Electric motor

An electric motor has a rotor, stator, and covers. A stator coil is a pre-wound coil inserted into slots of a stator core from its inner side. A no-lead-wire side coil end portion of the stator coil protrudes radially inward. A no-lead-wire side coolant chamber is liquid-tightly defined by the cover covering the no-lead-wire side coil end portion and a seal plate(s) that is attached from or on a radially inner side of the stator core so as to cover an opening between the inner peripheral edge of the cover and the inner peripheral edge of the stator core.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2010-257439 filed on Nov. 18, 2010 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to electric motors, and in particular to electric motors having covers that cover, respectively, coil end portions protruding toward the respective axial sides of a stator and that define, respectively, a coolant chamber storing therein a coolant.

2. Description of Related Art

An electric motor is known which is provided with a stator having a plurality of stator coils circumferentially arranged at an inner periphery of a cylindrical stator core. The stator coils are each wound around one or more of teeth protruding radially inward from the inner periphery of the stator core, and the axial ends of each stator coil protrude outward from the respective axial ends of the stator, forming “coil end portions”.

Lead wires are connected to the coils, and each coil is energized with the voltage externally supplied via the lead wires, so that a current occurs at the coil. At this time, a copper loss due to the electric resistance in the coil wire (e.g., a copper wire with an insulation coating) from which the coil is formed, and this causes the coil to heat up. As the coil thus heats up and its temperature increases, the insulation of the coil degrades. In particular, in the case of multi-phase alternating current electric motors, such insulation degradation may promote electric discharges between the coil end portions of coils for different phases, between which the electric potential difference is large. In order to prevent such electric discharges, coil end portions formed as described above are cooled using a coolant, such as a cooling oil.

Japanese Patent Application Publication No. 2006-271150, which is a related-art document, describes a motor generator cooling structure. In this cooling structure, coil end portions arranged in a generally annular form and each protruding outward from an axial end face of a stator core are liquid-tightly covered by a cooling jacket filled with an externally supplied cooling oil that contacts and thereby cools the coil end portions over the entire circumference. In the cooling structure, after the coils are wound, an adaptor is attached on slot openings at the inner periphery of the stator core, so as to seal the slot openings to prevent the cooling oil, after entering each slot from the cooling jacket, from leaking to the gap between the stator and the rotor.

Further, Japanese Patent Application Publication No. 2005-323416 describes a motor generator cooling structure in which a coil is disposed in slots of a stator core, the inside of each slot is made a coolant passage by closing the opening of the slot, which opens at the inner peripheral face of the stator core, cooling jackets are provided which surround, respectively, coil end portions protruding from the front and rear ends of the stator core, respectively, and thus form annular liquid-tight spaces, coolant inlets are formed at the lower sides of the respective cooling jackets at the front and rear ends of the stator core, coolant outlets are formed at the upper sides of the respective cooling jackets, and the coolant is made to flow from the lower side to the upper side in each cooling jacket.

Further, Japanese Patent Application Publication No. 2009-177864 describes a stator having a stator core and coils wound on the stator core, wherein coil end portions of the respective coils, which axially protrude from an axial end face of the stator core, are resin-molded to be made “resin-molded coil end portions”, and this stator having the resin-molded coil end portions is characterized in that a cavity is provided in the stator core to reduce its weight. According to Japanese Patent Application Publication No. 2009-177864, in order to prevent the resin from entering the cavity when the coil end portions are resin-molded, a pair of sealing steel plates are provided on the respective axial end faces of the stator core so as to fully cover the openings of the cavity.

In both the structures described in Japanese Patent Application Publications No. 2006-271150 and No. 2005-323416, the coil end portions protruding toward the respective axial sides from the respective end faces of the stator core are shaped to be located, as viewed axially, between the inner and outer peripheral faces of the stator core, and the liquid-tight coolant passages are formed by covering the coil end portions by the cooling jackets each C-shaped in section.

However, some stator coils are formed such that no-lead-wire side coil end portions, which are coil end portions on one side, are radially large in size, protruding from an end face of the stator core radially inward. In this structure, a gap or opening is created between the inner peripheral edge of the jacket and the inner peripheral edge of the stator core. In such a case, therefore, a liquid-tight coolant chamber can not be formed by simply covering the coil end portions by a cooling jacket that is C-shaped in section. As such, electric motors having stator coils formed as described above require some measures for covering the gap or opening between the inner peripheral edge of the cooling jacket and the inner peripheral edge of the stator core if a coolant chamber needs to be formed around the coil end portions. Japanese Patent Application Publication No. 2009-177864 does not address this issue at all.

