Abstract:
A locking mechanism for a bobbin case ( 5 ) is provided with a locking lever ( 35 ) supported pivotally in the bobbin cover ( 27 ). The locking lever is pivotal on a shaft ( 33 ). A hook-shaped end ( 51 ) is formed at the locking lever ( 35 ), which latches in the sleeve ( 9 ) in the hook and can hold the bobbin case ( 3 ) in the hook ( 1 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Swiss Patent Application No. 02061/10, filed Dec. 9, 2010, which is incorporated herein by reference as if fully set forth. 
       BACKGROUND 
       [0002]    The invention is directed to a locking mechanism for a bobbin case for a lower thread bobbin. 
         [0003]    The lower thread bobbin of sewing machines, particularly household sewing machines, can be supported directly in the bobbin carrier and thus be directly accessible. However, it may also be inserted into a bobbin case designed for said purpose, which in turn is supported in the bobbin carrier. The present invention relates to a lower thread bobbin supported in a bobbin case. 
         [0004]    A locking mechanism for a lower thread bobbin is known from EP 1541736 B1, in which on the bobbin case a locking mechanism that can be guided through the central opening in the bobbin is held on a spring and after the complete pressing down of the bobbin into the bobbin carrier, the bobbin automatically latches. The latter can be released from this latching by a radial displacement of the locking element towards the rotary axis of the bobbin. Then the bobbin case is ejected by the spring supporting the locking element. 
       SUMMARY 
       [0005]    The objective of the present invention is to provide a locking mechanism for a bobbin case used for a lower thread bobbin, by which the bobbin case latches in the bobbin carrier and is securely held there in all operating conditions. Additionally, an axial shifting of the bobbin case together with the bobbin out of the bobbin carrier shall be achieved after the release. 
         [0006]    This objective is attained by a locking mechanism according to the invention. Advantageous embodiments of the invention are described in greater detail below and in the claims. 
         [0007]    By a radially extending pressure upon the locking element provided in the surface of the bobbin case the fastened position, which holds the bobbin in the hook, can be released and simultaneously the partial ejection of the bobbin case with the bobbin can be initiated. The locking of a new bobbin case with a bobbin to be inserted in the hook occurs by an axial insertion of the bobbin case into the hook until it is completely located inside the recess of the hook. Here, no additional locking actions are required. During the sewing operation the bobbin held by the locking element is not restricted in any way by said locking element because the latter is not in contact with the bobbin in the operating state. When inserting the bobbin into the bobbin case, the case is held in a force-fitting manner by the locking element so that when inserting the bobbin case with the bobbin into the hook the bobbin cannot fall out of the bobbin case. During unlocking for the purpose of removing the bobbin case from the hook the bobbin located in the bobbin case is held by the locking element, as long as it is in operation, and the bobbin case can be removed from the hook without any additional manipulation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0008]    The invention is explained in greater detail using an illustrated exemplary embodiment. Shown are: 
           [0009]      FIG. 1  is an axial cross-sectional view through a hook with an inserted bobbin case and bobbin, 
           [0010]      FIG. 2  is a perspective view of a bobbin case at the side of the lid, 
           [0011]      FIG. 3  is an axial cross-sectional view through the bobbin case including the inserted bobbin, with the locking mechanism being engaged, 
           [0012]      FIG. 4  is an axial cross-sectional view through the bobbin case directly before the bobbin case is latched, 
           [0013]      FIG. 5  is an axial cross-sectional view through the bobbin case, with the locking mechanism unlatched, and the bobbin case exiting, 
           [0014]      FIG. 6  is an axial cross-sectional view through a bobbin case with a locking element in the position holding the bobbin, during the insertion into the hook, 
           [0015]      FIG. 7  is a view of a bobbin case without a bobbin and with the bobbin being removed. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    In  FIG. 1 , showing an axial cross-section through a hook  1  with a bobbin case  3  inserted therein and a bobbin  5  arranged in the bobbin case  3 , all features relevant for the invention are discernible. A sleeve  9  rests on an arbor  7  formed in the hook  1 . The sleeve  9  comprises a central cylindrical section  11 , with a circumferential clearance groove  13  being embodied at its periphery, with one side extending approximately perpendicular in reference to the axis of the sleeve  9  and its second side having an angle of approx. 45° . The lower end of the sleeve  9  is closed by a flange  15 , which in turn abuts at one side a collar  17  at the hook  1  and at the other side radially projects the collar  17 . The end of the sleeve  9  opposite the flange  15  comprises, for example, an interior diameter greater than the interior diameter of the sleeve in the other sections. Using a screw  21  engaging the arbor  7  and here engaging a threaded bore  19  the sleeve  9  is held at the arbor  7 . The sleeve  9  may represent an integral part of the hook  1 , i.e. not embodied as an element mounted thereon. 
