METHOD FOR MANUFACTURING STATOR FOR ROTATING ELECTRICAL MACHINE

A method for manufacturing a stator for a rotating electrical machine includes: installation step of installing coil pieces with rectangular cross section for stator coil in stator core; and joining step of joining ends of coil pieces by laser welding after installation step. The joining step includes a setting step of bringing the ends into contact with each other in radial direction that the ends cross over each other in an X-shape as viewed in the radial direction, and a radiation step of applying a laser beam with a wavelength of 0.6 μm or less in an axial direction toward a C-shaped side, as viewed in the radial direction, of a contact surface between the ends after the setting step. Part of the C-shaped side and part of an axially outer non-contact surface that is continuous with the contact surface between the ends are melted in the radiation step.

TECHNICAL FIELD

The present disclosure relates to methods for manufacturing a stator for a rotating electrical machine.

BACKGROUND ART

A method for manufacturing a stator is known in which ends of one coil piece and another coil piece for forming a stator coil for a rotating electrical machine are butted together and a laser beam is applied to those portions of the abutting ends that are to be welded together in such a manner that the radiation position moves in a loop (see, for example; Patent Document 1).

RELATED ART DOCUMENTS

Patent Documents

SUMMARY OF THE DISCLOSURE

Problem to be Solved by the Invention

In such related art as described in Patent Document 1, the ends of the coil pieces that are to be butted together have been machined into a C-shape (arc-shaped surfaces curved outward in the axial direction) as viewed in the radial direction so that the side surfaces (surfaces facing a laser beam radiation source) of the ends of the coil pieces become smoothly continuous. There is room for cost reduction in terms of the machining cost.

Accordingly, in one aspect, it is an object of the present disclosure to enable ends of coil pieces to be properly joined together at relatively low machining cost.

Means for Solving the Problem

According to one aspect of the present disclosure, a method for manufacturing a stator coil for a rotating electrical machine is provided that includes: an installation step of installing coil pieces with a rectangular cross section for a stator coil in a stator core; anda joining step of joining ends of the coil pieces by laser welding after the installation step.The joining step includesa setting step of bringing the ends into contact with each other in a radial direction in such a manner that the ends cross over each other in an X-shape as viewed in the radial direction, anda radiation step of applying a laser beam with a wavelength of 0.6 μm or less in an axial direction toward a C-shaped side, as viewed in the radial direction, of a contact surface between the ends after the setting step.Part of the C-shaped side and part of an axially outer non-contact surface that is continuous with the contact surface between the ends are melted in the radiation step.

Effects of the Invention

According to the present disclosure, it is possible to properly join the ends of the coil pieces at relatively low machining cost.

MODES FOR CARRYING OUT THE DISCLOSURE

Embodiments will be described in detail below with reference to the accompanying drawings. The dimensional ratios in the drawings are merely illustrative, and are not limited to these. The shapes etc. in the drawings may be partially exaggerated for convenience of explanation. In this specification, the term “predetermined” is used in the sense of “decided in advance.”

FIG.1is a sectional view schematically showing a sectional structure of a motor1(an example of a rotating electrical machine) according to an embodiment.

FIG.1shows a rotation axis12of the motor1. In the following description, the axial direction refers to a direction in which the rotation axis (rotation center)12of the motor1extends, and the radial direction refers to a radial direction about the rotation axis12. Therefore, the “radially outer side” and “radially outward” refer to a side away from the rotation axis12, and the “radially inner side” and “radially inward” refers to a side toward the rotation axis12. The circumferential direction corresponds to a rotation direction about the rotation axis12.

The motor1may be a vehicle drive motor that is used in, for example, a hybrid electric vehicle or a battery electric vehicle. However, the motor1may be used for any other purposes.

The motor1is of an inner rotor type, and a stator21is provided so as to surround the radially outer side of a rotor30. The radially outer side of the stator21is fixed to a motor housing10.

The rotor30is disposed radially inward of the stator21. The rotor30includes a rotor core32and a rotor shall34. The rotor core32is fixed to the radially outer side of the rotor shaft34and rotates with the rotor shaft34. The rotor shaft34is rotatably supported by the motor housing10via bearings14a,14b.The rotor shaft34defines the rotation axis12of the motor1.

The rotor Core32is made of, for example, magnetic steel laminations having an annular shape. Permanent magnets321are inserted inside the rotor core32. The number, arrangement, etc. of permanent magnets321may be determined as appropriate. In a modification, the rotor core32may be made of a green compact obtained by pressing and compacting magnetic powder.

End plates35A,35B are attached to both sides in the axial direction of the rotor core32. The end plates35A,35B may have a function to adjust an imbalance of the rotor30(function to eliminate the imbalance by being cut etc.) in addition to a support function to support the rotor core32.

As shown inFIG.1, the rotor shaft34has a hollow portion34A. The hollow portion34A extends along the entire axial length of the rotor shaft34. The hollow portion34A may function as an oil passage. For example, oil is supplied to the hollow portion34A from its one axial end as shown by arrow R1inFIG.1, and the oil flows along the radially inner surface of the rotor shaft34, so that the rotor core32can be cooled from the radially inner side. The oil flowing along the radially inner surface of the rotor shaft34may be injected radially outward through oil holes341,342formed in both ends of the rotor shaft34(arrows R5, R6) to cool coil ends220A,220B.