SUMMARY OF THE INVENTION

The invention provides an electric motor in which a coil end portion protruding radially inward is covered so as to form a liquid-tight coolant chamber.

An aspect of the invention relates to an electric motor. The electric motor has: a stator that is provided with a cylindrical stator core having, at an inner periphery thereof, a plurality of teeth arranged circumferentially and protruding, and a stator coil that is inserted into slots formed between the teeth of the stator core so as to provide coil windings around one or more of the teeth; a rotor that is rotatably provided in the stator; and covers that cover, respectively, a coil end portion being a part of the stator coil and protruding outward from one axial end face of the stator core and a coil end portion being a part of the stator coil and protruding outward from the other axial end face of the stator core, and that each define therein a coolant chamber in which a coil-end-cooling coolant is liquid-tightly stored. The stator coil is a pre-wound coil having a predetermined coil form and is inserted into the slots from the radially inner side of the stator core to provide the coil windings around the one or more of the teeth. The coil end portions include a lead-wire side coil end portion provided at one axial side to which a power feed line is connected and a no-lead-wire side coil end portion provided at the other axial side. The no-lead-wire side coil end portion is shaped to protrude to a position that is closer to the rotation axis of the rotor than the inner peripheral face of the stator core is. The coolant chamber in a no-lead-wire side where the no-lead-wire side coil end portion is present is formed liquid-tight by the cover covering the no-lead-wire side coil end portion and a seal member that is attached from or on the radially inner side of the stator core so as to cover an opening between the inner peripheral edge of the cover covering the no-lead-wire side coil end portion and the inner peripheral edge of the stator core.

The electric motor according to the aspect of the invention may be such that the seal member is constituted of a plurality of stepped-wedge-like seal plates that each have a large width portion at a radially inner side and are inserted, from the radially inner side of the stator core, into between the cover covering the no-lead-wire side coil end portion and a no-lead-wire side end face of the stator core, and the respective seal plates cover no-lead-wire side ends of radial openings of the respective slots of the stator core.

The electric motor according to the aspect of the invention may further have a cylindrical seal member that covers the inner peripheral face of the stator core so as to cover the radial openings of the respective slots over the entire axial lengths of the radial openings.

The electric motor according to the aspect of the invention may be such that the cylindrical seal member is integrally formed at the inner periphery of the cover covering the lead-wire side coil end portion.

The electric motor according to the aspect of the invention may be such that: the seal member includes a gear-shaped seal plate having: projecting portions that are formed at the outer periphery of the seal plate and fit in radial openings of the respective slots of the stator core when the seal plate is inserted into the inside of the stator core from a lead-wire side where the lead-wire side coil end portion is present; and root portions which are formed at the outer periphery of the seal plate and in which radial tip portions of the respective teeth of the stator core fit when the seal plate is inserted into the inside of the stator core from the lead-wire side; and the seal plate is inserted into the inside of the stator core from the lead-wire side, then moved out of the inside of the stator core, then set, in the no-lead-wire side, in a position between the cover covering the no-lead-wire side coil end portion and the no-lead-wire side end face of the stator core, then turned circumferentially between the cover covering the no-lead-wire side coil end portion and the no-lead-wire side end face of the stator core, so as to bring the projecting portions of the seal plate into contact with the axial end faces of tip portions of the respective teeth of the stator core, and then fixed in the position.

The electric motor according to the aspect of the invention may be such that: the seal member is a disc-spring-like seal plate of which the diameter is smaller than the inner diameter of the stator core when the seal member is inserted into the inside of the stator core from the lead-wire side, and increases when the seal plate is squashed in the no-lead-wire side, or is a split-ring-like seal plate that increases in diameter by being widened circumferentially; and the seal plate gets, by increasing in diameter in the no-lead-wire side, into between the protruding portion of the no-lead-wire side coil end portion and a no-lead-wire side end face of the stator core.

The electric motor according to the aspect of the invention may be such that the seal member has: a flange portion that covers the opening between the inner peripheral edge of the cover covering the no-lead-wire side coil end portion and the inner peripheral edge of the stator core; and a cylindrical portion that covers the inner peripheral face of the stator core so as to cover the radial openings of the respective slots over the entire axial lengths of the radial openings.

