Patent Application
20050046299
The present invention relates to a stator core of a dynamoelectric machine such as a generator or alternator, and in particular to a method for providing windings in stator cores with increased slot fill percentages and reduced coil end-turn heights.
Generators are found in virtually every motor vehicle manufactured today. These generators, also referred to as alternators, produce electricity necessary to power a vehicle's electrical accessories and charge a vehicle's battery. Generators must produce electricity in sufficient quantities to power a vehicle's electrical system. Furthermore, generators must produce electricity having the characteristics necessary to be compatible with a vehicle's electrical components. Further applications of the generator/alternator include providing sufficient torque for the starting of typical internal combustion engines. A generator typically includes a stator assembly comprising a stator core, stator windings, and a rotor.
Conventionally, the stator core contains the main current carrying windings (“stator windings”) in which electromotive force produced by magnetic flux is induced. The core contains a plurality of radially-inwardly projecting teeth separated by intervening slots. Each slot has an open end formed by tooth tips of adjacent stator teeth. The slot opening is conventionally relatively narrow, compared with the width of the slot itself. The narrow slot opening in conventional arrangements, however, is not an accident, but rather a deliberate choice, ostensibly to provide both a magnetic flux path and to provide for wire retention.
There are two basic ways in which conventional stator windings are manufactured. In the first instance, a continuous magnetic wire is wound into a wave or coiled pattern and then inserted into the slots of the stator core in primarily a radial direction. In the second instance, a number of hairpin-shaped conductor segments (i.e., including at least one “hairpin” or 180° end turn) are inserted axially into the stator core. After insertion, the two straight segment ends of the hairpin-shaped conductor segments extending out from the slots must be post formed into a correct position and shape and then joined to the segment ends of adjacent conductor segments in order to complete the electrical circuit. There are, however, shortcomings with these conventional arrangements.
The first shortcoming relates to a so-called “slot fill” factor, typically expressed as a percentage. Particularly, the “slot fill” is a percentage of the total cross-sectional area of stator windings, taken relative to the total available cross-sectional area in the slot. The relatively narrow slot opening formed by the tooth tips, which are typically stamped directly into a steel lamination into the desired profile, restricts entry (and accordingly the size) of the stator windings used in the generator. A typical stator size and fill configuration is shown in
One approach taken in the art to improve the “slot fill” of a generator is to use stator windings made up of hairpin-shaped conductor segments as discussed above. In this approach, pre-formed conductor segments are inserted axially into the stator slots throughout the iron core of the stator. The multiple segment ends of these hairpin-shaped conductor segments are then joined to create a continuous conductive loop in the stator. Since the conductor segments are inserted in an axial fashion, such hairpin-shaped conductor segments are not limited by such small slot openings known in the art. Consequently, the hairpin-shaped conductor segments can be of a larger cross-sectional area, and also be non-round in shape. With such a size and shape, it is possible to neatly stack the windings within the slot to increase the slot fill, which may approach 90%.
However, such an approach is not without its downfalls. For instance, because each hairpin-shaped conductor segment only occupies two slots, a large number of electrical connections between the segment ends of adjacent conductor segments is required in order to create a continuous stator winding. This results in significant cost increases due to increased labor, complexity and scrap rate, as well as decreased reliability. Additionally, because the cross-section of the end turn portion of the hairpin-shaped conductor is the same as that of the straight portions of the conductor in the slot, the end-turn segments of the conductors are unnecessarily tall, adding electrical resistance to the circuit, and unnecessarily increasing conductor usage and packaging requirements.
Another approach in the art involves deforming the tooth tips after inserting the hairpin-shaped conductor segments, as seen by reference to U.S. Pat. No. 4,176,444 entitled “METHOD AND APPARATUS FOR ASSEMBLING DYNAMOELECTRIC MACHINE STATORS” issued to Walker. Walker discloses a method for forming a stator including the steps of enlarging a slot opening between adjacent pairs of stator teeth by deforming the stator tooth tips (e.g., with a punch), placing prewound stator windings in selected core slots and thereafter reducing the slot opening between those certain adjacent pairs of teeth by reforming the tooth tips so as to provide a cylindrical shaped central bore stator. The disclosure of Walker, however, does not teach using a conductor having a width substantially equal to that of the slot itself.
