WO2010035639A2

WO2010035639A2 - Commutator motor, electric tool using same, and method of manufacturing same

Info

Publication number: WO2010035639A2
Application number: PCT/JP2009/065777
Authority: WO
Inventors: Hideyuki Tanimoto
Original assignee: Hitachi Koki Co., Ltd.
Priority date: 2008-09-25
Filing date: 2009-09-03
Publication date: 2010-04-01
Also published as: JP5408466B2; WO2010035639A3; JP2010081694A

Abstract

Provided are a commutator motor having a cooling wind path for improving an effect of cooling a stator and a rotor, and an electric motor using the commutator motor. A stator coil (4f), which is wound through a magnetic pole core portion (4c) is molded with a thermosetting resin. The resin-molded stator coil (4f) has a step difference portion (13) between an outer surface (3h) of a rotor core (3a) and an inner surface (4h) of a yoke core portion (4b). The step difference portion (13) faces a cooling wind path (10) and imparts a difference to the thickness of the stator coil (4f) in a radial direction of a rotation shaft (3d).

Description

DESCRIPTION

Title of the Invention COMMUTATOR MOTOR, ELECTRIC TOOL USING SAME, AND METHOD OF MANUFACTURING SAME

Technical Field [0001]

The present invention relates to a commutator motor including a stator coil that is sealed by resin molding and an electric tool using the commutator motor, and particularly to a commutator motor with an improved effect of cooling provided between the outer surface of its rotor core and the inner surface of its stator core with cooling air circulating therebetween and an electric tool using the commutator motor.

Background Art

[0002]

In a commutator motor shown in Fig. 8, a motor coil produces heat due to a field current of a stator coil bundle 4f (hereinafter, stator coil) that is in operation. As the motor starts, a rotor coil 3b also produces heat. Hence, an electric tool that uses a commutator motor needs to be designed to prevent the stator coil 4f or the rotor coil 3b from gaining a temperature above an allowable temperature.

[0003]

In efforts to downsize a motor used in electric tools, in order for the motor to realize a high output power and high workability, which are easier to achieve if the stator coil produces less heat, a coil winding slot in the stator core is dimensionally expanded to the limit so that the cross-sectional area of the conductor coil set in the slot may be as large as possible and hence the stator coil may produce less heat. [0004]

Further, as disclosed in Patent Literature 1 identified below, there is a publicly known technique of cooling a stator, which divides a coil end of a stator coil that is wound through a stator core into a plurality of portions in the radial direction to increase the heat radiation area of the stator coil. [0005]

Patent Literature 1 : Unexamined Japanese Patent Application KOKAI Publication No. 2001-292544

Summary of Invention

[0006]

However, as shown in Fig. 8, enlarging the area of the stator coil 4f makes a cooling wind path 10 between the inner surface 4h of the stator core 4a and the outer surface 3h of the rotor 3 narrower, leaving the rotor 3 undercooled (cooled insufficiently). This leads to an inevitable temperature rise of the rotor 3. [0007]

Meanwhile, the technique disclosed in Patent Literature 1 identified above of dividing a coil end of a stator coil into a plurality of portions in the radial direction requires complicated machining in the manufacturing process. Further, the technique disclosed in Patent Literature 1 identified above of dividing a coil end makes the coil end of the stator coil larger in the radial direction, incurring a problem that the motor housing or the electric tool housing becomes larger hi size. Furthermore, in a case where the motor housing or the like is made of metal, this technique requires electric insulation to be specially provided between the coil end of the stator coil and the housing because the coil end and the housing are close to each other. [0008]

Hence, an object of the present invention is to provide a commutator motor that overcomes the deficiencies of the conventional art described above with a cooling wind path that improves an effect of cooling a stator and a rotor and an electric tool using the commutator motor. [0009] To solve the problems described above, a commutator motor according to a first aspect of the present invention is a commutator motor that is housed in a housing and comprises: a rotor that extends in a direction of a rotation shaft; and stator that is disposed at an outer side of an outer surface of the rotor in proximity to the outer surface and extends in the direction of the rotation shaft, characterized in that, the rotor comprises a rotor core, and the stator comprises: a stator core that has: a yoke core portion; and a pair of magnetic pole core portions that oppose to each other and protrude from an inner surface of the yoke core portion to an outer surface of the rotor core; slots that are formed by the magnetic pole core portions and the yoke core portion; and a stator coil that is wound through the magnetic pole core portions in the slots, and that has a step difference portion that is positioned between the outer surface of the rotor core and the inner surface of the yoke core portion and by which the thickness of the stator coil is varied in a radial direction of the rotation shaft. [0010]

