Bobbin case for a sewing machine

Abstract

A bobbin case is used in a sewing machine for mounting a bobbin, and includes a case body having a base wall, a case shaft extending along a central line from the base wall for rotatably mounting the bobbin, and a rim having entry and exit holes to define a tensioning path therebetween, and a diverting concaivity configured to divert a running route which is disposed downstream of the tensioning path. A lead-out member is disposed downstream of the running route. A leaf spring is positioned on the rim, and is configured to guide an under thread of the bobbin to run along the tensioning path with an urging force, and continued on running along the running route to the lead-out member to be interlocked with an upper thread for a sewing action.

1 . A bobbin case adapted to be used in a sewing machine for mounting a bobbin which is disposed under a needle plate to supply an under thread, the bobbin case comprising:
 a case body having
 a base wall which defines an annular marginal region that surrounds a central line, and which has a portion cut out so as to form an offset surface that is offset from the central line, 
 a case shaft which extends from said base wall along the central line, and which is configured to permit the bobbin to be rotatably sleeved thereon so as to reel off the under thread to be led outwardly of said annular marginal region, and 
 front and rear rim segments which extend from said annular marginal region in a direction of the central line, and which are interconnected by said offset surface, said front rim segment extending angularly to terminate at a longitudinally extending edge, and having entry and exit holes which are angularly displaced from each other to define a tensioning path therebetween, and a diverting concavity which extends from said longitudinally extending edge angularly and toward said exit hole, and which is configured to divert a running route which is disposed downstream of the tensioning path, inwardly of said annular marginal region; 
   a lead-out member disposed on said offset surface and downstream of said diverting concavity for further leading the under thread toward the needle plate; and   a leaf spring which has a positioned segment disposed to be fastened to said front rim segment, and an urging segment which extends lengthwise from said positioned segment to terminate at a guiding end that is engaged in said exit hole, and that is configured to guide the under thread to run along the running route to said lead-out member through said diverting concavity, said urging segment being provided with an urging force such that the under thread led out of said entry hole to run along the tensioning path is subject to the urging force so as to be placed in a tensed state when the under thread exits said guiding end for continuing on running along the running route.   
     
     
         2 . The bobbin case according to  claim 1 , wherein said front rim segment extends in the direction of the central line to terminate at a circumferentially extending edge, and has outer and inner surface regions radially opposite to each other, said outer surface region having an inclined slit which extends through said inner surface region and which communicates said circumferentially extending edge with said entry hole so as to permit the under thread to be guided through said inclined slit into said entry hole. 
     
     
         3 . The bobbin case according to  claim 2 , wherein said guiding end is integrally formed with said urging segment and is bent to form a bearing surface facing said circumferentially extending edge. 
     
     
         4 . The bobbin case according to  claim 3 , wherein said diverting concavity has a diverting surface which is disposed to face said circumferentially extending edge and which is inclined gradually from said outer surface region to said inner surface region. 
     
     
         5 . The bobbin case according to  claim 1 , wherein said lead-out member is in form of a coil which defines a through passage for passage of the under thread.