Thus, in sum, it would be desirable to keep the “tooth tips” since they can improve low speed performance of the generator, among other things. However, the small slot opening which results from the “tooth tips” restricts the size of the stator windings, resulting in a low slot-fill stator having a reduced power output and a reduced efficiency. Additionally, it would be advantageous to utilize hairpin-shaped conductor segments in an effort to improve slot fill, however, the number of electrical connections required combined with the resulting excessive end turn height serves to increase the complexity and cost of winding the stator, as well as reducing reliability.
There is, therefore, a need to provide a method of making a dynamoelectric machine that minimizes or eliminates one or more of the problems set forth above.
One object of the present invention is to provide a stator core for a dynamoelectric machine, such as an alternating current (AC) generator, that solves one or more of the problems set forth above. The present invention provides a method that, during an initial step, provides a stator slot opening that is increased in width relative to conventional slot openings (i.e., approximately equal to the width of the slot itself). The increased size slot openings allow a wave-shaped conductor segment having a plurality of straight portions with end turn regions disposed in between adjacent straight portions in an alternating pattern to thereby define a pair of free segment ends on the outermost straight portions and positioned on the same axial side of the stator core, to be inserted (in a subsequent step) into the slots to thereby provide an increased slot fill and reliability, as well as a reduction in complexity and costs.
The wave-shaped conductor segments are formed in a manner wherein each of the two segment ends, the plurality of straight portions, and the end turn regions each have separate and distinct cross-section shapes. After the wave conductor segments have been formed to their desired shape, in one embodiment, the formed wave-shaped segments are loaded onto a tool that radially disposes the windings into the open slots of the stator. In alternate embodiments, the wave-shaped segments could be formed multiple ways: continuously, so that an entire phase of windings are formed in series requiring no post connections, or the formed waves could be manufactured in multiple parallel waves that would require a few post connections to complete the winding circuit for a given phase. Thereafter, in a subsequent step, the segment ends of adjacent wave-shaped stator windings are electrically connected in order to create a continuous stator winding, which results in a decreased number of required electrical connections, and which accordingly decreases the costs and complexity that exist in conventional arrangements. In a further subsequent step, the slot openings are closed up in order to provide an improved magnetic flux path and for winding retention. This is accomplished, in one embodiment, by cold-forming the ends of the stator teeth to form “tooth tips” after the core itself has been made and the wave-shaped conductor segments have been inserted into the open slots. The invention also provides another advantage, namely that of keeping the “tooth tips,” which improve performance, particularly at low speed.
A method according to the present invention thus involves providing a stator core having a plurality of teeth separated by intervening slots with a slot opening substantially equal to the slot width. The method further includes forming a continuous wave-shaped conductor segment having a plurality of straight portions with end turn regions disposed inbetween adjacent straight portions in an alternating pattern so as to define a pair of free segment ends on the outermost straight portions, and wherein the segment ends have a first cross-section shape, the straight portions have a second cross-section shape different than the first cross-section shape, and the end turn regions have a third cross-section shape different than both the first and second cross-section shapes. The method further includes inserting the wave-shaped conductor segment into the slots of the stator core.
Other features and advantages will be apparent to those of ordinary skill in the art from the detailed description and accompanying drawings describing and illustrating the invention by way of example only and not by way of limitation.
A stator core according to the present invention is also provided.
The operative features of the present invention are explained in more detail with reference to the drawings.
a is a cross-sectional view of a wave-shaped conductor taken along the line 3a-3a in
a is a cross-sectional view of a straight portion of a wave-shaped conductor suitable for the present invention taken along the line 4a-4a in
a is a cross-sectional view of an end-turn region of a wave-shaped conductor suitable for the present invention taken along the line 5a-5a in
Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,
With continued reference to
Slot 16 includes a closed end 30 adjacent to yoke 12 and a pair of sides 32 and 34 defined by adjacent teeth 141 and 142 (in addition to an open end defining slot opening 22 described in connection with
The depth of slot 16 may be selected to accept a plurality of stacked layers of individual stator winding conductors (as shown in
The increased slot opening 22 is achieved by producing (e.g., stamping) the profile shown in
a show the next step of the inventive method, namely forming a wave-shaped conductor segment 46 comprised of a continuous conductor having a first cross-section shape 48.
