GB2372297A

GB2372297A - Mounting of blade root of a variable pitch propeller

Info

Publication number: GB2372297A
Application number: GB0128085A
Authority: GB
Inventors: Jean Jacques Forest
Original assignee: Societe Nouvelle de Roulements SNR SA
Current assignee: NTN SNR Roulements SA
Priority date: 2000-11-30
Filing date: 2001-11-22
Publication date: 2002-08-21
Anticipated expiration: 2021-11-22
Also published as: FR2817233A1; GB0128085D0; GB2372297B; FR2817233B1

Abstract

A mounting device used for a variable pitch blade 1 in a rotary hub of a propeller 2, rotatable about the axis of the blade "B". Rotation is by means of three bearings, one oblique contact ball bearing "R2" and two roller bearings "R1 and R3". The bearings are arranged in the hub 2. The ball bearing "R2" may be sited between the roller bearings, and balls 13 inserted into the hub via a filling passage 35 between the external and internal portion of the hub. The exterior bearing race may be integral with the hub, the internal bearing race may be integrated with a skirt 16 surrounding the blade foot. Bearings may be pre-tensioned in the radial direction, and rollers may be guided by grooves 32. The assembly may include removable fixing means 41 that limit the axial movement, and facilitate release of balls through filling passage 35, and dismantling of the blade skirt 16 in the axial direction when fully removed.

Description

MOUNTING DEVICE FOR A BLADE FOOT OF A PROPELLER IN A HUB

The present invention relates to a mounting device for a blade of the type with a variable angle of incidence in a rotary hub, as illustrated in Figure I, about an axis A of an aircraft propeller.

s A mounting device is known from EP 0 324 617 wherein, as illustrated in Figures I and 2, said type of blade 1 is fixed to a hub 2 by one of its extremities, known as a blade foot 3. The foot 3 of the blade I can pivot substantially according to an axis B in a chamber 4 of the hub 2, by means of bearings R1 and R2. The axis B of the foot 3 substantially coincides with that of the blade 1.

lo The bearings R1 and R2 are arranged between the foot 3 and a lateral wall 5 of the chamber 4. Said wall 5, which is stepped, has a revolution substantially about a radial axis of the hub 2. After mounting of the blade 1, the axis B substantially coincides with said radial axis. The chamber 4 extends from the propeller centre side to an interior side 10, and from the side of the blade 1 to an exterior side 1 1.

Is In EP 0 324 617, the bearings R1 and R2 comprise at least a first bearing R1 with rollers 12 and a second bearing R2 with balls 13 in oblique contact. In the configuration of Figure 2, the bearing Rl is located in the vicinity of the exterior side 1 1, the bearing R2 in the vicinity of the interior side 10.

When the propeller turns, there are two actions upon the blade 1: to - a centrifugal or axial force that is a function of its speed of rotation and of its mass, - a bending moment at the blade foot caused by a radial force on the blade resulting from the interaction of the blade and the air it agitates.

The mounting device according to the teaching of EP 0 324 617 allows these actions to be compensated for: Is - the axial force is absorbed by the ball bearing R2; - the bending moment is absorbed by the assembly of the two bearings R1 and R2.

The recent appearance of composite materials for fabricating blades has allowed their mass to be reduced, and thus the axial force to which they are subjected. It has also allowed their dimensions to be increased, which has consequently increased the bending moment that the mounting device has to absorb. If the propeller rotation is s very fast, for example with high-powered engines, the rigidity of the mounting device according to the teaching of EP O 324 617 is insufficient. In these conditions, under the effect of the bending moment the second bearing R2 deforms excessively.

Consequently: - the balls 13 can leave the "base" of their bearing race. Their contact surface with lo their bearing race decreases and consequently the contact pressure to which they are subjected increases This phenomenon causes premature wear of the bearing R2; - excessive dislocation between the real and theoretical axes of rotation of the rollers 12 of the first bearing Rl known as "misalignment" is caused, which leads to premature failure of the roller bearing R1; - the sealing ring or rings isolating the lubricant introduced into the interior of the chamber 4 from the outside can become detached from their bearing surface Resulting leaks of lubricant mean increased maintenance, or even failure of the . mounting device.

