Manufacturing method for slotless stator, and slotless stator

Abstract: To obviate the need for a special fixation mechanism or adhesive, to thereby simplify the assembly of a slotless stator, two divided cores which complete a stator core having no slots by combining each part into a cylindrical shape, are assembled into a cylindrical shape so as to contain a stator winding having an outer diameter larger than an inner diameter of the stator core in the natural condition. By so doing, the stator winding is assembled inside the stator core in a radially inward compressed condition. At this time, since the stator winding functions as a spring pressing the inside of the stator core so as to expand in the normal direction (the radial outward direction), this is mechanically secured by the resilient force at that time to the inner periphery of the stator core. Hence there is no longer the need for a special fixation mechanism or adhesive.

Description: The present invention relates to a manufacturing method for a slotless stator where a stator winding is secured to the inner periphery of a stator core having no slots, and to a rotating electrical machine incorporating the slotless stator. Heretofore as a rotating electrical machine incorporating a slotless stator where a cylindrical shape stator winding is fitted to the inner periphery of a cylindrical shape stator core having no slots, there is known the rotating electrical machine disclosed in Japanese Patent No. 2554859. Moreover, in the same publication there is disclosed a method where a rod shape temporary support member on the outer periphery of which a stator winding has been preformed, is inserted from one end opening of a cylindrical shape stator core. The temporary support member is then withdrawn leaving the stator winding inside the stator core, and the stator winding is affixed to the inner periphery of the stator core by impregnating with resin and then hardening. However, with this method, since this involves inserting from the end opening of the stator core with the stator winding secured to the temporary support body, the outer diameter of the stator winding must be formed smaller than the inner diameter of the stator core. Consequently, by simply withdrawing the temporary support member and arranging the stator winding inside the stator core, the stator winding is not secured to the inner periphery of the stator core. Therefore, resin must be impregnated into the stator winding and hardenend, to secure the stator winding to the inner periphery of the stator core with adhesive force. Hence the assembly process becomes complicated. DE 1 613 202 A on which the preambles of claims 1 and 6 are based, discloses two core halves which are mounted - via an adhesive tape impregnated with curable resin - within a radially outer circumferential groove within and around the stator winding parts. JP 52057906 A discloses a rotating electric machine with a unitary ring shaped core, without disclosing the relationship between the outer diameter of the winding parts and the inner diameter of the core. If the machine is hot, the winding is pressed onto the core by thermal expansion. There, the winding part and the core are combined by elastic adhesive to keep these parts together when the machine is cold. WO 9401916 A discloses a silicon rubber sheet in a slot between stator cores. JP 03107354 A discloses to insert an armature winding into an iron core, and then soaking it in a resin bath. SUMMARY OF THE INVENTION The present invention takes into consideration the above situation, with the object of obviating the need for a special fixation mechanism or adhesive, to thereby simplify the assembly of a slotless stator. In order to achieve the above object, the present invention of claim 1 provides a manufacturing method for a slotless stator comprising providing a plurality of divided core sections which once assembled jointly define a cylindrically shaped stator core having a cylindrical shape and no slots, providing a cylindrical shaped stator winding having in an umcompressed condition an outer diameter at a position corresponding to the radially inside of said stator core larger than the inner diameter of said stator core; assembling said divided core sections into a cylindrical shape to form said stator core so as to contain said cylindrically shaped stator winding, the stator winding being thereby resiliently compressed and secured to an inner periphery of said stator core. That is to say, the manufacturing method for a slotless stator according to the present invention is characterized in comprising an assembly step where a plurality of divided cores which complete a stator core having no slots by combining each part into a cylindrical shape, are assembled into a cylindrical shape so as to contain a cylindrical shape stator winding having an outer diameter larger than an inner diameter of the stator core in a natural condition. With this construction, the stator winding is fitted inside the stator core in a condition of being compressed radially inwards. At this time, since the stator winding functions as a spring pressing the inside of the stator core so as to expand in the normal direction (the radial outward direction), this is pressed by the