Ram air turbine biasing assembly

An example ram air turbine biasing assembly includes a support member that holds a biasing member. The biasing member biases a component of a ram air turbine. The support member includes a step that limits movement of the component toward the biasing member.

BACKGROUND

This disclosure relates to ram air turbines utilized to provide emergency power for an aircraft. More particularly, this disclosure relates to biasing assemblies within a ram air turbine that supplies both electric and hydraulic power to an aircraft.

A ram air turbine is used to generate supplemental power in an aircraft by extracting power from an air stream along the exterior of the aircraft during flight. The ram air turbine includes a turbine that drives an electric motor or hydraulic pump. In operation, the turbine is moved from a stowed position within the aircraft to a position that provides clearance for blades of the turbine and the aircraft. The turbine is mounted at the end of a strut and drives a turbine drive shaft that in turn drives the electric motor or hydraulic pump.

The ram air turbine may experience extreme loads, such as during high level, short duration events (HLSDs). Biasing members of the ram air turbine can become damaged during such events. During an aircraft engine blade loss event, the severe HLSD vibrations occur first as the engine spools down. Then, as it continues to turn due to air loads, a high unbalance load continues to drive the longer duration windmilling vibrations. Either or both of these vibrations could significantly reduce the fatigue life of ram air turbine components without measures to limit impact loading.

SUMMARY

An example ram air turbine biasing assembly includes a support member that holds a biasing member. The biasing member biases a component of a ram air turbine. The support member includes a step that limits movement of the component toward the biasing member.

An example ram air turbine assembly includes a strut movable between a deployed position and a stowed position. The strut supports a turbine that is rotatable about a first axis. A drive shaft is rotatable about a second axis transverse to the first axis. The drive shaft drives a hydraulic pump and a generator. A gearbox rotatably couples rotation of the strut with the drive shaft. A gearbox bearing biasing member biases a gearbox bearing system away from the turbine. A gearbox bearing liner supports the gearbox bearing system. The gearbox bearing liner including a step that limits movement of the gearbox bearing system toward the gearbox bearing biasing member and minimizes HLSD impact loads. A similar stepped liner is used within the generator to limit motion of the generator rotor and minimize HLSD impact loads.

An example method of supporting a component in a ram air turbine assembly includes supporting the component using a support member, biasing the component using a biasing member, and limiting movement of the component toward the biasing member using a step of the support member.

DETAILED DESCRIPTION

Referring toFIGS. 1 and 2, an example ram air turbine assembly (RAT)10is mounted to an airframe12and is deployable to provide both electric power and hydraulic power. The example RAT10includes a turbine14that rotates responsive to air flow along the outside of the airframe12. The turbine14is supported at the end of strut22attached to a generator housing24. The generator housing24is mounted for rotation to the airframe12with a swivel post28.

A generator rotor32disposed within the generator housing24is coupled to a hydraulic pump38. The generator32generates electric power that can be supplied to an aircraft system such as is schematically indicated at40. The hydraulic pump38receives fluid from a fluid supply44and pumps the fluid to various systems indicated at42that utilize pressurized fluid for operation.

The turbine14rotates to drive a turbine shaft46about an axis48. The turbine shaft46drives a gearbox50. The example gearbox50is disposed aft of the turbine14and along the axis48of rotation of the turbine14and turbine shaft46. The example gearbox50drives a drive shaft52that rotates about an axis54that is transverse to the axis48. The drive shaft52extends from the gearbox50through the strut22to generator rotor32. The drive shaft52is coupled to drive the generator32at a desired speed.

The example gearbox50includes gears that provide a desired ratio of rotational speed between the turbine shaft46and the drive shaft52. In this example, the drive shaft52is rotated at a greater speed than the turbine shaft46. The gearbox50can be configured to provide any desired speed ratio relative to rotation of the turbine14.

The speed at which the drive shaft52is rotated is determined to provide the desired rotational speed required to drive the generator32and produce a desired amount of electrical energy at the desired frequency. The electrical energy produced by the generator32is then transmitted to the aircraft system schematically indicated at40.

A second drive shaft56couples the hydraulic pump38in rotation with the generator32such that the hydraulic pump38rotates at the same speed as the generator32. As the hydraulic pump38and the generator32are coupled to rotate together, the hydraulic pump38communicates pressurized fluid to the aircraft systems40at the same time as the generator32produces electric power.

The generator32is supported within the generator housing24at an end distal from the turbine14. The generator housing24includes a mounting bracket58and an integral swivel bracket60. The mounting bracket58attaches to an actuator62. The actuator62drives movement of the RAT10between a stowed position within the airframe12and the deployed position schematically shown inFIG. 1.

