Rotor for brushless electromotor and method for making same

Abstract

A rotor having permanent magnets for a brushless electromotor includes a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of, at least four magnetic poles. The magnetic poles are alternately provided substantially at equal distances from a rotational axis with slots to receive the respective permanent magnets such that the sides of the permanent magnets facing a rotary shaft have the same polarity. As a result, a compact and efficient rotor is obtained, and damage to or flying off of the permanent magnets is prevented.

We claim: 
     
       1. A rotor having permanent magnets for a brushless electromotor, comprising: a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of, at least four magnetic poles,   slots alternately provided on said magnetic poles at substantially equal distances from a rotational axis to receive said respective permanent magnets such that sides of said permanent magnets facing a rotary shaft have the same polarity,   slits provided on said magnetic poles with said permanent magnets and disposed outside said permanent magnets and oriented in conformity with direction of magnetism and on said magnetic poles with no permanent magnets for guiding magnetic flux to obtain a uniform distribution of magnetic flux on each magnet.   
     
     
       2. The rotor of claim 1, wherein a pair of bridges are provided at opposite ends of each slot so as to connect an outermost end to a base of said magnetic pole associated with this slot, said bridges having a sufficiently narrow width to assure that said bridges are saturated with magnetic flux passing through them. 
     
     
       3. A rotor having permanent magnets for a brushless electromotor, comprising: a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of, at least four magnetic poles,   slots alternatively provided on said magnetic poles it substantially equal distances from a rotational axis to receive said respective permanent magnets such that sides of said permanent magnets facing a rotary shaft have the same polarity,   a pair of bridges provided at opposite ends of each slot so as to connect an outermost end to a base of said magnetic pole associated with this slot, and   a flux limiting groove provided on an outer side of each bridge to reduce a sectional area of said bridge.   
     
     
       4. A rotor having permanent magnets for a brushless electromotor, comprising: a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of, at least four magnetic poles,   said magnetic poles being alternately provided with substantially at equal distances from a rotational axis with slots to receive said respective permanent magnets such that sides of said permanent magnets face a rotary shaft having the same polarity,   a single bridge being provided at a forward end of each slot in the direction of rotation so as to connect an outermost end to a base of said magnetic pole associated with this slot.   
     
     
       5. The rotor of claim 4, wherein said bridge has such a width that a leakage flux flows therethrough and said permanent magnet has such a thickness that a leakage flux is generated at axially opposite ends thereof. 
     
     
       6. The rotor of claim 4, wherein an end of said permanent magnet facing said bridge and axially opposite ends of said permanent magnet are covered with nonmagnetic material. 
     
     
       7. A rotor having permanent magnets for a brushless electromotor, comprising: a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of at least four magnetic poles,   slots alternatively provided on said magnetic poles at substantially equal distances from a rotational axis to receive said respective permanent magnets such that sides of said permanent magnets facing a rotary shaft have the same polarity,   an edge provided on inner periphery of said yoke with said slot for engagement with said permanent magnet as said permanent magnet is forced into said slot such that a tip of said edge is pressed against said permanent magnet.   
     
     
       8. The rotor of claim 7, wherein said silicon steel sheets have pressed recesses for engagement with each other to effect an integral lamination thereof, and projections are formed by inner peripheries of said silicon steel sheets deformed as said pressed recesses are formed in the proximity of said slot. 
     
     
       9. A rotor having permanent magnets for a brushless electromotor, comprising: a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of, at least four magnetic poles,   said magnetic poles being alternately provided with substantially at equal distances from a rotational axis with slots to receive said respective permanent magnets such that sides of said permanent magnets face a rotary shaft have the same polarity.   said yoke with said slot having an inner periphery provided with a projection for engagement with said permanent magnet as the latter is forced into said slot,   each of said projections having a triangular projection for engagement with said permanent magnet, a base of said triangular projection lying nearer to the axis of said yoke than to said inner periphery of said yoke defining said slot, and opposite sides of said triangular projection are connected to said inner periphery of said yoke defining said slot by notches formed at both ends of said base to provide a desired height of said triangular projection.   
     
