Abstract:
A pulley block has a body which rotatably supports a sheave, the block having a mounting pin which extends through a bore in the block. The pin has an enlarged head disposed internally of the body to retain the pin in the bore. Rotation of the pin may be prevented by a releasable locking arrangement comprising a groove formed transversely across the enlarged head of the pin and a lock member rotatably mounted in a hole extending within the block adjacent the head of the pin. The lock member is profiled for rotation between a locked position where a part of the lock member locates in the groove in the head of the pin to restrain rotation of the pin and a free position where the lock member is free of the head of the pin so that the pin may rotate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     a) Field of the Invention  
         [0002]     This invention relates to a pulley block and in particular a pulley block having a body rotatably supporting a sheave and a mounting pin by means of which the block may be connected to some other component.  
         [0003]     Though the pulley block of this invention may be used in a variety of circumstances, it has a particular application in relation to racing dinghies. As such, it will be described exclusively with reference to that use, even though the invention is not to be regarded as limited to that use.  
         [0004]     b) Description of the Prior Art  
         [0005]     Pulley blocks are used extensively on the running rigging of racing dinghies, to assist in the hoisting and trimming of the sails. Such pulley blocks are required to have very low friction in order to minimise losses and also to have relatively low weights. Further, such blocks must have some kind of mounting arrangement, whereby the block may be connected to some other component of the dinghy.  
         [0006]     A common mounting arrangement for a pulley block of the kind described above is to furnish the body of the block with a pin which projects from the block body, at right-angles to the axis of rotation of the pulley. Depending upon the intended use of the block, the pin may be provided with a variety of different connection arrangements but typically the pin will have a transverse hole externally of the block body and to which a shackle may be secured. In some blocks, the mounting pin is securely held against rotation with respect to the block body, whereas with others, the pin is freely rotatable with respect of the block body.  
         [0007]     It has been recognised that there are advantages in providing a block with a mounting pin which may be allowed freely to rotate, but which may also be locked against rotation, as required by the sailor. Various mechanisms have been proposed for this and it is also known to provide a mechanism which allows a pin either freely to rotate with respect to the body or which is permitted only a limited range of movement. These mechanisms add to the overall weight of the block and may also reduce the reliability, when the block is being used under extreme conditions.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     Having regard to the above, it is a principal aim of the present invention to provide a pulley block having a mounting pin which is either freely rotatable with respect to the block body or may be locked against rotation, but which is relatively simple and does not add significantly to the overall weight of the block.  
         [0009]     According to this invention, there is provided a pulley block having a body rotatably supporting a sheave, a mounting pin extending through a bore in the block which pin has an enlarged head disposed internally of the body to retain the pin in the bore. A locking arrangement is provided for the pin to restrain rotation of the pin with respect to the body. The locking arrangement includes a groove formed transversely across the head of the mounting pin and a lock member rotatably mounted in a hole extending within the block adjacent the head of the pin and substantially normally to the axis of said bore. The lock member is profiled for rotation between a locked position where a part of the member locates in the groove in the head of the pin and so restrains rotation of the pin, and a free position where the lock member is free of the head of the pin so that the pin may rotate in its bore. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The drawings show a specific embodiment of pulley block constructed and arranged in accordance with this invention, though solely by way of example. In the drawings:  
         [0011]      FIG. 1  is an isometric view of part of the embodiment of pulley block, from the outside and showing only one side cheek, a mounting pin and lock member, the sheave, the other side cheek and a connecting strap all having been removed for clarity;  
         [0012]      FIG. 2  is an isometric view on the assembly of  FIG. 1 , but from the other side and showing the mounting pin in a free setting;  
         [0013]      FIG. 3  is a view similar to that of  FIG. 2  but with part of the mounting pin cut away to show in better detail the pin lock mechanism;  
         [0014]      FIG. 4  is a partial rear view, with parts cut away, to show the mounting of the sheave on the side cheek; and  
         [0015]      FIG. 5  is an isometric view of a connecting strap for use with a block having two side cheeks as shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     With a block of this invention, adjustment either to permit the mounting pin freely to rotate or to lock the mounting pin against rotation is easily effected, merely by rotating the lock member typically through 180° between the free and locked positions. Further, as compared to a block having a freely rotatable pin, the block of this invention requires only the provision of the lock member together with suitable profiling of the head of the pin. As such, reliability of the block should not be compromised and there will be only a minimal increase in overall weight.  
