METHODS AND APPARATUS FOR A PERMANENT MAGNET MACHINE WITH ADDED ROTOR SLOTS
An internal permanent magnet machine (“IPM machine”) of the type used, for example, with traction motors and hybrid electric vehicles, includes a rotor with additional, small rotor slots configured to provide and averaging effect with respect to rotor barriers provided therein.
1 . An interior permanent magnet machine comprising:
a wound stator;
a rotor configured to magnetically interact with the wound stator, the rotor having an outer surface;
a plurality of rotor barriers provided within the rotor;
a plurality of permanent magnets disposed within the rotor, the plurality of permanent magnets having a minimum distance to the outer surface; and
a plurality of additional slots provided within the rotor at a distance from the outer surface that is less than or equal to the minimum distance of the plurality permanent magnets.
2 . The interior permanent magnet machine of claim 1 , wherein the additional slots have a cross-sectional area that is substantially less than an aggregate cross-sectional area of the rotor barriers.
3 . The interior permanent magnet machine of claim 1 , wherein the plurality of magnets are associated with a plurality poles, and wherein the plurality of additional slots comprises exactly two additional slots.
4 . The interior permanent magnet machine of claim 1 , wherein the plurality of magnets are configured in pairs defining a concave angle toward the outer surface of the rotor.
5 . The interior permanent magnet machine of claim 1 , wherein the plurality of additional slots are less than approximately 1.5 mm from the outer surface of the rotor.
6 . The interior permanent magnet machine of claim 1 , wherein the plurality of additional slots are evenly distributed around the outer surface of the rotor.
7 . The interior permanent magnet machine of claim 1 , wherein the plurality of additional slots are configured to average out the effect on torque ripple produced by the plurality of rotor barriers.
8 . A method of making an interior permanent magnet machine, comprising:
providing a wound stator;
providing a rotor configured to magnetically interact with the wound stator, the rotor having an outer surface;
forming a plurality of rotor barriers within the rotor;
placing a plurality of permanent magnets within the rotor, the plurality of permanent magnets having a minimum distance to the outer surface; and
forming a plurality of additional slots within the rotor at a distance from the outer surface that is less than or equal to the minimum distance of the plurality permanent magnets.
9 . The method of claim 8 , wherein the additional slots have a cross-sectional area that is substantially less than an aggregate cross-sectional area of the rotor barriers.
10 . The method of claim 8 , wherein the plurality of magnets are associated with a plurality poles, and wherein the plurality of additional slots comprises exactly two additional slots.
11 . The method of claim 8 , wherein the plurality of magnets are configured in pairs defining a concave angle toward the outer surface of the rotor.
12 . The method of claim 8 , wherein the plurality of additional slots are less than approximately 1.5 mm from the outer surface of the rotor.
13 . The method of claim 8 , wherein the plurality of additional slots are evenly distributed around the outer surface of the rotor.
14 . The method of claim 8 , wherein the plurality of additional slots are configured to average out the effect on torque ripple produced by the plurality of rotor barriers.
15 . A traction motor of the type used in connection with a hybrid electric vehicle, the traction motor comprising:
a wound stator;
a rotor configured to magnetically interact with the wound stator, the rotor having an outer surface;
a plurality of rotor barriers provided within the rotor;
a plurality of permanent magnets disposed within the rotor, the plurality of permanent magnets having a minimum distance to the outer surface; and
a plurality of additional slots provided within the rotor at a distance from the outer surface that is less than or equal to the minimum distance of the plurality permanent magnets.
16 . The traction motor of claim 15 , wherein the additional slots have a cross-sectional area that is substantially less than an aggregate cross-sectional area of the rotor barriers.
17 . The interior permanent magnet machine of claim 15 , wherein the plurality of magnets are associated with a plurality poles, and wherein the plurality of additional slots comprises exactly two additional slots.
18 . The interior permanent magnet machine of claim 15 , wherein the plurality of magnets are configured in pairs defining a concave angle toward the outer surface of the rotor.
19 . The interior permanent magnet machine of claim 15 , wherein the plurality of additional slots are less than approximately 1.5 mm from the outer surface of the rotor.
20 . The interior permanent magnet machine of claim 15 , wherein the plurality of additional slots are configured to average out the effect on torque ripple produced by the plurality of rotor barriers.