FR2786828A1 - Coaxial coupling between two shafts with adjustment to a support cushion in the plummer block. - Google Patents

Abstract

The annular cushion (25) is placed between the fixed housing (22,23) and a spherical surface (27) of a spherical bearing with a large radius of curvature contained in a plummer block (12,15,16). It is made up of two annular rings (25) placed on either side of the central plane of the outer surface of the spherical bearing.

Description

COAXIAL COUPLING DEVICE BETWEEN TWO SHAFTS

  The present application relates to a coaxial coupling device between two shafts, comprising a support at the level of this coupling as well as a single flexible connection system between the ends of these two shafts, said support comprising a block near this system. bearing fitted with a single row ball bearing and mounted in a fixed housing so as to be able to undergo slight radial and angular movements relative to this housing. It has been indicated that preferably an annular cushion of elastic material is interposed between a swiveling outer surface with a relatively large radius of curvature of the bearing block and the fixed housing, this cushion being able for example to comprise two rubber rings. The size of the radius of curvature is conditioned by the dimensions of the bearing

  integrated in the ring cushion.

  Such a coupling device, by self-aligning the shafts, corrects any misalignments due to

  positioning deviations of the mechanical parts concerned.

  As for the fixed housing, intended to contain the annular cushion of elastic material and to keep it pressed on the bearing block, it consisted of a generally cylindrical bearing body, closed by a cap.

  fixed to the body for example by screws.

  These basic provisions could have been improved by taking into account the following requirements. First of all, the need appeared to be able to regulate the tightening of the transmission bearings in helicopters much more precisely, given the relatively large deformations of the tail beams.

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  in flight, these beams supporting the corresponding transmission. This operation requires sufficient tightening to block the previous annular cushion and thus prevent its rotation, which would cause premature wear of the bearing. However, this tightening must remain limited to avoid damage to said annular cushion. With the previous arrangements, the tightening of the transmission bearings could not be precise enough because it depended on the compression

  extremely variable and deformation - important -

  of the annular cushion of elastic material. In addition, this deformation was determined by the direct abutment of the cap cited above against the bearing body after blocking the fixing screws, and this compulsory abutment therefore left neither possibility of adjustment of this compression of the annular cushion of elastic material, nor possibility of modifying, during servicing and maintenance operations, the initial setting to compensate for wear and play, or even modifying the initial settings of the bearing block for

  adapt to different operating conditions.

  In other words, there was on the one hand a real defect in the positional locking of the bearing, and on the other hand a lack as for the possibilities of adjustment of the relative position of the different parts and the

efforts in the bearing.

  Another disadvantage of the annular cushion also resided in the fact that the elastomer or the like constituting the cushion, damping noise and vibrations, made it difficult to detect bearing defects, such as excessive wear or matting of the surfaces in contact, or other conditions of

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  abnormal functioning such as excessive vibration level of the coupling or significant loss of fat. The present improvements, which make it possible to avoid these drawbacks, include the following provisions. First of all, the annular cushion of elastic material has been replaced by an annular cushion of relatively rigid and incompressible material and whose surface has a low coefficient of friction, this annular cushion consisting of two rings spaced from one another and arranged on either side of said plane

  transverse median of said swiveling outer surface.

  As soon as the cushion is rigid and relatively undeformable, it is in fact understood that it must consist of two separate rings, arranged on either side of the transverse plane of symmetry of said swiveling outer surface, otherwise it could not to be

mounted on it.

  For the constitution of these rings, it will be possible in particular to take PTFE, PVC or other similar materials, whether they are solid or used to constitute the coating of a rigid material, for example a metal such as steel or aluminum, this cushion anyway having a cross section generally adapted to the section of the annular space formed between the internal surface of said fixed casing and said swiveling external surface of the bearing block. Another variant would consist in using mixed materials, of the laminated type and known elsewhere, consisting of metal lamellae interposed between

elastomeric strips.

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  This will remedy all the drawbacks mentioned above, linked to the high compressibility of the elastomers and their qualities,

  including vibration damping.

