GB2409708A

GB2409708A - Mounting a blade with a variable angle of attack

Info

Publication number: GB2409708A
Application number: GB0500201A
Authority: GB
Inventors: Jean-Jacques Forest
Original assignee: Societe Nouvelle de Roulements SNR SA
Current assignee: NTN SNR Roulements SA
Priority date: 2003-11-21
Filing date: 2005-01-06
Publication date: 2005-07-06
Anticipated expiration: 2025-01-06
Also published as: FR2862609B1; GB0425756D0; FR2862609A1; GB0500201D0; GB2409708B

Abstract

The root of a variable angle-of-attack blade is mounted in a chamber 5 of a hub 2 by means of at least first and second bearings R1,R2, which are O-mounted, at least the first bearing R1 being of the conical roller type and having rollers 12. A detachable flange 40 is configured to block an axial displacement of the rollers 12 towards an outer side 11 of the hub 2. The bearings R1,R2 may be preloaded by means of screws 50 that pass through bores 48 and 49 in the flange 40 and a bearing cup 18 respectively, and are screwed into the rim of a strut 25. In an alternative preloading arrangement screws pass through bores in the flange and are screwed into the bearing cup, a strut (which may be in the form of a sleeve) being disposed coaxially between the cup and a shoulder of the hub.

Description

DEVICE FOR MOUNTING A BLADE WITH A

VARIABLE ANGLE OF ATTACK

The present invention relates to a device for mounting a blade 1 with a variable angle of attack in a rotary hub 2 of an aircraft propeller, as shown in Fig. 1.

Conventionally, as shown in Fig. 2, the blade 1 is fixed to a hub 2 by one of its ends known as a blade root 3. The root 3, surrounded by a protective skirt 4, is mounted to pivot about an axis B. which is substantially perpendicular to and intersects with the axis A of the blade 1, in a chamber 5 of the hub 2. This pivoting, driven by means of a device (not shown) coupled to an extension 6 of a cap 7 closing off the root 3, makes it possible to adjust the angle of attack of the blade 1.

The chamber 5 comprises a staged lateral wall 8 of revolution about a radial axis C of the hub 2 which, after mounting of the blade 1, is substantially merged with the axis B. The chamber 5 communicates with respect to the centre of the propeller via an inner side 10 and with respect to the blade 1 via an outer side 1 1.

First and second roller bearings, R1 and R2 respectively, in oblique contact, are mounted between the root 3 and the lateral wall 8 using a conventional so-called "O" mounting.

The roller bearings R1 and R2, disposed in the vicinity of the outer and inner sides 11 and 10 respectively are conical roller bearings 12 and ball bearings 13 respectively in oblique contact. Each roller 12, of axis D, comprises a large base 14 oriented towards the outer side 11.

Outer raceways 15 and 16 of the rollers 12 and balls 13 respectively are borne by a cup 18 and an outer ring 19 bearing on the wall 8 by means of protective components of plastics material 18' and 19' respectively. The outer ring 19 bears on a first shoulder 21 of the hub, locking it axially towards the outer side 1 1.

Inner raceways 22 and 23 and of the rollers 12 and balls 13 respectively are provided in the protective skirt 4.

A duct 24, passing through the hub 2, is provided for the introduction of the balls between the ring 19 and the skirt 4.

When the propeller rotates, the blade is subject to two actions: a centrifugal or axial force, which is a function of its speed of rotation and its mass; - a bending moment at the blade root due to a radial force on the blade resulting from the interaction between the blade and the air that it agitates.

In order efficiently to take up these actions, it is conventional to preload the roller bearings R1 and R2, i.e. to create and maintain a compression of their rolling bodies 12 and 13 within their raceways.

In order to obtain preloading of this type, GB-2 244 525 proposes to use a cup comprising an over-length extending externally to the chamber and provided with an external thread on which a nut is screwed to bear on the hub. The screwing of the nut therefore makes it possible to adjust the axial position, relative to the hub, of the cup of the first roller bearing.

As a result of assembly constraints, the axial guiding of the rollers is ensured solely by the inner raceway which comprises, for this purpose, shoulders extending on each side of the rollers.

By acting on the adjustment nut it is therefore possible to displace the cup towards the outer side, the rollers remaining in their initial axial position in relation to the blade root. The rollers, as a result of their conicity and their orientation, nevertheless oppose this displacement. The desired preloading is obtained by an appropriate screwing of the nut. This operation is laborious, time-consuming and difficult as a result of the dimensions and the weight of the components involved.

