A gas turbine engine assembly includes, among other things, a clutch configured to move from a first position to a second position in response to rotation of a gas turbine engine fan at a speed greater than a threshold speed. Whether the clutch is in the first position or the second position, the clutch permits rotation of the gas turbine engine fan in a first direction. When the clutch is in the first position, the clutch limits rotation of the gas turbine engine fan only in an opposite, second direction. The clutch is disposed within a compartment that is accessible and removable via removal of an aft engine cover structure. The clutch is removable on-wing.

BACKGROUND

This disclosure relates to a clutch and, more particularly, to a mechanical clutch that limits relatively high-speed, unlubricated gas turbine engine fan operation.

Turbomachines, such as gas turbine engines, typically include a fan, a turbine section, a compressor section, and a combustor section. Turbomachines may employ a geared architecture connecting the fan and the turbine section.

Air moving through a non-operating gas turbine engine may rotate (i.e., windmill) the fan of the gas turbine engine. In some examples, the gas turbine engine is one of a group of engines that propels an aircraft during flight, and windmilling occurs if the gas turbine engine shuts down during flight. In other examples, wind moving though a gas turbine engine parked on the ground causes windmilling. Gas turbine engines include complex systems that lubricate the fan when windmilling.

SUMMARY

A gas turbine engine assembly according to an example embodiment of the present disclosure includes, among other things, a clutch configured to move from a first position to a second position in response to rotation of a gas turbine engine fan at a speed greater than a threshold speed. Whether the clutch is in the first position or the second position, the clutch permits rotation of the gas turbine engine fan in a first direction. When the clutch is in the first position, the clutch limits rotation of the gas turbine engine fan only in an opposite, second direction. The clutch is disposed within a compartment that is accessible and removable via removal of an aft engine cover structure. The clutch is removable on-wing.

In a further non-limiting embodiment of the foregoing gas turbine engine assembly, the aft engine cover structure includes an engine exhaust cone.

In a further non-limiting embodiment of either of the foregoing gas turbine engine assemblies, the clutch is disposed within an aft bearing compartment and the aft engine cover structure further includes an aft bearing compartment cover plate, disposed axially inward of the exhaust cone. In a further non-limiting embodiment of any of foregoing gas turbine engine assemblies, the clutch is positioned within a gas turbine engine such that the clutch can be moved from an installed position within the gas turbine engine to an uninstalled position without removing any blades from the gas turbine engine.

In a further non-limiting embodiment of any of foregoing gas turbine engine assemblies, the clutch is coupled to a low speed spool of a gas turbine engine.

In a further non-limiting embodiment of any of foregoing gas turbine engine assemblies, the low speed spool is rotatably coupled to the gas turbine engine fan via a geared architecture.

In a further non-limiting embodiment of any of foregoing gas turbine engine assemblies, the clutch is positioned within a gas turbine engine aft the geared architecture relative to a direction of flow through the gas turbine engine.

In a further non-limiting embodiment of any of foregoing gas turbine engine assemblies, the threshold speed is less than an idling speed.

In a further non-limiting embodiment of any of foregoing gas turbine engine assemblies, the threshold speed is a threshold rotational speed of the fan.

In a further non-limiting embodiment of any of foregoing gas turbine engine assemblies, the clutch is an entirely mechanical clutch.

A gas turbine engine assembly according to another example embodiment of the present disclosure includes, among other things, a fan, a spool configured to rotatably drive the fan through a geared architecture, and a clutch coupled to the spool, the clutch moveable between a first position that permits windmilling rotations of the fan, and a second position that limits windmilling rotations of the fan in one direction. The clutch is a mechanical clutch. The clutch is disposed within a compartment that is accessible and removable via removal of an aft engine cover structure. The clutch is removable on-wing.

In a further non-limiting embodiment of the foregoing gas turbine engine assembly, the aft engine cover structure includes an engine exhaust cone.

In a further non-limiting embodiment of either of the foregoing gas turbine engine assemblies, the clutch is disposed within an aft bearing compartment and the aft engine cover structure further includes an aft bearing compartment cover plate, disposed axially inward of the exhaust cone.

In a further non-limiting embodiment of either of the foregoing gas turbine engine assemblies, the clutch is positioned aft the geared architecture relative to a direction of flow through the gas turbine engine.

