Abstract:
A universal joint comprises an input shaft comprising at one end thereof a first pair of arms and an output shaft comprising at one end thereof a second pair of arms. Respective opposed first pivot pins are provided on the distal ends of the first pair of arms and aligned along a first axis (P 1 ). Respective opposed second pivot pins are provided on the distal ends of the second pair of opposed arms and aligned along a second axis (P 2 ), the second axis (P 2 ) being perpendicular to the first axis (P 1 ). The joint further comprises a compliant ring extending around the input and output shafts and having first and second pairs of opposed openings for receiving the first and second pivot pins.

Description:
FOREIGN PRIORITY 
       [0001]    This application claims priority to European Patent Application No. 16162281.6 filed Mar. 24, 2016, the entire contents of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to universal joints. 
       BACKGROUND 
       [0003]    Universal joints are used in a wide range of applications to transmit rotary motion between an input and output shafts which may not be coaxial. 
         [0004]    One such application is in aircraft to transmit power from a centralised power drive unit to a plurality of actuators that are located along leading and trailing edges of wings. Depending upon the location of the power transmission line with respect to the wing neutral axis, the transmission line can see length changes as a function of wing bending in flight manoeuvres and in high load phases of normal take-off and landing cycles. This, together with the torque loads which the joints are intended to accommodate, can develop axial loads within the transmission system that must be reacted by suitable aircraft structure. These loads are a function of the spline size that connects the universal joints with associated actuators or shafts, and can develop in the order of 9 kN of axial load. Substantial aircraft structure must be provided to counter such forces. It would therefore be desirable to reduce the axial forces experienced in a transmission line and reduce the forces acting upon actuators, joints and supporting structure. 
       SUMMARY 
       [0005]    Disclosed herein is a universal joint which comprises an input shaft and an output shaft. The input shaft comprises at one end thereof a first pair of arms. The output shaft comprises at one end thereof a second pair of arms. Respective opposed first pivot pins are provided on the distal ends of the first pair of arms and aligned along a first axis. Respective opposed second pivot pins are provided on the distal ends of the second pair of arms and aligned along a second axis which is perpendicular to the first axis. The joint further comprises an axially compliant ring which extends around the input and output shafts and which has first and second pairs of opposed openings for receiving the first and second pivot pins. 
         [0006]    In one embodiment, the first and second pivot pins may project from the first and second arms and be received in the respective ring openings. 
         [0007]    Respective bushings may be received within the respective openings and the pivot pins be received within the bushings. 
         [0008]    In another embodiment, the respective first and second arms are formed with clevises and the respective pivot pins are received in the clevises and extend through the openings in the ring. 
         [0009]    The clevises may be provided with bushings which receive the pivot pins. 
         [0010]    In various embodiments, the ring may be formed with enlarged bosses through which the pivot pin receiving openings are formed, and webs extending between the bosses. 
         [0011]    The webs may have a ratio of radial depth to axial width of 1:1 to 20:1. 
         [0012]    The webs may have a rectangular, square or trapezoidal cross section. 
         [0013]    The ring may have, in the axial direction, a stiffness of less than or equal to 4 kN/mm, greater than or equal to 1.0 kN/mm or between 1 kN/mm and 4 kN/mm. 
         [0014]    The ring may be made from a fibre reinforced composite material. Alternatively, the ring may be made from a metallic material. 
         [0015]    The ring may comprise a plurality of ring elements laminated together face to face. 
         [0016]    The ring may be made by an additive manufacturing process. 
         [0017]    The disclosure also extends to a drive transmission system comprising a universal joint as discussed above. 
         [0018]    The disclosure also extends to an aircraft actuator system comprising a power drive unit and a plurality of actuators driven by the power drive unit through a drive transmission system as above. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]    Some embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0020]      FIG. 1  shows, schematically, a power transmission system in an aircraft; 
           [0021]      FIG. 2  shows, schematically, a universal joint in accordance with this disclosure for use in the system of  FIG. 1 ; 
           [0022]      FIG. 3  shows a cross section along line A-A of  FIG. 2 ; 
           [0023]      FIG. 4  shows a vertical cross section taken through a second universal joint in accordance with the disclosure; 
           [0024]      FIG. 5  shows a horizontal sectional cross section taken through the universal joint of  FIG. 4 ; 
           [0025]      FIG. 6  shows a view on A-A of  FIG. 4 ; 
           [0026]      FIG. 7  shows a view on B-B of  FIG. 4 ; 
           [0027]      FIG. 8  shows a laminated ring in accordance with the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    With reference to  FIG. 1 , an aircraft  2  comprises a central power drive unit  4  (shown schematically) having a rotary power output shaft  6 . The power output shaft  6  is connected to a series of actuators  8  arranged along the aircraft wing  10 . The actuators  8  may be used to move wing control surfaces such as flaps, slats, spoilers and so on. Power is transmitted between the actuators  8  by shafts  12 . The shafts  12  are coupled by universal joints  14  which will accommodate angular misalignments between the shafts  12 . 
