Abstract:
The invention concerns a controllable variable length link device. It comprises a first half-link ( 12 ) having a first end ( 12   a ) for connection to a driving system ( 16 ) and a second end ( 12   b ), a second half-link ( 14 ) having a first end ( 14   a ) for connection to a driven system ( 18 ) and a second end ( 14   b ), a rotary displacement member ( 20 ) including a rotator shaft ( 22 ) and a rotary head ( 24, 26 ) cooperating with said second ends ( 12   b,    14   b ) of said links to bring about opposite movement of said half-links, bearing means ( 34, 36 ) in which said rotator shaft ( 22 ) is mounted, respective means ( 38, 40 ) for guiding said two half-links ( 12, 14 ) in translation in at least two parallel directions, said drive means being mechanically connected to said bearing means; and means for driving said shaft ( 22 ) in rotation in both directions in accordance with a predetermined law.

Description:
[0001]     The present invention consists in a link device of controllable variable length usable in particular, although not exclusively, for the transmission kinematics in a variable pitch vane control system, a guide vane control device using a link of that kind, a turbomachine compressor using a control device of that kind, and a jet engine using said link device.  
       BACKGROUND OF THE INVENTION  
       [0002]     Turbomachine compressors, and turbojet stators in particular, may include a variable-pitch guide vane stage arranged on a casing. The position of the vanes is controlled by a rotary ring that is connected to each guide vane by a link. Thus the angle of attack of the vanes can be controlled as a function of flight conditions by a control system that drives the rotation of the ring. The link of the invention can be used with advantage in the control system.  
         [0003]     More generally, many kinematic systems use a link to transmit a driving rotary movement to a driven rotary movement. In prior art systems this link has a constant length.  
         [0004]     Links of variable length are also known in the art but the length of the link can be modified only when the link is not operating.  
         [0005]     In certain transmission systems it is necessary to be able to apply a relatively complex law governing the transmission from one rotary movement to another rotary movement.  
         [0006]     An object of the present invention is to provide a link the length whereof may be varied when the link is operating.  
         [0007]     It is equally beneficial for a link of the above kind to be fitted into the kinematic system as a replacement for a link of fixed length without having to modify the rest of the kinematic system.  
       SUMMARY OF THE INVENTION  
       [0008]     A first object of the present invention is to provide a link device which, on the one hand, has a length that may be varied while it is operating and, on the other hand, is so constituted that it can be substituted for a link of fixed length in a kinematic transmission system.  
         [0009]     To achieve the above object, the controllable variable length link device of the invention comprises: 
        a first half-link having a first end for connection to a driving system and a second end,     a second half-link having a first end for connection to a driven system and a second end,     a rotary displacement member including a rotator shaft and a rotary head cooperating with said second ends of said links to bring about opposite movement of said half-links,     bearing means in which said rotator shaft is mounted,     respective means for guiding said two half-links in translation in at least two parallel directions, said drive means being mechanically connected to said bearing means, and     means for driving said shaft in rotation in both directions.        
 
         [0016]     Clearly, because the two half-links are joined together by a rotary displacement member including a rotator shaft, it is possible to assign to the rotary displacement member a rotation law that yields a link length variation law and therefore a law governing the kinematic relationship between the driving and driven systems.  
         [0017]     Note also that the first ends of the two half-links are exactly the same as the ends of a conventional type link and that the link of the invention may be substituted for a conventional link in a kinematic system without the other portions thereof having to be modified.  
         [0018]     The guide means of the link device preferably each comprise a portion of a half-link close to its second end having a cylindrical external surface with generatrices parallel to the axis of the half-link and a guide member rigidly connected to the bearing means having a passage conjugate with said cylindrical surface to guide movement in translation of the half-link.  
         [0019]     The expression “cylindrical surface” is to be understood as referring to any surface generated by the movement of a generatrix along a closed curve, which may be a circle, an ellipse, a square, a rectangle, etc.  
         [0020]     Clearly, thanks to these guide members, the relative travel of the two half-links is effected in a perfectly defined direction.  
         [0021]     It preferably comprises a casing in which said bearing means and the two guide members are mounted.  
         [0022]     In a first embodiment of the link device the rotary head of the rotary member is a yoke comprising two arms extending radially relative to said shaft, each arm being connected to the second end of one half-link.  
