Resin double helical gear and gear train using same

A gear train comprising a first resin double helical gear and a second double helical gear meshing therewith, said first resin double helical gear comprising:

• a first gear portion arranged on one side in face width directions from a substantially central portion in the face width directions, said first gear portion having teeth which are helical in a direction;
• and
• a second gear portion arranged on the other side in the face width directions from the substantially central portion in the face width directions, said second gear portion having teeth which are helical in a direction opposite to that of said first gear portion,
• wherein said first gear portion and said second gear portion are molded so as to be integrated with each other in such a shape that a pair of helical gear halves being helical in opposite directions to each other are stuck together.

A gear train comprising:

• an output gear of a motor, said output gear being a resin double helical gear;
• a first idle gear meshing with the output gear, said first idle gear being a resin double helical gear;
• a second idle gear rotatable with the first idle gear, said second idle gear being a spur gear;
• and
• a driven gear which is mounted on a roller shaft so as to be rotatable therewith and which meshes with the second idle gear, said driven gear being a spur gear.

A resin double helical gear molded by injecting a resin into a cavity defined by causing a first die to butt a second die, said resin double helical gear comprising:

• a first gear portion arranged on one side in face width directions from a central portion in the face width directions, said first gear portion being molded by said first die so as to have teeth which are helical in a direction;
• a second gear portion arranged on the other side in the face width directions from the central portion in the face width directions, said second gear portion being molded by said second die so as to have teeth which are helical in a direction opposite to that of said first gear portion and each of which is connected to a corresponding one of the teeth of said first gear portion to form a chevron-shaped top portion in a butt portion between said first and second gear portions;
• and
• a meshing relief portion formed by cutting the chevron-shaped top portion off, from a tooth crest to a portion near a bottom land so as to decrease a tooth thickness.

A resin double helical gear molded by injecting a resin into a cavity defined by causing a first die to butt a second die, said resin double helical gear comprising:

• a first gear portion arranged on one side in face width directions from a central portion in the face width directions, said first gear portion being molded by said first die so as to have teeth which are helical in a direction;
• a second gear portion arranged on the other side in the face width directions from the central portion in the face width directions, said second gear portion being molded by said second die so as to have teeth which are helical in a direction opposite to that of said first gear portion and each of which is connected to a corresponding one of the teeth of said first gear portion to form a chevron-shaped top portion in a butt portion between said first and second gear portions;
• and
• a meshing relief portion formed by recessing a reverse to the chevron-shaped top portion from a tooth crest to a portion near a bottom land so as to prevent said reverse from contacting a chevron-shaped top portion of a companion gear meshing with said resin double helical gear.