According to the electric motors of the aspect of the invention, the opening between the inner peripheral edge of the cover and the inner peripheral edge of the stator core is covered by the seal member that is attached from or on the radially inner side of the stator core, and therefore the coolant chamber provided around the no-lead-wire side coil end portion protruding radially inward is sealed more reliably. As such, it is possible to prevent leaks of the coolant from the coolant chamber, enhance the cooling of the stator coil, and achieves an improved insulation of the stator coil.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, example embodiments of the invention will be described in detail with reference to the accompanying drawings. It is to be noted that the shapes, forms, materials, values, directions, and so on, specified in the following descriptions are no more than examples for facilitating understanding of the invention, and thus they may be changed as needed in accordance with the use, purpose, specification, etc.

In the following, the coolant used in each of the electric motors of the respective example embodiments is a cooling oil. However, it is to be noted that the coolants applicable to cooling structures according to the invention are not limited to it, but they include various other coolants, such as cooling water (e.g., LLC (Long Life Coolant)).

Further, in this specification, the terms “axial direction”, “axially”, “axial”, and the like, refer to the direction of the rotation axis of the rotor, the direction of the central axis of the cylindrical stator, and the directions corresponding to them, the terms “radial direction”, “radially”, “radial”, and the like, refer to the directions perpendicular to such axial directions, and the terms “circumferential direction”, “circumferentially”, “circumferential”, and the like, refer to each direction along the circumference of a circle drawn about a given point of the rotation axis on a plane perpendicular to the rotation axis.

FIG. 1shows an axial section of an electric motor10of an example embodiment of the invention. The electric motor10is a three-phase alternating current electric motor, for example, and it will hereinafter be referred to as “motor10” where necessary. The motor10has a rotor12and a stator14.

The rotor12has a rotor core16that is columnar and a rotor shaft18that penetrates the center of the rotor core16. In the rotor core16, multiple permanent magnets (not shown in the drawings) are embedded at equiangular positions close to the outer peripheral face of the rotor core16. The both ends of the rotor shaft18are rotatably supported, respectively, by bearings (not shown in the drawings) attached in a motor case (not shown in the drawings). Further, the rotor core16is constituted of a plurality of generally circular electromagnetic steel plates that are axially stacked on top of each other and each have a shaft insert hole, magnet insert holes, and so on.

The stator14has a stator core20, stator coils22, and covers24aand24b. The stator core20is cylindrical and is constituted of, for example, a plurality of ring-shaped electromagnetic steel plates that are manufactured by punching electromagnetic steel plates into a ring shape and are then stacked and joined together by caulking, welding, adhesion, clamping, or the like. Created between the outer peripheral face of the rotor core of the rotor12, which is provided on the radially inner side of the stator14, and the inner peripheral face of the stator core20is a gap g extending over the entire circumference and having an uniform radial length. Preferably, the gap g is minimized to increase the motor efficiency, however it is designed also in consideration of other requirements, such as preventing the rotor core16from contacting the inner peripheral face of the stator core20during rotation of the rotor12.

Multiple teeth26are formed at the inner periphery of the stator core20. The teeth26are equiangularly arranged and protrude radially inward. The teeth26extend axially and are equal in axial length to the stator core20. Provided between the respective teeth26adjacent to each other circumferentially are slots28(refer toFIG. 2). The total number of the slots28is equal to that of the teeth26.

The stator coils22are each provided around one or more of the teeth26and formed of, for example, a copper wire having an insulation coating. In this example embodiment, the stator coils22are pre-wound coils, each wound beforehand into a predetermined coil form using a winding machine (winding form), or the like, and then attached by being inserted into the slots28from the radially inner side of the stator core20. Each stator coil22is provided in the form of “distributed winding”, that is, the axially extending portions of each stator coil22are inserted into two of the slots28that are a predetermined distance away from each other circumferentially across two or more of the teeth26.

FIG. 2shows a cross section of the stator coils22set in the slots28. In this example embodiment, the stator coils22are each formed of a rectangular coil wire having a flat rectangular cross section. In this example embodiment, six windings of the coil wire(s)21are radially stacked in each slot28. The insulation between the stator core20and the stator coils22may be increased by interposing an insulation paper between the inner face of each slot28and the coil wire(s)21or filling resin into a gap between the inner face of each slot28and the coil wire(s)21if any. Further, in a case where there are gaps between the respective windings in each slot28, the gaps may be filled with resin such that the coil wires21are supported by the slots28. Further, if the gaps between the respective windings in each slot28are filled with resin, the cooling oil is prevented from entering the slots28from a cooling oil chamber, which will be described later, and therefore the cooling oil is prevented from flowing out to the gap g via radial openings29, in the radially inner face of the stator core20, of the respective slots28, thereby avoiding an increase in the rotational resistance against the rotor12, which may be caused if the cooling oil flows out to the gap g.