  In order to be able to conveniently adjust the radial compression of said relatively rigid annular cushion on said swiveling external surface of the bearing block, provision will also be made for said fixed housing to comprise means for adjusting the amplitude of axial engagement of said cover on said body, and means for adjusting the

tightening said fixing screws.

  Thus, we will no longer be dependent on the uncontrollable compression of the cushion elastomer, and on the contrary we will be able to precisely control this radial pressure exerted on the annular cushion, for example according to manufacturing tolerances, and even modify the settings at during the lifetime of the coupling device, to take account, in particular, of wear,

  this by gradually absorbing the relative axial clearances

  important items, initially provided between the cover

and the housing body.

  The reason why these axial clearances must be relatively large lies in the fact that, as mentioned above, the radius of curvature of the swiveling outer surface of the bearing block is relatively large, since it is only a question of compensating for slight misalignment of trees compared to

to the rolling axis.

  As a result, the appearance of a small radial clearance, for example at the level of the bearing, will result in a relatively large axial offset of the cover of the fixed casing relative to its body. This will be better understood later, but we can also note here

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  that it is also the relative importance of the radius of curvature of said swiveling outer surface which makes it appropriate to use an annular cushion made of PTFE or coated with PTFE or other material with a low coefficient of friction, to avoid its jamming, disassembly, between the swiveling surface in question and the surface

internal of the fixed housing.

  We saw above that the rigid annular cushion had to be made up of two separate rings to be able to

  be mounted on said swiveling outer surface.

  According to an additional characteristic of the present invention, the spacing between these two rings is such that, seen from the center (C) of symmetry of said swiveling outer surface, the angle (y) between these two rings is greater than the angle (a) jamming of the two rings between said swiveling surface and said internal surface

of the fixed housing.

  This is indeed the necessary condition so that the two rings can be removed without being trapped

  by friction between the two aforementioned surfaces.

  Since the two rings are made of PTFE or are coated with PTFE or any other material with a low or very low coefficient of friction, the wedging angle a is very small, and so it will be the same for the angle y, which means that the spacing between the two rings may be very small. This allows the assembly to remain compact, despite the

  division of the ring cushion into two rings.

  On these common bases, the invention can be implemented according to different embodiments, as regards the constitution of the means of adjustment and

tightening mentioned above.

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  In a first embodiment, the device comprises adjustment and tightening means generally constituted by a set of screws securing the cover to the body of the housing extending around S of said bearing block, the tightening of these screws being adjusted. thanks

to a torque limiter.

  Thus, it is possible to adjust at the same time the amplitude of the axial engagement of the housing cover on the housing body, and the radial pressure exerted, under the effect of assembly and conical centering thus produced, by the annular cushion on the swiveling outer surface of the bearing, all without the housing body having

  vis-à-vis the cover an axial stop effect.

  This embodiment will be preferred for an application to helicopter transmissions, since it will make it possible to limit the radial clearances as much as possible and to reduce them very easily, without any dismantling, in the event that they have increased due to wear or a matting

  parts in contact, due to vibrations.

  In the other cases and in a second embodiment of the device, separate adjustment and tightening means are used, the means for adjusting the amplitude of axial engagement of said cover on said body comprising a stack of peelable shims clamped between a flange of the housing body and a flange of its cover, while the clamping means comprise a set of screws securing the cover to the body

  of the housing by crossing said flanges.

  Advantageously also, it is possible to provide that the space provided between the two rings constituting the annular cushion forms a sealed passage of grease.

  between an external lubricator and said bearing.

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  According to one embodiment, said bearing can be contained in a seal holder housing, these seals being mounted, on either side of said bearing, to ensure the seal between said housing and the rotating surfaces of the coupling, to which case said rigid annular cushion is interposed between said fixed housing and

  a swiveling outer surface of the seal holder housing.

  According to another embodiment, said rigid annular cushion is interposed between said fixed casing and a swiveling outer surface of an outer ring of the bearing, in which case said bearing directly has its own seals, on either side of the row of

  balls, between its outer ring and its inner ring.

  According to another important arrangement of the invention, such a device can also be characterized in that said flexible connection system is mounted between the end of one of the shafts and a coupling section, which is wedged on a sleeve of coupling rigidly fixed to the end of the other shaft, and in that said bearing block support is disposed at the junction between said section and

said sleeve.

