1. Field of the Invention
The present invention relates to an on-vehicle rotary electric machine, and an electric power steering system having the same.
2. Description of the Related Art
In an on-vehicle rotary electric machine such as an electrical motor for power steering, an inner rotor-type rotary electric machine having a rotor arranged at the center of a stator core held by a chassis is commonly used. Shrink-fit or press-fit is often used to fix the stator core to the chassis.
Due to a weight-saving demand, the chassis of the on-vehicle rotary electric machine is often formed by die-casting of aluminum, while the stator core is formed of a magnetic steel sheet. Therefore, when a temperature of the electrical motor becomes higher than expected, due to a difference in linear expansion coefficient between the chassis and the stator core, there is a problem in that the holding power by interference between the chassis and the stator core is decreased.
As a result, there is a risk that the stator core may be rotated against the chassis.
In view of such a problem, there has been proposed a structure for preventing rotation of a stator core by providing a rotation stopping member between the stator core and a bracket placed on the upper surface of the stator core (see, for example, JP 2011-67056 A).
However, a member dedicated for preventing rotation of the stator core is added in the structure according to JP 2011-67056 A, which becomes a factor of cost increase as well as a hindrance for downsizing the electrical motor.
An on-vehicle rotary electric machine according to a first aspect of the present invention includes: a rotor; a cylindrical stator core arranged so as to surround a periphery of the rotor via a space, and having a plurality of teeth formed in an inner periphery thereof; a bobbin installed in each of the plurality of teeth; a stator coil wound around each of the bobbins installed in the teeth; a bottomed cylindrical chassis having a bottom faced with one of end portions in the axial direction of the stator core, and holding an outer periphery of the stator core; and a terminal layout board provided with a terminal to which a lead wire of the stator coil is connected, arranged to face the other end portion in the axial direction of the stator core, and fixed to the chassis. A first engaging portion is formed at least in either the bottom or the terminal layout board at a position facing the bobbin, and a second engaging portion that engages with the first engaging portion is formed in an opposing part that faces the first engaging portion in the bobbin.
An on-vehicle rotary electric machine according to a second aspect of the present invention includes: a rotor; a stator core arranged so as to surround a periphery of the rotor via a space, and including a plurality of divided stator cores having a tooth formed in an inner periphery thereof; a bobbin installed in each of the plurality of teeth; a stator coil wound around each of the bobbins installed in the teeth; a bottomed cylindrical chassis having a bottom faced with one of end portions in the axial direction of the stator core, and holding an outer periphery of the stator core; a terminal layout board provided with a terminal to which a lead wire of the stator coil is connected, and arranged to face the other end portion in the axial direction of the stator core; and a divided stator core holding ring that integrally holds the plurality of divided stator cores arranged in a ring shape, and is sandwiched between the terminal layout board and the stator core. The terminal layout board is fixed to the chassis so as to sandwich the divided stator core holding ring and the stator core between the bottom of the chassis and the terminal layout board.
An electric power steering system according to a third aspect of the present invention includes: a steering mechanism for transmitting steering operation of a steering wheel to a steered wheel; and the on-vehicle rotary electric machine according to any of the first and second aspects. Steering assist force is given to the steering mechanism by the on-vehicle rotary electric machine.
According to the present invention, the rotation of the stator core against the chassis can be prevented without adding a member dedicated for preventing rotation of the stator core.
Embodiments for carrying out the present invention are described herein with reference to the drawings.
As in
When the steering wheel SW is rotated with the pinion shaft 4, rotary motion of the pinion shaft 4 is converted into linear motion of the rack shaft, and a steered wheel 8 changes direction via a tie rod 6 and a knuckle arm 7 that are connected to both ends of the rack shaft. The electrical motor 9 for giving steering assist force is supported by and fixed to the chassis 5. A control unit 11 drives the electrical motor 9 based on output from a torque sensor housed in the chassis 5.
