Electric motor, electric tool having the motor, and electric motor production method

1. Field of the Invention

The present invention relates to an electric motor having a coil that has been molded with resin, an electric tool provided with the electric motor, and a method of manufacturing the electric motor.

2. Description of the Related Art

Numerous configurations for electric motors provided in electric tools have been proposed. One technology attempts to stabilize the shapes of the coil and stator core by wrapping a part of the coil with an insulating paper, fitting the coil into a slot of the stator core while deforming the coil, and immersing the coil and stator core in varnish to fix the two as an integral unit.

Another method for stabilizing the shapes of the coil and stator core is disclosed in Japanese patent application publication No. HEI-8-9601. The method involves deforming the coil partially wrapped in an insulating paper to fit into the slot of the stator core and covering the coil and part of the stator core with a resin to form an integral unit.

However, in the conventional electric motor described above, the portion of the coil wrapped in the insulating paper has poor heat dissipation. Further, the process of deforming the coil to fit into the slot of the stator core requires a skilled technique, as well as much time and expense to complete. Also, reusability of the stator core is poor when the coil and stator core are fixed together with varnish or resin because a prolonged time and effort is needed to remove the coil from the stator core.

Further, when fitting the coil into the stator core, gaps are formed between adjacent magnet wires, unnecessarily increasing the amount of resin needed to cover the coil because the resin flows into the gaps, and therefore increasing the weight of the motor. It is also difficult to form air paths between the coil and stator core after the coil has been fitted into the stator core.

In view of the foregoing, it is an object of the present invention to provide an electric motor capable of drastically increasing cooling efficiency, and to provide an electric tool provided with the electric motor.

Another object of the present invention is to provide a method of manufacturing the electric motor that can reduce manufacturing costs and improve the reusability of the stator core.

In order to attain the above and other objects, the present invention provides a housing, an electric motor, and a fan. The housing is formed with an air inlet for taking in air, and an air outlet for exhausting air. The electric motor includes a stator core, a first molded coil, a second molded coil, and a rotor. The stator core is accommodated in and fixed to the housing. The stator core includes a first coil mounting portion, and a second coil mounting portion opposing the first coil mounting portion and providing a hollow area in cooperation with the first coil mounting portion. The first molded coil is mounted in the first coil mounting portion and includes a first coil entirely covered with a resin. The second molded coil is mounted in the second coil mounting portion and opposes the first molded coil. The second molded coil includes a second coil entirely covered with a resin. The rotor is rotatably disposed in the hollow area and between the first molded coil and the second molded coil. The fan is disposed in the housing for cooling the first coil and second coil by drawing air into the housing through the air inlet and blowing the air out of the housing through the air outlet.

In another aspect of the invention, there is provided a motor including the stator core, the first molded coil, the second molded coil, and rotor.

In another aspect of the invention, there is provided a method of manufacturing an electric motor includes manufacturing a first coil by winding a magnet wire a prescribed number of turns, and manufacturing a second coil by winding a magnet wire a prescribed number of turns, integrally manufacturing a first molded coil and a second molded coil by disposing the first coil and the second coil opposite each other in close proximity and covering the first coil and second coil with a resin, and interposing the integrated first molded coil and second molded coil between a first stator core having a first coil mounting portion and a second stator core having a second coil mounting portion, and mounting the first molded coil and the second molded coil in the first coil mounting portion and the second coil mounting portion, respectively.

In another aspect of the invention, there is provided a method for manufacturing an electric motor includes manufacturing a first coil by winding a magnet wire a prescribed number of turns, and manufacturing a second coil by winding a magnet wire a prescribed number of turns, manufacturing a first molded coil by covering the first coil with a resin, manufacturing a second molded coil separately from the first molded coil by covering the second coil with a resin, positioning the first molded coil and the second molded coil opposite to each other in close proximity, and interposing the first molded coil and the second molded coil between a first stator core having a first coil mounting portion and a second stator core having a second coil mounting portion, and mounting the first molded coil and the second molded coil in the first coil mounting portion and the second coil mounting portion, respectively.