Although the motor1having a specific structure is shown inFIG.1, the motor1may be have any structure as long as it has a stator coil24(described later) joined by welding. Accordingly, for example, the rotor shall34may not have the hollow portion34A, or may have a hollow portion with an inside diameter significantly smaller than that of the hollow portion34A. While a specific cooling method is disclosed inFIG.1, the motor1may be cooled by any method. Therefore, for example, an oil introduction pipe inserted into the hollow portion34A may be provided, or oil may be dropped from an oil passage in the motor housing10from the radially outer side toward the coil ends220A,220B.

AlthoughFIG.1shows the inner rotor motor1in which the rotor30is disposed inside the stator21, the present disclosure may be applied to other types of motors. For example, the present disclosure may be applied to an outer rotor motor in which the rotor30is concentrically disposed outside the stator21, or a dual rotor motor in which the rotor30is disposed both outside and inside the stator21.

Next, the configuration related to the stator21will be described in detail with reference toFIG.2and the subsequent figures.

FIG.2is a plan view of a stator core22alone.FIG.3is a diagram schematically showing a pair of coil pieces52that is installed in the stator core22.FIG.3shows the relationship between the pair of coil pieces52and slots220on the radially inner side of the stator core22shown opened out flat. InFIG.3, the stator core22is shown by dashed lines, and part of the slots220is not shown.

The stator21includes the stator core22and the stator coil24.

For example, the stator core22is made of, for example, magnetic steel laminations having an annular shape. In a modification, however, the stator core22may be made of a green compact obtained by pressing and compacting magnetic powder. The stator core22may be composed of divided cores in the circumferential direction, or may be in a form in which the stator core22is not divided in the circumferential direction. The plurality of slots220in which the stator coil24is wound is formed on the radially inner side of the stator core22. Specifically, as shown inFIG.2, the stator core22includes an annular back yoke22A and a plurality of teeth22B extending radially inward from the back yoke22A, and the slots220are formed between the teeth22B in the circumferential direction. Any number of slots220may be formed. In the present embodiment, 48 slots220are formed as an example.

The stator coil24includes a U-phase coil, a V-phase coil, and a W-phase coil (hereinafter referred to as “phase coils” when the phases U, V, and W are not distinguished from each other). The starting end of each phase coil is connected to an input terminal (not shown). The finishing end of each phase coil is connected to the finishing ends of the other phase coils to form a neutral point of the motor1. That is, the stator coil24is connected in a star connection. However, the manner of connection of the stator coil24may be changed as appropriate according to the required motor characteristics etc. For example, the stator coil24may be connected in a delta connection instead of the star connection.

Each phase coil is formed by joining a plurality of coil pieces52.FIG.4is a schematic front view of one coil piece52. The coil pieces52are in the form of segment coils that are separate, easy-to-install units of phase coils (e.g. units each to be inserted into two slots220). The coil piece52is formed by coating a linear conductor (rectangular wire)60having a rectangular cross section with an insulating coating62. In the present embodiment, the linear conductor60is made of, for example, copper. In a modification, the linear conductor60may be made of a different conductor material such as iron.

Before being installed in the stator core22, the coil piece52may be formed into a substantially U-shape having a pair of straight portions50and a connecting portion54connecting the pair of straight portions50. When installing the coil piece52in the stator core22, the pair of straight portions50is inserted into the slots220(seeFIG.3). As shown inFIG.3, the connecting portion54thus extends in the circumferential direction across a plurality of teeth22B (and therefore a plurality of slots220) at the other axial end of the stator core22. Although the connecting portion54may extend across any number of slots220, the connecting portion54extends across three slots220inFIG.3. After being inserted into the slots220, the straight portions50are bent at an intermediate position in the circumferential direction, as shown by long dashed double-short dashed lines inFIG.4. Each straight portion50is thus turned into a leg portion56extending in the axial direction in the slot220and a crossover portion58extending in the circumferential direction at one axial end of the stator core22.

InFIG.4, the pair of straight portions50is bent in directions away from each other. However, the present disclosure is not limited to this. For example, the pair of straight portions50may be bent in directions toward each other. The stator coil24may also have a neutral point coil piece etc. that connects the finishing ends of the three-phase coils to form a neutral point.

A plurality of leg portions56of the coil pieces52shown inFIG.4is inserted into one slot220side by side in the radial direction. A plurality of crossover portions58extending in the circumferential direction is thus arranged side by side in the radial direction at the one axial end of the stator core22. As shown inFIG.3, the crossover portion58of one coil piece52protruding from one slot220and extending toward a first side in the circumferential direction (e.g., clockwise direction) is joined to the crossover portion58of another coil piece52protruding from another slot220and extending toward a second side in the circumferential direction (e.g., counterclockwise direction).

In the present embodiment, for example, six coil pieces52are installed in one slot220. Hereinafter, these coil pieces52are also referred to as first turn, second turn, and third turn from outside to inside in the radial direction, with the outermost coil piece52in the radial direction being the first turn. In this case, the first turn coil piece52and the second turn coil piece52are joined at their tip ends40by a joining process described later, the third turn coil piece52and the fourth turn coil piece52are joined at their tip ends40by the joining process described later, and the fifth turn coil piece52and the sixth turn coil piece52are joined at their tip ends40by the joining process described later.

