Cooling air supply control system for air cycle machine

An air supply controller is configured to supply cooling air to an air cycle machine. The controller includes a chamber having a first inlet configured to receive air from a first source, a second inlet configured to receive air from a second source, and an outlet configured to pass air from first inlet and/or the second inlet to an air cycle machine. A control member is disposed within the chamber and configured to move from a first position to a second position. When the control member is in the first position it obstructs an airflow from the second inlet to the outlet and permits an airflow from the first inlet to the outlet. When the control member is in the second position it obstructs the airflow from the first inlet to the outlet and permits the airflow from the second inlet to the outlet.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to an air cycle machine and, more particularly, to a cooling air supply control system for an air cycle machine.

Conventional aircraft environmental control systems (ECSs) incorporate an air cycle machine, also referred to as an air cycle cooling machine, for use in cooling and dehumidifying air for an aircraft cabin. Such air cycle machines may include two or more wheels disposed at axially spaced intervals along a common shaft. The wheels are part of, for example, a compressor rotor, a turbine rotor, a fan rotor, an additional turbine rotor, or an additional compressor rotor. In some cases the turbine or turbines drive both the compressor and the fan.

On aircraft powered by turbine engines, the air to be conditioned in the air cycle machine is typically compressed air bled from one or more of compressor stages of the turbine engine. In conventional systems, this bleed air passes through the air cycle machine compressor where it is further compressed. The compressed air is passed through a heat exchanger to cool the compressed air sufficiently to remove moisture and dehumidify the air. The dehumidified compressed air is expanded in the turbine of the air cycle machine to both extract energy from the compressed air so as to drive the shaft and also to cool the expanded turbine exhaust air before it is supplied to the aircraft cabin as conditioned cooling air.

A flow path of an air cycle machine can also include a heat exchanger cooling flow that draws air through the heat exchanger, past a fan rotor, and dumps the flow into an overboard duct. The fan rotor can be used to establish the flow when insufficient ram air is available to draw air through the heat exchanger.

Bearings are used and employed within air cycle machines. As the air cycle machine operates, the bearings will heat up. The heat can lead to damage to the bearings or to other components of the air cycle machine. Thus, bearing cooling air is fed into the air cycle machine for the purpose of maintaining operational temperatures for the bearings i.e., relatively cool temperatures.

Hydrodynamic fluid film journal bearings, also called journal air bearings or foil bearings, can be used to provide support to rotatable components such as shafts. A typical journal bearing may include a journal sleeve, a bump foil, an intermediate foil, and a top foil. During operation, rotation of the rotatable component causes a working fluid to form a cushion (often referred to as an “air bearing”) that supports the rotatable component with little or no direct contact between the rotatable component and the foils of the bearing. Journal bearings provide fluid cushions for radial loads.

Similarly, hydrodynamic fluid film thrust bearings generate a lubricating non-linear air film between a portion of a rotating shaft or other rotatable component and the bearing. One typical bearing arrangement utilizes welded subassemblies. A top subassembly includes an annular main plate having multiple arcuate, corrugated foils welded to the main plate. A corresponding number of arcuate top foils are supported by bump foils. A bottom subassembly includes another annular main plate having multiple arcuate bump foils welded to the main plate. Thus, during operation, rotation of the rotatable component or shaft causes a working fluid to form in and around the corrugated foils to provide an air bearing. The bump foils provide a desired spring rate to cushion the rotatable component as the shaft moves axially. Thus, thrust bearings provide fluid cushions for axial loads.

During operation, the bearings may be rotated at high speeds which result in heat generation. The heat can lead to failure of the bearings by compromising the structural integrity of the components of the bearings. To reduce the risk of failure of the bearings, cooling air is conveyed and passed over bearing surfaces to remove the heat from the bearing.