There is therefore a real need for simplification, or even omission, of this procedure to adjust the preloading.

An assembly device as disclosed in GB-2 244 525 cannot, however, be readily dismantled or re-installed. It is in particular impossible to remove or insert the rollers without dismantling the second roller bearing.

There is therefore a need for an assembly device whose first roller bearing R1, which can be preloaded, could be assembled or dismantled independently from the second roller bearing R2.

According to an aspect of the present invention, there is provided a device for mounting a blade with a variable angle of attack in a rotary hub of an aircraft propeller, wherein the root of this blade may pivot substantially along the axis of the blade in a chamber of the hub by means of at least first and second oblique contact roller bearings which are O-mounted, at least the first roller bearing being of the conical roller type. This device is remarkable in that it also comprises a detachable flange rigid with the hub and configured to block an axial displacement of these rollers towards an outer side of the chamber.

It is therefore possible to block the axial displacement of the rollers 12 towards the outer side 11 solely by means of the flange. The inner raceway of the rollers 12 may then be shaped so that it no longer opposes the removal or insertion, via the outer side l l, of the rollers 12 after dismantling of the flange. No dismantling of the second roller bearing R2 is then needed for these operations.

According to further preferred characteristic features of the device of the invention: - the inner and outer raceways of the rollers are configured to enable the removal of these rollers via the outer side when the flange is dismantled; - the flange is configured to close off the outer side of the chamber; - the flange bears on a lateral surface of a cup of the first roller bearing; - axial plays J and J' are provided, in an assembled position of the blade, between the flange and the hub and between the flange and the skirt.

According to a first embodiment, the device comprises a strut whose first and second ends bear on the cup and on an outer ring of the second roller bearing respectively, the flange preferably being fixed to the cup by means of at least one screw passing through the flange and the cup and screwed into the strut; - according to a second embodiment, the device comprises a strut disposed between the cup and an annular shoulder of the hub in order axially to block the cup in the direction of the inner side, the flange preferably being secured to the cup by means of at least one screw passing through the flange and screwed into the cup; - in each of the embodiments, the strut is configured such that, in a stop position of the screw in which the cup is clamped between the flange and the strut, the rollers are in a predetermined preloading position; - the hub is in one piece.

The present invention also relates to a method of assembly of a blade with a variable angle of attack in a rotary hub of an aircraft propeller, wherein the root of this blade may rotate substantially along the axis of the blade in a chamber of the hub by means of at least first and second oblique contact roller bearings, which are O mounted, at least the first roller bearing comprising rollers.

This method is remarkable in that it comprises the following stages: successive installation in the chamber of the root, a strut and a cup of the first roller bearing, the strut being configured axially to block the cup towards an inner side of the chamber; - mounting of the rollers between the cup and the root; - fixing of a flange on the hub, which flange can be dismantled and is configured axially to block the rollers towards an outer side of the chamber.

Further characteristic features and advantages of the present invention are set out in the following description of preferred non-limiting embodiments made with reference to the accompanying drawings, in which: Fig. 1, described above, is a simplified perspective view of a blade 1 mounted onahub2; Fig. 2, partially described above, is a cross-section through a device of the invention according to a preferred embodiment; and Fig. 3 is a cross-section through a device according to a variant of the invention.

Identical reference numerals are used in the various Figures to designate identical or similar components.

The axis to which implicit reference is made when the adjectives "axial" and "radial" are used is the axis B. except when these adjectives are used to qualify the displacement of a roller. The "axial displacement of a roller" is then understood as the displacement of this roller about its axis D.

The description of Fig. 2 is continued below.

In this embodiment of the invention, a strut 25 is mounted in the chamber 5 between the outer ring 19 and the cup 18.

First and second ends, 27 and 29 respectively, of the strut 25 bear on first lateral surfaces, 31 and 33 respectively, of the cup 18 and the outer ring 19 respectively. The bearing points of the first and second ends of the strut 25 are axially spaced from one another by a length X determined as a function of the desired preloading of the roller bearings Rl and R2, as will be described in further detail below.

The strut 25 is formed as a substantially cylindrical sleeve whose first end 27 is provided with an annular rim 35.

An annular flange 40 surrounds the root 3 so as to close off the chamber 5 on the outer side 11. O-ring seals 41 and 42, disposed between the flange 40, on one hand, and the skirt 4 and the hub 2 respectively, on the other hand, ensure that this closure is leak-tight.