The above and other objects, features, and advantages of the invention will become more apparent from reading the following description of the preferred embodiments taken in connection with the accompanying drawings in which:

FIG. 1 is a partial cross-sectional view showing a portable circular saw according to a first embodiment of the present invention;

FIG. 2 is a perspective view of an electric motor according to the first embodiment;

FIG. 3 is a cross-sectional view of the motor in FIG. 2 along a direction orthogonal to the longitudinal direction of the motor;

FIG. 4A is a perspective view of a first coil constituting the motor of FIG. 2 ;

FIG. 4B is a perspective view showing the first coil and a second coil constituting the motor of FIG. 2 , wherein the coils confront each other in close proximity;

FIG. 4C is a perspective view showing a first molded coil and second molded coil integrally formed in the motor of FIG. 2 ;

FIG. 4D is a perspective view illustrating a step for interposing the integrated first molded coil and second molded coil between a first stator core and a second stator core;

FIG. 5 is a cross-sectional view showing a motor according to a second embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 6 is a cross-sectional view showing a motor according to a third embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 7 is a cross-sectional view showing a motor according to a forth embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 8 is a cross-sectional view showing a motor according to a fifth embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 9 is a cross-sectional view showing a motor according to a sixth embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 10 is a cross-sectional view showing a motor according to a seventh embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 11A is a schematic diagram showing a structure of a first coil according to an eighth embodiment;

FIG. 11B is a cross-sectional view taken along a line Xb-Xb in FIG. 11A ;

FIG. 11C is a perspective view showing a first molded coil according to the eighth embodiment;

FIG. 11D is a cross-sectional view showing a motor according to the eighth embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 12A is a schematic diagram showing a structure of a first coil according to a ninth embodiment of the preferred embodiment;

FIG. 12B is a cross-sectional view taken along a line Xib-Xib in FIG. 12A ;

FIG. 12C is a perspective view showing a first molded coil according to the ninth embodiment;

FIG. 12D is a cross-sectional view showing a motor according to the ninth embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 13 is a cross-sectional view showing a motor according to a tenth embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 14 is a cross-sectional view showing a motor according to an eleventh embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 15 is a cross-sectional view showing a motor according to a twelfth embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 16 is a cross-sectional view showing a motor according to a thirteenth embodiment taken along a direction orthogonal to the longitudinal direction of the motor;

FIG. 17 is a cross-sectional view showing a motor according to a fourteenth embodiment taken along a direction orthogonal to the longitudinal direction of the motor; and

FIG. 18 is a cross-sectional view showing a motor according to a fifteenth embodiment taken along a direction orthogonal to the longitudinal direction of the motor.

A motor for a electric tool according to preferred embodiments of the present invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. The electric tool of the present invention is applied to a portable electric circular saw.

A motor for a portable electric circular saw 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1 through 4D . As shown in FIG. 1 , a portable electric circular saw 1 includes a housing 2 which internally supports and houses a motor 20 , a handle 3 , a saw blade 4 , a saw cover 5 , a base 6 , and a fan 7 . An air inlet duct 2 a which connects the interior and exterior of the housing 2 is formed on one end of the housing 2 . The handle 3 is provided integrally with the housing 2 or linked to the housing 2 as a separate member. A switch (not shown) is provided to control the drive of the motor 20 . The saw blade 4 is rotatable in only a normal rotation direction which can cut a workpiece. The saw cover 5 is mounted to the housing 2 , and is shaped so as to cover the upper half of the periphery of the saw blade 4 .

A fan airflow outlet 5 a is formed on the saw cover 5 to discharge the fan airflow (not shown). The base 6 is connected to the housing 2 via the saw cover 5 and has a bottom surface 6 a that slides on the workpiece. The base 6 is formed with an opening (not shown) through which the saw blade 4 is projected downward beyond the bottom surface 6 a. The motor 20 has a first molded coil 22 , a second molded coil 23 and a rotor 24 . The fan 7 is fixed to an output shaft 26 rotatably supported with the rotor 24 to cool the first coil 22 , the second coil 23 and the rotor 24 .