In a further non-limiting embodiment of either of the foregoing gas turbine engine assemblies, the spool is a low speed spool.

A method of controlling rotation of a gas turbine engine fan according to an exemplary aspect of the present disclosure includes, among other things, engaging a clutch to prevent rotation of a gas turbine engine fan in a first direction when a rotational speed of the gas turbine engine fan is below a threshold speed, the clutch being removable on-wing, and disengaging the clutch when the rotational speed of the gas turbine engine fan meets or exceeds the threshold speed. The clutch disposed within a compartment that is accessible and removable via removal of an aft engine cover structure. The clutch is removable on-wing.

In a further non-limiting of the foregoing method, the aft engine cover structure includes an engine exhaust cone.

In a further non-limiting embodiment of either of the foregoing methods, the clutch is disposed within an aft bearing compartment and the aft engine cover structure further includes an aft bearing compartment cover plate, disposed axially inward of the exhaust cone.

In a further non-limiting embodiment of any of the foregoing methods, the method includes positioning the clutch within a gas turbine engine such that the clutch can be moved from an installed position within the gas turbine engine to an uninstalled position without removing any blades from the gas turbine engine.

In a further non-limiting embodiment of any of the foregoing methods, the method includes coupling the clutch to a spool of a gas turbine engine that rotatably drives the gas turbine engine fan through a geared architecture.

DETAILED DESCRIPTION

To facilitate discussion of the engine, the fan and gear architecture are often referred to as the engine propulsor. The compressor section, combustor and turbine section, on the other hand, are often referred to as the gas generator. However, other component groupings and monikers may be utilized without limiting the nature or scope of the disclosed embodiments.

A mid-turbine frame58of the engine static structure36is arranged generally between the high pressure turbine54and the low pressure turbine46. The mid-turbine frame58further supports bearing systems38in the turbine section28as well as setting airflow entering the low pressure turbine46.

In one disclosed embodiment, the gas turbine engine20includes a bypass ratio greater than about ten (10:1) and the fan diameter is significantly larger than an outer diameter of the low pressure compressor44. It should be understood, however, that the above parameters are only exemplary of one embodiment of a gas turbine engine including a geared architecture and that the present disclosure is applicable to other gas turbine engines.

The example gas turbine engine includes the fan42that comprises in one non-limiting embodiment less than about twenty-six (26) fan blades. In another non-limiting embodiment, the fan section22includes less than about twenty (20) fan blades. Moreover, in one disclosed embodiment the low pressure turbine46includes no more than about six (6) turbine rotors schematically indicated at34. In another non-limiting example embodiment the low pressure turbine46includes about three (3) turbine rotors. The example low pressure turbine46provides the driving power to rotate the fan section22and therefore the relationship between the number of turbine rotors34in the low pressure turbine46and the number of blades in the fan section22disclose an example gas turbine engine20with increased power transfer efficiency.

The use of the gear reduction between the low speed spool30and the fan42allows an increase of speed to the low pressure turbine46. In the past, the speed of the low pressure turbine46and the low pressure compressor44has been somewhat limited in that the fan speed cannot be unduly large. The maximum fan speed is at its outer tip, and in larger engines, the fan diameter is much larger than it may be in smaller power engines. However, the use of the gear reduction has freed the designer from limitation on the speeds of the low pressure turbine46and the low pressure compressor44speeds caused by a desire to not have unduly high fan speeds.

During typical operation of the engine20, a pump64delivers a lubricant (e.g., oil) to the fan42and other areas of the engine20, such as the geared architecture48. When the engine20operates, the fan42rotates around the axis A in a direction D1. The lubricant lubricates the fan42, the geared architecture48, etc.

The example pump64is powered by rotations of the fan42in the direction D1. If the rotations in the direction D1are fast enough, the pump64delivers lubricant. Relatively low-speed rotations may not provide enough force to power the pump64. However, these low-speed rotations do not typically require much, if any, lubricant. Windmilling rotations caused by winds that are less than 25 miles per hour (10 kilometers per hour) are considered low-speed rotations in one example.