The flange 40 bears axially on a second lateral surface 44 of the cup 18 opposite the first lateral surface 31. Axial plays J and I' are provided between the flange 40 and the hub 2, and between the flange 40 and the skirt 4 respectively.

Screws 50 pass fully through the flange and cup bores, 48 and 49 respectively, which are not tapped, and are screwed into the rim 35 of the strut 25. The strut 25 and the hub 2 are configured such that, in the mounted position of the blade as shown in Fig. 2, neither the rim 35 nor the screws 50 bear axially, towards the inner side 10, on the hub 2.

Each screw 50 is provided with a head 52 bearing, via a washer 54, on an outer surface 56 of the flange 40. Gaskets (not shown) are preferably disposed under the heads of the screws 50 in order to ensure leaktightness.

The flange 40 is thus fixed on the cup 18, as the cup 18, constrained between the strut 25 and the rollers 12, is itself axially locked with respect to the hub 2. The flange 40 is thus rigid with the hub 2 without being in direct contact therewith.

The screws 50 are preferably distributed in a substantially equi-angular manner about the root 3.

In this embodiment of the invention, the flange 40 comprises a guiding end 60 for the rollers 12 configured to block their axial displacements, i.e. along their axes D, towards the outer side 11.

Preferably, the inner and outer raceways 22 and 15 of the first roller bearing R1 are borne by surfaces shaped to enable, when the flange 40 is dismantled, a removal or insertion of the rollers 12 on the outer side 11. The guiding of the rollers 12 on the outer side 11 is preferably ensured solely by the end 60 of the flange 40. The retention of the rollers 12 in the direction of the inner side 10 is preferably ensured solely by a retaining shoulder 62 provided in the skirt 4.

The possible shapes of the end 60 of the flange 40 and the retaining shoulder 62 are known to a person skilled in the art, the objective being to guide the rollers and to ensure their preloading along their axis D. In this embodiment of the invention, the flange 40 simultaneously carries out the following functions: - in cooperation with the screws 50 and the strut 25, axial traction of the cup 18 towards the outer side 11 so as to preload the roller bearings R1 and R2; - axial guiding of the rollers 12 towards the outer side 11; and - closure of the outer side 11 of the chamber 5.

The threefold function of the flange 40 also advantageously makes mounting extremely simple.

In a variant of the invention shown in Fig. 3, a strut 25', for instance in the shape of a sleeve, is disposed coaxially between the cup 18 and a second shoulder of the hub 64, first and second ends, 27' and 29' respectively, of the strut 25' bearing on the first surface 31 of the cup 18 and on the shoulder 64.

The screws 50, bearing on the outer surface 56 of the flange 40 pass through the untapped bore 48 of the flange 40 and are screwed into a tapped bore 66 in the cup 18.

In a "dismantled" position of the device of the invention (not shown), the root 3, the cup 18, the strut 25, the rollers 12 and the balls 13 are dismantled but the outer ring 19 of the second roller bearing R2 is in position on the hub 2.

The mounting of the root 3 on the hub 2 takes place in the following chronological stages: a) insertion of the root 3 into the chamber 5; b) insertion of the balls 13 via the duct 24 and positioning of the root 3, by traction towards the outer side 11, so as to keep the balls 13 substantially within their raceways 16 and 23; the duct 24 is then conventionally closed, for instance by a cap (not shown); c) insertion into the chamber 5 of the strut 25 or 25', then the plastic member 18' and the cup 18; d) mounting of the conical rollers in the raceways 15 and 22 of the first roller bearing R1; and e) after mounting, where necessary, of the gaskets 41 and 42, mounting of the flange 40 and tightening of the screws 50.

The final stage e) is now examined in further detail in relation to the device shown in Fig. 2.

Prior to tightening of the screws (stage e)), - the balls 13 are in position but are not stressed; - the second end 29 of the strut 25 may bear on the outer ring 19 without stressing it; - the first surface 31 of the cup 18 may bear on the first end 27 of the strut 25 without stressing it; and - the rollers 12 are positioned substantially in contact with their outer and inner raceways 15 and 22 respectively.

The strut 25, the cup 18, the flange 40, the skirt 4 and the rollers 12 are configured such that the tightening of the screws 50 leads to a compression of the rollers 12 and balls 13.

The tightening of the screws 50 axially closes up the strut 25 and the flange 40.