In the inner periphery side of the stator core 12, a rotor 18 having a shaft 15, a magnet 16, and a magnet cover 17 is provided. The rotor 18 is rotatably supported by a bearing 19F in the front and a bearing 19R in the rear thereof. The bearing 19F is held by a bottom 10b formed in one end in the axial direction of the chassis 10. The bearing 19R is held by the busbar mold 100 fixed to the other end of the chassis 10 in the axial direction.
A lead wire 14a of the coil 14 wound around the bobbin 13 (see
In
In this embodiment, each tooth 120 is sandwiched between a pair of the uniformly-shaped bobbins 13 in the axial direction; however, it is also possible to fit a bobbin, which is formed of an upper portion and a lower portion as a single part, into each tooth 120 from the tip end side thereof. By using a two-part configuration as in
As in
Each of the divided cores 12a, around which the coil 14 is wound, is arranged and integrated into a ring shape as in
The stator fixing ring 23 is formed either of a metal or a resin to be a single part. As in
In the peripheral region of the busbar mold 100, a fixing hole 100a is provided for fixing the busbar mold 100 to the chassis 10 with a screw. There is also provided a coil through hole 100h for positioning the lead wire 14a of the coil 14 in relation to the busbar terminal 110, in the same number as the number of busbar terminals 110. Furthermore, an engaging hole 100c, to which the engaging projection 13a formed on the end-face of the bobbin 13 is inserted, is formed in the same number as the divided cores 12a.
The busbar mold 100 is arranged above the stator core 12 (on the other side of the bottom 10b). In this arrangement, an engaging projection 13a of the bobbin 13 is inserted into an engaging hole 100c of the busbar mold 100. In other words, the engaging projection 13a functions as a positioning member for the busbar mold 100.
The busbar mold 100 is fixed to the chassis 10 with a screw. Note that by setting the size in the axial direction of the ring 23a so that the stator fixing ring 23 comes into contact with the underside of the busbar mold 100, when the busbar mold 100 is screwed, the stator core 12 is sandwiched between the bottom 10b of the chassis 10 and the busbar mold 100. Subsequently, the engaging projection 13a of the bobbin 13 is thermally caulked. By thermal caulking, not only is the engaging projection 13a inserted into the engaging hole 100c, but also an effect of restraining the stator core rotation is improved due to connection between the engaging projection 13a and the busbar mold 100. The lead wire 14a of the coil 14 is thermally caulked at a hook 110a provided at a tip end portion of the busbar terminal 110.
In the past, shrink-fit or press-fit has been performed to fix the stator core 12 to the chassis 10. The stator core 12 receives reaction force of torque generated when the electrical motor is rotated; however, interference with the chassis 10 is ensured so that receipt of the reaction force is not a problem under a normally-used temperature condition. Nevertheless, in the case of an on-vehicle electrical motor such as a power steering motor, the temperature of the electrical motor may easily become higher due to an influence of heat such as of an engine. In such a case, due to a difference in linear expansion coefficient, the interference between the stator core and the chassis may easily become loose, and the stator core 12 may be rotated against the chassis 10 by the reaction force of the torque.
In a first embodiment, no part dedicated for restraining the rotation is added, unlike the electrical motor described in JP 2011-67056 A. The engaging projections 13a are formed in end portions in the axial direction of the bobbin 13, provided from before. The engaging projections 13a are engaged with the engaging hole 10a of the chassis 10 and with the engaging hole 100c formed in the busbar mold 100. As a result, by this engagement structure, the rotation of the stator core 12 can be prevented in the case where an unexpected temperature rise occurs, and the interference between the stator core and the chassis becomes loose.
As a structure for restraining the rotation of the stator core against the chassis, besides a method of providing a dedicated member for restraining the rotation as in JP 2009-201235 A, for example, there have been known the following structures. That is, a structure in which a groove is formed along the circumferential direction in the inner periphery surface of the chassis, and another groove is formed along the axial direction in the outer periphery surface of the stator, and then an adhesive is flowed into these grooves (JP 2008-312347 A, for example), and a structure in which a fan-shaped projection is formed in an outer periphery surface of the stator, which projection is fitted into a fan-shaped recess formed in an inner periphery surface of the chassis (JP 2009-201235 A, for example).