Referring back toFIG. 1, each stator coil22has coil end portions23aand23bprotruding outward from the respective end faces of the stator core20. The coil end portions23aand23bof the stator coils22are successively arranged in an annular form corresponding to the annular shape of the stator core20, as viewed axially.

Lead wires (power feed lines) (not shown in the drawings) via which power is externally supplied are connected to the coil end portions23ashown in the right side ofFIG. 1. More specifically, since the motor10is a three-phase alternating current electric motor, three lead wires for the U-phase coil, V-phase coil, and W-phase coil are connected to the lead-wire side coil end portions23a. In the following descriptions, the coil end portions to which the lead wires are connected will be referred to as “lead-wire side coil end portions” where necessary, while the coil end portions in the side opposite to where the lead-wire side coil end portions are present will be referred to as “no-lead-wire side coil end portions” where necessary. Further, the axial side where the lead wires are present (the right side inFIG. 1) will be referred to as “lead-wire side” where necessary, while the other axial side (the left side inFIG. 1) will be referred to as “no-lead-wire side” where necessary.

The lead-wire side coil end portions23aprotrude axially from the end face of the stator core20and are located, as viewed axially, between the outer and inner peripheral faces of the stator core20. On the other hand, the no-lead-wire side coil end portions23bare formed such that they extend radially inward along the axial end face of the stator core20and each protrude to a position closer to the rotor rotation axis than the inner peripheral face of the stator core20is, that is, than top faces27of the respective teeth26at the radially inner side (refer toFIG. 2) are.

In this example embodiment, the protruding portion of each no-lead-wire side coil end portion23bis rectangular in section, but it may be formed into various other shapes. For example, the radially inner side outline of the protruding portion of each no-lead-wire side coil end portion23bmay be rounded (e.g., U-shaped), as viewed in section.

Multiple bolt insert portions30protrude radially outward at the outer periphery of the stator core20. The bolt insert portions30are, for example, three, and they are equiangularly arranged. A bolthole penetrates the inside of each bolt insert portion30. Bolts32are inserted into the respective boltholes from one axial side, and nuts34are screwed to bolt tips33of the respective bolts32at the other axial side, whereby the stator core20, the lead-wire side cover24a, and the no-lead-wire side cover24bare joined together.

Meanwhile, internal thread holes may be provided at the motor case, and the bolt tips33of the respective bolts32may be screwed into the respective internal thread holes to fasten the stator14.

The lead-wire side cover24ais fixed to the stator core20so as to cover the lead-wire side coil end portions23a, while the no-lead-wire side cover24bis fixed to the stator core20so as to cover the no-lead-wire side coil end portions23b. In the motor10of this example embodiment, the lead-wire side coil end portions23aand the no-lead-wire side coil end portions23bare different in shape and size, and therefore the two covers24aand24bare made different in shape, size, and sealing structure in accordance with the lead-wire side coil end portions23aand the no-lead-wire side coil end portions23b.

More specifically, the lead-wire side cover24ais C-shaped (or bracket-shaped) in section and is annular, covering the lead-wire side coil end portions23aover the entire circumference. Further, preferably, the lead-wire side cover24ais made of a resin material that is insulative and non-magnetic. The lead-wire side cover24ahas, at its outer periphery, tabs36shaped correspondingly to the respective bolt inset portions30of the stator core20, and the bolts32are inserted into insert holes formed at the respective tabs36, whereby the lead-wire side cover24ais fixed on the lead-wire side end face of the stator core20.

On the other hand, the no-lead-wire side cover24bis C-shaped (or bracket-shaped) in section and is annular, covering the no-lead-wire side coil end portions23bover the entire circumference, as is the lead-wire side cover24a. However, since the no-lead-wire side coil end portions23bprotrude radially inward and thus are large in size, the no-lead-wire side cover24bis radially sized such that it protrudes radially inward more than the no-lead-wire side coil end portions23bdo, in order to cover the no-lead-wire side coil end portions23b.