The main object of the present invention is to provide a mounting device having to increased rigidity, particularly with long blades turning at high speed.

This o 3cct is achieved with a m.ountil.g device for a blade with a Invariable angle of incidence in a rotary hub of an aircraft propeller, the foot of said blade being able to pivot substantially according to the axis of said blade in a chamber of said hub by means of bearings arranged between said foot and said chamber, said chamber Is extending in said hub between an interior side and an exterior side, and said bearings comprise at least first and second bearings, respectively with rollers and with balls in oblique contact, said first bearing being positioned in the vicinity of one of said sides, distinguished in that said device comprises inter alla at least a third bearing, with rollers, positioned in the vicinity of the other of said sides.

By virtue of said characteristics, during rotation of the hub 2, the bending moment is mainly absorbed by the first R1 and third R3 roller bearings. However, these bearings are particularly suitable for absorbing radial forces associated with said bending moment. Hardly any demand is made radially upon the second bearing R2. The s rigidity of the device is thus increased and large bending moments, particularly during rotation of long blades of composite materials turning at high speed, can be absorbed without endangering the reliability of the device. The amount of maintenance is consequently limited.

According to other features, lo - the device is distinguished in that said bearing with balls in oblique contact is positioned axially between said first and third bearings, - the device is distinguished in that the rollers of at least one of said first and third bearings are substantially cylindrical and oriented substantially parallel to the axis B of said blade foot, is - the device is distinguished in that said second bearing is mounted without pre-

tensioning, - the device is distinguished in that at least one of said first and third bearings is mounted in a radially pre-tensioned manner, the device is distinguished in that said blade foot is surrounded with a skirt, and in to that at least one of said bearings has an interior bearing race integrated with said skirt, which improves the compactness of the mounting device, - the device is distinguished in that said rollers of said first bearing are guided axially by a groove formed in said skirt, the device is distinguished in that said chamber comprises a lateral wall, and in that Is at least one of said bearings comprises an exterior bearing race integrated with said lateral wall, the device is distinguished in that said second bearing comprises an exterior ring

and an internal ring, said balls being capable of rolling in a space located between said exterior ring and said interior ring, and in that in an operating position, a flange that is fixed to said foot by removable fixing means and is capable of bearing upon said hub, limits the axial translational displacement of said foot towards the interior side and keeps said rolling balls in said space, - the device is distinguished in that it comprises a passage having a diameter slightly greater than that of said balls, opening out on the one hand at the exterior of said hub, and on the other hand into said chamber in the vicinity of said space, and in that after removal of said fixing means, said foot is movable in an axial translational manner lo between said operating position and a dismantled position in which said balls are moveable between said space and the exterior of said hub, via said passage, - the device is distinguished in that said second bearing comprises an exterior bearing race through said exterior ring of said second bearing, in that said third bearing comprises an exterior bearing race through an exterior ring of said third bearing, and in that said exterior ring' of said third bearing is shaped in order to bear upon said exterior ring of said second bearing, which avoids having to use a supplementary piece such as a brace or circlip in order to clamp it axially towards the exterior side 11, and also allows the speed of the mounting and dismantling operations to be improved, - the device is distinguished in that said rollers of said third bearing are guided to axially by a groove carried by said exterior ring of said third bearing, - the device is distinguished in that said passage crosses said hub and said exterior ring of said third bearing, - the device is distinguished in that said flange is fixed to said foot by said fixing means, is axially moveable between a position where it bears upon said hub and a :s separated position without contact with said hub, - the device is distinguished in that said exterior and interior rings of said second bearing are configured, in said dismantled position, to prevent said balls from leaving said space from the side of said second bearing opposite to that where said passage opens out into said chamber, which allows the speed of the mounting and dismantling

operations to be improved, - the device is distinguished in that said first bearing comprises an exterior ring and an interior bearing a race carried by a supporting part fixed to said foot, and in that said foot is guided in an axial translational manner between said dismantled and operating s positions by first and second supports, the first support being that of the rollers of said first bearing on the exterior ring of said first bearing and the second support being that of the rollers of said third bearing on said supporting part, said first support being radially at least as eccentric as said second support with respect to said axis B of said foot. This guiding of the blade 1 during its introduction into the chamber 4 facilitates

lo maintenance.

