Patent Description:
A gas turbine engine generally includes a fan and a core arranged in flow communication with one another. Additionally, the core of the gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air is provided from the fan to an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section to the turbine section. The flow of combustion gasses through the turbine section drives the turbine section and is then routed through the exhaust section, e.g., to atmosphere.

Conventional gas turbine engines include rotor assemblies having shafts, compressor impellers, turbines, couplings, sealing packs, and other elements for optimal operation under given operating conditions. These rotor assemblies have a mass generating a constant static force due to gravity, and also generate a dynamic force due, e.g., to imbalances in the rotor assembly during operation, accelerations, etc. In addition to radial shaft forces, the rotating assembly also experiences axial forces generated from, e.g., internal pressures between the turbomachinery stages and the thrust of the gas turbine engine. Such gas turbine engines include radial bearings and thrust bearings to sustain and support these forces while permitting rotation of the rotor assembly.

For example, the sum of the axial forces may result in a net axial force or thrust. Such thrust may be in the forward or aft direction. The thrust bearing may be employed to absorb this thrust and allow the rotor assembly to continue rotation.

In certain situations, the net axial force or thrust acting on the thrust bearing may switch direction from forward to aft or vice-versa; such a situation is referred to as cross-over. As such, if not compensated for, cross-over may lead to unloaded ball bearings in the thrust bearing. Unloaded ball bearings may reduce radial centering of the rotor, resulting in altered seal clearances. Low rotor thrust on the bearings can also cause the ball bearings to slip relative to the raceways and potentially cause skidding damage. Also, low rotor thrust may reduce the effective bearing stiffness, possibly having an adverse impact on rotordynamics.

To prevent cross-over conditions, some rotor assemblies are designed such that the resultant thrust remains unidirectional, either forward or aft, under a wide range of operating conditions. Such designs may lead to oversized and overweight bearings to compensate for unidirectional turbine assemblies. For instance, the thrust bearing must be capable of supporting the thrust loads while being limited to only receiving forward or aft net force.

Therefore, a lighter, smaller thrust bearing in a system capable of correcting for thrust cross-over would be useful. More specifically, a rotor thrust system capable of utilizing both the forward and aft capabilities of a thrust bearing while having reduced size and weight would be particularly beneficial. <CIT> discloses a vibration sensor for sensing vibration in a bearing. <CIT> discloses an apparatus for measuring a bearing thrust load on gas turbine engine bearing assemblies.

Aspects and advantages will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In one aspect, the present invention is directed to a rotor thrust balancing system for a turbomachine, according to claim <NUM>. In another aspect, the present invention is directed toward a method of balancing rotor thrust on a thrust bearing of a turbomachine, according to claim <NUM>.

These and other features, aspects and advantages will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate aspects of the invention and, together with the description, serve to explain certain principles of the invention.

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended FIGS. , in which:.

A system is generally provided for balancing rotor thrust for a turbomachine, along with methods of doing the same. In one embodiment, the system includes a rotating drive shaft, a thrust bearing, and a first waveguide sensor. The rotating drive shaft generally couples a turbine section of the turbomachine and a compressor section of the turbomachine. In one embodiment, the thrust bearing includes a plurality of ball bearings, an inner race, and an outer race, such that the inner race is coupled to the rotating drive shaft and the outer race is coupled to a fixed structure. According to one particular embodiment, the first waveguide sensor is coupled to the outer race at a first end of the waveguide sensor. Generally, the waveguide sensor may communicate a vibrational frequency from the thrust bearing to a second end of the waveguide sensor.

In certain embodiments, the rotor thrust balancing system for a turbomachine prevents the thrust bearing from operating in a cross-over condition. Avoidance of the cross-over condition may reduce the occurrence of unloaded ball bearings in the thrust bearing. For example, prevention of cross-over may allow for better radial centering of the rotor and proper seal clearances. Avoiding slippage on the ball bearings relative to the raceways may prevent skidding damage. Further, preventing low rotor thrust may help to insure the correct effective bearing stiffness and avert an adverse impact on rotor dynamics.

In certain embodiments, the ability to measure rotor thrust cross-over and correct for it would allow a product engine to have a larger range of rotor thrust, without increasing the overall magnitude of rotor thrust in any one direction. Additionally, a lower magnitude of bearing thrust load allows for a smaller, lighter weight bearing. For example, bearing size may be minimized by centering the rotor thrust near zero, or a null position, while still avoiding the cross-over condition, allowing for smaller magnitudes of thrust load. Further, replacing measurement technology such as accelerometers with waveguide sensors may allow for the sensor to be attached at the bearing, where accelerometers may not have enough reliability. For example, the part with the lowest reliability of a waveguide sensor, e.g. the piezoelectric sensor, may be mounted exterior of the engine where it is subjected to less heat and is more easily replaceable.

It should be appreciated that, although the present subject matter will generally be described herein with reference to a gas turbine engine, the disclosed systems and methods may generally be used on thrust bearings within any suitable type of turbine engine, including aircraft-based turbine engines, land-based turbine engines, and/or steam turbine engines. Further, though the present subject matter is generally described in reference to a high pressure spool of a turbine engine, it should also be appreciated that the disclosed system and method can be used on any spool within a turbine engine, e.g. a low pressure spool or an intermediate pressure spool.

