Patent Description:
Aircraft engines typically include a number of rotating components or parts mounted together via mounting devices, such as bearings, providing suitable support and allowing rotational movement between the components. Roller bearings and/or journal bearings are often used for rotating shafts in such engines, including in their gearboxes. Journal bearings employ a journal shaft rotating in a sleeve. To lubricate journal bearings, a fluid such as oil is used to create a film between the journal shaft and the gear sleeve. While suitable for their intended purposes, improvements of such journal bearings is sought.

<CIT> relates to journal bearing assembly with dual oil cavities for gas turbine engines.

<CIT> relates to journal pins in an epicyclic gear system.

<CIT> relates to a contra-rotating bearing device for a contra-rotating propeller wherein a sufficient oil film is formed on the bearing surface of a contra-rotating bearing which supports the inner shaft of the contra-rotating propeller so that an excellent bearing function can be obtained.

According to an aspect of the present invention, there is provided a journal shaft for a journal bearing assembly of an aircraft engine as claimed in claim <NUM>.

According to another aspect of the present invention, there is provided a journal bearing assembly for an aircraft engine as claimed in claim <NUM>.

<FIG> illustrates a gas turbine engine <NUM> of a type preferably provided for use in subsonic flight and configured for driving a load <NUM>, such as, but not limited to, a propeller or a helicopter rotor or rotorcraft rotor. Depending on the intended use, the engine <NUM> may be any suitable aircraft engine, and may be configured as a turboprop engine or a turboshaft engine. The gas turbine engine <NUM> generally comprises in serial flow communication a compressor section <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 section <NUM> for extracting energy from the combustion gases. Also shown is a central longitudinal axis <NUM> of the engine <NUM>. Even though the present description specifically refer to a turboprop engine as an example, it is understood that aspects of the present disclosure may be equally applicable to other types of combustion engines in general, and other types of aircraft engines in particular, including but not limited to turboshaft or turbofan engines, hybrid-electric engines, auxiliary power units (APU), and the like.

The engine <NUM> also includes rotating parts or assemblies, such as gear assemblies <NUM> (e.g., epicycle reduction systems, planetary/reduction gearboxes (RGB), or other types of rotating assemblies) with rotating components mounted thereto using mounting devices allowing rotational and/or axial movement. In the embodiment shown, the gear assembly <NUM> is mounted at the front end of the engine <NUM>, though it may be at other locations in the engine <NUM>. An example of a gear assembly <NUM> as used in the engine <NUM> is shown in <FIG>. In the depicted embodiment, the gear assembly <NUM> is part of a reduction gearbox (RGB) of the engine <NUM>. In one possible embodiment, the RGB may include, for example, an epicycle reduction system, also known as epicyclic gear train, epicyclic gearbox, planetary gearbox, etc. As a contemplated embodiment among others, an input torque through a sun shaft <NUM> is rotatably outputted through a sun gear <NUM> as an output torque through gear carriers <NUM> via a plurality of planet gears <NUM> rotatably connected to the gear carriers <NUM> and ring gears <NUM>.

