Abstract:
Electric machine end turn connectors are used with an electromagnetic device having a ferromagnetic core with a plurality of core slots. Coils are held within the plurality of core slots. The coils are comprised of a plurality of pins positioned within the plurality of core slots. Each of the plurality of pins includes a main body and two tapered ends. When one of the pins is positioned in one of the core slots, the main body of the pin is held within the core slot and the tapered ends of the pin protrude from the stator slot. The plurality of pins form the working lengths of the coils. Two end caps are positioned upon the ferromagnetic core. Each end cap includes a plurality of jumpers. Each jumper includes a bridge portion and two perpendicular connection channels. Each connection channel includes a slit which runs along the connection channel and terminates in a mouth. A heat shrink material surrounds the connection channels. The two end caps are positioned on opposite sides of the ferromagnetic core such that the tapered ends of the pins protruding from the core slots are received by the connection channels of the plurality of jumpers. The connected pins and jumpers form completed coils. To secure the connection between the pins and jumpers, heat is applied to the heat shrink material surrounding the connection channels, thereby causing the connection channels to tightly grasp the pins.

Description:
BACKGROUND  
       1. FIELD OF THE INVENTION  
         [0001]    The present invention relates to a stator coil for an electric motor, and more specifically, it relates to a stator coil which reduces the protrusion of coil windings from the stator in the direction of a center axis of the electric motor.  
         2. BACKGROUND OF THE INVENTION  
         [0002]    [0002]FIGS. 1A and 1B show a structure of a prior art stator coil for a conventional electric motor. The electric motor is a three phase electric motor which includes a stator  102  having a plurality of slots  104  and a rotor  106  which confronts the stator. In FIGS. 1A and 1B the stator  102  is depicted as a straight line, but in fact, the stator is cylindrical with the stator slots  104  opening toward the center rotor  106 . FIG. 1A is a top plan view of the stator coil, and FIG. 1B is a side elevational view of the stator coil as seen from the rotor. Although not shown in FIG. 1A because of the linear depiction of the stator and rotor, the rotor is completely surrounded by the stator slots  104 . Windings, also referred to as coils, are wound through the stator slots  104  to create respective phases of the coils. The coils include three coil phases, including coil  108 A carrying phase A, coil  108 B carrying phase B, and coil  108 C carrying phase C. Each of the coils  108 A,  108 B, and  108 C is comprised of a bundle of copper wires. The portion of coil actually within a stator slot is called the “working portion”  110  of the coil, while the portion of coil leading from one slot to the next is called the “crossover portion” or an “end turn”  112  of the coil. The end turns of a coil are not useful to the electric motor, other than to provide electrical connections between the working portions of a coil. In fact, the end turns generate much additional heat for the electric motor, and thus it is desirable to limit the size of the end turns. Furthermore, because the end turns take up valuable space within the electric motor, it is desirable to reduce the size of the end turns to provide for an electric motor of reduced size.  
           [0003]    As shown in FIG. 1B, when the coils are wound through the stator slots, the end turns protrude above the surface of the stator. This end turn protrusion occurs because the bundle of copper wires within the coil is relatively rigid and can not be wound with extremely sharp, near right-angle, turns in the crossover portion. Instead, the end turns flow smoothly with wide loops from one stator slot to the next. These looping turns result in a great deal of wasted end turn height above and below the stator slots. The large size of the end turns cause additional heat to be generated by the electric motor. In addition, the extra space required to house the large end turns make it difficult to reduce the size of the electric motor.  
           [0004]    Size considerations are a great concern in many modern electric motor applications. For example, modern automobile engine compartments have become increasingly cramped. Large electric motors used as starter motors in the engine compartment only add to the cramped condition. Thus, it would be advantageous for starter motors to be reduced in size to provide for more space in modern electric motor applications.  
           [0005]    In addition to the above, conventional stator coils must be wound into the slots of the stator. This process involves complicated and expensive robotic machinery that must thread the wires on the slots of the stator to create the stator coils. Alternatively, individuals on an assembly line must hand wind wires through the stator slots to create the coils. Regardless of the method used, the process of placing coils on the stator windings is a significant cost contributor during construction of the electric motor. Thus, it would be advantageous to provide an electric motor with coils that may be easily placed within the stator slots during production of the electric motor.  
