The magnetic powder used in these clutches is carbonyl E iron. The iron particles are spherical with an average diameter of 8 micrometers (8 microns). When subjected to a magnetic field that saturates the magnetic pole, the powder can support approximately 207 kPa (30 lbs. per square inch) in shear. The rotor of a clutch such as shown in the cross section drawing, having a diameter of 127 mm (5 in) and a width of 51 mm (2 in), can transmit a torque of approximately 258 J (190 ft. lbs.) without slipping. The clutch at the far right in the photograph is one removed from a Renault automobile. The model on the left is a cut-away demonstration clutch as used in a smaller automobile such as a Subaru. The clutch in the upper left is the first magnetic-particle clutch built at NIST in the late 40s. It was designed so the shaft bearings were far above the powder mix to prevent the powder affecting the bearings. In the other two later clutches, special slinger-labrinths were employed to keep the iron powder out of the ball bearings. The electro magnets of these two auto clutches also serve as the flywheels of the engines.
Last Updated on October 28, 2004
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