Stator for electric rotating machine

A stator for an electric rotating machine includes an annular stator core, an outer cylinder fitted on a radially outer surface of the stator core, and a stator coil mounted on the stator core. The stator core is comprised of a plurality of stator core segments that are arranged in a circumferential direction of the stator core so as to adjoin one another in the circumferential direction. The stator coil is fixed to the stator core by a thermosetting resin that is set by induction-heating the stator core. Each of the stator core segments is formed by laminating a plurality of steel sheets in an axial direction of the stator core and fixing at least some of the steel sheets by staking. The number of staking portions formed in one of the steel sheets is different from the number of staking portions formed in another one of the steel sheets.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Japanese Patent Application No. 2014-43452, filed on Mar. 6, 2014, the content of which is hereby incorporated by reference in its entirety into this application.

BACKGROUND

1 Technical Field

The present invention relates to stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.

2 Description of Related Art

Conventionally, electric rotating machines, which are used in motor vehicles as electric motors and electric generators, include a rotor and a stator that is disposed in radial opposition to the rotor. The stator includes an annular (or a hollow cylindrical) stator core and a stator coil. The stator core has a plurality of slots arranged in a circumferential direction of the stator core. The stator coil is mounted on the stator core so as to be received in the slots of the stator core. Moreover, to reduce iron loss, the stator core is generally formed by laminating a plurality of steel sheets in the axial direction thereof.

Patent Document 1 (i.e., Japanese Patent Application Publication No. JP2010288424A) discloses an annular stator core which is comprised of a plurality of stator core segments that are arranged in the circumferential direction of the stator core so as to adjoin one another in the circumferential direction. Moreover, also for the purpose of reducing iron loss, each of the stator core segments is formed by laminating a plurality of steel sheets in the axial direction of the stator core.

Patent Document 2 (i.e., Japanese Patent Application Publication No. JP2011097790A) discloses a heating device that includes an induction coil for induction-heating a stator core which has a stator coil mounted thereon.

Specifically, the heating device disclosed in Patent Document 2 is designed to fix the stator coil to the stator core by heating and thereby setting (or hardening) a liquid thermosetting resin (e.g., varnish) with the heat of the stator core that is induction-heated.

More specifically, the liquid thermosetting resin is impregnated into predetermined portions of the stator coil, which are received in the slots of the stator core, and retained at the predetermined portions. Then, the induction coil of the heating device, which is placed at a predetermined position radially inside the annular stator core, is energized to induction-heat the stator core to the setting temperature of the thermosetting resin. Consequently, with increase in the temperature of the stator core, the thermosetting resin is heated and set, thereby fixing the stator coil to the stator core.

However, since the thermosetting resin is initially in the liquid state, it may be difficult to impregnate the thermosetting resin into the predetermined portions of the stator coil and retain the same at the predetermined portions. Consequently, it may be difficult to set the thermosetting resin at the predetermined portions.

SUMMARY

According to exemplary embodiments, there is provided a stator for an electric rotating machine. The stator includes an annular stator core, an outer cylinder fitted on a radially outer surface of the stator core, and a stator coil mounted on the stator core. The stator core is comprised of a plurality of stator core segments that are arranged in a circumferential direction of the stator core so as to adjoin one another in the circumferential direction. The stator coil is fixed to the stator core by a thermosetting resin that is set by induction-heating the stator core. Each of the stator core segments is formed by laminating a plurality of steel sheets in an axial direction of the stator core and fixing at least some of the steel sheets by staking. The number of staking portions formed in one of the steel sheets is different from the number of staking portions formed in another one of the steel sheets.

With the above configuration, in induction-heating the stator core for setting the thermosetting resin, it is possible to set the temperature rise gradient in the stator core segments in the axial direction of the stator core to a desired state, thereby retaining and setting the thermosetting resin at desired positions.