Referring now to the drawings, <FIG> illustrates a cross-sectional view of one embodiment of a gas turbine engine <NUM> that may be utilized within an aircraft in accordance with aspects of the present subject matter, with the engine <NUM> being shown having a longitudinal or axial centerline axis <NUM> extending therethrough for reference purposes. In general, the engine <NUM> may include a core gas turbine engine (indicated generally by reference character <NUM>) and a fan section <NUM> positioned upstream thereof. The core engine <NUM> may generally include a substantially tubular outer casing <NUM> that defines an annular inlet <NUM>. In addition, the outer casing <NUM> may further enclose and support a compressor section <NUM>. For the embodiment show, the compressor section <NUM> includes a booster compressor <NUM> and a high pressure compressor <NUM>. The booster compressor <NUM> generally increases the pressure of the air (indicated by arrow <NUM>) that enters the core engine <NUM> to a first pressure level. The high pressure compressor <NUM>, such as a multi-stage, axial-flow compressor, may then receive the pressurized air (indicated by arrow <NUM>) from the booster compressor <NUM> and further increase the pressure of such air. The pressurized air exiting the high pressure compressor <NUM> may then flow to a combustor <NUM> within which fuel is injected into the flow of pressurized air, with the resulting mixture being combusted within the combustor <NUM>.

For the embodiment illustrated, the outer casing <NUM> may further enclose and support a turbine section <NUM>. Further, for the depicted embodiment, the turbine section <NUM> includes a first high pressure turbine <NUM> and second low pressure turbine <NUM>. For the illustrated embodiment, high energy combustion products <NUM> are directed from the combustor <NUM> along the hot gas path of the engine <NUM> to the high pressure turbine <NUM> for driving the high pressure compressor <NUM> via a first, high pressure drive shaft <NUM>. Subsequently, the combustion products <NUM> may be directed to the low pressure turbine <NUM> for driving the booster compressor <NUM> and fan section <NUM> via a second, low pressure drive shaft <NUM> generally coaxial with first drive shaft <NUM>. After driving each of turbines <NUM> and <NUM>, the combustion products <NUM> may be expelled from the core engine <NUM> via an exhaust nozzle <NUM> to provide propulsive jet thrust.

Additionally, as shown in <FIG>, the fan section <NUM> of the engine <NUM> may generally include a rotatable, axial-flow fan rotor assembly <NUM> surrounded by an annular fan casing <NUM>. It should be appreciated by those of ordinary skill in the art that the fan casing <NUM> may be supported relative to the core engine <NUM> by a plurality of substantially radially-extending, circumferentially-spaced outlet guide vanes <NUM>. As such, the fan casing <NUM> may enclose the fan rotor assembly <NUM> and its corresponding fan blades <NUM>. Moreover, a downstream section <NUM> of the fan casing <NUM> may extend over an outer portion of the core engine <NUM> so as to define a secondary, or by-pass, airflow conduit <NUM> providing additional propulsive jet thrust.

It should be appreciated that, in several embodiments, the low pressure drive shaft <NUM> may be directly coupled to the fan rotor assembly <NUM> to provide a direct-drive configuration. Alternatively, the low pressure drive shaft <NUM> may be coupled to the fan rotor assembly <NUM> via a speed reduction device <NUM> (e.g., a reduction gear or gearbox or a transmission) to provide an indirect-drive or geared drive configuration. Such a speed reduction device(s) <NUM> may also be provided between any other suitable shafts and/or spools within the engine as desired or required.

During operation of the engine <NUM>, it should be appreciated that an initial air flow (indicated by arrow <NUM>) may enter the engine <NUM> through an associated inlet <NUM> of the fan casing <NUM>. For the illustrated embodiment, the air flow <NUM> then passes through the fan blades <NUM> and splits into a first compressed air flow (indicated by arrow <NUM>) that moves through conduit <NUM> and a second compressed air flow (indicated by arrow <NUM>) which enters the booster compressor <NUM>. In the depicted embodiment, the pressure of the second compressed air flow <NUM> is then increased and enters the high pressure compressor <NUM> (as indicated by arrow <NUM>). After mixing with fuel and being combusted within the combustor <NUM>, the combustion products <NUM> may exit the combustor <NUM> and flow through the high pressure turbine <NUM>. Thereafter, for the shown embodiment, the combustion products <NUM> flow through the low pressure turbine <NUM> and exit the exhaust nozzle <NUM> to provide thrust for the engine <NUM>.

In certain embodiments, the engine <NUM> may be an adaptive cycle engine or a variable cycle engine. Gas turbine engines <NUM> may balance performance between energy efficiency and high thrust production by designing a by-pass ratio between the airflow conduit <NUM> and the core gas turbine engine <NUM>. The by-pass ratio may be defined by the ratio of the first compressed airflow <NUM> that moves through the airflow conduit <NUM> and the second compressed air flow <NUM> that moves through the core gas turbine engine <NUM>. Generally a gas turbine engine <NUM> with a high by-pass ratio corresponds to an efficient gas turbine engine <NUM>, but the gas turbine engine <NUM> may have a relatively lower maximum thrust. Similarly, a gas turbine engine <NUM> with a low by-pass ratio may have a higher maximum thrust, but the gas turbine engine <NUM> may have a lower efficiency.

Adaptive cycle engines or variable cycle engines may incorporate a variable by-pass ratio design. For example, the by-pass ratio may be adjusted to a lower value when high thrust is required, such as take-off conditions. Similarly, the by-pass ratio may be adjusted to a higher value when high efficiency is desired, such as at cruise conditions. The adjustment of the by-pass ratio may be accomplished by modify the area of the airflow conduit <NUM> and the inlet of the core gas turbine engine <NUM>. In another embodiment, additional ducts may be used to selectively pass more or less air to either the core gas turbine engine <NUM> or the airflow conduit <NUM>.

