(12) United States Patent (12) United States Patent
`
`Nitta et ai.
`Nitta et al.
`
`
`
`111111 111111
`
`
`1111111111111111111111111111111111111111111111111111111111111 1111111111111111111111111111111111111111111111111111111111111
`
`US006265804Bl US006265804Bl
`US 6,265,804 BI
`US 6,265,804 Bl
`*Jui. 24, 2001
`*Jul. 24, 2001
`
`(10) Patent No.:
`(10) Patent No.:
`(45) Date of Patent:
`(45) Date of Patent:
`
`(54) ELECTRIC MOTOR WITH SPLIT STATOR
`(54) ELECTRIC MOTOR WITH SPLIT STATOR
`CORE AND METHOD OF MAKING THE
`CORE AND METHOD OF MAKING THE
`SAME
`SAME
`
`
`
`(75) (75)
`
`Inventors: Isamu Nitta, Yokahama; Kinya
`Inventors: Isamu Nitta, Yokahama; Kinya
`Hayashi, Toki, both of (JP)
`Hayashi, Toki, both of (lP)
`
`(73) Assignee: Kabushiki Kaisha Toshiba, Kanagawa
`(73) Assignee: Kabushiki Kaisha Toshiba, Kanagawa
`(lP)
`(JP)
`
`
`
`( *) Notice: ( *) Notice:
`
`
`This patent issued on a continued pros(cid:173)This patent issued on a continued pros(cid:173)
`
`ecution application filed under 37 CFR ecution application filed under 37 CFR
`
`1.53( d), and is subject to the twenty year 1.53( d), and is subject to the twenty year
`
`patent term provisions of 35 U.S.C. patent term provisions of 35 U.S.c.
`154(a)(2).
`154(a)(2).
`
`
`Subject to any disclaimer, the term of this Subject to any disclaimer, the term of this
`
`patent is extended or adjusted under 35 patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`U.S.c. 154(b) by 0 days.
`
`(21) Appl. No.: 09/391,450
`(21) Appl. No.: 09/391,450
`
`(22) Filed:
`(22) Filed:
`
`Sep. 8, 1999
`Sep. 8, 1999
`
`(30)
`(30)
`
`Foreign Application Priority Data
`Foreign Application Priority Data
`
`
`Sep. 8, 1998 Sep. 8, 1998
`
`Dec. 22, 1998 Dec. 22, 1998
`
`Aug. 17, 1999 Aug. 17, 1999
`
`
`(JP) ................................................. 10-253716 (JP) ................................................. 10-253716
`
`(JP) ................................................. 10-364401 (JP) ... ... ... ... .... ... ... ... ... .... ... ... ... ... ..... 10-364401
`(JP) ................................................. 11-230540
`(JP) ................................................. 11-230540
`
`Int. Cl?
`Int. CI?
`
`
`
`(51) (51)
`
`.............................. H02K 1!12; H02K 1!06;
`.............................. H02K 1/12; H02K 1/06;
`
`H02K 1!00; H02K 1/04 H02K 1/00; H02K 1/04
`(52) U.S. Cl. .......................... 310/259; 310/217; 310/193;
`(52) U.S. CI. .......................... 310/259; 310/217; 310/193;
`310/43
`310/43
`(58) Field of Search ..................................... 310/269, 254,
`(58) Field of Search ..................................... 310/269, 254,
`
`310/258, 259, 216, 217, 218, 179, 185, 310/258, 259, 216, 217, 218, 179, 185,
`
`193, 43, 45; 29/596 193, 43, 45; 29/596
`
`
`
`(56) (56)
`
`References Cited
`References Cited
`
`
`U.S. PATENT DOCUMENTS U.S. PATENT DOCUMENTS
`
`4,015,154 * 3/1977 Tanaka et a!. 4,015,154 * 3/1977 Tanaka et al.