It is preferred that: the commutator motor comprises a cooling wind path that is formed between the outer surface of the rotor core and the inner surface of the yoke core portion; the step difference portion face the cooling wind path; and the thickness of the step difference portion be smaller than the thickness, in the radial direction of the rotation shaft, of the stator coil that is in the slots. [0011]

It is preferred that a conductor portion of the stator coil that is wound in the slots be covered with an insulation sheet member, and another conductor portion of the stator coil that faces the cooling wind path be exposed from the insulation sheet member. [0012]

It is preferred that the maximum width, in the radial direction of the rotation shaft, of the another conductor portion of the stator coil that is exposed from the insulation sheet member be smaller than the maximum width, in the radial direction of the rotation shaft, of the conductor portion of the stator coil that is wound in the slots and shielded by the insulation sheet member from a cooling wind. [0013]

In a cross section of the commutator motor that is taken perpendicularly to the direction of the rotation shaft and whose center line is positioned substantially equidistantly from the pair of opposing magnetic pole core portions and extends passing a center of the rotation shaft, the distance between the center line and a farthest portion of the step difference portion from the center line may be larger than the distance between the center line and a closest end of the magnetic pole core portions to the center line. [0014]

It is preferred that a spacing distance in the radial direction between the step difference portion and the outer surface of the rotor core is equal to or larger than 2 mm. [0015]

The stator core may be constituted by a plurality of partial cores. [0016]

The housing may be made of a metal material. [0017]

It is preferred that the stator coil is molded with a resin. [0018] An electric tool according to a second aspect of the present invention is an electric tool that comprises: a housing; an electric motor housed in the housing; a head tool mounted on an end of the housing to machine a workpiece; and a power transmission mechanism housed in the housing to drive the head tool by a motive power from the electric motor, characterized in that, the electric motor is constituted by the commutator motor described above. [0019]

A method of manufacturing a commutator motor according to a third aspect of the present invention is a method of manufacturing a commutator motor that is housed in a housing and comprises: a rotor that extends in a direction of a rotation shaft; and stator that is assembled of two partial stators that are disposed at an outer side of an outer surface of the rotor in proximity to the outer surface and extend in the direction of the rotation shaft, characterized in that, the rotor comprises a rotor core, and each of the two partial stators comprises: a stator core that has: a yoke core portion; and a magnetic pole core portion that protrudes from an inner surface of the yoke core portion to an outer surface of the rotor core; slots that are formed by the magnetic pole core portion and the yoke core portion; and a stator coil that is molded with a resin and wound through the magnetic pole core portion in the slots, and that has a step difference portion that is positioned between the outer surface of the rotor core and the inner surface of the yoke core portion and by which a thickness of the stator coil is varied in a radial direction of the rotation shaft, where the method comprises: setting the stator coil in the stator core of each of one partial stator and the other partial stator of the two partial stators; sandwiching the stator core, in which the stator coil is set, between a lower mold and an upper mold, between which a predetermined cavity is defined, such that the stator core is set in the cavity, and pressing the stator coil to shape the stator coil into a form having a predetermined dimension; injecting a thermosetting resin into the cavity and molding the stator coil; joining the one partial stator and the other partial stator of the two partial stators together to be assembled into the stator such that the magnetic pole core portions oppose to each other; and housing the stator and the rotor in the housing. [0020]

According to the present invention, the stator coil that is molded with a resin has a step difference portion (recess portion) that is positioned between the outer surface of the rotor core and the inner surface of the stator core and by which the thickness, in a radial direction of the rotation shaft (3d), of the stator coil is varied. Accordingly, the cooling wind path for the stator coil and a rotor coil is expanded, improving the effect of cooling the commutator motor.

Brief Description of Drawings [0021] Fig. 1 is a cross section of a disk grinder that uses a commutator motor according to an embodiment of the present invention.

Fig. 2 is a cross section of the commutator motor shown in Fig. 1 taken along a line A-A.