Traditionally, the bearing cooling flow is supplied from a single high pressure, cool temperature source. For example, the bearing cooling flow is traditionally sourced from the turbine inlet of the air conditioning system, with the source of the air to the air conditioning system a compressor stage of the engine of the aircraft. Check valves may be used to close the cooling air inlet to close the bearing cooling circuit in order to reduce leakage and impact system efficiency when the air cycle machine is not running, effectively shutting off the cooling air supply when not in use.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, an air supply controller is configured to supply cooling air to an air cycle machine, the controller including a chamber having a first inlet configured to receive air from a first source, a second inlet configured to receive air from a second source, and an outlet configured to pass air from at least one of the first inlet and the second inlet to an air cycle machine, and a control member disposed within the chamber and configured to move within the chamber from a first position to a second position. When the control member is in the first position the control member obstructs an airflow from the second inlet to the outlet and permits an airflow from the first inlet to the outlet, and when the control member is in the second position the control member obstructs the airflow from the first inlet to the outlet and permits the airflow from the second inlet to the outlet.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, in general, provides a control system for providing a cooling air flow to hydrodynamic fluid film bearing assemblies. The control system provides, in some embodiments, a simple control member design with no actuators, motors, or other types of controls, although in some embodiments such operational features may be included without departing from the scope of the invention, and may be included depending on the requirements or design of a particular air cycle machine. Further, the control systems and methods disclosed herein can be employed in existing air cycle machines without substantial modification.

FIG. 1is a cross-sectional view of an exemplary hydrodynamic fluid film journal bearing assembly (“journal bearing100”), which represents one type of foil hydrodynamic bearing that may employ embodiments of the invention. The journal bearing100includes a journal sleeve102that defines an outer diameter surface104and an inner diameter surface106. The journal sleeve102is substantially cylindrical and is arranged about a central axis. It should be noted that the journal sleeve can have a conventional cylindrical shape, or can be shaped with a weight-reduced profile, or configured as other shapes or configurations, andFIG. 1merely presents an exemplary configuration of a journal bearing100.

InFIG. 1, a number of foils are arranged inside the journal sleeve102. The journal bearing100includes a bump foil108, an intermediate foil110, and a top foil122. The bump foil108, the intermediate foil110, and the top foil112are each formed from thin sheets of material (e.g., nickel-based alloys, steel, or similar materials) wrapped in a generally cylindrical shape and positioned in a bore of the journal sleeve102. The bump foil108is corrugated, allowing a working fluid and/or cooling fluid to flow through the spaces formed between adjacent corrugations. The bump foil108is positioned adjacent to the inner diameter surface106of the journal sleeve102. The foils108,110, and112are retained relative to the journal sleeve102with bent portions114that engage a key slot116.

A rotatable component like a shaft (not shown) can be positioned inside the journal bearing100, radially inward from the top foil112. A radially inner surface of the top foil112exposed to the rotatable component can optionally be coated with a suitable dry film lubricant. Use of such a dry film lubricant can reduce friction caused by the rotatable component contacting the top foil112when accelerating to operating speed, when decelerating from operating speed, when stopped, and when subject to incidental contact with the top foil122during regular operation. Even with the application of a dry film lubricant, during operation heat is generated on the surfaces of the foils108,110, and112of journal bearing100, which can lead to structural failure of the journal bearing100. Accordingly, moving air is passed over the surfaces of the journal bearing100to remove the heat and prevent the journal bearing100from overheating and failing. However, under atypical system operation, loads exceeding bearing capacity will be imposed on a bearing leading to an associated increase in bearing cooling flow temperature and bearing failure.

Now referring toFIG. 2, an exploded view of an exemplary hydrodynamic fluid film thrust bearing assembly (“thrust bearing200”), which represents another type of foil hydrodynamic bearing that may employ embodiments of the invention, is shown. The thrust bearing200ofFIG. 2has a different construction than the journal bearing100ofFIG. 1. This is because journal bearings, such as shown inFIG. 1, operate with radial loads, whereas thrust bearings, as shown inFIG. 2, operate with axial loads. However, both types of bearings operate similarly by employing hydrodynamic fluid films, such as air or other fluids, to both provide bearing lubricant and cooling flows to prevent overheating.