         [0023]     Clearly, in this first embodiment, by imposing a particular rotation law on the shaft of the rotary member, the lengths of the two half-links connected to the ends of the arms of the yoke vary as a function of the selected law.  
         [0024]     In a second embodiment of the link device each half-link has near its second end a rack portion and the head of the rotary member is a pinion meshing with said racks.  
         [0025]     Clearly the second embodiment has the same advantages as the first and, moreover, provides for a greater stroke of each half-link than the first embodiment because the head of the rotary member can turn more than once.  
         [0026]     A second object of the present invention is to provide a variable pitch guide vane control device comprising a link device of the above type.  
         [0027]     A third object of the invention is to provide a turbomachine compressor comprising a link device of the above type.  
         [0028]     A fourth object of the invention is to provide a turbomachine comprising a link device of the above type. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     Other features and advantages of the invention will become more clearly apparent on reading the following description of embodiments of the invention given by way of nonlimiting example. The description refers to the appended figures:  
         [0030]      FIG. 1  is an exploded perspective view of a first embodiment of a simplified form of the link of the invention.  
         [0031]      FIG. 2  is an exploded perspective view of part of the  FIG. 1  link.  
         [0032]      FIG. 2A  is a partial exploded perspective view of the link equipped with a first control system.  
         [0033]      FIG. 2B  is a partial exploded perspective view of the link equipped with a second control system.  
         [0034]      FIG. 2C  is a partial exploded perspective view of the link equipped with a third control system.  
         [0035]      FIG. 3  is a partial plan view of a second embodiment of the link of the invention.  
         [0036]      FIG. 4  is a partial perspective view of the  FIG. 3  link.  
         [0037]      FIG. 5  is a perspective view of the whole of the second embodiment of the link.  
         [0038]      FIG. 6  is a view in median section of the central portion of the second embodiment of the link showing a system for adjusting the distance between the axes of the two half-links using rings forming cams.  
         [0039]      FIGS. 6A  to  6 C are perspective views of the components of the rings enabling them to rotate and for immobilizing them. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]     The whole of a first embodiment of the variable length link device  10  will be described first with reference to  FIG. 1 .  
         [0041]     The link comprises two half-links  12  and  14  having respective first ends  12   a  and  14   a  respectively connected to a driving rotary system  16  and to a driven rotary system  18  and two ends  12   b  and  14   b  connected to a yoke system  20 . The yoke  20  consists of a rotator shaft  22  and two arms  24  and  26  extending perpendicularly to the geometrical axis XX′ of the shaft  22 . The ends  12   b  and  14   b  of the half-links  12  and  14  are connected to the ends of the arms  24  and  26  of the yoke. The yoke  20  is mounted in a casing  28  formed, for example, by a lower plate  28   a  having two rims  30  and  32  at its ends and by an upper plate  34  fixed to the rims  30  and  32  of the lower plate. The lower plate  28   a  and the upper plate  28   b,  when fastened together, include two aligned bearings  34  and  36  in which are respectively mounted the shaft  22  for rotating the yoke and an extension  22   a  of that shaft.  
         [0042]     The rims  30  and  32  at the ends of the lower plate  28   a  include two aligned passages  38  and  40  in which the ends  12   b  and  14   b  of the half-links  12  and  14  can slide. As explained in more detail later, the passages  38  and  40  constitute guide members for the ends of the half-links and therefore for the links.  
         [0043]     It is clear how the first embodiment of the variable length link  10  works. A system for driving rotation of the shaft  22  of the yoke imposes thereon a specific law of rotation about the axis XX′ relative to the casing  28 . That rotation law evidently brings about the rotation of the arms  24  and  26  of the yoke and therefore the modification of the total length L of the link. Imposing an appropriate rotation law on the yoke  20  imposes on the link  10  a corresponding law governing the variation of its length.  