Each coil piece52is covered with the insulating coating62as described above, but the insulating coating62is removed only from the tip ends40. This is to ensure electrical connection with other coil pieces52at the tip ends40.

FIG.5is a diagram showing the joined tip ends40of the coil pieces52and the portions near the tip ends40.FIG.5schematically shows a circumferential range D1of a welding target portion90.FIG.6is a diagram schematically showing the welding target portion90as viewed from the radiation side.FIGS.7A to7Care sectional views taken along lines A-A, B-B, and C-C inFIG.5passing through the welding target portion respectively. InFIGS.7A to7C, the range of a molten pool formed during welding is schematically shown by hatched areas1102.FIG.8is a diagram showing joined tip ends of coil pieces52′ and portions near the tip ends40′ according to a comparative example as comparison with the configuration of the present embodiment shown inFIG.5.

The Z direction along the axial direction is defined inFIG.5. Hereinafter, for convenience of explanation, “upper” refers to the Z1 side in the Z direction (that is, the radiation side from which a laser beam110is radiated), and “lower” refers to the Z2 side in the Z direction. The X direction along the radial direction and the X1 and X2 sides in the X direction are defined inFIG.6.

When joining the tip ends40of the coil pieces52, the tip end40of one coil piece52and the tip end40of another coil piece52are brought into contact with each other in the radial direction such that these tip ends40cross over each other in an X-shape in the view shown inFIG.5(as viewed in a direction perpendicular to a contact surface401, that is, as viewed in the radial direction). Hereinafter, for convenience of explanation, the configurations related to the one coil piece52are sometimes denoted by signs with the letter “A” at the end, like tip end40A, and the configurations related to the another coil piece52are sometimes denoted by signs with the letter “B” at the end, like tip end40B, in order to distinguish them from each other.

In this case, the welding target portion90extends linearly along the contact surface401as shown by the range D1inFIG.6. That is, the welding target portion90extends linearly along the range D1with a width of a range D2shown inFIGS.7A to7C, as viewed from the radiation side of the laser beam110(see arrow W inFIG.5). In the example shown inFIG.5, the contact surface401has the shape of a rhombus as viewed in the radial direction, with the upper two sides of the rhombus forming a C-shape facing downward, and the lower two sides of the rhombus forming a C-shape facing upward.

In the present embodiment, in the view shown inFIG.5(as viewed in the radial direction), the one coil piece52and the another coil piece52cross over each other in an X-shape as described above, and the welding target portion90extends on both sides of a point of intersection P0. Specifically, the welding target portion90is set along a C-shaped side (upper two sides of the rhombus) formed by axial outer end faces42A,42B of both tip ends40in the view shown inFIG.5(as viewed in the radial direction). Specifically, the welding target portion90is set in a range D11from a point of intersection P1to the point of intersection P0and a range D12from a point of intersection P2to the point of intersection P0in the view shown inFIG.5(as viewed in the radial direction). P1is the point of intersection between the axial outer end face42A (end face facing upward) of the tip end40A of a coil piece52A and an axial inner end face43B (end face facing downward) of the tip end40B of a coil piece52B, and P2is the point of intersection between the axial outer end face42B (end face facing upward) of the tip end40B of the coil piece52B and an axial inner end face43A (end face facing downward) of the tip end40A of the coil piece52A.

In this case, the welding target portion90is preferably a portion other than a portion near the point of intersection P1and a portion near the point of intersection P2(e.g., a section from a point of intersection P3to a point of intersection P4). This is because it is difficult to ensure a sufficient welding depth (see dimension L1inFIG.5) in the portion near the point of intersection P1and the portion near the point of intersection P2. The circumferential range D1of the welding target portion90may be adapted so as to ensure a required joining area between the coil pieces52, required welding strength, etc.

In the present embodiment, the joining method for joining the tip ends40of the coil pieces52is welding. In the present embodiment, the welding method may be arc welding represented by TIG welding, or may be laser welding in which a laser beam source is used as a heat source. The axial length of the coil ends220A,220B can be reduced by using the laser welding instead of the TIG welding. That is, in the case of the TIG welding, the tip ends of the coil pieces to be brought into contact with each other need to be bent axially outward so as to extend in the axial direction. In the case of the laser welding, however, such bending is not necessary, and as shown inFIG.5, welding can be implemented with the tip ends40of the coil pieces52to be brought into contact with each other extending in the circumferential direction. The axial length of the coil ends220A,220B can thus be reduced compared to the case where the tip ends40of the coil pieces52to be brought into contact with each other are bent axially outward so as to extend in the axial direction.

In the laser welding, as schematically shown inFIG.5, the welding laser beam110is applied to the welding target portion90in the two tip ends40that are in contact with each other. The radiation direction (propagation direction) of the laser beam110is substantially parallel to the axial direction, and is a direction from outside in the axial direction toward the axial outer end faces42A,42B of the two tip ends40that are in contact with each other. In the case of the laser welding, heating can be locally performed. Therefore, only the tip ends40and the portions near the tip ends40can be heated, and damage (carbonization) etc. to the insulating coating62can be effectively reduced. As a result, the plurality of coil pieces52can be electrically connected while maintaining appropriate insulation performance.