Referring generally to <FIG>, various views of embodiments of a rotor thrust balancing system <NUM> for a turbomachine, such as, but not limited to, the gas turbine engine <NUM> of <FIG>, are illustrated in accordance with aspects of the present subject matter. For reference purposes, the turbomachine defines a centerline <NUM> extending the length of the turbomachine. In the embodiment shown, the system <NUM> includes a rotating drive shaft <NUM>, a thrust bearing <NUM>, and a first waveguide sensor <NUM>. For the embodiment shown, the rotating drive shaft <NUM> couples a turbine section <NUM> of the turbomachine and a compressor section <NUM> of the turbomachine. The thrust bearing <NUM> may include a plurality of ball bearings <NUM>, an inner race <NUM>, and an outer race <NUM>. For the depicted embodiment, the inner race <NUM> is coupled to the rotating drive shaft <NUM>, and the outer race <NUM> is coupled to a fixed structure, such as a thrust bearing compartment housing <NUM>. In the exemplary embodiment, a first waveguide sensor <NUM> is coupled to the outer race <NUM> at a first end <NUM> of the first waveguide sensor <NUM>. Further, the first waveguide sensor <NUM> may communicate a vibrational frequency from the thrust bearing <NUM> to a second end <NUM> of the first waveguide sensor <NUM>.

Referring again to <FIG> particularly, the system <NUM> generally includes a rotating drive shaft <NUM> coupling a turbine section <NUM> and a compressor section <NUM> of the turbomachine. In one embodiment, the rotating drive shaft <NUM> is the high pressure drive shaft <NUM> coupling the high pressure turbine <NUM> to the high pressure compressor <NUM>. Together, the high pressure turbine <NUM>, the high pressure compressor <NUM>, and the high pressure drive shaft <NUM> may be referred to as a high pressure spool <NUM>. In another embodiment, the rotating drive shaft <NUM> is the low pressure drive shaft <NUM> coupling the low pressure turbine <NUM> to a low pressure compressor, such as the booster compressor <NUM>, and the fan section <NUM>. Alternatively, the low pressure drive shaft <NUM> may couple the low pressure turbine <NUM> to the booster compressor <NUM> only or to the fan section <NUM> only. Together, the low pressure turbine <NUM>, the low pressure drive shaft <NUM>, and at least one of the booster compressor <NUM> or fan section <NUM> may be referred to as a low pressure spool <NUM>. In a further embodiment (not shown), the rotating drive shaft <NUM> may be an intermediate pressure drive shaft coupling an intermediate compressor to an intermediate turbine. Together, the intermediate pressure drive shaft, intermediate pressure compressor, and intermediate pressure turbine may be referred to as an intermediate pressure spool.

It should be recognized, in further embodiments, the invention may include any combination of the low pressure drive shaft <NUM>, the high pressure drive shaft <NUM>, and the intermediate pressure drive shaft. For example, both the high pressure drive shaft <NUM> and the low pressure drive shaft <NUM> may be coupled to thrust bearings <NUM> and waveguide sensors <NUM> as described in more detail below.

Referring now to <FIG>, views of one embodiment of a bearing compartment sealing system <NUM> containing a thrust bearing <NUM> are illustrated in accordance with aspects of the present subject matter. Specifically, <FIG> is a cross-sectional view of the sealing system <NUM> for containing the lubrication of a thrust bearing compartment housing <NUM> relative to a rotating drive shaft <NUM> of the gas turbine engine <NUM>. <FIG> is a close-up cross-sectional view of the sealing system <NUM> shown in <FIG>, particularly illustrating a labyrinth seal <NUM> and a carbon seal <NUM>, such as a hydrodynamic seal, disposed at axially opposite ends of the bearing compartment housing <NUM>.

As shown in <FIG>, the sealing system <NUM> may generally isolate a bearing compartment housing <NUM> from the high pressure drive shaft <NUM>, which rotates relative thereto. Although, the sealing system <NUM> may isolate any stationary component and any rotating shaft (e.g., the low pressure drive shaft <NUM>) in the engine <NUM>. For the embodiment shown, the relative rotation occurs when one or more stator vanes <NUM> direct the combustion products <NUM> flowing through a conduit <NUM> onto one or more turbine blades <NUM> coupled to the high pressure drive shaft <NUM>. A thrust bearing <NUM> supports the high pressure drive shaft <NUM> relative to various fixed components in the engine <NUM>. Further, for the illustrated embodiment, the bearing compartment housing <NUM> at least partially radially encloses the thrust bearing <NUM>, thereby forming a sump or compartment <NUM> preferably having a radial shape in which the thrust bearing <NUM> is disposed. Lubricant (e.g., oil) for lubricating the various components of the thrust bearing <NUM> may circulate through the compartment <NUM>. For the illustrated embodiment, a high pressure cavity <NUM> is disposed exterior to the bearing compartment housing <NUM>. In the exemplary embodiment, bleed air from the compressor section <NUM>, the turbine section <NUM>, and/or the fan section <NUM> flows through a bleed air port <NUM> to pressurize the high pressure cavity <NUM> to a pressure relatively greater than the pressure in the compartment <NUM>.

For the depicted embodiment, at least two seals, such as the labyrinth seal <NUM> and the carbon seal <NUM>, separate the high pressure drive shaft <NUM> and the bearing compartment housing <NUM>. Although, the at least two seals may be any suitable type of seal. For example, in other embodiments, multiple lab seals, carbon seals, and/or hydrodynamic seals may be utilized in the sealing system <NUM>. For the illustrated embodiment, the labyrinth seal <NUM> and the carbon seal <NUM> separate the high pressure cavity <NUM> and the compartment <NUM>. <FIG> illustrates the labyrinth seal <NUM> disposed upstream of the carbon seal <NUM>; although, the carbon seal <NUM> may be positioned downstream of the labyrinth seal <NUM> as well.

In this respect, for the illustrated embodiment, the bearing compartment housing <NUM>, the at least two seals (e.g., the labyrinth seal <NUM> and the carbon seal <NUM>), and the high pressure drive shaft <NUM> collectively enclose the compartment <NUM>. That is, the combination the bearing compartment housing <NUM>, the at least two seals, and the high pressure drive shaft <NUM> may entirely surround the compartment <NUM> axially, radially, and circumferentially. Furthermore, for the illustrated embodiment, the at least two seals (e.g., the labyrinth seal <NUM> and the carbon seal <NUM>) are the only seals that enclose the compartment <NUM>, but it should be recognized that in other embodiment any number of seal may be used to enclose the compartment <NUM>, such as three or more.

