can be seen in <FIG>, the bearing housing cover <NUM> is mountable to the bearing housing <NUM> at an upstream end thereof. The bearing housing cover <NUM> may also be referred to as the front bearing housing cover <NUM>, while a rear bearing housing cover <NUM> is mountable to a downstream end of the bearing housing <NUM>. A plurality of bolts <NUM> or other like fasteners may be used to fasten the bearing housing covers <NUM>, <NUM> to the bearing housing <NUM>. Illustratively, each bolt <NUM> may pass through a bolt hole <NUM> on the flange <NUM> of the front bearing housing cover <NUM>, through a bore <NUM> in the bearing housing <NUM> and then through a corresponding bolt hole (not shown) in the rear bearing housing cover <NUM>. In some cases, the bolt holes <NUM> in front bearing housing cover <NUM> and/or the bolt holes in the rear bearing housing cover <NUM> may be threaded for secure attachment. In some cases, the bore <NUM> may be threaded as well. Other forms of attachment may be contemplated as well.

The rear bearing housing cover <NUM> includes a plurality of air passages <NUM>. When the bearing housing covers <NUM>, <NUM> are mounted to the bearing housing <NUM>, air passageways in fluid communication with the air passages <NUM>, <NUM>, for instances the bores <NUM>, allow airflow F to flow between air passages <NUM> in the front bearing housing cover <NUM> and the air passages <NUM> in the rear bearing housing cover <NUM>. For instance, air may pass through hollow portions of the bolts <NUM> themselves, and/or around the bolts <NUM> within the bores <NUM>. As discussed above, the airflow F can be diverted to various components downstream of the bearing housing <NUM> for cooling and/or sealing purposes. The dimensions of the air passages <NUM>, <NUM> may vary, for instance based on the cooling and/or sealing needs of these various components.

As shown in <FIG> and <FIG>, the bearing housing cover <NUM> further includes an inner ring <NUM> and a lip <NUM> to control the incoming air entering the bearing housing <NUM>. The width of the inner ring <NUM> may vary to alter the size of the central baffle opening <NUM>, for instance in response to engine requirements for temperature and pressure gradients. When installed, the lip <NUM> extends radially inwardly into close proximity with an outer surface of a runner <NUM> supporting the front carbon seal <NUM> to thus define a narrow air gap <NUM> through which the airflow F may enter the bearing housing <NUM>. The inner diameter of the lip <NUM> may be coated for a labyrinth seal with the runner <NUM>. In some cases, the airflow F entering through the narrow gap <NUM> may aid in sealing the front carbon seal <NUM>. The downstream end of the bearing housing <NUM> may similarly include a narrow air gap <NUM> formed by an outer surface of a runner <NUM>. Airflow F may thus be provided to the downstream end of the bearing housing <NUM>, for instance to aid in sealing the rear carbon seal <NUM>. This airflow F may be diverted from the exit of the air passages in the rear bearing housing cover <NUM>, although other airflow sources may be contemplated as well.

In different cases, the thickness of the baffle <NUM>, i.e. between the front baffle face <NUM> and the rear baffle face <NUM>, can vary. For instance, larger engines with different dynamic responses may require a thicker baffle <NUM> to ensure structural integrity. Alternatively, in smaller engines, a thinner baffle <NUM> may be used to reduce the overall weight of the engine <NUM>. In certain cases, the thickness of baffle <NUM> may vary, for instance in radial or circumferential directions. For instance, the baffle <NUM> may be thinner at the circumferential positions where the stiffening elements <NUM> meet the rear baffle face <NUM>. In addition, the baffle <NUM> may be thicker at other circumferential positions to provide additional structure where necessary. Alternatively, the baffle <NUM> may be thicker towards the central baffle opening <NUM> and become thinner towards the radial outer edge of the baffle <NUM>. The reverse configuration may be contemplated as well. The thickness of the baffle <NUM> may also vary based on the dynamic tuning requirements of the baffle <NUM>, as will be discussed in further detail below.