Fig. 3 is a cross section of a stator that constitutes the commutator motor shown in Fig. 2.

Fig. 4 is a cross section of a mold used for shaping the stator shown in Fig. 3 into a resin-molded member. Fig. 5 is a top view of the stator shown in Fig. 4 taken along a line B-B. Fig. 6 is a cross section of a pair of partial stators, which are molded with resin. Fig. 7 is a cross section of a modified example of the commutator motor according to the embodiment of the present invention. Fig. 8 is a cross section of a commutator motor according to a conventional art.

Best Mode for Carrying Out the Invention [0022]

These objects and other objects and advantages of the present invention will become more apparent upon reading of the following detailed description and the attached drawings. [0023]

An embodiment of the present invention will now be specifically explained with reference to Fig. 1 to Fig. 7. Note that any components that have the same function will be denoted by the same reference numeral and will not be explained repeatedly. [0024]

[Configuration of Electric Tool]

Fig. 1 is a diagram showing, in a cross section, the entire configuration of an electric tool or a disk grinder 1 to which a commutator motor 30 according to an embodiment of the present invention is applied. The disk grinder 1 is constituted by a motor housing 2, in which the commutator motor 30 according to the present invention is housed, a gear cover 7, in which power transmission mechanism members 3e and 3f that transmit an output of a rotation shaft 3d of the motor 30 to a grinding wheel 8 are housed, a tail cover 6, in which a switch and switch circuit (unillustrated) of the commutator motor 30 are housed, and a power supply cable 6a. [0025]

The commutator motor 30 housed in the motor housing 2 includes a rotor (armature) 3 fixed on the rotation shaft 3d and a stator 4 fixed on the motor housing 2. A cooling fan 5 is fixed on the output side of the rotation shaft 3d. Rotating the cooling fan 5 introduces external cooling air (cooling wind) from air intake vents 2a formed in the tail cover 6. The cooling wind flows through the motor housing 2 or through a cooling wind path in the gap between the rotor 3 and the stator 4 and is emitted to the outside of the gear cover 7 from a fan wind purge vent 2b formed in the gear cover 7. [0026]

In the gear cover 7 is housed a power transmission mechanism, which includes a first bevel gear (pinion gear) 3e that is connected to the rotation shaft 3d of the commutator motor 30 and a second bevel gear 3f that engages with the first bevel gear 3e. The power transmission mechanism converts the rotation speed and torque of the commutator motor 30 to be oriented in a direction perpendicular to the axial direction of the rotation shaft 3d of the commutator motor 30 for them to be transmitted to a spindle 3g. The grinding wheel (grinder) 8 is mounted on the spindle 3g as its head tool, thus the grinding wheel 8 can grind or cut a workpiece. The grinding wheel 8, which has a circular shape, is covered with a protection cover 8a having a semicircular shape. [0027]

[Configuration of Commutator Motor] Fig. 2 is a cross section of the commutator motor 30 taken along a line A-A of Fig. 1. The stator 4 has a stator core 4a, which, for example, has a length of 45 to 60 mm in the axial direction, and an outer diameter of 50 mm. The stator core 4a has a pair of magnetic pole core portions (north pole and south pole) 4c that oppose to each other, and a pair of curved yoke core portions 4b that link the pair of magnetic pole core portions 4c to each other. As a whole, the stator core 4a has a substantially circular contour when seen in a cross section. The pair of magnetic pole core portions 4c are disposed substantially symmetrical with respect to a plane 14 that includes the center of rotation of the commutator motor 30 and is substantially perpendicular to the spindle 3g (or with respect to a horizontal center line 14 that extends horizontally (in a left-to-right direction) in Fig. 2).