`
`......................... 310/42 ......................... 310/42
`
`4,365,180 * 12/1982 Licata et a!. ......................... 310/216 4,365,180 * 12/1982 Licata et al. ......................... 310/216
`
`4,665,329 * 5/1987 Raschbichler .......................... 310/13 4,665,329 * 5/1987 Raschbichler .......................... 310/13
`
`4,672,253 * 6/1987 Tajima et a!. ........................ 310/269 4,672,253 * 6/1987 Tajima et al. ........................ 310/269
`
`4,818,911 * 4/1989 Taguchi et a!. ...................... 310/259 4,818,911 * 4/1989 Taguchi et al. ...................... 310/259
`
`4,990,809 * 2/1991 Artus et a!. .......................... 310/192 4,990,809 * 2/1991 Artus et al. .......................... 310/192
`
`5,592,731 * 1!1997 Huang eta!. .......................... 29!596 5,592,731 * 1/1997 Huang et al. .......................... 29/596
`
`5,739,614 * 4/1998 Suzuki eta!. ........................ 310/180 5,739,614 * 4/1998 Suzuki et al. ........................ 310/180
`
`5,859,486 * 1!1999 Nakahara et a!. 5,859,486 * 1/1999 Nakahara et al.
`
`................... 310/254 ................... 310/254
`
`5,912,515 * 6/1999 Ackermann et a!. .............. 310/67 R 5,912,515 * 6/1999 Ackermann et al. .............. 310/67 R
`
`
`
`FOREIGN PATENT DOCUMENTS FOREIGN PATENT DOCUMENTS
`
`
`4-29536 4-29536
`
`1!1992 (JP) . 1/1992 (JP).
`
`* cited by examiner * cited by examiner
`
`
`Primary Examiner-Elvin Enad Primary Examiner-Elvin Enad
`
`Assistant Examiner-Dang Dinh Le Assistant Examiner---nang Dinh Le
`(74) Attorney, Agent, or Firm-Pillsbury Winthrop LLP
`(74) Attorney, Agent, or Firm-Pillsbury Winthrop LLP
`
`(57)
`(57)
`
`ABSTRACT
`ABSTRACT
`
`
`An electric motor includes a rotor and a stator including a An electric motor includes a rotor and a stator including a
`
`plurality of unit cores each of which has two ends. The unit plurality of unit cores each of which has two ends. The unit
`
`cores are disposed so that the ends of each unit core are cores are disposed so that the ends of each unit core are
`
`adjacent to the ends of the neighboring unit cores respec(cid:173)adj acent to the ends of the neighboring unit cores respec(cid:173)
`
`tively. Each unit core includes a yoke section and a plurality tively. Each unit core includes a yoke section and a plurality
`
`of salient poles which are integral with the yoke section and of salient poles which are integral with the yoke section and
`
`on which windings are wound respectively. Adjacent por(cid:173)on which windings are wound respectively. Adjacent por(cid:173)
`
`tions of the unit cores are selected so that magnetic fluxes tions of the unit cores are selected so that magnetic fluxes
`
`passing through the respective adjacent portions are sub(cid:173)passing through the respective adjacent portions are sub(cid:173)
`
`stantially the same. stantially the same.