A pinion gear 8 is disposed at an end of the output shaft 26 . The output shaft 26 and the pinion gear 8 are rotatably supported by first bearings 9 and 10 . The first bearings 9 and 10 are provided on the air inlet duct 2 a side of the housing 2 and on the saw cover 5 , respectively. A drive shaft 11 extending parallel to the output shaft 26 is rotatably supported by second bearings 12 and 13 within the saw cover 5 . The drive shaft 11 extends through the saw cover 5 , and a gear 14 is coaxially fixed to the drive shaft 11 . The gear 14 is in a meshing engagement with the pinion gear 8 . A pair of saw blade locking members 15 are attached to the drive shaft 11 . The saw blade locking members 15 are not rotatable relative to the drive shaft 11 and pinch the saw blade 4 therebetween.

The portable electric circular saw 1 further includes a safety cover 16 pivotably supported by the drive shaft 11 . The safety cover 16 is adapted to cover substantially a lower half of the outer periphery of the saw blade 4 and can be retracted into the saw cover 5 . The safety cover 16 has a lever 16 a for manual pivotal movement operations. The safety cover 16 is urged by an urging member (not shown), such as a spring. FIG. 1 shows the initial state of the safety cover 16 , where the most part of the safety cover 16 projects downward beyond the bottom surface 6 a of the base 6 so as to prevent the outer periphery of the saw blade 4 from being exposed. When a cutting operation is conducted, the front end of the safety cover 16 abuts the rear end of the workpiece. As the user slides the portable electric circular saw 1 on the workpiece in the cutting direction, the safety cover 16 is pivotably moved about the drive shaft 11 and enters the saw cover 5 against the urging force of the urging member, exposing the saw blade 4 at the bottom surface 6 a of the base 6 .

Next, the motor 20 will be described with reference to FIG. 2 and FIG. 3 . The rotor 24 has been omitted from FIGS. 2 and 3 . The motor 20 includes a stator core 21 , the first molded coil 22 and second molded coil 23 (see also FIG. 4C ) configured as an integral unit, and the rotor 24 (see FIG. 1 ). The stator core 21 is supported and fixed by a plurality of ribs (not shown) in the housing 2 and includes a first stator core 21 A and a second stator core 21 B opposing the first stator core 21 A.

The first stator core 21 A includes a first coil mounting portion 21 A 1 and a pair of first stator core legs 21 A 2 . The first molded coil 22 is mounted on the first coil mounting portion 21 A 1 . The pair of first stator core legs 21 A 2 extend from both ends of the first coil mounting portion 21 A 1 in the circumferential direction of the rotor 24 and along the outer periphery of the rotor 24 . Similarly, the second stator core 21 B includes a second coil mounting portion 21 B 1 and a pair of second stator core legs 21 B 2 . Free ends of the first stator core legs 21 A 2 fit into free ends of the second stator core legs 21 B 2 opposing the first stator core legs 21 A 2 , thereby forming a hollow area 21 a into which the rotor 24 is loosely inserted.

The first coil mounting portion 21 A 1 includes a first contact surface 21 C and a second contact surface 21 D those extending along the axis of the stator core 21 substantially parallel to each other for contacting and supporting a pair of first axial portions 22 D of the first molded coil 22 described later. Similarly, the second coil mounting portion 21 B 1 includes a third contact surface 21 E and a fourth contact surface 21 F those substantially parallel to each other for contacting and supporting a pair of second axial portions 23 D of the second molded coil 23 described later. Here, the first contact surface 21 C and third contact surface 21 E are positioned substantially in the identical plane, I-I in FIG. 3 , and the second contact surface 21 D and fourth contact surface 21 F are also positioned substantially in another identical plane II-II in FIG. 3 .

The first molded coil 22 has a first coil 22 A that is entirely covered with a thermosetting resin 25 that is electrically insulating and has high thermal conductivity, such as a vinylester resin with alumina filler. Similarly, the second molded coil 23 includes a second coil 23 A entirely covered with the thermosetting resin 25 . The first molded coil 22 includes a pair of first circumferential portions 22 C, and a pair of first axial portions 22 D. The second molded coil 23 also includes a pair of second circumferential portions 23 C, and a pair of second axial portions 23 D. The pairs of first and second circumferential portions 22 C and 23 C project outward from both axial ends of the stator core 21 (see FIG. 2 ), and are roughly arc-shaped along the periphery of the rotor 24 , respectively. The pairs of the first and second axial portions 22 D and 23 D extend inside the stator core 21 in the axial direction of the rotor 24 , respectively.

