Driving force transmission device and image forming apparatus

A driving force transmission device provided in a drive train which transmits a driving force coming from a drive source to a driven member, the driving force transmission device comprising:

• a drive gear configured to rotate by being coupled to the drive source;
• a driven gear including a gear portion, which has a plurality of teeth meshing with the drive gear, and a partially toothless gear portion, which is a region having no teeth meshing with the drive gear, and configured to rotate in response to the gear portion meshing with the drive gear and to stop rotating in response to the partially toothless gear portion facing the drive gear;
• a first cam member configured to rotate in conjunction with rotation of the driven gear;
• a second cam member configured to rotate in conjunction with rotation of the driven gear;
• a first elastic member configured to apply an urging force to the first cam member;
• a contact portion configured to come into contact with the first cam member by the urging force of the first elastic member;
• and
• a follower member configured to be urged by a second elastic member and be moved by the second cam member,
• wherein the first cam member includes (i) a home cam surface configured to come into contact with the contact portion in such a manner that, when the partially toothless gear portion faces the drive gear, rotation of the driven gear is limited, and (ii) an assist cam surface configured to come into contact with the contact portion when an elastic force of the second elastic member is charged according to rotation of the driven gear, and
• wherein the assist cam surface comes into contact with the contact portion in such a manner that an elastic force of the first elastic member is released according to rotation of the driven gear.

A driving force transmission device provided in a drive train which transmits a driving force coming from a drive source to a driven member, the driving force transmission device comprising:

• a drive gear configured to rotate by being coupled to the drive source;
• a driven gear including a gear portion, which has a plurality of teeth meshing with the drive gear, and a partially toothless gear portion, which is a region having no teeth meshing with the drive gear, and configured to rotate in response to the gear portion meshing with the drive gear and to stop rotating in response to the partially toothless gear portion facing the drive gear;
• a first cam member configured to rotate in conjunction with rotation of the driven gear;
• a second cam member configured to rotate in conjunction with rotation of the driven gear;
• a first elastic member configured to apply an urging force to the first cam member;
• a contact portion configured to come into contact with the first cam member by the urging force of the first elastic member;
• and
• a follower member configured to be urged by a second elastic member and be moved by the second cam member,
• wherein the first cam member includes (i) a home cam surface configured to come into contact with the contact portion in such a manner that, when the partially toothless gear portion faces the drive gear, rotation of the driven gear is limited, and (ii) at least one of a cancel cam surface and an assist cam surface,
• wherein the cancel cam surface comes into contact with the contact portion in such a manner that, when an elastic force of the second elastic member is released according to rotation of the driven gear, an elastic force of the first elastic member is charged according to rotation of the driven gear, and
• wherein the assist cam surface comes into contact with the contact portion in such a manner that, when the elastic force of the second elastic member is charged according to rotation of the driven gear, the elastic force of the first elastic member is released according to rotation of the driven gear.