The present invention also relates to an engine distinguished in that it is fitted with a device according to the invention and to an aircraft distinguished in that it is fitted with at least one engine fitted with a device according to the invention.

Further features and advantages of the present invention will be evident from reading the description that follows hereinafter, and from examination of the attached

drawings, in which - Figure 1, described hereinabove, shows a simplified perspective view of a blade 1 mounted on a hub 2.

- Figure 2, partly described hereinabove, shows a cross-section of the device in its to operating state, that is to say in a position allowing normal rotation of the propeller, in accordance with a preferred embodiment, - Figure 3 shows a cross-section view of the device in the dismantled position, according to a preferred embodiment.

In the description and the claims that follow, unless it is stated to the contrary, the

:s direction with respect to which reference is implicitly made when the adjectives "axial" and "radial" or the adverbs "axially" and "radially" are used, is that of the axis B.

Reference is now made to Figure 2. The rollers 12 of the first bearing R1 are substantially cylindrical and substantially oriented parallel to the axis B of the blade foot 3.

The exterior bearing races of the first Rl and second R2 bearings are carried by s exterior rings, respectively 14 and 15, fixed to the wall 5. The interior bearing race of the first bearing is integrated with a skirt 16 surrounding the foot 3. The interior bearing race of the second roller is carried by an interior ring 17 fixed to the skirt 16.

The metal skirt 16 protects the blade I from pressures exerted by the different rolling bodies. The blade 1 can thus be constructed of composite materials.

lo The exterior 15 and interior 17 rings old the second bearing R2 are axially offset with respect to one another. The exterior ring 15 is closer to exterior side 11 than the interior ring 17. The exterior ring 14 of the first bearing is axially clamped towards the interior side 10 by the shape of the hub 2 and towards the exterior side I 1 by a circlip 19 fixed in the hub 2. A groove 20 integrated into the skirt 16 axially guides the rollers is 12 of the first bearing Rl. The exterior ring 15 of the second bearing R2 is clamped axially towards the exterior side I 1 by the shape of the hub 2. The interior ring 17 of the second bearing R2 is clamped axially towards the interior side 10 by the shape of the skirt 16. The balls 13 kept in the operating position between the rings 15 and 17 clamp said rings respectively towards the interior side 10 and towards the exterior side 20 11.

The device further comprises a third bearing R3 comprising rollers 30 and positioned in the vicinity of the side of the chamber 4 opposite that in the proximity of which the first bearing R1 is located.

In the preferred embodiment, the bearings R1 and R3 are spaced as far apart as Is possible from one another along the axis B. In order to allow this maximum spacing, the bearing R2 with balls 13 is located axially between the two bearings R1 and R3.

Absorption of the bending moment, mainly by the bearings R1 and R3 is thus at maximum. In the device according to the invention, the precise axial positioning of the bearing R

between the bearings R1 and R3 can be as desired. In Figure 2, the bearing R2 is positioned in the vicinity of the bearing R3.

The rollers 30 of the third bearing 1 3 are substantially cylindrical, and oriented substantially parallel to the axis B of the blade foot 3.

s The third bearing R3 comprises an exterior bearing race carried by an exterior ring 31, said ring carrying a groove 32 serving to axially guide the rollers 30. The interior bearing race of the third bearing is carried by a supporting part 32' of the skirt 16.

It is to be noted that the surfaces of all the integrated bearing races are preferably surface treated by quenching to provide a hardness of the order of 50 to 60 Rockwell.

lo The integration of some bearing races into the skirt 16 improves the compactness of the assembly.

The exterior ring 31, clamped axially towards the interior side 10 by a circlip 33 fixed in the hub 2, comprises an annular curve widening 33' such as to bear upon the exterior ring 15 of the second bearing R2 and to thus be clamped axially towards the is exterior side 11. This curve widening 33' thus avoids a supplementary piece having to be used, such as a brace or a circlip, for axially clamping the exterior ring 31 towards the exterior side 11.

All the exterior rings 14, 15 and 31 bear upon the hub 2 by means of plastics material pieces, respectively 34a, 34b and 34c. The wall 5 of the chamber 4 of the hub 2 is thus to protected from high pressures that would be exerted over a significant period upon said wall S. The hub 2 can thus be fabricated in light metal, such as aluminiurn, or in light alloy. This weight benefit is an undoubted advantage for aircraft.