A lead-wire side cooling oil chamber38ais provided around the lead-wire side coil end portions23ain the lead-wire side cover24a. The lead-wire side cooling oil chamber38astores therein the cooling oil fed via a cooling oil feed hole (not shown in the drawings). The lead-wire side ends of the radial openings29of the respective slots28of the stator core20are sealed by seal plates (seal members)40a, keeping the lead-wire side cooling oil chamber38aliquid-tight.

On the other hand, a no-lead-wire side cooling oil chamber38bis provided around the no-lead-wire side coil end portions23bin the no-lead-wire side cover24b. The no-lead-wire side cooling oil chamber38bstores therein the cooling oil fed via a cooling oil feed hole (not shown in the drawings). The no-lead-wire side ends of the radial openings of the respective slots28and an annular opening39between the radially inner peripheral edge of the no-lead-wire side cover24band the inner peripheral edge of the stator core20are sealed by seal plates (seal members)40b, keeping the no-lead-wire side cooling oil chamber38bliquid-tight.

According to the structure described above, the cooling oils stored, respectively, in the lead-wire side cooling oil chamber38aand the no-lead-wire side cooling oil chamber38bcontact the lead-wire side coil end portions23aand the no-lead-wire side coil end portions23baxially, and radially, whereby the entireties of the lead-wire side coil end portions23aand no-lead-wire side coil end portions23bare cooled efficiently, that is, the entireties of the respective stator coils22can be cooled efficiently. As a result, the insulation of the stator coils22can be maintained or improved, and the current density at each stator coil22can be increased for a higher output of the motor.

While the cooling oil feed holes via which the cooling oils are fed, respectively, to the lead-wire side cooling oil chamber38aand the no-lead-wire side cooling oil chamber38bare individually provided at the covers24aand24bin the respective axial sides in the example presented above, a single cooling oil feed hole may alternatively be provided. In this case, for example, the lead-wire side cooling oil chamber38aat one axial side and the no-lead-wire side cooling oil chamber38bat the other axial side are interconnected via a communication passage (not shown in the drawings) and the cooling oil is fed to one of the cooling oil chambers38aand38bvia the single cooling oil feed hole and then delivered to the other via the communication passage.

Meanwhile, the cooling oils heated through the cooling of the stator coils22are discharged to the outside via a cooling oil drain hole(s) (not shown in the drawings), then cooled through heat radiation at an oil cooler, or the like, and then recirculated to the cooling oil chambers using an oil pump(s), or the like.

First Example Embodiment

In the following, the seal structure for the cooling oil chambers in the motor10of the first example embodiment will be described with reference toFIGS. 3 to 5.FIG. 3is an enlarged sectional view, taken axially, of the upper half of the stator14of the motor10shown inFIG. 1.FIG. 4is a view illustrating how seal plates40bare attached in the no-lead-wire side of the motor10.FIG. 5is a view illustrating how seal plates40aare attached in the lead-wire side of the motor10.

Referring toFIG. 3, the no-lead-wire side cooling oil chamber38bis defined by the no-lead-wire side cover24band the seal plates40b. The seal plates40bcover the annular opening39between a radially inner peripheral edge25of the no-lead-wire side cover24band an inner peripheral edge20aof the stator core20. Preferably, the seal plates40bare made of a non-magnetic material, such as resin, which does not affect the magnetic characteristic of the stator core20.

Referring toFIG. 4, the seal plates40bare multiple separate stepped-wedge-like members, the number of which is equal to the number of the teeth26and which are arranged circumferentially. Each seal plate40bis generally T-shaped, having a large width portion41bat the radially inner side and a tapered extension portion42at the radially outer side. Each seal plate40bis inserted, from the radially inner side, into between the no-lead-wire side cover24band the no-lead-wire side end face of the stator core20while the lead-wire side cover24aand no-lead-wire side cover24bare temporarily, and lightly, attached on the store core20using the bolts32and nuts34. That is, each seal plate40bis inserted in a direction perpendicular to the axial direction and then fixed in position. After all the seal plates40bare inserted over the entire circumference, the bolts32are tightened up, pressing and thus sealing the contact boundary between the no-lead-wire side cover24band the seal plates40b. It is to be noted that an additional sealer, such as a gasket, O-ring, sealant, and adhesive, may be provided at or applied to the contact boundary to enhance the sealing effect.

