Magnetic Gears and Couplings

The conversion of mechanical energy to electrical energy or vice versa is achieved with large electromechanical volumes at low rotation speeds. Gears are a convenient way to convert the slow speed, high torque side of ocean energy to a high speed, low torque counterpart. Mechanical gearboxes are beset by life and maintenance issues. If direct drive conversion is employed, the equipment is huge in both physical size and cost, due to the properties indigenous to materials available and practical today. The size of the electromechanical device can be reduced proportional to the speed ratio realized by the gear. Unfortunately, mechanical gears with large ratios are anything but small, a fact well known in the wind industry. The difficulty has much to do with the number of teeth that can be engaged at one time. Sharing teeth drives the costs up considerable due to mechanical machining requirements of multiple stages and parallel linkages. Delivery supply quotes for the larger gears runs 18-24 months in the wind industry. These devices typically operate with 95-96% efficiency. We calculate that the efficiency of a magnetic gear could achieve 97.5-98% with a torque density of 160 kN-m/m3. A comparison to a direct drive windmill generator shows that a 50:1 magnetic gear has a torque density close to 8 times greater than a direct drive generator. This would suggest that a magnetic gear with a 1/50th sized conventional generator could replace an electromechanical system 8 times larger. When a magnetic field simulation proved this 8:1 advantage over a superconducting direct drive alternative, this team became convinced that this technology could make significant inroads in the evolution of advanced gearing technologies.