This closing up is impeded by the contact of the rollers 12 with the end 60 of the flange 40. Under the action of the end 60 on the rollers 12, the rollers 12 are pushed into their outer and inner raceways 15 and 22 which tends to displace the cup 18 and the strut 25 towards the inner side 10 and the skirt 4 towards the outer side 11. These displacements are caused to be opposing by the balls 13 compressed under the effect of the thrust of the strut 25 on the outer ring 19 towards the inner side 10, and the skirt 4 thrust towards the outer side 11.

The axial position of the cup 18 becomes more precise as the screws 50 are tightened.

As soon as the rollers 12 start to be stressed, the tightening of the screws 50 becomes more difficult, but may nevertheless be continued until the cup 18 is clamped between the strut 25 and the flange 40.

As the cup 18 is of a substantially incompressible material, the continued tightening of the screws 50 then becomes impossible unless an extremely high torque is exerted. The screws 50 are then "fully" tightened in a "stop position".

Advantageously, the user, feeling a sudden locking of the screws 50, detects this stop position without complex measurement tools.

The axial position of the end 60, the width Y of the cup 18, the width X of the strut and the position of the raceways 15 and 22 of the rollers 12 and the raceways 16 and 23 of the balls 13 are determined such that in the stop position: - the surfaces of the rollers 12 in contact with the raceways 15 and 22 are compressed to a value corresponding to a desired level of preloading; - the rollers 12 are substantially not compressed along their axes D; and - the flange 40 is not in contact with the hub 2.

Advantageously, the preloading value is determined, in a definitive manner, during machining of the components. The adjustment is carried out "blank" by the bearing producer, and makes it possible to machine the strut 25 to the dimension X in order to obtain the desired preloading. On the apparatus, it is then enough to lock the screws 50 to obtain this same preloading. This provides a very high level of simplicity and a very high degree of precision of the preloading operation. The preloading operations, which conventionally last several hours, are reduced to a few minutes, as the procedure to adjust the preloading is omitted.

It will be appreciated that the precision of the stop position determines that of the preloading of the rollers 12. It is therefore necessary to manufacture the flange 40, the cup 18, the skirt 4 and the hub 2 with an appropriately adapted precision.

The axial length X of the strut 25 and the distance separating the inner raceways 22 and 23 of the rollers 12 and the balls 13 are also determined such that the compression of the rollers 12 goes together with a compression of the balls 13 between the outer ring 19 and the skirt 4 and such that, in the stop position of the screws 50, the balls 13 are preferably stressed to a predetermined value.

Advantageously, the axial spacing X of the cup 18 and the outer ring 19 is not determined by the shape of the wall 8 of the chamber 5, which enables a higher machining tolerance of this wall.

Advantageously, the retention of the various assembly components of the invention in their respective positions is ensured solely by the screws 50. The number of components is therefore advantageously reduced.

The assembly of the device shown in Fig. 3 is similar to that of the device shown in Fig. 2.

The tightening of the screws 50 axially closes up the cup 18 and the flange 40.

This closing up is impeded by the contact of the rollers 12 on the end 60 of the flange 40. Under the action of the end 60 on the rollers 12, the rollers 12 are thrust into their outer and inner raceways 15 and 22 which tends to displace the cup 18 towards the inner side 10 and the skirt 4 towards the outer side 11.

The displacement of the cup 18 towards the inner side 10 is limited by the strut 25' which itself abuts on the shoulder 64.

The displacement of the skirt 4 towards the outer side 11 is limited by the action of the balls 13.

As a result of the configuration of the strut 25', the cup 18, the flange 40, the skirt 4, the bills 13 and the rollers 12, the tightening of the screws 50 thus causes a compression of the balls 13 and the rollers 12 in their respective raceways.

As soon as the rollers start to be stressed, the tightening of the screws 50 becomes difficult but can be continued, however, until the cup 18 is clamped against the flange 40. The stop position is then reached.

In the stop position, the compression of the balls 13 between the outer ring 19 and the skirt 4 depends on the length X' of the strut 25' but also on the axial distance X" separating the first and second shoulders, 21 and 64 respectively, of the hub 2.

Whatever the embodiment, the position of the root 3 with respect to the hub 2 and the preloading of the roller bearings R1 and R2 are advantageously set precisely solely by the screwing of the screws 50 into the flange 40.

Conventionally, moreover, a correctly adjusted preloading at the time of assembly of the device rapidly becomes incorrect after a few hours of operation of the blade. In practice, the conical rollers 12 occupy their final positions in their raceways only after rotating for several hours. This leads to play which, to be eliminated, requires a second preloading operation.