     
       10. The rotor of claim 9, wherein said edge is provided on at least one of upper and lower inner peripheries of said yoke with said slot. 
     
     
       11. Rotor having permanent magnets for a brushless electromotor, comprising: a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of, at least four magnetic poles,   slots alternately provided on said magnetic being at substantially equal distances from a rotational axis to receive said respective permanent magnets such that sides of said permanent magnets facing rotary shaft have the same polarity,   slits disposed outside said permanent magnets and oriented in conformity with direction of magnetism and each of said magnetic poles with no permanent magnets for guiding magnetic flux to obtain a uniform distribution of magnetic flux on each magnet; and   a heat pipe embedded in said yoke to be brought into contact with a middle portion of an inner side of one of said permanent magnets. .Iadd.   
     
     
       12.  A rotor having permanent magnets for a brushless electromotor, comprising: a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of at least four magnetic poles,   slots provided on said magnetic poles at substantially equal distances from a rotational axis to receive said respective permanent magnets, and   slits provided on said magnetic poles with said permanent magnets and disposed outside said permanent magnets and oriented in conformity with direction of magnetism for guiding magnetic flux to obtain a uniform distribution of magnetic flux on each magnet. .Iaddend..Iadd.13. A rotor according to claim 12, which further comprises a pair of bridges provided at opposite ends of each slot so as to connect an outermost end to a base of said magnetic pole associated with this slot, said bridges having a sufficiently narrow width to assure that said bridges are saturated with magnetic flux passing through them. .Iaddend..Iadd.14. A rotor according to claim 13, which further comprises a flux limiting groove provided on an outer side of each bridge to reduce a sectional area of said bridge. .Iaddend..Iadd.15. A rotor according to claim 14, wherein said bridge has such a width that a leakage flux flows therethrough and said permanent magnet has such a thickness that a leakage flux is generated at axially opposite ends thereof. .Iaddend..Iadd.16. A rotor having permanent magnets for a brushless electromotor, comprising:   a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of at least four magnetic poles,   slots provided on said magnetic poles at substantially equal distance from a rotational axis to receive said permanent magnets,   at least one edge provided on an inner periphery of at least one of said slots for engagement with at least one of said permanent magnets as said one permanent magnet is forced into said one slot such that a tip of said edge is pressed against said one permanent magnet. .Iaddend..Iadd.17. A rotor according to claim 16, wherein said silicon steel sheets having pressed recesses for engagement with each other to effect an integral lamination thereof, and projections are formed by inner peripheries of said silicon steel sheets deformed as said pressed recesses are formed in the proximity of said slots. .Iaddend..Iadd.18. A rotor having permanent magnets for a brushless electromotor, comprising:   a yoke formed from a plurality of silicon steel sheets laminated together and provided along its outer periphery with even number of at least four magnetic poles,   said magnetic poles being provided with substantially at equal distances from the rotational axis with slots to receive said respective permanent magnets,   said yoke with at least one of said slots having an inner periphery provided with a projection for engagement with one of said permanent magnets as the latter is forced into said one slot,   said projection having a triangular projection for engagement with said one permanent magnet, a base of said triangular projection lying nearer to the axis of said yoke than to said inner periphery of said yoke defining said one slot, and opposite sides of said triangular projection being connected to said inner periphery of said yoke defining said one slot by notches formed at both ends of said base to provide a desired height of said   
     
     
        triangular projection. .Iaddend..Iadd.19.  A rotor according to claim 18, wherein said edge is provided on at least one of upper and lower inner peripheries of said yoke with said slot. .Iaddend..Iadd.20. A rotor according to claim 12, which further comprises a heat pipe embedded in said yoke to be brought into contact with a middle portion of an inner side of one of said permanent magnets. .Iaddend.