Patent Description:
Circumferential seals are used in machines such as gas turbine engines. A typical engine example is to seal oil and air inside of bearing compartments. Typical seals are segmented carbon seals. Segment ends may interfit to reduce leakage between segments. Or there may be two stages of seal with segment boundaries circumferentially offset. Alternative seal materials being developed include ceramics, plastics and metals.

Seal runners provide the rotating sealing surface (face) the carbon sealing elements sit and seal on. A typical situation has the sealing surface as an outer diameter (OD) surface. Such a sealing surface must remain generally cylindrical (limited "coning" and runout) during all operating conditions in order to provide a good seal and prevent oil leakage. Seal runners are typically a simple metal ring with a shoulder. The seal runner may include a metallic substrate with a hard and coating at the sealing surface. Also, seal material may include a lubricious addition. For example, the seal ring(s) may be at least locally impregnated with a salt or other material to reduce friction.

<CIT>, "Integrated labyrinth and carbon seal", discloses a single-stage carbon seal with shaft-integral seal runner.

<CIT>, "Internally cooled seal runner", discloses a two-stage carbon seal.

<CIT>, "Circumferential flow channel for carbon seal runner cooling", discloses a single-stage carbon seal with labyrinth backup.

<CIT>, "Oil cooled runner", discloses another single-stage carbon seal.

Separately from sealing, such machines may be subject to trim balance procedures. After the rig or engine is at least partially assembled, trim balance weights can be added to balance the rotating components of the engine and reduce operating vibrations. A typical engine will have its rotor formed with one or more integral circumferential arrays of weight mounting features. Exemplary trim balancing is done by running the engine (or otherwise driving rotation of a rotor) and plotting the amplitude and phase angle of the engine response. Then, a trial balance weight is added to the engine rotor at an arbitrary angular location (e.g., a random one of the features). Again, the rotation is driven and the amplitude and phase angle of the engine response with trial weight is plotted. Using this trial weight response, the final location (particular mounting location) and magnitude (weight mass) is determined. The trial weight is removed and the final weight (if within max. weight spec. ) is then added to this calculated location. If calculated weight exceeds a maximum (associated with limiting local flange deformation), a calculated pair or more of weights may be placed at two or more locations centered on the original calculated location.

Trim balance weights are usually placed on compressor/turbine rotors away from the centerline of the engine to provide the maximum level of imbalance correction. This maximizes the effect of a given weight size and allows finer gradations of circumferential position.

A number of different balance weight mounting feature constructions are known. Axially protruding flanges are shown in <CIT>, "Turbine balancing", and <CIT>, "Radial balancing clip weight for rotor assembly". A radially inwardly projecting flange is shown in <CIT>, "Turbomachine rotor balancing system". The '<NUM> patent and the '<NUM> patent illustrate fastening rivets. The `<NUM> patent shows clip-type weights without additional fastener(s).

<CIT> and <CIT> disclose prior art machines comprising a labyrinth seal with a balance assembly.

In one aspect, there is provided a machine as set forth in claim <NUM>.

An optional embodiment may include the sealing section axially overlapping the mounting section.

An optional embodiment may include the first hub and the second hub being angled off-radial in the same direction.

An optional embodiment may include the single metallic piece being a Ti alloy.

An optional embodiment may include the sealing section including a chromium carbide coating.

An optional embodiment may include the mounting section having an inner diameter spline engaging a spline of the inner member.

An optional embodiment may include the spline of the inner member being a castellated rim.

An optional embodiment may include the mounting section having an interference fit with the inner member.

An optional embodiment may include the mounting features each comprising one or more mounting holes. Each of the one or more weights may be mounted via one or more fasteners extending through the one or more mounting holes.

An optional embodiment may include the one or more seal rings being two seal rings.

An optional embodiment may include the mounting features provide <NUM> to <NUM> discrete circumferential mounting locations.

An optional embodiment may include the machine being a turbine engine wherein the inner member is a shaft and the outer member is static structure.

A further aspect includes a method for manufacturing the machine. The method comprises: mounting the seal runner to the inner member; and after the mounting of the seal runner, mounting said one or more weights to said one or more of the mounting features.

An optional embodiment may include the mounting of the seal runner comprising interference fitting.

An optional embodiment may include the mounting of the weights comprising inserting at least one fastener through each of the weights.

