Inlet shroud assembly

An inlet shroud assembly includes a hub and a shroud for a ram air fan. The hub includes a center bore, a first frustoconical section, a plurality of slotted cooling holes located on the first frustoconical section, a second frustoconical section, a plurality of circular cooling holes located on the second frustoconical section, a rim, a central cavity, and an annular cavity. The shroud includes a central disk with a center bore, a circular flange located on a radially outer edge of the central disk, and an outer disk with a web portion and a tip portion, the tip portion having a curved lip.

BACKGROUND

The present invention relates to an environmental control system. In particular, the invention relates to a ram air fan assembly for an environmental control system for an aircraft.

An environmental control system (“ECS”) aboard an aircraft provides conditioned air to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the ECS before the air is delivered to the aircraft cabin. As heat is removed from the air, it is dissipated by the ECS into a separate stream of air that flows into the ECS, across heat exchangers in the ECS, and out of the aircraft, carrying the excess heat with it. Under conditions where the aircraft is moving fast enough, the pressure of air ramming into the aircraft is sufficient to move enough air through the ECS and over the heat exchangers to remove the excess heat.

While ram air works well under normal flight conditions, at lower flight speeds, or when the aircraft is on the ground, ram air pressure is too low to provide enough air flow across the heat exchangers for sufficient heat removal from the ECS. Under these conditions, a fan within the ECS is employed to provide the necessary airflow across the ECS heat exchangers. This fan is called a ram air fan.

As with any system aboard an aircraft, there is great value in an improved ram air fan that includes innovative components designed to improve the operational efficiency of the ram air fan or to reduce its weight.

SUMMARY

According to the present invention, an inlet shroud assembly includes a hub and a shroud for a ram air fan. The hub includes a central hub with a center bore, a first frustoconical section radially outward and axially forward of the central hub, a plurality of slotted cooling holes on the first frustoconical section, a second frustoconical section radially outward and axially forward of the first frustoconical section, a plurality of circular cooling holes on the second frustoconical section, a rim radially outward and axially forward of the second frustoconical section, a central cavity axially forward of the central hub, and an annular cavity radially outward and axially forward of the central hub. The shroud includes a central disk with a center bore, a circular flange located on a radially outer edge of the central disk, and an outer disk. The outer disk includes a web portion extending radially outward and axially rearward of the central disk and a tip portion extending radially outward of the first section with a curved lip extending axially forward towards the central disk.

DETAILED DESCRIPTION

FIG. 1illustrates ram fan air assembly10incorporating the present invention. Ram air fan assembly10includes fan housing12, bearing housing14, inlet housing16, outer housing18, and inner housing20. Fan housing12includes fan struts22, motor24(including motor rotor25and motor stator26), thrust shaft28, thrust plate30, and thrust bearings32. Bearing housing14includes journal bearing shaft34and shaft cap36. Fan housing12and bearing housing14together include tie rod38and journal bearings40. Inlet housing16contains fan rotor42, shroud44, and hub45, in addition to a portion of tie rod38. Outer housing18includes terminal box46and plenum48. Within outer housing18are diffuser50, motor bearing cooling tube52, and wire transfer tube54. A fan inlet is a source of air to be moved by ram air fan assembly10in the absence of sufficient ram air pressure. A bypass inlet is a source of air that moves through ram air fan assembly10when sufficient ram air pressure is available.

As illustrated inFIG. 1, inlet housing16and outer housing18are attached to fan housing12at fan struts22. Bearing housing14is attached to fan housing12and inner housing20connects motor bearing cooling tube52and wire transfer tube54to bearing housing14. Motor bearing cooling tube52connects inner housing20to a source of cooling air at outer housing18. Wire transfer tube54connects inner housing20to outer housing18at terminal box46. Motor stator26and thrust plate30attach to fan housing12. Motor rotor25is contained within motor stator26and connects journal bearing shaft34to thrust shaft28. Journal bearing shaft34, motor rotor25, and thrust shaft28define an axis of rotation for ram fan assembly10. Fan rotor42is attached to thrust shaft28with tie rod38extending along the axis of rotation from shaft cap36at the end of journal bearing shaft34through motor rotor25, thrust shaft28, and fan rotor42to hub45and shroud44. Nuts (not shown) secure shaft cap36to journal bearing shaft34on one end of tie rod38and hub45and shroud44to fan rotor42at opposite end of tie rod38. Thrust plate30and fan housing12contain a flange-like portion of thrust shaft28, with thrust bearings32positioned between the flange-like portion of thrust shaft28and thrust plate30; and between the flange-like portion of thrust shaft28and fan housing12. Journal bearings40are positioned between journal bearing shaft24and bearing housing14; and between thrust shaft28and fan housing12. Hub45, shroud44, fan rotor42, and a portion of fan housing12are contained within inlet housing16. Diffuser50is attached to an inner surface of outer housing18. Plenum48is a portion of outer housing18that connects ram air fan assembly10to the bypass inlet. Inlet housing16is connected to the fan inlet and outer housing18is connected to the fan outlet.