In one exemplary embodiment, for each of the stator core segments, the plurality of steel sheets forming the stator core segment include a plurality of first steel sheets and a plurality of second steel sheets. The number of staking portions formed in each of the first steel sheets is larger than the number of staking portions formed in each of the second steel sheets. The first steel sheets are arranged at both end parts of the stator core segment in the axial direction of the stator core, and the second steel sheets are arranged at a central part of the stator core segment in the axial direction.

In another exemplary embodiment, for each of the stator core segments, the plurality of steel sheets forming the stator core segment include a plurality of first steel sheets and a plurality of second steel sheets. The number of staking portions formed in each of the first steel sheets is larger than the number of staking portions formed in each of the second steel sheets. The first steel sheets are arranged at a central part of the stator core segment in the axial direction of the stator core, and the second steel sheets are arranged at both end parts of the stator core segment in the axial direction.

In the above exemplary embodiments, the second steel sheets may be fixed by at least one fixing means selected from staking, welding and adhesive bonding.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments and their modifications will be described hereinafter with reference toFIGS. 1-13. It should be noted that for the sake of clarity and understanding, identical components having identical functions throughout the whole description have been marked, where possible, with the same reference numerals in each of the figures and that for the sake of avoiding redundancy, descriptions of the identical components will not be repeated.

First Embodiment

FIG. 1shows the overall configuration of an electric rotating machine1which includes a stator20according to a first embodiment.

In the present embodiment, the electric rotating machine1is configured as an electric motor for use in a motor vehicle.

As shown inFIG. 1, the electric rotating machine1further includes a housing10, a rotating shaft13and a rotor14in addition to the stator20. The housing10is comprised of a pair of cup-shaped housing pieces10aand10bwhich are jointed together at the open ends thereof. The housing10has a pair of bearings11and12mounted therein, via which the rotating shaft13is rotatably supported by the housing10. The rotor14is received in the housing10and coaxially fixed on the rotating shaft13. The stator20is fixed in the housing10so as to surround the radially outer periphery of the rotor14.

The rotor14includes a plurality of permanent magnets that form a plurality of magnetic poles on the radially outer periphery of the rotor14facing the radially inner periphery of the stator20. The polarities of the magnetic poles alternate between north and south in the circumferential direction of the rotor14. The number of the magnetic poles can be suitably set according to the design specification of the electric rotating machine1. In the present embodiment, the number of the magnetic poles is set to be equal to, for example, eight (i.e., four north poles and four south poles).

Referring now toFIGS. 2A-2B and 3, the stator20includes an annular (or a hollow cylindrical) stator core30, a three-phase stator coil40and an outer cylinder37. In addition, the stator20may further have insulating paper interposed between the stator core30and the stator coil40.

As shown inFIGS. 4-7, the stator core30includes an annular back core portion33, a plurality of stator teeth34and a plurality of slots31. Each of the stator teeth34extends from the back core portion33radially inward. The stator teeth34are equally spaced from one another in the circumferential direction of the stator core30at predetermined intervals. Each of the slots31is formed between one circumferentially-facing pair of side surfaces34aof the stator teeth34so as to open on the radially inner periphery of the stator core30. Moreover, each circumferentially-facing pair of the side surfaces34aof the stator teeth34, which define one of the slots31therebetween, extend parallel to each other. Consequently, each of the slots31radially extends at a constant circumferential width. In addition, for each of the slots31, the depth direction of the slot31is coincident with a radial direction of the stator core30.

In the present embodiment, the stator coil40is configured as a double-slot distributed winding. Accordingly, in the stator core30, there are provided two slots31per magnetic pole of the rotor14that has the eight magnetic poles and per phase of the three-phase stator coil40. That is, the total number of the slots31formed in the stator core30is equal to 48 (2×8×3). In addition, the total number of the stator teeth34formed in the stator core30is also equal to 48.

Moreover, in the present embodiment, the stator core30is comprised of a plurality (e.g.,24) of stator core segments32. The stator core segments32are arranged in the circumferential direction of the stator core30so as to adjoin one another in the circumferential direction. Each of the stator core segments32includes two stator teeth34and one slot31formed between the two stator teeth34. Further, each circumferentially-adjoining pair of the stator core segments32together form one slot31therebetween.