The swivel bracket60mounts to the swivel post28to connect the actuator to RAT10. The strut22is attached to the generator housing24and therefore moves with the pivoting movement of the generator housing24. The hydraulic pump20is mounted to the generator housing24and therefore also rotates with the generator housing24during movement to the deployed position.

Referring toFIG. 3, an example ram air turbine biasing assembly64includes a support member, such as a bearing liner66, which provides a biasing member support surface68. A biasing member70is supported by the biasing member support surface68. In this example, the biasing member70is an annular wave spring that, during typical operation, biases a component of the RAT10. In this example, the component is a gearbox bearing system72biased by the biasing member70axially away from the turbine14in a direction D1. The gearbox bearing system72helps to rotatably support the gearbox50. The biasing member70preloads the gearbox bearing system72in an axial direction to bias the turbine shaft through the gearbox forward bearing into the housing for support.

As will be explained in greater detail, the example bearing liner66includes a step74that limits movement of the gearbox bearing system72toward the biasing member70. A shim stack78is used with the step74assist in limiting the movement of the gearbox bearing system72toward the biasing member70.

A first side80of the biasing member70directly contacts the biasing member support surface68, and an opposite, second side82of the biasing member70directly contacts the shim78. When sufficient force is applied to the gearbox bearing system72in a direction opposite the direction D1, the shim78also contacts the step74. Contact between the shim78and the step74prevents the gearbox bearing system72from compressing the biasing member70past the step74.

In some examples, the step74is located a distance d1from the bearing member support surface68, and the biasing member70extends axially a distance d2when the biasing member70is not compressed. The first distance d1is from 86% to 98% of the second distance d2in such an example. Other examples may include other relationships. Biasing member70stress and cycling fatigue life may dictate certain relationships.

The gearbox bearing system72may move toward the biasing member70during a high level short duration event. Vibrations experienced during such events are especially damaging to components like the RAT10due to the RAT10having a relatively large cantilevered mass on the end of the strut22, which amplifies the vibration amplitude. During a high level short duration event, the turbine14may be shaken vigorously back and forth along the axis48, which causes the biasing member70to compress. The step74limits the amount of minimum to maximum stress variation on the biasing member70.

Generally, the amount of compression on the biasing member70when the gearbox bearing system72moves toward the biasing member70is limited to a gap g between the step74and the shim stack78. The same shim that protects the biasing member limits this gap to a small value, typically less than 0.015 inches (3.81 mm). The small gap limits the magnitude of the impact loading between the bearing and the bearing liner. This reduces the total housing fatigue stress during HLSD or windmilling after an engine blade failure. An additional benefit of shimming this gap is to keep the adjacent gear from impacting with its mating gear, which could cause damage.

AlthoughFIG. 3shows an axial side of the ram air turbine biasing assembly64, the assembly extends circumferentially about the axis48. In other examples, the biasing assembly64is not annular, or even circumferentially extending.

During assembly of the RAT10, the distance d2of the biasing member68is shimmed at the same time that the gap g is shimmed because the step74controls the minimum distance d2of the biasing member68. In some examples, the gap g is shimmed to be from about 0.003 inches (0.0762 mm) to about 0.014 inches (0.3556 mm). Such sizes of the gap g may help reduce impact loads on the gearbox bearing system72and on gears of the gearbox50as well as improve a useful life of the biasing member70.

Referring toFIG. 5, another example ram air turbine bearing biasing assembly84includes a bearing liner86providing a biasing member support surface88that supports and holds a biasing member90. The bearing liner86is another type of support member. Support members other than liners are used in other examples.

In this example, the biasing member90is an annular wave spring that, during typical operation, biases a generator bearing system92axially away from the hydraulic pump38in a direction D2. The generator bearing system92is another type of component of the RAT10. Components other than bearing systems may be biased as well. The generator bearing system92helps to rotatably support the rotating portions of the generator32. The biasing member90preloads the generator bearing system92in an axial direction.

The generator bearing system92and the gearbox bearing system72(FIG. 3) are both types of components within the RAT10. As with the bearing liner66, the bearing liner86includes a step94that limits compression of the biasing member90. In this example, the step94together with a shim96limit movement of the generator bearing system92toward the hydraulic pump38to limit compression of the biasing member90and limit HLSD and windmilling impact loads.

Features of the disclosed examples include limiting the amount of compression on biasing members within a ram air turbine. Limiting the compression may prevent damage to the biasing members and may prove beneficial for the adjacent seals. As known, seals may leak if components are shifted from normal operating positions.