Notably, operating the engine20is not required to power the pump64. For example, the fan42may power the pump64when the fan42is windmilling. Windmilling, as is known, refers to rotations of the fan42that are not due to engine operations. In one example, the engine20is secured to a parked aircraft, and the engine20is exposed to wind W. The wind W causes the fan42to windmill.

Rotations of the fan42in a direction D2, which is opposite the direction D1, do not cause the pump64to deliver lubricant. In one example, rotation in the direction D2does not cause the pump64to deliver lubricant because rotation in the direction D2runs the pump64in a reverse direction.

Unlubricated rotations can damage the fan42, the geared architecture48, etc., especially if these rotations are high-speed rotations. Accordingly, the example engine20includes a clutch assembly68that limits rotation of the fan42in the direction D2. The clutch assembly68is an exemplary gas turbine engine assembly.

As known, when blades or vanes need to be removed from an engine, the engine typically must be removed from the wing. Accordingly, components of the engine that can only be accessed if blades or vanes are removed are not components that can be maintained or repaired while the engine is on-wing.

The example clutch assembly68is removeable with the engine20mounted on-wing. That is, the clutch assembly68can be moved from an installed position within the engine20to an uninstalled position68′ without removing any blades internal to the engine20, or without removing any vanes internal to the engine20. The clutch assembly68can be maintained with the engine20mounted on-wing and without removing the entire engine20from pylon mounts of the aircraft wing. In this example, the clutch assembly68is accessible for maintenance after removing an exhaust cone72and an aft bearing compartment cover74.

In this example, the clutch68is coupled to the low speed spool30of the engine20. The clutch68selectively limits rotations of the low speed spool30to limit rotations of the fan42. Limiting the rotations of the low speed spool30requires less holding torque than directly limiting rotations of the fan42, due to the geared architecture48stepping down the rotational speed of the fan42relative to the low speed spool30. Since the clutch68is coupled to the low speed spool30rather than directly to the fan42, a smaller clutch can be used.

The example clutch68is positioned within the engine20aft the geared architecture48relative to a direction of flow through the engine20. Specifically, the example clutch68is located in a rear bearing compartment66of the engine20. The clutch68may be located in other areas of the engine20in other examples.

The example clutch assembly68moves between a first position shown inFIG. 2Aand a second position shown inFIG. 2B. The clutch assembly68is in the first position when the fan42is not rotating, or when the fan42is rotating at a rotational speed less than a threshold speed. The fan42and the low speed spool30are rotatably coupled to each other. In the first position, the clutch assembly68blocks rotation of the low speed spool30to block rotation of the fan42in the direction D2. The clutch assembly68thus ensures any windmilling rotations of the fan42are in a direction suitable for powering the pump64. The clutch assembly68moves to the second position when the fan42rotates at speeds above the threshold speed.

In one example, the threshold speed corresponds to rotations of the fan42when wind moves at 25 miles per hour (40 kilometers per hour) through the engine fan section22. A rotational speed of the fan42exceed the threshold speed when the speed of the wind though the fan section22is greater than 25 miles per hour (40 kilometers per hour).

In the second position, the clutch assembly68is disengaged. The clutch assembly68offers very little resistance to rotation when the clutch assembly68is in the second position. Because there is very little resistance, the clutch assembly68is not significantly worn when the clutch assembly68is in the second position, which increases the useful life of the clutch assembly68.

As can be appreciated, rotations of the fan42above the threshold speed are always in the direction D1. The threshold speed is typically set below an idle speed of the engine20to ensure that the clutch assembly68is always in the second position when the engine20is idling.

An actuation assembly70controls movement of the clutch assembly68between the first position and the second position. The example actuation assembly70(and the clutch assembly68) are mechanical devices. That is no wiring or electrical signals are required to move the clutch assembly68between the first position and the second position. That is, the actuation assembly70is driven exclusively by centrifugal force and the mechanical action of levers and springs. No outside energy source, such as electrical or hydraulic motors, are required to actuate the mechanism other than mechanical rotation of the fan42. On the other hand, in some other examples, the actuation assembly, the clutch assembly, or both, may incorporate non-mechanical devices. Such non-mechanical devices include, for example, electronic, electromechanical, and/or hydraulic assemblies or components thereof, as would be appreciated by one of ordinary skill reading the present disclosure.