The large width portions41bof the respective seal plates40bare tightly arranged along the entire circumference, covering the annular opening39between the radially inner peripheral edge25of the no-lead-wire side cover24band the inner peripheral edge20aof the stator core20. Further, each of the no-lead-wire side ends of the radial openings29of the respective slots28is covered by one of corner portions41clocated at the radially outer side of the large width portion41bof the corresponding seal plate40band one of the corner portions41cof the large width portion41bof the seal plate40badjacent to the former seal plate40b, whereby the no-lead-wire side cooling oil chamber38bis sealed liquid-tightly. In the meantime, the tip of the extension portion42of each seal plate40bis fit into a recess formed in the no-lead-wire side cover24band then fixed in position by being securely sandwiched between the no-lead-wire side cover24band the stator core20.

Meanwhile, the sealing structure for the lead-wire side cooling oil chamber38ais almost the same as described above. That is, the lead-wire side cooling oil chamber38ais sealed by the multiple seal plates40athat are inserted radially and then fixed in their positions by being sandwiched between the lead-wire side cover24aand the lead-wire side end face of the stator core20. For the lead-wire side cooling oil chamber38a, it is sufficient that only the lead-wire side ends of the radial openings29of the respective slots28of the stator core20be covered, and therefore a radial length L2of the large width portion41bof each seal plate40ais shorter than a radial length L1of the large width portion41bof each seal plate40bin the no-lead-wire side, which is the only difference of the seal plates40afrom the seal plates40b.

As described above, in the motor10of the first example embodiment, the seal plates40bare inserted into the stator core20from the radially inner side so as to cover the opening39between the inner peripheral edge25of the no-lead-wire side cover24band the inner peripheral edge20aof the stator core20. Therefore, it is possible to reliably seal the no-lead-wire side cooling oil chamber38bthat is provided around the no-lead-wire side coil end portions23bprotruding radially inward. This prevents leaks of the cooling oil from the no-lead-wire side cooling oil chamber38b, enhances the cooling of the stator coils22, and achieves an improved insulation of the stator coils22.

Further, since the gaps between the respective windings in each slot28and/or the gap between the inner wall face of each slot28and the windings in the same slot28are filled up with resin, or the like, there is no possibility that the cooling oil enter the slots28from the end face of the stator core20and then leak to the inner periphery of the stator core20or to the radially inner side of the stator core20.

Second Example Embodiment

In the following, the sealing structure for the cooling oil chambers in the motor10of the second example embodiment will be described with reference toFIGS. 6 to 9.FIG. 6is an enlarged sectional view corresponding toFIG. 3and illustrating how seal plates44are attached in the motor10of the second example embodiment.FIG. 7is a plan view of each seal plate44.FIG. 8is a view illustrating how the two seal plates44, after inserted into the stator core20from the lead-wire side, are moved toward the no-lead-wire side.FIG. 9is an enlarged partial view illustrating how the seal plates44are offset from each other circumferentially and set in their positions in the no-lead-wire side.

The seal plates (seal members)44for liquid-tightly sealing the no-lead-wire side cooling oil chamber38bcover, liquid-tightly, the opening39between the inner peripheral edge25of the no-lead-wire side cover24band the inner peripheral edge20aof the stator core20and the no-lead-wire side ends of the radial openings29of the respective slots28of the stator core20. In this example embodiment, the two seal plates44are stacked on each other (in contact with each other).

Referring toFIG. 7, each of the seal plates44is gear-shaped, having projecting portions45that fit into the radial openings29of the respective slots28of the stator core20and root portions49into which the radial tip portions27of the respective teeth26of the stator core20fit. The projecting portions45and the root portions46are alternately arranged at the outer periphery of each seal plate44. A shaft hole47into which the rotor shaft18is inserted is formed at the center of each seal plate44. Preferably, the seal plates44are also made of a non-magnetic material, such as resin, which does not affect the magnetic characteristic of the stator core20.

The seal plates44are set in their position as follows. First, the two seal plates44are inserted, from the lead-wire side, into the stator core20in which the respective stator coils22have been already set. Then, the lead-wire side cover24aand the no-lead-wire side cover24bare temporarily, and lightly, attached on the stator core20using the bolts32and the nuts34.