In the present embodiment, each of the stator core segments32is formed by laminating a plurality of magnetic steel sheets in the axial direction of the stator core30. Each of the magnetic steel sheets is formed, by blanking with a press machine, into a predetermined shape. In addition, each of the magnetic steel sheets has a thickness of, for example, substantially 0.3 mm.

Moreover, for each of the stator core segments32, at least some of the magnetic steel sheets forming the stator core segment32are fixed together by staking. The number of staking portions formed in one of the magnetic steel sheets is different from the number of staking portions formed in another one of the magnetic steel sheets.

More particularly, in the present embodiment, for each of the stator core segments32, the magnetic steel sheets forming the stator core segment32include a plurality of first steel sheets35and a plurality of second steel sheets36. The number of staking portions formed in each of the first steel sheets35is larger than the number of staking portions formed in each of the second steel sheets36. Moreover, as shown inFIGS. 3 and 5, the first steel sheets35are arranged at both end parts of the stator core segment32in the axial direction of the stator core30, and the second steel sheets36are arranged at a central part of the stator core segment32in the axial direction.

Specifically, as shown inFIG. 6, each of the first steel sheets35has a first staking portion38a, a second staking portion38band a third staking portion38cthat are respectively formed at three different positions in the back core portion33. The first staking portion38ais circumferentially centered in the first steel sheet35and radially extends between a radially inner end and a radial center of the back core portion33. The second and third staking portions38band38care circumferentially positioned respectively close to opposite circumferential ends of the first steel sheet35. Moreover, both the second and third staking portions38band38care radially positioned close to a radially outer end of the back core portion33and extend perpendicular to the radial direction in which the first staking portion38aextends.

On the other hand, as shown inFIG. 7, each of the second steel sheets36has only a first staking portion38aformed in the back core portion33. The first staking portion38ais circumferentially centered in the second steel sheet36and radially extends between the radially inner end and the radial center of the back core portion33.

That is, the first staking portions38aof the second steel sheets36are formed at the same circumferential and radial positions as the first staking portions38aof the first steel sheets35. In other words, the first staking portions38aof the first and second steel sheets35and36are continuously formed in the axial direction of the stator core30.

In addition, though not shown in the figures, each of the staking portions of the first and second steel sheets35and36includes a recess formed in one of the major surfaces of the steel sheet and a protrusion formed on the other major surface. In the staking process, for each axially-adjacent pair of the first and second steel sheets35and36, the protrusion (or protrusions) of the staking portion (or staking portions) of one of the steel sheets of the pair is (or are respectively) press-fitted into the recess (or recesses) of the staking portion (or staking portions) of the other steel sheet. Consequently, the first and second steel sheets35and36are fixed to one another.

The number (or the lamination thickness) of the first steel sheets35can be suitably set in a desired range within which it is possible to quickly set (or harden) a liquid thermosetting resin applied for fixing the stator coil40to the stator core30. That is, by varying the number (or the lamination thickness) of the first steel sheets35, it is possible to set the temperature rise gradient in the lamination direction of the steel sheets of the stator core segment32to a desired state.

In the present embodiment, the lamination thickness of the first steel sheets35at each axial end part of the stator core segment32is set to be substantially 10% of the thickness of the entire stator core segment32. Accordingly, the lamination thickness of the second steel sheets36at the axial central part of the stator core segment32is set to be substantially 80% of the thickness of the entire stator core segment32.

The outer cylinder37is made, for example, of a ferrous metal. As shown inFIGS. 2A-2B and 3, the outer cylinder37is fitted on the radially outer surfaces of the stator core segments32to maintain the annular shape of the stator core30. In addition, all the radially outer surfaces of the stator core segments32together constitute the radially outer surface of the stator core30.

In the present embodiment, the axial length of the outer cylinder37is set to be substantially equal to the axial length of the stator core30. The outer cylinder37is press-fitted on the radially outer surface of the stator core30.