The gear assembly <NUM> shown in <FIG> includes one or more mounting devices such as a journal bearing assembly <NUM>. As shown in <FIG>, the journal bearing assembly <NUM> includes a journal shaft <NUM> (also referred to as a journal or a shaft), an optional pin <NUM> (see <FIG> for an example of a pin-less journal bearing assembly), and, in this particular embodiment, a bearing sleeve <NUM>. In certain alternate embodiments, the bearing sleeve <NUM> may integrated directly into a surrounding component, such that the journal shaft <NUM> rotates within another bore, for example defined within the gear carrier or other suitable housing. The journal shaft <NUM> is thus rotatably mounted within a bore defined by a surrounding component, which component can be, for example, the sleeve <NUM>, a gear, a carrier, another suitable shaft housing, etc. The journal bearing assembly <NUM> may be used for interfacing a rotating part to a structure. In the example shown, the rotating part is one or more gears such as planet gears <NUM> configured to rotate at speeds between <NUM>,<NUM> and <NUM>,<NUM> revolutions per minute (RPM), although other rotational speeds and arrangements are possible. The gear may be an epicycle gear of epicyclic reduction system, mounted on the journal bearing assembly <NUM> which is supported at both ends between two axially spaced supports forming at least part of the structure of the epicyclic gear system, the structure being for instance a carrier <NUM>. In an embodiment, there are a plurality of planet gears <NUM> (illustratively three planets 24a, 24b 24c) on the carrier <NUM>, the planet gears <NUM> being interconnected for concurrent rotation. The supports may be annular blocks (not shown) supporting the pin <NUM> at its opposed ends. The illustrated pin <NUM> is hollow with a pin inner cavity <NUM> and may be optionally closed at one end via a fastener such as a bolt <NUM> and a washer <NUM>. A lubricating fluid film, such as an oil film, may be received between rotating components of the journal bearing assembly <NUM> to facilitate rotation of said components relative to one another, as will be discussed in further detail below. The pin inner cavity <NUM> may thus include an inlet <NUM> and at least one outlet passage <NUM> for oil to flow through. Such pin outlet passages <NUM> are illustratively radially-extending pin outlet passages <NUM> (also referred to as "pin radial passages") that extend from a radially inner pin surface <NUM> that defines the pin inner cavity to a radially outer pin surface <NUM>. While the illustrated pin <NUM> includes two such pin outlet passages <NUM>, other numbers of outlet passages may be contemplated.

The journal bearing assembly <NUM> may or may not include the sleeve <NUM> disposed radially outwardly to the journal shaft <NUM> relative to a longitudinal axis A of the journal bearing assembly <NUM>. Such sleeve <NUM> may be used to form an outer peripheral surface of the journal bearing assembly <NUM>, upon which the planet gears <NUM> are mounted in the illustrated embodiment. Otherwise, an outer surface of the journal shaft <NUM> may contact directly the rotating part it supports, e.g., the planet gears <NUM> in the illustrated embodiment, as will be discussed in further detail below.

Referring to <FIG> and <FIG>, an embodiment of a journal bearing assembly <NUM> is shown. The journal shaft <NUM> may be a monolithic piece. While journal shaft <NUM> is shown to be cylindrical, other shapes are possible such as frusto-conical, and the journal shaft <NUM> may have various surface features such as grooves, slots and channels, as will be discussed in further detail below. The journal shaft <NUM> includes a shaft body extending along the longitudinal axis A, which is the rotation axis of the rotating part, illustratively the three planet gears 24a, 24b, 24c. An inner cavity <NUM> or pin-receiving cavity <NUM> (a. , through hole) extends along the longitudinal axis A and defines a radially inner surface <NUM> of the journal shaft <NUM>, also referred to as a pin-engaging surface <NUM> that engages the radially-outer pin surface <NUM>. Stated differently, the radially inner surface <NUM> of the journal shaft <NUM> is radially spaced apart from the longitudinal axis A to define the inner cavity <NUM>. The journal shaft <NUM> has a radially outer surface <NUM> that is configured for interfacing and supporting the rotating part, either directly (in a sleeveless embodiment) or via the optional sleeve <NUM>. The pin-receiving cavity <NUM> may thus receive the pin <NUM> of the gear assembly <NUM> when mounted within such assembly <NUM>. The shaft <NUM> may include various compliance features <NUM> at the distal ends of the journal shaft <NUM>, which may also be referred to as undercuts or axial depressions.