In the illustrated embodiment, the wave spans two and one-half wave cycles, however, it should be noted that this arrangement is simply exemplary, and not limiting in nature. In actuality, the wave may span n/2 wave cycles, wherein “n” is any integer greater than zero. The wave-shaped segments can be constructed such that the total number of straight portions 50 disposed into the slots are continuously connected by a single wave. Alternatively, to improve handling in manufacturing, these wave-shaped segments may be independent, requiring post-insertion connections to complete the winding circuit.
Next, as can be seen in
a show how end turn regions 52 of the wave-shaped conductor segment 46 are shaped into relatively thin rectangular shaped cross-section, thereby defining a third cross-section shape 62, which is different from both first cross-section shape 48 and second cross-section shape 56.
The steps of forming the various shapes may be performed in any order.
As can be seen in
The method may include the further step of inserting a stator slot liner (insulator) 36 in slot 16 (
The ball roller 68 may be rolled along the bottom of tooth 14 (i.e., the inside diameter of the stator core 10) in an axial direction. This movement deforms the material at the bottom (i.e., radially innermost) of tooth 14 to define a final “tooth tip” 74 (shown in
In accordance with the invention, an enlarged stator slot opening is combined with a wave-shaped conductor segment having two segment ends with a first cross-section shape and positioned on the same axial side of the stator upon insertion into the stator core (although, if design requires, the segment ends may exit on opposite ends of the stator if necessary), a plurality of straight portions with a second cross-section shape different than the first cross-section shape wherein the width of the straight portions is substantially equal to the width of one of the slots in the stator core, and a plurality of end turn regions with a third cross-section shape different than the first and second cross-section shapes, and sized to a width that eliminates interference between conductors passing in the end turn region, wherein the end turns are disposed inbetween straight portions in an alternating pattern. The wave-shaped conductor segment is inserted in a radially-outwardly direction starting from the central bore through the slot openings and into the slots, and then the tooth tips are cold-formed on the radially-innermost ends of the stator teeth. The features of the invention allow the wave-shaped conductor segment to be inserted radially through an increased-size slot opening compared to the slot openings found in conventional arrangements. The segment ends of adjacent wave-shaped conductor segements can then be connected to form a single continuous stator winding. The use of wave-shaped conductor segments having different cross-sections in the winding ends, straight portions, and end turn regions allows for reduced electrical connections, complexity and cost as compared to the conventional methods discussed above, and because these windings can be radially inserted, this invention allows for higher slot fill as well as increased generator output and efficiency afforded by the post winding cold forming process. The change in cross-section in the end turn region allows for the minimization of coil heights because of the thickness of the conductor is designed to eliminate interference between conductors in the region. This allows for a stator with a lower coil resistance, and thereby also reduces the cost of the product due to the elimination of unnecessary copper in the end turn region. The closed-up slot opening, which is now reduced in width (akin to a conventional slot opening), provides an improved magnetic flux path and performance (particularly at low speed), and further provides a wire retention function.
It should be noted that when forming the cross-section of the end turn regions, the change in cross-section may be so dramatic that the magnetic wire insulation typically on the round conductor will be overly stressed and damaged due to the significant increase in the perimeter of the new cross-section. Accordingly, in alternate embodiments, in the extreme case where the insulation will not survive the forming process, uninsulated copper wire will be used. This will be cheaper to purchase, and the savings will need to be used to post insulate the formed wave prior to inserting it into the stator core. Another option would be to place an open meshed sleeving over the entire wave-shaped segment, and then insert it into the stator. In this embodiment, no slot liner would be required. Rather, the mesh sleeve would provide a space factor between all of the conductor inserted into the stator. Next, an electrically insulating material such as a varnish or potting compound would be placed over the windings in the core, providing the necessary dielectric strength to isolate the conductors. If the insulation can survive the wave forming process, it may be desirable to place a “bondable” top coat on the conductor so that after insertion, the bondable coating can be heat activated to bond and lock the segments together as required for AC electric machines.