[0028]

One magnetic pole core portion 4c and one yoke core portion 4b that adjoin each other form one slot, so a pair of slots Sl and a pair of slots S2 are formed for the magnetic pole core portions 4c respectively. A stator coil bundle 4f (hereinafter, a "stator coil bundle" will be simply referred to as "stator coil") is set in each pair of slots Sl and slots S2. The spacing distance DI l between adjoining stator coils 4f is approximately 6 mm at a maximum, and each stator coil 4f, which is made of a conductor that has as large a cross-sectional area as possible to realize a lower specific resistance, is wound through the magnetic pole core portion 4c. The use of the conductor having a large cross-sectional area can reduce heat production of the stator coils 4f. The stator core 4a, which is in close contact with the stator coils 4f, is provided with an insulation sheet 9 made of a material having an electrical insulating property. This imparts basic insulation between the stator core 4a and the stator coils 4f. [0029]

As will be described later, the stator coils 4f is molded with a thermosetting resin, so as to be fixed and improve their heat radiation performance. As shown in Fig. 2, the resin-molded stator coils 4f (hereinafter, the stator coils 4f may sometimes be called resin-molded member 4f) are covered with (shielded by) the insulation sheet 9 in the slots Sl and S2. The resin-molded members 4f have a covered portion maximum width (thickness) Dl 8 in the radial direction of the stator coils 4f. A portion of the resin-molded member 4f that is not covered with the insulation sheet 9 has an uncovered portion maximum width (thickness) D19 in the radial direction, which is smaller than the covered portion maximum width Dl 8 (D19<D18), forming a step difference portion (recess portion) 13 of the resin-molded members 4f. The step difference portion 13 can enlarge the cross-sectional area of a cooling wind path 10 that is formed between the rotor 3 and the stator 4 and extends along the direction of the rotation shaft. Further, the step difference portion 13 can expose the conductor of the stator coils 4f directly to the cooling wind, with no intervention of the insulation sheet 9. Hence, the step difference portion

13 can improve the performance of cooling the stator coils 4f. [0030]

As shown in Fig. 2, when considering distance from the horizontal center line 14, which is positioned substantially equidistantly from the pair of opposing magnetic pole core portions 4c and extends passing the center of rotation of the motor's cross section, the end 13a of the step difference portion 13 of the stator coils 4f is at a distance Dl 3 from the horizontal center line 14, which is larger than the vertical distance Dl 5 between a protruding end 4d of each magnetic pole core portion 4c and the horizontal center line

14 (D13>D15). As shown in a modified example of Fig. 7, the end 13a of the step difference portion may be at a distance D13 that is substantially equal to the vertical distance D15 (D13=D15). [0031]

The above-described configuration of the commutator motor 30 enables as thick a coil bundle 4f as possible to be set in a region in the slots Sl and S2 that is unable to be part of the cooling wind path 10 for the rotor 3 as being out of the range of the vertical distance Dl 5. On the other hand, the step difference portion 13 formed in a region that is within the range of the vertical distance Dl 5 to be able to form the cooling wind path 10 for the rotor 3 enables as thin a coil bundle 4f as possible to be set. Hence, the step difference portion 13 can make the cooling wind path 10 formed between the inner surface 4h of the stator 4 and the outer surface 3h of the rotor 3 larger in size than conventional. This can improve the effect of cooling the rotor 3, as well as the effect of cooling the stator 4 with the enlargement of the stator coils 4f. [0032]

The smaller maximum width Dl 9 at the step difference portion 13 that is defined in the radial direction of the coil can define the spatial distance Dl 6 between the rotor core 3 a and a conductor 4fl, which is an uncovered portion of the coil resin-molded members 4f, to be equal to or larger than 2 mm. The spatial distance Dl 7 between the stator core 4a and a conductor 4f2, which is another uncovered portion of the coil 4f can also be defined to be equal to or larger than 2 mm. Which means, the rotor core 3 a and the stator core 4a can meet a requirement provided by Electrical Appliance and Material Safety Law laid down by a ministerial ordinance, as regards basic insulation between them and the conductors 4fl and 4f2. Hence, even if the motor housing 2 (see Fig. 1), which houses and supports the stator core 4a and the rotor core 3 a, is made of a metal material, which has a large breaking strength, sufficient electrical insulation can be ensured between the motor housing 2 and the electric circuit. [0033]

In the embodiment described above, in terms of distance from the horizontal center line 14, which extends in a radial direction of the circular cross section of the motor, the end 13a of the step difference portion 13 provided to each stator coil 4f is at the distance Dl 3 from the horizontal center line 14, which is larger than the vertical distance Dl 5 between the protruding end 4d of each magnetic pole core portion 4c and the horizontal center line 14 (D13>D15). Such a step difference portion 13 makes it easier for the cooling wind to reach a retired portion of the coils 4f that is deep inside the slots Sl and S2. The insulation sheet 9 covers a limited range that extends from a dividing position 4e, at which the stator core 4a is divided, to about the magnetic pole protruding end 4d of each magnetic pole core portion 4c. Hence, approximately a half of the surface of each resin-molded member 4f or the stator coil faces the cooling wind path 10. This structure can achieve a remarkably greater effect of cooling the rotor 3 and the stator coils 4f than the modified example shown in Fig. 7 can. [0034]