`
`12 Claims, 14 Drawing Sheets
`12 Claims, 14 Drawing Sheets
`
`158
`15a
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`15b
`15b
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`17
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`
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`17 17
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`
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`29d 29c 29d 29c
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`
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`29c 29d 29c 29d
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`
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`31 31
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`Page 1 of 22
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`PETITIONERS' EXHIBIT 1003
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`

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`u.s. Patent
`U.S. Patent
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`Jul. 24, 2001 Jui. 24, 2001
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`
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`Sheet 1 of 14 Sheet 1 of 14
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`US 6,265,804 Bl US 6,265,804 BI
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`3 3
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`2 2
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`3
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`
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`FIG. 1 FIG. 1
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`Page 2 of 22
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`u.s. Patent
`U.S. Patent
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`Jul. 24, 2001 Jui. 24, 2001
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`Sheet 2 of 14
`Sheet 2 of 14
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`US 6,265,804 Bl US 6,265,804 BI
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`8a 7
`8'1 7
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`11 c] 11
`11 !i\ 11
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`Be
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`7 7
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`8b
`8b
`
`Be
`Be
`
`
`
`FIG. 2 FIG. 2
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`Page 3 of 22
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`

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`u.s. Patent
`U.S. Patent
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`Jul. 24, 2001 Jui. 24, 2001
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`
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`Sheet 3 of 14 Sheet 3 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`15a
`15a
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`15b
`15b
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`~17
`
`17
`17
`
`17
`
`
`
`FIG. 3 FIG. 3
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`Page 4 of 22
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`

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`u.s. Patent
`U.S. Patent
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`Jui. 24, 2001
`Jul. 24, 2001
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`Sheet 4 of 14
`Sheet 4 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`
`
`20j 20j
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`
`
`20i 20i
`
`
`
`20h 20h
`
`20g
`20g
`
`20f
`
`
`
`20e 20e
`
`20d
`20d
`
`20e
`
`
`
`201 201
`
`18
`18
`
`20 20
`20 20
`
`
`
`17 17
`
`20f
`20f
`
`20g
`
`20h
`
`
`
`20i 20i
`
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`20b 20b
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`20c 20e
`
`20d
`
`20e
`20e
`
`
`
`20h 20h
`
`FIG. 4
`FIG. 4
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`Page 5 of 22
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`

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`u.s. Patent
`U.S. Patent
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`
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`Jul. 24, 2001 Jui. 24, 2001
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`
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`Sheet 5 of 14 Sheet 5 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`
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`29 29
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`
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`31 31
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`
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`FIG. 5 FIG. 5
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`Page 6 of 22
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`

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`u.s. Patent
`U.S. Patent
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`Jul. 24, 2001 Jui. 24, 2001
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`
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`Sheet 6 of 14 Sheet 6 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`
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`23 23
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`
`24 24
`25
`25
`29c
`29c
`
`
`
`31 31
`
`29
`29
`290
`29d
`29b
`29b
`29d
`29d
`
`31
`31
`
`29d
`29d
`
`29d
`
`28
`
`31
`31
`
`
`
`FIG. 6 FIG. 6
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`Page 7 of 22
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`u.s. Patent
`U.S. Patent
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`
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`Jul. 24, 2001 Jui. 24, 2001
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`
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`Sheet 7 of 14 Sheet 7 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`
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`29 29
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`
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`29d 29d
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`FIG. 7
`FIG. 7
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`Page 8 of 22
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`u.s. Patent
`U.S. Patent
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`Jul. 24, 2001 Jui. 24, 2001
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`
`
`Sheet 8 of 14 Sheet 8 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`Page 9 of 22
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`

`

`u.s. Patent
`U.S. Patent
`
`
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`Jul. 24, 2001 Jui. 24, 2001
`
`
`
`Sheet 9 of 14 Sheet 9 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`