         [0017]    A coil spring  23  is placed onto the sleeve  9  and supported and fixed at one side at the flange  15 . 
         [0018]    The bobbin case  3  comprises a casing  25  and, in  FIG. 1  at the front, a cover  27  spherically shaped at the outside. This transfers arc-shaped into the casing  25 . A slot-shaped opening  29  is provided in the cover  27 , extending diagonally, and a recess  31 , extending perpendicular in reference to the opening  29 , and not completely penetrating the cover  27 . A shaft  33  is located in the recess  31 , which penetrates a two-arm locking lever  35 . The locking lever  35  is located in a slot-shaped opening  29 . A torsion spring  37  (shown only partially) encompasses the shaft  33  and contacts with its first end the interior of the cover  27 ; its second end  39  penetrates the locking lever  35  in a bore  41  or contacts it at the outside (cf.  FIG. 5 ). 
         [0019]    Arranged asymmetrically in reference to the shaft  33 , the locking lever  35  comprises one latching leg  45  projecting essentially perpendicularly from the primary leg  43 , which extends parallel to the cover  27  and, at a distance therefrom, one braking leg  47 . It is further discernible from  FIGS. 1 and 2  that a recessed grip  49  is provided in the cover  27  of the bobbin  5 , allowing for pushing down the locking lever  35  on the shaft  33  using a finger and thus pivoting it so that the hook-shaped end  51  at the latching leg  45  can be released from its spring-loaded latching position in the clearance groove  13 . In the pivoted and released position the back of the latching leg  45  contacts the wall of the bore  53  in the bobbin  5  in a friction-fitting manner. Immediately after the pivoting of the locking lever  35  the bobbin case  3  is axially ejected out of the hook  1  by the tension force of the coil spring  23 , because the second end of the spring  23  contacts a stop  55  in the bobbin case  3  (cf.  FIG. 5 ). The bobbin case  3  can now manually be removed from the hook  1 . Here, the bobbin  5  is held in a friction-fitting fashion by the back of the latching leg  45  of the locking lever  35 . As soon as the force F upon the locking lever  35  reduces, i.e. when the operating person grasps the bobbin case peripherally with two fingers, locking lever  35  rotates in the clockwise direction and holds the bobbin  5  via the back of the braking leg  47  (cf.  FIG. 6 ). 
         [0020]    It is discernible from  FIG. 7  that the latching leg  45  is pivoted in the clockwise direction to the very right by the force of the torsion spring  37  and contacts a cam-shaped end  59  embodied on the primary leg  43  at a stop  61  in the opening  29 . 
         [0021]    A refilled lower thread bobbin  5  is inserted from above into the bobbin case  3 . Here, it glides against a certain resistance over the angled surface  57  of the braking leg  47  of the locking lever  35  downwards and is here held in position by the back of the brake leg  47 . Thus, when inserting the bobbin case  3  into the hook  1  this way the bobbin  5  is held and cannot fall out, even when the bobbin case  3  is tilted slightly downwards. As soon as the hook-shaped end  51  of the latching leg  45  contacts the sleeve  9  the locking lever  35  is slightly pivoted in the counter-clockwise direction. During the further insertion the hook-shaped end  51  glides along the casing of the sleeve  9  until the hook-shaped end  51  reaches the clearance groove  13  and can latch here. Now, the bobbin case  3  including the bobbin  5  is held in the hook  1  and cannot fall out of it any more. Both the latching leg  45  as well as the braking leg  47  are located in the latched position at a distance from the interior wall of the bore in the bobbin  5 . Thus, the latter is held freely rotational. In this position the exterior surface of the primary leg  43  is also located below the exterior contour of the cover  27 . 
       LIST OF REFERENCE CHARACTERS 
       [0022]      1  hook 
         [0023]      3  bobbin case 
         [0024]      5  bobbin 
         [0025]      7  arbor 
         [0026]      9  sleeve 
         [0027]      11  cylindrical section 
         [0028]      13  clearance groove 
         [0029]      15  flange 
         [0030]      17  collar 
         [0031]      19  threaded bore 
         [0032]      21  screw 
         [0033]      23  helical spring 
         [0034]      25  casing of  3 . 
         [0035]      27  cover 
         [0036]      29  opening 
         [0037]      31  recess 
         [0038]      33  shaft 
         [0039]      35  locking lever 
         [0040]      37  torsion spring 
         [0041]      39  end of  37   
         [0042]      41  bore 
         [0043]      43  primary leg 
         [0044]      45  latching leg 
         [0045]      47  braking leg 
         [0046]      49  recessed grip 
         [0047]      51  hook-shaped end 
         [0048]      53  bore 
         [0049]      55  recess 
         [0050]      57  angled surface 
         [0051]      59  end of  43   
         [0052]      61  stop