         [0044]     As shown better in  FIG. 2 , at their second ends  12   b  and  14   b  the half-links  12  and  14  consist of end parts  42  and  44  whose cross section is square or rectangular and larger than that of the main portion of the half-links. These end parts  42  and  44  therefore define two parallel lateral faces  46  and upper and lower faces  48 . These four surfaces of the end parts  42  and  44  are precision ground to constitute guide faces. The end parts  42  and  44  are constrained to slide in the passages  38  and  40  formed in the rims  30  and  32  at the ends of the lower portion  28   a  of the casing  28 . The lateral faces  50  of the passages  38  and  40  and the bottom  52  of those passages are also precision ground. Likewise the lower face  54  of the plate  28   b  of the casing. The end parts  42  and  44  of the half-links are therefore guided in translation by the passages  38  and  40  of the casing, those passages being aligned on a common axis YY′ that constitutes the longitudinal axis of the link  10 . The end parts  42  and  44  of the half-links terminate in a thinner portion  56  and  58  in which oblong holes  60  and  62  are formed for connecting the half-links to the arms  24  and  26  of the yoke  20 . Moreover, the end parts  56  and  58  are cranked relative to the longitudinal axes of the half-links  12  and  14  so that the latter are aligned. The arms  24  and  26  of the yoke constitute brackets in which are engaged pins  59  and  61  penetrating the oblong holes  62  and  60 .  
         [0045]     Clearly, when the yoke is rotated, that rotation is converted into a movement in translation of the half-links  12  and  14  along the longitudinal axis YY′ of the link. The holes  34  and  36  in which the shaft  22  of the yoke and its end  22   a  are fitted are preferably provided with bearings.  
         [0046]     As already mentioned briefly, various systems S c  may be used to control the time law of rotation of the yoke  20  according to the required law of variation of the length of the link.  FIG. 2A  shows a first system  70  consisting of a half-shaft  72  mounted to pivot in a bearing  73  fastened to a fixed frame. This half-shaft, which is parallel to the drive shaft  22 , is connected to a half-arm  74  orthogonal to its pivot axis. The end  74   a  of the half-arm  74  is fastened orthogonally to the shaft  22  of the yoke and its second end  74   b  slides in a sleeve forming a bearing  75  attached to the end of the vertical half-shaft  72 .  
         [0047]     There is obtained in this way a law of rotation of the shaft  22  of the yoke whereby, when the link is moved, the shaft  22  of the yoke is constrained to remain on a circle of variable radius centered on the geometrical axis of the half-shaft  72  of the drive system  70 .  
         [0048]      FIG. 2B  shows a second embodiment of the yoke rotation law drive system S c . This system consists of an arm  80  orthogonal to the shaft  22  of the yoke whose second end  80   a  is equipped with a roller  82 . The roller  82  is constrained to move in a slot  84  formed in a plate  86  fastened to a frame. The slot  84  has a shape adapted to impose on the shaft  22  of the yoke a rotation law corresponding to the required law of variation of the length of the link  10 .  
         [0049]      FIG. 2C  represents a third embodiment of the drive system S c  of the rotation law of the yoke  20 . This system consists of a stepper motor  86  whose casing is fixed directly to the lower portion  28   a  of the casing  28  of the link  10 . A required law of variation of the length of the link is obtained by appropriately controlling the rotation of the stepper motor  86  in relation to the rotation of the driving system S m .  
         [0050]      FIG. 3  is a highly simplified representation of a second embodiment of the variable length link of the invention. The latter again consists of two half-links  12 ′ and  14 ′. The second ends  12 ′ b  and  14 ′ b  of the half-links are equipped on their facing faces with racks  100  and  102 . The yoke  20  of the first embodiment is replaced by a toothed pinion  104  whose rotation axis is orthogonal to the longitudinal axes of the half-links  12 ′ and  14 ′. Clearly the pinion  104  meshes with the racks  100  and  102  of the half-links  12 ′ and  14 ′. Thus according to the direction of rotation imparted to the pinion  104 , the half-links are moved in parallel opposite directions corresponding either to a reduction of the total length of the link or to an increase of that length.  
         [0051]      FIG. 4  is a somewhat simplified exploded perspective view of the second embodiment. This figure shows the racks  100  and  102  of the half-links  12 ′ and  14 ′ and the drive pinion  104 . The drive pinion  104  is fastened to a drive shaft  106  whose end  106 a is extended beyond the pinion  104 .  
         [0052]      FIG. 5  shows that the ends  12   b  and  14   b  of the half-links  12 ′ and  14 ′ and the drive pinion  104  are mounted in a casing  110  consisting of an upper half-shell  110   a  and a lower half-shell  110   b.  The casing  110  defines in its median plane two bearings  112  formed in the respective half-shells for mounting the drive shaft  106  and its extension  106   a.  The casing  110  also defines passages for guiding movement in translation of the ends  12 ′ b  and  14 ′ b  of the half-links. In the particular embodiment considered here, the half-links  12 ′ and  14 ′ have a circular cross section and the guide passages  114  and  116  therefore also have a circular cross section. These passages are parallel of course, because the half-links are offset. The casing  110  also defines an internal volume communicating with the guide passages  114  and  116  to receive the pinion  104  and enable it to mesh with the racks  100  and  102 .  
