Patent Description:
Various types of machines include rotating parts that operate in an environment where different internal areas are preferably sealed relative to one another. Machinery such as turbomachines, including gas turbine engines, may include rotating components such as a fan, a compressor, and a turbine. Rotor shafts may connect the rotating components, forming a rotor group or spool. Various sealing apparatus are used in the rotating equipment, such as to retain oil within lubricated compartments, to prevent oil from entering unwanted areas, and/or to separate different pressurized areas. Some of the parts may rotate at very high speeds, and other machine operating states may subject the seals to extreme environmental conditions.

Some turbomachines include two or more coaxial rotor shafts, for example a high pressure turbine (HPT) shaft and a low pressure turbine (LPT) shaft. Various areas within turbomachines may include oil, which is preferably maintained in its intended spaces by the seals. When the faces of these seals are loaded, such as due to differential pressures within the machine, undesirable effects such as heat and wear may be generated. Providing effective sealing becomes more challenging when the operational bandwidth of machines is extended, which may produce more extreme conditions. A prior art sealing system according to the preamble of claim <NUM> is known from <CIT>.

Accordingly, it is desirable to provide systems that provide effective sealing between different internal areas of a machine with rotating parts, while delivering improved performance characteristics. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. The sealing system according to the invention is defined in claim <NUM>.

This brief summary is provided to describe select concepts in a simplified form that are further described in the Detailed Description section.

Noncontacting intershaft seal systems as disclosed herein, may include force generating mechanisms to reduce unwanted contact related effects. In a number of embodiments, a sealing system includes an outer shaft that has a hollow interior. An inner shaft extends through the hollow interior of the outer shaft. Spaced apart end plates encircle and rotate with the inner shaft. A gland opening is defined between the inner and outer shafts and between the end plates. A ring is disposed in the gland opening. The end plates include force generating elements that generate desirable forces to separate the ring from the end plates, reducing contact related heat generation and wear.

In a number of additional embodiments, a sealing system includes an outer shaft having a hollow interior. An inner shaft extends through the hollow interior of the outer shaft. One end plate encircles the inner shaft and rotates with the inner shaft within the hollow interior. Another end plate encircles the inner shaft and rotates with the inner shaft within the hollow interior. A spacer encircles the inner shaft and axially spaces the end plates. A gland opening is defined in an area between the inner and outer shafts and between the end plates. A split ring is disposed in the gland opening and operates to expand during rotation to engage and rotate with the outer shaft. The end plates include force generating elements that generate forces acting to separate the split ring from the end plates.

In a number of other embodiments, a sealing system includes an outer shaft having a hollow interior. An inner shaft extends through the hollow interior of the outer shafts. The inner and the outer shafts rotate relative to one another. A pair of end plates encircle the inner shaft and rotate with the inner shaft within the hollow interior. A spacer encircles the inner shaft and axially spaces the end plates. A gland opening is defined between the inner and outer shafts and between the end plates. A split ring is disposed in the gland opening and is configured to expand in response to rotationally generated forces to engage and rotate with the outer shaft. The split ring is not fixed to the outer shaft. The end plates include force generating magnets configured to generate forces acting to separate the split ring from the end plates. The split ring includes a series of magnets configured to repel both of the force generating magnets. The split ring comprises a low friction material, including in areas disposed between the series of magnets and the end plates. The end plates each include a section of material that is disposed between the force generating magnets and the split ring. The areas of low friction material and the sections of material separate the magnetic elements from adjacent components.

In the following description, a system provides sealing between relatively rotating shafts while minimizing the effects of contact between parts. A sealing system includes an inner shaft extending through the hollow interior of an outer shaft. Axially spaced plates between the shafts define a gland opening. A ring, which may be split and not fixed to either shaft, is disposed in the gland opening. The ring may be configured to expand under the effects of rotation to engage and rotate with the outer shaft. Both of the plates include include force generating elements, such as magnetic elements and/or hydrodynamic elements (not claimed), to generate forces that act to keep the ring separated from the plates during operationally induced axial excursions of the shafts. Maintaining separation may reduce heat generation and wear leading to longer service lives and other desirable outcomes. For example, if contact does occur, the resulting heat generated and parasitic loss will be minimized. As a result, higher operating speeds and maximum pressures may be achieved that would otherwise be impractical.