resilient force at that time against the inner periphery of the stator core. Therefore, by this resilient force the stator winding is mechanically secured to the inner periphery of the stator core, and hence a special fixation mechanism or adhesive is not required. Furthermore, when a current flows in the stator winding, heat is generated so that an outward expanding force acts on the stator winding. Hence at the time of operating, this is secured even more stably. With the manufacturing method for a slotless stator according to the present invention, in the case where a resilient material is inserted between the divided core and the stator winding, the resilient force acting in the normal direction can be further strengthened, and hence the stator winding can be more stably secured. In particular, in the case where a silicone sheet which contains a filler with good thermal conductivity such as boron nitride, such as used for transistor heat dissipation purposes is used as the resilient material, the heat dissipation is improved and cooling efficiency is also improved. With the method of constructing a slotless stator according to the present invention as described above, there is no need for an adhesive for securing the stator winding to the inner periphery of the stator core. However there is the case where the stator winding is immersed in a resin such as varnish in order to electrically insulate between the windings. In this case, preferably the resin is impregnated, in a condition with the stator winding secured to the inner periphery of the stator core. With this construction, the situation where resin which is thickly attached to the outer peripheral side of the stator winding hardens so that elastic restoration of the stator winding is restricted, can be effectively avoided. That is to say, when the stator winding is fitted to inside the stator core after being impregnated with resin, the resin hardens before fitting, giving the undesirable situation in that fixation utilising the resilient force of the stator winding becomes difficult. With the above construction, this undesirable situation does not arise. In a further aspect, the invention of claim 6 provides a slotless stator including a cylindrical stator core having no slots and a cylindrically shaped stator winding mounted within said stator core, wherein said cylindrical stator core includes a plurality of divided core sections which jointly define the cylindrical stator core characterized in that said stator winding is secured to an inner periphery of said stator core in a resiliently compressed condition only by a resilient force of said stator winding generated by the jointly mounted core sections. Also with this construction, in the above manner, the stator winding inside the stator core functions as a spring, so that this is mechanically secured to the inner periphery of the stator core by the resilient force. Hence a special fixation mechanism or adhesive is not required, giving a rotating electrical machine with simple assembly for the slotless stator. Further, the invention provides a rotating electrical machine with a slotless stator of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal cross-section showing an embodiment of a rotating electrical machine according to the present invention. Fig. 2 is a diagram for explaining an embodiment of a manufacturing method for a slotless stator winding according to the present invention, being a perspective view showing a condition where a band shape body is formed from a plurality of coil segments. FIG. 3 is a perspective view showing a stator winding formed by wrapping the band shape body comprising the plurality of coil segments, into a cylindrical shape. FIG. 4 is a diagram showing a condition where the stator winding is immersed in an alcohol solvent in which BN particles have been mixed. FIG. 5 is a perspective view showing a condition where the stator winding is being fitted inside a stator core of divided construction. FIG. 6 is a transverse cross-section showing a condition where the stator winding is arranged inside divided cores which are oppositely arranged at a predetermined spacing. FIG. 7 is a transverse cross-section showing the divided cores assembled into a cylindrical shape so as to contain the stator winding. FIG. 8 is a diagram showing a condition where the stator core and stator winding are immersed in a varnish tank while being held together. FIG. 9 is a longitudinal cross-section showing the completed slotless stator with the varnish hardened. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereunder is a description of embodiments of the present invention with reference to the drawings. FIG. 1 shows a rotating electrical machine 3 incorporating a slotless stator 1. This rotating electrical machine 3 is suitable for use in a high speed rotating electric machine which is used for example at several kW to several tens of kW, and at rotational speeds above several ten thousand rpm. With the rotating electrical machine 3, the outer shape is formed from a casing 5, and a rotor 7 is rotatably arranged via bearings (not shown) along a central axis of the casing 5. An oil passage 6 constituting one part of an oil pressure circuit 4 is formed in the casing 5. Lubricating oil is supplied to the oil passage 6 from a supply source 8, and by means of this lubricating oil, lubrication of the bearings and cooling of the slotless stator 1 is simultaneously performed. At this time, the cooling of the slotless stator 1 is performed in sequence from the inner periphery to the outer periphery, as shown by the arrow in FIG. 1. A permanent magnet serving as a magnetic field generating device is incorporated into the rotor 7. The permanent magnet is constructed so that p (where p is an even number of two or more) magnetic poles for generating a magnetic flux in the radial direction, are formed on the outer surface of the rotor 7. For the permanent magnet, a rare earth magnet such as a Sm-Co, Nd-Fe-B sintered magnet is suitable. The slotless stator 1 is arranged around the rotor 7, forming a small gap 11 via an inner tube (omitted from the figure). This inner tube is for containing the lubricating oil which flows on the inner peripheral side of the slotless stator 1 (shown by the arrow in FIG. 1), and is made for example from a zirconia ceramic having non magnetic and non conducting properties. The inner tube may be replaced with another ceramic material such as alumina. The slotless stator 1 is one which is not formed with slots for securing a stator winding 15. Moreover, the slotless stator 1 is constructed with the stator winding 15 located on the rotor 7 side and a stator core 17 located on the casing 5 side. The stator winding 15 having an outer diameter larger than the inner diameter of the stator core 17 in the natural condition is arranged inside the stator core 17 with a resiliently contracted diameter. The stator core 17 is in the form of a hollow cylindrical body with a cylindrical surface which is not formed with slots on the inner peripheral surface, and is secured to the casing 5 so that the oil passage 6 for passing lubricating oil (shown by the arrow in FIG. 1) is formed between the outer periphery thereof and the inner periphery of the casing 5. Moreover, the stator core 17, as shown in FIG. 5 through FIG. 7 is made up of two divided cores 13 evenly divided circumferentially. The division surfaces 13A of these divided cores 13 are respectively formed with an engaging protrusion and engaging recess 12a, 14a and 12b, 14b. The engaging protrusion and engaging recess 12a, 14a of one of the divided cores 13 engage with the engaging recess and engaging protrusion 14a and 12b of the other divided core 13. In FIG. 5, the shape of the divided cores 13 is simplified, and a more accurate shape is as shown in FIG. 6 and FIG. 7. The stator winding 15 is of a hollow cylindrical shape having an outer diameter larger than the inner diameter of the stator core 17 in the natural condition, and is secured to the stator core 17 via an insulation layer 19 so that the inner peripheral face of the stator core 17 faces the outer peripheral face of the stator winding 15. Next is a description using FIG. 2 through FIG. 9, of an embodiment of a manufacturing method for the slotless stator according to the present invention. At first, a hollow cylindrical shape stator winding 15 is formed by combining together a plurality of approximately rhombic shape coil segments 23a, 23b, and 23c. The coil segments 23a, 23b and 23c are formed by forming turns by winding a wire sheaf 25 of a plurality of fine wires composed of conductors bundled together, through one turn in an approximate rhombic shape, and then winding and arranging a plurality of the turns so that the turns are sequentially shifted continuously so as to be adjacent to each other in the direction of one diagonal A1 of the rhombic shape (refer to FIG. 2). Then after sequentially shifting and overlapping the coil segments 23a, 23b and 23c in the direction of the diagonal line A1 to form a band shape body 27, the band shape body 27 is rolled into a hollow cylindrical shape to thereby give the hollow cylindrical shape stator winding 15 (refer to FIG. 3). After this, the stator winding 15 is immersed in an alcohol solvent 16 into which BN particles 18 have been mixed so that the BN particles 18 are filled from the surface of the stator winding 15 to the interior (refer to FIG. 4). Here rather than immersing, a technique involving dripping may be used. After this, the stator winding 15 is withdrawn from the alcohol solvent 16 and air dried to evaporate the volatile alcohol. Next, the silicone sheet 19a (omitted from FIG. 5) constituting one portion of the insulating layer 19 is wrapped around the outer periphery of the stator winding 15, and the stator winding 15 is then assembled inside the stator core 17. Hereunder is a detailed description using FIG. 6 and FIG. 7, of the steps of assembling the stator winding 15 inside the stator core 17. At first, the two divided cores 13 are oppositely arranged so that the inner peripheral faces thereof face each other with a constant gap in the vertical direction. This gap is set sufficiently larger than the outer diameter of the stator winding 15. Then the stator winding 15 is mounted on the inner peripheral face of the lower divided core 13, using a rod shape jig M. This divided core 13, and the upper divided core 13 are then brought together to engage the engaging protrusions 12a and 12b with