Referring toFIG. 8, the two seal plates44are pushed toward the no-lead-wire side with the projecting portions45and root portions49being almost tightly fit to the radial openings29of the slots28and the radial tip portions27of the teeth26, respectively. Then, referring toFIG. 9showing the seal plates44as viewed axially, after the seal plates44have been set in their positions between the no-lead-wire side cover24band the stator core20where the axially outer of the seal plates44is in contact with the no-lead-wire side cover24b, one of the seal plates44, which is drawn by solid lines inFIG. 9, is slightly turned in one circumferential direction (e.g., clockwise) such that each projecting portion45of the same seal plate44partially overlaps, as viewed axially, the axial end face of the radial tip portion27of the corresponding one of the teeth26of the stator core20, while the other seal plate44, which is drawn by single-dot lines inFIG. 9, is slightly turned in the other circumferential direction (e.g., counterclockwise) such that each projecting portion45of the same seal plate44partially overlaps, as viewed axially, the axial end face of the radial tip portion27of the corresponding one of the teeth26of the stator core20, which is adjacent to the former corresponding one of the teeth26. In this state, the seal plate44on the axially outer side is in tight contact with the radially protruding portions of the no-lead-wire side coil end portions23b. That is, as viewed axially, the two seal plates44are circumferentially offset from each other such that the slots28, which are formed between the respective teeth26, are covered by the projecting portions45of the respective seal plates44. Then, the bolts32are tightened to press the inner peripheral edge25of the no-lead-wire side cover24bliquid-tightly against the seal plates44.

In the second example embodiment, as described above, the two seal plates44are attached from the radially inner side of the stator core20so as to liquid-tightly cover the annular opening39between the inner peripheral edge25of the no-lead-wire side cover24band the inner peripheral edge20aof the stator core20and the no-lead-wire side ends of the radial openings29of the respective slots28of the stator core20. Therefore, it is possible to reliably seal the no-lead-wire side cooling oil chamber38bthat is provided around the no-lead-wire side coil end portions23bprotruding radially inward. This prevents leaks of the cooling oil from the no-lead-wire side cooling oil chamber38b, enhances the cooling of the stator coils22, and achieves an improved insulation of the stator coils22.

The sealing structure for the lead-wire side cooling oil chamber38ain this example embodiment is not specifically described above. However, the seal plates44described above or the seal plates40ain the first example embodiment may be used for sealing the lead-wire side cooling oil chamber38a. Alternatively, other sealer, such as a gasket, O-ring, sealant, and adhesive, may be provided or applied to seal only the lead-wire side ends of the radial openings29of the respective slots28of the stator core20. Note that such sealing structures may be applied to the third and fourth example embodiments described later.

Third Example Embodiment

In the following, the motor10of the third example embodiment will be described with reference toFIGS. 10,11A, and11B.FIG. 10illustrates how a seal plate46is attached in the motor10of the third example embodiment.FIG. 11Ais a perspective view of the seal plate46.FIG. 11Bis a perspective view of the seal plate46when squashed.

Referring toFIG. 10, the seal plate46is inserted into the stator core20from the lead-wire side and then pushed in the direction indicated by an arrow48inFIG. 10with the lead-wire side cover24aand the no-lead-wire side cover24bbeing temporarily, and lightly, attached on the stator core20using the bolts32and the nuts34. Referring toFIG. 11A, the seal plate46is shaped like a disc spring and is smaller, before attached in the motor10, in diameter than the inner diameter of the stator core20. More specifically, the seal plate46is an annular member of which the portion between the inner and outer peripheral edges is dented, toward one axial side, into an annular groove. Thus formed, the seal plate46increases in diameter as shown inFIG. 11Bwhen squashed. In this example embodiment, too, preferably, the seal plate46is made of a non-magnetic material, such as resin, which does not affect the magnetic characteristic of the stator core20.

After inserted from the lead-wire side then moved to the no-lead-wire side, the seal plate46is squashed by inserting, for example, a columnar tool from the lead-wire side, so that the seal plate46increases in diameter, causing the outer periphery of the seal plate46to get into between the protruding portions of the no-lead-wire side coil end portions23band the end face of the inner peripheral edge of the stator core20, referring toFIG. 10. Then, the bolts32are tightened to press the inner peripheral edge25of the no-lead-wire side cover24bagainst the seal plate46liquidly tightly.