The pairs of first circumferential portions 22 C and first axial portions 22 D form a substantially rectangular shape, and are mounted around the first coil mounting portion 21 A 1 . Similarly, the pairs of second circumferential portions 23 C and second axial portions 23 D form a substantially rectangular shape, and are mounted around the second coil mounting portion 21 B 1 . The first axial portions 22 D have first opposing surfaces 22 E that oppose the rotor 24 . The second axial portions 23 D have second opposing surfaces 23 E that oppose the rotor 24 .

An opening S 1 (see FIG. 4D ) is defined by the first circumferential portions 22 C and first axial portions 22 D, while an opening S 2 is defined by the second circumferential portions 23 C and second axial portions 23 D. As shown in FIG. 3 , the first axial portions 22 D are formed continuously from and integrally with the second axial portions 23 D, thereby configuring the first and second molded coils 22 and 23 as an integral unit.

Air paths 27 through which fan airflow can pass are provided between one of the continuously formed first and second axial portions 22 D and 23 D and the opposing first and second stator core legs 21 A 2 and 21 B 2 , and between the remaining one of the continuously formed first and second axial portions 22 D and 23 D and the opposing first and second stator core legs 21 A 2 and 21 B 2 .

Next, operation of the circular saw 1 will be described. When a switch (not shown) on the circular saw 1 is turned to the ON position, a power supply (not shown) supplies an electric current to the first and second coils 22 A and 23 A and the rotor 24 . The current generates a magnetic field between the first coil 22 A and second coil 23 A. The magnetic field and the current flowing through the rotor 24 generate a force that rotates the rotor 24 . Rotations of the rotor 24 cause the output shaft 26 to rotate, and the rotational force of the output shaft 26 is transferred to the saw blade 4 via the pinion gear 8 , gear 14 , drive shaft 11 , and saw blade locking members 15 , whereby the saw blade 4 rotates in a normal direction for performing a cutting operation.

During the cutting operation, the rotations of the output shaft 26 also rotate the fan 7 . The rotating fan 7 draws air into the housing 2 via the air inlet 2 a . The air passes through the air paths 27 and cools the first and second molded coils 22 and 23 in which heat is generated by the flowing current. The fan airflow flows in the radial direction of the fan 7 and in the axial direction of the rotor 24 , and is discharged from the fan airflow outlet 5 a.

By providing the air path 27 , the area of the surface that dissipates heat generated in the first and second molded coils 22 and 23 is about 40% greater than that in a conventional motor. Hence, the cooling efficiency of the fan airflow increases dramatically, thereby increasing the service life of the motor 20 and greatly improving the rated input of the circular saw 1 . Further, the circular saw 1 can be operated with the motor 20 at application of greater load which is a load about 1.15 as large as the load to be applied to a conventional motor.

Since the first and second coils 22 A and 23 A are covered entirely by the thermosetting resin 25 , the shapes of these components can be stabilized. The thermosetting resin 25 is also unlikely to deform from heat even when the motor 20 reaches high temperatures as the result of application of a large load. Since the first and second coils 22 A and 23 A are unlikely to deform by heat, it is possible to prevent the first and second circumferential portions 22 C and 23 C from deforming and coming into contact with the rotor 24 , thereby improving the durability of the motor 20 . By configuring the first and second molded coils 22 and 23 as an integral unit, the shapes of the first and second coils 22 A and 23 A can be further stabilized.

By covering the first and second coils 22 A and 23 A entirely with the thermosetting resin 25 that is electrically insulating and highly heat conductive, there is no need to wrap insulating paper having poor heat conductivity about the first and second axial portions 22 D and 23 D as is done in conventional coils. Therefore, this construction can improve heat dissipation from the first and second axial portions 22 D and 23 D. By setting the width of the air path 27 in the radial direction of the stator core 21 wider than the width of the air inlet 2 a , foreign matter that enters the housing 2 via the air inlet 2 a will not clog the air path 27 , which can prevent the reduction of the cooling capability of the motor 20 , thereby ensuring good rotational performance.

Deep slots for holding coils to the stator core may not be formed in the first and second coil mounting portions 21 A 1 and 21 B 1 , thereby shortening the paths of magnetic flux generated by the current flowing through the first and second coils 22 A and 23 A. Hence, it is possible to reduce magnetic resistance and improve the rotational performance of the motor 20 .

