Abstract:
A transmission joint for angularly connecting a first and a second member, and having a coupling member interposed functionally between the first and second member and extending about an axis; the coupling member has: a first portion connectable angularly to the first member, a second portion connectable angularly to the second member and located radially outwards of the first portion, and an intermediate portion interposed radially between the first and second portion and elongated in a direction crosswise to the axis; the intermediate portion of the coupling member has, from the first portion to the second portion, a first portion decreasing in thickness crosswise to the direction, and a second portion of constant thickness.

Description:
[0001]    The present invention relates to a transmission joint, in particular for aircraft application. 
       BACKGROUND OF THE INVENTION 
       [0002]    Transmission joints are used to angularly connect a drive shaft and a driven shaft, and to permit movement and tilt of the shaft axes. 
         [0003]    More specifically, transmission joints comprise a tubular coupling member with a hub angularly integral with the drive shaft; and a ring positioned radially outwards of the hub and angularly integral with the driven shaft. 
         [0004]    More specifically, the joints may comprise a single coupling member, with the hub and ring connected directly to the drive shaft and driven shaft. 
         [0005]    Alternatively, the joints may comprise a number of coupling members angularly integral with one another; in which case, the hub of one of the coupling members is connected to the drive shaft, and the hub of another of the coupling members is connected to the driven shaft. 
         [0006]    The coupling member also comprises a thin-walled portion, or so-called diaphragm, interposed radially between the hub and ring and elongated in a direction perpendicular to the drive and driven shaft axes. 
         [0007]    Diaphragms are known, for example, as described in Patent BE-456920, in which the profile of the diaphragm comprises, from the hub to the ring, a portion decreasing in thickness and a portion increasing in thickness. 
         [0008]    More specifically, the profile is asymmetrical with respect to the extension direction of the diaphragm. 
         [0009]    Diaphragms are also known, for example, as described in Patent U.S. Pat. No. 5,158,504, in which the profile is symmetrical with respect to the extension direction of the diaphragm. 
         [0010]    More specifically, the profile of these diaphragms comprises, from the hub to the ring, a portion decreasing in thickness and a portion increasing in thickness. 
         [0011]    The diaphragm profile of known joints provides, in operating conditions, for transmitting a predetermined torque from the drive shaft to the driven shaft with a wide margin of safety, and for maintaining below a predetermined value the fatigue stress caused by periodic variations in the mutual position of the drive and driven shaft axes. 
         [0012]    The Applicant has found known joints to be less than satisfactory, on account of the known diaphragm profile failing to minimize the weight and overall size of the joint. 
         [0013]    In other words, the Applicant has found it possible to improve the diaphragm profile in such a way as to reduce the weight and, hence, overall size of the joint as compared with known solutions, while at the same time maintaining the same margin of safety as regards torque transmission and reduction of fatigue stress caused by periodic variations in the mutual position of the drive and driven shaft axes. 
         [0014]    The Applicant has also found it possible, by appropriately designing the diaphragm profile, to reduce the weight and, hence, overall size of the joint, while at the same time reducing buckling phenomena caused when the thin-walled diaphragm is subjected to the twisting moment transmitted by the drive shaft. 
         [0015]    Finally, the Applicant has also found it possible, by appropriately designing the diaphragm profile, to reduce in-service generation of forced oscillations caused by resonance phenomena between the natural frequencies of the system containing the diaphragm, and the rotation frequencies of the drive or driven shaft. 
       SUMMARY OF THE INVENTION 
       [0016]    It is an object of the present invention to provide a transmission joint which, by appropriate design of the diaphragm profile, is lighter than known joints of the type described above, while at the same time reliably transmitting torque to the driven shaft and allowing misalignment and tilt of the drive and driven shaft axes. 
         [0017]    According to the present invention, there is provided a joint as claimed in the attached Claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
           [0019]      FIG. 1  shows an axial section of a coupling member of a transmission joint in accordance with the present invention; 
           [0020]      FIG. 2  shows a larger-scale axial half-section, with parts removed for clarity, of a detail of  FIG. 1 ; 
           [0021]      FIGS. 3 to 6  show axial sections of respective embodiments of the transmission joint in  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    With reference to  FIGS. 1 to 3 , number  1  indicates a transmission joint for angularly connecting a drive shaft  2 , rotating about a respective axis, to a shaft  4  (only shown in  FIG. 3 ) rotating coaxially with shaft  2 . 
         [0023]    More specifically, transmission joint  1  receives torque from shaft  2 , and transmits it to shaft  4 . 
         [0024]    In addition to transmitting torque from shaft  2  to shaft  4 , joint  1  also permits any in-service misalignment and tilt of the axes of shaft  2  and shaft  4 . 
         [0025]    More specifically, joint  1  comprises a pair  20  ( FIG. 3 ) of coupling members  5   a,    5   b  interposed functionally and axially between shafts  2  and  4 . 
         [0026]    Each coupling member  5   a,    5   b  is tubular, and extends along an axis A coincident, in use, with the axes of shafts  2  and  4 . 