         [0029]    As discussed above, deflection of the aircraft wing  10  will result in changes in length and loads within the power transmission line, which loads will have to be reacted by structure in the wing  10 , adding to the weight of the wing  10 , which is undesirable. 
         [0030]    To mitigate this problem, this disclosure proposes in various embodiments, a universal joint which will be able to accommodate such movements, thereby limiting the magnitude of loads transferred to the aircraft structure allowing appropriate down-sizing and weight reduction. 
         [0031]      FIGS. 1 and 2  illustrate a first embodiment of universal joint  20  in accordance with the disclosure. 
         [0032]    The universal joint  20  comprises an input shaft  22 , an output shaft  24  and a ring  26  surrounding overlapping ends of the input and output shafts  22 ,  24 . 
         [0033]    The input shaft  22  and output shaft  24  are substantially the same in construction in this embodiment. Each shaft  22 ,  24  comprises a splined coupling  28  at one end for coupling to an adjacent shaft or actuator, for example. Of course other form of couplings may be used if appropriate. The other end of each shaft  22 ,  24  comprises a pair of outwardly extending opposed arms  30 . Each arm  30  is formed with an outwardly extending hinge pin  32 . The pins  32  of the output shaft  24  are aligned along a pivot axis P 1  and the pins  32  of the input shaft  22  are aligned along pivot axis P 2  which is arranged at right angles to the axis P 1  as shown in  FIG. 3 . The axes P 1  and P 2  may intersect, for example in a no-load condition of the joint. 
         [0034]    The hinge pins  32  are received within the ring  26 . The ring  26  comprises a generally annular body  34  which comprises a plurality of bosses  36  connected by webs  38 , in this case arcuate webs  38 . In this embodiment, the webs  38  are rectangular in cross section. The bosses  36  each comprise an opening  40  for receiving a respective hinge pin  32 . The openings  40  are lined with a bushing  42  and a cap  44  supporting the bushing  42 . 
         [0035]    The arrangement of the pins  32  and openings  40  allows the input and output shafts  22 ,  24  to pivot about the orthogonal axes P 1  and P 2 , in the manner of a traditional universal joint. 
         [0036]    The webs  38  are relatively thin and therefore relatively flexible. For example, in some embodiments, the ratio between the axial web thickness T and radial web width W may be between 1:1 and 1:20. By axial as used herein is meant in a direction along or parallel to the axis of the central axis A of the ring  26 , and by radial is meant in a direction generally radially extending from the central axis A of the ring  26 . Each web  38  may be flat, i.e. lie in a plane, or be contoured, for example having a wave-like profile. 
         [0037]    The ring  26  may be made from any appropriate material, such as a fibre reinforced plastics material, or a metal such as titanium and may be made by any suitable process, for example an additive manufacturing process, 
         [0038]    The universal joint  20  is able better to accommodate axial forces and deflections than prior art universal joints while at the same time providing sufficient torsional stiffness for rotary load transmission. The ring  26  is, by virtue of its relatively flexible webs  38 , able to deflect under axial loads, thereby reducing forces in other parts of the system. Typically the axial stiffness of the joint  20  may be less than 1.0 N/mm. However, the axial stiffness may be less than 4.0 kN/mm, for example in the range of 1.0 kN/mm to 4.0 kN/mm. 
         [0039]    The axial stiffness of the ring  26  will be determined to a significant extent by the length of the relatively thin webs  38 . A second embodiment of the disclosure which facilitates the provision of longer and thus potentially more flexible webs will now be described with reference to  FIGS. 4 to 7 . 
         [0040]    The universal joint  120  of the second embodiment comprises an input shaft  122 , an output shaft  124  and a ring  126  surrounding overlapping ends of the input and output shafts  122 ,  124 . 
         [0041]    The input shaft  122  and output shaft  124  are substantially the same in construction in this embodiment. Each shaft  122 ,  124  comprises a splined coupling  128  at one end for coupling to an adjacent shaft or actuator, for example. Of course other form of couplings may be used if appropriate. The other end of each shaft  122 ,  124  comprises a pair of outwardly extending opposed arms  130 . In this embodiment, however, each arm  130  is formed with a clevis  132  having inner and outer limbs  134 ,  136 . Aligned openings  138  are formed through the clevis limbs  134 ,  136 . 