In the modified example shown in Fig. 7, in terms of distance from the horizontal center line 14, which is positioned substantially equidistantly from the pair of opposing magnetic pole core portions 4c and extends to pass the center of rotation of the cross section of the motor, the end 13a of the step difference portion is formed at the distance Dl 3 from the horizontal center line 14, which is substantially equal to the vertical distance Dl 5 between the protruding end 4d of each magnetic pole core portion 4c and the horizontal center line 14 (D13=D15). Hence, the portion in the vicinity of the step difference portion 13 has a substantially right-angled cross sectional shape (or a cross sectional shape of a stair of a staircase), making it easier to make the resin-molded body of the stator coils 4f. [0035]

[Assembly of Commutator Motor]

Next, the procedures of assembling the commutator motor 30 according to the embodiment shown in Fig. 2 will be explained with reference to Fig. 3 to Fig. 6. [0036] (1) As shown in Fig. 3, a stator coil (coil bundle) 4f is set in the stator core 4a to assemble a partial stator 22a (see Fig. 6), which is one of partial stators of a single stator. [0037]

(2) As shown in Fig. 4, the stator core 4a and the stator coil 4f are sandwiched between a lower mold 20 and an upper mold 21, between which a cavity 20a having prescribed dimensions is defined, such that the stator core 4a and the stator coil 4f are set in the cavity 20a. Then, the stator coil bundle 4f is pressed and shaped into a form having the prescribed dimensions. [0038]

(3) Then, a thermosetting resin is injected through a runner (unillustrated) into the cavity 20a defined between the lower mold 20 and the upper mold 21 (see Fig. 4). Then, the stator coil 4f is molded to form a resin-molded member 22a (see Fig. 6) of the stator 4, which is an integrated body of the stator coil 4f to the stator core 4a. At this time, as shown in Fig. 5, coil ends 4g that protrude in a bundle from both ends of the stator core 4a in the direction of the rotation axis are also set in the cavity 20a defined between the lower mold 20 and the upper mold 21 and resin-molded. [0039] After the thermosetting resin injected into the cavity between the molds 20 and 21 is cured, the molds 20 and 21 are released from each other and a pair of partial stators 22a and 22b are hence obtained, as shown in Fig. 6. Resin molding by the molds 20 and 21 forms a molded resin filler 12 hi the gaps between the conductor wires of the conductor 4f. [0040]

(4) Next, the pair of partial stators 22a and 22b are joined together and assembled into the stator 4. [0041]

As the above described assembling procedures have revealed, the stator core 4a is a divided core and hence allows a larger stator coil bundle 4f to be set therein. The ability to sandwich the stator coil 4f between the lower mold 20 and the upper mold 21 from beneath and above facilitates shaping of the stator coil bundle 4f and can prevent coil breakage during shaping. Further, the molds 20 and 21 can be easily detached when resin molding sealing is completed. [0042]

In a disk grinder that is assembled by incorporating the commutator motor 30 according to the embodiment described above into the motor housing 2 shown in Fig. 1, air that is taken hi through the ah- intake vents 2a by the cooling fan 5 circulates through the cooling wind path 10 (see Fig. 2) in the commutator motor 30, efficiently dissipating heat produced by the rotor 3 and stator 4 in the commutator motor 30. Hence, an electric tool with a high output power and excellent electric insulation can be provided. [0043] Thought having been explained by way of embodiment, the invention of the present inventor is not limited to the embodiment described above but may be modified in various respects within the scope of the spirit of the invention. [0044] The present application is based on Japanese Patent Application No. 2008-245077 filed on September 25, 2008 and including specification, claims, drawings and summary. The disclosure of the above Japanese Patent Application is incorporated herein by reference in its entirety.

Claims

CLAIMS Claim 1.