Next, a method of manufacturing the motor 20 of the first embodiment will be described with reference to FIG. 4 A through FIG. 4D . The first coil 22 A shown in FIG. 4A is manufactured by winding magnet wire a prescribed number of turns. The second coil 23 A having the same shape as the first coil 22 A is manufactured in the same way. Next, as shown in FIG. 4B , the first and second coils 22 A and 23 A are disposed such that a pair of first axial equivalent portions 22 A 1 of the first coil 22 A approach and oppose second axial equivalent portions 23 A 1 of the second coil 23 A. In FIG. 4C the integrated first molded coil 22 and second molded coil 23 are manufactured by covering the entire first and second coils 22 A and 23 A with the thermosetting resin 25 .

Next, as shown in FIG. 4D , a portion of the first coil mounting portion 21 A 1 is inserted into the opening S 1 until the pair of first axial portions 22 D contact the first contact surface 21 C and second contact surface 21 D (see FIG. 3 ). Similarly, a portion of the second coil mounting portion 21 B 1 is inserted into the opening S 2 until the pair of second axial portions 23 D contact the third contact surface 21 E and fourth contact surface 21 F. In this way, the motor 20 of FIG. 2 is manufactured such that the integrated first molded coil 22 and second molded coil 23 are interposed between the first stator core 21 A and second stator core 21 B.

Manufacturing the motor 20 in this way eliminates the need for an operation requiring a skilled technique, as in the conventional manufacturing method of deforming the coil to fit into a slot of the stator core. Accordingly, the manufacturing method of the present embodiment facilitates manufacturing of the motor 20 and reduces time and cost of such manufacturing. Further, since the first and second molded coils 22 and 23 are manufactured as an integral unit by covering the first and second coils 22 A and 23 A disposed in close proximity to each other with the thermosetting resin 25 , manufacturing costs are less than those for covering each coil separately with resin. Further, by configuring the first and second molded coils 22 and 23 as an integral unit, gaps and the like do not form between the first and second molded coils 22 and 23 when mounted in the stator core 21 , thereby securely fixing the first and second molded coils 22 and 23 to the stator core 21 .

Since the first molded coil 22 and second molded coil 23 can be easily separated from the stator core 21 after the motor 20 has been used, reusability of the stator core is much better than that of a conventional motor in which the coil and stator core have been fixed together by varnish. Further, since only the first and second coils 22 A and 23 A are covered with the thermosetting resin 25 , the shape of the metal molds can be simplified, thereby reducing manufacturing costs.

Further, the air paths 27 shown in FIG. 3 can be easily provided by hardening the first and second coils 22 A and 23 A with the thermosetting resin 25 and subsequently interposing the first and second molded coils 22 and 23 between the first and second stator cores 21 A and 21 B. Further, a manufacturing operation is no longer necessary for deforming the coil while fitting the coil into the slot of a stator core, thereby reducing the number of gaps that may be formed between adjacent magnet wires of the first and second coils 22 A and 23 A. As a result, less of the thermosetting resin 25 is required to cover the first and second coils 22 A and 23 A, reducing the overall weight of the motor 20 .

Next, a motor according to a second embodiment of the present invention will be described with reference to FIG. 5 . As shown in FIG. 5 , a plurality of protrusions 28 integrally protrude from the first and second axial portions 22 D and 23 D. The plurality of protrusions 28 connect the first and second axial portions 22 D and 23 D to the first and second stator core legs 21 A 2 and 21 B 2 and partition the air paths 27 . With this construction, the first molded coil 22 and second molded coil 23 can be securely fixed to the stator core 21 .

FIG. 6 shows a motor according to a third embodiment of the present invention. In the third embodiment, a plurality of protrusions 29 integrally protrude from the first and second stator core legs 21 A 2 and 21 B 2 so as to connect the first and second stator core legs 21 A 2 and 21 B 2 to the first and second axial portions 22 D and 23 D and partition the air paths 27 . With this construction, the first molded coil 22 and second molded coil 23 can be securely fixed to the stator core 21 .