         [0017]     There may be two grooves formed across the head of the pin, at an angle to one another and preferably at right-angles to each other, such that the pin may be locked in a selected one of two possible angular orientations. Typically, and for the case of a pin having a transverse mounting hole externally of the block body, these positions will be with the transverse mounting hole extending either parallel to the rotational axis of the sheave, or at 90° to that axis.  
         [0018]     The, or each if there is more than one, groove in the head of the mounting pin preferably is of part-circular shape, in cross-section. Then, the lock member may be mostly cylindrical and mounted such that the cylindrical surface of the lock member will be located in a groove in the head of the pin, so as to lock the pin against rotation. By providing the lock member with a relieved portion along its length and which may be brought adjacent the head of the pin by rotation of the lock member, the pin may be freed for rotation. To lock the pin once more, it should be set at the required position, rotationally, and then the lock member is turned through about 180°, so as to bring the cylindrical surface of the lock member once more into engagement with a groove in the head.  
         [0019]     An embodiment of pulley block of this invention comprises a pair of opposed cheeks between which the sheave is rotatably supported, together with a bridging portion connecting the opposed cheeks. In this arrangement, the pin should be mounted within a bore in the bridging portion, with the lock member also mounted therein, immediately adjacent the head of the pin and with the axis of the lock member extending parallel to the rotational axis of the sheave. To permit the block to have minimal weight, the sheave may be in the form of an annulus rotatably supported by the cheeks, by means of respective opposed races formed on the internal surface of each cheek and on the outer surfaces of the annular sheave, with balls disposed between the respective opposed races. The block may be formed in two similar parts moulded from a plastics material and each defining one cheek, the two parts being held together by a clamping arrangement. Further, the lock member may also be moulded from a plastics material, so minimising an increase in weight of the block as compared to a simple block having a freely rotatable pin.  
         [0020]     Referring now to the drawings, these show a preferred embodiment of pulley block of this invention. This pulley block has a pair of moulded plastics body parts  10  only one of which is shown in  FIG. 1 . Each body part defines a side cheek  11  and includes half of a bridging member  12  such that when the two body parts are fitted together, the bridging member is completed and serves to hold the two side cheeks  11  parallel and spaced apart by a distance sufficient to accommodate an annular rotatable sheave  13  ( FIG. 4 ) therebetween, supported on balls running on races provided respectively on the side cheeks  11  and the sheave  13 . The assembly of the two body parts  10  is held together by a metallic strap ( FIG. 5 , to be described below) and two bolts (not shown) or similar retaining fasteners extending through aligned holes  14 ,  15  in the two body parts and which will lie within the bore of the annular sheave of the completed block, the bolt which passes through hole  14  also passing through the metallic strap. For smaller blocks, it may not be necessary to provide two fasteners nor hole  15 , as shown for example in  FIG. 3 .  
         [0021]     The bridging member halves, when assembled to form the complete bridging member  12 , define a bore  16  extending at right-angles to the axis of rotation of a mounted sheave. A mounting pin  17  has an enlarged head  18  which is accommodated in the bore  16 , for free rotation with respect thereto. As shown in the drawings, the mounting pin has a transverse hole  19  externally of the block body, whereby the block may be attached to some other component by means of a shackle (not shown), the shackle pin extending through the hole  19  of the block mounting pin  17 .  
         [0022]     The pin  17  is retained in bore  16  by means of the U-shaped metallic strap  21  ( FIG. 5 ) having a base section  22  from which extend two arms  23  substantially at right-angles to the base section. At its free end, each arm  23  has an enlarged portion  24 , extending arcuately in the plane of the arm and symmetrically with respect to the length of the arm. Each enlarged portion  24  tapers in the arcuate direction away from the arm, and has a hole which registers with hole  14  of the body parts, when the strap is fitted thereto. The base section  22  has a central hole  25  through which the pin  17  passes, the diameter of the hole  25  being smaller than that of the enlarged head  18  of the pin. In this way, on completion of the block, loads are transferred by the strap from the body parts  10  to the pin  17 .  