The thrust bearing200includes three layers, but may include more or fewer layers. A first layer202comprises multiple arcuate top foils204that are spaced circumferentially relative to one another about a central axis. The top foils204are supported by a second layer206having a corresponding number of arcuate bump foils208arranged circumferentially beneath the top foils204. The bump foils208are corrugated to provide cushioning and accommodate a cooling airflow through the thrust bearing200. A third layer210is provided as an annular main plate212that supports the bump foils208. Similar to a journal bearing, the top foils204of the thrust bearing may be coated in a dry film lubricant. The three layers202,206, and210may be secured to one another, for example, by spot welding.

Similar to the journal bearing100ofFIG. 1, moving air is passed over the surfaces of the thrust bearing200to remove the heat and prevent the thrust bearing200from overheating and failing. However, again, under atypical system operation, loads exceeding bearing capacity will be imposed on a bearing leading to an associated increase in bearing cooling flow temperatures and to bearing failure.

The above described hydrodynamic bearings can be employed in air cycle machines of aircraft. The hydrodynamic bearings provide a long lasting bearing with minimal to no required maintenance. This is because the bearings employ air as both a lubricating fluid and as a cooling fluid. This means that no lubricating or cooling liquids, such as oils, need to be replaced over time.

Turning now toFIG. 3, an air cycle machine300is part of an environmental control system that is configured to supply conditioned air, for example, to a cabin of an aircraft. The air cycle machine300is a four-wheel air cycle machine, with four rotors on a single shaft304. The four rotors are fixed together and are supported by bearing elements. There are, thus, four bearings configured within the air cycle machine300which are arranged along an airflow passage306, which is represented by the path of arrows inFIG. 3. The air flow passage306provides air as both a lubricating fluid for the hydrodynamic bearings and as a cooling air flow to remove heat generated by the bearings during operation. Although described herein as a four-wheel air cycle machine, this is presented for illustrative and explanatory purposes, and other air cycle machines or other device/configurations may be used without departing from the scope of the invention, such as, for example, three-wheel air cycle machines.

In the exemplary configuration ofFIG. 3, two of the four bearings are thrust bearings and two are journal bearings. The thrust bearings are located at the inlet side of the airflow passage306and the journal bearings located further downstream in the airflow passage306. A first thrust bearing308is configured as an outboard thrust bearing and a second thrust bearing310is configured as an inboard thrust bearing. After the thrust bearings308and310, in the direction of the airflow passage306, a first journal bearing312is configured as a turbine journal bearing and then, toward the outlet of the airflow passage306, a second journal bearing314is configured as a fan journal bearing. The thrust bearings308,310are configured to operate with axial loads, and the journal bearings312,314are configured to operate with radial loads within the engine302.

As a non-limiting example, the air cycle machine300may operate at 20,000-50,000 RPM. However, other rotational speeds of operation may be used without departing from the scope of the invention. As such, during operation, each of the bearings308,310,312,314will generate heat due to viscous shear of the hydrodynamically generated film of air between the bearing top foil and the rotating shaft which can lead to structural failure of the bearings. To dissipate the heat, air flows through airflow passage306and passes over the bearings308,310,312,314to provide a cooling factor through and/or over the bearings. The supply of cooling air impacts the efficiency of the entire system, such as the power and efficiency of an aircraft. Thus, providing an efficient supply, both in terms of air temperature/pressure and demands on the system, is beneficial.

The cooling air in airflow passage306is supplied from a cooling air inlet316. Traditionally, the inlet316is fluidly connected to a single air supply source, which is usually a single, high pressure, cool temperature source (not shown). For example, the traditional source may be a turbine air flow that supplies bleed air.

Turning now toFIG. 4, an exemplary cooling air flow control system in accordance with the invention is shown. Cooling airflow control system400fluidly connected to a cooling airflow passage of an air cycle machine401, e.g., fluidly connected to air passage306ofFIG. 3. Thus, the cooling airflow control system400fluidly connects to the air cycle machine401by means of an outlet402, which may be the same as air cycle machine inlet316ofFIG. 3, or fluidly connected thereto by intermediate channels, pathways, etc.

