Patent ID: 6561516
Filing Date: 2003-05-13
Classification: F16J,G11B

Abstract:
A seal for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed about the shaft, the seal comprising and outer member including:an annular magnet positioned between the shaft and the hub; a top pole piece and a bottom pole piece coupled to opposite poles of the magnet, the top and bottom pole pieces comprising a material which is magnetically permeable, and having annular shapes with interior radii that are larger than the radius of the outer surface of the shaft to define a concave region in which a ferrofluid is held, an inner member including an annular ring supported from the shaft and extending into the concave region and supporting a short, axially extended pole piece at an end thereof to define a contoured gap in the concave region where the ferrofluid is held, the surface of the pole piece having a relatively uniform spacing from an inner surface of the recess, wherein the contoured gap includes a characteristic contour defined as a set of points within the concave region of the ferrofluid that are equidistant between a surface of the concave region and an outer surface of the pole piece, and usable to define a Power Index (PI)=(AÃ—R{circumflex over ( )}2)/&Dgr;Ã—V) wherein A=surface area of the characteristic contour R=maximum radius of the contour about the axis of rotation &Dgr;=average gap between the inner and outer member V=total volume of the fluid and wherein the seal is optimized for PI<700.