         [0023]     Each body part  10  is provided with a groove dimensioned to accommodate the U-shaped strap  21 , such that the external surface of the strap is essentially flush with the outer surface of the block body. The bridging member  12  includes a groove part  27  within which the base section  22  of the strap  21  extends, whereby the head  18  of the pin  17  may bear directly on the strap. Further, each cheek has a further groove part  28  to accommodate the respective arm  23  of the strap, that further groove part extending to the hole  14  and defining a recess  29  to accommodate the enlarged portion  24  of the strap. As shown in the drawings, the side walls  30  of the groove and recess extend essentially at right-angles to the major area of the groove; similarly, the side walls  32  of the strap  21  also extend at right-angles to the plane of the strap arms, whereby a close interfit may be achieved between the strap and the body parts defining the groove parts  28  and recess  29 .  
         [0024]     As shown in  FIGS. 2 and 3 , the enlarged head  18  of the mounting pin has two transverse grooves  34 , 35  extending at right-angles to each other across the end surface of the enlarged head  18 . A lock member  36 , generally of cylindrical form, extends through a bore  37  defined by the bridging member halves  12 , which bore extends parallel to the rotational axis of a mounted sheave and with the axis of the bore intersecting the axis of bore  16  which carries the mounting pin  17 . The lock member  36  has a relieved portion  38 , formed by a cut-away sector in the cylindrical surface of the lock member, which relieved portion extends for a distance slightly greater than the diameter of the enlarged head  18 .  
         [0025]     Each end face  39  of the lock member  36  is provided with a transverse slot  40 , engageable for example by a screwdriver to effect rotation of the lock member about its own axis. Two notches  41  are formed in the periphery of the lock member at the opposed ends of the slot  40 , a slug  42  being let into the bridging member to interact with those notches, so giving two detent rotational positions for the lock member  36 . Those positions respectively correspond to the relieved portion  38  being aligned with the enlarged head  18  of the mounting pin  17 , and the relieved portion being diametrically opposed to that head. The strap  21  ( FIG. 5 ) has two holes  45  formed in its arms  23  which register with the lock member  36  and serve to retain the lock member in its bore in bridging member  12 , when the strap has been fitted to the block body.  
         [0026]     As mentioned above, an annular sheave is carried between the side cheeks  11 . The sheave is provided with outwardly-directed races adjacent its internal bore and each cheek is formed with a corresponding race  43  ( FIGS. 2 and 3 ). A plurality of balls run on the facing races on the two sides of the sheave, thereby supporting the sheave for free rotation about its axis.  
         [0027]     Sufficient strength is imparted to the body by means of the metallic strap ( FIG. 5 ) which wraps round the two side cheeks  11  and over the bridging member formed by the two bridging member halves  12 , the metallic strap being held in place by means of a fastening extending through the hole  14  nearer the mounting pin  17 . The holes  14 , 15  are formed in thickened portions  44  of the side cheeks, which abut each other when the two body parts are fitted together, so forming a rigid structure. The enlarged head  18  of pin  17  bears directly on the strap, to impart loads thereto as required.  
         [0028]     Once the pulley block has fully been assembled as described above, the mounting pin  17  may freely rotate with respect to the block body when the lock member  36  is set as shown in  FIGS. 2 and 3 . The lock member is held in that position by virtue of the interengagement of slug  42  with a notch  41  in the lock member  36 . If the mounting pin  17  is to be locked against rotation, it is set to the required position with the transverse hole  19  either parallel to or at right-angles to the axis of the lock member, and then the lock member is turned through 180° by means of a screwdriver so as to engage the slug  42  with the opposed notch  41  in the lock member. This brings the cylindrical surface of the lock member into one of the grooves  34 , 35  in the enlarged head of the mounting pin, so securing the mounting pin against rotation with respect to the block body.  
         [0029]     It will of course be appreciated that the locking arrangement for the mounting pin  17  may be used with other designs of block, besides those having an annular sheave as described above.