The cooling airflow control system400may have two airflow inlets, which may be selectively controlled or opened to determine a fluid airflow supply to the air cycle machine401. For example, as shown inFIG. 4, the cooling airflow control system400includes a first inlet404and a second inlet406. The first inlet404is fluidly connected to a first source408, such as a bleed line of a turbine, such that the air cycle machine401may be supplied with air from the first source408. The second inlet406may be fluidly connected to a second source410, such as a pressure compressor, such that the air cycle machine401may be supplied with air from the second source410. For example, if the second source is configured as a pressure compressor, the air supplied to the air cycle machine401will be pre-treated, e.g., compressed and/or thermally treated, prior to entering the airflow passage of the air cycle machine401.

The airflow supply to the air cycle machine401is controlled, in part, by a control member412. The control member412is configured to block, prevent, suppress, stop, or otherwise impede airflow, at least partially, from one or both of the two inlets404,406of the cooling airflow control system400. The control member412, as shown inFIG. 4, is configured as a sliding seal or other sealing device. In some such embodiments, the control member412is configured as a poppet, plug, or stopper (e.g., as shown inFIG. 4), and in other embodiments, the control member may be configured as a flap valve or valve-type configuration (e.g., as shown inFIG. 5). Those of skill in the art will appreciate that other types of control members may be employed without departing from the scope of the invention, and the embodiments described herein are provided for illustrative and explanatory purposes only. In some embodiments, as shown inFIG. 4, the control member412is movably or slidably engaged within a chamber414. The control member412is movable between at least a first position and a second position within the chamber414.

In the first position, the control member412may block or prevent airflow from the second source410and permit airflow from the first source408to the air cycle machine401, through a portion of the chamber414. The first position is shown, for example, as the solid line representation of the control member412, with the airflow through the cooling airflow control system400shown in solid line arrows.

In the second position, the control member412may block or prevent airflow from the first source408and permit airflow from the second source410to the air cycle machine401, through a portion of the chamber414. The second position is shown, for example, as the dashed line representation of the control member412, with the airflow through the cooling airflow control system400shown in dashed line arrows.

The control member412is movable from the first position to the second position and/or from the second position to the first position, in part, by one or more springs or other type of actuating and/or biasing device(s)416,418. The control member412is guided within the chamber414by a guide420, which may be a tie rod or other similar device.

The biasing members416,418are configured to compress and/or expand based on a relative pressure, which determines which airflow supply (first source408or second source410) will be used for cooling the bearings of air cycle machine401. As such, the biasing members416,418may have different spring forces and the control member412may be moved within the chamber414based on the compression/extension of the biasing members416,418.

For example, a control pressure Pcontrolmay be predetermined such that a first biasing member416is extended or expanded and a second biasing member418is compressed, in the presence of the control pressure Pcontrol. That is, when a pressure of the air within the cooling airflow control system400is equal to the control pressure Pcontrol, the control member412is in the first position. As noted, in the first position (solid line representation), airflow flows from the turbine408to the air cycle machine401.

The control pressure Pcontrolmay be set such that the pressure is equal to ambient pressure Pambwhen an aircraft is on the ground, thus Pcontrol=Pamb. This is controlled, in part, by a first block422, which may support the first biasing element416. Air flow with ambient pressure Pambis supplied from the first source408, which, for example, pulls air from outside the aircraft, through a turbine, and a portion of the air is bled to the first inlet404. In this example, supply from the first source408occurs when the aircraft is on the ground and/or at low altitudes. However, as the aircraft attains higher altitudes, the outside air pressure drops and lowers in temperature.

To provide efficient use of power and airflows, air compressors are employed in the aircraft. The compressors will compress the incoming air to a compressor pressure Pcis. A portion of the compressor-supplied air having compressor pressure Pciswill be fed into the second inlet406from the second source410. When the pressure of the air in the inlet406(Pcis) exceeds the air pressure of the air supplied from the first source408in the first inlet404(Pamb), the spring force of the first biasing member416will be exceeded, and the first biasing member416will compress. As the first biasing member416compresses, the control member412will slide along guide420from the first position toward the second position (dashed lines shown inFIG. 4), within the chamber414. At the same time, the second biasing member418will expand from a second block424.

