GB2371837A

GB2371837A - Pitch adjustment mechanism

Info

Publication number: GB2371837A
Application number: GB0130143A
Authority: GB
Inventors: Nigel Hayward
Original assignee: PRO DESIGN SOLUTIONS Ltd
Current assignee: PRO DESIGN SOLUTIONS Ltd
Priority date: 2000-12-19
Filing date: 2001-12-18
Publication date: 2002-08-07
Anticipated expiration: 2021-12-18
Also published as: GB2371837B; GB0130143D0; GB0031025D0

Abstract

The mechanism comprises a propeller shaft 12 mounted on a hub 10, the shaft being angularly adjustable relative to the hub to adjust the blade pitch but constrained against movement axially of the shaft by thrust bearings 18, 20, 22. An adjustment member or sleeve 28 is located between the shaft and hub and is constrained against angular movement relative to the hub but is capable of axial movement relative to the shaft to which it is attached by a coupling arrangement comprising a projection 32 with a roller on one of the shaft and sleeve 34 engaging in a slot 30 in the other. Axial movement of the adjustment member causes angular movement of the shaft. The adjustment member may be moved hydraulically 36 38, 40 or by centrifugal force against disc springs 44. Application in aircraft propellers or wind turbines.

Description

"Pitch Adjustment Mechanism"

This invention relates to a mechanism for use in the adjustment of the pitch of, for example, propeller blades or the blades of a turbine.

Aircraft engines of the propeller type are preferably fitted with devices to permit adjustment of the pitch of the propeller blades as, if the engine fails in flight and the propeller stops or rotation thereof slows, the loads exerted upon the propeller by the air flow over the propeller are significant and could result in damage to or deformation of the bearing assemblies located within the propeller hub or even the loss of one or more of the propeller's blades.

Wind driven turbines are used increasingly to drive electrical generators.

Such turbines are often shut down under high wind conditions in order to avoid damage thereto which may occur at excessive rotational speeds. When shut down, the blades are moved to their positions of least resistance.

It is an object of the invention to provide a pitch adjustment mechanism for use in adjusting the pitch of blades.

According to a first aspect of the invention there is provided a pitch adjustment mechanism comprising a shaft mounted upon a hub, the shaft being angularly adjustable relative to the hub to adjust the pitch of a blade but constrained against axial movement, and an adjustment member located between the shaft and the hub and constrained against angular movement relative to the

hub but capable of axial movement relative to the hub, and a coupling arrangement whereby the adjustment member is coupled to the shaft, the coupling arrangement comprising inter-engaging formations provided on the adjustment member and the shaft adapted such that axial movement of the adjustment member causes angular movement of the shaft.

The inter-engaging formations may comprise a projection associated with one of the adjustment member and the shaft, the projection riding within angular groove, recess or slot formed in the other of the adjustment member and the shaft.

The adjustment member conveniently comprises a sleeve encircling part of the shaft. The shaft conveniently comprises a part of a propeller or turbine blade.

The adjustment member may be moveable by the application of engine oil or hydraulic fluid under pressure thereto. Alternatively, it may be moveable under the action of centrifugal force, in use, for example against the action of a resilient biassing means. Such an arrangement is advantageous as, in the event of a loss of fluid pressure, the centrifugal force experienced by the adjustment member can move the adjustment member and the shaft to a predetermined angular position.

According to a second aspect of the invention there is provided a pitch

adjustment mechanism comprising first and second fluid chambers, and an adjustment member having surfaces exposed to the fluid pressures within the chambers so that the position of the adjustment member is controlled by controlling the fluid pressures of the chambers.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view, partly in section, of a pitch adjustment mechanism in accordance with an embodiment of the invention; Figure 2 is a view similar to Figure 1 illustrating an alternative embodiment; Figure 3 is a view illustrating a modification to the embodiment of Figure 2; and Figures 4 to 7 illustrate further modifications.

The pitch adjustment mechanism illustrated in Figure 1 forms part of an aircraft engine. The pitch adjustment mechanism comprises a hub 10 arranged to carry a propeller shaft 12. The shaft 12 may be integral with the propeller blade, forming the root thereof, or may be connected to the propeller blade using any suitable technique. The mounting of the propeller shaft 12 relative to the hub 10 is such as to permit angular movement to occur therebetween but to restrict relative axial movement of the shaft 12 relative to the hub 10. In order

to facilitate angular movement of the shaft 12 relative to the hub 10 bearing assemblies 14, 16 are provided. As illustrated in Figure 1 the inboard bearing assembly 16 conveniently comprises inner and outer tracks 18,20 within which rollers 22 ride, the inner track 18 being carried by a shoulder forming part of the shaft 12, the outer track 20 bearing against a shoulder formed within the hub 10.

