GB2402718A

GB2402718A - Ram air turbines

Info

Publication number: GB2402718A
Application number: GB0411958A
Authority: GB
Inventors: Daryl John Burford
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 2003-06-12
Filing date: 2004-05-27
Publication date: 2004-12-15
Anticipated expiration: 2024-05-27
Also published as: GB2402718B; GB0313563D0; GB0411958D0

Abstract

A ram air turbine has blades 1 mounted on a hub 5. Inside the hub each blade 1 support a counterweight 60 arranged to alter the pitch of the blades as speed varies. Each counterweight 60 is coupled with an actuator 91 by which the angle of the blades can be altered remotely. The turbine is stopped rotating by altering the angles of the blades 1 such that the hub 5 rotates slightly in the reverse direction, which causes a sprag clutch 52 to lock the turbine 5. The actuator 91 is also coupled with an additional brake 100, which is applied after the clutch 52 locks.

Description

RAM AIR TURBINES

This invention relates to ram air turbines.

Ram air turbines have a propeller connected by a shaft to an electrical generator or hydraulic pump. The propeller is mounted in the airstream of an aircraft to rotate the propeller and thereby produce electrical or hydraulic power. Ram air turbines may be used in emergency situations, such as when the normal source of electrical or hydraulic power in an aircraft fails. They can also be used to provide power to wing-mounted aircraft in-flight refuelling systems.

Examples of ram air turbines are described in US 2003/0002983, US 5398780, US 2002/0081203, US 6260667, US 6422816, US 5779446, US 5685694, US 5562417, US 5452988, US 5484120, US 5257907, US 5145324, US 5122036, US 4701104, US 5671737, US 4743163, US 4717095, WO 00/37797, EP 0522874, GB 2072271, GB 2151712, US 2003/0011198, US 2002/0154999, US 2002/0122717, EP 0713008, EP 0712996, EP 0095908, EP 00095270 and others.

It is an object of the present invention to provide an alternative ram air turbine.

According to one aspect of the present invention there is provided a ram air turbine including a hub rotatable about an axis and a plurality of blades mounted radially with the hub with a variable pitch, the turbine including actuator means operable to alter the pitch of the blades and to prevent substantial rotation of the hub.

The turbine may include means for preventing substantial reverse rotation of the hub, the actuator means being arranged to displace the blades so that their pitch causes a reverse force to be applied to the hub thereby preventing substantial rotation of the hub. The turbine may include a brake operable to brake rotation of the hub in addition to the actuator means.

The actuator means preferably extends coaxially of a shaft rotated with the hub and is displaceable linearly against the action of a spring. The turbine preferably includes pitch altering means coupled with the blades such as to vary the pitch of the blades automatically with speed. Preferably the pitch altering means includes a mass attached with each blade that is displaced about the pitch axis of the blade by rotation of the hub about the axis of the shaft.

The turbine may include a member coupled with each blade, the member being urged axially of the shaft axis by resilient means such as to tend to rotate the blades about their pitch axes in a sense to increase torque applied to the blades by the airstream.

According to another aspect of the present invention there is provided a ram air turbine including a hub, means mounting the hub for rotation about its axis in one direction but preventing substantial rotation in an opposite direction, a plurality of blades mounted radially with the hub, and pitch altering means within the hub coupled with said blades such as to vary the pitch of the blades from a first position where the blades tend to rotate the hub in the one direction to a second position where the blades tend to rotate the hub in the opposite direction and where rotation of the hub is thereby substantially prevented.

The mounting means may include a backstop clutch, such as a spray clutch.

According to a third aspect of the present invention there is provided a ram air turbine including a hub rotatable about an axis, a plurality of blades mounted radially with the hub, pitch altering means within the hub coupled with the blades such as to vary the pitch of the blades, brake means operable to prevent substantial rotation of the hub, and actuator means operable both to operate the brake and to displace the pitch altering means to reduce torque applied to the blades.