The stator coil40is comprised of a plurality (e.g., 8) of wave-shaped electric wires45. In the present embodiment, the stator coil40is formed by first stacking the electric wires45to form a flat band-shaped electric wire assembly and then spirally rolling the flat band-shaped electric wire assembly into a hollow cylindrical shape as shown inFIG. 8.

Moreover, after being mounted to the stator core30, each of the wave-shaped electric wires45includes a plurality of in-slot portions46and a plurality of turn portions47. Each of the in-slot portions46is received in a corresponding one of the slots31of the stator core30. Each of the turn portions47is located outside the slots31of the stator core30and connects a corresponding adjacent pair of the in-slot portions46that are respectively received in two different ones of the slots31of the stator core30.

As shown inFIG. 9, in the present embodiment, each of the electric wires45is implemented by a rectangular wire that is configured with an electric conductor48and an insulating coat49that covers the outer surface of the electric conductor48. The electric conductor48is made, for example, of copper and has a substantially rectangular cross section. The insulating coat49is two-layer structured to include an inner layer49aand an outer layer49b. The thickness of the insulating coat49(i.e., the sum of thicknesses of the inner and outer layers49aand49b) is set to be in the range of 100 nm to 200 nm.

The stator core30and the stator coil40are assembled in the following way. First, the stator teeth34of the stator core segments32are respectively inserted into the spaces formed between stacks of the in-slot portions46of the electric wires45from the radially outside of the stator coil40; each of the stacks includes eight radially-aligned in-slot portions46of the electric wires45. Consequently, the stator core segments32are arranged along the stator coil40into an annular shape. Then, the outer cylinder37is fitted onto the radially outer surfaces of the stator core segments32, thereby fastening the stator core segments32together to form the stator core30.

After the assembly of the stator core30and the stator coil40, the in-slot portions46of the electric wires45are respectively received in the corresponding slots31of the stator core30. More specifically, for each of the electric wires45, each adjacent pair of the in-slot portions46are respectively received in a corresponding pair of the slots31which are separated from each other by a predetermined number (e.g., 3 (the number of phases)×2 (the slot multiplier number)=6 in the present embodiment) of the slots31. Moreover, each of the turn portions47, which connects the corresponding adjacent pair of the in-slot portions46, protrudes from a corresponding one of axial end faces30aof the stator core30.

Consequently, in each of the slots31of the stator core30, there are received a predetermined number (e.g.,8in the present embodiment) of the in-slot portions46of the electric wires45so as to be radially aligned with each other. Moreover, as shown inFIGS. 2B and 3, all of those turn portions47of the electric wires45which protrude outside of the slots31on one axial side of the stator core30together make up a first annular coil end part41of the stator coil40; all of those turn portions47of the electric wires45which protrude outside of the slots31on the other axial side of the stator core30together make up a second annular coil end part42of the stator coil40.

Furthermore, in the present embodiment, to secure the vibration resistance of the stator coil40mounted on the stator core30, the stator coil40is fixed to the stator core30by applying a liquid thermosetting resin to the stator coil40and setting the thermosetting resin by induction-heating the stator core30using a heating device50as shown inFIG. 10.

More specifically, in the present embodiment, as the thermosetting resin, a liquid varnish60is applied to the in-slot portions46of the stator coil40received in the slots31of the stator core30. The applied varnish60is then impregnated into voids in the slots31and remains in the voids and on the surfaces of the in-slot portions46of the stator coil40.

The heating device50includes a power supply51and an induction coil52. The power supply51is an AC power supply that is configured to supply high-frequency electric current to the induction coil52. The induction coil52is formed to have a spiral shape with its outer diameter set to be smaller than the inner diameter of the annular stator core30. The induction coil52is placed radially inside the stator core30so as to be surrounded by the stator core30.

When the high-frequency electric current is supplied from the power supply51to the induction coil52, magnetic flux will be created around the induction-coil52, inducing eddy current in the stator core30. Consequently, the stator core30will be heated by the eddy current loss occurring therein. Further, the in-slot portions46of the stator coil40will also be heated by the heat conducted from the stator core30.

