Resin gear

Abstract

A resin gear comprises a rim in an outer peripheral part of a plate, teeth provided on an outer periphery of the rim, a boss provided in a central part of the plate, and a circular rib between the boss and the rim. The resin gear is manufacturable by injection molding that a molten material is injected into a cavity through a plurality of gates arranged at almost equally spaced intervals circumferentially on a forming portion for the circular rib in a direction perpendicular to a side of the plate. The resin gear includes a plurality of inner thin-wall portions on the plate between the circular rib and the boss and a plurality of outer thin-wall portions on the plate between the circular rib and the rim, each of the inner thin-wall portions and the outer thin-wall portions being symmetrically shaped with respect to the radial line passing through each gate corresponding point.

1 . A resin gear comprising:
 a circular plate;   a rim provided in an outer peripheral part of the plate;   teeth formed on an outer periphery of the rim;   a boss provided in a central part of the plate; and   a circular rib provided on the plate between the boss and the rim and concentrically with the plate;   the resin gear being manufacturable by injection molding in which a molten material is injected into a cavity through a plurality of gates arranged at almost equally spaced intervals circumferentially on a forming portion for the circular rib in a manner that the molten resin is injected in a direction perpendicular to a side of the plate,   wherein the resin gear is formed with inner thin-wall portions on the plate between the circular rib and the boss, each of the inner thin-wall portions being symmetrical with respect to a radial line passing through each of a plurality of gate corresponding points which correspond to the gates respectively.   
   
   
       2 . The resin gear according to  claim 1 , wherein each inner thin-wall portion is of a length in a radius direction, which is shorter in a section closer to a midpoint between adjacent two of the gate corresponding points. 
   
   
       3 . The resin gear according to  claim 2 , wherein the inner thin-wall portions respectively aligned with the gate corresponding points are equal in shape so that a thick-wall portion has one of a polygonal outer shape and a petaloid outer shape on the plate between the circular rib and the boss. 
   
   
       4 . The resin gear according to  claim 1 , further comprising a boss on a back side of the plate including an axially protruding cylindrical portion on an outer periphery of which a small-diameter gear is formed. 
   
   
       5 . The resin gear according to  claim 1 , further including outer thin-wall portions on the plate between the circular rib and the rim, the outer thin-wall portion being symmetrical with respect to the radial line passing through each of the gate corresponding points which correspond to the gates respectively. 
   
   
       6 . The resin gear according to  claim 2 , further including outer thin-wall portions on the plate between the circular rib and the rim, the outer thin-wall portion being symmetrical with respect to the radial line passing through each of the gate corresponding points which correspond to the gates respectively. 
   
   
       7 . The resin gear according to  claim 3 , further including outer thin-wall portions on the plate between the circular rib and the rim, the outer thin-wall portion being symmetrical with respect to the radial line passing through each of the gate corresponding points which correspond to the gates respectively. 
   
   
       8 . The resin gear according to  claim 5 , wherein each outer thin-wall portion is of a length in the radius direction, which is shorter in a section closer to the midpoint between adjacent two of the gate corresponding points. 
   
   
       9 . The resin gear according to  claim 6 , wherein each outer thin-wall portion is of a length in the radius direction, which is shorter in a section closer to the midpoint between adjacent two of the gate corresponding points. 
   
   
       10 . The resin gear according to  claim 7 , wherein each outer thin-wall portion is of a length in the radius direction, which is shorter in a section closer to the midpoint between adjacent two of the gate corresponding points. 
   
   
       11 . The resin gear according to  claim 8 , wherein the outer thin-wall portions respectively aligned with the gate corresponding points are equal in shape so that the outer thin-wall portions wholly have one of a polygonal outer shape and a petaloid outer shape on the plate between the circular rib and the rim. 
   
   
       12 . The resin gear according to  claim 9 , wherein the outer thin-wall portions respectively aligned with the gate corresponding points are equal in shape so that the outer thin-wall portions wholly have one of a polygonal outer shape and a petaloid outer shape on the plate between the circular rib and the rim. 
   
   
       13 . The resin gear according to  claim 10 , wherein the outer thin-wall portions respectively aligned with the gate corresponding points are equal in shape so that the outer thin-wall portions wholly have one of a polygonal outer shape and a petaloid outer shape on the plate between the circular rib and the rim. 
   
   
       14 . The resin gear according to  claim 5 , further comprising a boss on a back side of the plate including an axially protruding cylindrical portion on an outer periphery of which a small-diameter gear is formed. 
   
   
       15 . A resin gear comprising:
 a circular plate;   a rim provided as an outer peripheral part of the plate;   teeth formed on an outer periphery of the rim;   a boss provided in a central part of the plate; and   a circular rib provided on the plate between the boss and the rim and concentrically with the plate;   the resin gear being manufacturable by injection molding that a molten material is injected into a cavity through a plurality of gates arranged at almost equally spaced intervals circumferentially on a forming portion for the circular rib in a manner that the molten resin is injected in a direction perpendicular to a side of the plate,   wherein the resin gear is formed with an outer thin-wall portion on the plate between the circular rib and the rim, the outer thin-wall portion being symmetrical with respect to a radial line passing through each gate corresponding point corresponding to each gate.   
   
   
       16 . The resin gear according to  claim 15 , wherein each outer thin-wall portion is of a length in the radius direction, which is shorter in a section closer to the midpoint between adjacent two of the gate corresponding points. 
   
   
       17 . The resin gear according to  claim 16 , wherein the outer thin-wall portions respectively aligned with the gate corresponding points are equal in shape so that the outer thin-wall portions wholly have one of a polygonal outer shape and a petaloid outer shape on the plate between the circular rib and the rim.