         [0053]     It goes without saying that the three drive systems fixing the rotation law of the shaft  22  of the yoke  20  of the first embodiment of the invention may be used to fix the rotation law of the pinion  104  used in the second embodiment.  
         [0054]     It must also be noted that the second embodiment has all the advantages of the first embodiment. It additionally has the advantage of enabling greater variation of the total length of the link because, in the case of the yoke, the rotation angle of the latter is limited, whereas in the case of the pinion  104  meshing with the racks  100  and  102 , there is no limit on the rotation of the pinion.  
         [0055]     In the second embodiment of the link, it is important to be able to adjust very accurately the distance between the axes of the two half-links  12 ′ and  14 ′ to ensure meshing with minimum backlash between the pinion  104  and the racks  100  and  102  of the half-links.  FIG. 6  shows one embodiment of a system for adjusting this distance between the axes.  
         [0056]      FIG. 6  represents one embodiment of the system for adjusting the distance between the axes of the two half-links  12 ′ and  14 ′. Simplifying, this adjustment is obtained by means of cam rings mounted on the half-links on either side of the rack and engaging in passages formed in the casing.  
         [0057]     More precisely,  FIG. 6  represents the lower half-shell  110   b  of the casing  110 . In each passage  114 ,  116  there is formed at its end a first internal bore  118  whose diameter is greater than the main diameter of the passages  114  and  116  with a shoulder formed by a spot facing  120  of greater diameter but of shorter length. In each of the bores  118 ,  120  is mounted a ring  122  forming a cam, each ring consisting of a tubular portion  122   a  engaged in the bore  118  and an end flange  122   b  engaged in the spot facing  120 . The external faces of the rings forming cams are coaxial with the axes YY′ of the passages  114  and  116  and the inside diameter d 1  of these rings defines an inside surface cam to the axes YY′ and adapted to receive the portions of the half-links disposed on respective opposite sides of the racks  100  and  102 . These rings  122  form guide bearings for the half-links. Thus by adjusting the angular orientation of the four rings  122  forming cams, the distance e between the axes of the half-links  12 ′ and  14 ′ can be adjusted accurately.  
         [0058]     It goes without saying that it must be possible to immobilize the rings  122  forming cams in translation and in rotation relative to the casing  110  when the angular orientation to obtain the required distance between the axes of the two half-links has been imparted to them.  
         [0059]      FIGS. 6A  to  6 C show one embodiment of the means for immobilizing the rings  122 .  
         [0060]     To enable rotation of the rings  122  and to immobilize them against rotation after they have been moved to the required angular position, two washers  124  and  126  are placed between the flange  122   b  and the bottom of the bore  120 . The lower washer  126  has on its lower face two dogs  128  that are able to penetrate into grooves  130  formed in the bottom of the spot facing  120 . The upper face of the washer  126  carries radially disposed teeth  132 . The washer  124  has on its upper face two dogs  134  that are able to penetrate into notches  136  formed in the flange  122   b  of the ring  122 . Its lower face is provided with teeth  138  conjugate with the teeth  132  of the washer  126 . The assembly consisting of the ring  122  and the washers  124  and  126  is immobilized against movement in translation in the bores  118  and  120  by a plate  140  screwed to the casing  110 . Each plate  140  has an extension  142  that bears on the outside face of the flange  122   b  of the ring  122 .  
         [0061]     When the plates  140  are screwed to the casing  110 , the teeth  132  and  138  are interengaged and the ring is immobilized against rotation. On the other hand, if the plates are unscrewed, the teeth  132  and  138  are no longer interengaged and it is possible to turn the ring  122  and the washer  124  relative to the washer  126  constrained to rotate with the casing. Thanks to the large number of teeth  132  and  138 , it is possible to adjust accurately the angular orientation of the rings  122  and therefore the distance between the axes of the half-links  12 ′ and  14 ′.  
         [0062]     It goes without saying that other systems could be used for adjusting the distance between the axes of the two half-links.