A further aspect includes a method for manufacturing or using the machine. The method comprises: rotating the inner member about the axis; measuring vibrational parameters of the rotating inner member; and mounting said one or more balance weights to improve the balance of the inner member.

<FIG> generically shows an example of a gas turbine engine <NUM> having a centerline or central longitudinal axis <NUM>. The example is a turbojet, namely a two-spool turbojet. However, the teachings below may apply to other configurations including turboprops, turbofans, turboshafts, industrial gas turbines, and the like and to other spool arrangements. The engine generally has a case structure (case) <NUM> extending from an upstream inlet <NUM> to a downstream outlet <NUM>. From upstream to downstream, the engine has a plurality of sections: low pressure compressor (LPC) <NUM>, high pressure compressor (HPC) <NUM>, combustor <NUM> (e.g., annular shown or alternatively can-type), high pressure turbine (HPT) <NUM>, and low pressure turbine (LPT) <NUM>. Each of the LPC, HPC, HPT, and LPT comprises one or more stages of blades on the associated low spool or high spool and one or more stages of vanes interspersed with the blade stages. The low spool has a low shaft <NUM> linking the LPT to the LPC and the high spool comprises a high shaft <NUM> linking the HPT to the HPC.

<FIG> shows a seal system <NUM> in the engine <NUM> sealing between an outer member and an inner member mounted for rotation about an axis relative to the outer member. In exemplary engine <NUM>, the axis is the centerline <NUM>. The exemplary inner member is a shaft (e.g., the high shaft <NUM>) and the outer member is fixed/static/grounded structure such as the case <NUM>. The particular exemplary situation places the seal system <NUM> near the forward end <NUM> of the high shaft <NUM>. The exemplary seal system <NUM> is positioned to isolate a first space <NUM> (<FIG>) from a second space <NUM>. The exemplary first space <NUM> is an air cavity between the LPC <NUM> and HPC <NUM> whereas the exemplary second space <NUM> is an oil-wetted bearing compartment. The seal system <NUM> includes a seal housing <NUM> mounted to the outer member. In the illustrated example, an outer section <NUM> of the seal housing <NUM> is mounted in sealed press fit relation with the outer member <NUM> (e.g., inter-section frame <NUM>). Exemplary mounting rotationally keys the seal housing via a radial tab <NUM> of the outer portion <NUM> in an axial slot <NUM> in the inner diameter surface of the receiving compartment of the static member <NUM>. Exemplary axial securing/fastening is via a lock ring <NUM> in a circumferential inner diameter (ID) groove in the surrounding static member <NUM>.

The seal housing <NUM> carries one or more seal rings (e.g., a forward ring <NUM> and an aft ring <NUM>). Exemplary rings <NUM>, <NUM> are segmented carbon rings with intra-segment boundaries (not shown) of the two rings circumferentially offset. The exemplary seal housing <NUM> has an inner section <NUM> carrying the seal rings and radially inwardly spaced from the outer section <NUM> by a web <NUM>. The exemplary inner section <NUM> itself includes a labyrinth <NUM> for further sealing.

The seal rings <NUM>, <NUM> may be retained by conventional means such as a lock ring <NUM> in an inner diameter (ID) groove in the inner section <NUM>. The seal rings each have an inner diameter (ID) surface <NUM> in contacting or facing relationship to an outer diameter surface portion <NUM> of a sealing section <NUM> of a seal runner <NUM> mounted to the inner member.

As so far described, the seal system <NUM> may be representative of any of numerous existing configurations. However, the seal system <NUM> integrates a balanced system <NUM>. The balance system comprises a circumferential array of mounting features <NUM> on the seal runner <NUM>. For balancing, one or more weights <NUM> are mounted to one or more of the mounting features <NUM>. Exemplary mounting features comprise mounting holes <NUM>. An exemplary mounting system involves one hole <NUM> per mounting feature (and thus circumferential weight mounting location) with the holes <NUM> evenly circumferentially spaced. An exemplary number of holes is twelve to sixty (or narrowly twelve to thirty-six with an exemplary eighteen). Although these exemplary numbers provide a relatively even intervals measured in degrees (e.g., sixty holes representing a six degree interval) other values are possible. Typically, only a small number (if any) of the features will bear weights (e.g., one to three total weights).

