Fan-coupling device with unitary magnetic pole construction

A fan-coupling device, comprising:

• a housing comprised of a case and a cover, the housing being mounted on a rotary shaft via a first bearing;
• a partition plate located inside the housing, the partition plate dividing the interior of the housing into an oil sump chamber and a torque transmission chamber, the partition plate including an oil feed hole configured to allow fluid to flow between the oil sump chamber and the torque transmission chamber;
• an oil feed valve, comprising a spring portion and an armature, the oil feed valve configured to cover the oil feed hole in the partition plate and to open the oil feed hole when a force is applied to the armature;
• and
• a magnetic circuit configured to cause a magnetic force to be applied to the armature of the oil feed valve sufficient to cause the oil feed valve to open the oil feed hole, the magnetic circuit comprising:
• a ring-shaped electromagnet mounted on the rotary shaft via a second bearing;
• and
• a magnetic pole disposed between the electromagnet and the armature of the oil feed valve, the magnetic pole being of a unitary construction and comprising:
• a thin choke area disposed in a top surface, the thin choke area being thinner than other portions of the top surface;
• and
• a ridge disposed around the periphery of the top surface of the magnetic pole, the ridge extending above the top surface.