In the embodiment illustrated in <FIG>, a close-up view of the thrust bearing <NUM> and bearing compartment housing <NUM> is shown. For example, the bearing <NUM> includes an inner race <NUM> extending circumferentially around an outer surface <NUM> of the high pressure drive shaft <NUM>. In the shown embodiment, an outer race <NUM> is disposed radially outward from the inner race <NUM> and mates with a fixed structure, such as the interior surface of the bearing compartment housing <NUM>. The inner and outer races <NUM>, <NUM> may have a split race configuration. For the depicted embodiment, the inner and outer race <NUM>, <NUM> sandwich at least one ball bearing <NUM> therebetween. Preferably, the inner and outer races <NUM>, <NUM> sandwich at least three ball bearings <NUM> therebetween. In other embodiments, the inner race <NUM> and outer race <NUM> may sandwich at least one cylinder to form the thrust bearing <NUM>.

<FIG> also more closely illustrates the labyrinth seal <NUM> and the carbon seal <NUM>. For the embodiment depicted, the labyrinth seal <NUM> and the carbon seal <NUM> (such as a hydrodynamic seal) are non-contact seals, which require no contact between the stationary and moving components when operating at high speed. Non-contact seals typically have a longer service life than contact seals. Still, in other embodiments, one or both of the seals may be contact seal. Each type of seal may operate in a different manner. For the depicted embodiment, the labyrinth seal <NUM> includes inner surface <NUM> and an outer surface <NUM>. For example, a tortuous path (not shown) extending between the inner and outer surfaces <NUM>, <NUM> prevents lubricant from escaping the bearing compartment houses <NUM>. For the exemplary embodiment shown, the air pressure on an outer side <NUM> of the labyrinth seal <NUM> (i.e., in the high pressure cavity <NUM>) is greater than the air pressure on the inner side <NUM> of the labyrinth seal <NUM> (i.e., in the compartment <NUM>). In this respect, the stationary and rotating components may be separated by an air film during relative rotation therebetween.

Nevertheless, for the embodiment shown, the carbon seal <NUM>, such as a hydrodynamic seal, includes one or more grooves <NUM> separating the stationary and rotating components. The air pressure on an outer side <NUM> of the carbon seal <NUM> (i.e., in the high pressure cavity <NUM>) may be greater than the air pressure on the inner side <NUM> of the carbon seal <NUM> (i.e., in the compartment <NUM>). As such, for the embodiment shown, air from the high pressure cavity <NUM> flows through the grooves <NUM> into the compartment <NUM>, thereby creating an air film between the stationary and rotating components. Still, in other embodiments, the carbon seal <NUM> may be a contacting carbon seal.

In one embodiment, the carbon seal <NUM> is proximate to and in sealing engagement with a hairpin member <NUM> of the high pressure drive shaft <NUM>. For example, the hairpin member <NUM> includes a radially outer shaft portion <NUM> radially offset from a radially inner shaft portion <NUM> by a radial wall <NUM>. In this respect, for the embodiment depicted, the radially outer shaft portion <NUM>, the radially inner shaft portion <NUM>, and the radial wall <NUM> define a cavity <NUM> therebetween. In one embodiment, the radially outer shaft portion <NUM> is in sealing engagement with the carbon seal <NUM>. In this respect, the radially outer shaft portion <NUM> may contact the carbon seal <NUM> when the high pressure drive shaft <NUM> is stationary or rotating at low speeds. Nevertheless, for the illustrated embodiment, the carbon seal <NUM> lifts off of the radially outer shaft portion <NUM> when the high pressure drive shaft <NUM> rotates at high speeds.

For the embodiment illustrated, the hairpin member <NUM> may improve the performance of the gas turbine engine <NUM>. For example, lubricant from the compartment <NUM> is able to contact and cool the radially inner side of the radially outer shaft portion <NUM> of the hairpin member <NUM>. This, for the embodiment shown, cools the radially outer side of the radially outer shaft portion <NUM>, which is in contact with the carbon seal <NUM> at low speeds and proximate to the carbon seal <NUM> at high speeds. That is, heat from the radially outer side may conduct through the radially outer shaft portion <NUM> to the radially inner side thereof, which is cooled by lubricant. This keeps the carbon seal <NUM> cooler, which, in turn, permits the gas turbine engine <NUM> to run hotter and faster, thereby improving the performance thereof for the illustrated embodiment.

For the shown embodiment, the pressure on the outer side <NUM> of the labyrinth seal <NUM> and the outer side <NUM> of the carbon seal <NUM> should be substantially the same. That is, the air pressure in the high pressure cavity <NUM> should be substantially the same throughout to prevent the creation of air flow currents. These air currents could direct air away from the carbon seal <NUM>.

Referring now to <FIG>, a view of a rotor thrust balancing system <NUM> for a turbomachine is illustrated in accordance with aspects of the present subject matter. For the illustrated embodiment, the system <NUM> includes at least one waveguide sensor <NUM>, such as the first waveguide sensor <NUM>, coupled to the outer race <NUM> of the thrust bearing <NUM> at a first end <NUM>, <NUM> of the waveguide sensor <NUM>. It should be recognized the inner race <NUM> may be coupled to any rotating drive shaft <NUM>. For example, the rotating drive shaft <NUM> may be the high pressure drive shaft <NUM>. In another embodiment, the rotating drive shaft <NUM> may be the low pressure drive shaft <NUM>.

It should be recognized that, in other embodiments, the waveguide sensor <NUM> may be coupled to the bearing compartment housing <NUM>. As shown in the embodiment of <FIG>, the waveguide sensor <NUM> communicates a vibrational frequency from the thrust bearing <NUM> to a second end <NUM>, <NUM> of the waveguide sensor <NUM>. The terms "communicating," "communicative," "communication," "communicates," "communicatively," and variation of the preceding, as used herein, mean direct communication or indirect communication such as through a memory system or another intermediary system.