the engaging recesses 14a and 14b. By so doing, the stator winding 15 is assembled inside the stator core 17 in a radially inward compressed condition. At this time, since the stator winding 15 functions as a spring pressing the inside of the stator core 17 so as to expand in the normal direction (the radial outward direction), this is pressed by the resilient force at that time against the inner periphery of the stator core 17. By this resilient force, the stator winding 15 is mechanically secured to the inner periphery of the stator core 17, and hence a special fixation mechanism or adhesive is not required. Moreover, since the stator winding 15 is assembled inside the stator core 17 with the silicone sheet 19a wrapped around the outer periphery thereof, the resilient force acting in the normal direction is further strengthened, so that the stator winding 15 is more stably secured. After this, the stator core 17 and the stator winding 15 are held together as one and immersed in a varnish impregnation tank 31 (refer to FIG. 8). At this time, since the outer peripheral face of the stator winding 15 and the inner peripheral face of the stator core 17 are in close contact with the silicone rubber sheet 19a, there is practically no impregnation with varnish. Then, after impregnating varnish into the stator winding 15, the stator core 17 and the stator winding 15 are withdrawn from the varnish impregnating tank 31 as one. Then by heat hardening the varnish, the manufacture of the slotless stator is completed (refer to FIG. 9). As described above, with the manufacturing method for a slotless stator according to the present invention, by assembling the two divided cores 13 into a cylindrical shape so as to contain the stator winding 15 having an outer diameter larger than the inner diameter of the stator core 17 in the natural condition, the stator winding 15 functions as a spring and produces a resilient force pressing the inside of the stator core 17 so as to expand in the normal direction (the radial outward direction). Therefore, the stator winding 15 is mechanically secured by this resilient force to the inner periphery of the stator core 17. Consequently, as well as high accuracy axial alignment not being required, as with the case where the stator winding 15 is inserted from one open end of a stator core formed integrally in a cylindrical shape, adhesive or a special fixation mechanism for securing the stator winding 15 inside the stator core 17 is not required. Hence the assembly of the slotless stator 1 can be performed very easily. Moreover, since the stator core 17 and the stator winding 15 are immersed in a varnish impregnation tank 31 with the stator winding 15 secured to the inner periphery of the stator core 17, the varnish is hardly impregnated into the outer peripheral side of the stator winding 15. Consequently, the situation where varnish which is thickly attached to the outer peripheral side of the stator winding 15 hardens so that the elastic restoration of the stator winding 15 is restricted, can be effectively avoided. Hence the stator winding 15 can be stably secured to the inner periphery of the stator core 17. Furthermore, when a current flows in the stator winding 15, heat is generated so that an additional outward expanding force acts. Hence at the time of operating, the stator winding 15 is secured even more stably. Moreover, with the present embodiment, since the silicone sheet 19a is disposed between the divided core 13 and the stator winding 15, the resilient force acting in the normal direction is further strengthened, so that the stator winding 15 is even more stable secured. In particular, in the case where a silicone sheet which contains a filler with good thermal conductivity such as boron nitride, such as used for transistor heat dissipation purposes is used as the resilient material, since the thermal conductivity is higher than varnish, the heat dissipation for the stator winding 15 is improved and cooling efficiency also improved. In particular, with the present embodiment, since lubricating oil is circulated on the inner peripheral side of the stator winding 15, a further improvement in the cooling efficiency is achieved. Here with the above embodiment, the cylindrical shape stator winding 15 is formed by combining together the approximately rhombic shape plurality of coil segments 23a, 23b, and 23c. However this may of course be formed by some other method. Moreover, the stator core 17 is constructed from two divided cores 13. However the number of divisions may be three or more. As will be clear from the above description, with the present invention, by having a divided construction for the stator core, and assembling a stator winding having an outer diameter greater than the inner diameter of the stator core thereinside, this functions as a spring for producing a resilient force in the normal direction on the stator winding. By this resilient force, the stator winding is mechanically secured to the inner periphery of the stator core. Therefore a special fixation mechanism or adhesive is not required, thus simplifying assembly of the slotless stator. Furthermore, in the case where a resilient material is disposed between the divided core and the stator winding, the