In the present embodiment, as shown inFIG.7A, the laser beam110is applied so as to melt the edge on the contact surface401side of the axial outer end face42A of the tip end40of the coil piece52A (edge forming the C-shaped side) and the edge on the contact surface401side of the axial outer end face42B of the tip end40of the coil piece52B (edge forming the C-shaped side), at the connection position of the range D11and the range D12, namely at the point of intersection P0. A required joining area can thus be easily obtained by the laser beam110at such a point of intersection P0as shown inFIG.7A.

In the present embodiment, as shown inFIGS.7B and7C, the laser beam110melts, in each of the range D11and the range D12, the edges on the contact surface401side of the axial outer end faces42A,42B (part of the C-shaped side) and part of an axially outer non-contact surface409that is continuous with the contact surface401. In the case where the tip ends40A,40B of the coil pieces52A,52B are crossed over each other in an X-shape as viewed in the radial direction as described above, the tip ends40A,40B have non-contact surfaces409A,409B extending upward continuously from the contact surface401, respectively. In the present embodiment, the reliability of the welded portion can be improved by implementing welding using such non-contact surfaces409A,409B. There are no such non-contact surfaces409A,409B in the comparative example shown inFIG.8, which will be described later.

For example, in the range D11inFIG.6, as shown by the hatched areas1102of the molten pool inFIG.7B, the laser beam110is applied so as to melt the edge on the contact surface401side of the axial outer end face42A of the tip end40A (edge forming the C-shaped side) and the edge on the contact surface401side of the non-contact surface409of the tip end40B (edge at the boundary with the contact surface401). A required joining area can thus be easily obtained by the laser beam110even in such a welding target portion90having a stepped portion in the axial direction at the contact surface401as shown inFIG.7B.

Similarly, in the range D12inFIG.6, as shown by the hatched areas1102of the molten pool inFIG.7C, the laser beam110is applied so as to melt the edge on the contact surface401side of the axial outer end face42B of the tip end40B (edge forming the C-shaped side) and the edge on the contact surface401side of the non-contact surface409of the tip end40A (edge at the boundary with the contact surface401). A required joining area can thus be easily obtained by the laser beam110even in such a welding target portion90having a stepped portion in the axial direction at the contact surface401as shown inFIG.7C.

In the present embodiment, as shown inFIGS.7A to7C, the radial range D2of the welding target portion90is a range about the contact surface401between the tip ends40of the two coil pieces52. The radial range D2of the welding target portion90may correspond to the diameter of the laser beam110(beam diameter). That is, the laser beam110is applied in such a manner that the radiation position changes linearly in the circumferential direction without substantially changing in the radial direction. In other words, the laser beam110is moved so that the radiation position changes in a linear pattern parallel to the contact surface401. The laser beam110can thus be more efficiently applied to the linear welding target portion90compared to the case where the radiation position is changed in, for example, a loop (spiral) or zigzag (meandering) pattern. In the range D11, the laser beam110may be applied to the contact surface401from the X1 side in the X direction. In the range D12, the laser beam110may be applied to the contact surface401from the X2 side in the X direction.

In the comparative example as shown inFIG.8, when joining the tip ends40′ whose axial outer end faces42′ have been machined into convex arc-shaped surfaces, one tip end40′ and another tip end40′ are butted together so as to form a C-shape in the view shown inFIG.8(as viewed in a direction perpendicular to the contact surface401).

In the case of such a comparative example, the axial outer end faces42′ of the tip ends40′ are machined into convex arc-shaped surfaces. This can reduce irregularities in the axial direction in a welding target portion90′, but is disadvantageous in terms of machining cost because machining (e.g., press stamping) is required.

On the other hand, according to the present embodiment, the axial outer end faces42A,42B of the tip ends40are not machined into convex arc-shaped surfaces, unlike the tip ends40′ of the comparative example. That is, each tip end40has the axial outer end face42A,42B and a tip end face44that are continuous with each other and form a substantially right angle as viewed in the radial direction. Therefore, since the tip end40according to the present embodiment can be substantially formed by merely removing the insulating coating62, the manufacturing cost can be reduced unlike the comparative example. The “substantially right angle” is a concept that not only includes a perfect right angle but also allows deviations (deviations from the perfect right angle) due to machining errors etc.

According to the present embodiment, the smaller the bending angle α of the coil piece52, the easier it is to obtain a relatively large dimension L1even though the point of intersection P3(and also the point of intersection P4) is separated farther from the point of intersection P0(that is, even though the length of the range D11increases). Being able to obtain a relatively large dimension L1means that it is easier to ensure a relatively large welding depth (and thus joining area). It is therefore easy to increase the length of the range D1in which a required joining area can be ensured. The smaller the bending angle α of the coil piece52, the more the axial size of the coil ends220A,220B can be reduced. Therefore, according to the present embodiment, the length of the range D1in which a sufficient welding depth can be ensured can be increased while reducing the axial size of the coil ends220A and220B. The greater the length of the range D1having a required joining area, the higher the reliability of the welded portion tends to be.

In the present embodiment, the tip ends40A,40B are crossed over each other in an X-shape in such a manner that an entire tip end face44A of the tip end40A is located above the axial outer end face42B of the tip end40B and an entire tip end face44B of the tip end40B is located above the axial outer end face42A of the tip end40A as viewed in the radial direction. In this case, it is easy to obtain a relatively long range D1in which a required joining area can be ensured. Moreover, in this case, the laser beam110can be reliably applied to the range (range on the point of intersection P0side) between the tip end face44A of the tip end40A and the tip end face44B of the tip end40B in the circumferential direction.