Such a bearing assembly serves to retain the shaft 12 against axial movement relative to the hub 10 as well as permitting angular movement to occur therebetween. In the arrangement illustrated in Figure 1, the outboard bearing assembly 16 serves mainly to stabilise and guide the shaft 12 for angular movement relative to the hub 10, but may also serve to restrict axial movement of the shaft 12 in use.

Adjacent the outboard bearing assembly 16, the shaft 12 carries an oil seal arrangement in the form of a flange 24, the outer periphery of which carries an oil seal ring 26 which bears against a surface of the hub 10.

An adjustment member in the form of a sleeve 28 is located between the shaft 12 and the hub 10. The sleeve 28 is keyed to the hub 10 in such a manner as to permit the sleeve 28 to move axially relative to the hub 10 whilst restraining the sleeve 28 against angular movement relative to the hub 10. As illustrated in Figure 1, the sleeve 28 is formed with an elongate, angled slot 30, the shaft 12 being provided with a projection 32 carrying a roller 34 arranged to ride within

the slot 30. The co-operation between the roller 34 and the slot 30 is such that when the sleeve 28 moves axially relative to the hub 10, as the sleeve 28 is restrained against angular movement relative to the hub 10 and as the shaft 12 is restrained against axial movement relative to the hub 10, the movement of the sleeve 28 forces the shaft 12 to move angularly relative to the hub 10 as the roller 34 rides within the slot 30.

Oil flow channels 36,38 are provided within the hub 10 to permit the supply of oil under pressure to either the inboard end or the outboard end of the sleeve 28 to cause the sleeve 28 to move axially relative to the hub 10. The supply of oil under pressure through the channels 36, 38 occurs under the control of a valve 40 illustrated diagrammatically in Figure 1. With the valve 40 in the position illustrated, oil under pressure is being supplied to the flow channel 36 which communicates with the outboard end of the sleeve 28, the inboard end of the sleeve 28 being connected through the flow channel 38 to a relatively low pressure fluid source. Under such circumstances, the sleeve will tend to move in the inboard direction, such movement of the sleeve causing the shaft 12 to move in the direction illustrated by arrow 42 in Figure 1. Movement of the valve 40 to a position in which fluid under pressure is supplied to the flow channel 38 whilst the flow channel 36 is connected to a relatively low pressure source would cause movement of the shaft 12 in the opposite direction, and movement of the

valve 40 to a position in which the flow channels 36, 38 are closed would tend to hold the sleeve 28 in a fixed position, thus holding the shaft 12 against angular movement relative to the hub 10.

The length of the slot 30 is chosen to permit the blade 12 to be moved through a desired angle. For example, it is envisaged that the blade 12 should be able to moved through an angle of 103 . Conveniently, the angle of the blade 12 is monitored using suitable sensors, for example rotary variable displacement transducer units. In the event that the angle of the blade 12 at a given time is undesirable, then information to that effect may be passed to the pilot of the aircraft or to an automated control unit to cause operation of the valve 40 in such a manner as to supply oil or other fluid under pressure to the appropriate end of the sleeve 28 to cause movement of the shaft 12 towards its desired position. In order to minimise the effects of centrifugal induced accelerations, the sensors are conveniently located as near to the axis of rotation of the hub as possible.

The effect of centrifugal force upon the sleeve 28 will result in the fluid pressure necessary to cause movement of the sleeve 28 in the inboard direction to be higher than the fluid pressure necessary to cause movement of the sleeve 28 in the opposite direction. Although in some circumstances this may be undesirable, it may be used to provide a fail-safe system in that, in the event of a loss of oil pressure, the sleeve 28 will move in the outboard direction and the

pitch adjustment mechanism may be arranged such that when the sleeve 28 occupies its outermost position, the pitch of the blade 12 is that of least resistance thus minimising the risk of damage to the propeller arrangement.

Although in the arrangement described hereinbefore oil is used in the control of the mechanism, it will be appreciated that other hydraulic fluids could be used.