           [0006]    For the foregoing reasons there is a need for an electric motor which includes stator coils with reduced profile end turns, thereby reducing the heat generated by the electric motor, and allowing the electric motor to be reduced in size. There is also a need for an electric motor with stator coils that may be easily positioned within the stator slots for ease of manufacture.  
         SUMMARY  
         [0007]    The present invention is directed to an electromagnetic device having a novel set of windings that satisfies the need for an electric motor with reduced profile end turns which may be easily manufactured. The windings of the present invention have sharp end turns which take up less space than prior art stator windings with large looping end turns. Furthermore, the windings are easily incorporated in the stator slots and allow the stator core to be produced at a significantly reduced cost.  
           [0008]    The electromagnetic device comprises a rotor and an opposing stator having a plurality of stator slots facing the rotor. Stator coils are held within the plurality of stator slots. The stator coils are comprised of a plurality of pins positioned within the plurality of stator slots. Each of the plurality of pins includes a main body and two tapered ends. When one of the pins is positioned in one of the stator slots, the main body of the pin is held within the stator slot and the tapered ends of the pin protrude from the stator slot. The plurality of pins form the working lengths of the stator coils.  
           [0009]    Two end caps are positioned upon the stator. Each end cap includes a plurality of jumpers and each jumper includes a bridge portion with two perpendicular connection channels. Each connection channel includes a slit which runs along the connection channel and terminates in a mouth. A heat shrink material surrounds the connection channels. The two end caps are positioned on opposite sides of the stator such that the tapered ends of the pins protruding from the stator slots are received by the connection channels of the plurality of jumpers, and the connected pins and jumpers form completed coils. To secure the connection between the pins and jumpers, heat is applied to the heat shrink material surrounding the connection channels. When heat is applied to the heat shrink material, and inward force is placed upon the connection channels. The slit extending along each connection channel allows the diameter of the connection channel to decrease as the inward pressure is applied. As the diameter of the connection channels decrease, each connection channel is secured to the tapered end of the pin inserted into the connection channel.  
           [0010]    Thus, the jumpers of the present invention provide for reduced profile end turns. Furthermore, the coil structure is easily assembled upon the stator core by inserting pins into the slots and connecting the pins with jumpers. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1A shows a top plan view of a prior art stator coil for a conventional electric motor;  
         [0012]    [0012]FIG. 1B shows a side elevational view of the prior art stator coil of FIG. 1;  
         [0013]    [0013]FIG. 2A shows a side view of pin for use as a working length in the coil of the present invention;  
         [0014]    [0014]FIG. 2B shows another side view of the pin of FIG. 2A;  
         [0015]    [0015]FIG. 3A shows a top plan view of a stator with the pins of FIG. 2A inserted into the stator slots;  
         [0016]    [0016]FIG. 3B shows a side elevational view of the stator of FIG. 3A;  
         [0017]    [0017]FIG. 4A shows a perspective view of a jumper for use as an end turn of the coil of the present invention;  
         [0018]    [0018]FIG. 4B shows a perspective view of a jumper having side extensions;  
         [0019]    [0019]FIG. 5 shows a top plan view of an end cap for use with the stator of FIG. 3A;  
         [0020]    [0020]FIG. 6 shows a side elevational view of the stator of FIG. 3A connected to the end cap of FIG. 5;  
         [0021]    [0021]FIG. 7 shows a cross-sectional view of a connection between the pin of FIG. 2A and the jumper of FIG. 4;  
         [0022]    [0022]FIGS. 8A and 8B show an alternative embodiment of pins for use with the coil of the present invention;  
         [0023]    [0023]FIG. 9A shows a plan view of an exemplary arrangement of jumpers within the end cap;  
         [0024]    [0024]FIG. 9B shows a side view of the exemplary arrangement of jumpers of FIG. 9A along lines B-B;  
         [0025]    [0025]FIG. 9C shows a side cross-sectional view of the exemplary arrangement of jumpers of FIG. 9A along lines C-C.  
     
    
     DESCRIPTION  
       [0026]    With reference to FIGS.  2 - 4 , the present invention comprises, a ferromagnetic core structure in the form of a stator  20  having a number of slots  22  which hold pins  12 . The pins are joined together by jumpers  30 . Together, the pins and jumpers form stator coils which provide for electric current flow. The pins  12  are used as the working lengths of the stator coils while the jumpers  30  are used as the coil end turns. The jumpers include ninety (90) degree turns which allow the pins to be connected while minimizing the space required for the end turns.  