In the third example embodiment, as described above, the seal plate46is attached from the radially inner side of the stator core20so as to liquid-tightly cover the opening39between the inner peripheral edge25of the no-lead-wire side cover24band the inner peripheral edge20aof the stator core20and the no-lead-wire side ends of the radial openings29of the respective slots28of the stator core20. Therefore, it is possible to reliably seal the no-lead-wire side cooling oil chamber38bthat is provided around the no-lead-wire side coil end portions23bprotruding radially inward. This prevents leaks of the cooling oil from the no-lead-wire side cooling oil chamber38b, enhances the cooling of the stator coils22, and achieves an improved insulation of the stator coils22.

Fourth Example Embodiment

In the following, the sealing structure in the motor10of the fourth example embodiment will be described with reference toFIGS. 12A and 12B.FIG. 12Ais a plan view showing the shape of a seal plate50used in the fourth example embodiment, andFIG. 12Bis a view illustrating how the seal plate50, which is shaped like a split ring (or which is in the shape of the letter “C”), increases in diameter.

Referring toFIG. 12A, the seal plate50is a split-ring-like seal plate of which both circumferential ends51aand51boverlap each other and which is smaller in diameter than the inner diameter of the stator core20, before the seal plate50is attached in the motor10. Thus, the seal plate50can be inserted into the stator core20from the lead-wire side and then moved toward the no-lead-wire side as in the third example embodiment.

Then, as shown inFIG. 12B, the ends51aand51bof the seal plate50are moved circumferentially away from each other and then butted against each other, whereby the diameter of the seal plate50is increased and maintained. The use of the seal plate50shaped like a split ring as describe above provides the same effects and advantages as those in the third example embodiment.

Fifth Example Embodiment

In the following, the sealing structure in the motor10of the fifth example embodiment will be described with reference toFIG. 13.FIG. 13is an enlarged sectional view corresponding toFIG. 3and showing a seal member used in the motor10of the fifth example embodiment together with the seal plate46in the third example embodiment.

In this example embodiment, a cylindrical seal member52is provided which covers the inner peripheral face of the stator core20so as to cover the radial openings29of the respective slots28over their entire axial lengths. Preferably, the seal member52is formed integrally at the inner periphery of the lead-wire side cover24a. However, the seal member52may be provided as a part separate from the lead-wire side cover24a.

For example, the seal member52is set in position by being press-fit to the inner periphery of the stator core20from the lead-wire side after the seal plate46in the third example embodiment is set in position in the no-lead-wire side. A sealer, such as a gasket, O-ring, sealant, and adhesive, may be provided at or applied to the boundary between the cylindrical seal member52and the seal plate46, at which they are pressed against each other.

According to the structure described above, since the cylindrical seal member52is provided on the radially inner side of the stator core20to cover the radial openings29of the respective slots28over their entire axial lengths, the cooling oil can be more reliably prevented from leaking to the gap g from the cooling oil chambers38aand38bat the respective axial sides via the slots28. It is to be noted that the sealing effect of the seal plate46is as described above.

Sixth Example Embodiment

In the following, the sealing structure in the motor10of the sixth example embodiment will be described with reference toFIG. 14.FIG. 14is an enlarged sectional view corresponding toFIG. 3and showing a seal member54in the sixth example embodiment.

The seal member54has a flange portion56that covers, in the no-lead-wire side, the opening39between the inner peripheral edge25of the no-lead-wire side cover24band the inner peripheral edge20aof the stator core20and a cylindrical portion58that covers the inner peripheral face of the stator core20so as to cover the radial openings29of the respective slots28over their entire axial lengths. A lead-wire side portion of the cylindrical portion58serves as a part of the inner peripheral wall face of the lead-wire side cooling oil chamber38a.

The seal member54may be set in position in the same manner as the cylindrical seal member52in the fifth example embodiment is. However, since the seal member54of the sixth example embodiment additionally has the flange portion56that is a seal plate covering the opening39of the no-lead-wire side cooling oil chamber38b, the sixth example embodiment provides an advantage that the cooling chambers38aand38bat the respective axial sides can be made simpler in structure, as well as the effects and advantages of the foregoing example embodiments.

While the invention has been embodied as the sealing structure for the cooling chambers in the motor10in each of the first to sixth example embodiments, it is to be understood that the invention is not limited to any of the structures and arrangements described above, but it may be embodied with various modifications and improvements.

For example, the seal plates and seal members employed in the first to sixth example embodiments may be used in various combinations.

Further, while the stator coils22, which are pre-wound coils, are provided on the stator core20in the form of “distributed winding”, the invention may also be embodied as, for example, an electric motor having, as stator coils, pre-wound coils provided around the respective teeth in the form of “concentrated winding”.