`
`40 40
`
`
`
`FIG. 9 FIG. 9
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`Page 10 of 22
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`

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`u.s. Patent
`U.S. Patent
`
`
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`Jul. 24, 2001 Jui. 24, 2001
`
`
`
`Sheet 10 of 14 Sheet 10 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`-------42 -------42
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`F I G. 1 0 FIG. 1 0
`
`Page 11 of 22
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`

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`u.s. Patent
`U.S. Patent
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`
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`Jul. 24, 2001 Jui. 24, 2001
`
`
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`Sheet 11 of 14 Sheet 11 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`42
`
`43a
`42
`
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`F I G. 11 FIG. 11
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`Page 12 of 22
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`u.s. Patent
`U.S. Patent
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`Jul. 24, 2001 Jui. 24, 2001
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`
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`Sheet 12 of 14 Sheet 12 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`29d
`29d
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`51 51
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`FIG. 1 2
`F I G. 1 2
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`FIG. 1 3
`F I G. 1 3
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`52
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`F I G. 1 4
`FIG. 1 4
`
`FIG. 1 5
`F I G. 1 5
`
`Page 13 of 22
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`

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`u.s. Patent
`U.S. Patent
`
`Jui. 24, 2001
`Jul. 24, 2001
`
`Sheet 13 of 14
`Sheet 13 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`Page 14 of 22
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`u.s. Patent
`U.S. Patent
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`Jul. 24, 2001 Jui. 24, 2001
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`
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`Sheet 14 of 14 Sheet 14 of 14
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`
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`US 6,265,804 Bl US 6,265,804 BI
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`63a
`63a
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`F I G. 1 8 FIG. 1 8
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`Page 15 of 22
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`

`

`US 6,265,804 B 1
`US 6,265,804 B 1
`
`
`1 1
`ELECTRIC MOTOR WITH SPLIT STATOR
`ELECTRIC MOTOR WITH SPLIT STATOR
`CORE AND METHOD OF MAKING THE
`CORE AND METHOD OF MAKING THE
`SAME
`SAME
`
`
`
`BACKGROUND OF THE INVENTION BACKGROUND OF THE INVENTION
`
`
`
`5 5
`
`SUMMARY OF THE INVENTION
`SUMMARY OF THE INVENTION
`
`
`Therefore, an object of the present invention is to provide Therefore, an object of the present invention is to provide
`
`an electric motor in which the unbalance in the magnetic an electric motor in which the unbalance in the magnetic
`
`attractive forces acting between the unit cores can be attractive forces acting between the unit cores can be
`
`restrained so that the vibration and noise are prevented, and restrained so that the vibration and noise are prevented, and
`
`a method of making the motor. a method of making the motor.
`
`Another object is to provide an electric motor which is Another object is to provide an electric motor which is
`
`provided with a stator core including a plurality of unit cores provided with a stator core including a plurality of unit cores
`
`and in which the iron loss can be reduced. and in which the iron loss can be reduced.
`
`The present invention provides an electric motor com(cid:173)The present invention provides an electric motor com(cid:173)
`
`prising a rotor and a stator including a plurality of unit cores prising a rotor and a stator including a plurality of unit cores
`
`each of which has two ends. The unit cores are disposed so each of which has two ends. The unit cores are disposed so
`
`that the ends of each unit core are adjacent to the ends of the that the ends of each unit core are adj acent to the ends of the
`
`neighboring unit cores respectively. Each unit core includes neighboring unit cores respectively. Each unit core includes
`
`a yoke section and a plurality of salient poles which are a yoke section and a plurality of salient poles which are
`
`integral with the yoke section and on which concentrated integral with the yoke section and on which concentrated
`
`windings are wound. In this construction, each unit core is windings are wound. In this construction, each unit core is
`
`disposed so that the yoke section thereof is adjacent to the disposed so that the yoke section thereof is adjacent to the
`
`yoke sections of the neighboring unit cores and so that the yoke sections of the neighboring unit cores and so that the
`
`salient poles thereof are separate from the salient poles of the 60 salient poles thereof are separate from the salient poles of the 60
`
`neighboring unit cores. Further, the salient poles are neighboring unit cores. Further, the salient poles are
`
`arranged circumferentially with a regular pitch. Further, a arranged circumferentially with a regular pitch. Further, a
`
`number of the salient poles of each unit core is equal to a number of the salient poles of each unit core is equal to a
`
`number of phases of the windings multiplied by any integer. number of phases of the windings multiplied by any integer.
`
`Additionally, each of the portions of the unit cores adjacent 65 Additionally, each of the portions of the unit cores adjacent 65
`
`to each other is set so as to assume an angular position where to each other is set so as to assume an angular position where
`
`a multiple obtained by multiplying a pitch angle of the a multiple obtained by multiplying a pitch angle of the
`
`
`1. Field of the Invention 1. Field of the Invention
`
`This invention relates to an electric motor provided with This invention relates to an electric motor provided with
`
`a split stator core including a plurality of circumferentially a split stator core including a plurality of circumferentially
`
`disposed unit cores and a method of making such a motor. disposed unit cores and a method of making such a motor.