In operation, ram air fan assembly10is installed into an environmental control system aboard an aircraft and connected to the fan inlet, the bypass inlet, and the fan outlet. When the aircraft does not move fast enough to generate sufficient ram air pressure to meet the cooling needs of the ECS, power is supplied to motor stator26by wires running from terminal box46, through wire transfer tube54, inner housing20, and bearing housing14. Energizing motor stator26causes rotor24to rotate about the axis of rotation of ram fan assembly10, rotating connected journal bearing shaft34and thrust shaft28. Fan rotor42, hub45, and shroud44also rotate by way of their connection to thrust shaft28. Journal bearings40and thrust bearings32provide low friction support for the rotating components. As fan rotor42rotates, it moves air from the fan inlet, through inlet housing20, past fan struts22and into the space between fan housing12and outer housing18, increasing the air pressure in outer housing18. As the air moves through outer housing18, it flows past diffuser50and inner housing20, where the air pressure is reduced due to the shape of diffuser50and the shape of inner housing20. Once past inner housing20, the air moves out of outer housing18at the fan outlet.

Components within bearing housing14and fan housing12, especially thrust bearings32, journal bearings40and motor24, generate significant heat and must be cooled. Cooling air is provided by motor bearing cooling tube52which directs a flow of cooling air to inner housing20. Inner housing20directs flow of cooling air to bearing housing14, where it flows past components in bearing housing14and fan housing12, cooling bearings32,40and motor components. Cooling air then exits fan housing12through cooling holes in rotor42.

FIG. 2Ais a front elevation view of hub45.FIG. 2Bis a cross-sectional view of hub45. Referring toFIGS. 2A-2B, hub45includes center axis C, center bore60, central hub62, first frustoconical section64, second frustoconical section66, rim68, slotted cooling holes70, circular cooling holes72, central cavity74, annular cavity76, and internal flange78. Center bore60is centered on central axis C in the middle of central hub62. Center bore60has an outer diameter of about 0.371 inches (9.42 millimeters (mm)) to 0.372 inches (9.45 mm) and receives a portion of tie rod38. Central hub62has an outer diameter of about 1.1395 inches (28.94 mm) to 1.1405 inches (28.97 mm) and extends radially outward from center bore60. The axially rearward face of central hub62is placed against shroud44.

First frustoconical section64is radially outward and axially forward of central hub62. First frustoconical section64is angled 43 degrees to 47 degrees from central hub45and has a radially outward and axially forward diameter of about 1.1395 inches (28.943 mm) to 1.1405 inches (28.969 mm). Slotted cooling holes70are located on first frustoconical section64and include five holes equally spaced around center bore60. Slotted cooling holes70have circumferential width Wsof about 0.633 inches (16.078 mm) to 0.713 inches (18.110 mm). The centers of slotted cooling holes70are located at radius Rsabout 0.660 inches (16.764 mm) to 0.700 inches (17.780 mm) from center axis C.

Second frustoconical section66is radially outward and axially forward of first frustoconical section64. Rim68is radially outward and axially forward of second frustoconical section68. Second frustoconical section66is angled 68 degrees to 72 degrees from central hub45and has a radially outward and axially forward diameter of about 3.27 inches (83.058 mm) to 3.32 inches (84.328 mm). Circular cooling holes72are located on second frustoconical section66and include eleven holes equally spaced around center bore60. Circular cooling holes72have diameter Dcof about 0.37 inches (9.398 mm) to 0.38 inches (9.652 mm). The centers of circular cooling holes72are located at radius Rcabout 1.19 inches (30.226 mm) to 1.21 inches (30.734 mm) from center axis C.