A passage 3 5 with a diameter slightly greater than that of the balls 13 crosses the hub 2 and the ring 31. It opens out on the one hand onto the exterior 36 of the hub 2, on the Is other hand into the chamber 4 in the vicinity of the space 37 located between the rings 15 and 17.

A flange 40 of substantially annular shape crossed at its centre by the foot 3, is fixed to the skirt 16 by removable fixing means 41, for example, by one or more screws. When

the propeller is not rotating, it can bear against the hub 2 by means of a supporting piece 42 of plastics material with a low friction coefficient (supporting position), or be separated therefrom (separated position), a clearance J being provided between the hub 2 and the flange 40.

s A lubricant in the interior of the chamber 4 is isolated from the exterior by two sealing rings 43 and 44 inserted and fixed into grooves machined respectively in the hub 2 and in the skirt 16. The seal 43 avoids any leakage between the exterior ring 14 of the first bearing upon which it bears and the hub 2. The seal 44 avoids any leakage between the skirt 16 and the exterior ring 14 of the first bearing upon which it bears.

lo When rotating, the turning seal 44 rubs on the exterior ring 14 of the first bearing. The hub 2 is thus protected from this rubbing A stopper 46 covers the extremity of the blade 1 placed in the interior of the hub 2.

This stopper carries an extension 47 serving as coupling means for the blade I to a device for controlling the angle of incidence of said blade (not shown) placed in the Is interior of the hub 2.

Reference is now made to Figure 3, in which it is evident that the flange 40 and the screw or screws 41, visible in Figure 2, are removed.

The foot 3 of the blade is introduced into the chamber 4 beyond its operating position, described with reference to Figure 2, such that the rings 15 and 17 are spaced further 20 apart from one another. These rings 15 and 17 are shaped so that their spacing, which is within a range of values detellllined according to the shape of the rings and their relative arrangement, allows the balls 13 to leave the space 37 located between the rings 15 and 17 via a single one of the apertures in said space 37. In the position described in Figure 3, the spacing allows the balls 13 to leave the space 37 by the is aperture on the side of the passage 35, but not by the aperture on the side of the chamber 4.

In another embodiment of the invention, not shown, in order to stop the balls 13 from leaving the space 37 by the aperture on the side of the chamber 4, a piece, for example, a foam ring, is fixed onto the hub 2 or onto the skirt 16 such as to at least partially fill

the chamber 4.

The passage 35 opens out into the chamber 4 in the immediate proximity of the ring 15, such that the balls 13 not retained in the space 37 can travel via said passage 35 between said space 37 and the exterior 36 of the hub 2.

s Between the operating position and the dismantled position, the rollers 12 remain bearing upon exterior ring 14. In the same way, the rollers 30 remain bearing upon the supporting part 32' of the skirt 16. The exterior ring 14 and the supporting part 32' each comprise an annular curve widening for this purpose.

The axial translation of the blade foot 3 in the chamber 4 is guided by these two lo supports. The grooves 20 and 32 axially retain respectively the rollers 12 and 30 during said translation, respectively with respect to the skirt 16 and the hub 2.

In order that the blade 1 can be introduced into the chamber 4 of the single-block hub 2 as far as the dismantled position, it is necessary that the bearing surface of the rollers 12 is at least as eccentric with respect to the axis B of the foot 3 as that of the rollers is 30.

The operation of mounting the device according to the invention is carried out in the following manner.

Before the first mounting of the foot 3 in the chamber 4, the skirt 16 is immovably fixed to the foot 3, generally by milling. The stopper 46 is immovably fixed to the foot 20 3. The rollers 12 are arranged on the skirt 16, then mounted in a cage. The seal 44 and the ring 17 are also positioned on their respective bearing surfaces machined into the skirt 16. The seal 43, then the plastics piece 34a intended to separate the exterior ring 14 of the Is hub 2, then the exterior ring 14 and the circlip 19, are put into position.