Depending on the configuration, the journal bearing assembly <NUM> may have its journal shaft <NUM> fixed to the pin <NUM>, such that the sleeve <NUM> (if present) or the rotating part (in a sleeveless embodiment) rotates about the pin <NUM> and the journal shaft <NUM>. If present, the sleeve <NUM> concurrently rotates with the rotating part fixed thereon. In another embodiment, the journal bearing assembly <NUM> may have its journal shaft <NUM> rotatably engaged with the rotating part it supports, such that the journal shaft <NUM> may be rotatable relative to the pin <NUM> and may have the rotating part mounted thereto rotatable relative to the journal shaft <NUM>, for instance with the sleeve <NUM> fixed to the rotating part or to the journal shaft <NUM>.

As discussed above, a lubricating fluid such as oil may be provided through the pin inlet <NUM>. The oil may flow through the pin inner cavity <NUM> towards the radially-extending pin outlet passages <NUM>. Each pin outlet passage <NUM> extends from the radially inner pin surface <NUM> to the radially outer pin surface <NUM> which interfaces with the radially inner surface <NUM> of the journal shaft <NUM>. In the depicted case, the radially inner surface <NUM> includes at least one circumferential oil chamber <NUM> (illustratively two circumferential oil chambers <NUM>) extending about the radially inner surface <NUM> and aligned with the pin outlet passages <NUM>. As such, the oil exiting from the pin outlet passages <NUM> may collect in respective circumferential oil chambers <NUM>. At least one oil passage <NUM> (illustratively two oil passages <NUM>) extend radially through the journal shaft <NUM> with inlet sections 60a in fluid communication with respective circumferential oil chambers <NUM> and outlet sections 60b in fluid communication with an oil pocket <NUM> on the radially outer surface <NUM> of the journal shaft <NUM>. In the shown case, oil passages <NUM> extend through the journal shaft <NUM> in a direction normal to the longitudinal axis A, although other directions may be contemplated. While two circumferential oil chambers <NUM> and two oil passages <NUM> are shown, the number of may vary and may be selected to match the number of pin outlet passages <NUM>.

The various passages <NUM>, <NUM> and circumferential oil chambers <NUM> may be sized and shaped to control the flow of oil to the radially outer surface <NUM> of the journal shaft. The oil pocket <NUM> may hold oil (or another lubrication fluid) to be distributed between the radially-outer surface <NUM> of the journal shaft <NUM> and a radially-inner surface <NUM> of the sleeve <NUM>. In an exemplary embodiment, oil may enter the pin inner cavity <NUM> through oil inlet <NUM>, pass through outlet passages <NUM> to circumferential oil chambers <NUM>, then pass through oil passages <NUM> through journal shaft <NUM> to the oil pocket <NUM>. The oil passages <NUM> may be configured for feeding oil to the oil pocket <NUM> at a pressure of about <NUM> PSI, although other pressures may be contemplated. The oil may then create a lubricating film between the radially-outer surface <NUM> of the journal shaft <NUM> and the radially-inner surface <NUM> of the sleeve <NUM> (or between the radially-outer surface <NUM> of the journal shaft <NUM> and the one or more gears <NUM> being supported in a sleeveless configuration).

Referring to <FIG>, the oil pocket <NUM> includes a radially inner base surface <NUM>, also referred to as a recessed base surface, that is illustratively concentric with the radially outer surface <NUM> of the journal shaft <NUM>. Other non-concentric base configurations may be contemplated. The oil pocket <NUM> further includes interconnecting transition surfaces <NUM>, illustratively a pair of interconnecting transition surfaces <NUM>, extending between the radially inner base surface <NUM> of the oil pocket <NUM> and the radially outer surface <NUM> of the journal shaft <NUM>. The pair of interconnecting transition surfaces <NUM> provide a fluid-dynamically smooth and edgeless transition between the radially inner base surface <NUM> and the radially outer surface <NUM> of the journal shaft <NUM>. The expression "fluid-dynamically smooth and edgeless transition" as used herein is understood to mean that the junction between the interconnecting transition surfaces <NUM> and the radially outer surface <NUM> does not include sharp or pointed edges. This smooth or seamless design provides a gradual decrease in the pressure gradient between the oil pocket <NUM> and the radially outer surface <NUM> of the journal shaft <NUM>, which may decrease the journal bearing assembly's propensity towards oil-related cavitation damage. The interconnecting transition surfaces <NUM> between the oil pocket <NUM> and the radially outer surface <NUM> of the journal shaft <NUM> may thus be said to be fluid-dynamically smooth.