In some embodiments, first and second blocks422,424may be configured as pistons or be piston-like. Thus, in some embodiments, the air pressure (PAMBor Pcis) may act as a driving force against the first and second blocks422,424to move the control member412via the guide420, which operably connects the two blocks422,424and the control member412, as shown inFIG. 4.

When the aircraft then descends, and the air pressure changes, the air supplied from the first source408at pressure Pambwill exceed the pressure Pcisof the air supplied from the second source410, and Pambwill approach Pcontrolwhich will force the first biasing member416to expand and the second biasing member418to compress, thus returning the control member412to the first position (solid lines inFIG. 4).

In some embodiments, the first biasing member416may be fixedly connected or attached to one or both of the first block422and the control member412and the second biasing member418may be fixedly connected or attached to one or both of the second block424and the control member412. Further, in some embodiments, the guide420may be fixedly connected or attached to one or both of the first block422and the second block424.

Thus, in some, the control member412configuration enables a passive controlling of the air supply source to an air cycle machine401.

Turning now toFIG. 5, alternative exemplary embodiment of the invention is shown. Various elements ofFIG. 5are substantially similar to various elements of the embodiment ofFIG. 4, and thus like features are numbered the same but with a “5” preceding the number rather than a “4.”

The primary difference between the embodiments ofFIG. 4andFIG. 5is the configuration of the control member512. InFIG. 5, control member512is configured as a flap valve. The control member512may have a elasticity or other characteristic that enables change from the first position (solid line) to a second position (dashed line). In the embodiment ofFIG. 5, because the configuration of the control member512is different, the chamber514is similarly changed to accommodate the operation of the cooling airflow control system500. In some embodiments, the control member512may be configured on a hinge or similar structure that is configured to enable changing from the first position to the second position based on the relative pressure differences between the air supplied by the first source508and the second source510.

Although the embodiments ofFIGS. 4 and 5have been described with respect to passive control systems, an active control system may be employed without departing from the scope of the invention. For example, with reference toFIGS. 4 and 5, a computer or other type of electronic or mechanical controller, hereinafter referred to as a processor, can be operationally connected or in communication with the control member412,512. The processor can be configured with algorithms, programs, programming, etc. that operationally controls the supply source of cooling air flow for the bearings of the air cycle machine. Further, in some embodiment, a mechanical controller may be used, wherein a sensing of comparative pressures is determined, and a selection of the supply air source is made. Thus, various other embodiments that are active may be used without departing from the scope of the invention.

Advantageously, in some embodiments, a simple control member, such as a spring/poppet control design with no actuators, motors, or other types of controls are required to efficiently supply cooling air to an air cycle machine. Further, in some embodiments, controllers, motors, or other types of controls may be used.

Advantageously, when employed on an aircraft, the system disclosed herein takes advantage of low bleed temperatures associated with environmental control systems. For example, the compressor of an environment control system may provide inlet air temperatures that are sufficient for cooling bearings of an air cycle machine. Further, when in flight, efficiency may be gained by tapping off cooling flow prior to performing work on the air in the air cycle machine, e.g., heat transfer in a heat exchanger. Furthermore, because the sourcing inlet sizes of traditional turbine supplies are optimized for ground cooling, using a second inlet source (such as a compressor) reduces the cooling flow tapped during flight.

Further, advantageously, embodiments of the invention enable a reduction of engine bleed tap-off from the air conditioning system while in flight, thus increasing engine efficiency and reducing fuel burn. Further, tapping off cooling air within the air conditioning system prior to passing through the compressor and primary heat exchanger improve the air cycle machine and heat exchanger efficiencies, which enables a reduction in size requirements and corresponding weight of both elements. Further, the increased efficiency provided and enabled by embodiments of the invention provide a domino effect by further improving engine efficiency and fuel burn because less bleed flow is tapped off the engine. Similarly, another domino effect is a reduced aircraft weight which results in a reduction in fuel burn.

Further, for example, although described herein as first and second sources being a turbine and a compressor, those of skill in the art will appreciate that other configurations are possible without departing from the scope of the invention.

Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.