In the examples given herein, a noncontacting intershaft seal system is described in association with an aircraft gas turbine engine, but the disclosure is not limited in utility to such applications. In the example of a gas turbine engine, the environment is challenging with pressure loadings potentially leading to wear and service life limitations. Accordingly, a noncontacting seal system is useful to reduce wear and extend service life. The current disclosure is applicable to other applications when noncontacting seal systems are also useful in rotating structures, including in high temperature environments. So, although described in the aircraft context, various features and characteristics disclosed herein may be used in other contexts and applications where a noncontacting seal system is useful, including intershaft applications. For example, various other engine environments, as well as different types of rotating machinery will benefit from the features described herein. Thus, no particular feature or characteristic is constrained to an aircraft or a gas turbine engine, and the principles are equally embodied in other vehicles, or in other equipment, and in other applications.

As noted above, the noncontacting seal systems described herein may be employed in a variety of applications. By way of an exemplary embodiment as illustrated in <FIG>, an engine <NUM> is configured as a gas turbine engine for aircraft propulsion. The engine <NUM> includes an intake <NUM>, with a fan section <NUM> disposed in a fan case <NUM>. The fan section <NUM> draws air into the engine <NUM> and accelerates it. The air is directed through plural paths, such as one to the engine core <NUM>, and another through a bypass duct <NUM>. A compressor section <NUM> compresses the air delivered to the engine core <NUM> and sends it to a combustion section <NUM>. In the combustion section <NUM> the air is mixed with fuel and ignited for combustion. Combustion air is directed into a turbine section <NUM>. The hot, high-speed air flows within the turbine case <NUM> and over the turbine blades <NUM> which spin on shafts <NUM>, <NUM> about an axis <NUM>. The air from the turbine section <NUM> rejoins that from the bypass duct <NUM> and is discharged through an exhaust section <NUM> including through a propulsion nozzle <NUM>.

The axis <NUM> defines an axial direction <NUM>, with a radial direction <NUM> projecting from the axis <NUM> and normal thereto. One of both of the shafts <NUM>, <NUM> may rotate, and each may rotate in either direction relative to the other. The shaft <NUM> has a hollow interior and is configured as an outer shaft, with the shaft <NUM> extending through the hollow interior and configured as an inner shaft. The shafts <NUM>, <NUM> are rotatable relative to one another and as result, the shafts <NUM>, <NUM> define a gap <NUM> between them.

The turbine section <NUM> includes one or more turbines. In the depicted embodiment, the turbine section <NUM> includes two turbines, a high-pressure turbine <NUM>, and a low-pressure turbine <NUM>. However, it will be appreciated that the engine <NUM> may be configured with a different number of turbines. As the rotors of the turbines <NUM>, <NUM> rotate, they drive equipment in the engine <NUM> via the concentrically disposed shafts <NUM>, <NUM> and are configured as spools. Specifically, the high-pressure turbine <NUM> may drive the compressor section <NUM> via a high-pressure spool <NUM> including the shaft <NUM>, and the low-pressure turbine <NUM> may drive the fan section <NUM> via a low-pressure spool <NUM> including the shaft <NUM>. In the case of the low-pressure turbine <NUM>, the rotor is omitted for simplicity.

The gap <NUM> may contain a number of seal assemblies, including, for example, seal assembly <NUM>. The seal assembly <NUM> seals an area <NUM> of a gas such as air from an area <NUM> that may be lubricated and may contain a gas such as air with some oil content. The areas <NUM>, <NUM> may have pressure fluctuations, and may be at different pressure levels from one another. With additional reference to <FIG>, an area around the seal assembly <NUM> is schematically illustrated and is removed from the engine <NUM> for clarity. The shaft <NUM> is disposed along the axis <NUM> around which it may rotate. The shaft <NUM> includes an inner wall <NUM> defining a hollow interior <NUM>. The shaft <NUM> is also disposed on the axis <NUM> around which it may rotate. The shaft <NUM> extends through the hollow interior <NUM> defining the gap <NUM> as an elongated annular space between the shafts <NUM>, <NUM>. The seal assembly <NUM> is disposed in the gap <NUM> to seal the area <NUM> from the area <NUM>. In a number of embodiments, the area <NUM> is adjacent the compressor section <NUM> and so may generally be at higher pressures than the area <NUM>.