Referring to <FIG>, the stiffening elements <NUM>' may have shapes or sizes that vary from one to the other. Illustratively, each alternating web <NUM>' terminates at a different height on the annular collar <NUM>, alternating between reaching midway up the annular collar <NUM> and reaching a point just below the flange <NUM>. Such variations in height may, for instance, aid in reducing the weight of the bearing housing cover <NUM>, provide additional rigidity in strategic locations, and/or aid in dynamically tuning the baffle <NUM>. In addition, the webs <NUM>' shown in <FIG> are thicker than those in <FIG>, for instance for added strength.

Referring to <FIG>, in the shown case the stiffening elements <NUM>" are in the form of ribs <NUM>" extending from the rear baffle face <NUM> to the annular collar <NUM>. The number, spacing and thickness of the ribs <NUM>" may vary, for instance based on structural and/or weight requirements. The positioning of the ends of the ribs <NUM>" on the rear baffle face <NUM> and/or on the annular collar <NUM> may vary as well. In some cases, the ribs <NUM>" may be hollow, for instance to save weight, while in other cases they may be solid for added rigidity. Combinations of hollow and solid ribs <NUM>", for instance in alternating order, may be contemplated as well. Alternative or additional structural features may be contemplated as well, for instance struts, dimples and/or lightening holes. Such features may contribute towards increasing the structural rigidity and/or reducing the weight of the bearing housing cover <NUM>, as well as aiding in dynamically tuning the baffle <NUM>.

As discussed above, the bearing housing cover <NUM> with the integrated impeller baffle <NUM> is manufactured or otherwise formed from a single piece of material. Various manufacturing techniques may be contemplated, such as machining from a solid material, casting, or other suitable techniques. Compared to traditional non-integrated impeller baffles, there are fewer required manufacturing steps, as the baffle does not need to be stamped and then welded or brazed to the bearing housing. In addition, the part tolerances between the baffle <NUM> and bearing housing cover <NUM> may be improved relative to non-integrated impeller baffles as the two parts are integrated. As there are fewer welding and/or brazing joints that could potentially fail, the risk of loose hardware may be lowered with the integrated baffle <NUM> design. The herein described impeller baffle <NUM> may be easier to mount or assemble to the bearing housing than non-integrated baffles due to its integration in the bearing housing cover <NUM>, and the reduced part count may reduce the required assembly time.

As discussed above, the integrated impeller baffle <NUM> of the bearing housing cover <NUM> may be dynamically tuned. As the baffle's <NUM> natural frequencies are typically within running range of the engine <NUM>, such dynamic tuning may be done to prevent undesirable vibrations. As the bearing housing cover <NUM> with the integrated impeller baffle <NUM> is manufactured from a single part, there may be an opportunity during the design process to tune the baffle's <NUM> dynamic response to avoid unwanted natural frequencies. As discussed above, such tuning may be done by optimizing the stiffening elements <NUM>, for instance by altering the type, spacing, and number of stiffening elements <NUM>. Such tuning may also be done by varying the thickness of the baffle <NUM>. Other dynamic tuning methods may be contemplated as well.

Claim 1:
A gas turbine engine (<NUM>) comprising:
a centrifugal compressor (<NUM>) having an impeller (<NUM>);
a bearing housing (<NUM>) located downstream from the impeller (<NUM>), the bearing housing (<NUM>) including a bearing (<NUM>) within an interior chamber, the bearing (<NUM>) rotationally supporting the impeller (<NUM>); and
a bearing housing cover (<NUM>) comprising:
an annular collar (<NUM>) having a flange (<NUM>) mountable to an exterior surface of the bearing housing (<NUM>); and
an impeller baffle (<NUM>) integrally formed with the annular collar (<NUM>), the impeller baffle (<NUM>) having an annular body with a front baffle face (<NUM>) positionable adjacent a rear face (<NUM>) of the impeller (<NUM>), a rear baffle face (<NUM>), and a central baffle opening (<NUM>)
characterised in that
the rear baffle face (<NUM>) has a plurality of stiffening elements (<NUM>, <NUM>', <NUM>") extending from the rear baffle face (<NUM>) to the annular collar (<NUM>), and in that the bearing housing cover (<NUM>) further comprises
a plurality of air passages (<NUM>) extending at least partially axially between the front baffle face (<NUM>) and the flange (<NUM>), wherein, upon mounting the flange (<NUM>) to the exterior surface of the bearing housing (<NUM>), the plurality of air passages (<NUM>) are in fluid communication with air passageways through the bearing housing (<NUM>).