As described previously, in the present embodiment, each of the first steel sheets35of the stator core segments32has the three staking portions38a-38cformed therein; each of the second steel sheets36of the stator core segments32has only the single staking portion38aformed therein. Therefore, the eddy current loss occurring in the first steel sheets35will be higher than that occurring in the second steel sheets36; thus, the temperature of the first steel sheets35will be increased more quickly than that of the second steel sheets36. Consequently, the varnish60present in the vicinity of the first steel sheets35will be first set (or hardened) in a short time.

Further, as described previously, in the present embodiment, the first steel sheets35are arranged at both the axial end parts of each of the stator core segments32and the second steel sheets36are arranged at the axial central part of each of the stator core segments32. Consequently, the varnish60that has not been set yet in the vicinity of the second steel sheets36will be trapped therein by the varnish60that has been quickly set in the vicinity of the first steel sheets35. Thereafter, with further increase in the temperature of the second steel sheets36, the varnish60present in the vicinity of the second steel sheets36will also be set.

Accordingly, in the present embodiment, it is possible to retain and set the varnish60at all the desired positions (or over the entire axial length of the stator core segments32).

The above-described stator20according to the present embodiment has the following advantages.

In the present embodiment, the stator20of the electric rotating machine1includes the annular stator core30, the outer cylinder37fitted on the radially outer surface of the stator core30, and the stator coil40mounted on the stator core30. The stator core30is comprised of the stator core segments32that are arranged in the circumferential direction of the stator core30so as to adjoin one another in the circumferential direction. The stator coil40is fixed to the stator core30by the varnish60that is set by induction-heating the stator core30. Each of the stator core segments32is formed by laminating the first and second steel sheets35and36in the axial direction of the stator core30and fixing at least part (more particularly, all in the present embodiment) of the steel sheets35and36by staking. The number of staking portions formed in each of the first steel sheets35(i.e., 3) is larger than the number of staking portions formed in each of the second steel sheets36(i.e., 1).

With the above configuration, in induction-heating the stator core30for setting the liquid varnish60present at predetermined portions (i.e., the in-slot portions46) of the stator coil40, it is possible to quickly set the varnish60in the vicinity of the first steel sheets35in a short time. Consequently, it is possible to set the temperature rise gradient in the stator core segments32in the axial direction of the stator core30to a desired state, thereby retaining and setting the liquid varnish60at desired positions.

Moreover, in the present embodiment, for each of the stator core segments32, the first steel sheets35are arranged at both the end parts of the stator core segment32in the axial direction of the stator core30, and the second steel sheets36are arranged at the central part of the stator core segment32in the axial direction.

With the above arrangement, it is possible to trap, by the varnish60that has been quickly set in the vicinity of the first steel sheets35, the varnish60that has not been set yet in the vicinity of the second steel sheets36. Consequently, it is possible to reliably retain and set the liquid varnish60over the entire axial length of the stator core segments32.

Second Embodiment

This embodiment illustrates a stator20A which has almost the same structure as the stator20according to the first embodiment. Accordingly, the differences of the stator20A from the stator20will be mainly described hereinafter.

As shown inFIGS. 11-12, in the present embodiment, each of the stator core segments32A is also formed by laminating the first and second steel sheets35and36in the axial direction of the stator core30and fixing all of them by staking.

However, in contrast to the first embodiment, the first steel sheets35are arranged at the central part of the stator core segment32A in the axial direction of the stator core30(or in the lamination direction of the first and second steel sheets35and36), and the second steel sheets36are arranged at both the end parts of the stator core segment32A in the axial direction (or in the lamination direction).

Accordingly, in the present embodiment, the lamination thickness of the first steel sheets35at the axial central part of the stator core segment32A is set to be substantially 80% of the thickness of the entire stator core segment32A. The lamination thickness of the second steel sheets36at each axial end part of the stator core segment32A is set to be substantially 10% of the thickness of the entire stator core segment32A.

