Patent Description:
Advanced high performance engines, such as those used in commercial jetliners, utilize main shaft bearing compartment seals to seal a main shaft bearing compartment and minimize lubricant from escaping the bearing compartment. Carbon seals are typically used for this purpose, and enable the engine and bearing compartment to function with minimal impact on the thrust specific fuel consumption, thermal management system, or the lubrication system.

Existing engine main shaft seals experience elevated occurrences of anti-rotation slot wear and sporadic anti-rotation sleeve/pin wear (alternately referred to as notching). These wear conditions have a negative impact on the reliability metrics of an engine incorporating the existing engine main shaft seals. Existing engine main shaft seals utilize hard chrome plating to minimize wear conditions. The hard chrome plating has a negative impact on current Green Engine Materials of Concern metrics.

A seal arrangement having the features of the preamble of claim <NUM> is disclosed in <CIT>. Other seal arrangements having anti-rotation pin assemblies are disclosed in <CIT> and <CIT>.

The present invention provides a seal arrangement for a turbine engine, as set forth in claim <NUM>.

In an embodiment of the foregoing seal arrangement for a turbine engine, the sleeve contacts the elongated seal carrier contact surface.

In a further embodiment of the foregoing seal arrangement for a turbine engine, an exterior surface of the sleeve and an exterior surface of the pin body have a reduced roughness relative to a roughness of the elongated seal carrier content surface roughness, thereby minimizing sleeve and pin notching.

In a further embodiment of the foregoing seal arrangement for a turbine engine, each of the anti-rotation pin assemblies is characterized by an absence of chrome plating.

In a further embodiment of the foregoing seal arrangement for a turbine engine, the seal carrier includes a single failure mode, and the single failure mode is slot wear.

In a further embodiment of the foregoing seal arrangement for a turbine engine, the elongated seal carrier contact surface has an axial length longer than an axial length of a support portion of the seal carrier.

The fan section <NUM> drives air along a bypass flowpath while the compressor section <NUM> drives air along a core flowpath for compression and communication into the combustor section <NUM> then expansion through the turbine section <NUM>. Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures.

The engine <NUM> generally includes a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A relative to an engine static structure <NUM> via several bearing systems <NUM>. It should be understood that various bearing systems <NUM> at various locations may alternatively or additionally be provided.

The inner shaft <NUM> is connected to the fan <NUM> through a geared architecture <NUM> to drive the fan <NUM> at a lower speed than the low speed spool <NUM>. A combustor <NUM> is arranged between the high pressure compressor <NUM> and the high pressure turbine <NUM>.

The mid-turbine frame <NUM> includes airfoils <NUM> which are in the core airflow path.

The engine <NUM> is, in one example, a high-bypass geared aircraft engine. In a further example, the engine <NUM> bypass ratio is greater than about six (<NUM>), with an example embodiment being greater than ten (<NUM>), the geared architecture <NUM> is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM> and the low pressure turbine <NUM> has a pressure ratio that is greater than about <NUM>. In one disclosed embodiment, the engine <NUM> bypass ratio is greater than about ten (<NUM>:<NUM>), the fan diameter is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about <NUM>:<NUM>. The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>.

The fan section <NUM> of the engine <NUM> is designed for a particular flight condition -- typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>). The flight condition of <NUM> Mach and <NUM>,<NUM> ft (<NUM>), with the engine at its best fuel consumption - also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')" - is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about <NUM> ft / second (<NUM>/s).

<FIG> illustrates a front view of a turbine engine <NUM> main shaft seal arrangement <NUM>. The main shaft seal arrangement <NUM> includes a housing <NUM> surrounding a seal carrier <NUM>. Disposed within the seal carrier <NUM> is a seal <NUM> such as a carbon seal. The seal <NUM> is at least approximately circular and seals a main shaft bearing compartment of the turbine engine <NUM>. The seal carrier <NUM> is prevented from rotating about the engine centerline axis A via two anti-rotation pin assemblies <NUM>, <NUM> that interface with the seal carrier <NUM>. The anti-rotation pin assemblies <NUM>, <NUM> are each positioned in a corresponding anti-rotation slot <NUM>, <NUM> of the seal carrier <NUM>. Two assembly guide pins <NUM>, <NUM> further aid in prevention of damage or disengagement of the seal assembly during handling or installation of the seal into the turbine engine <NUM>. Each of the assembly guide pins <NUM>, <NUM> are positioned in assembly guide slots <NUM>, <NUM>.

The seal carrier <NUM> is positioned axially relative to the housing <NUM> using multiple springs (illustrated in <FIG>). The springs are spaced circumferentially about the seal carrier <NUM> and interfaces with the seal carrier <NUM> via multiple spring fastener features <NUM> (or guides). The springs provide axial loading to maintain contact between the seal <NUM> and a rotating sealplate,that is part of the spool or shaft assembly.

