This application is based on and claims priority from Japanese Patent Application No. 2010-55468, filed on Mar. 12, 2010, the content of which is hereby incorporated by reference in its entirety into this application.
1. Technical Field
The present invention relates to electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.
2. Description of the Related Art
Conventionally, electric rotating machines, which are used in, for example, motor vehicles as electric motors and electric generators, generally include a stator and a rotor. The stator includes a hollow cylindrical stator core, a stator coil, and an insulator. The stator core is formed by laminating a plurality of magnetic steel sheets and has a plurality of slots that are formed in the radially inner surface of the stator core and spaced in the circumferential direction of the stator core. The stator coil is mounted on the stator core so as to be partially received in the slots of the stator core. The insulator is interposed between the stator core and the stator coil so as to electrically insulate them from each other. The rotor is rotatably disposed radially inside the stator core.
Moreover, in a liquid-cooled electric rotating machine, the heat generated by the stator coil during operation is generally dissipated by using a liquid coolant. For example, cooling oil is supplied to drop on coil ends of the stator coil; the coil ends protrude outside the slots of the stator core respectively on opposite axial sides of the stator core. Then, the cooling oil spreads along the surfaces of the coil ends, flowing into gaps between the insulator and the stator core and between the insulator and the stator coil. Consequently, the heat resistance between the stator coil and the stator core is lowered, thereby allowing the heat generated by the stator coil to be effectively transmitted to the stator core.
However, due to manufacturing tolerances, the stator core may have uneven internal walls which define the slots of the stator core. In this case, if the insulator is disposed in partial contact with the internal walls of stator core, it will be difficult for the cooling oil to spread over the entire axial length of each of the gaps between the insulator and the stator core. Consequently, air will remain in the gaps between the insulator and the stator core, thereby keeping high the heat resistance between the stator coil and the stator core. As a result, it will be difficult for the heat generated by the stator coil to be effectively transmitted to the stator core.
To solve the above problem, Japanese Patent Application Publication No. 2005-12989 (to be referred to as Patent Document 1 hereinafter) discloses a first technique. According to the first technique, a plurality of cooling oil passages are formed in the stator core. Each of the cooling oil passages extends in a radial direction of the stator core so as to fluidically connect one of the slots of the stator core to the radially outside of the stator core. Consequently, the cooling oil can be supplied from the radially outside of the stator core into the slots of the stator core via the cooling oil passages (see, paragraph [0042] and FIGS. 2-6 of Patent Document 1).
However, with the first technique disclosed in Patent Document 1, at least part of the magnetic steel sheets forming the stator core are made, by the corresponding cooling oil passages, to be discontinuous in the circumferential direction of the stator core. Consequently, the strength of each of the discontinuous magnetic steel sheets and thus the strength of the entire stator core may be considerably lowered.
Moreover, Patent Document 1 also discloses a second technique for solving the above-described problem. According to the second technique, all of the magnetic steel sheets forming the stator core are divided into a plurality of groups each of which includes a predetermined number of the magnetic steel sheets.
Moreover, between each adjacent pair of the groups, there is welded a spacer to form a gap therebetween. Consequently, via the gaps formed between the adjacent groups of the magnetic steel sheets, the slots of the stator core become fluidically connected to the radially outside of the stator core. As a result, the cooling oil can be supplied from the radially outside of the stator core into the slots of the stator core via the gaps (see, paragraphs [0061]-[0062] and FIG. 8 of Patent Document 1).
However, with the second technique disclosed in Patent Document 1, it is necessary to prepare and weld the spacers for forming the gaps. Consequently, the manufacturing cost will be increased. In addition, the magnetic steel sheets may be deformed during the welding of the spacers.
Japanese Patent Application Publication No. 2000-50552 (to be referred to as Patent Document 2 hereinafter) discloses a third technique for solving the above-described problem. According to the third technique, silicone is first applied on the insulator (or insulating sheets). Then, the insulator having the silicone applied thereon is inserted into the slots of the stator core. Consequently, the gaps between the insulator and the stator core are filled with the silicone. As a result, the heat resistance between the stator coil and the stator core is lowered, thereby allowing the heat generated by the stator coil to be effectively transmitted to the stator core.