Rim68is radially outward and axially forward of second frustoconical section66. Rim68has a flat face and an outer diameter of about 4.83 inches (122.682 mm) to 4.84 inches (122.936 mm). Central cavity74extends radially outward from center bore60and rearward of the forward face of hub45. Central cavity74has an outer diameter of about 1.5242 inches (38.715 mm) to 1.5252 inches (38.740 mm) and is located in first frustoconical section64. Internal flange78is radially outward of central cavity74. Internal flange78has an inner diameter of about 1.5242 inches (38.715 mm) to 1.5252 inches (38.740 mm) and an outer diameter of about 1.955 inches (49.657 mm) to 1.965 inches (49.911 mm). Annular cavity76extends radially outward from internal flange78and rearward of the forward face of hub45. Annular cavity76has an outer diameter of about 2.835 inches (72.009 mm) to 2.845 inches (72.263 mm) and is located in second frustoconical section66.

Hub45is preferably made out of aluminum, but any suitable material could be used. Further, hub45is machined in the embodiment shown, but any suitable method of manufacture could be used. Central cavity74is shaped to receive a portion of fan rotor42. Central hub42is shaped to fit into a cavity in shroud44to create an inlet shroud assembly. The inlet shroud assembly is further capable of being placed at one end of tie rod38.

When ram air fan assembly10is in use, the components in bearing housing14and fan housing12generate a lot of heat. Motor bearing cooling tube52will intake a cooling air flow to cool these components. The air exits inner housing20through cooling holes in fan rotor42, as seen inFIG. 1. This cooling air flow then travels through slotted cooling holes70and circular cooling holes72in hub12. The air flowing through slotted cooling holes70is air used to cool the inside diameter of motor rotor25. The air flowing through circular cooling holes72is air used to cool thrust bearings32. The size of slotted cooling holes70and circular cooling holes72enhances the air flow through hub12. The quantity and shape of slotted cooling holes70and circular cooling holes72help to enhance the structural strength of hub45.

FIG. 3is a cross-sectional view of shroud44. Shroud44includes center axis C, center bore80, central disk82, circular flange84, and outer disk86. Center bore80is centered on center axis C of shroud44and has a diameter of about 0.385 inches (9.779 mm) to 0.395 inches (10.033 mm). Central disk82extends radially outward from central bore80and has an outer diameter of about 1.1369 inches (28.877 mm) to 1.1379 inches (28.903 mm). Circular flange84is located on the axially forward face at the outer edge of central disk82. Circular flange84extends axially forward about 0.14 inches (3.556 mm) to 0.16 inches (4.064 mm) from central disk82. The radially inward surface of circular flange84and the axially forward face of central disk82create a cavity that is capable of receiving hub45.

Outer disk86has a thickness of about 0.08 inches (2.032 mm) to 0.10 inches (2.540 mm) and an outer diameter of about 6.545 inches (166.243 mm) to 6.665 inches (169.291 mm). Outer disk86has web portion88with a substantially flat surface that extends radially outward and axially rearward of central disk82. Web portion88extends at an angle of about 72 degrees to 76 degrees from central disk82. Outer disk86also has a tip portion89that extends radially outward of central disk82with a curved lip that extends axially forward. Tip portion89curves axially forward at an angle of about 83.6 degrees to 87.6 degrees. Shroud44is made out of aluminum in the embodiment shown, but any suitable material could be used. Further, shroud44is machined in the embodiment shown, but any suitable method of manufacture could be used.

Shroud44is press fit to hub45. As the cooling air flows through hub45, the curvature of shroud44directs the air outside of inner housing20. The shape of shroud44is designed to move the cooling air flow into inlet housing16and through the blades of fan rotor42. Further, shroud44is shaped to prevent the cooling air from stalling or recirculating. The shape of shroud44allows ram air fan assembly10to ingest an optimal amount of cooling air flow, which lowers the amount of air that needs to be taken from the engine. This lessens the amount of power consumption that is needed to cool the airplane.

