Stator core of vehicle rotary electric machine and method of manufacturing the same

Abstract: Each tooth of a stator core (1) has circumferential projections (201) at an inner tooth edge and circumferential notches (21) at a base portion adjacent to a core back portion (3) of the teeth (2) at the base portion is larger than a width of the same at the tooth edge. Therefore, the magnetic reluctance of the teeth (2) does not increase. In addition, a plurality of the magnetic strips (10) can be formed from a long and thin magnetic sheet (100). This increases the yield percentage of the magnetic strip (10) and reduces a manpower of manufacturing the magnetic strip (10). Further, the notches (21) make it easy to wind the magnetic strip (10) into a cylindrical core.

Description: The present invention relates to a stator core of a vehicle rotary electric machine, such as an AC generator, to be mounted in a passenger car, a truck, etc. In order to supply an inexpensive vehicle rotary machine, a magnetic stator core is usually comprised of a spirally wound magnetic strip. Such a stator core can provide a high yield percentage of magnetic material and can be manufactured at a high manufacturing speed. In order to meet a recent demand for a high power generator, conductors are to be disposed in the slots of the stator core at as a high space factor as possible. As shown in JP-A11-299136, a pair long and thin magnetic sheets is stamped out to form a pair of magnetic strips that has a plurality of teeth and a core back in order to increase the yield percentage of the magnetic strips, the teeth of one of the pair of magnetic strips are respectively formed from portions inside slots of the other magnetic strip. Thereafter, each the magnetic strip is spirally wound into a cylindrical stack with the slots of one layer being aligned with those of another layer until the cylindrical stack has a prescribed thickness. Then, the stack is welded or riveted. Because two or more magnetic strips are formed at one time, the manpower and cost for manufacturing the stator cores can be reduced. In order to moderate stress of a magnetic strip when it is spirally wound, JP-A-48-24204 discloses teeth whose tooth width becomes narrower toward the core back. In other words, slot width is widened at the middle thereof. This reduces strain of the strip when it is spirally wound and makes the size and shape of a cylindrical stator core accurate. Because the magnetic reluctance of the air gap between the rotor and the stator is the largest in the magnetic circuit of a generator, the tooth edge formed at the inner periphery of the stator has a wider cross-section of a magnetic path than the rest of the tooth. In other words, each tooth has a pair of circumferential projections to increase the width of the tooth. As the space factor of the conductors increases, the slot area is narrowed to thereby widen the cross-section of the tooth. If the teeth of one of the pair of magnetic strips are respectively formed from portions inside slots of the other magnetic strip as disclosed in JP-A-299136, it is not possible to provide such a circumferentially wide tooth. If the tooth width is narrowed at the middle thereof as shown in JP-A-48-24204, a widened tooth edge of one of a pair of magnetic strips can be formed from the portion inside a widened slot of the other magnetic strip. However, if the tooth is narrowed at the middle, the magnetic reluctance of the teeth increases, and the magnetic flux flowing through the stator core decreases significantly. This lowers the output power. A stator core of a vehicle AC generator that has an outside diameter between 90 mm and 140 mm is usually comprised of a laminated steel strip of a thickness between 0.5 mm and 1.0 mm. It is necessary to have a margin (or clearance) if teeth and slots are formed from a steel strip of the above thickness. However, if the thickness is reduced to a thickness less than 0.2 mm, the edge of the sheet may be drawn because of the low rigidity thereof. As a result, the projections of the tooth edge can not have proper length, and a sufficient cross-section of the magnetic flux from the rotor can not be provided. Therefore, a main object of the invention is to provide a powerful and inexpensive vehicle rotary electric machine having a stator core that is free from the above problems. In other words, the invention is to provide a stator core of a powerful vehicle rotary machine that can be manufactured at a high yield percentage and a high speed. In more detail, the invention is to improve the yield percentage of the magnetic strip forming the stator core, to reduce manpower of manufacturing the magnetic strip, to reduce the magnetic reluctance of the stator core and to improve the space factor of the conductor coils. A precise definition of the invention is given in the claims. According to a main feature of the invention, each of teeth of the stator core has at least a circumferential projection at an inner edge thereof and at least a circumferentially extending notch at a base portion thereof, and a circumferential width of the teeth at the base portion is wider than a circumferential width of the teeth at the tooth edge from which the projection extends. According to the above structure, the cross-section of the teeth at the middle thereof is not narrower than the cross-section at the base thereof. This shape prevents the magnetic reluctance thereof from increasing. In addition, it is possible to manufacture a plurality of magnetic strips from a long magnetic sheet. As a result, the yield percentage of the magnetic strip can be improved and the manpower for manufacturing the magnetic strip can be reduced. In addition, the magnetic strip can be wound easily because of the notches. According to another feature of the invention, the notch and projection are complementary to each other in shape before the magnetic strip is spirally wound, and the width of the notch is reduced after the strip is wound. Therefore, the yield percentage of the magnetic strip is drastically improved. Because the radial width of the notch is automatically reduced when the magnetic strip is wound, the magnetic reluctance from the teeth to the core back can be reduced. According to another feature of the invention, the slot has parallel walls facing each other in circumferential directions. Therefore, it is easy to align the conductors in the slots, resulting in improvement of the space factor. According to another feature of the invention, the magnetic strip is thicker than 0.2 mm and thinner than 0.5 mm. This thickness makes it possible to form the magnetic strips with small marginal portions and stamp out two magnetic strips at once in order to reduce cost and prevents the tooth edge frbm deforming. Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: Fig. 1 is a fragmentary enlarged view of an axial end of a stator core of a vehicle AC generator according to a first embodiment of the invention; Fig. 2 is an explanatory diagram showing a step of manufacturing a pair of magnetic strips according to the first embodiment from a long and thin magnetic sheet; Fig. 3 is an explanatory diagram showing a step of spirally winding the magnetic strip according to the first embodiment; Fig. 4 is a perspective view of the stator core according to the first embodiment; Fig. 5 is a fragmentary cross-sectional view of the stator core according to the first embodiment; Fig. 6 is a fragmentary cross-sectional view of a stator core according to a variation of the first embodiment of the invention; The invention can be applied to a vehicle rotary electric machine such as a generator or a motor. For example, it is mounted in an engine and driven by the engine as an AC generator. It is also mounted in an engine as a motor. Some vehicle AC generators as applications of the vehicle rotary electric machine according to embodiments of the invention are described with reference to the appended drawings, hereafter. A stator core of a vehicle AC generator according to a first embodiment of the invention is described with reference to Figs. 1- 5 . A cylindrical stator core 1 is comprised of a spirally wound and laminated magnetic strip 10 that is as thick as 0.35 mm. The magnetic strip 10 has a plurality of teeth 2 and a core back 3 from which the plurality of teeth 2 extends. When wound and laminated, tooth edges 20 of teeth 2 are disposed radially inside, as shown in Fig. 3. A plurality of conductor coils 5 is disposed in each slot 6 formed between adjacent teeth 2, as shown in Fig. 5, so that an electromotive force can be generated in the conductor coils 5 when a rotor having a field coil (not shown) supplies an alternating magnetic flux. A pair of circumferential notches 21 is formed at opposite sides of a base portion of each tooth 2 adjacent to the core back 3. A width B of the base between the notches 21 is set larger than a minimum width A between a pair of circumferential projections 201 formed at the tooth edge 20. Each slot 6 has a pair of walls 23 and 24 facing each other in the circumferential direction. The pair of walls 23 and 24 becomes parallel after the magnetic strip 10 is wound up. The pair of projections 201 is almost the same in shape as a slot bottom 210 that includes the pair of notches 21. When a pair of magnetic strips 10 is formed from a long and thin magnetic sheet 100 such as a hoop of a steel sheet, the tooth edges 20 of one magnetic strip 10 and the slot bottom 210 of the other magnetic strip 10 is sheared and separated without any clearance or margin except for clearances or marginal portions 200 at opposite sides of each tooth 2, as shown in Fig. 2. This increases the yield percentage of the magnetic strip. Because the thickness of the magnetic strip 10 is 0.35 mm, the projections 201 do not deform and keep the magnetic reluctance at a low level. Thus, the magnetic cross-section of the teeth 2 is the smallest at the base of the projections 201, i.e. at the tooth edge 20 from which the projections 201 extend. In other words, the cross-section of middle portion of the teeth 2 between the base of the projections 201 and the core back 3 is not smaller than the magnetic cross-section at the base of the projections 201. The radial width of each notch 21 is narrowed when the magnetic strip 10 is spirally wound. Accordingly, the magnetic reluctance around the notches 21 is reduced when the stator core 1 is completed. In addition, a plurality of magnetic strips 10 can be formed from a single long and thin magnetic sheet 100, and the notches 21 make the winding step of the magnetic strip 10 easier. Further, the parallel walls 23 and 24 make it easy to align the conductor coils in the slot 6, as shown in Fig. 5 so that a high space factor can be provided, resulting in a high power generator. As a variation, the conductor coils can have a rectangular cross-section to be fitted to the inside walls of each slot 6 including parallel walls, as shown in Fig. 6. This increases the space factor so that more output power can be provided. In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.