FIG.9is a diagram showing the relationship between the laser wavelength and the laser absorptivity (hereinafter sometimes simply referred to as “absorptivity”) of samples of various materials.FIG.9shows characteristics of the samples of various materials, namely copper (Cu), aluminum (Al), silver (Ag), nickel (Ni), and iron (Fe), where the abscissa represents the wavelength λ, and the ordinate represents the absorptivity.

Copper that is a material of the linear conductor60of the coil piece52has an absorptivity as low as about 10% for an Infrared laser (laser with a wavelength of 1064 nm) that is commonly used in the laser welding, as shown by a black circle at the intersection with a dotted line of λ2=1.06 μm inFIG.9. That is, in the case of the infrared laser, most of the laser beam110is reflected and not absorbed by the coil piece52. Therefore, a relatively large amount of heat input is required in order to obtain a required joining area between the coil pieces52to be joined, and welding may become unstable due to the high heat effect.

In view of this, in the present embodiment, a green laser is used instead of the infrared laser. The “green laser” is a concept including not only a laser with a wavelength of 532 nm, that is, an SHG (Second Harmonic Generation: second harmonic) laser but also lasers with wavelengths close to 532 nm. In a modification, a laser with a wavelength of 0.6 μm or less that does not belong to the category of the green laser may be used. The wavelength of the green laser can be obtained by, for example, converting a fundamental wavelength generated by a YAG laser or a YVO4 laser through an oxide single crystal (e.g., LBO: lithium triborate).

Copper that is a material of the linear conductor60of the coil piece52has an absorptivity as high as about 50% for the green laser, as shown by a black circle at the intersection with a dotted line of λ1=0.532 μm inFIG.9. Therefore, according to the present embodiment, a required joining area between the coil pieces52can be ensured with a smaller amount of heat input than in the case of using the infrared laser.

The characteristic that the absorptivity is higher for the green laser than for the infrared laser is remarkable in copper as shown inFIG.9, but can be observed not only in copper but also in many of other metal materials. Therefore, welding with the green laser may be implemented even when a material other than copper is used for the linear conductor60of the coil piece52.

FIG.10is a diagram illustrating how the absorptivity changes during welding.FIG.10shows a characteristic100G for the green laser and a characteristic100R for the infrared laser, where the abscissa represents the laser power density, and the ordinate represents the laser absorptivity of copper.

FIG.10shows points P100, P200where copper starts to melt and a point P300where a keyhole is formed in the case of the green laser and the infrared laser. As shown by the points P100, P200inFIG.10, it can be seen that, with the green laser, copper starts melting with a lower laser power density than the infrared laser. It can also be seen that, due to the difference in absorptivity described above, the difference between the absorptivity at the point P300where a keyhole is formed and the absorptivity at the start of radiation (that is, the absorptivity when the laser power density is 0) is smaller for the green laser than for the infrared laser. Specifically, a change in absorptivity during welding is about 80% for the infrared laser, while a change in absorptivity during welding is about 40% for the green laser, which is about half the change for the infrared laser.

As described above, in the case of the infrared laser, the change (increase) in absorptivity during welding is as relatively large as about 80%. Therefore, the keyhole is more likely to become unstable, and variations in welding depth and welding width and disturbance of a molten pool (e.g., spatter etc.) are more likely to occur. On the other hand, in the case of the green laser, the change (increase) in absorptivity during welding is as relatively small as about 40%. Therefore, the keyhole is less likely to become unstable, and variations in welding depth and welding width and disturbance of a molten pool (e.g., spatter etc.) are less likely to occur. Spatter is metal particles etc. expelled by irradiation with a laser etc.

In the case of the infrared laser, the absorptivity is low as described above. It is therefore common to compensate for the low absorptivity by making the beam diameter relatively small (e.g., φ0.075 mm). This also contributes to the keyhole becoming unstable.FIG.11Bis an illustration of a keyhole etc. when the infrared laser is used, where1100indicates a weld bead,1102indicates a molten pool, and1104indicates a keyhole. Arrow R1116schematically shows how gas is released. Arrow R110schematically shows how the radiation position of the infrared laser is moved due to the small beam diameter. In the case of the infrared laser, the absorptivity is low and it is difficult to make the beam diameter relatively large, as described above. Therefore, a relatively long movement trajectory of the radiation position including meandering (relatively long continuous radiation time) tends to be necessary in order to obtain a required melting width.

On the other hand, in the case of the green laser, the absorptivity is relatively high as described above, and it is possible to make the beam diameter relatively large (e.g., φ0.1 mm or more). A large, stable keyhole can thus be formed. As a result, gas release is improved, and spatter etc. can be effectively reduced.FIG.11Ais an illustration of a keyhole etc. when the green laser is used. The definitions of the signs are as described above with reference toFIG.11B. In the case of the green laser, it can be easily visually understood fromFIG.11Ahow a keyhole is stabilized and gas release is improved due to the increased beam diameter. In the case of the green laser, unlike the infrared laser, the absorptivity is relatively high and it is possible to make the beam diameter relatively large, as described above. Therefore, the movement trajectory of the radiation position (radiation time) necessary to obtain a required melting width (see the radial range D2of the welding target portion90shown inFIGS.7A to7C) can be made relatively short (small).