The exemplary holes <NUM> are formed extending radially through a balancing section <NUM> of the seal runner <NUM>. The exemplary balancing section <NUM> is axially spaced from the sealing section <NUM>. In the exemplary implementation, it is spaced forward of the sealing section <NUM>. The exemplary seal runner <NUM> also includes a mounting section <NUM>. The mounting section <NUM> extends from a forward end (rim) <NUM> to an aft end <NUM> and has an inner diameter (ID) surface <NUM> and an outer diameter (OD) surface <NUM>. A first hub <NUM> extends between the mounting section <NUM> and the sealing section <NUM> and a second hub <NUM> extends between the mounting section <NUM> and the balancing section <NUM>. The exemplary first hub <NUM> is an aft hub extending from near the aft end <NUM> of the mounting section <NUM> radially outwardly and forwardly to merge with a forward end <NUM> portion of the sealing section <NUM> so as to leave the remainder of the sealing section axially cantilevered aftward to a free distal aft end <NUM>. This allows a flow <NUM> of cooling fluid (e.g., oil) to flow from axially forward of seal ring <NUM> to axially aft of sealing ring <NUM> to dissipate heat in sealing section <NUM>. Similarly, the second hub <NUM> also extends radially outwardly and forwardly to merge with an aft end <NUM> of the balancing section <NUM>.

The balancing section <NUM> extends to a free distal forward end <NUM>. At this forward end <NUM>, the balancing section has a radially inwardly extending flange <NUM> extending to an inner diameter (ID) rim <NUM>. The flange <NUM> provides structural reinforcement as discussed below. At the junction of the forward hub <NUM> and balancing section <NUM>, a second flange <NUM> extends radially inward to a rim <NUM> and has a forward face <NUM>. As is discussed further below, this second flange <NUM> also provides structural reinforcement but also provides a portion of the mounting features. The balancing section <NUM> has an inner diameter (ID) surface <NUM> (<FIG>) and an outer diameter (OD) surface <NUM> with the holes <NUM> extending radially therebetween. The exemplary weights <NUM> are positioned radially inboard of the ID surface <NUM>, each having an outer diameter (OD) surface or end <NUM> abutting the ID surface <NUM>. The weights further have an inner diameter (ID) surface or end <NUM>. The exemplary weights have a square footprint or planform characterized by a forward face or end <NUM>, an aft face or end <NUM>, and first and second circumferential end faces <NUM> and <NUM> (<FIG>).

The aft face <NUM> (<FIG>) abuts the forward face <NUM> of the second flange <NUM> to register the weight <NUM>. For fastening via a fastener <NUM>, the weight <NUM> has a radial bore (e.g., a through-bore) <NUM>. The exemplary through-bore is threaded such as via a self-locking thread insert <NUM> (to prevent fastener <NUM> (a threaded fastener such as a screw or bolt) from backing out during operation) in a metallic body of the weight. The exemplary weights are steel or nickel alloys. The exemplary fastener <NUM> is a bolt (e.g., flanged twelve-point bolt shown or hex- or socket-head bolt) whose head underside abuts the OD surface <NUM> and whose threaded shank extends through the hole <NUM> into the threaded bore <NUM> of the weight to secure the weight OD end <NUM> against the ID surface <NUM>. Alternative fasteners (not shown) used with unthreaded bores may be rivets. Alternative weights may include separate or integral clips for mounting and may reflect any appropriate existing balance weight mounting technology. For example, it may be particularly appropriate to use similar weights or mounting technologies on the seal runner as are used elsewhere in the engine or as may be used in other engines of the given manufacturer.

<FIG> also shows aspects of anti-rotation coupling of the seal runner <NUM> to the shaft <NUM>. The exemplary anti-rotation coupling involves splines <NUM> of the mounting section <NUM> circumferentially interdigitated with castellations <NUM> of the forward rim <NUM> of the shaft <NUM>. To define the castellations <NUM>, slots between the castellations fully separate the castellations. Alternative implementations may leave some inner diameter (ID) material intact so that the castellations become more conventional outer diameter (OD) splines.

