Neo magnets boost fuel economy

A disassembled ECF motor has four new injection-molded Neo arcs installed (arrows), and the armature winding removed in preparation for rewinding. Permanent-magnet performance is measured by a demagnetization characteristic. The standard ceramic ferrite magnet has the lowest magnetic properties, compared to two different types of bonded Neo magnet. The higher the remanence ( ) of a magnet, the better it can reduce current draw in a dc motor. The product of a magnet's operating flux density ( ) and its magnetizing force ( ) is a direct measure of its energy density. The maximum, ( , is commonly used as a figure of merit for a permanent-magnet material. Clockwise, from the top, the graph shows typical fluxdensity distributions calculated by FEA at a motor current of 20 A for compression-molded Neo, ferrite, and injection-molded Neo. The color contours indicate that the flux-density levels both in the outer housing and in the armature teeth are nearing saturation. The flux density in the steel laminations and outer housing is kept below 18,000 Gauss to avoid saturation which would increase core losses. Torque versus current and torque versus efficiency graphs show that the total armature current is reduced and the efficiency is increased for any given output torque by using Neo magnets. As of last year, the average car employed about twodozen electric motors, actuators, and sensors containing permanent magnets. This number is expected to increase to well over 30 by 2005. The growing use of electromechanical devices places increasing loads on the power system. So automakers are seeking out ways to increase efficiency and lessen alternator current draw. The engine-cooling fan (ECF) and the heating/ventilation/air-conditioning (HVAC) blower motors have the greatest combined current draw and operating duty cycle. These two brushed-dc motors, using ceramic ferrite magnets, currently draw a combined continuous 35 to