         [0042]    The openings  138  are lined with respective bushings  140  which receive a respective hinge pin  142  which is received within the clevis opening  138 . Each hinge pin  142  is retained within the clevis opening  138  by suitable means. The hinge pins  142  of the output shaft  124  are aligned along a pivot axis P 1  and the pins  142  of the input shaft  122  are aligned along pivot axis P 2  which is arranged at right angles to and, in for example a no-load condition, intersects the axis P 1  as shown in  FIG. 6 . 
         [0043]    The ring  126  comprises a generally annular body  144  which comprises a plurality of bosses  146  connected by webs  148 , in this case arcuate webs  148 . As in the earlier embodiment, the webs  148  are rectangular in cross section. The bosses  146  each comprise an opening  150  for receiving a respective hinge pin  142 . 
         [0044]    As in the earlier embodiment, the arrangement allows the input and output shafts  122 ,  124  to pivot about the orthogonal axes P 1  and P 2 , in the manner of a traditional universal joint. 
         [0045]    The axial stiffness provided by the second embodiment may be as for the first embodiment. However, the second embodiment may allow improved flexibility or reduced stresses in the ring  126 . Specifically, the use of a clevis  132  and pin  142  allows the pin  142  to be of a smaller diameter than the pin  32  in the earlier embodiment. This in turn allows the ring  126  to have smaller bosses  146 , meaning that the webs  148  of material between the bosses  146  may be longer than in the earlier embodiment, resulting in improved flexibility. This is apparent from a comparison of  FIGS. 3 and 6  for example. 
         [0046]    Thus in both embodiments, the ring  26 ,  126  acts as a torque ring, transmitting torque between the input and output shafts but also acts to accommodate some axial movement of the input and output shafts relative to each other. 
         [0047]    The axial stiffness of the joints  20 ,  120  may be greater than 1.0 N/mm. However, the axial stiffness may be less than 4.0 kN/mm, for example in the range of 1.0 kN/mm to 4.0 kN/mm. Thus the ring may deflect axially for example 1 mm when subject to an axial load of  41 A. 
         [0048]    As discussed above, the torque ring  26 ,  126  may be made in a number of ways. For example, the ring  26 ,  126  may be made from a composite material, for example a fibre reinforced plastics material. The layup of the reinforcement may be such as to provide the necessary torsional stiffness and at the same time the desired axial stiffness. In an alternative embodiment the ring may be made from a metallic material, for example titanium. 
         [0049]    The ring  26 ,  126  may be a unitary construction or an assembly. In one embodiment the ring may comprise a stack of ring elements suitably joined. Such an embodiment is disclosed in  FIG. 8 . 
         [0050]    In this embodiment, a ring  226  comprises three ring elements  228 ,  230 ,  232  suitably joined together. Of course the ring  226  could comprise more or fewer ring elements. The ring elements may be formed of a low modulus metallic material such as Titanium. Each ring element  228 ,  230 ,  232  comprises a boss portion  234  and a web portion  236 . The ring elements are joined, for example bonded, at the boss portions  234 , and openings  236  formed through the boss portions  234  to receive the hinge pins. The openings  236  can be part formed in the ring elements  228 ,  230 ,  232  and finish machined. The construction method may allow for a universal joint of a given torsional stiffness and strength whilst providing a very low axial stiffness as a result of the ring element depth/width proportions. 
         [0051]    In an alternative arrangement, the ring  226  could be made from an additive manufacturing process, avoiding the need for the separate fabrication and assembly of multiple elements. 
         [0052]    From the above, it will be seen that the disclosure provides a universal joint which has a degree of axial compliance which absorbs axial forces acting on the joint. Thus results in lower loads to be reacted at aircraft structural mountings, allowing a reduction in aircraft structure weight. The resilience of the ring also allows the joint to return to its original condition once the loads have been removed. 
         [0053]    The geometry of the ring  26 ,  126  and the material chosen for it contribute to the desired stiffness, and the skilled person will be able to tailor the geometry and material to achieve the desired stiffness. For example, while generally rectangular section webs  38 ,  148  are disclosed, other cross sectional shapes may be used. Also, while the rings  26 ,  126  are shown as generally circular in shape, other shapes, for example more square shapes may be used. 
         [0054]    It will also be appreciated that other modifications may be made to the embodiments disclosed without departing from the scope of the disclosure.