The plastics pieces 34b and 34c intended to separate respectively the rings 15 and 31 of the hub 2, the ring 1 S. then the ring 31 on which the rollers 30 have been previously

fixed and mounted in a cage, and the circlip 33 are put into position, taking care to align the hole pierced into the ring 31 with that pierced into the hub 2 in order to form the passage 35.

Apart from changing pieces, particularly because of wear, future mounting operations will not require the steps described hereinabove to be carried out.

To continue mounting, the blade foot 3 is introduced into the chamber 4 as far as a position substantially identical to that described in Figure 3.

This introduction is guided in axial translation by the supports of the rollers 12 and 30,

respectively on the exterior ring 14 and the supporting part 32'.

lo The balls 13 are then introduced via the passage 35 into the space 37 between the rings 15 and 17.

Pulling the foot 3 towards the exterior side 11 allows the balls 13 to come into contact with their hearing races carried by the rings 15 and 17.

The flange 40 is then screwed into a supporting position onto the skirt 16, optionally is leaving a clearance, onto the hub 2, such as to limit the axial movement of the foot 3 towards the interior side 10 of the chamber 4. The balls 13 are thus kept substantially in contact with their bearing races.

The passage 35 is covered, for example, by a stopper.

The method of mounting described hereinabove allows a single-piece hub 2 to be used, to which has the advantage of improving the rigidity of the assembly, its sealing and its reliability The dismantling of the foot 3 is carried out by reversing the mounting operation described hereinabove.

Then the hub 2 turns, the blade 1 is slightly axially displaced due to the effect of Is centrifugal force, towards the periphery of the propeller.

In the preferred embodiment, if it were bearing upon the hub 2, the flange 40 would

separate from it. All friction between the hub 2 and flange 40 is thus eliminated.

The tightening of the screws 41 allows pre-tensioning of the balls 13. In the preferred embodiment, no pre-tensioning is necessary. Indeed, when the hub 2 turns, the centrifugal force exerted upon the blade 1 tends to move axially towards the rings 15 and 17, and thus to constrain the balls 13.

The lack of pre-tensioning avoids an operation that is expensive as it takes a long time during maintenance works, and is delicate, as it directly affects the bearing performances constrained in this way.

Radial constraining means, not shown, are also conceivable as standard on the bearings lo R1 and R3 with rollers.

It is to be recalled that pre-tensioning consists of pre-constraining the rolling bodies, generally between two rings, an exterior and an interior one. Without pre-tensioning, under the effect of the different forces that are exerted pieces carrying their bearing races, the rolling bodies can, at a given moment, not all be acted upon, or are acted is upon in an unequal manner, which is detrimental to their longevity.

During rotation of the hub 2, the bending moment is mainly absorbed by the bearings R1 and R3 with rollers.

The rollers 12 and 30 of these have rectilinear bearing surfaces, substantially axial, greater than those of the balls of bearings of the same size as the bearings R1 and R3.

to These rollers 12 and 30 are thus particularly suitable for absorbing large stresses exerted perpendicular to their axes.

Spaced apart to the maximum, the first bearing R1 being close to one of the sides 10 and 11 of the chamber 4, and the third bearing R3 close to the other one, the bearings R1 and R3 with rollers combine their effects to provide good absorption of the bending :s moment, substantially without deformation.

Little demand is thus made upon the bearing R2 with balls 13 with oblique contact by the bending moment.

The mounting device according to the invention thus hardly changes shape under the effect of the bending moment. Consequently, the balls 13 continue to roll substantially within their bearing races whatever the bending moment applied to the blade 1, and misalignments of the rollers are reduced.

Large bending moments, particularly during the rotation of long blades in composite materials, turning at high speed, can be absorbed by a device according to the invention, without premature wear of the bearings, which limits the amount of maintenance. The improvement in rigidity of the mounting device also guarantees better sealing.

lo Moreover, the mounting and dismantling operations of the blade 1 are facilitated by the absence of pre-tensioning Maintenance is thus quicker and thus less costly. The configuration of the pieces and their arrangement also contribute to the speed of these operations. Moreover, the device according to the invention allows a single-piece hub 2 to be used, s which limits the risks of lubricant leakage and improves reliability still further. It lastly allows a light metal or light alloy hub 2 to be used, which lightens the aircraft.