<FIG> illustrates a cross sectional side view of the main shaft seal arrangement <NUM> of <FIG>. The seal carrier <NUM> includes a primary body portion <NUM> that holds a seal <NUM> in place. Extending radially outward from the primary body portion <NUM> of the seal carrier <NUM> is an anti-rotation slot <NUM>, <NUM>. An anti-rotation pin assembly <NUM> is positioned within the anti-rotation slot <NUM>, <NUM> and prevents the seal carrier <NUM> from rotating about the engine centerline axis A. The anti-rotation slot <NUM>, <NUM> includes an axially elongated section <NUM>. The axially elongated section <NUM> provides a greater surface area for contact between the anti-rotation pin assembly <NUM> and the anti-rotation slot <NUM>, <NUM>. The larger contact surface area resulting from the elongated section <NUM> reduces the contact pressure placed on the contact surface by the anti-rotation pin assembly <NUM> by spreading the load over a greater area. Reducing the contact pressure in turn decreases the rate at which the anti-rotation pin assembly <NUM> wears the contact surface and increases the lifespan of the seal arrangement <NUM>.

The seal carrier <NUM> also includes multiple receiving slots for receiving the assembly guide pins <NUM> illustrated in <FIG>. The assembly guide slots <NUM>, <NUM> do not include the illustrated elongated section <NUM>. Inclusion of the elongated section <NUM> in the assembly guide slots <NUM>, <NUM> is unnecessary because the assembly guide pins <NUM> do not contact the seal carrier <NUM> after assembly is completed, unless the seal carrier <NUM> is already in a failure mode.

<FIG> illustrates an isometric sectional view of a main engine shaft seal arrangement. As with the previously described examples of <FIG>, a main engine shaft seal <NUM> is circumferentially surrounded by a seal carrier <NUM>. The seal carrier <NUM> is loaded axially using multiple springs <NUM>. Each of the springs interfaces with, or is guided by, a spring retention feature <NUM> on the seal carrier <NUM> on one axial end of the spring <NUM> and contacts the housing <NUM> on an opposite axial end <NUM> of the spring <NUM>.

The seal carrier <NUM> includes two approximately identical anti-rotation slots <NUM>. A first anti-rotation slot <NUM> is illustrated in <FIG>, and the other anti-rotation slot <NUM> is disposed <NUM> degrees apart from the first anti-rotation slot <NUM> such that the two anti-rotation slots <NUM> are opposing each other. Each anti-rotation slot <NUM> includes at least one axially elongated axial contact surface <NUM>. The illustrated example includes two facing axially elongated contact surfaces <NUM> in each anti-rotation slot <NUM>. The axially elongated contact surface <NUM> is elongated along the engine centerline axis A (illustrated in <FIG> and <FIG>) relative to a support portion <NUM> of the seal carrier <NUM>.

An anti-rotation pin assembly <NUM> is positioned in the anti-rotation slot <NUM>. The anti-rotation pin assembly <NUM> includes a central anti-rotation pin <NUM> radially surrounded by a sleeve <NUM>. The sleeve <NUM> abuts a pin feature <NUM> on one end and an anti-rotation pin cap <NUM> on an opposite end. The anti-rotation pin cap <NUM> is connected to the end of the pin <NUM> using any known fastening technique. The pin feature <NUM> and the anti-rotation pin cap <NUM> maintain the sleeve <NUM> in position about the anti-rotation pin <NUM> and maintain the pin in the pin retention slot. The anti-rotation pin assembly <NUM> is rigidly fixed to the housing on one end and contacts each of the elongated axial contact surfaces <NUM> along a sleeve surface <NUM>. The axial retention pin cap <NUM> prevents the seal carrier <NUM> from moving axially out of position.

When a tangential vector force is applied to the seal <NUM>, the force is transferred to the seal carrier <NUM>, causing the seal carrier <NUM> to rotate and the pin sleeve <NUM> to contact the axially elongated contact surface <NUM>. The anti-rotation pin assembly <NUM> prevents the seal carrier <NUM> from continuing to rotate about the engine centerline axis A after the pin sleeve <NUM> contacts the axially elongated contact surface <NUM>. During operation of the turbine engine <NUM>, the engine parts expand and contract causing the parts to axially shift. To facilitate this axial shifting, the springs <NUM> compress or extend in order to maintain a desired axial load. A greater contact surface area between the sleeve walls <NUM> and the axially elongated contact surface <NUM> results in a lesser wear of the contact surface <NUM>. The axial length of the axially elongated axial contact surface <NUM> is maximized within allowable tolerances. In one example, the axially elongated contact surface <NUM> has an axial length equal to an axial length from an edge of the seal carrier <NUM> to the housing <NUM> minus an axial movement tolerance of the seal carrier <NUM>.

