Electromagnetic clutch unit, four-wheel-drive vehicle, control method for the electromagnetic clutch unit, and control method for the four-wheel-drive vehicle

An electromagnetic clutch unit configured to connect a first rotary member and a second rotary member, which are rotatable relative to each other, such that torque is transmitted between the first rotary member and the second rotary member, the electromagnetic clutch unit comprising:

• an electromagnetic coil that generates electromagnetic force upon energization of the electromagnetic coil;
• a friction mechanism including a first friction member connected to the first rotary member so as to be non-rotatable relative to the first rotary member, and a second friction member connected to the second rotary member so as to be non-rotatable relative to the second rotary member and frictionally engageable with the first friction member by the electromagnetic force;
• a lock sleeve connected to the second rotary member so as to be non-rotatable relative to the second rotary member, and movable in an axial direction of the electromagnetic clutch unit between a first position at which the lock sleeve is engaged with the second rotary member but is not engaged with the first rotary member and a second position at which the lock sleeve is engaged with both the first rotary member and the second rotary member;
• and
• a pressing member that constitutes a magnetic path extending over the pressing member and the second friction member, and that presses the lock sleeve with the electromagnetic force to move the lock sleeve from the first position to the second position.