A ram air turbine according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an end view of the turbine; and Figure 2 is a cross-sectional side elevation view of the turbine.

The turbine has four blades 1 to 4 extending radially outwardly from a central hub structure 5, which rotates an axial shaft 6 extending rearwardly to an hydraulic pump or electrical generator (not shown). The turbine is mounted on a refuelling pod beneath the wing of an aircraft located in the airstream around the aircraft.

The hub structure 5 includes a casing or spinner 50 having a domed, aerodynamic shape facing forwardly into the airstream and supported at its rear end by a bearing provided by a backstop clutch 52 on a fixed chassis 53. The operation of the clutch 52 will be described later. The hub 5 has four apertures 54 equally spaced around its circumference in which are fixed the outer part of bearings 55. The inner part of each bearing 55 is fixed with the inner, root portion 56 of a respective one of the blades 1 to 4 such that each blade is angularly displaceable about a radially-extending pitch axis 57. The interior of the hub structure 5 contains pitch altering means in the form of a counterweight 60 fixed to each blade root 56. The counterweights 60 are asymmetric in shape about the pitch axis 57 having a forwardly-extending arm 61 with an enlarged mass 62 at its end, displaced from the pitch axis. The shape of the counterweights 60 is such that rotation of the hub structure 5 about its axis along the shaft 6 applies a moment to the blades 1 to 4 tending to rotate them about the pitch axis 57. The sense of this rotation is to alter the pitch of the blades 1 to 4 to reduce the torque applied to the blades by the airstream as the speed of rotation increases.

Each counterweight 60 carries on an inwardly-facing surface 63 a bearing 64 of disc shape rotatable about a radially-extending axis. The disc shape bearing 64 locates in a slot 70 in the outside of a governor 71. The governor 71 takes the form of a cylindrical sleeve extending axially around the shaft 6 and has an inwardly-directed flange 72 at its forward end. The governor 71 is mounted on a retainer member 80 and is freely slidable in an axial direction but is urged forwardly by a helical spring 75 between the inner surface of the governor and the outer surface of the retainer. One end of the spring 75 bears on the flange 72 and its opposite end bears on an flange 81 projecting outwardly from the rear end of the retainer 80.

With the governor 71 in its forward position, as shown, the pitch angle of the blades I to 4 is such that the airflow applies a maximum torque to the blades. The clutch 52 is arranged to allow free forward rotation of the hub structure 5 with low friction. As the speed of rotation of the turbine increases, the counterweights 60 turn the blades 1 to 4 to reduce the torque and, in doing so, the disc shape bearings 64 are displaced along an arc centred on the axis 57, thereby moving the governor 71 rearwardly against the action of the spring 75. The spring 75 controls the rate at which the pitch of the blades 1 to 4 varies with speed and returns the blades towards their initial position as speed falls.

The retainer 80 is mounted inwardly of the governor 71 and has an outer cylindrical collar 82 with an outwardly-projecting flange 83 at its forward end, which limits forward displacement of the governor by engagement with its flange 72. The collar 82 is supported by an internal, radially-extending plate 84 supporting the outer ring of a bearing assembly 85.

The bearing assembly 85 is fixed with an inner linear actuator assembly 90 and enables the retainer 80 to rotate freely about the axis of the shaft 6 relative to the linear actuator assembly.

The linear actuator assembly 90 comprises two main components namely an actuator 91 and a hollow, tubular member 92 displaceable by the actuator. The actuator 91 is of cylindrical shape and is fixed securely at its rear end 93 with the chassis 53. The actuator 91 may be of various different forms. In the present example it comprises an electric motor 191 driving a ballscrew 192, which engages a thread 193 around the outside of the member 92. In this way, the member 92 is displaced axially relative to the actuator 91 by the action of the actuator. Alternatively, the actuator assembly could be an electrically-operated solenoid or the like. The actuator 91 is powered and operated remotely either manually or automatically in response to a sensor or the like. The actuator 91 need not be electrically operated but could be operated hydraulically, pneumatically, by a cable or the like. The actuator member 92 supports the inner part of the bearing assembly 85, and hence supports the retainer member 80, towards its forward end 94. The rear end 95 of the actuator member 92 is flat and provides a lateral actuation surface.