However, with the third technique disclosed in Patent Document 2, for completely filling the gaps between the insulator and the stator core with the silicone, it is necessary to evenly apply the silicone on the insulator by, for example, vacuum impregnation. Consequently, the manufacturing cost will be increased.
According to an embodiment, there is provided an electric rotating machine which includes a stator, a rotor, and a housing. The stator includes a hollow cylindrical stator core and a stator coil mounted on the stator core. The stator core is formed by laminating a plurality of magnetic steel sheets and has a plurality of slots that are formed in the radially inner surface of the stator core and spaced in the circumferential direction of the stator core. The stator coil is partially received in the slots of the stator core to have a pair of coil ends that protrude outside the slots of the stator core respectively on opposite axial sides of the stator core. The rotor is rotatably disposed radially inside the stator core. The housing receives both the rotor and the stator with a gap formed between the inner surface of the housing and the radially outer surface of the stator core; the gap makes up an outside coolant passage in which a coolant is to flow. Furthermore, each of the magnetic steel sheets forming the stator core has a plurality of through-holes that are formed to penetrate the magnetic steel sheet in the axial direction of the stator core. All of the magnetic steel sheets forming the stator core are divided into a plurality of groups each of which includes axially-adjacent n of the magnetic steel sheets, where n is an integer not less than 2. For each of the groups, corresponding a of the through-holes of the n magnetic steel sheets of the group communicate with one other to form an inside coolant passage that fluidically connects the outside coolant passage with a corresponding one of the slots of the stator core.
With the above configuration, the coolant can flow from the outside coolant passage into each of the slots of the stator core via the corresponding inside coolant passages. Consequently, the heat resistance between the stator core and the stator coil can be reduced, thereby more effectively transmitting the heat generated by the stator coil to the stator core. As a result, it is possible to suppress the increase in the resistance of the stator coil due to the heat generated by the stator coil, thereby ensuring high efficiency of the electric rotating machine. Moreover, it is also possible to prevent the insulating coat of the stator coil from being damaged by the heat generated by the stator coil. Furthermore, since the inside coolant passages are formed without making the magnetic steel sheets discontinuous in the circumferential direction, it is possible to ensure the strength of each of the magnetic steel sheets and thus the strength of the entire stator core.
According to another embodiment, there is provided an electric rotating machine which includes a stator, a rotor, and supplying means. The stator includes a hollow cylindrical stator core and a stator coil mounted on the stator core. The stator core is formed by laminating a plurality of magnetic steel sheets and having a plurality of slots that are formed in the radially inner surface of the stator core and spaced in the circumferential direction of the stator core. The stator coil is partially received in the slots of the stator core to have a pair of coil ends that protrude outside the slots of the stator core respectively on opposite axial sides of the stator core. The rotor is rotatably disposed radially inside the stator core. The supplying means supplies a coolant to the coil ends of the stator coil. Furthermore, in those internal walls of the magnetic steel sheets which define the slots of the stator core, there are formed grooves that extend in the axial direction of the stator core.
With the above configuration, if an insulator is interposed between the stator coil and the stator core in partial contact with the internal walls of the magnetic steel sheets, it is possible for the coolant to flow through the grooves to occupy the entire axial length of each of the gaps between the insulator and the internal walls of the magnetic steel sheets. As a result, the heat resistance between the stator core and the stator coil can be reduced, thereby more effectively transmitting the heat generated by the stator coil to the stator core.
The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.
In the accompanying drawings:
Preferred embodiments of the present invention will be described hereinafter with reference to
In the present embodiment, the electric rotating machine 1 is configured as a brushless motor for use in, for example, a motor vehicle. As shown in
Referring to
The stator coil 3 is wound around each of the stator teeth 22 so as to be partially received in the slots 23 of the stator core 2. In addition, all of those portions of the stator coil 3 which protrude from the same axial end face of the stator core 2 together make up a coil end 32 of the stator coil 3. That is, the stator coil 3 includes two coil ends 32 that protrude outside the slots 23 of the stator core 2 respectively on opposite axial sides of the stator core 2.