The arrangement illustrated in Figure 2 is similar to that of Figure 1, and like reference numerals will be used to denote parts performing like functions. The arrangement of Figure 2 is intended for use in a wind turbine application and is intended to achieve automated feathering of the blades as the rotational speed of the turbine reaches a predetermined level. The arrangement of Figure 2 differs from that of Figure 1 in that the flow channels 36,38 are not provided, and instead a first set of disc springs 44 are provided at the outboard end of the sleeve 28, a second set of disc springs 46 being provided at the inboard end of the sleeve 28.

In use, when the turbine is not rotating, then the sleeve 28 will occupy an axial position governed by the relative forces applied thereto by the springs 44, 46. Obviously, the angular position occupied by the shaft 12 will depend upon the position occupied by the sleeve 28. As the turbine rotates, the sleeve 28 will experience a centrifugal force urging it in the outboard direction against the

action of the first set of disc springs 44. When the centrifugal force experienced by the sleeve 28 is sufficient to cause it to move against the action of the disc springs 44, then such movement will cause the shaft 12 to move angularly relative to the hub 10 as described hereinbefore. The arrangement is such that when the sleeve 28 moves in the outboard direction, the shaft 12 is moved towards a position in which the blade is feathered. If the rotational speed of the arrangement falls, then the centrifugal force experienced by the sleeve 28 will be reduced and the sleeve 28 will tend to move under the action of the disc springs 44 to return the blade 12 towards its original angular position. Such an arrangement can therefore be used to avoid operation of the wind turbine at excessive speeds.

The modification to the arrangement of Figure 2 illustrated in Figure 3 is such as to cause the shaft 12 to move in the opposite direction in response to movement of the sleeve 28 in the outboard direction, this being achieved by altering the angle of the slot 30. It will be appreciated that a similar technique could be used in relation to the arrangement of Figure 1.

The invention is not limited to the arrangements described hereinbefore, and it will be appreciated that a number of modifications may be introduced into the arrangement without departing from the scope of the invention. By way of example, the responsiveness of the pitch adjustment mechanism may be modified

by adjusting the angle of the slot 30. Further, alternative techniques for coupling the sleeve 28 to the shaft 12 may be incorporated. These include the provision of inter-engaging angled teeth or threads formed upon these components or the use of a recess formed in the sleeve 28 rather than a slot extending through the sleeve 28. Further, the recess could be formed within the shaft 12, the sleeve 28 carrying an inwardly extending projection arranged to be received within the recess of the shaft 12.

Figures 4 to 7 illustrate further modifications to the arrangements described hereinbefore. The arrangements of Figures 4 to 7 are, for the most part, identical to one another but are intended to work in slightly different ways.

The arrangement of Figure 4 does not include any spring biasing and so is very similar to that of Figure 1. The arrangement of Figures 5 and 6 includes spring biasing and so is similar to that of Figure 2. The arrangement of Figure 7 is similar to that of Figure 6, but the spring biasing is in the opposite direction. In each case, passages communicate with chambers at each end of the sleeve. The passages may serve simply to vent the chambers, or alternatively may be used to supply fluid under pressure to the chambers.

Claims

1. A pitch adjustment mechanism comprising a shaft mounted upon a hub, the shaft being angularly adjustable relative to the hub to adjust the pitch of a blade but constrained against axial movement, and an adjustment member located between the shaft and the hub and constrained against angular movement relative to the hub but capable of axial movement relative to the hub, and a coupling arrangement whereby the adjustment member is coupled to the shaft, the coupling arrangement comprising inter-engaging formations provided on the adjustment member and the shaft adapted such that axial movement of the adjustment member causes angular movement of the shaft.

2. A mechanism according to Claim 1, wherein the inter-engaging formations comprise a projection associated with one of the adjustment member and the shaft, the projection riding within angular groove, recess or slot formed in the other of the adjustment member and the shaft.

3. A mechanism according to Claim 1 or Claim 2, wherein the adjustment member comprises a sleeve encircling part of the shaft.

4. A mechanism according to Claim 3, wherein the sleeve is spring biased in one direction.

5. A mechanism according to Claim 3 or Claim 4, wherein the sleeve is moveable by hydraulic pressure applied thereto.

6. A pitch adjustment mechanism comprising first and second fluid chambers, and an adjustment member having surfaces exposed to the fluid pressures within the chambers so that the position of the adjustment member is controlled by controlling the fluid pressures of the chambers.

7. A pitch adjustment mechanism substantially as hereinbefore described with reference to any one of the accompanying drawings..