`
`2. Description of the Prior Art 2. Description of the Prior Art
`
`For the purpose of effective utilization of steel material, For the purpose of effective utilization of steel material,
`
`the prior art has provided an annular split stator core formed the prior art has provided an annular split stator core formed
`
`by disposing a plurality of circumferentially split unit cores by disposing a plurality of circumferentially split unit cores
`
`into a generally circularly or squarely annular configuration. into a generally circularly or squarely annular configuration.
`
`More specifically, when annular steel sheets which are to be More specifically, when annular steel sheets which are to be
`
`stacked into a stator core are punched out of steel sheets, stacked into a stator core are punched out of steel sheets,
`
`portions of each steel sheet outside and inside the annular portions of each steel sheet outside and inside the annular
`
`configuration are left unused. The above-mentioned annular configuration are left unused. The above-mentioned annular
`
`split stator core provided by the prior art is directed to a split stator core provided by the prior art is directed to a
`
`reduction in such unused portions of the steel sheets. reduction in such unused portions of the steel sheets.
`
`However, a location of portions of the unit cores adjacent However, a location of portions of the unit cores adjacent
`
`to each other is selected at random. This results in unbalance to each other is selected at random. This results in unbalance
`
`in magnetic attractive forces acting between the unit cores, in magnetic attractive forces acting between the unit cores,
`
`whereupon vibration and noise are produced. whereupon vibration and noise are produced.
`
`Each of a number of steel sheets stacked together into a Each of a number of steel sheets stacked together into a
`
`unit core is formed by punching a silicon steel sheet having unit core is formed by punching a silicon steel sheet having
`
`a surface treated for electrical insulation by a press. The a surface treated for electrical insulation by a press. The
`
`punching sometimes results in warpage and/or burrs in ends punching sometimes results in warpage and/or burrs in ends
`of the silicon steel sheet. In a stator core formed by annularly 30
`of the silicon steel sheet. In a stator core formed by annularly 30
`
`disposing a plurality of unit cores, when the unit cores disposing a plurality of unit cores, when the unit cores
`
`adjacent to each other are displaced in the direction of stack adj acent to each other are displaced in the direction of stack
`
`of the steel sheets or when one or more steel sheets have the of the steel sheets or when one or more steel sheets have the
`
`warpage and/or burrs, the steel sheets of each unit core are warpage and/or burrs, the steel sheets of each unit core are
`
`electrically short-circuited by the ends of the steel sheets of electrically short-circuited by the ends of the steel sheets of
`
`the other unit core. This results in eddy currents flowing in the other unit core. This results in eddy currents flowing in
`
`the direction of stack of steel sheets in the unit core, so that the direction of stack of steel sheets in the unit core, so that
`
`an iron loss is increased. an iron loss is increased.
`
`
`
`25 25
`
`2
`2
`
`salient poles agrees with a multiple obtained by multiplying salient poles agrees with a multiple obtained by multiplying
`
`a pitch angle of magnetic poles of the rotor. a pitch angle of magnetic poles of the rotor.
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`Upon excitation of the windings of the above-described Upon excitation of the windings of the above-described
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`motor, a rotating magnetic field is generated so that the rotor motor, a rotating magnetic field is generated so that the rotor
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`is rotated. An amount of magnetic flux passing through each is rotated. An amount of magnetic flux passing through each
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`yoke section changes momentarily as the rotor is rotated. yoke section changes momentarily as the rotor is rotated.
