Patent ID: 8240447

Claim:
A drive force transmission apparatus comprising: a permanent magnet that is displaceable between a first position and a second position; a magnet position changing means for rotating the permanent magnet between the first position and the second position about a rotational axis of the permanent magnet; a rotor that is rotated upon receiving a rotational drive force from an external drive power source, wherein the rotor exerts a first magnetic attractive force in cooperation with the permanent magnet upon placing of the permanent magnet into the first position, and the rotor exerts no magnetic attractive force or a second magnetic attractive force, which is smaller than the first magnetic attractive force, in cooperation with the permanent magnet upon placing of the permanent magnet into the second position; an armature that is connected to an external driven-side apparatus and is coupleable with the rotor to transmit the rotational drive force from the rotor to the external driven-side apparatus, wherein the armature is spaced from the rotor by a predetermined gap in an uncoupled state of the armature, in which the armature is uncoupled from the rotor; and a resilient member that holds the armature such that the predetermined gap is maintained between the rotor and the armature in the uncoupled state of the armature, wherein: the armature is magnetically attracted to and is coupled with the rotor against an urging force of the resilient member by the first magnetic attractive force of the rotor when the permanent magnet is placed into the first position; and the armature is urged away from and is decoupled from the rotor by the urging force of the resilient member when the permanent magnet is placed into the second position.