FIG.12is a diagram illustrating a welding method using the green laser according to the present embodiment.FIG.12schematically shows time-series waveforms of laser output during welding, where the abscissa represents time, and the ordinate represents laser output.

In the present embodiment, as shown inFIG.12, welding is implemented by pulsed radiation of the green laser at a laser output of 3.8 kW. InFIG.12, a pulse oscillation of a laser oscillator is implemented so that the laser output is 3.8 kW only for 10 msec, and after an interval of 100 msec. a pulse oscillation of the laser oscillator is again implemented so that the laser output is 3.8 kW only for 10 msec. Hereinafter, one pulse radiation (pulse radiation for 10 msec) that can be performed by one pulse oscillation as described above is also referred to as “one pass.” InFIG.12, radiations from the first pass (N=1) to the third pass (N=3) are shown by pulse waveforms130G, where N indicates Nth pass. For comparison,FIG.12also shows a pulse waveform130R of pulsed radiation of the infrared laser.

In the case of the green laser, the output of the laser oscillator is low (e.g., up to 400 W for continuous radiation), and it is difficult to obtain a high output necessary to ensure deep penetration (e.g., a laser output as high as 3.0 kW or more). That is, since the green laser is generated through a wavelength conversion crystal such as an oxide single crystal as described above, the output decreases when passing through the wavelength conversion crystal. Therefore, when continuous radiation of the laser beam of the green laser is attempted, a high output necessary to ensure deep penetration cannot be obtained.

In this regard, in the present example, a high output necessary to ensure deep penetration (e.g., a laser output as high as 3.0 kW or more) is obtained by pulsed. radiation of the green laser, as described above. This is because, even when an output of, for example, only up to 400 W can be obtained by continuous radiation, a output as high as, for example, 3.0 kW or snore can be achieved by pulsed radiation. Pulsed radiation is thus implemented by accumulating continuous energy for increasing peak power and performing pulsed oscillation. In the case where the circumferential range D1of one welding target portion90is relatively wide as in the present embodiment, the one welding target portion may be subjected to a plurality of pulse oscillations. That is, the one welding target portion may be irradiated with two or more passes at a relatively high laser output (e.g., laser output of 3.0 kW or more). This makes it easy to ensure deep penetration in the entire welding target portion90and makes it possible to achieve high-quality welding even when the circumferential range D1of the welding target portion90described above is relatively wide.

Although the interval is a specific value of 100 msec inFIG.12, the interval can be set as desired, and may be minimized within a range in which a required high output is ensured. Although the laser output is a specific value of 3.8 kW inFIG.12, the laser output may be changed as appropriate within a range in which a required welding depth is ensured, as long as the laser output is 3.0 kW or more.

FIG.12also shows the pulse waveform130R when the infrared laser is continuously applied at a laser output of 2.3 kW for a relatively long time of 130 msec. Unlike the green laser, the infrared laser can be continuously applied at a relatively high laser output (2.3 kW). As described above, however, in the case of the infrared laser, a relatively long movement trajectory of the radiation position including meandering (relatively long continuous radiation time) is necessary in order to obtain a required melting width. In this case, the amount of heat input is about 312 J, which is significantly larger than about 80 J (in the case of two passes) that is the amount of heat input in the case of the green laser shown inFIG.12.

As described above, according to the present embodiment, the use of the green laser enables welding with a laser beam for which the material of the linear conductor of the coil piece52(in this example, copper) has higher absorptivity compared to the infrared laser. Accordingly, the movement trajectory of the radiation position (time) necessary to obtain a required melting width (see the radial range D2of the welding target portion90shown inFIGS.7A to7C) can be made relatively short (small). That is, due to an increased keyhole per pulse oscillation with a. relatively large beam diameter, the number of pulse oscillations necessary to obtain a required melting width can be made relatively small. As a result, a necessary joining area between the coil pieces52can be ensured with a relatively small amount of heat input.

According to the present embodiment, one welding target portion is irradiated with two or more passes of the green laser. This makes it easy to ensure deep penetration in the entire welding target portion90and makes it possible to achieve high-quality welding even when the circumferential range D1of the welding target portion90is relatively wide.

In the present embodiment, as described above, the tip ends40A,40B of the coil pieces52A,52B are crossed over each other in an X-shape as viewed in the radial direction. Therefore, each of the tip ends40A,40B has the non-contact surface409extending upward continuously from the contact surface401. The non-contact surface409can cause reflection of the laser beam110and may contribute to reduced reliability of the welded portion. Such reflection from the non-contact surface409is remarkable in the case of the infrared laser for which the absorptivity is low as described above. As described above, there is no such a non-contact surface409in the comparative example shown inFIG.8.

In this regard, in the present embodiment, as described above, welding is implemented using the green laser for which the absorptivity is high. Therefore, reflection of the laser beam110at the non-contact surface409is reduced. As a result, as shown inFIGS.7B and7Cand as described above, the laser beam110can also be applied to the non-contact surface409in such a manner that a molten pool is also formed in the non-contact surface409. Therefore, a welded portion that is continuous from the non-contact surface409to the contact surface401can be formed.