The vibrational frequency communicated from the waveguide sensor <NUM> may generally be used to evaluate the health of any bearing. For example, a cracked or worn ball bearing <NUM> may alter a frequency of the thrust bearing <NUM>. As such, a change in a frequency communicated by the waveguide sensor <NUM> may indicate a ball bearing <NUM> that needs maintenance or replacement. Further, a change in the frequency of the thrust bearing <NUM> may also indicate a damaged or defective inner race <NUM> or the outer race <NUM>. As such, in certain embodiments, the system <NUM> may be used to monitor bearing health, such as the health of a thrust bearing <NUM>.

The waveguide sensor <NUM> as described here may include a structure that guides waves along a path while reducing the loss of energy. For instance, the waveguide reduces the loss of energy or signal decay by restricting expansion to along one or two dimensions. In embodiments of the disclosed system <NUM>, the waveguide sensor <NUM> communicates vibrations or sonic waves along the length of the waveguide sensor <NUM> from the first end <NUM>, <NUM> to the second end <NUM>, <NUM>. For example, the waveguide sensor <NUM> may be a metal wire extending the length of the waveguide sensor <NUM> at least partially enclosed within a sheath. The metal wire may be directly mounted to a bearing of interest, such as the thrust bearing <NUM>, or the bearing compartment housing <NUM>. For the depicted embodiment, waveguide sensors <NUM> are mounted on both a forward end <NUM> and an aft end <NUM> of the thrust bearing <NUM>. As such, the waveguide sensors <NUM> may sense both low rotor thrust and determine the direction the thrust bearing <NUM> is loaded, as described in more detail below.

Further, the waveguide sensor <NUM> may allow a measuring device to receive signals at the second end <NUM>, <NUM> that originate at the first end <NUM>, <NUM>. More specifically, for the embodiment shown, the waveguide sensor <NUM> communicates a vibrational signal from the thrust bearing <NUM> to the exterior of the engine <NUM>, outside the core gas turbine engine <NUM>, or both. As such, the second end <NUM>, <NUM> of the waveguide sensor <NUM> may be located outside the engine <NUM>, outside the core gas turbine engine <NUM>, or both.

In certain embodiments, the system <NUM> includes a control sensor at the second end <NUM>, <NUM> of the waveguide sensor <NUM>. Still referring to <FIG>, the control sensor may be a piezoelectric sensor <NUM>. The piezoelectric sensor <NUM> described here may include a device that uses the piezoelectric effect to determine changes in pressure, acceleration, temperature, strain, or force by converting them into an electric charge. For example, piezoelectric sensors <NUM> are known that generate a change in voltage when deformed by a force. As such, some piezoelectric sensors <NUM> produce a readable fluctuation in voltage or current when exposed to a vibration, such as the vibrational frequency communicated to the second end <NUM>, <NUM> of the waveguide sensor <NUM> and subsequently to the piezoelectric sensor <NUM>.

Referring now to <FIG>, in the embodiments illustrated, the system <NUM> may include a first waveguide sensor <NUM> and a second waveguide sensor <NUM>. More specifically, the first end <NUM> of the first waveguide sensor <NUM> may be coupled to the outer race <NUM> at a forward end <NUM> relative to the centerline <NUM>. Similarly, the first end <NUM> of the second waveguide sensor <NUM> may be coupled to the outer race <NUM> at an aft end <NUM> relative to the centerline <NUM>. It should be recognized that in further embodiments the system <NUM> may include only one waveguide sensor <NUM> or may include three or more waveguide sensors <NUM>.

Further, the vibrational frequency communicated by the waveguide sensor <NUM> may be any frequency associated with a bearing. For example, the vibrational frequency communicated may be a ball passing frequency. For the embodiment depicted, the ball passing frequency may be the rate at which the ball bearing <NUM> passes a particular location on one of the races <NUM>, <NUM>. The term ball passing frequency may generally refer to the ball passing frequency on the inner race <NUM> or the ball passing frequency on the outer race <NUM>. The ball passing frequency may be analytically predicted based on thrust bearing <NUM> geometry and rotor speed. For instance, a degree of curvature of the races <NUM>, <NUM>, an internal radial clearance between the inner race <NUM> and outer race <NUM>, and the number of ball bearings <NUM> may be used to predict the ball passing frequency.

In the embodiment shown, the waveguide sensor <NUM> is coupled to the outer race <NUM>. As such, the ball passing frequency communicated by the waveguide sensor <NUM> may the outer ball passing frequency. In the case of a cross-over condition, neither a forward or aft force is applied to the bearing. Such a condition may lead to an unloaded ball bearing <NUM> that slips instead of rotating smoothly. For example, the ball bearing <NUM> may skid on the inner race <NUM> instead of rotating. As such, the ball passing frequency on the outer race <NUM> may drop indicating a bearing slip and therefore a crossover condition on the thrust bearing <NUM>. For example, the ball passing frequency may drop approximately five percent to ten percent below the predicted value, indicating a bearing slip. Further, the ball passing frequency may drop to approximately zero, indicating a bearing that is in a near full slip condition.

Referring now particularly to <FIG>, the system <NUM> may include a control system communicatively linked to the control sensor (e.g. the piezoelectric sensor <NUM>) located at the second end <NUM>, <NUM> of the waveguide sensor <NUM>. For example, the first waveguide sensor <NUM> may have a second end <NUM>. Similarly, the second waveguide sensor <NUM> may have a second end <NUM>. As such, the vibrational frequency, such as the ball passing frequency, may be communicated to the control system. For example, the system <NUM> may include a Full Authority Digital Engine Control (FADEC) system <NUM> in communication with the piezoelectric sensor <NUM> via a communicative cable <NUM>. For the embodiment shown, the piezoelectric sensor <NUM> communicates the ball passing frequency of the thrust bearing <NUM> to the FADEC <NUM> of the engine <NUM>.