A commutator motor housed in a housing and comprising: a rotor that extends in a direction of a rotation shaft; and stator that is disposed at an outer side of an outer surface of the rotor in proximity to the outer surface and extends in the direction of the rotation shaft, characterized in that, the rotor comprises a rotor core, and the stator comprises: a stator core that has: a yoke core portion; and a pair of magnetic pole core portions that oppose to each other and protrude from an inner surface of the yoke core portion to an outer surface of the rotor core; slots that are formed by the magnetic pole core portions and the yoke core portion; and a stator coil that is wound through the magnetic pole core portions in the slots, and that has a step difference portion that is positioned between the outer surface of the rotor core and the inner surface of the yoke core portion and by which a thickness, in a radial direction of the rotation shaft, of the stator coil is varied.

Claim 2.

The commutator motor according to claim 1, comprising a cooling wind path that is formed between the outer surface of the rotor core and the inner surface of the yoke core portion, wherein the step difference portion faces the cooling wind path, and a thickness of the step difference portion is smaller than a thickness, in the radial direction of the rotation shaft, of the stator coil that is in the slots.

Claim 3.

The commutator motor according to claim 2, wherein a conductor portion of the stator coil that is wound in the slots is covered with an insulation sheet member, and another conductor portion of the stator coil that faces the cooling wind path is exposed from the insulation sheet member.

Claim 4.

The commutator motor according to claim 3, wherein a maximum width, in the radial direction of the rotation shaft, of the another conductor portion of the stator coil that is exposed from the insulation sheet member is smaller than a maximum width, in the radial direction of the rotation shaft, of the conductor portion of the stator coil that is wound in the slots and shielded by the insulation sheet member from a cooling wind.

Claim 5.

The commutator motor according to claim 1, wherein in a cross section of the commutator motor that is taken perpendicularly to the direction of the rotation shaft and whose center line is positioned substantially equidistantly from the pair of opposing magnetic pole core portions and extends passing a center of the rotation shaft, a distance between the center line and a farthest portion of the step difference portion from the center line is larger than a distance between the center line and a closest end of the magnetic pole core portions to the center line.

Claim 6.

The commutator motor according to claim 1 , wherein a spacing distance in the radial direction between the step difference portion and the outer surface of the rotor core is equal to or larger than 2 mm.

Claim 7.

The commutator motor according to claim 1, wherein the stator core is constituted by a plurality of partial cores.

Claim 8.

The commutator motor according to claim 1 , wherein the housing is made of a metal material.

Claim 9.

The commutator motor according to claim 1, wherein the stator coil is molded with a resin.

Claim 10. An electric tool, comprising: a housing; an electric motor housed in the housing; a head tool mounted on an end of the housing to machine a workpiece; and a power transmission mechanism housed in the housing to drive the head tool by a motive power from the electric motor, characterized in that, the electric motor is constituted by the commutator motor according to claim 1.

Claim 11.

A method of manufacturing a commutator motor that is housed in a housing and comprises: a rotor that extends in a direction of a rotation shaft; and stator that is assembled of two partial stators that are disposed at an outer side of an outer surface of the rotor in proximity to the outer surface and extend in the direction of the rotation shaft, characterized in that, the rotor comprising a rotor core, and each of the two partial stators comprising: a stator core that has: a yoke core portion; and a magnetic pole core portion that protrudes from an inner surface of the yoke core portion to an outer surface of the rotor core; slots that are formed by the magnetic pole core portion and the yoke core portion; and a stator coil that is molded with a resin and wound through the magnetic pole core portion in the slots, and that has a step difference portion that is positioned between the outer surface of the rotor core and the inner surface of the yoke core portion and by which a thickness, in a radial direction of the rotation shaft, of the stator coil is varied, wherein the method comprises: setting the stator coil in the stator core of each of one partial stator and the other partial stator of the two partial stators; sandwiching the stator core, in which the stator coil is set, between a lower mold and an upper mold, between which a predetermined cavity is defined, such that the stator core is set in the cavity, and pressing the stator coil to shape the stator coil into a form having a predetermined dimension; injecting a thermosetting resin into the cavity and molding the stator coil; joining the one partial stator and the other partial stator of the two partial stators together to be assembled into the stator such that the magnetic pole core portions oppose to each other; and housing the stator and the rotor in the housing.