A helical spring 96 embraces the forward end 94 of the actuator member 92 and extends between the forward side of the retainer plate 84 and an inner surface of the spinner 50. The spring 96 applies a force to the retainer 71 tending to push it and the actuator member 92 rearwardly. During operation of the ram air turbine, the actuator 91 is powered to hold the actuator member 92 at the position shown in Figure 2 where it is displaced fully forwardly.

When the actuator 91 is de-energized, it allows the actuator member 92 to be displaced by the spring 96 rearwardly. The actuator 91 could be operated in a reverse sense to assist rearward displacement of the actuator member 92.

When the actuator member 92 moves to the right it displaces the retainer 80 rearwardly, to the right, causing the flange 83 on the retainer to push against the flange 72 on the governor 70 so as also to push this to the right. As the governor 70 moves to the right, the engagement of its slot 70 with the disc shape bearings 64 on the blade roots 56 displaces the blades 1 to 4 angularly about their pitch axes 57. The sense in which the blades 1 to 4 are rotated is such as reduce the surface area presented to the airskeam. The coupling between the actuator member 92 and the blades 1 to 4 is such that the blades are rotated beyond a position of zero torque by about 1 to an orientation in which the torque applied by the airstream to the blades causes the hub 5 to rotate slightly in a reverse direction. As soon as the hub 5 starts to rotate in a reverse direction the backstop clutch 52 locks to prevent further rotation. The clutch 52 is a conventional centrifugal lift-off spray type clutch such as the Formsprag clutch available from Colfax Power Transmission Group in Matzingen, Switzerland. The clutch 52 has multiple sprays that rotate and engage between the inner and outer parts of the clutch to prevent further rotation. Alternative devices to prevent reverse rotation could be used. The hub 5, therefore, slows down, goes slightly into reverse and is then stopped by the clutch 52 for as long as force is applied by the blades tending to rotate the hub rearwardly.

Rearward movement of the actuator member 92 also brings its rear end 95 into engagement with a brake assembly 100 after locking of the clutch 52. The brake assembly includes two discs 101 mounted on the shaft 6 and two discs 102 mounted on the brake housing 103, which is fixed with the chassis 53. The discs 101 and 102 are mounted with the shaft 6 and housing 103 respectively by means of cooperating, longitudinally- extending splines so that the discs can be displaced longitudinally but cannot rotate relative to their mountings. When the actuator member 92 moves rearwardly, its rear end 95 engages the disc spring 104 in the brake assembly 100 and pushes this and the two sets of discs 101 and 102 together. When the discs 101 and 102 contact, friction is applied between them tending to brake rotation of the shaft 6, the hub 5 and the blades 1 to 4.

The main force stopping rotation of the hub 5 is provided by the operation of the backstop clutch 52, the purpose of the brake assembly 100 being to prevent rotation of the hub when there is no airstream acting on the blades or when the airstream is in a reverse direction, such as when the aircraft is stationary on the ground. It will be appreciated that, in its stationary state, the orientation of the blades 1 to 4 will be such that a reverse airstream will tend to cause forward rotation ofthe hub 5, which would release the clutch 52 and would thereby allow the hub to rotate if it were not for the brake 100.

It can be seen, therefore, that failure of power to the actuator 91 will cause the blades 1 to 4 to move to a feathered position with minimal drag and will cause the hub 5 to stop rotating.

When the turbine needs to be started again, the linear actuator assembly 90 is operated to displace the actuator member 92 and retainer 80 forwardly thereby removing the braking force applied by the brake assembly 100. The governor 71 follows the retainer 80 forwardly, because of the action of the spring 75, thereby rotating the blades 1 to 4 to the pitch where they generate maximum torque. As soon as the torque applied to the blades tends to rotate the hub 5 forwardly, the clutch 52 releases and allows the hub to rotate. As the speed of the turbine increases, the counterweights 60 rotate the blades 1 to 4 to reduce torque and move the governor 71 rearwardly away from the flange 83 on the retainer 80, against the action of the spring 75.

