Sensor assembly having embedded wires within a powder metal core and a method therefor

A magnetoresistive position sensor comprising:

• a magnetic body having a first portion and a second portion, said second portion defining a first surface of said magnetic body, said first portion of said magnetic body comprising compacted particles of a neodymium-iron-boron alloy having high magnetic coercivity which are substantially individually coated with an electrically insulative coating, said second portion of said magnetic body comprising compacted particles of a ferromagnetic material which are substantially individually coated with an electrically insulative coating, said compacted particles of said ferromagnetic material being disposed adjacent said first surface of said magnetic body;
• and
• a plurality of electrically conductive wires embedded within said magnetic body, said plurality of electrically conductive wires being coated with an electrically insulative material, each of said electrically conductive wires having a terminal end which terminates substantially at said first surface of said magnetic body so as to be substantially coplanar with said first surface of said magnetic body;
• and
• a semiconductor sensing element electrically connected to at least one of said plurality of electrically conductive wires at said first surface of said magnetic body;
• whereby said magnetic body, said plurality of electrically conductive wires and said semiconductor sensing element form a stationary portion of the magnetoresistive position sensor, said semiconductor sensing element being adapted to sense flux density variations along a width of said magnetic body in a direction of relative movement by an exciter portion which is adapted to move past said stationary portion.

A method for manufacturing a magnetoresistive position sensor, comprising the following steps:

• providing at least one electrically conductive wire coated with an electrically insulative material;
• locating said at least one electrically conductive wire within a molding die so that said at least one electrically conductive wire extends from a first surface of said molding die into a cavity;
• filling said cavity with a first powder metal composition, a floor of said cavity being defined by said first surface of said molding die, and walls of said cavity being defined by an interior surface of a mold, said first powder metal composition comprising particles of a high coercivity magnetic material which have been substantially individually coated with an electrically insulative coating;
• adding to said cavity a second powder metal composition comprising particles of a ferromagnetic material which have been substantially individually coated with an electrically insulative coating, said at least one electrically conductive wire being enveloped by said first and second powder metal compositions within said cavity;
• and
• compacting said first and second powder metal compositions at a sufficient pressure and temperature and for a sufficient duration, so as to form a fully dense magnetic body from said powder metal compositions wherein said at least one electrically conductive wire is substantially embedded within said magnetic body, and wherein said ferromagnetic material is disposed adjacent a first end of said magnetic body, the remainder of said magnetic body comprising said high coercivity magnetic material;
• such that a terminal end of said at least one electrically conductive wire is substantially coplanar with said first end of said magnetic body, so as to facilitate the subsequent electrical connection of said at least one electrically conductive wire to a semiconductor magnetoresistive sensor disposed on said first end of said magnetic body.

A method for manufacturing a magnetoresistive position sensor comprising the following steps:

• providing at least one electrically conductive wire coated with an electrically insulative material;
• locating said at least one electrically conductive wire within a molding die so that said at least one electrically conductive wire extends from a surface of said molding die into a cavity;
• filling said cavity with a first powder metal composition, a floor of said cavity being defined by said surface of said molding die, and walls of said cavity being defined by an interior surface of a mold, said first powder metal composition comprising particles of high coercivity neodymium-iron-boron permanent magnet material which have been substantially individually coated with an electrically insulative coating;
• adding to said cavity a second powder metal composition comprising particles of a ferromagnetic material which have been substantially individually coated with an electrically insulative coating, said at least one electrically conductive wire being enveloped by said first and second powder metal compositions within said cavity;
• and
• compacting said first and second powder metal compositions at a sufficient pressure and temperature and for a sufficient duration, so as to form a fully dense magnetic body from said powder metal compositions wherein said at least one electrically conductive wire is substantially embedded within said magnetic body, and wherein said ferromagnetic material is disposed adjacent a first surface of said magnetic body, the remainder of said magnetic body comprising said high coercivity magnetic material, such that said at least one electrically conductive wire terminates substantially at said first surface of said magnetic body;
• and
• electrically connecting a semiconductor magnetoresistive sensing element to said at least one electrically conductive wire at said first surface of said magnetic body, such that said sensing element is adapted to sense flux density variations along the width of said magnetic body in a direction of relative movement by an exciter portion which is adapted to move past said stationary portion.