In the present embodiment, the laser output in one pass may be substantially constant, as shown inFIG.13.FIG.13is a schematic diagram showing an example of how the laser output (and welding heat input) of one pass changes with the radiation position. A change characteristic150P of the laser output according to the radiation position and a change characteristic150L of the welding heat input according to the radiation position are schematically shown inFIG.13. InFIG.13, an area Q14represents the overall amount of heat input of one pass.

In the example shown inFIG.13, one pass is started from a position P10that is a radiation start position. That is, one pulse oscillation is started from the position P10. In this case, the laser output rises to a predetermined value (in this example, 3.8 kW as an example) at the position P10(see arrow R140). The radiation position is then linearly changed from the position P10to a position P12. During this period, the laser output is kept at the predetermined value (in this example, 3.8 kW as an example) (see arrow R141). When the radiation position reaches the position P12that is a radiation end position, the laser output is reduced from the predetermined value (in this example, 3.8 kW as an example) to 0 (see arrow R142). That is, one pulse oscillation is ended. Even when the radiation position reaches the position P12, the radiation position may be changed until it further moves to a position P13that is separated by a small distance from the position P12. During this period, a small amount of welding heat input may be generated due to residual laser output (see Q14inFIG.13). In a modification, the change in radiation position may be ended when the radiation position reaches the position P12or a position immediately before the position P12(not shown).

According to such a radiation mode, the laser output rises to the predetermined value (in this example, 3.8 kW as an example) at the position P10, but the welding heat input does not instantly increase to its maximum value until the actual laser output reaches the predetermined value. Therefore, the welding heat input gradually increases while the radiation position changes from the position P10to a position P11, as shown by the change characteristic150L inFIG.13. The laser output is instantaneously reduced to 0 at the position P12, but the welding heat input is kept at the maximum value until immediately before the position P12.

Such a radiation mode can be applied in various manners to the range D1of the welding target portion90described above.

For example, when the range D1of the welding target portion90described above is covered by one pass in the radiation mode shown inFIG.13, the range D1of the welding target portion90described above may be included in the section from the position P10to the position P12or the position P13or in the section from the position P11to the position P12or the position P13.

When the range D1of the welding target portion90described above is covered by two passes in the radiation mode shown inFIG.13, each of the range D11and the range D12in the range D1of the welding target portion90described above may be included in the section from the position P10to the position P12or the position P13or from the position P11to the position P12or the position P13for the first pass.

In particular, in the present embodiment, the above ranges D11, D12in the welding target portion90are symmetrical with respect to the point of intersection P0as viewed in the radial direction, as shown inFIG.5. Therefore, in the present embodiment, it is preferable that the range D1of the welding target portion90be covered by two passes.

In this case, in the first pass, the position P10or the position P11may correspond to the point of intersection P3, and the position P12or the position P13may correspond to the point of intersection P0. In the second pass, the position P10or the position P11may correspond to the point of intersection P4, and the position P12or the position P13may correspond to the point of intersection P0. In this case, each of the range D11and the range D12can be welded in such a manner that the range D11and the range D12have the same joining area.

Alternatively, in the first pass, the position P10or the position P11may correspond to the point of intersection P0, and the position P12or the position P13may correspond to the point of intersection P3. In the second pass, the position P10or the position P11may correspond to the point of intersection P0, and the position P12or the position P13may correspond to the point of intersection P4. In this case, each of the range D11and the range D12can be welded in such a manner that the range D11and the range D12have the same joining area.

In either case, the radiation range (that is, the range of movement of the radiation position) of the first pass and the radiation range of the second pass may overlap in a range about the point of intersection P0. This makes it easy to reliably ensure a required joining area at the point of intersection P0.

In a modification, the laser output in one pass may not be constant, as shown inFIG.14.FIG.14is a schematic diagram showing another example of how the welding heat input of one pass changes with the radiation position. As inFIG.13, a change characteristic150P of the laser output according to the radiation position and a change characteristic150L of the welding heat input according to the radiation position are schematically shown inFIG.14.

In the example shown inFIG.14, one pass is started from the position P10that is a radiation start position. That is, one pulse oscillation is started from the position P10. In this case, the laser output rises to a predetermined value (in this example, 3.8 kW as an example) at the position P10(see arrow R140). The radiation position is then linearly changed from the position P10to the position P12. While the radiation position is changed from the position P10to a position P14, the laser output is kept at the predetermined value (in this example, 3.8 kW as an example) (see arrow R141). When the radiation position reaches the position P14, the laser output is reduced stepwise from the predetermined value (in this example, 3.8 kW as an example) to 0 while the radiation position is further changed (see arrow R143). Specifically, when the radiation position reaches the position P14, the laser output is reduced by one decrement. When the radiation position then reaches the position P12, the laser output is further reduced by one decrement. When the radiation position then reaches a position P15that is a radiation end position, the laser power is further reduced to 0. Even when the radiation position reaches the position P15, the radiation position may be changed until it further moves to a position P16that is separated by a small distance from the position P15. During this period, a small amount of welding heat input may be generated due to residual laser output (see Q14inFIG.13). In a modification, the change in radiation position may be ended when the radiation position reaches the position P15.

Such a radiation mode can also be applied in various manners to the range D1of the welding target portion90described above.

