Motor, method for manufacturing rotor, and electric power steering apparatus

Abstract

A motor is provided with a rotor of which an inner portion made from a material having a lower density than an outer portion is fitted inside the outer portion around whose outer surface magnets are fixed; wherein the inner portion is shrink fitted or pressure fitted inside the outer portion. The rotor is manufactured by a simple process without the need to keep the rotor at high temperature for a set period of time as in the case of sinter bonding. A plurality of cut out holes is formed in the inner portion to make the rotor more lightweight.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional drawing showing the construction of the motor of the present invention;

FIG. 2 is a horizontal cross-sectional drawing of the rotor as seen from the section II-II of FIG. 1;

FIG. 3 is a drawing that explains the construction for fastening the outer portion and inner portion of the rotor;

FIG. 4 is a drawing that explains the construction for fastening the outer portion and inner portion of the rotor; and

FIG. 5 is a drawing showing an example of an electric power steering apparatus provided with the motor of the present invention.

Claims

1. A motor, comprising: a rotor of which an inner portion made from a material having a lower density than an outer portion is fitted inside said outer portion around whose outer surface magnets are fixed; whereinsaid inner portion is shrink fitted inside said outer portion.

2. The motor of claim 1, wherein cut out holes are formed in said inner portion.

3. The motor of claim 1, wherein said outer portion is made of ferrous material, and said inner portion is made of aluminum or magnesium.

4. A motor, comprising: a rotor of which an inner portion made from a material having a lower density than an outer portion is fitted inside said outer portion around whose outer surface magnets are fixed; whereinsaid inner portion is pressure fitted inside said outer portion.

5. The motor of claim 4, wherein cut out holes are formed in said inner portion.

6. The motor of claim 4, wherein said outer portion is made of ferrous material, and said inner portion is made of aluminum or magnesium.

7. A method for manufacturing a rotor of which an inner portion made from a material having a lower density than an outer portion is fitted inside said outer portion around whose outer surface magnets are to be fixed, comprising the steps of: preparing a cylindrical-shaped first member to be said outer portion, and a column-shaped second member to be said inner portion, so that the inner diameter of said first member is less than the outer diameter of said second member;heating said first member so that the inner diameter of said first member becomes greater than the outer diameter of said second member;fitting said second member inside of said expanded first member; andcooling said first member to integrate said first member and said second member by shrink fitting.

8. The manufacturing method of claim 7, wherein said first member is made from a ferrous material, and said second member is made from aluminum or magnesium.

9. A method for manufacturing a rotor of which an inner portion made from a material having a lower density than an outer portion is fitted inside said outer portion around whose outer surface magnets are to be fixed, comprising the steps of: preparing a cylindrical-shaped first member to be said outer portion, and a column-shaped second member to be said inner portion, so that the inner diameter of said first member is less than the outer diameter of said second member;positioning said prepared first and second members so that they are concentric; andapplying pressure to one or both of said first member and said second member in the axial direction to fit said second member inside said first member and integrate said first member and second member by pressure fitting.

10. The manufacturing method of claim 9, wherein said first member is made from a ferrous material, and said second member is made from aluminum or magnesium.

11. An electric power steering apparatus comprising: a steering wheel;a steering mechanism that is connected to said steering wheel; anda motor that assists steering by applying its torque to said steering mechanism; whereinsaid motor comprises a rotor of which an inner portion made from a material having a lower density than an outer portion is fitted by shrink fitting or pressure fitting inside said outer portion around whose outer surface magnets are fixed.

12. The electric power steering apparatus of claim 11, wherein cut out holes are formed in said inner portion.

13. The electric power steering apparatus of claim 11, wherein said outer member is made of ferrous material, and said inner member is made of aluminum or magnesium.