For the shown embodiment, once the ball passing frequency has been communicated to the control system, the control system determines whether the thrust bearing <NUM> is in a cross-over condition. For example, the FADEC <NUM> may receive a signal from the piezoelectric sensor <NUM> via communicative cable <NUM> and determine if the ball passing frequency is below a first threshold. In one exemplary embodiment, ball passing frequencies below the first threshold may correspond to a thrust bearing <NUM> in the cross-over condition.

Further, the system <NUM> may be used to determine and monitor the direction of the rotor thrust using the two waveguide sensors <NUM>, <NUM>. For example, the FADEC <NUM> may receive signals from the piezoelectric sensors <NUM> coupled to the waveguide sensors <NUM>, <NUM>. As such, for the embodiment illustrated, the FADEC <NUM> receives the ball passing frequency at both the forward end <NUM> and the aft end <NUM> on the outer race <NUM>. While the frequency of the ball passing frequency at both locations may be the same, the magnitude of the ball passing frequency may be different. For example, a forward acting rotor thrust may create a higher magnitude of the ball passing frequency on the forward end <NUM> of the outer race <NUM>. Conversely, an aft acting rotor thrust may create a higher magnitude of the ball passing frequency on the aft end <NUM> of the outer race <NUM>. As such, for the embodiment shown, the FADEC <NUM> compares the magnitude of the ball passing frequency at both the forward and aft ends <NUM>, <NUM> of the outer race <NUM> and determines the direction of the rotor thrust acting on the thrust bearing <NUM> and high pressure drive shaft <NUM>.

Referring now to <FIG> generally and to <FIG> particularly, the system <NUM> may change a force acting on the high pressure drive shaft <NUM> to remove the thrust bearing <NUM> out of the cross-over condition. For example, the system <NUM> may include a thrust cavity <NUM> in contact with the high pressure drive shaft <NUM>. For the depicted embodiment, a changing pressure of the thrust cavity <NUM> moves the high pressure drive shaft <NUM> forward or aft relative to the centerline <NUM> of the engine <NUM>. For instance, the thrust cavity <NUM> may be defined by a fixed structure <NUM>, a rotating structure <NUM>, and at least one thrust cavity seal <NUM>. The thrust cavity seals <NUM> may be any seal known in the art, such as but not limited to, a labyrinth seal, a hydrodynamic seal, or a carbon seal <NUM>. For example, a changing pressure in the thrust cavity <NUM> may modify the force the thrust cavity <NUM> applies on the rotating structure <NUM>. It should be recognized, for the depicted embodiment, that the high pressure drive shaft <NUM> includes the rotating structure <NUM>. For instance, the rotating structure <NUM> may be coupled to the high pressure drive shaft <NUM> or may be formed in a single piece with the high pressure drive shaft <NUM>. Thus, for the illustrated embodiment, the force applied to the rotating structure <NUM> of the high pressure drive shaft <NUM> is transferred to the thrust bearing <NUM> to push it away from the cross-over condition either forward or aft.

It should also be recognized that the gas engine <NUM> may include one or more radial bearing <NUM> positioned between the rotating drive shaft 31or the rotating structure <NUM> and the fixed structure <NUM>. The radial bearing <NUM> may generally support the rotating drive shaft <NUM> from radial forces perpendicular relative to the centerline <NUM>.

Further, the control system, such as the FADEC <NUM>, may send a signal in response to a cross-over condition in the thrust bearing <NUM> to pressurize the thrust cavity <NUM>. For example, the FADEC <NUM> may communicate a signal via a communicative cable <NUM> to a valve <NUM> to increase or reduce the pressure supplied to the thrust cavity <NUM>. For the depicted embodiment, the valve <NUM> is coupled to the high pressure compressor <NUM> and receives a pressurized fluid, such as air, via a first line <NUM>. Further, in the embodiment shown, the valve <NUM> is coupled to the thrust cavity <NUM> via a second line <NUM>. As such, for the embodiment shown, the signal from the FADEC <NUM> selectively opens the valve <NUM> so that bleed air pressurizes the thrust cavity <NUM> via the second line <NUM>. It should be recognized that the pressurized fluid may originate from any source, such as, but not limited to, the booster compressor <NUM>, the high pressure turbine <NUM>, the low pressure turbine <NUM>, or a pump. Furthermore, the thrust cavity <NUM> may be used to remove the thrust bearing <NUM> from a crossover condition by bleeding air from the thrust cavity <NUM>, thus reducing the force applied to the high pressure drive shaft <NUM>.

In one embodiment, the FADEC <NUM> is closed loop control system. For example, an initial set point or range may be selected for a difference between the magnitudes of the ball passing frequency at the forward end <NUM> to the ball passing frequency at the aft end <NUM> of the outer race <NUM>. Such a difference may represent a thrust bearing <NUM> loaded in the forward or aft direction by a desirable thrust load. In one embodiment, the FADEC <NUM> may compare the actual difference between the ball passing frequencies and the set point and calculate an adjustment representing the difference between the set point and the actual difference. Further, the FADEC <NUM> may then use this adjustment as an input to modify the force applied by the thrust cavity <NUM> on the rotating structure <NUM>. As such, the closed loop control system may keep the thrust bearing <NUM> at the desired set point or range.