In previous journal bearing designs, cavitation may occur under operation of the engine at the radially outer surface of the journal shaft in an area localized at the junction between the oil pocket and the radially outer surface. The sharp or pointed edges of these junction points, which may be referred to as fluid-dynamically unsmooth transition surfaces, may cause a notable pressure gradient between the oil pocket and the radially outer surface, which may contribute to a propensity towards cavitation in these previous journal bearing designs.

Referring to <FIG>, the shape of the interconnecting transition surfaces <NUM> may vary to provide the smooth and edgeless transition to the radially outer surface <NUM>. For instance, the axial profile of each interconnecting transition surface <NUM> along the axis A may follow a curve based on a linear function, a polynomial function, a sinusoidal function, or a double radius curve. Other curve types may be contemplated as well. To achieve the fluid-dynamically smooth and edgeless transition between the radially inner base surface <NUM> and the radially outer surface <NUM> of the journal shaft <NUM>, each interconnecting transition surface <NUM> may be tangent to the radially outer surface <NUM> (or nearly tangent) at their junction.

In the embodiment shown in <FIG>, the oil pocket <NUM> may be referred to as an axially-extending oil pocket <NUM> and may be geometrically defined by an overall axial length L1 of the oil pocket <NUM>, an axial length L2 of each interconnecting transition surface, and a radial depth H between the radially outer surface <NUM> of the journal shaft <NUM> and the radially inner base surface <NUM> of the oil pocket <NUM>. Other oil pocket geometries, such as tangentially-extending oil pockets, may be contemplated as well. In the shown case, oil pocket <NUM>, including the pair of interconnecting transition surfaces <NUM>, is symmetric about a longitudinal center C of the journal shaft <NUM>. As such, radial depth H is consistent along the axial length of the radially inner base surface <NUM>, and the axial length L2 for each interconnecting transition surface <NUM> is alike. In other embodiments, the oil pocket's geometry may be asymmetric about the longitudinal center C (or about another reference point), and the two interconnecting transition surfaces <NUM> may be shaped differently, with different axial lengths L2.

The overall axial length L1 and radial depth H may be selected based on the lubrication requirements of the journal bearing assembly <NUM>. For instance, to accommodate additional oil for the journal bearing assembly <NUM>, one or both of the axial length L1 and the radial depth H of the oil pocket <NUM> may be increased. In addition, the axial length L1 may increase proportionally with an overall axial length of the journal bearing <NUM>, as well as based on the number of oil passages <NUM>. Respective values for L1 and H may also be selected along with axial length L2 to provide a smooth and edgeless transition between the radially inner base surface <NUM> and the radially outer surface <NUM> of the journal shaft <NUM>. Other considerations may additionally affect the various dimensions of the oil pocket <NUM>.

The values for axial length L2 may be selected based on the overall axial length L1 of the oil pocket <NUM> and the depth H to provide a smooth and edgeless transition between the radially inner base surface <NUM> and the radially outer surface <NUM> of the journal shaft <NUM>. In an exemplary embodiment, the axial length L2 of each interconnecting transition surface <NUM> may occupy about ten to thirty percent of the overall axial length L1 of the oil pocket <NUM>. Other percentages may be contemplated. The various dimensions of the oil pocket <NUM> may be selected to ensure a tangent line T of each interconnecting transition surface <NUM> does not exceed a maximum angle θ relative to longitudinal axis A. The maximum angle θ is about <NUM> degrees. Preferably, the maximum angle is between about <NUM> to <NUM> degrees. Other maximum angles θ may be contemplated. In other cases, the maximum angle θ may represent an average slope of the tangent line T of each interconnecting transition surface <NUM> rather than a localized maximum angle. The axial length L2 of each interconnecting transition surface <NUM> may thus be selected based on, for instance, the overall axial length L1, the radial depth H, and the maximum tangent angle θ. The function defining the shape of each interconnecting transition surface <NUM> may impact the selected dimensions as well.