         [0027]    Each coupling member  5   a,    5   b  comprises a hub  6  and an annular portion  7 , which define an inner radial end and an outer radial end, respectively, of coupling member  5   a,    5   b.    
         [0028]    Hub  6  of coupling member  5   a  (on the left in  FIG. 3 ) is connected angularly, e.g. by welding or other systems, to shaft  2  to receive motion. 
         [0029]    Portions  7  of coupling member  5   a  and coupling member  5   b  (on the right in  FIG. 3 ) are connected angularly, e.g. welded, to each other, so that coupling member  5   a  rotates coupling member  5   b.    
         [0030]    Hub  6  of coupling member  5   b  is connected angularly to shaft  4  to transmit rotation of coupling member  5   b  to shaft  4 . 
         [0031]    Each coupling member  5   a,    5   b  also comprises a portion—hereinafter referred to as diaphragm  8 —interposed radially between relative hub  6  and relative portion  7 . 
         [0032]    More specifically, diaphragm  8  is thin-walled and elongated in a direction D radial with respect to axis A. 
         [0033]    Being much larger radially than axially, diaphragm  8  is in the form of a membrane and therefore highly flexible. 
         [0034]    From hub  6  to portion  7 , diaphragm  8  advantageously comprises a portion  9  decreasing in thickness crosswise to direction D, and a portion  10  of constant thickness. 
         [0035]    More specifically, the size and shape of diaphragm  8  are optimized on the basis of a fatigue calculation method covering the whole volume of the joint. 
         [0036]    As shown in  FIGS. 1 and 2 , portion  9  is bounded radially inwards by an annular section  11  contiguous to hub  6 , and radially outwards by an annular section  12 . 
         [0037]    Portion  10  is bounded radially inwards by section  12 , and radially outwards by an annular section  13  contiguous to portion  7 . 
         [0038]    Diaphragm  8  is bounded laterally by two opposite faces  14 ,  15 . 
         [0039]    More specifically, face  14  is flat to simplify machining and quality control. 
         [0040]    Adjacent to annular section  13  ( FIG. 1 ), face  14  is connected to a radially inner end of portion  7 . 
         [0041]    Adjacent to section  11 , face  14  is contiguous to a lateral face  25  of hub  6 . 
         [0042]    More specifically, face  25  is flat and coplanar with face  14 . 
         [0043]    Face  15  is shaped so that it slopes with respect to and converges with face  14  along portion  9  from section  11  to section  12 , and is parallel to face  14  along portion  10 . 
         [0044]    Adjacent to section  11 , face  15  is connected to a face  26 , opposite face  25 , of hub  6 . 
         [0045]    More specifically, from section  11  towards axis A, face  26  comprises a portion  27  connected to an inner radial end of face  15 ; and a flat portion  28  sloping with respect to the plane of face  14 . 
         [0046]    More specifically, portion  27  is shaped so as to be tangent, at section  11 , to the analytic curve defining face  15  at portion  9 . 
         [0047]    Portion  28  slopes with respect to direction D so that hub  6  increases in thickness from section  11  towards axis A. 
         [0048]    Coupling members  5   a,    5   b  are arranged ( FIG. 3 ) with faces  14  facing each other and interposed axially between faces  15 . 
         [0049]    The material of diaphragm  8  is selected to ensure a predetermined yield and lightness of diaphragm  8 . 
         [0050]    In actual use, shaft  2  rotates coupling member  5   a  about axis A; coupling member  5   a  in turn rotates coupling member  5   b;  and, finally, coupling member  5   b  rotates shaft  4  about axis A. 
         [0051]    By virtue of their axial and flexural rigidity, coupling members  5   a,    5   b  permit in-service axial misalignment and tilt of the axes of shafts  2  and  4 . 
         [0052]    Number  1 ′ in  FIG. 4  indicates as a whole a further embodiment of a joint in accordance with the present invention. 
         [0053]    Joint  1 ′ is similar to, and only described below insofar as it differs from, joint  1 , the corresponding or equivalent parts of joints  1 ,  1 ′ being indicated, where possible, using the same reference numbers. 
         [0054]    Joint  1 ′ differs from joint  1  by comprising two pairs  20 ′,  21 ′ of coupling members  5   a ′,  5   b′.    
         [0055]    More specifically, one pair  20 ′ (on the left in  FIG. 4 ) of coupling members  5   a ′,  5   b ′ is angularly integral with shaft  2 ′, and the other pair  21 ′ (on the right in  FIG. 4 ) of coupling members  5   a ′,  5   b ′ is angularly integral, on axially opposite sides, with shaft  4 ′ and pair  20 ′ of coupling members  5   a ′,  5   b′.    
         [0056]    More specifically, hub  61  of coupling member  5   a ′ of pair  20 ′ is welded angularly integral with shaft  2 ′. 
         [0057]    Portions  7 ′ of coupling members  5   a ′,  5   b ′ of pair  20 ′ are riveted angularly integral with each other. 
         [0058]    Hub  6 ′ of coupling member  5   b ′ of pair  20 ′ is welded angularly integral with hub  6 ′ of coupling member  5   a ′ of pair  21 ′. 