With the present invention, the stop position is preferably determined to take account of this play. Advantageously, it is then possible to carry out a single preloading operation.

During the preloading operation, the user preloads the roller bearings until he feels the stop position of the screws 50. He is then assured of the correct preloading of the roller bearings after the final positioning of the rollers. This leads to extremely simple maintenance.

Advantageously, the device of the invention enables the use of a singlepiece hub 2 which improves the rigidity of mounting, its leak-tightness and its reliability.

It enables rapid, reliable and faultless preloading of the rollers 12 and the balls 13 of the roller bearings R1 and R2 respectively.

The dismantling of the root 3 takes place in the reverse order of stages a) to e) as described above.

After dismantling of the flange 40, it is possible to remove the rollers 12 without necessarily going on to the subsequent stages d) to a). It is therefore very advantageously possible to replace the rollers 12 without having to dismantle the overall device, which further facilitates maintenance.

As can be clearly seen, the device of the invention makes it possible to mount and dismantle the first roller bearing R1, in particular its conical rollers 12, independently from the second roller bearing R2.

It will be appreciated that the present invention is not limited to the embodiments described and illustrated, which are given purely by way of non-limiting

example.

For instance, in other embodiments, the roller bearing R2 could comprise cylindrical or conical rollers.

The inner raceways of one or a plurality of the roller bearings R1 and R2 could be borne by add-on rings.

Claims

1. A device for mounting a blade with a variable angle of attack in a rotary hub of an aircraft propeller, wherein the root of this blade may pivot substantially along the axis of the blade in a chamber of the hub by means of at least first and second oblique contact roller bearings, which are O-mounted, at least the first roller bearing being of the conical roller type, and the device also comprises a detachable flange rigid with the hub and configured to block an axial displacement of these rollers towards an outer side of the chamber.

2. A device as claimed in claim 1, wherein the inner and outer raceways of the rollers are configured to enable the removal of these rollers via the outer side when the flange is dismantled.

3. A device as claimed in claim 1 or 2, wherein the flange is configured to close off the outer side of the chamber.

4. A device as claimed in any one of the preceding claims, wherein the flange bears on a lateral surface of a cup of the first roller bearing.

5. A device as claimed in any one of the preceding claims, wherein axial plays are provided, in an assembled position of the blade, between the flange and the hub, and between the flange and the skirt.

6. A device as claimed in claim 4 or 5, further comprising a strut whose first and second ends bear on the cup and on an outer ring of the second roller bearing.

7. A device as claimed in claim 6, wherein the flange is fixed to the cup by means of at least one screw passing through the flange and the cup and screwed into the strut.

8. A device as claimed in claim 4 or 5, further comprising a strut disposed between the cup and a shoulder of the hub in order axially to block the cup in the direction of the inner side.

9. A device as claimed in claim 8, wherein the flange is fixed to the cup by means of at least one screw passing through the flange and screwed into the cup.

10. A device as claimed in any one of claims 6 to 9, wherein the strut is configured such that, in a stop position of the screw in which the cup is clamped between the flange and the strut, the rollers are in a predetermined preloading position.

11. A device as claimed in any one of the preceding claims, wherein the hub is in one piece.

12. A propeller comprising a device as claimed in any one of the preceding claims.

13. A method of assembly of a blade with a variable angle of attack in a rotary hub of an aircraft propeller, wherein the root of this blade may pivot substantially along the axis of the blade in a chamber of the hub by means of at least first and second oblique contact roller bearings, which are O-mounted, at least the first roller bearing comprising rollers, the method comprising the following steps: - successive installation in the chamber of the root, a strut and a cup of the first roller bearing, the strut being configured axially to block the cup towards an inner side of the chamber; - mounting of the rollers between the cup and the root; and fixing of a flange on the hub, which flange can be dismantled and is configured axially to block the rollers towards an outer side of the chamber.

14. A device for mounting a blade with a variable angle of attack in a rotary hub of an aircraft propeller, substantially as herein described with reference to, or with tar reference to and as illustrated in, Figs. 1 and 2 or Figs. 1 and 3 of the accompanying drawings.

15. A method of assembly of a blade with a variable angle of attack in a rotary hub of an aircraft propeller, substantially as herein described with reference to Figs. 1 and 2 or Figs. 1 and 3 of the accompanying drawings.