The exemplary splines <NUM> are adjacent the forward end <NUM> (<FIG>) of the mounting section <NUM>. For stability, adjacent the aft end <NUM>, there may be an interference fit at an aft contact location <NUM> between the ID surface <NUM> along an inner diameter (ID) protrusion <NUM> and the shaft <NUM> OD surface along a corresponding outer diameter (ID) protrusion <NUM>. Similarly, there may be an interference at a forward contact location <NUM> aft of the splining leaving a gap <NUM> intermediate the contact locations <NUM> and <NUM>.

Manufacture/techniques may be those corresponding to existing seal manufacture techniques and balance weight manufacture techniques. The seal housing <NUM> and seal runner <NUM> (or substrate <NUM> (<FIG>) thereof) may be machined of an alloy (e.g., a titanium alloy such as Ti6Al4V). The machining may include a general turning operation to define the overall profile combined with drilling of the holes <NUM> and milling (e.g., end milling) of slots to separate the splines <NUM>. Conventional protective coatings (not shown) may be provided. Additionally, a wear-resistant hard coating <NUM> (<FIG> - e.g., chromium carbide) may be applied to the metallic substrate <NUM> of the seal runner to form the surface <NUM> (e.g., via spraying such as thermal spraying).

Installation of the seal runner may be via a press-fit and/or a thermal interference fit (e.g., heating the seal runner and/or cooling the shaft <NUM>) to allow the seal runner mounting section <NUM> to be slid onto the shaft <NUM> and nest the castellations <NUM> and splines <NUM>. For further securement and retention, <FIG> shows a circumferential lock ring <NUM> extending through an inner diameter groove in the castellations <NUM> and splines <NUM>.

As noted above, the flanges <NUM> and <NUM> add structural integrity to maintain circularity of the balancing section <NUM> under circumferential loads including the centrifugal load of the weight(s). As with conventional balancing, there may be multiple sizes of weights <NUM> (e.g., an exemplary two to four). <FIG> shows a single large weight <NUM> at a twelve o'clock position (clearly as the engine rotates the position will change). <FIG> shows how two different weights <NUM>' may be circumferentially spaced. In conventional balancing, two smaller weights <NUM>' at two adjacent holes effectively simulate a larger weight at a non-existent mounting location between such two holes.

As rotor speeds increase with new technologies (e.g., higher strength alloys capable of handling the radial pull), the requirements for engine imbalance will become more stringent to reduce engine vibrations to a minimum. Thus it may be advantageous to use the seal runner to add balancing beyond existing balance locations (planes on a given spool). Because seal runners are typically at the outermost area of each bearing compartment, they are often accessible during assembly/balancing. Depending on engine architecture, if the compressor/turbine rotor area is inaccessible, the seal runner could provide an alternate area to add trim balance weights in place of an existing area (existing on a baseline engine or, more generally on alternative engines). Furthermore, local balancing near the seal may improve seal life.

In an example of three different weight sizes, it may be easy to provide several options to counteract both the imbalance's amplitude and phase in the engine. After rotating the rotor or spool to find the as-is response, then adding a trial weight at an arbitrary location, the final magnitude and angle of the final correction can be found. For example, a target correction could be at <NUM>-degrees and <NUM> oz-in (<NUM> mNm). A single available large weight <NUM> could be too great and a single available small weight <NUM>' could be too small. For example, one large weight <NUM>, mounted at <NUM>-degrees would produce <NUM> oz-in (<NUM> mNm) of correction; one small weight <NUM>' mounted at <NUM>-degrees would produce <NUM> oz-in (<NUM> mNm) of correction; but two small weights <NUM>' mounted at <NUM>-degrees and <NUM>-degrees would produce the desired <NUM> oz-in (<NUM> mNm) of correction at <NUM>-degees.

The axial spacing of contact locations <NUM> and <NUM> may be selected to create a long wheelbase of the mounting section <NUM> for the supporting the sealing section <NUM>. Any deflection or radial offset (e.g., even due to machining tolerance and not limited to dynamic deflection) between centers of <NUM> and <NUM>, causing a slope between mounting section <NUM> and rotor centerline <NUM> would translate to a similar slope in the sealing section <NUM>. If the contact locations <NUM> and <NUM> were closer together, an identical radial offset would produce a greater slope difference between the rotor centerline <NUM>. The sealing performance is impacted by the deviation in the axis of rotation of the seal runner to the rotor centerline. Thus, the axial offset between contact locations <NUM> and <NUM> helps address this. An exemplary length of the gap <NUM> is <NUM> to <NUM>% of a diameter (more narrowly, <NUM> to <NUM>%) of the shaft at one or both of the contact locations <NUM> and <NUM>.