The insulator 31 is interposed between the stator core 2 and the stator coil 3 so as to electrically insulate them from each other. More specifically, in each of the slots 23 of the stator core 2, the insulator 31 is interposed between the stator coil 3 and those internal walls of the stator core 2 which define the slot 23. In addition, the insulator 31 may be configured with insulating paper, insulating sheets or an electrically-insulative resin.
The rotor 4 is rotatably disposed radially inside the stator core 2. The rotor 4 includes a plurality of permanent magnets (not shown) that form a plurality of magnetic poles on the radially outer periphery of the rotor 4. The polarities of the magnetic poles alternate between north and south in the circumferential direction of the rotor 4 (or in the circumferential direction of the stator core 2). At the radial center of the rotor 4, there is formed a through-hole 41 in which a rotating shaft 42 is fixedly fitted. The rotating shaft 42 has an opposite pair of axial end portions that are supported by the housing 5 via a pair of bearings 51, respectively.
In operation, the stator creates a rotating magnetic field when electric current is supplied to the stator coil 3. The rotating magnetic field causes the rotor 4 to rotate together with the rotating shaft 42, thereby outputting torque through the rotating shaft 42.
The housing 5 has formed therein cooling oil inlets 52, through which a coolant is supplied from the outside to the inside of the housing 5. In the present embodiment, the coolant is implemented by cooling oil.
The cooling oil, which is introduced into the housing 5 through the cooling oil inlets 52, drops on the coil ends 32 of the stator coil 3. It should be noted that the cooling oil inlets 52 constitute means for supplying the cooling oil to the coil ends 32. In addition, it is assumed that the upward and downward directions in
Then, the cooling oil spreads along the surfaces of the coil ends 32 of the stator coil 3, flowing into the gaps between the magnetic steel sheets 21 (i.e., the stator core 2) and the insulator 31 and between the stator coil 3 and the insulator 31. In addition, the cooling oil also flows into an outside cooling oil passage 53 by means of capillary action; the outside cooling oil passage 53 is made up of the annular gap between the radially outer surface of the stator core 2 and the inner surface of the housing 5.
Each of the magnetic steel sheets 21 has a plurality of through-holes 24 that are formed to penetrate the magnetic steel sheet 21 in the thickness direction of the magnetic steel sheet 21 (or in the axial direction of the stator core 2) and are equally spaced in the circumferential direction of the stator core 2. Moreover, each of the through-holes 24 is radially aligned with a corresponding one of the slots 23 of the stator core 2.
Referring further to
Moreover, as shown in
Furthermore, as shown in
In operation, referring to
In the present embodiment, the dimensions of each of the inside cooling oil passages 25 are set so as to allow the cooling oil to flow from the outside cooling oil passage 53 into the corresponding slot 23 of the stator core 2 via the inside cooling oil passage 25 by means of capillary action.
More specifically, in the present embodiment, the dimensions of each of the inside cooling oil passages 25 are set so as to satisfy the following inequality:
2×(a+t)×σ cos θ≧a×t×b×ρ×g (1),
where a represents the width (in m) of each of the through-holes 24 of the magnetic steel sheets 21 in the circumferential direction of the stator core 2,
t represents the thickness (in m) of each of the magnetic steel sheets 21 in the axial direction of the stator core 2,
σ represents the surface tension (in N/m) of the cooling oil,
θ represents the contact angle (in °) between the cooling oil and those internal walls of the magnetic steel sheets 21 which define the through-holes 24 (see
b represents the length (in m) of a back portion 28 of the stator core 2 (i.e., the length of each of the inside cooling oil passages 25 in the radial direction of the stator core 2),
ρ represents the density (in kg/m3) of the cooling oil, and
g represents the gravitational acceleration (in m/s2).
In addition, the left and right sides of the above inequality (1) respectively represent the driving force Fσ due to the surface tension of the cooling oil and the gravity Fg of the cooling oil.