Many types of clutches are suitable for use in the clutch assembly68.FIGS. 3A-4Bshow an example ramp/roller clutch78for use in the clutch assembly68ofFIGS. 2A-2B. The clutch78includes many features of the clutch described in U.S. Pat. No. 4,531,620, the contents of which are incorporated herein by reference.

The clutch78is shown in the first position inFIGS. 3A and 4A. The clutch78is shown in the second position inFIGS. 3B and 4B.

In this example, an actuator80includes a pair of centrifugal weights82aand82bthat rotate with portions of the clutch78around an axis X. When the clutch78is used within the engine20, the axis X may or may not be coaxial with the axis A of the engine20.

The weights82aand82brotate together with the fan42. The weights82aand82bare biased radially inward to a position that holds the clutch78in the first position.

When the fan42rotates in the direction D1faster than the threshold speed, the centrifugal force on the weights82aand82bexceeds the biasing force and the weights82aand82bare cast radially outward away from the axis X. As will be explained in more detail, this radial movement of the weights82aand82bcauses the clutch78to move from the first position to the second position.

When the rotation of the fan42no longer exceeds the threshold speed, the weights82aand82bmove back toward the axis X, which moves the clutch78back to the first position.

The clutch78includes a shaft84that is coupled in rotation together with the low speed spool30. When the clutch78is in the first position, rollers88contact a housing90. When the clutch78is in the first position, the rollers88, an inner cage92and an outer cage94rotate together relative to the housing90in a clockwise direction. In this example, the housing90is mounted to a fixed bearing support or an engine static structure. In this example, the shaft84is an inner shaft, and the housing90is an outer cylindrical shaft.

Rotating the low speed spool30and the shaft84in the counter-clockwise direction causes the rollers88to bind between ramped surfaces96of the shaft84and the cylindrical housing90. Thus, when the clutch78is in the first position, the low speed spool30and the fan42are only rotatable in one direction.

When the rotations of the first shaft84in a clockwise direction exceed the threshold speed, the weights82aand82bare thrown radially outward due to centrifugal force. The radial movement of the weights82aand82bpivots arms98aand98b, respectively. The arms98aand98bmove the inner cage92axially against a biasing force provided by a spring100. The inner cage92rotates with respect to the shaft84when moved axially, which permits the rollers88to move circumferentially relative to the shaft84and move into recessed areas102. When the rollers88are in the recessed areas102, the rollers88are radially spaced from the housing90. A circumferential spring (not shown) may encourage this movement.

Relative rotation of the inner cage92thus permits the rollers88to disengage from the housing90and move radially inward to a position within an outer cage94. The clutch78is then considered to have moved to the second position.

Again, in the second position, the rollers88are radially spaced from the housing90. The outer cage94is also radially spaced from the housing90. The resulting clearance between the housing90and these portions of the clutch78enables the shaft84to freely rotate with little, if any, resistance from the rollers88, or other portions of the clutch78. Since none of these parts contact each other, little, if any, wear occurs when the clutch78is in the second position. When the rotational speed of the shaft84decreases, the circumferential force holding the weights82aand82bdecreases. The spring100is then able to move the inner cage92back to a position that holds the rollers88radially against the housing90, i.e., the first position.

Referring toFIG. 5, the example clutch78may be located within a compartment, such as an aft bearing compartment66of the engine20. The aft bearing compartment cover plate74directly houses the clutch78. The aft bearing compartment cover plate74is disposed axially inward of the exhaust cone72. The exhaust cone72and the aft bearing compartment cover plate74are types of aft engine covers. In this example, the exhaust cone72and the aft bearing compartment cover plate74together provide an aft engine cover structure. The aft bearing compartment66is accessible and removable via removal of the aft engine cover structure.

The shaft84of the clutch78extends to connect to the low speed spool30via a splined connection104. The shaft84includes a lubrication distributor and scoop108. A lubricant nozzle112communicates lubricant to the scoop108.

The clutch78is secured within the compartment66using a relatively flexible support114, which allows the clutch78to center on the axis A, particularly at low speeds. Notably, the clutch68positioned within the bearing compartment66can be removed when the engine20is on-wing by removing the exhaust cone72(FIG. 1) and aft bearing compartment cover plate74.

Features of the disclosed examples include a clutch experiencing very little wear at rotational speeds above a threshold speed.