In general, the seal assembly <NUM> includes an end plate <NUM> adjacent the area <NUM>, and an end plate <NUM> adjacent the area <NUM>. The end plate <NUM> is spaced from the end plate <NUM> by a spacer <NUM> defining a gland opening <NUM>. A ring, designated as split ring <NUM>, is disposed in the gland opening <NUM>. The end plates <NUM>, <NUM> and the spacer <NUM> are disposed to move, if at all, with the shaft <NUM>. For example, they may be press-fit and/or keyed onto, or otherwise fixed to the shaft <NUM> to rotate therewith. The end plates <NUM>, <NUM> and the spacer <NUM> may be made of a nonmagnetic material such as a nickel-chromium alloy. The split ring <NUM> is not fixed to either the shaft <NUM> or the shaft <NUM>, and is expandable under rotationally induced centrifugal forces to frictionally engage the shaft <NUM> to rotate therewith. The split ring <NUM> may be made of a low friction material such as a carbon containing material. Preferably, the split ring <NUM> is maintained in the gland opening <NUM> between the end rings <NUM>, <NUM>, without contacting either of the end rings <NUM>, <NUM> during operation of the engine <NUM>.

It has been found that contact during high speed relative rotation of the shafts <NUM>, <NUM> may lead to heat and wear that if significant enough, may result in reduced service life. For example, translation of the shafts <NUM>, <NUM> relative to one another along the axis <NUM> during axial excursions may occur as a result of operation variations of the engine <NUM>, such as pressure fluctuations. If compensation is not provided, such as through the features of the seal assembly <NUM>, rub between the various plates/rings as measured by a pressure velocity factor, may be undesirably high. The pressure-velocity limit for a seal is the highest combination of pressure and velocity at which that seal operates with normal wear. Beyond the pressure-velocity limit, the seal may experience an undesirable amount of wear due to a high level of rub. Accordingly, the seal assembly <NUM> has a number of features to reduce or avoid rub and to maintain operation below the pressure-velocity limit. As a result, the pressure-velocity limit may be extended for broadening the operational range of the engine <NUM>.

In a number of embodiments, the seal assembly <NUM> is configured to induce forces to offset the forces that drive axial excursions of the shafts <NUM>, <NUM> relative to one another. The seal assembly <NUM> includes a magnetic system <NUM> to generate offsetting forces. Also for example, the seal assembly <NUM> may include a hydrodynamic system <NUM> to generate offsetting forces. In a number of embodiments, the seal assembly <NUM> may include only the magnetic system <NUM>. For example, the seal assembly <NUM> is illustrated in <FIG> with only the magnetic system <NUM>. In other embodiments, the seal assembly <NUM> may include both of the systems (magnetic system <NUM> and hydrodynamic system <NUM>), as illustrated in <FIG>.

In the magnetic system <NUM>, a magnetic ring <NUM> is contained in an annular groove <NUM> of the end plate <NUM> and a magnetic ring <NUM> is contained in an annular groove <NUM> of the end plate <NUM>. The magnetic ring <NUM> is spaced away from the gland opening <NUM> by a section <NUM> so that the material of the end plate <NUM> defines the surface <NUM> facing the split ring <NUM>, preventing any potential for contact between the magnetic ring <NUM> and the split ring <NUM>. The magnetic ring <NUM> is also spaced away from the gland opening <NUM> by a section <NUM> so that the material of the end plate <NUM> defines the surface <NUM> facing the split ring <NUM> preventing any potential for contact between the magnetic ring <NUM> and the split ring <NUM>. The split ring <NUM> carries at least one magnet <NUM>, which may be a series of magnets <NUM>. The base material of the split ring <NUM>, which may be a low friction material, defines the surface <NUM> facing the end plate <NUM> preventing any potential for contact between the magnet(s) <NUM> and the end plate <NUM>. Similarly, the base material of the split ring <NUM> defines the surface <NUM> facing the end plate <NUM> preventing any potential for contact between the magnet(s) <NUM> and the end plate <NUM>. As a result, an area of the low friction base material is disposed between the magnet(s) <NUM> and the end plates <NUM>, <NUM>. The magnetic system <NUM> is configured with magnetic poles so that the magnetic ring <NUM> and the magnet(s) <NUM> repel each other along the axis <NUM> and so that the magnet(s) <NUM> and the magnetic ring <NUM> also repel each other along the axis <NUM>. The effect is to act to center the split ring <NUM> within the gland opening <NUM>.