  In the application to helicopters, it will also be advantageous to provide that one of the shafts is a subcritical transmission shaft connected to the main gearbox of a helicopter, the other shaft being a supercritical shaft connected to its gearbox. rear transmission, the reverse arrangement being

also possible.

  Two embodiments of the invention will now be described by way of non-limiting examples, with reference to the figures in the attached drawing in which:

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  - Figure 1 is an axial sectional view of a coupling device between two shafts of a

  rear helicopter transmission, more particularly

  the transmission of power between the main gearbox driving the rotor

  lift from a helicopter, and the trans-

  rear mission driving the tail torque rotor; - Figure la is a partial axial sectional view of the housing; - Figure 2 is a right view of the housing cover; and - Figure 3 is an axial sectional view of another embodiment of the coupling device

coaxial between two trees.

  In the first embodiment shown in axial section in FIG. 1, two trees have been referenced in 1 and 2, the tree 1 being for example a subcritical tree

  transmission connected to the main transmission

  blade of a helicopter, and shaft 2 a supercritical shaft connected to its rear gearbox. At the end of the shaft 1 to be coupled to the corresponding end of the shaft 2 is provided a conical coupling sleeve 3 fixed on the shaft 1 by a crown of

  bolts 4 (which could be replaced by rivets).

  Similarly, at the end of the shaft 2 is provided a coupling sleeve 5. This sleeve consists of a cylindrical section 5a connected by a ring of rivets 6 to the end of the shaft 2 , and a conical section 5b secured to the end of the conical sleeve 3 by grooves 7. As for the two sections 5a and 5b, they are elastically connected to each other by a single flexible connection system 8 of the "Thomas coupling" type,

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  known in this technique as the "flector", and fixed by a ring of bolts 9 between a flange 10 of the section 5a and a flange 11 of the section 5b. (It is recalled here for the record that a flector is a flexible rotating coupling which may include one or more blades

flexible metal).

  The coupling support thus obtained comprises in this embodiment a bearing block with single row of balls, the outer ring 12 of which is held, by a ring 13, in an inner annular groove 14 of a housing seals 15 with swiveling outer surface 27. The inner ring 16 of said row of bearing balls is held against a peripheral shoulder 18 of the end of the section Sb of the sleeve 5 by the axial tightening of a cap 17 on

the end of the sleeve 3.

  In 19 there are shown two conventional reinforced annular seals capable of sealing the bearing vis-à-vis the outside, and fixed for this purpose under shoulders 20 of the seal holder housing 15, the lips of these seals rubbing on the rotating surfaces 21 of the coupling. An annular cushion of rigid synthetic material, for example made of PTFE or of metal coated with PTFE (polytetrafluoroethylene) is interposed between the seal carrier housing 15 and a fixed housing, the latter consisting of a bearing body 22 closed by a cap 23 fixed to the body 22 by axial clamping screws 24 (see also Figure 2); said rigid annular cushion consists of two rings 25 slightly spaced one of

  the other and arranged on either side of the transverse plane

  sal of symmetry containing the center of symmetry C of the swiveling surface 27 as well as the center of the balls of the

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  bearing, these rings being compressed between the bottom of the bearing body 22 and this swiveling outer surface

27 of the seal holder housing 15.

  This surface 27 is swiveling to allow a slight angular offset of the fixed housing 22, 23 relative to the axis of the shaft 1. To do this, a spherical surface 27 can be provided. It allows, thanks to such a surface, a relaxation of the stresses in the bearings and the structure when the fixed housing is installed poorly aligned with respect to the shaft 1, for example

  due to positioning deviations of the block supports

  bearing. It should be noted that the space 26 provided between the rings 25 provides, thanks to these rings, a sealed passage for the grease coming from an external lubricator 28 and

  directed on the bearing, the housing 15 having opposite

  screw of the lubricator a radial channel 29.