In case of a method of using an adhesive, however, contamination may occur due to deterioration of the adhesive, which may increase no-load loss of the electrical motor. In case of a structure having a groove or a recess in the inner periphery surface of the chassis, due to a fitting structure, the surface needs to be machine processed, which takes time and efforts. In contrast, in a structure according to this embodiment, the originally-provided bobbin 13 is used. Thus, use of an adhesive or additional processing in the inner periphery surface of the chassis is not necessary, and an effect of restraining rotation can be obtained easily.
In the above described embodiment, the bobbin 13 is engaged with both the bottom 10b of the chassis 10 and the busbar mold 100, but a rotation prevention effect can still be obtained in a structure of engaging the bobbin 13 on the chassis side only. Note that by engaging the bobbin 13 also with the busbar mold 100, and providing a rotation prevention mechanism at both ends in the axial direction by sandwiching the stator core 12, in addition to an improved rotation prevention effect, it is also possible to obtain an effect of restraining dismantling of the stator core 12 assembled in a ring shape, due to external force or a vibration. In addition, such effects can be further enhanced by thermal caulking of the engaging projection 13a.
When fixing the stator core 12 to the chassis 10 by shrink-fit or the like, it is necessary to align relative position between the lead wire 14a of the coil 14 and the busbar terminal 110 of the busbar mold 100. Therefore, positioning of the stator core 12 relative to the chassis 10 also becomes important. According to this embodiment, when the stator core 12 is inserted into the chassis 10, positioning of the stator core 12 can be achieved by engaging the engaging projection 13a of the bobbin 13 with the engaging hole 100c of the chassis 10. Furthermore, when the busbar mold 100 is fixed to the chassis 10, positioning of the busbar mold 100 can be achieved easily by inserting the engaging projection 13a of the bobbin 13 into the engaging hole 100c.
The stator fixing ring 23 is a member for integrating a plurality of divided cores 12a into a ring shape. In this embodiment, the stator fixing ring 23 further functions as a rotation restraint member in the case where the stator core 12 becomes loose against the chassis 10. Therefore, the size of the ring 23a of the stator fixing ring 23 in the axial direction should be set so that the ring 23a is sandwiched between the stator core 12 and the busbar mold 100 when the busbar mold 100 is screwed to the chassis 10.
As a result, in the case where the fixing of the stator core 12 becomes loose and the stator core 12 begins to rotate, the rotation is restrained by frictional force between the ring 23a and the busbar mold 100. Therefore, even in the case where the bobbin 13 is configured not to be provided with the engaging projection 13a as in
Furthermore, since the stator core 12 is fixed by being sandwiched between the busbar mold 100 and the bottom 10b of the chassis 10, the ring-shaped stator core 12 can be held firmly. Accordingly, the interference may be increased in the shrink-fit between the chassis 10 and the stator core 12, or an area of welding of the divided cores 12a may be decreased.
In the above-described embodiment, the number of the engaging projections 13a provided to one of the end portions in the axial direction of the stator core 12, and the number of the engaging holes 10a on the side of the chassis 10 are set to be equal; however, the numbers may also be different. In such a case, an intermediate member may be arranged between the stator core 12 and the chassis 10. In the intermediate member, in a surface facing the stator core 12, an engaging hole may be formed in the same number as the engaging projections 13a, and in a surface facing the chassis 10, an engaging projection may be formed in the same number as the engaging holes 10a. In such a configuration, the stator core 12 divided into a different number can be used with the same chassis 10.
Note that in the above-described embodiment, a projection (engaging projection 13a) is formed on the side of the bobbin 13 as an engaging portion, and a hole (engaging holes 10a, 100c) is formed in the chassis 10 and the busbar mold 100, but the relationship may be reversed. In other words, as in
Note that as an engaging portion on the side of the busbar mold 100, an engaging portion is provided in a shape such as in
In this embodiment as well, the engaging portion 13c is formed in the end portions in the axial direction of the bobbin 13, provided from before, and the engaging portion 13c is engaged with an engaging portion (10f, 10g) of the chassis 10 and an engaging portion (100e, 100f) formed in the undersurface of the busbar mold 100. Therefore, as in the above-described first embodiment, the rotation of the stator core 12 can be prevented even in the case where the interference is decreased.