Moreover, as in the first embodiment, to secure the vibration resistance of the stator coil40mounted on the stator core30, the stator coil40is fixed to the stator core30by applying the liquid varnish60(i.e., thermosetting resin) to the in-slot portions46of the stator coil40and setting the liquid varnish60by induction-heating the stator core30using the heating device50as shown inFIG. 9.

More specifically, when high-frequency electric current is supplied from the power supply51of the heating device50to the induction coil52, the stator core30will be induction-heated. At this time, since the number of staking portions formed in each of the first steel sheets35of the stator core segments32A is set to be larger than that formed in each of the second steel sheets36, the temperature of the first steel sheets35will be increased more quickly than that of the second steel sheets36. Moreover, as described previously, in the present embodiment, the first steel sheets35are arranged at the axial central part of each of the stator core segments32A and the second steel sheets36are arranged at both the axial end parts of each of the stator core segments32A. Consequently, in each of the stator core segments32A, the varnish60present at the axial central part of the stator core segment32A (or in the vicinity of the first steel sheets35) will be first set in a short time; then, the varnish60present at the axial end parts of the stator core segment32A (or in the vicinity of the second steel sheets36) will be set later.

Accordingly, in the present embodiment, it is possible to reliably retain and set the varnish60at desired positions (in particular, at the axial central part of each of the stator core segments32A).

As described above, in the stator20A according to the present embodiment, each of the stator core segments32A is formed by laminating the first and second steel sheets35and36in the axial direction of the stator core30and fixing all of them by staking. The number of staking portions formed in each of the first steel sheets35(i.e., 3) is larger than the number of staking portions formed in each of the second steel sheets36(i.e., 1).

Consequently, it is possible to set the temperature rise gradient in the stator core segments32A in the axial direction of the stator core30to a desired state, thereby retaining and setting the liquid varnish60at desired positions.

In particular, in the stator20A according to the present embodiment, since the first steel sheets35are arranged at the axial central part of each of the stator core segments32A, it is possible to quickly set the varnish60present at the axial central part (or in the vicinity of the first steel sheets35).

While the above particular embodiments have been shown and described, it will be understood by those skilled in the art that various modifications, changes and improvements may be made without departing from the spirit of the present invention.

For example, in the previous embodiments, each of the stator core segments is formed by laminating, in the axial direction of the stator core30, two types of steel sheets having different numbers of staking portions formed therein, i.e., the first steel sheets35each having the three staking portions38a-38cformed therein and the second steel sheets36each having only the single staking portion38aformed therein. However, each of the stator core segments may also be formed by laminating, in the axial direction of the stator core30, three or more types of steel sheets having different numbers of staking portions formed therein. In this case, it is possible to more reliably set the temperature rise gradient in the stator core segments in the axial direction of the stator core30to a desired state.

Moreover, in the previous embodiments, the outer cylinder37is press-fitted on the radially outer surface of the stator core30. However, the outer cylinder37may also be fitted on the radially outer surface of the stator core30by other methods, such as shrink fitting.

In the previous embodiments, the second steel sheets36are fixed by staking so that each of the second steel sheets36has the single staking portion38aformed therein. However, the second steel sheets36may be fixed by welding, instead of staking, so as to have a weld39formed on the radially outer surface of the stator core segment32B in the axial direction of the stator core30. In this case, the number of staking portions formed in each of the second steel sheets36can be regarded as being equal to 0, which is smaller than the number of staking portions formed in each of the first steel sheets35(i.e., 3). In addition, the welding process may be performed using conventional welding methods, such as resistance welding.

Furthermore, the second steel sheets36may be fixed by at least one fixing means selected from staking, welding and adhesive bonding so that the number of staking portions formed in each of the second steel sheets36is smaller than the number of staking portions formed in each of the first steel sheets35.

In the previous embodiments, the present invention is directed to the stators20and20A for the rotating electric machine1which is configured as an electric motor. However, the present invention can also be applied to stators for other electric rotating machines, such as a stator for an electric generator and a stator for a motor-generator that selectively functions either as an electric motor or as an electric generator.