Referring now particularly to <FIG>, a schematic view of one embodiment of a thrust cavity <NUM> located in the turbine section <NUM> of the engine <NUM> is illustrated according to aspects of the present subject matter. As shown, for the illustrated embodiment, the thrust cavity <NUM> is defined by a fixed structure <NUM>, a rotating structure <NUM>, and two thrust cavity seals <NUM>. In the exemplary embodiment, the thrust cavity <NUM> may modify a force either forward or aft on the rotating drive shaft <NUM> relative to the centerline <NUM>. For example, an increasing pressure supplied to the thrust cavity <NUM> increases pressure on the rotating structure <NUM> and may apply a force on the rotating drive shaft <NUM>, such as the high pressure drive shaft <NUM>, in the aft direction. Similarly, for the embodiment shown, a decreasing pressure supplied to the thrust cavity <NUM> decreases the pressure on the rotating structure <NUM> and may allow the net force on the high pressure drive shaft <NUM> to move the high pressure drive shaft <NUM> in the forward direction. It should be recognized, for the exemplary embodiment, that either an increase or a decrease in pressure may be used to change the force acting on the high pressure drive shaft <NUM> and move the thrust bearing <NUM> out of a cross-over condition. It should be recognized that, in other embodiments, the thrust cavity <NUM> may be located in the compressor section <NUM> and the rotating drive shaft <NUM> may be the low pressure drive shaft <NUM>.

Referring now particularly to <FIG>, a schematic view of one embodiment of a thrust cavity <NUM> located aft of the high pressure compressor section <NUM> is illustrated according to aspects of the present subject matter. In the shown embodiment, one thrust cavity seal <NUM> is at least partially defined by a compressor discharge pressure (CDP) seal <NUM>. For example, the CDP seal <NUM> may be any type of seal known in the art, such as, but not limited to, a labyrinth seal <NUM>. For the embodiment shown, the thrust cavity <NUM> is pressurized by leaking air through the bleed air port <NUM> from the high pressure compressor section <NUM>. For instance, pressurized air from the bleed air port <NUM> may pressurize the thrust cavity <NUM> though the CDP seal <NUM>. The thrust cavity <NUM>, in the shown embodiment, is defined by the thrust seals <NUM>, the fixed structure <NUM>, and the rotating structure <NUM>. As such, the force applied to the high pressure drive shaft <NUM> may be modified by changing the pressure in the thrust cavity <NUM> to supply more or less pressure to the rotating structure <NUM>. More particularly, for the illustrated embodiment, more or less air may be bled from the high pressure compressor section <NUM>.

It should be recognized that in further embodiments the force acting on the rotating structure <NUM> may be modified by changing the volume of the thrust cavity <NUM>. More particularly, increasing the volume of the thrust cavity <NUM> may increase the surface area of the rotating structure <NUM>. As such, the pressure in the thrust cavity <NUM> may act on a larger surface area and generate a greater force on the high pressure drive shaft <NUM>. Similarly, decreasing the volume of the thrust cavity <NUM> may decrease the surface area of the rotating structure <NUM>. As such, the pressure in the thrust cavity <NUM> may act on a smaller surface area and generate less force on the high pressure drive shaft <NUM>.

Referring now to <FIG>, an embodiment of the system <NUM> for balancing rotor thrust is illustrated using two thrust cavities <NUM> according to aspects of the present disclosure. For example, the system <NUM> may include a first thrust cavity <NUM> forward of the thrust bearing <NUM>, such as at or near the high pressure compressor <NUM>. Further, for the illustrated embodiment, the system <NUM> includes a second thrust cavity <NUM> aft of the thrust bearing <NUM>, such as at or near the high pressure turbine <NUM>. As shown, the pressure in the first thrust cavity <NUM> may be increased in order to apply a forward force on the rotating structure <NUM> and the high pressure drive shaft <NUM>. Similarly, the pressure in the second thrust cavity <NUM> may be increased in order to apply an aft force to the rotating structure <NUM> and the high pressure drive shaft <NUM>. As such, the system <NUM> may move the thrust bearing <NUM> from a cross-over condition by apply a force to the rotating drive shaft <NUM>, such as the high pressure drive shaft <NUM>, either forward or aft by increasing the pressure in the first thrust cavity <NUM> or the second thrust cavity <NUM> respectfully. Further, <FIG> illustrates the waveguide sensor <NUM> extending outside of the engine <NUM>, such as to a control system.

It should be recognized that the system <NUM> may balance the rotor thrust on the thrust bearing <NUM> using any thrust cavity <NUM> in contact with a rotating drive shaft <NUM>. For example, any sealed cavity in contact with the rotating drive shaft <NUM> or a rotating structure <NUM> coupled to the rotating drive shaft <NUM> may be pressurized to supply a force axially to the rotating drive shaft <NUM>. Further, the system may be used to balance rotor thrust on the low pressure drive shaft <NUM> or an intermediary pressure drive shaft.

Referring now to <FIG>, a schematic view of one embodiment of a thrust cavity <NUM> located in the turbine section <NUM> and including two rotating structures <NUM> is illustrated according to aspects of the present subject matter. As shown, for the illustrated embodiment, the thrust cavity <NUM> is defined by a first rotating structure <NUM> coupled to the high pressure drive shaft <NUM>, a second rotating structure <NUM> coupled to the low pressure drive shaft <NUM>, and a plurality of thrust cavity seals <NUM>. In the exemplary embodiment, an increasing pressure supplied to the thrust cavity <NUM> increases pressure on the rotating structures <NUM>, <NUM>. For example, an increasing pressure may apply a forward force on the first rotating structure <NUM> and thus a forward force on the high pressure drive shaft <NUM>. Similarly, for the embodiment shown, an increasing pressure may apply an aft force on the second rotating structure <NUM> and thus an aft force on the low pressure drive shaft <NUM>. Thus, for the embodiment shown, the thrust cavity <NUM> allows for a linked high pressure and low pressure drive shaft <NUM>, <NUM> adjustment.