Specifically, suppose that t=0.4 mm and b=14 mm. Then, in
Specifically, suppose that a=5 mm and t=0.4 mm. Then, in
After having described the overall configuration of the electric rotating machine 1 according to the present embodiment, the advantages thereof will be described hereinafter.
In the electric rotating machine 1, each of the magnetic steel sheets 21 forming the stator core 2 has the through-holes 24 that are formed to penetrate the magnetic steel sheet 21 in the axial direction of the stator core 2. All of the magnetic steel sheets 21 forming the stator core 2 are divided into a plurality of groups each of which includes five axially-adjacent magnetic steel sheets 21. For each of the groups, five corresponding through-holes 24 of the five magnetic steel sheets 21 of the group communicate with one another in the axial direction of the stator core 2, forming the inside cooling oil passage 25 that fluidically connects the outside coolant passage 53 with the corresponding slot 23 of the stator core 2.
With the above configuration, the cooling oil can flow from the outside cooling oil passage 53 into each of the slots 23 of the stator core 2 via the corresponding inside cooling oil passages 25. Consequently, the heat resistance between the stator core 2 and the stator coil 3 can be reduced, thereby more effectively transmitting the heat generated by the stator coil 3 to the stator core 2. As a result, it is possible to suppress the increase in the resistance of the stator coil 3 due to the heat generated by the stator coil 3, thereby ensuring high efficiency of the electric rotating machine 1. Moreover, it is also possible to prevent the insulating coat of the stator coil 3 from being damaged by the heat generated by the stator coil 3.
Furthermore, since the inside cooling oil passages 25 are formed without making the magnetic steel sheets 21 discontinuous in the circumferential direction, it is possible to ensure the strength of each of the magnetic steel sheets 21 and thus the strength of the entire stator core 2.
In the present embodiment, each of the through-holes 24 of the magnetic steel sheets 21 is formed so as to be radially aligned with a corresponding one of the slots 23 of the stator core 2.
With the above configuration, each of the inside cooling oil passages 25 is accordingly radially aligned with a corresponding one of the slots 23 of the stator core 2. Consequently, during the process of laminating the magnetic steel sheets 21 to form the stator core 2, it is unnecessary to circumferentially position the magnetic steel sheets 21 for placing each of the inside cooling oil passages 25 in fluid communication with a corresponding one of the slots 23 of the stator core 2. As a result, it is possible to simplify the laminating process, thereby lowering the manufacturing cost of the stator core 2.
In the present embodiment, the dimensions of each of the inside cooling oil passages 25 are set so as to allow the cooling oil to flow from the outside cooling oil passage 53 into the corresponding slot 23 of the stator core 2 via the inside cooling oil passage 25 by means of capillary action.
Setting the dimensions as above, it is possible to supply the cooling oil from the outside cooling oil passage 53 into each of the slots 23 of the stator core 2 without employing an additional supplying means. Moreover, since the amount of the cooling oil supplied into each of the slots 23 is regulated by the capillary action, it is possible to suppress leakage of the cooling oil from the slots 23 to the rotor 4. Consequently, it is possible to suppress accumulation of the cooling oil in the gap between the stator core 2 and the rotor 4, thereby minimizing torque loss due to the shearing resistance of the cooling oil.
Further, in the present embodiment, the dimensions of each of the inside cooling oil passages 25 are set so as to satisfy the above-described inequality (1); the left and right sides of the inequality (1) respectively represent the driving force Fσ due to the surface tension of the cooling oil and the gravity Fg of the cooling oil.
Setting the dimensions as above, it is possible to reliably supply, by means of capillary action, the cooling oil from the outside cooling oil passage 53 into each of the slots 23 of the stator core 2 regardless of the orientation of the electric rotating machine 1 in the motor vehicle.
As shown in
However, with the above configuration, at least part of the magnetic steel sheets 201 forming the stator core 200 are made, by the corresponding cooling oil passages 202, to be discontinuous in the circumferential direction of the stator core 200. Consequently, the strength of each of the discontinuous magnetic steel sheets 201 and thus the strength of the entire stator core 200 may be considerably lowered.