Hub45and shroud44are press fit together by lining them up along center axis C that runs through center bore60and center bore80. The axially forward face of central disk82and the radially inward surface of circular flange84form a cavity in shroud44. The rearward face and radially outward surface of central hub62form a flange on hub45. The flange on hub45is designed to fit in the cavity on shroud44. Hub45and shroud44are then fit together by press fitting to form inlet shroud assembly90, although any suitable connection could be used, including other fits, adhesives, or fasteners. As stated above, the hub and shroud are machined parts made of aluminum in the embodiment shown, but any suitable material and method of manufacture can be used.

Inlet shroud assembly90is used in ram air fan assembly10to direct the cooling air flowing through inner housing20out into inlet housing16. Once the cooling air is in inlet housing16, the blades on fan rotor42will move the air into the space between inner housing20and outer housing18until it is expelled out of the forward end of outer housing18. Inlet shroud assembly90is placed on tie rod38to keep fan rotor42in place in ram air fan assembly10. Slotted cooling holes70and circular cooling holes72meter how much cooling air flows through journal bearings40, thrust bearings32, and motor rotor25. The cooling air flows over these components to reduce the heat that is being generated when these parts are operated. The shape, size, and location of slotted cooling holes70and circular cooling holes72on inlet shroud assembly90enhances the cooling air flow split between thrust bearings32and motor rotor25. Enhancing the air flow split minimizes the amount of cooling air flow needed, which reduces the amount of power consumption that is required to cool the airplane.

FIG. 5. is a block diagram showing a method92for installing inlet shroud assembly90in ram air fan assembly10. The method includes: machining hub45(step94); machining shroud44(step95); connecting hub45and shroud44by press fitting them together to form inlet shroud assembly90(step96); balancing inlet shroud assembly90(step97); connecting inlet shroud assembly90with motor rotor25, thrust shaft28, fan rotor42, bearing shaft34, and shaft cap36(step98); and placing tie rod38through cap shaft36and inlet shroud assembly90and fastening a nut on each end of tie rod90(step99).

Step94includes machining hub45, and step95includes machining shroud44. Hub45and shroud44are each machined as individual pieces in the embodiment shown, but they can be machined together. Hub45and shroud44are preferably made of aluminum, although any suitable material can be used. Additionally, hub45and shroud44can be manufactured by any suitable means.

Step96includes fitting hub45and shroud44together, preferably by press fitting. This can be done in a variety of ways. One way is to shrink hub45by immersing it in liquid nitrogen, causing it to freeze and contact. Hub45can then be placed in a cavity on shroud44designed to receive hub45. Hub45and shroud44form inlet shroud assembly90. Inlet shroud assembly90can then be placed in a warmer environment. As hub45warms back up to room temperature it will expand and form a secure connection with shroud44. A second way to fit hub45and shroud44together would be by using a hydraulic press to push hub45into shroud44. Further, hub45and shroud44can be connected in many other ways, including other fits or using adhesives or fasteners. If hub45and shroud44are machined together in the first step, then this step is unnecessary.

Step97includes balancing inlet shroud assembly90. This can be done using a balancing machine. Inlet shroud assembly90will be rotated on a shaft to determine the speed and rotating phase of inlet shroud assembly90. A known weight will then be added to inlet shroud assembly90at a known angle so it can be measured how the weight affects the balance of inlet shroud assembly90. This measure can be compared to the original measure to determine the weight and angles needed to bring the part into balance.

Step98includes connecting motor rotor25, thrust shaft28, fan rotor42, bearing shaft34, and shaft cap36, to inlet shroud assembly90. These parts can be connected with various connections, including interference fits, fasteners, or other methods. Connections must be secure so that all part rotate together.

Step99includes placing tie rod38through shaft cap36and inlet shroud assembly90. Tie rod38is then stretched using a machine that pulls on each end of tie rod38. Nuts can then be fastened onto each end of tie rod38and the stretch on tie rod38can be released. This secures a pre-load on tie rod38. The pre-load on tie rod38clamps together the parts to ensure secure connections and promote uniform rotation. The process of stretching tie rod38, tightening the nuts, and releasing the stretch can be performed an additional time to add more pre-load to tie rod38.