resilient force in the normal direction is further strengthened. Hence the securing force for the stator winding can be further increased. In particular, in the case where a silicone sheet which contains a filler with good thermal conductivity such as boron nitride, such as used for transistor heat dissipation purposes is used as the resilient material, the heat dissipation is improved. Hence not only is the securing strength improved but also an improvement in cooling efficiency can be achieved. Moreover, in the case where a resin is impregnated into the stator winding, by impregnating the resin in a condition with the stator winding secured to the inner periphery of the stator core, the resin is no longer thickly attached to the outer peripheral side of the stator winding. Therefore the restriction on elastic restoration of the stator winding due to the resin attached to the outer periphery hardening can be effectively avoided. Hence the stator winding can be stably secured inside the stator core. Moreover, with the stator winding according to the present invention, by arranging the cylindrical shape stator winding having a larger outer diameter than the inner diameter of the stator core in a resiliently compressed condition inside the cylindrical stator core having no slots, then in the above manner, the stator winding functions as a spring inside the stator core, so that this is mechanically secured to the inner periphery of the stator core by the resilient force. Hence a special fixation mechanism or adhesive is not required, thus simplifying assembly of the slotless stator. To obviate the need for a special fixation mechanism or adhesive, to thereby simplify the assembly of a slotless stator, two divided cores which complete a stator core having no slots by combining each part into a cylindrical shape, are assembled into a cylindrical shape so as to contain a stator winding having an outer diameter larger than an inner diameter of the stator core in the natural condition. By so doing, the stator winding is assembled inside the stator core in a radially inward compressed condition. At this time, since the stator winding functions as a spring pressing the inside of the stator core so as to expand in the normal direction (the radial outward direction), this is mechanically secured by the resilient force at that time to the inner periphery of the stator core. Hence there is no longer the need for a special fixation mechanism or adhesive.

Claims: A manufacturing method for a slotless stator (1) comprising: providing a plurality of divided core sections (13) which once assembled jointly define a cylindrically shaped stator core (17) having a cylindrical shape and no slots, providing a cylindrical shaped stator winding (15) having in an umcompressed condition an outer diameter at a position corresponding to the radially inside of said stator core (17) larger than the inner diameter of said stator core (17); assembling said divided core sections (13) into a cylindrical shape to form said stator core (17) so as to contain said cylindrically shaped stator winding (15), the stator winding (15) being thereby resiliently compressed and secured to an inner periphery of said stator core. A manufacturing method for a slotless stator according to claim 1, comprising a further step of inserting a resilient material between said divided core sections (13) and said stator winding (15). A manufacturing method for a slotless stator according to claim 2, wherein a silicone sheet (19a) is used as said resilient material. A manufacturing method for a slotless stator according to any of claims 1 to 3, comprising a further step of impregnating resin into the stator (1) in a condition with said stator winding (15) secured to an inner periphery of said stator core (17). A manufacturing method for a slotless stator according to claim 4, comprising a further step of hardening the resin after the resin impregnating step. A slotless stator (1) including a cylindrical stator core (17) having no slots and a cylindrically shaped stator winding (15) mounted within said stator core (17), wherein said cylindrical stator core (17) includes a plurality of divided core sections (13) which jointly define the cylindrical stator core (17) characterized in that said stator winding (15) is secured to an inner periphery of said stator core (17) in a resiliently compressed condition only by a resilient force of said stator winding (15) generated by the jointly mounted core sections (13). A slotless stator according to claim 6, further comprising a resilient material (190) inserted between said stator core (17) and said stator winding (15). A slotless stator according to claim 7, wherein a silicone sheet is used as said resilient material. A slotless stator according to claim 7, further comprising resin, said resin being impregnated in said stator winding (15), in a condition with said stator winding (15) secured to an inner periphery of said stator core (17). A rotating electrical machine incorporating a slotless stator (1) according to any of claims 6-9.

Inventors: FUKUDA TAKEO, OZAWA MASARU, FUKUDA, TAKEO, OZAWA, MASARU
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 2000
Main classification: H02K15
IPC codes: H02K15, H02K1, H02K3