Clearly, the present invention is not limited to the embodiment described and shown, provided by way of an illustrative example and non-limiting. For example, in other embodiments, the rollers of the first and third bearings, respectively 14 and 30, could :zo be conical or differently oriented. The exterior bearing races of one or more of the bearings R1, R2 and R3 could be hltegrated illtO the wall 5. The interior bearing race of the second bearing R2 could be integrated into the skirt 16.

Claims

1. A mounting device for a blade with a variable angle of incidence in a rotary hub of an aircraft propeller, the foot of said blade being able to pivot substantially according to the axis of said blade in a chamber of said hub by s means of bearings arranged between said foot and said chamber, said chamber extending in said hub between an interior side and an exterior side, and said bearings comprise at least first and second bearings, respectively with rollers and with balls in oblique contact, said first bearing being positioned in the vicinity of one of said sides, said device further comprising a third bearing, lo with rollers, positioned in the vicinity of the other of said sides.

2. A device according to claim 1, wherein said second bearing with balls in oblique contact is positioned axially between said first and third bearings.

3. A device according to claim 1 or 2, wherein the rollers of at least one of said first and third bearings are substantially cylindrical and oriented substantially is parallel to the axis B of said blade foot.

4. A device according to any one of the previous claims, wherein said second bearing is mounted without pre-tensioning.

5. A device according to any one of the preceding claims, wherein at least one of said first and third bearings is mounted in a radially pretensioned manner.

to

6. A device according to any one of the preceding claims, wherein said blade foot is surrounded with a skirt, and in that at least one of said bearings has an interior bearing race integrated with said skirt.

7. A device according to claim 6, wherein said rollers of said first bearing are guided axially by a groove formed in said skirt.

is

8. A device according to any one of the preceding claims, wherein said chamber comprises a lateral wall, and in that at least one of said bearings comprises an exterior bearing race integrated with said lateral wall.

9. A device according to any one of the preceding claims, wherein said second bearing comprises an exterior ring and an internal ring, said balls being capable of rolling in a space located between said exterior ring and said interior ring, and in that in an operating position, a flange that is fixed to said foot by removable fixing means and is capable of bearing upon said hub, limits the axial translational displacement of said foot towards the interior side and keeps said rolling balls in said space.

10. A device according to claim 9, comprising a passage having a diameter slightly greater than that of said balls, opening out on the one hand at the exterior of lo said hub, and on the other hand into said chamber in the vicinity of said space, and in that after dismantling of said fixing means, said Plot is movable in an axial translational manner between said operating position and a dismantled position in which said balls are moveable between said space and the exterior of said hub, via said passage.

s

11. A device according to one of claims 9 or 10, wherein said second bearing comprises an exterior bearing race carried by said exterior ring of said second bearing, in that said third bearing comprises an exterior bearing race carried by an exterior ring of said third bearing, and in that said exterior ring of said third bearing is shaped in order to bear upon saicl exterior ring of said second 2 bearing.

12. A device according to claim 11, wherein said rollers of said third bearing are guided axially by a groove carried b y said exterior ring of said third bearing.

13 A device according to any one of claims I I to 12, wherein said passage crosses said hub and said exterior ring of said third bearing.

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14. A device according to any one of claims 9 to 13, wherein said flange, fixed to said foot by said fixing means, is axially moveable between a position where it bears upon said hub and a separated position without contact with said hub.

15. A device according to any one of claims 10 to 14, wherein said exterior and interior rings of said second bearing are shaped in order, in said dismantled

position, to prevent said balls from leaving said space from the side of said second bearing opposite to that where said passage opens out into said chamber.

16. A device according to any one of claims 10 to 15, wherein said first bearing s comprises an exterior ring and an interior bearing race carried by a supporting part fixed to said foot, and in that said foot is guided in an axial translational manner between said dismantled and operating positions by first and second supports, the first support being that of the rollers of said first bearing on the exterior ring of said first bearing and the second support being that of the lo rollers of said third bearing on said supporting part, said first support being radially at least as eccentric as said second support with respect to said axis B of said foot.

17. An engine fitted with a device according to any one of the preceding claims.

18. An aircraft fitted with at least one engine according to claim 17.

s

19. A mounting device for a blade with a variable angle of incidence in a rotary hub substantially as described herein with reference to the drawings hereof.