Claims: A stator core (1) of a vehicle rotary electric machine comprising a spirally wound magnetic strip (10) having a core back portion (3), a plurality of teeth (2) extending radially inward from said core back portion (3) at equal intervals and a plurality of slots formed between each pair of said teeth (2); wherein each of said teeth (2) comprises at least a circumferential projection (201) at an edge portion thereof, characterized in that at least a circumferential notch (21) is formed at a base portion of said teeth (2) adjacent to said core back portion (3), a circumferential width of said teeth (2) at said base portion is wider than a circumferential width of said teeth (2) at said edge portion from which said circumferential projection (201) extends. The stator core (1) of a vehicle rotary electric machine as claimed in claim 1, wherein said notch (21) and projection (201) are complementary to each other in shape before said magnetic strip (10) is spirally wound, and the radial width of said notch is reduced after said strip (10) is wound. The stator core (1) of a vehicle rotary electric machine as claimed in claim 1, wherein said slot has parallel walls (23, 24) facing each other in circumferential directions. The stator core (1) of a vehicle rotary electric machine as claimed in claim 1, wherein said magnetic strip (10) is thicker than 0.2 mm and thinner than 0.5 mm. A method of manufacturing a stator core (1) of a vehicle rotary electric machine characterized by comprising the steps of: stamping a pair of magnetic strips (10) having a plurality of teeth (2) and a plurality of slots from a magnetic sheet (100) so that said teeth (2) of one strip (10 ) are respectively disposed in said slots of the other; and winding one of said pair of magnetic strip (10) into a spiral shape so that edges of said teeth (2) are disposed radially inside; wherein said step of stamping comprises a step of forming a circumferential notch (21) at a base portion of said teeth (2 ) and a circumferential projection (201) at an edge of the same so that said teeth (2) have a shape complementary to said slots and a step of forming said base portion of said teeth (2) to have a wider circumferential width than a circumferential width of said edge portion thereof from which said circumferential projection extends. The method as claimed in claim 5, characterized in that said step of winding comprises a step of reducing radial gaps of said notches (21).

Inventors: NAKAMURA SHIGENOBU, NAKAMURA, SHIGENOBU
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 2001
Main classification: H02K1
IPC codes: H02K1, H02K3, H02K15