         [0059]    Portions  7 ′ of coupling members  5   a ′,  5   b ′ of pair  21 ′ are riveted angularly integral with each other. 
         [0060]    Hub  6 ′ of coupling member  5   b ′ of pair  21 ′ is welded angularly integral with shaft  4 ′. 
         [0061]    Number  1 ″ in  FIG. 5  indicates as a whole a third embodiment of a joint in accordance with the present invention. 
         [0062]    Joint  1 ″ is similar to joints  1 ,  1 ′, and only described below insofar as it differs from joint  1 ′, the corresponding or equivalent parts of joints  1 ,  1 ′,  1 ″ being indicated, where possible, using the same reference numbers. 
         [0063]    More specifically, joint  1 ″ differs from joint  1 ′ by coupling member  5   b ″ of pair  21 ″ not being connected directly to shaft  4 ″. 
         [0064]    In this case, coupling member  5   b ″ of pair  21 ″ is welded angularly to a further coupling member  5 ″, in turn welded angularly to shaft  4 ″. 
         [0065]    More specifically, hub  6 ″ of further coupling member  5 ″ is connected angularly to hub  6 ″ of coupling member  5   b ″ of pair  21 ″, and portion  7 ″ of further coupling member  5 ″ is connected angularly to shaft  4 ″. 
         [0066]    Number  1 ′″ in  FIG. 6  indicates as a whole a fourth embodiment of a joint in accordance with the present invention. 
         [0067]    Joint  1 ′″ is similar to, and only described below insofar as it differs from, joints  1 ,  1 ′,  1 ″, the corresponding or equivalent parts of joints  1 ,  1 ′,  1 ″,  1 ′″ being indicated, where possible, using the same reference numbers. 
         [0068]    Joint  1 ′″ differs from joints  1 ,  1 ′,  1 ″ by comprising a single coupling member  5 ′″. Portion  7 ′″ of coupling member  5 ′″ is welded angularly integral with shaft  4 ′″, and hub  6 ′″ of coupling member  5 ′″ is angularly integral with the drive shaft (not shown) by means of a weld and a flange  20 ′″. 
         [0069]    Operation of joints  11 ,  1 ″,  1 ′″ is identical to that of joint  1 , and therefore not described. 
         [0070]    The advantages of transmission joint  1 ,  1 ′,  1 ″,  1 ′″ according to the present invention will be clear from the foregoing description. 
         [0071]    In particular, the Applicant has found that joint  1 ,  1 ′,  1 ″,  1 ′″, by virtue of the design of the profile of diaphragm  8 ,  8 ′,  8 ″,  8 ′″, provides for minimizing the weight and, hence, overall size of joint  1 ,  1 ′,  1 ″,  1 ′″, while at the same time ensuring reliable torque transmission between shafts  2 ,  4 ;  2 ′,  4 ′;  2 ″,  4 ″; and between flange  20 ′″ and shaft  4 ′″. 
         [0072]    The Applicant has also found that joint  1 ,  1 ′,  1 ″,  1 ′″, by virtue of the design of diaphragm  8 ,  8 ′,  8 ″, S′″, provides for maintaining sufficient axial and flexural rigidity to ensure fatigue stress caused by misalignment and tilt of the axes of shaft  2 ,  2 ′,  2 ″ and shaft  4 ,  4 ′,  4 ″ is maintained below a predetermined value. 
         [0073]    The design of diaphragm  8 ,  8 ′,  8 ″,  8 ′″ also provides for reducing buckling and resonance phenomena generated during operation of joint  1 ,  1 ′,  1 ″,  1 ′″. 
         [0074]    The design of diaphragm  8 ,  8 ′,  8 ″,  8 ′″ can also be adapted easily to different operating requirements of joint  1 ,  1 ′,  1 ″,  1 ′″. 
         [0075]    In fact, for each load configuration on diaphragm  8 ,  8 ′,  8 ″,  8 ′″, it is possible to determine an optimum location of sections  11  and  12  with respect to axis A, and an optimum thickness pattern of portion  9 ,  9 ′,  9 ″,  9 ′″ alongside an increase in the distance from axis A. 
         [0076]    Another advantage of the present invention lies in the flat shape of face  14 ,  14 ′,  14 ″,  14 ′″, which provides for easy machining and dimensional control of the face. 
         [0077]    Clearly, changes may be made to joint  1 ,  1 ′,  1 ″,  1 ′″ as described and illustrated herein without, however, departing from the scope defined in the accompanying Claims. 
         [0078]    In particular, joint  1 ,  1 ′,  1 ″,  1 ′″ may comprise a single coupling member  5   a,    5   b ;  5   a ′,  5   b ′;  5   a ″,  5   b ″;  5 ′″; with the hub  6 ,  6 ′,  6 ″,  6 ′″ connected directly to shaft  2 ,  2 ′,  2 ″, and portion  7 ,  7 ′,  7 ″,  7 ′″ connected directly to shaft  4 ,  4 ′,  4 ″,  4 ′″.