FIG. 7 shows a motor according to a fourth embodiment of the present invention. As shown in FIG. 7 , the first and second contact surfaces 21 C and 21 D need not be substantially parallel to each other, and the third and fourth contact surfaces 21 E and 21 F need not be substantially parallel to each other in contrast to the forgoing embodiments. The first opposing surfaces 22 E and second opposing surfaces 23 E are out of contact from the first stator core 21 A and second stator core 21 B. An angle between the inner surface of the first stator core legs 21 A 2 and the first and second contact surfaces 21 C and 21 D is greater than that of the forgoing embodiments. Similarly, an angle between the inner surface of the second stator core legs 21 B 2 and the third and fourth contact surfaces 21 E and 21 F is greater than that of the forgoing embodiments. With this construction, the first molded coil 22 and second molded coil 23 can be easily mounted in the stator core 21 .

FIG. 8 shows a motor according to a fifth embodiment of the present invention. Here, in addition to the shape of the stator core 21 shown in FIG. 7 , a first coil holding portion 21 D 1 and a second coil holding portion 21 E 1 are provided on inside ends of the second contact surface 21 D and third contact surface 21 E with respect to the radial direction of the stator core 21 . The first coil holding portion 21 D 1 and the second coil holding portion 21 E 1 are in contact with the first and second opposing surfaces 22 E and 23 E. With this construction, the first and second molded coils 22 and 23 can be securely fixed to the first and second stator cores 21 A and 21 B.

FIG. 9 shows a motor according to a sixth embodiment of the present invention. As shown in FIG. 9 , first spacers 30 are provided between the stator core 21 and the first and second molded coils 22 and 23 . This construction can eliminate slight gaps formed between the stator core 21 and the first and second molded coils 22 and 23 , eliminating a looseness or rattling therebetween. Hence, this construction prevents damage to the first molded coil 22 and second molded coil 23 caused by vibrations or impacts. By further forming the first spacers 30 with an electrically insulating material, this construction can improve the insulating capacity of the stator core 21 .

FIG. 10 shows a motor according to a seventh embodiment of the present invention. Here, the entire periphery of the stator core 21 or at least a part of the periphery of the stator core 21 are covered with a resin 31 . With this construction, a motor 120 is configured such that the integrated structure of the stator core 21 including the first stator core 21 A and second stator core 21 B can be maintained even when the housing 2 that supports and fixes the motor 120 is insufficiently rigid. Hence, it is possible to reduce the number of ribs (not shown) in the housing 2 described above. The cooling air paths provided between the housing 2 and the stator core 21 can also be increased to further improve the cooling efficiency of fan airflow in the motor 120 because of reduction in ribs.

FIGS. 11A-11D show a motor according to an eighth embodiment of the present invention. As shown in FIGS. 11A and 11B , a first coil 222 A corresponding to the first coil 22 A of the first embodiment includes of a first outer coil 222 A 1 , and a first inner coil 222 A 2 . Air path equivalent areas 32 A are formed between the first outer coil 222 A 1 and first inner coil 222 A 2 on opposing sides of the first outer coil 222 A 1 . The first coil 222 A is shaped similar to the first coil 22 A in FIG. 4A . The first coil 222 A is disposed opposite a second coil 223 A having the shape identical with the first coil 222 A (see FIG. 11D ), and both are covered entirely with the thermosetting resin 25 to produce a first molded coil 222 and a second molded coil 223 having the same structure. The first molded coil 222 shown in FIG. 11C corresponding to the first molded coil 22 in the first embodiment includes a first outer molded coil 222 - 1 and a first inner molded coil 222 - 2 . Air paths 32 are thus provided in the first molded coil 222 . A motor 220 having the air paths 32 is produced by fitting the first and second molded coils 222 and 223 between the first and second stator cores 21 A and 21 B. The motor 220 having this construction can obtain the same effects as the motor 20 having the air paths 27 according to the first embodiment described above.