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`However, when a plurality of salient poles are provided so However, when a plurality of salient poles are provided so
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`as to correspond to each of the phases, the yoke sections of as to correspond to each of the phases, the yoke sections of
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`the stator core have at an interval of a predetermined angle the stator core have at an interval of a predetermined angle
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`10 portions where amounts of magnetic flux passing there(cid:173)10 portions where amounts of magnetic flux passing there(cid:173)
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`through become the same. In the present invention, the through become the same. In the present invention, the
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`number of salient poles of each unit core is determined so number of salient poles of each unit core is determined so
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`that the interval of the predetermined angle coincides with that the interval of the predetermined angle coincides with
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`the adjacent portions of the unit cores. Accordingly, the the adjacent portions of the unit cores. Accordingly, the
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`15 amounts of magnetic flux passing through the respective 15 amounts of magnetic flux passing through the respective
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`adjacent portions of the unit cores become approximately adjacent portions of the unit cores become approximately
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`the same although changing momentarily. Consequently, the same although changing momentarily. Consequently,
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`when the adjacent portions of the unit cores are located so when the adjacent portions of the unit cores are located so
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`as to correspond to positions where the magnetic fluxes as to correspond to positions where the magnetic fluxes
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`20 passing the respective yoke sections are substantially the 20 passing the respective yoke sections are substantially the
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`same, the magnetic attractive forces acting between the unit same, the magnetic attractive forces acting between the unit
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`cores can be balanced to be canceled, whereupon occurrence cores can be balanced to be canceled, whereupon occurrence
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`of the vibration and noise due to the magnetic attractive of the vibration and noise due to the magnetic attractive
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`forces can be prevented. forces can be prevented.
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`Each unit core preferably includes the salient poles the Each unit core preferably includes the salient poles the
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`number of which is represented as CM(Nt/CD(Nt, Np ), Nf) number of which is represented as CM(Nt/CD(Nt, Np), Nf)
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`where CM(A, B) is a common multiple of integers A and B, where CM(A, B) is a common multiple of integers A and B,
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`CD(A, B) is a common divisor of integers A and B, Nt is a CD(A, B) is a common divisor of integers A and B, Nt is a
`total number of salient poles of a stator, which is equal to or total number of salient poles of a stator, which is equal to or
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`larger than 2, Np is a total number of magnetic poles of a larger than 2, Np is a total number of magnetic poles of a
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`rotor, which is equal to or larger than 2, and Nf is the number rotor, which is equal to or larger than 2, and Nf is the number
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`of winding phases. of winding phases.
`In a case where the positions where the magnetic fluxes
`In a case where the positions where the magnetic fluxes
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`passing through the yoke sections are substantially the same 35 passing through the yoke sections are substantially the same
`35
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`are obtained when a rotor used With the above-described are obtained when a rotor used With the above-described
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`stator has a plurality of magnetic poles, a total number of stator has a plurality of magnetic poles, a total number of
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`magnetic poles of the rotor is preferably equal to the number magnetic poles of the rotor is preferably equal to the number
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`of unit cores multiplied by any positive number, in addition of unit cores multiplied by any positive number, in addition
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`to the condition that the number of salient poles of each unit 40 to the condition that the number of salient poles of each unit
`40
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`core is equal to the number of winding phases multiplied by core is equal to the number of winding phases multiplied by
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`any positive integer. any positive integer.
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`The number of unit cores is obtained when a divisor The number of unit cores is obtained when a divisor
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`common to the above-mentioned total numbers Nt and Np is common to the above-mentioned total numbers Nt and Np is
`45 found. Accordingly, when the total number Np is divided by 45 found. Accordingly, when the total number Np is divided by
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`the number of unit cores, the least number of salient poles the number of unit cores, the least number of salient poles
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`that can be provided on a single unit core is obtained. that can be provided on a single unit core is obtained.
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`Accordingly, the number of salient poles of each unit core Accordingly, the number of salient poles of each unit core
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`can be obtained from a multiple common to the least number can be obtained from a multiple common to the least number
`50 of salient poles and the total number Nf of winding phases. 50 of salient poles and the total number Nf of winding phases.
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`The salient poles preferably have different shapes of distal The salient poles preferably have different shapes of distal
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`ends and arranged in a pattern in which said salient poles ends and arranged in a pattern in which said salient poles
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`having the different shapes of distal ends adjoin each other, having the different shapes of distal ends adjoin each other,
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`the pattern being repeated circumferentially. The number of the pattern being repeated circumferentially. The number of
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`55 the salient poles of each unit core is equal to a common 55 the salient poles of each unit core is equal to a common
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`multiple to a number of the distal end shapes of the salient multiple to a number of the distal end shapes of the salient
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`poles and the number of winding phases. poles and the number of winding phases.