Furthermore, the engaging portion 10f or 10g formed in the chassis 10 has a recess-and-projection structure, and thus can be formed at the same time as the chassis 10 is molded. Therefore, unlike the configuration of forming the engaging hole 10a in a bottom 10b of the chassis 10 in
Furthermore, the engaging portion 13c formed at the end portion in the axial direction of the bobbin 13 is not cylindrical as the engaging projection 13a in
As described above, the electrical motor 9, which is an on-vehicle rotary electric machine, includes as in
Therefore, even in the case where fixing between the chassis 10 and the stator core 12 becomes loose due to a temperature rise or the like, rotation of the stator core 12 can be restrained as the engaging projection 13a and the engaging hole are engaged. Furthermore, the rotation restraint effect can be further improved by engaging the engaging projections 13a of the bobbin 13, provided to both ends in the axial direction of the stator core 12, with the engaging hole of the chassis 10 and the busbar mold 100. Furthermore, when the stator core 12 is assembled to the chassis 10, positioning of the stator core 12 can be easily made by engaging the engaging projection 13a with the engaging hole.
Furthermore, the bobbin 13 is formed of resin. The engaging projection 13a penetrates through the engaging hole 100c of the busbar mold 100, and a portion that projects out to the other side of the busbar mold 100 is thermally caulked. As in
Furthermore, the electrical motor 9 further includes a stator fixing ring 23, which is arranged in a gap in the axial direction between the busbar mold 100 and the stator core 12, integrally holds a plurality of the divided cores 12a arranged in a ring shape, and is sandwiched between the busbar mold 100 and the stator core 12. The stator fixing ring 23 and the stator core 12 may be sandwiched between the bottom 10b of the chassis 10 and the busbar mold 100. In such a configuration, even in the case where the fixing of the stator core 12 becomes loose and the stator core 12 begins to rotate, the rotation restraint effect is further enhanced by friction force between the stator fixing ring 23 and the busbar mold 100. Therefore, even in the case where the bobbin 13 is configured not to be provided with the engaging projection 13a, the rotation restraint effect can be obtained by the stator fixing ring 23 alone.
Furthermore, the electric power steering system may include: a steering mechanism for transmitting the steering operation of the steering wheel to the steered wheel; and the above-described on-vehicle electrical motor 9, which gives the steering assist force to the steering mechanism. In the electric power steering system, the electrical motor 9 is provided in the lower part of an engine room, whereby it may be easily exposed to a high temperature environment. Therefore, by using the above-described electrical motor 9 having a high rotation restrain effect, a highly-reliable electric power steering system can be obtained.
Note that each of the above-described embodiments may be used alone or combined, since an effect of each embodiment may be obtained alone or in synergy. An effect of each embodiment may be obtained either alone or in synergy. Furthermore, note that the above descriptions are only exemplary. Interpretation of the invention is neither limited nor bound by a correlation between a description in the above embodiments and a description in the claims.
For example, the stator core 12 may be configured to have either a divided core structure or an integral structure, as long as the bobbin 13 is provided. Furthermore, in the above-described embodiments, a plurality of the divided cores 12a is integrated by using the stator fixing ring 23 or by welding, but it is also possible to configure a plurality of the divided cores 12a to be grasped collectively by a jig and assembled into the chassis 10. The chassis 10 is a bottomed cylindrical chassis, but it may also be configured as the cylindrical chassis 10 having a bottom 10b, a separate part, fixed with a bolt as in
In the above-described embodiments, an electric power steering system has been given as an example; however, an on-vehicle rotary electric machine according to the embodiments is also applicable to an oil circulation motor of a transmission or an engine starter motor.
Number | Date | Country | Kind |
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2012-088779 | Apr 2012 | JP | national |