Concentrated winding salient-pole shaded pole motors having multiple short circuited shading coils for each pole and methods of making same

A salient-pole shaded pole motor including a stator assembly and rotor assembly;

• the stator assembly comprising a magnetizeable core having a magnetizeable yoke and a plurality of magnetically spaced apart pole pieces each having a leading and trailing pole tip, with the leading tip of each pole piece magnetically spaced from the trailing pole tip of a pole piece next adjacent thereto;
• said stator assembly further including first and second electrically short circuited shading coils disposed on and thereby identifying each of the trailing pole tips, and a winding comprising at least one concentrated group of conductor turns accommodated closely adjacent to at least one of the pole pieces;
• all of said shading coils being of substantially the same cross-sectional area and adjacent pairs of said coils on a given pole tip lying in planes generally parallel one to another and also to a radial line extending between such coil pairs;
• the motor exhibiting, during excitation of the winding by a given voltage, a locked rotor torque to maximum torque ratio of at least about 0.33;
• said rotor assembly including a short circuited squirrel cage rotor spaced by an air gap from bore defining faces of the pole pieces, and the leading pole tip of each pole piece being configured to have a high reluctance establishing step with a span of about one-third of a pole pitch;
• the first shading coil having a span of from about thirty electrical degrees to about fifty-nine electrical degrees;
• and the second shading coil having a span less than the span of the first shading coil.

A salient-pole shaded pole motor including a stator assembly and rotor assembly;

• the stator assembly comprising a magnetizeable core having a magnetizeable yoke and a plurality of magnetically spaced apart pole pieces each having a leading and trailing pole tip, with the leading tip of each pole piece magnetically spaced from the trailing pole tip of a pole piece next adjacent thereto;
• said stator assembly further including first and second electrically short circuited shading coils disposed on and thereby identifying each of the trailing pole tips, and a winding comprising at least one concentrated group of conductor turns accommodated closely adajcent to at least one of the pole pieces;
• all of said shading coils being of substantially the same cross-sectional area and adjacent pairs of said coils on a given pole tip lying in planes generally parallel one to another and also to a radial line extending between such coil pairs;
• the motor exhibiting, during excitation of the winding by a given voltage, a locked rotor torque to maximum torque ratio of at least about 0.33;
• said rotor assembly including a shaft and a plurality of conductors that establish a short circuited squirrel cage rotor spaced by an air gap from bore defining faces of the pole pieces;
• said pole pieces each including a portion extending generally radially outwardly from the shaft, and said magnetizeable yoke substantially encompassing the pole pieces and plurality of conductors;
• the leading pole tip of each pole piece being configured to have a high reluctance establishing step with a span of about one-third of a pole pitch;
• the first shading coil having a span of from about thirty electrical degrees to about fifty-nine electrical degrees;
• the second shading coil having a span less than the span of the first shading coil;
• and wherein the trailing pole tips and yoke define an insulated area for accommodating a net cumulative area AW of winding conductor material, and wherein the cross-sectional area of the shading coils is approximately equal to about ten to fifteen percent of the area AW.

A shaded pole motor comprising a stator assembly having at least one excitable winding, a rotor assembly, and means for supporting the rotor assembly in spaced apart air gap defining relation with the stator assembly and for permitting rotation of the rotor assembly relative to the stator assembly during excitation of said winding;

• said stator assembly including a magnetizeable core having yoke portions, and circumferentially and magnetically spaced apart pole pieces;
• at least one of the pole pieces having a leading pole tip configured to establish a relatively high magnetic reluctance therealong, as compared to another region of such pole piece;
• said at least one of the pole pieces also having at least two short circuited shading coils disposed along the trailing pole tip thereof and having first and second spans respectively;
• and said pole pieces being magnetically spaced apart so that the leading pole tip of each pole piece is spaced from the trailing pole tip of the pole piece adjacent thereto;
• said trailing pole tips and yoke portions mutually establishing windows for conductors of the excitable winding, with the maximum cumulative cross-sectional area of conductors AW being defined as the product of the cross-sectional conductive area of a given size of conductor times the total number of conductors of said given size than can be accommodated in said windows;
• said rotor assembly including a short circuited squirrel cage winding, and the locked rotor torque to maximum torque ratio for the motor being greater than about thirty-three one hundredths;
• the first and second spans of the shading coils both being less than the span of the high reluctance region of the leading pole tip;
• and wherein the shading coil of greater span has a cross-sectional area of from about ten to about fifteen percent of the area AW.

A method of making a stator assembly for a shaded pole motor, the stator assembly comprising a core having a magnetizeable yoke and a plurality of spaced apart magnetizeable pole pieces each having magnetically spaced apart leading and trailing pole tips, with the leading tip of each pole piece displaced in space from the trailing pole tip of a pole piece next adjacent thereto;

• said stator assembly further including at least first and second shading coil means disposed along one of the pole tips of each of the pole pieces, and a winding comprising conductor turns accommodated closely adjacent to at least one of the pole pieces;
• the stator assembly being of particular utility in motors having, during excitation of said winding by a given voltage, a locked rotor torque to maximum torque ratio of at least about 0.33, and the other pole tip of each of the pole pieces being configured to establish a higher reluctance to air gap magnetic flux as compared to the reluctance to air gap magnetic flux along the face of each pole piece in the vicinity of the center of the pole pieces;
• the method comprising:
• providing a first shading coil means accommodating region along each pole piece of a first span;
• providing a second shading coil means accommodating region of a second span along each pole piece with the second span being greater than the first span, but also being less than sixty electrical degrees;
• providing a high magnetic reluctance characteristic on a stepped construction basis generally corresponding to the high magnetic reluctance characteristic of a stepped pole piece having a step of a preselected span in a predetermined range;
• accommodating shading coil means in the shading coil accommodating regions;
• and placing turns of winding material about at least one pole piece.