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`In the above-described arrangement pattern of the salient In the above-described arrangement pattern of the salient
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`poles, the arrangement pattern of salient poles of each unit poles, the arrangement pattern of salient poles of each unit
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`core needs to correspond to those in the adjacent unit cores core needs to correspond to those in the adjacent unit cores
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`in addition to the condition that the number of salient poles in addition to the condition that the number of salient poles
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`of each unit core is equal to the number of winding phases of each unit core is equal to the number of winding phases
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`multiplied by any positive integer. This is met when the multiplied by any positive integer. This is met when the
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`number of salient poles is a common multiple to the number number of salient poles is a common multiple to the number
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`of types of distal ends of the salient poles and the number of of types of distal ends of the salient poles and the number of
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`winding phases. In this case, the multiple is preferably a winding phases. In this case, the multiple is preferably a
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`least common multiple. least common multiple.
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`Page 16 of 22
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`

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`US 6,265,804 B 1 US 6,265,804 B 1
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`3 3
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`The invention also provides an electric motor comprising The invention also provides an electric motor comprising
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`a rotor and a stator core including a plurality of unit cores a rotor and a stator core including a plurality of unit cores
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`each of which has two ends. The unit cores are disposed so each of which has two ends. The unit cores are disposed so
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`that the ends of each unit core are adjacent to the ends of the that the ends of each unit core are adj acent to the ends of the
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`neighboring unit cores with electrically insulating clearance neighboring unit cores with electrically insulating clearance
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`maintaining members being interposed therebetween, maintaining members being interposed therebetween,
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`respectively. Each unit core is formed by stacking a number respectively. Each unit core is formed by stacking a number
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`of steel sheets each of which has a surface to which a of steel sheets each of which has a surface to which a
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`treatment for electrical insulation is applied. Since the ends treatment for electrical insulation is applied. Since the ends
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`of the adjacently disposed unit cores are separated from each of the adjacently disposed unit cores are separated from each
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`other by the clearance maintaining members, the ends can be other by the clearance maintaining members, the ends can be
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`insulated from each other such that eddy current loss is insulated from each other such that eddy current loss is
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`reduced. reduced.
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`In a preferred form, the clearance between the ends of In a preferred form, the clearance between the ends of
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`each unit core and the neighboring unit cores is set to be in each unit core and the neighboring unit cores is set to be in
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`a range between 0.01 and 0.15 mm. a range between 0.01 and 0.15 mm.
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`BRIEF DESCRIPTION OF THE DRAWINGS BRIEF DESCRIPTION OF THE DRAWINGS
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`Other objects, features and advantages of the present Other objects, features and advantages of the present
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`invention will become clear upon reviewing the following invention will become clear upon reviewing the following
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`description of the preferred embodiments, made with refer(cid:173)description of the preferred embodiments, made with refer(cid:173)
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`ence to the accompanying drawings, in which: ence to the accompanying drawings, in which:
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`FIG. 1 is a plan view of a stator core of an electric motor FIG. 1 is a plan view of a stator core of an electric motor
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`of a first embodiment in accordance with the present inven(cid:173)of a first embodiment in accordance with the present inven(cid:173)
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`tion; tion;
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`FIG. 2 is a plan view of a stator core and a rotor of an FIG. 2 is a plan view of a stator core and a rotor of an
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`electric motor of a second embodiment in accordance with electric motor of a second embodiment in accordance with
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`the invention; the invention;
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`FIG. 3 is a plan view of an assembly of a rotor and stator FIG. 3 is a plan view of an assembly of a rotor and stator
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`core of an electric motor of a third embodiment in accor(cid:173)core of an electric motor of a third embodiment in accor(cid:173)
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`dance with the invention; dance with the invention;