It should be recognized that, for the illustrated embodiment, a decreasing pressure may supply a decreased force on both the first rotating structure <NUM> and the second rotating structure <NUM>. For instance, a decreasing pressure supplied to the thrust cavity <NUM> decreases the pressure on the first rotating structure <NUM> and may allow the net force on the high pressure drive shaft <NUM> to move the high pressure drive shaft <NUM> in the aft direction. Similarly, for the embodiment shown, a decreasing pressure supplied to the thrust cavity <NUM> decreases the pressure on the second rotating structure <NUM> and may allow the net force on the low pressure drive shaft <NUM> to move the low pressure drive shaft <NUM> in the forward direction.

Referring now to <FIG>, a flow diagram of one embodiment of a method <NUM> for balancing rotor thrust on a thrust bearing <NUM> of a turbomachine is illustrated in accordance with aspects of the present disclosure. The method <NUM> may be used on any turbomachine, such as, but not limited to the gas turbine engine <NUM> of <FIG>. Further, the method <NUM> may be used generally with the system <NUM> described in <FIG> or with any other capable system.

At step <NUM>, the method <NUM> may include communicating a vibrational frequency from the thrust bearing <NUM> to the exterior of the turbomachine using a waveguide sensor <NUM> coupled to the thrust bearing <NUM>. In certain embodiments, the vibrational frequency is a ball passing frequency, such as the ball passing frequency on the outer race <NUM> of the thrust bearing <NUM>. In the exemplary embodiment, another step <NUM> includes communicating the vibrational frequency to a control sensor communicatively coupled to a control system. In one embodiment, the control sensor is the piezoelectric sensor <NUM>. The control system may be the FADEC control system <NUM> of <FIG>.

In one embodiment, the method <NUM> includes at <NUM> comparing the magnitude of a first ball passing frequency communicated from a first waveguide sensor <NUM> at a forward end <NUM> of the thrust bearing <NUM> relative to the centerline <NUM> to a second ball passing frequency communicated from a second waveguide sensor <NUM> at an aft end <NUM> of the thrust bearing <NUM> relative to the centerline <NUM>. Further, the method <NUM> may include at <NUM> determining the direction of the rotor thrust acting on a rotating drive shaft <NUM> relative to the centerline <NUM> based on the difference between the magnitude of first ball passing frequency and the second ball passing frequency. It should be recognized that the rotating drive shaft <NUM> may be the high pressure drive shaft <NUM>, the low pressure drive shaft <NUM>, or any other suitable drive shaft.

At <NUM>, the exemplary method <NUM> includes determining whether the thrust bearing <NUM> is in a cross-over condition. For example, determining the cross-over condition may include determining if a ball passing frequency of the thrust bearing <NUM> is below a first threshold. For instance, a ball passing frequency below the first threshold for the system <NUM> may indicate the thrust bearing <NUM> is in a cross-over condition. In the depicted embodiment, another step <NUM> includes changing the pressure of a thrust cavity <NUM> in contact with a rotating drive shaft <NUM> in response to a cross-over condition of the thrust bearing <NUM>. For example, the method <NUM> may include communicating a signal from the control system, such as a FADEC system <NUM>, to a valve <NUM>. For certain embodiments, the valve <NUM> is coupled to and receives a pressurized fluid from a compressor section <NUM> of the turbomachine (e.g. the engine <NUM>) and selectively transfers the pressurized fluid to a thrust cavity <NUM> in contact with the rotating drive shaft <NUM>. In other embodiments, the pressurized fluid may be received from the turbine section <NUM>. For the depicted embodiment, the pressure in the thrust cavity <NUM> acts on a rotating structure <NUM> defining the thrust cavity <NUM>. As such, the exemplary method <NUM> includes at <NUM> changing a force on a rotating drive shaft <NUM>, such as the high pressure drive shaft <NUM> or the lower pressure drive shaft <NUM>, to remove the thrust bearing <NUM> out of the cross-over condition. For instance, the changing pressure of the thrust cavity <NUM> may modify the pressure acting on the area of the rotating structure <NUM>. This changing pressure may modify the force applied to the rotating drive shaft <NUM>.

Referring now to <FIG>, a flow diagram of another embodiment of a method <NUM> for balancing rotor thrust on a thrust bearing <NUM> of the turbomachine is illustrated in accordance with aspects of the present disclosure. The method <NUM> may generally have similar steps to the method <NUM>. For example, the method <NUM> may share steps <NUM>-<NUM> with the method <NUM>. At step <NUM>, the method <NUM> may include communicating a ball passing frequency from the thrust bearing <NUM> to the exterior of the turbomachine using a waveguide sensor <NUM> coupled to the thrust bearing <NUM>. In the exemplary embodiment, another step <NUM> includes communicating the ball passing frequency to a control sensor communicatively coupled to a control system. In one embodiment, the control sensor is the piezoelectric sensor <NUM>. The control system may be the FADEC control system <NUM> of <FIG>.

Claim 1:
A rotor thrust balancing system (<NUM>) for a turbomachine, wherein the turbomachine defines a centerline (<NUM>) extending a length of the turbomachine, the system comprising:
a rotating drive shaft (<NUM>) coupling a turbine section (<NUM>) and a compressor section (<NUM>) of the turbomachine;
a thrust bearing (<NUM>) supporting the rotating drive shaft (<NUM>) of the turbomachine, the thrust bearing (<NUM>) comprising:
a plurality of ball bearings (<NUM>);
an inner race (<NUM>) coupled to the rotating drive shaft (<NUM>); and
an outer race (<NUM>) coupled to a fixed structure (<NUM>);
a first waveguide sensor (<NUM>) coupled to the outer race (<NUM>) at a first end (<NUM>) of the waveguide sensor (<NUM>), wherein the waveguide sensor (<NUM>) communicates a vibrational frequency from the thrust bearing (<NUM>) to a second end (<NUM>) of the waveguide sensor (<NUM>); and
a valve (<NUM>) configured to reduce or increase pressure supplied to a thrust cavity (<NUM>), wherein the thrust cavity (<NUM>) modifies a force either forward or aft on the rotating drive shaft (<NUM>) relative to the centerline (<NUM>).