The actuator 91 could take various different forms. Its construction could be such that, when no power is applied to the actuator, the actuator member is displaced fully forwardly, so that the brake is off and the blades are positioned solely by the action of the counterweights. In such an arrangement, power would be supplied to the actuator to rotate the blades to a reverse torque position and brake the turbine. Alternatively, the actuator could be arranged so that it holds the actuator member in any position until power is applied to the actuator to displace the actuator member forwards or backwards. In this arrangement the actuator member could be displaced forwardly by applying power in one sense to the actuator and it would remain in this position until power is applied to the actuator in the opposite sense when it would be displaced rearwardly to brake the turbine. The turbine would remain stationary until power were applied to displace the actuator member forwardly.

It can be seen, therefore, that the ram air turbine alters the pitch angle of its blades during normal use to minimize variations in its speed of rotation. The turbine can be turned off when not in use by operation of the operation of the linear actuator, which both stops rotation and moves the blades to a configuration of minimum drag. The use of the backstop clutch brings several advantages. It makes use of force provided by the turbine itself to effect stopping. Because its braking effect is provided at very low speed there is minimal friction and wear to components. The clutch enables a considerably smaller brake to be used than would be the case if the brake alone were required to stop rotation of the hub.

Claims

1. A ram air turbine including a hub rotatable about an axis and a plurality of blades mounted radially with the hub with a variable pitch, wherein the turbine includes actuator means operable both to alter the pitch of the blades and to prevent substantial rotation of the hub.

2. A turbine according to Claim 1 including means for preventing substantial reverse rotation of the hub.

3. A turbine according to Claim 1 or 2, wherein the actuator means is arranged to displace the blades so that their pitch causes a reverse force to be applied to the hub thereby preventing substantial rotation of the hub.

4. A turbine according to any one of the preceding claims, wherein the turbine includes a brake operable to brake rotation of the hub in addition to the actuator means.

5. A turbine according to any one of the preceding claims, wherein the actuator means extends coaxially of a shaft rotated with the hub and is displaceable linearly against the action of a spring.

6. A turbine according to any one of the preceding claims including pitch altering means coupled with the blades such as to vary the pitch of the blades automatically with speed.

7. A turbine according to Claim 6, wherein the pitch altering means includes a mass attached with each blade that is displaced about the pitch axis of the blade by rotation of the hub about the axis of the shaft.

8. A turbine according to Claim 6 or 7 including a member coupled with each blade, wherein the member is urged axially of the shaft axis by resilient means such as to tend to rotate the blades about their pitch axes in a sense to increase torque applied to the blades by the airstream.

9. A ram air turbine including a hub, means mounting the hub for rotation about its axis in one direction but preventing substantial rotation in an opposite direction, a plurality of blades mounted radially with the hub, and pitch altering means within the hub coupled with said blades such as to vary the pitch of the blades from a first position where the blades tend to rotate the hub in the one direction to a second position where the blades tend to rotate the hub in the opposite direction and where rotation of the hub is thereby substantially prevented.

10. A turbine according to Claim 9, wherein the mounting means includes a backstop clutch.

11. A turbine according to Claim 10, wherein the backstop clutch is a spray clutch.

12. A ram air turbine including a hub rotatable about an axis, a plurality of blades mounted radially with the hub, pitch altering means within the hub coupled with the blades such as to vary the pitch of the blades, brake means operable to prevent substantial rotation of the hub, and actuator means operable both to operate the brake and to displace the pitch altering means to reduce torque applied to the blades.

13. A ram air turbine substantially as hereinbefore described with reference to the accompanying drawings.

14. Any novel and inventive feature or combination of features as hereinbefore described.