In a standard configuration, this type of rubbing can result in two possible wear patterns, each with its own associated failure mode. In one wear pattern, the seal carrier <NUM> wears into the anti-rotation pin assembly <NUM> in a wear process referred to as "notching". Notching can result in a sudden and dramatic failure. In the opposite wear pattern, the sleeve <NUM> wears into the axially elongated contact surface <NUM> in a wear process referred to as "slot wear. " Slot wear occurs over a longer period of time, and does not result in sudden or dramatic failure. Thus, slot wear is a more benign failure mode than notching.

In order to ensure that the seal carrier arrangement enters the more benign slot wear failure mode when a failure occurs, the pin sleeve <NUM> is constructed of a material that is hard relative to the axially elongated contact surfaces <NUM>. Furthermore, the surface texture or roughness is targeted to encourage the sleeve <NUM> to resist wear more than the slot <NUM>. By ensuring that the pin sleeve <NUM> is harder than the axially elongated contact surfaces <NUM>, and the roughness are appropriately targeted, the arrangement ensures that the pin sleeve <NUM> will abrade the axially elongated contact surface <NUM>, rather than vice versa, when rubbing between the pin sleeve <NUM> and the axially elongated contact surface <NUM> occurs. Another factor that can affect the failure mode is contact between a guide pin and the corresponding pin slot. With this in mind, the circumferential clearance of the pin slot is set to avoid pin notching failure mode by increasing the clearance between the pin and the pin slot as much as possible.

Previous designs utilized a chrome based plating to reduce wear between the sleeve <NUM> and the axially elongated contact surface <NUM>. The manufacturing processes utilized to chrome plate the sleeve <NUM> and the axially elongated contact surfaces <NUM> negatively impacts current Green Engine Materials of Concern metrics, and as such chrome plating is an undesirably wear solution.

An example process used to reduce the wear in place of the chrome plating is controlling the roughness of the contacting surfaces <NUM>, <NUM>. The roughness of both the seal carrier sleeve <NUM> and the axially elongated contact surfaces <NUM> is controlled to encourage minimal wear of the sleeve <NUM>, thereby reducing the wear from contact rubbing between the axially elongated contact surface <NUM> and the anti-rotation pin sleeve <NUM>.

<FIG> illustrates an isometric sectional view of a main engine shaft seal assembly guide pin slot <NUM>, not forming part of the present invention. Unlike the anti-rotation pin assembles <NUM> illustrated in <FIG>, assembly guide pins <NUM> are a single assembly guide pin <NUM> component connected on one axial end to a housing <NUM> and extending through an assembly guide pin slot <NUM>. The assembly guide pin <NUM> does not contact the assembly guide pin slot <NUM> during operation unless the seal assembly <NUM> has entered a failure mode. As a result of the lack of contact, the assembly guide pin <NUM> does not typically wear against the slot surfaces <NUM> until a failure has already occurred. The hardness and surface roughness of the slot and pin are also optimized to avoid the failure mode of pin notching.

While the above illustrated example is described with regards to two opposing anti-rotation pins, it is understood that additional anti-rotation pin assemblies can alternately be used to the same effect.

Claim 1:
A seal arrangement for a turbine engine comprising:
an at least approximately circular seal (<NUM>);
a seal carrier (<NUM>) disposed about said seal, wherein said seal carrier (<NUM>) maintains said seal (<NUM>) in a position;
a housing (<NUM>) surrounding said seal carrier (<NUM>), wherein said seal carrier (<NUM>) is maintained in axial position relative to said housing (<NUM>) via a plurality of springs (<NUM>), wherein the springs (<NUM>) are spaced circumferentially about the seal carrier (<NUM>) and interface with the seal carrier (<NUM>) via spring retention features (<NUM>);
a plurality of anti-rotation pin assemblies (<NUM>) and a plurality of anti-rotation slots (<NUM>), the anti-rotation pin assemblies (<NUM>) rigidly connected to said housing (<NUM>) on a first end and each anti-rotation pin assembly (<NUM>) received in a corresponding anti-rotation slot (<NUM>) of said seal carrier (<NUM>) on a second end, wherein said anti-rotation pin assemblies (<NUM>) are aligned axially with said seal carrier (<NUM>) and said seal (<NUM>); and
wherein each of said anti-rotation slots (<NUM>) comprises an axially elongated seal carrier contact surface (<NUM>) contacting a corresponding one of the anti-rotation pin assemblies (<NUM>), wherein each of said anti-rotation pin assemblies (<NUM>,<NUM>) comprises a pin body (<NUM>), a sleeve (<NUM>) disposed about said pin body (<NUM>) and an end cap (<NUM>) connected to said pin body (<NUM>), wherein said pin body and said end cap (<NUM>) are arranged such that said sleeve (<NUM>) cannot be removed while said end cap (<NUM>) is attached to said pin body (<NUM>); characterised in that
said sleeve (<NUM>) and said pin body (<NUM>) are each constructed of a material that is hard relative to said axially elongated seal carrier contact surface (<NUM>).