FIGS. 12A-12D show a motor according to a ninth embodiment of the present invention. As shown in FIGS. 12A and 12B , a first coil 322 A corresponding to the first coil 22 A of the first embodiment includes a second outer coil 322 A 1 and a second inner coil 322 A 2 spaced away from the second outer coil 322 A 1 . The first coil 322 A is formed in a shape similar to the first coil 22 A of FIG. 4A . The first coil 322 A is disposed opposite a second coil 323 A (see FIG. 12D ) of the same shape and both are covered entirely with the thermosetting resin 25 to produce a first molded coil 322 and a second molded coil 323 . The first molded coil 322 corresponding to the first molded coil 22 of the first embodiment is configured of a second outer molded coil 322 - 1 and a second inner molded coil 322 - 2 and has air paths 33 . A motor 320 having the air paths 33 is produced by fitting the first and second molded coils 322 and 323 between the first and second stator cores 21 A and 21 B. The motor 320 having this construction can obtain the same effects as the motor 20 having the air paths 27 according to the first embodiment.

A motor according to a tenth embodiment of the present invention is shown in FIG. 13 . The tenth embodiment presents a modification to a shape of a stator core 121 . In this embodiment, the stator core 121 includes a first coil mounting portion 121 A 1 and a second coil mounting portion 121 B 1 those corresponding to the first and second coil mounting portions 21 A 1 and 21 B 1 of the first embodiment, and a pair of third stator core legs 121 A 2 connecting both ends of the first coil mounting portion 121 A 1 to both ends of the second coil mounting portion 121 B 1 .

A motor according to an eleventh embodiment of the present invention is shown in FIG. 14 . A stator core 221 of the eleventh embodiment includes a pair of fourth stator core legs 221 A 2 formed by extending both ends of the third stator core legs 121 A 2 described above farther along the circumference of the rotor 24 , and a first coil mounting portion 221 A 1 and a second coil mounting portion 221 B 1 corresponding to the first and second coil mounting portions 121 A 1 and 121 B 1 , but modified to correspond to the shape of the fourth stator core legs 221 A 2 .

FIG. 15 shows a motor according to a twelfth embodiment of the present invention. As shown in FIG. 15 , a first molded coil 422 and a second molded coil 423 are formed with openings S 3 and S 4 corresponding to the openings S 1 and S 2 of the first embodiment but narrower in the circumferential direction of the rotor 24 than the openings S 1 and S 2 . First and second coil mounting portions 421 A 1 and 421 B 1 corresponding to the first and second coil mounting portions 21 A 1 and 21 B 1 of the first embodiment are inserted into the openings S 3 and S 4 . Engaging portions 421 A 3 and 421 B 3 are formed on the radially outer side of the first and second coil mounting portions 421 A 1 and 421 B 1 . A stator core outer peripheral portion 421 C that is substantially cylindrical in shape is provided around the first and second molded coils 422 and 423 . The stator core outer peripheral portion 421 C has engaging grooves 421 a and 421 b that engage with the engaging portions 421 A 3 and 421 B 3 , while forming air paths 34 between the stator core outer peripheral portion 421 C and the first and second molded coils 422 and 423 .

FIG. 16 shows a motor according to a thirteenth embodiment of the present invention. A stator core 521 of FIG. 16 includes a first stator core 521 A and a second stator core 521 B. In this variation, air paths are not provided between the first and second stator cores 521 A and 521 B and the first and second coils 22 A and 23 A.

FIG. 17 shows a motor according to a fourteenth embodiment of the present invention. In the first embodiment, the first and second axial portions of the first and second coils 22 A and 23 A are formed continuously with each other to configure the first and second molded coils 22 and 23 as an integral unit. On the contrary in the fourteenth embodiment, the first and second molded coils 22 and 23 are configured separate from each other. With this construction, only one of the first and second coils 22 A and 23 A is covered with the thermosetting resin 25 at one time, thereby simplifying the shape of the metal molds.

FIG. 18 shows a motor according to a fifteenth embodiment of the present invention. When the first molded coil 22 and second molded coil 23 are configured separate from each other as in the fourteenth embodiment, second spacers 35 are interposed between the first molded coils 22 and second molded coils 23 as shown in FIG. 18 according to a fifteenth embodiment. This configuration prevents slight gaps from forming between the stator core 21 and the first and second molded coils 22 and 23 , thereby eliminating looseness or rattling between the stator core 21 and the first and second molded coils 22 and 23 . As a result, the fifteenth embodiment can prevent damage to the first and second molded coils 22 and 23 caused by vibrations or impacts.

While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims. Further, the present invention may be applied to various tools other than the circular saw described above.