In the hydrodynamic system <NUM>, the end plate <NUM> includes a series of grooves <NUM> configured to pump fluid generating pressures/forces to maintain separation between the surfaces <NUM>, <NUM>. Similarly, the end plate <NUM> includes a series of grooves <NUM> configured to pump fluid to maintain separation between the surfaces <NUM>, <NUM>. During relative rotation between the shafts <NUM>, <NUM>, the generated hydrodynamic forces offset those forces that operate to drive axial excursions, including those that would otherwise result in contact between relatively rotating parts.

A pressure balancing system <NUM> is formed in the split ring <NUM>. The pressure balancing system <NUM> includes an annulus <NUM> formed through the surface <NUM> and defines an annular grove around the side of the split ring <NUM> facing the end plate <NUM>. Similarly, an annulus <NUM> is formed through the surface <NUM> and defines an annular groove around the side of the split ring <NUM> facing the end plate <NUM>. The pressure balancing system <NUM> includes at least one opening <NUM>, which may be a series of openings formed axially through the split ring <NUM> providing a path for pressure communication between the annulus <NUM> and the annulus <NUM>. The annuli <NUM>, <NUM> beneficially provide open areas around the entire circumference of the split ring <NUM>, while the openings <NUM> provide cross communication with minimal material removal.

Referring to <FIG>, the end plate <NUM> is illustrated showing its ring-like shape. The magnet ring <NUM> is contained in the annular groove <NUM>. The magnet ring <NUM> is inserted through side <NUM> of the end plate <NUM>, which faces the area <NUM>. The end plate <NUM> includes an outer peripheral surface <NUM> that is spaced from the shaft <NUM> (<FIG>), and an inner peripheral surface <NUM> sized to fit securely over the shaft <NUM> (<FIG>). The end plate <NUM> and the magnet ring <NUM> are similarly constructed with the magnet ring <NUM> inserted through the side <NUM> (<FIG>) of the end plate <NUM>, which faces the area <NUM>.

As shown in <FIG>, the split ring <NUM> is illustrated removed from the seal assembly <NUM> for visibility. The split ring <NUM> is ring-like in shape with a split line <NUM> formed by ends <NUM>, <NUM> of the split ring <NUM> that are separated by a gap <NUM>. The split line <NUM> enables the split ring <NUM> to expand/contract/flex so that its outer diameter <NUM> may change in size in response to forces. For example, during rotation of the shaft <NUM> and/or the shaft <NUM>, the split ring <NUM> will spin and centrifugal forces will cause the outer diameter <NUM> to grow, forcing the outer peripheral surface <NUM> against the shaft <NUM>. During operation of the engine <NUM>, under frictional force, relative motion is resisted by the friction between the shaft <NUM> and the split ring <NUM> so that the split ring <NUM> rotates with the shaft <NUM> relative to the end plates <NUM>, <NUM>.

The split ring <NUM> includes the annulus <NUM> with the openings <NUM> formed axially through the split ring at the annulus <NUM> and into the annulus <NUM> as visible in <FIG>. The magnet(s) <NUM> are inserted into the inner peripheral surface <NUM>. For example, a series of openings <NUM> may be formed as bores through the inner peripheral surface <NUM> or may otherwise be formed into the split ring <NUM> through the inner peripheral surface <NUM>. The magnet(s) <NUM> may then be inserted into the openings <NUM> and secured therein.