Referring to <FIG>, another embodiment of a journal bearing assembly <NUM> according to the present disclosure is shown, with like reference numerals referring to like features. In particular, the various characteristics, options and alternatives of the oil pocket <NUM> shown in <FIG> and described above are also applicable to the oil pocket <NUM> of the journal bearing assembly shown in <FIG>, and vice-versa.

The journal bearing assembly <NUM> may be referred to as a "pin-less" journal bearing assembly <NUM>, as it does not include an insertable pin. Rather, the journal shaft <NUM> is structured to satisfy the functions of the pin <NUM> in the journal bearing assembly <NUM> shown in <FIG>. In particular, lubricating oil is directed directly into the inner cavity <NUM> of the journal shaft <NUM>. The inner cavity <NUM> may thus include an oil inlet (for instance towards one of the axial ends of the inner cavity <NUM>) and an oil outlet (at least one, illustratively two, oil passages <NUM>). The shown oil passages <NUM> extend radially through the journal shaft <NUM> with inlet sections 60a in fluid communication with the inner cavity <NUM> and outlet sections 60b in fluid communication with the oil pocket <NUM> on the radially outer surface <NUM> of the journal shaft <NUM>. In addition, the inner cavity <NUM> may be closed at one or both axial ends by a fastener such as a bolt <NUM> and a washer <NUM>.

It can be appreciated from the foregoing that at least some embodiments disclose a journal bearing assembly having a journal shaft with an oil pocket on a radially outer surface thereof having with smooth and edgeless transitional surfaces, thereby allowing the risk of cavitation damage to various components of the journal bearing to be minimized.

In the present disclosure, when a specific numerical value is provided (e.g. as a maximum, minimum or range of values), it is to be understood that this value or these ranges of values may be varied, for example due to applicable manufacturing tolerances, material selection, etc. As such, any maximum value, minimum value and/or ranges of values provided herein (such as, for example only, the angle of the tangent line of the interconnecting transition surfaces), include(s) all values falling within the applicable manufacturing tolerances. Accordingly, in certain instances, these values may be varied by ± <NUM>%. In other implementations, these values may vary by as much as ± <NUM>%. A person of ordinary skill in the art will understand that such variances in the values provided herein may be possible without departing from the intended scope of the present disclosure, and will appreciate for example that the values may be influenced by the particular manufacturing methods and materials used to implement the claimed technology.

Claim 1:
A journal shaft (<NUM>) for a journal bearing assembly (<NUM>) of an aircraft engine (<NUM>), comprising:
a shaft body extending along a longitudinal axis (A), the shaft body having a radially outer surface (<NUM>) and a radially inner surface (<NUM>) radially spaced apart from the longitudinal axis (A) to define an inner cavity (<NUM>); and
an oil pocket (<NUM>) defined in the radially outer surface (<NUM>), one or more passages (<NUM>) extending through the shaft body from the radially inner surface (<NUM>) to the oil pocket (<NUM>) to provide fluid communication between the inner cavity (<NUM>) and the oil pocket (<NUM>), the oil pocket (<NUM>) including a radially inner base surface (<NUM>) and interconnecting transition surfaces (<NUM>) extending between the radially inner base surface (<NUM>) of the oil pocket (<NUM>) and the radially outer surface (<NUM>) of the shaft body, wherein the interconnecting transition surfaces (<NUM>) form a fluid-dynamically smooth and edgeless transition to the radially outer surface (<NUM>) of the journal shaft (<NUM>),
characterised in that:
the interconnecting transition surfaces (<NUM>) define a tangent line relative to the longitudinal axis (A) with a maximum angle (θ) of about six degrees.