For example, when the range D1of the welding target portion90described above is covered by one pass in the radiation mode shown inFIG.14, the range D1of the welding target portion90described above may be included in the section from the position P10to the position P15.

When the range D1of the welding target portion90described above is covered by two passes in the radiation mode shown inFIG.14, each of the range D11and the range D12in the range D1of the welding target portion90described above may be included in the section from the position P10to the position P15for the first pass.

In particular, in the present embodiment, the above ranges D11, D12in the welding target portion90are symmetrical with respect to the point of intersection P0as viewed in the radial direction, as shown inFIG.5. Therefore, in the present embodiment, it is preferable that the range D1of the welding target portion90be covered by two passes. In this case, in the first pass, the position P10may correspond to the point of intersection P3, and the position P15may correspond to the point of intersection P0. In the second pass, the position P10may correspond to the point of intersection P4, and the position P15may correspond to the point of intersection P0. In this case, each of the range D11and the range D12can be welded in such a manner that the range D11and the range D12have the same joining area.

Alternatively, in the first pass, the position P10may correspond to the point of intersection P0, and the position P15may correspond to the point of intersection P3. In the second pass, the position P10may correspond to the point of intersection P0, and the position P15may correspond to the point of intersection P4. In this case, each of the range D11and the range D12can be welded in such a manner that the range D11and the range D12have the same joining area.

In either case, the radiation range of the first pass and the radiation range of the second pass may overlap in a range about the point of intersection P0. This makes it easy to reliably ensure a required joining area at the point of intersection P0.

Lastly, the flow of a method for manufacturing the stator21of the motor1according to the present embodiment will be outlined with reference toFIG.15.

FIG.15is a flowchart schematically showing the flow of the method for manufacturing the stator21of the motor1.

First, this manufacturing method includes an installation step of installing the coil pieces52in the stator core22(step S150). This manufacturing method further includes a joining step of joining the tip ends40of the coil pieces52by laser welding after the installation step (step S152). The method for joining the tip ends40of the coil pieces52by laser welding is as described above.

In this case, the joining step includes a setting step of setting the tip ends40of the coil pieces52so that the tip ends40of each pair of coil pieces52contact each other in the radial direction so as to cross over each other in an X-shape as shown inFIG.5as described above (step S1521). In the setting step, the tip ends40of each pair of coil pieces52may be kept in contact with each other in the radial direction so as to cross over each other in an X-shape by using a jig etc.

The joining step includes a radiation step of applying the laser beam110to the welding target portion90as described above after the setting step (step S1522). The setting step and the radiation step may be performed in batches of one or more predetermined number of welding target portions90at a time, or may be performed on all the welding target portions90of one stator21at a time. This manufacturing method may be ended when the stator21is completed by performing various necessary steps as appropriate after the joining step.

Although the embodiments are described in detail above, the present disclosure is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the claims. It is also possible to combine all or part of the constituent elements of the embodiments described above. Of the effects of each embodiment, those related to dependent claims are additional effects distinct from generic concepts (independent claim).

For example, in the above embodiment, as a preferred example, the tip ends40A,40B are crossed over each other in an X-shape in such a manner that the entire tip end face44A of the tip end40A is located above the axial outer end face42B of the tip end40B and the entire tip end face44B of the tip end40B is located above the axial outer end face42A of the tip end40A as viewed in the radial direction, as described above. However, the present disclosure is not limited to this. For example, as in a modification shown inFIG.16, tip ends400A,400B may be crossed over each other in an X-shape in such a manner that only a radially outer part of a tip end face440A is located above an axial outer end face420B of the tip end400B and only a radially outer part of a tip end face440B of the tip end400B is located above an axial outer end face420A of the tip end400A as viewed in the radial direction. In this case, the laser beam110may also be applied to the edges on the contact surface401side of the tip end faces440A,440B.

In the above embodiment, the radiation direction of the laser beam110is substantially parallel to the contact surface401. For example, the radiation direction of the laser beam110may be deviated by such a relatively small angle α as shown inFIG.17(e.g., ±10 degrees) as viewed parallel to the contact surface401. There are cases where welding is performed on a plurality of portions by changing the angle from a radiation source of the laser beam HO using a mirror (not shown). In such cases, the angle α tends to be larger than 0 but relatively small (e.g., ±10 degrees). Even when the angle α is larger than 0, as in the case where the angle α is 0, the radiation width of the laser beam may include the C-shaped side described above (edges on the contact surface401side of the axial outer end faces42A,42B), the non-contact surface409A or409B, and the contact surface401, as viewed in a direction parallel to the contact surface401. The expression “the radiation width includes the C-shaped side etc.” means that the radiation range having a width corresponding to the radiation width of the laser beam as shown inFIG.17and extending in the radiation direction (shown by a hatched area R16inFIG.17) includes the C-shaped side etc. The angle α (and the range D2described above) may be adapted so that opposite outer surfaces405,406(seeFIG.17) of the tip ends40A,40B that are parallel to the contact surface401will not be irradiated with the laser beam110in the radiation step described above. In this case, since the melted portion is small, the influence of heat on the insulating coatings62of the coil pieces52is reduced, and the portion of each coil piece52from which the insulating coating62is removed can be minimized. As a result, cost reduction can be achieved.

DESCRIPTION OF THE REFERENCE NUMERALS