The end plate <NUM> is illustrated in <FIG> removed from the seal assembly <NUM> for visibility, showing its ring-like shape and aspects of the hydrodynamic system <NUM>. The grooves <NUM> are formed through the surface <NUM>. In this embodiment, the grooves <NUM> are spiral shaped. For example, they may be spiral cut into the surface <NUM> to act as pumping elements. During relative rotation of the end plate <NUM>, the grooves <NUM> move fluid in a radially outward flow <NUM> as a lower pressure is developed near the inboard ends <NUM> of the grooves <NUM>, and a higher pressure is developed near the outboard ends <NUM> of the grooves <NUM>.

As depicted in <FIG>, axial excursions <NUM> of the shafts <NUM>, <NUM> may occur during operation of the engine <NUM>. In this example, the surface <NUM> of the split ring <NUM> approaches the surface <NUM> of the end plate <NUM>. The magnetic system <NUM> and/or the hydrodynamic system <NUM> are configured to resist contact between the surfaces <NUM> and <NUM>, including during the axial excursions <NUM>. In operation, the magnetic system <NUM> operates to provide force to resist contact. The magnet ring <NUM> and the magnet(s) <NUM> include facing poles <NUM>, <NUM>, respectively, that have the same polarity. In this case the poles <NUM>, <NUM> are both north poles and face each other across the space <NUM> between the surfaces <NUM>, <NUM> tending to push the end plate <NUM> and the split ring <NUM> apart. It should be noted that the axial excursion <NUM> may be due to forces external to the seal assembly <NUM> and may be transient. The repulsive force between the magnet ring <NUM> and the magnet(s) <NUM> is continuous and the magnitude of the force is a factor of the proximity between the end ring <NUM> and the split ring <NUM>. As a result, as the size of the space <NUM> closes, the force of repulsion increases. The magnet(s) <NUM> and the magnet ring <NUM> similarly repel one another. In this example, the south pole <NUM> of the magnet(s) <NUM> faces the south pole <NUM> of the magnet ring <NUM> across the space <NUM> between the split ring <NUM> and the end plate <NUM>.

Referring additionally to <FIG>, when the axial excursions <NUM> may move the split ring <NUM> and the end plate <NUM> so that the surfaces <NUM>, <NUM> approach each other, the magnitude of the repulsive force increases and contact between the surfaces <NUM>, <NUM> is avoided or minimized. The effect of operation of the magnetic system <NUM> is to seek a balance to substantially center the split ring <NUM> in the gland opening <NUM>. In this context, substantially centered means avoiding contact between the surfaces <NUM>, <NUM> and between the surfaces <NUM>, <NUM>.

The hydrodynamic system <NUM> generally includes the grooves <NUM>, <NUM>, the annuli <NUM>, <NUM> and the opening(s) <NUM>. As the surfaces <NUM>, <NUM> approach one another during an axial excursion <NUM> as shown in <FIG>, the grooves <NUM> act to generate a pressurized fluid film in the space <NUM> generating a force that opposes contact between the surfaces <NUM>, <NUM>. The generated force increases as the surfaces <NUM>, <NUM> become close and so the hydrodynamic force is highest as contact becomes incipient. The grooves <NUM> act to create a pumping action that flows fluid in the radial direction <NUM> (outward). A corner <NUM> of the split ring <NUM> is formed at the junction of the surface <NUM> and the inner peripheral surface <NUM>. An inlet <NUM> is located at a radially inward position relative to the corner <NUM>. A relatively low pressure is generated at the inlet <NUM> of the grooves <NUM> and a relatively high pressure is generated at the outlet <NUM> of the grooves <NUM>. For example, when the space <NUM> is reduced to a few thousandths of a millimeter of film thickness, the hydrodynamic force is beneficially effective in inhibiting contact between the surfaces <NUM>, <NUM>.

The opening(s) <NUM> communicate pressure through the split ring <NUM> so that the pressures in the two annuli <NUM>, <NUM> are balanced. The relatively high pressure generated at the outlet <NUM> of the grooves <NUM> due to the hydrodynamic pressure profile operates on a segment <NUM> of the surface <NUM> of the split ring <NUM> between the annulus <NUM> and the corner <NUM>. In particular, the segment <NUM> includes a dam region <NUM> between the grooves <NUM> and the annulus <NUM>. The grooves <NUM> pump fluid over the dam region <NUM> with resistance and into the annulus <NUM> with less resistance effectively generating force to resist contact between the surfaces <NUM>, <NUM>.