  It should also be noted that in this embodiment there is initially (after the first assembly) a relatively large axial clearance i between the edge of the cover 23 and a shoulder 22a of the housing body, and another axial clearance j, of the same order of magnitude, between the end of the body 22 and the bottom 23a of the

cover 23 (figure la).

  Thanks to these arrangements and as already explained above, it will be possible to precisely regulate the radial pressure exerted on the swiveling surface, notwithstanding the manufacturing tolerances, and to easily compensate for the

  clearances appearing during operation.

  In the embodiment of FIG. 3, an embodiment has still been described that can be envisaged for helicopters, insofar as the cost and the mass of the

  device are not mandatory conditions.

  il 2786828 The essential difference with the previous embodiment, independently of the adjustment and tightening means, resides in the absence of the seal holder box 15, the seals of the bearing 12 ', 16', referenced in 19 ' , being directly attached to the outer ring 12 ', their lips being in contact with the peripheral bearings 21' of the inner ring 16 'In this case, it is the outer ring 12' which may comprise, in contact with the rings in PTFE or similar 25 ', a spherical swivel surface 27'. The fixed housing containing the rings 25 'and the bearing can be constituted, as in the first embodiment, by a bearing body 22' closed by a cap 23 'by means of axial clamping screws 24'. The originality of this arrangement, from the point of view of the means for adjusting the axial positioning of the cover 23 ', and of its tightening on the housing body 22', lies in the fact that a stack 30 of peelable shims is sandwiched between flanges 31 and 32, respectively of the body 22 ′ and of the cover 23 ′, which are crossed by the screws 24 ′, a clearance k being formed internally to prevent direct abutment of the

cover on the housing body.

  Thus, it is also possible to conveniently adjust the initial axial position of the cover 23 ′ with respect to the housing body 22 ′, and thus thus precisely adjust the radial pressure exerted by the rigid annular cushion.

  '-25' on ring 12 ', then, during operation-

  nement, compensate for the radial clearances due to wear or matting of the parts in contact, this by peeling more or less

stacking 30.

  In the two embodiments which have just been described, the mounting of the coupling device is simplified, because as long as the caps 23 and 23 ′ are not

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  that approached, the bearing is swiveled and realizes by itself its alignment on the shaft during its installation. This limited self-aligning character constitutes an essential feature of this assembly. When the assembly is finished, the caps close the whole while compressing the rigid rings 25 and 25 '; the ball joint is then blocked and becomes a relatively stiff assembly radially and perfectly resistant to corrosion and the risk of seizing. During operation, the radial and angular play of the mounting of the bearing allows it to accommodate deformations of the structure which carries the fixed housing, as well as the bending of the shafts, in particular the shaft opposite to that which carries the "flector. ". The functional effort being almost zero, correct assembly and good quality seals allow us to hope for a duration of

extremely long life.

  Other advantages of the invention reside in the simplicity of the device, which uses only a single flector between the two shafts, and a simple bearing without preload. The aforementioned self-alignment avoids carrying out an alignment of the structure or a resumption of machining or setting. The structure itself need not be particularly rigid. Finally there is a significant gain in weight compared to: devices that use two flectors, between a central sleeve supported by a bearing, and the ends respectively

  of the two shafts to be coupled.

  As already indicated, the invention finds a particularly interesting application in helicopters, for the transmission of power between the main gearbox driving the lift rotor, and the rear gearbox 13n

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  driving the tail torque rotor. In particular, the invention makes it possible to provide a section 5b as short as possible, that is to say to reduce the distance between the bearing surface of the bearing block and the flexible connection system (flector 8). As a result, the efficiency of the fiector is increased, which consequently reduces the stresses

  transmitted to the various elements of the bearing block.

  It should be noted that the annular cushion of rigid material could be in one piece, instead of being made up of two rings 25 or 25 ', in which case this piece could be crossed by vents for the passage of

the fat.