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`FIG. 4 is a view similar to FIG. 3, showing a modified FIG. 4 is a view similar to FIG. 3, showing a modified
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`form of the third embodiment; form of the third embodiment;
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`FIG. 5 is an enlarged transverse sectional plan view of FIG. 5 is an enlarged transverse sectional plan view of
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`connecting portions of unit cores in an electric motor of a connecting portions of unit cores in an electric motor of a
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`fourth embodiment in accordance with the invention; fourth embodiment in accordance with the invention;
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`FIG. 6 is a plan view of the motor of the fourth embodi(cid:173)FIG. 6 is a plan view of the motor of the fourth embodi(cid:173)
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`ment; ment;
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`FIG. 7 is an enlarged longitudinal sectional plan view of FIG. 7 is an enlarged longitudinal sectional plan view of
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`the connecting portions of the motor shown in FIG. 6; the connecting portions of the motor shown in FIG. 6;
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`FIG. 8 is a graph showing the relationship between the FIG. 8 is a graph showing the relationship between the
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`clearance between the ends of the unit cores and the iron clearance between the ends of the unit cores and the iron
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`loss; loss;
`FIG. 9 is a transverse sectional plan view of an electric 45 FIG. 9 is a transverse sectional plan view of an electric 45
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`motor of a fifth embodiment in accordance with the inven-motor of a fifth embodiment in accordance with the inven-
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`tion; tion;
`FIG. 10 is a partially enlarged transverse sectional plan
`FIG. 10 is a partially enlarged transverse sectional plan
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`view of the motor shown in FIG. 9; view of the motor shown in FIG. 9;
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`FIG. 11 is a transverse sectional plan view of a molding FIG. 11 is a transverse sectional plan view of a molding
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`die, showing a method of making the motor shown in FIG. die, showing a method of making the motor shown in FIG.
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`9; 9;
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`30 30
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`4 4
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`motor of the inner rotor type in which a rotor is disposed motor of the inner rotor type in which a rotor is disposed
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`inside a stator. Referring to FIG. 1, a split stator core 1 of the inside a stator. Referring to FIG. 1, a split stator core 1 of the
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`motor is shown. The split stator core 1 comprises three unit motor is shown. The split stator core 1 comprises three unit
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`cores 2. Each unit core 2 is made by stacking a number of cores 2. Each unit core 2 is made by stacking a number of
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`5 punched silicon steel sheets. Outer circumferential faces of 5 punched silicon steel sheets. Outer circumferential faces of
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`ends of each unit core 2 adjacent to ends of the other unit ends of each unit core 2 adjacent to ends of the other unit
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`cores 2 are welded together to be connected to each other. As cores 2 are welded together to be connected to each other. As
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`a result, each end of each unit core is adjacent to one of the a result, each end of each unit core is adj acent to one of the
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`ends of the neighboring unit core with a minute clearance ends of the neighboring unit core with a minute clearance
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`10 therebetween. 10 therebetween.
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`Each unit core 2 includes a yoke section 3 and three Each unit core 2 includes a yoke section 3 and three
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`salient poles 4a to 4c extending from the yoke section 3. salient poles 4a to 4c extending from the yoke section 3.
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`Windings are wound on the salient poles 4a to 4c of each Windings are wound on the salient poles 4a to 4c of each
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`unit core 2 into a concentric winding (not shown) so that the unit core 2 into a concentric winding (not shown) so that the
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`15 salient poles 4a to 4c are in phase with those of the other unit 15 salient poles 4a to 4c are in phase with those of the other unit
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`cores 2 respectively. More specifically, windings of phase a cores 2 respectively. More specifically, windings of phase a
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`are wound on the three salient poles 4a respectively and are wound on the three salient poles 4a respectively and
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`windings of phase b are wound on the three salient poles 4b windings of phase b are wound on the three salient poles 4b
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`respectively. Further, windings of phase c are wound on the respectively. Further, windings of phase c are wound on the
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`20 three salient poles 4c respectively. Thus, three-phase wind(cid:173)20 three salient poles 4c respectively. Thus, three-phase wind(cid:173)
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`ings are wound on the stator core 1 and the number of salient ings are wound on the stator core 1 and the number of salient
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`poles and the number of winding phases are equal to each poles and the number of winding phases are equal to each
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`other in each unit core 2. other in each unit