As the surfaces <NUM>, <NUM> approach one another during an axial excursion <NUM> as shown in <FIG>, the grooves <NUM> act to generate a pressurized fluid film in the space <NUM> generating a force that opposes contact between the surfaces <NUM>, <NUM>. The generated force increases as the surfaces <NUM>, <NUM> become close and so the hydrodynamic force is highest as contact becomes incipient. The grooves <NUM> act to create a pumping action that flows fluid in the radial direction <NUM> (outward). An inlet <NUM> is located radially inward from the corner <NUM>. A relatively low pressure is generated at the inlet <NUM> to the grooves <NUM> and a relatively high pressure is generated at the outlet <NUM> of the grooves <NUM>. The opening(s) <NUM> communicate pressure through the split ring <NUM> so that the pressures in the annuli <NUM>, <NUM> are balanced. The relatively high pressure generated at the outlet <NUM> of the grooves <NUM> due to the hydrodynamic pressure profile operates on a segment <NUM> of the surface <NUM> of the split ring <NUM> between the annulus <NUM> and the corner <NUM>. In particular, the segment <NUM> includes a dam region <NUM> between the grooves <NUM> and the annulus <NUM>. The grooves <NUM> pump fluid over the dam region <NUM> with resistance and into the annulus <NUM> with lower resistance effectively generating force to resist contact between the surfaces <NUM>, <NUM>.

The effect of the hydrodynamic system <NUM>, such as in combination with those of the magnetic system <NUM>, is effective in extending the service life of the engine <NUM> by minimizing heat generation and wear. While the magnetic system <NUM> operates to seek centering of the spilt ring <NUM> in the gland opening <NUM> and opposes contact with increasing force as the spaces <NUM>, <NUM> become small, the hydrodynamic system <NUM> provides a boost as the spaces <NUM>, <NUM> become very small.

The potential for the axial excursions <NUM> may be greater than the spacing between the split ring <NUM> and the end plates <NUM>, <NUM> and so in the absence of the magnetic system <NUM> and/or the hydrodynamic system <NUM>, repeated and/or sustained contact between the surfaces <NUM>, <NUM> or the surfaces <NUM>, <NUM> may lead to heat generation and wear that reduces service life. The axial excursions <NUM>, if unopposed, may be of a magnitude, such as <NUM>-<NUM> millimeters in this example. The design size of the spaces <NUM>, <NUM> may be fractions of a single millimeter. Accordingly, the magnetic system <NUM> and/or the hydrodynamic system <NUM> provide mechanisms to reduce the axial excursions <NUM>, while inhibiting surface contacts.

Accordingly, an intershaft seal system with a seal assembly <NUM> provides noncontacting operation to reduce heat generation and wear. Pressure loading capability is increased. For example, the pressure differential between the areas <NUM>, <NUM> on opposite sides of the seal assembly <NUM> is a function of the operational state of the engine <NUM>. Extending the operational range of the engine <NUM> would otherwise be limited by contact heat generation and wear if not for the added features of the seal assembly <NUM>. Contact related outcomes are eliminated or reduced by means of magnetic force and/or hydrodynamic effects. By eliminating contact during translations and higher differential pressures, service life may be significantly extended. In the event contact does occur, the resulting heat and parasitic loss is minimized. The seal assembly <NUM> enables operating speeds and pressures above otherwise realistic maximums.

Claim 1:
A sealing system comprising:
an outer shaft (<NUM>) having a hollow interior (<NUM>);
an inner shaft (<NUM>) extending through the hollow interior of the outer shaft;
a first plate (<NUM>) encircling the inner shaft and configured to rotate with the inner shaft;
a second plate (<NUM>) encircling the inner shaft and configured to rotate with the inner shaft, the second plate axially spaced from the first plate so that a gland opening (<NUM>) is defined between the inner and outer shafts and between the first and second plates; and
a ring (<NUM>) disposed in the gland opening,
the first plate including a first force generating element (<NUM>) configured to generate a first force to separate the ring from the first plate,
the second plate including a second force generating element (<NUM>) configured to generate a second force to separate the ring from the second plate, characterised in that the first and second force generating elements comprise magnet rings, and comprising a series of magnets in the ring.