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Claims (11)

RESELL I CATIONS   1. Coaxial coupling device between two shafts (1, 2) comprising a support at the level of this coupling and a flexible connection system (8) between the ends of said shafts (1, 2), said support comprising   near said flexible connection system (8) a block   bearing (12, 15, 16; 12 ', 16') provided with a single row ball bearing and mounted in a fixed generally cylindrical housing (22, 23; 22 ', 23') by   through an annular cushion (25; 25 ') inter-   placed between said fixed housing (22, 23; 22 ', 23') and a swiveling external surface (27, 27 ') in the form of a sector   spherical with relatively large radius of curvature of the block   bearing (12, 15, 16; 12 ', 16'), this swiveling outer surface having a median transverse plane of symmetry perpendicular to the axis of the two said shafts, device in which said fixed housing (22, 23; 22 ', 23 ') has a cover (23; 23') suitable for being axially sliding and secured to a body (22; 22 ') by axially extending fixing screws, characterized on the one hand in that said ring cushion   (25; 25 ') is made of relatively rigid material and   pressible, with a low coefficient of friction surface, and has a cross section generally adapted to the section of the annular space formed between the internal surface of said fixed housing (22, 23; 22 ', 23') and said swiveling external surface of the bearing block (12, 15, 16; 12 ', 16'), this annular cushion consisting of two rings (25; 25 ') spaced from each other and arranged on either side of said transverse plane median of said swiveling outer surface, and on the other hand that said fixed housing comprises adjustment means (24; 2786828   24 ') of the amplitude of axial engagement of said cover (23; 23') on said body (22; 22 '), and means for adjusting the tightness of said fixing screws, thus making it possible to adjust the radial compression of said cushion relatively rigid annular (25; 25 ') on said swiveling outer surface of the bearing block (12, 15, 16; 12 ', 16').   2. Coaxial coupling device according to claim i, characterized in that relatively large axial clearances (i, j) are provided between the cover   (23) and the body (22) of said housing: ixe.   3. Coaxial coupling device according to claim 1 or 2, characterized in that the spacing between the two rings (25; 25 ') constituting the annular cushion is such that, seen from the center (C) of symmetry of said surface external patellar: e, the angle (p) between these two rings is greater than the angle (E) of jamming of the two rings between said swiveling surface and said internal surface of the fixed housing.   4. Coaxial coupling device according to claim 1, characterized in that it comprises adjustment and tightening means generally constituted by a set of screws (24) securing the cover to the body of the housing extending around said bearing block (12, 15, 16), the tightening of these screws (24) being adjusted by to a torque limiter.   5. Coaxial joining device according to claim 1, characterized in that it comprises adjustment means (30) and clamping (24 ') separate, the means for adjusting the amplitude of axial engagement of said cover on said body comprising a stack (30) of peelable shims clamped between a flange (31) of the housing body and a flange (32) of its cover, while the 16 2786828   clamping means comprise a set of screws (24 ') securing the cover (23') to the body (22 ') of the   housing crossing said flanges.   6. Axial coupling device according to claim 1, characterized in that the two said   rings (25) provide a space (26) between them   creating a sealed passage of grease between a lubricator   outside (28) and said bearing (12, 16).   7. Axial coupling device according to claim 1, characterized in that said bearing (12, 16) is contained in a seal holder housing (15), these seals (19) being mounted, on either side of said bearing (12, 16), to seal between said housing (15) and rotary bearing surfaces (21) of mating.   8. Axial coupling device according to claim 5, characterized in that said rigid annular cushion (25 ') is interposed between said fixed housing (22', 23 ') and a swiveling outer surface (27')   of the bearing outer ring (12 ', 16').   9. Axial coupling device according to claim 8, characterized in that said bearing (12 ', 16') directly has its own seals (19 '), on either side of the row of balls, between its ring   outer (12 ') and its inner ring (16').   10. Axial coupling device according to claim 1, characterized in that said flexible connection system (8) is mounted between the end of one of the shafts (2) and a coupling section (5b), which is wedged on a coupling sleeve (3) rigidly fixed to the end of the other shaft (1), and in that said bearing block support (12, 15, 16; 12 ', 16') is disposed 17 2786828   at the junction between said section (5b) and said sleeve (3).   11. Axial coupling device according to claim 1, characterized in that one of the shafts is a subcritical shaft (1) of transmission connected to the main gearbox of a helicopter, the other shaft being a supercritical shaft (2) connected to its box   rear transmission, or vice versa.