The forward hub <NUM> may be optimized to provide at least a small amount of local deflection in and around the balancing feature <NUM>. The small axial undercut <NUM> radially outward of the forward end <NUM> creates a hinge point for any radial deflections seen in the balancing feature <NUM>. This helps to isolate deflections in the balancing feature <NUM> from passing to the mounting section <NUM> and therefrom to the sealing area <NUM>. Flanges <NUM> and <NUM> help maintain balancing section <NUM> circularity and resist outward radial flaring Cross section flexing outward about the aft end <NUM>) exceeding the stress capabilities of the material.

To further limit deflection in the sealing area <NUM>, the area radially outward of contact location <NUM> and protrusion <NUM> creates a second hinge point for any radial deflections seen in the forward area of mounting section <NUM> caused by the centrifugal force of the weights <NUM>. Radially outward from the hinge point, hub <NUM> may be optimized to provide support/stiffness and helps to maintain cylindricity/circularity of sealing section <NUM>.

This deflection isolation does not necessarily isolate the rotating member (e.g., shaft, spool) from the force generated by the balance weights <NUM>, <NUM>', because the seal runner is interference-fit and anti-rotation mounted on the shaft. So the centrifugal pull from the weights would still be seen at the shaft.

The hub configuration discussed above results in an axial overlap of the sealing section <NUM> and the mounting section <NUM> caused by having the slope of the aft hub <NUM> forming a z-shaped local cross section with the mounting section <NUM> and sealing section <NUM>. Thus, in the example, both seal rings are fully within the axial span of the mounting section.

The exemplary hubs <NUM> and <NUM> are at identical angles θ<NUM> and θ<NUM> off axial to make machining easier. Thus only one tooling angle needs to be set when turning on a lathe. The angle on the aft side of <NUM> allows cooling fluid flow <NUM> to travel forward to cool the sealing section <NUM> adjacent both seal rings <NUM> and <NUM>. Exemplary θ<NUM> and θ<NUM> are <NUM>° to <NUM>°, more narrowly <NUM>° to <NUM>°.

Claim 1:
A machine comprising:
an outer member;
an inner member mounted for rotation about an axis (<NUM>) relative to the outer member; and
a seal system (<NUM>) comprising:
a seal housing (<NUM>) mounted to the outer member;
one or more seal rings (<NUM>, <NUM>) held by the seal housing (<NUM>) and having an inner diameter surface (<NUM>); and
a seal runner (<NUM>) mounted to the inner member and having a first outer diameter surface portion (<NUM>) contacting or facing the inner diameter surface (<NUM>) of the one or more seal rings (<NUM>, <NUM>),
wherein:
the seal runner (<NUM>) has a circumferential array of mounting features (<NUM>); and
one or more weights (<NUM>) are mounted to one or more of the mounting features (<NUM>);
wherein the seal runner (<NUM>) has:
a mounting section (<NUM>) mounted to the inner member;
a sealing section (<NUM>) including the first outer diameter surface portion (<NUM>) radially outwardly spaced from the mounting section (<NUM>);
a first hub (<NUM>) between the mounting section (<NUM>) and the sealing section (<NUM>), wherein the first hub (<NUM>) is an aft hub extending from near an aft end (<NUM>) of the mounting section (<NUM>) radially outwardly and forwardly to merge with a forward end portion (<NUM>) of the sealing section (<NUM>) so as to leave the remainder of the sealing section (<NUM>) axially cantilevered aftward to a free distal aft end (<NUM>);
a balancing section (<NUM>) including the mounting features (<NUM>); and
a second hub (<NUM>) between the mounting section (<NUM>) and the balancing section (<NUM>), the second hub (<NUM>) extending radially outwardly and forwardly to merge with an aft end (<NUM>) of the balancing section (<NUM>),
wherein the mounting section (<NUM>), the sealing section (<NUM>), the first hub (<NUM>), the balancing section (<NUM>), and the second hub (<NUM>) are formed on a single metallic piece, and
wherein the one or more seal rings (<NUM>, <NUM>) are carbon seal rings.