Moreover, with the above configuration, for allowing each of the slots 203 to have one of the cooling oil passage 202 fluidically connected thereto, it is necessary to circumferentially position the magnetic steel sheets 201 during the process of laminating them. Consequently, the laminating process may become complicated, thereby increasing the manufacturing cost of the stator core 200.
In the present embodiment, as shown in
Moreover, in the present embodiment, each of the grooves 26 has a substantially semicircular cross section perpendicular to the axial direction of the stator core 2. The magnetic steel sheets 21 also have rounded edge portions 27 that are respectively formed at axial ends of the internal walls of the magnetic steel sheets 21. Further, the radius r of the cross sections of the grooves 26 is set to be less than the radius R of the rounded edge portions 27 of the magnetic steel sheets 21.
In addition, the grooves 26 may be formed, for example by grinding, in the respective magnetic steel sheets 21 before laminating them. Otherwise, the grooves 26 may also be formed after laminating the magnetic steel sheets 21 together. In the latter case, the grooves 26 would be aligned with one another in the laminating direction of the magnetic steel sheets 21 (or in the axial direction of the stator core 2).
In operation, the cooling oil, which is introduced into the housing 5 through the cooling oil inlets 52 (see
In the present embodiment, as described above, there are formed the grooves 26 in the internal walls of the magnetic steel sheets 21. Consequently, even if the insulator 31 is disposed in partial contact with the internal walls of the magnetic steel sheets 21 as shown in
Further, as described above, the radius r of the cross sections of the grooves 26 is set to be less than the radius R of the rounded edge portions 27 of the magnetic steel sheets 21. Consequently, it is possible to reliably retain the cooling oil between the insulator 31 and the rounded edge portions 27 of the magnetic steel sheets 21.
In contrast, if the radius r of the cross sections of the grooves 26 was not less than the radius R of the rounded edge portions 27, the cooling oil would easily flow through the grooves 26, making it difficult to retain the cooling oil between the insulator 31 and the rounded edge portions 27.
In this comparative example, as shown in
Consequently, the cooling oil, which flows into the gap between the insulator 31 and the internal walls of the magnetic steel sheets 21 from one axial side of the stator core 2, will be blocked at the contact spot 211. As a result, there will be formed an air layer 212 in the gap on the other axial side of the contact spot 211, thereby keeping high the heat resistance between the stator coil 3 and the stator core 2.
While the above particular embodiments of the present invention 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 invention.
For example, in the previous embodiments, the electric rotating machine 1 is a brushless motor. However, the invention may also be applied to other types of electric motors and electric generators.
In the first embodiment, all of the magnetic steel sheets 21 forming the stator core 2 are divided into a plurality of groups each of which includes five axially-adjacent magnetic steel sheets 21; for each of the groups, five corresponding through-holes 24 of the magnetic steel sheets 21 of the group communicate with one another to form one inside cooling oil passage 25.
However, it is also possible that: each of the groups includes n axially-adjacent magnetic steel sheets 21; and for each of the groups, n corresponding through-holes 24 of the magnetic steel sheets 21 of the group communicate with one another to form one inside cooling oil passage 25, where n is an. integer not less than 2 and different from five.
In the second embodiment, the means for supplying the cooling oil to the coil ends 32 of the stator coil 3 is constituted by the cooling oil inlets 52. However, the electric rotating machine 1 may also have other means for supplying the cooling oil to the coil ends 32. For example, the electric rotating machine 1 may further include cooling oil pipes each of which is inserted into the housing 5 to have an open end thereof located in close vicinity to one of the coil ends 32 of the stator coil 3.
Furthermore, it is also possible to combine the configurations of the stators according to the first and second embodiments to form a stator which includes both the inside cooling oil passages 25 described in the first embodiment and the grooves 26 described in the second embodiment.
Number | Date | Country | Kind |
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2010-055468 | Mar 2010 | JP | national |