Drive transmission device and image forming apparatus incorporating the same

A drive transmission device comprising:

• a drive transmission member to receive a driving force from a drive source, and
• a rotation shaft that is inserted into an insertion portion of the drive transmission member to be held, the rotation shaft having a D-cut shape with a rounded segment extending in an axial direction of the rotation shaft, and with flat portions arranged at different positions in the axial direction, the rotation shaft including:
• a first shaft portion along the axial direction having a first flat portion, the first flat portion extending in the axial direction from an endmost surface of a tip end of the rotation shaft that is perpendicular to a longitudinal axis of the rotation shaft, and
• a second shaft portion along the axial direction having
• a first inclined surface extending in the axial direction from the first flat portion and being inclined with respect to the first flat portion, and
• a second flat portion extending in the axial direction from the first inclined surface,
• wherein the insertion portion has a D-cut shape where an inner-wall surface comprises an inner-wall flat portion and an inner-wall rounded portion, and further has an entrance edge portion and an exit edge portion opposite the entrance edge portion with a second inclined surface,
• where in the D-cut shape of the insertion portion extends from the entrance edge portion to the exit edge portion,
• wherein the inner-wall flat portion contacts the second flat portion when the second flat portion is press-fitted into the insertion portion, and
• wherein, after the first shaft portion of the rotation shaft passes a second inclined surface of the entrance edge portion, the second inclined surface is pressed in contact with the first inclined surface of the rotation shaft and the rotation shaft is inserted while the drive transmission member is being deformed.