         [0027]    As shown in FIGS. 2A and 2B, each pin  12  is made of copper and comprises a main body  14  and tapered ends  16 . FIG. 2A shows a first side view of a pin  12 , while FIG. 2B shows a second side view with the pin  12  rotated ninety (90) degrees. The tapered ends  16  of the pins  12  may be rounded or rectangular in shape. In the embodiment shown herein, the tapered ends are rounded. The main body  14  of each pin is coated with an epoxy material which insulates the pin from other pins. The tapered ends  16  of each pin are bare un-coated copper. By exposing the copper on the tapered ends of the pin, conductive connections may be made between the pins  12  and the jumpers  30 . Because the pins  12  are all of similar shape they are easily mass produced. In addition, to assist in the assembly process, multiple pins are generally pre-fabricated into a molded piece designed to fit snugly into one of the stator slots  22 . A molded piece is made for each slot  22  of the stator  20 . The molded pieces are comprised of a plastic metal or plastic coated iron, and multiple pins  12  are situated in each molded piece. Once a molded piece is cured, the pins in the molded piece are fixed within the molded piece. Thus, multiple pins may easily be inserted into a stator slot and held in place by simply inserting the molded piece into the stator slot.  
         [0028]    The pins  12  are inserted lengthwise into the slots  22  of a stator  20 , so that the tapered ends  16  of the pins stick out of the slots  22 . FIG. 3A shows a top plan view of the stator  20  with the pins  12  positioned within the slots  22 . FIG. 3B shows a side elevational view of the stator, as seen from the rotor. In FIGS. 3A and 3B, and other figures herein, the stator  20  is depicted in a linear fashion for convenience of display, but in fact, the stator is cylindrical with the stator slots  104  opening toward a rotor which is concentric with the stator  12 , as is standard in the art. Thus, the rotor rotates about a center axis which is also the center axis of the stator. The pins  12  are positioned within the stator slots  22  parallel to this center axis. The stator includes a top face  24  and a bottom face  26 . As can be seen from FIG. 3B, the tapered ends of the pins extend from the stator slots  22  above the top face  24  and below the bottom face  26 , while the main bodies of the pins are contained within the slots  22 .  
         [0029]    Jumpers  30  are used to connect the tapered ends  16  of the pins  12  extending from the stator  20 . A perspective view of an exemplary jumper is shown in FIG. 4. The term end turns is used interchangeably herein to also reference the jumpers. Each jumpers  30  is comprised of copper and includes a bridge portion  32  and connection channels  34  extending perpendicularly from the ends of the bridge portion. Each connection channel  34  includes a mouth  36  for receiving a tapered end  16  of one of the pins  12 . In addition, each connection channel  34  includes a slit  44  which extends along the connection channel and down to the mouth  36 . When a tapered end of a first pin is placed in one mouth of a jumper and the tapered end of a second pin is placed in the other mouth of the jumper, an electrically conductive path is formed from the first pin, through the jumper, and into the second pin.  
         [0030]    The jumpers  30  are embedded in an end cap  40  made of a plastic or similar non-conductive material. FIG. 5 shows the jumpers  30  embedded in one of the end caps  40  with the connection channels  34  showing. The end cap  40  is shown in a linear fashion in FIG. 5, but the end cap  40  is actually cylindrical having a similar diameter to that of the stator. The bridge portions  32  and connection channels  34  of the jumpers are totally embedded in the end cap  40 , with only the mouths  36  of the connection channels  34  revealed on the surface of the end cap  40 . The mouths  36  emerge from the surface of the end cap  40  so the mouths may be joined with the tapered ends  16  of the pins  12 .  
         [0031]    [0031]FIG. 5 further shows the specific location of the mouths  36  of two different jumpers to provide an example of electric current flow through the end cap. A first jumper embedded in the end cap includes one mouth  38  and another mouth  39 . These two mouths  38  and  39  join to pins in the +A and −A phases of the stator slots to form a coil portion for the A phase coil. Similarly, a second jumper includes mouths  41  and  42  for connection to pins which form a coil portion of the C phase coil. Of course, the first jumper and second jumper which help form these coil portions can not interfere with each other, thus, each jumper must be formed to avoid contact with other jumpers. To this end, some jumpers will include longer connection channels than others to place the bridge portion of the jumper in a different plane than surrounding jumpers within the end cap. In addition, the jumpers may include side extensions  33 , as shown in FIG. 4B. The side extensions  33  may be used for some jumpers to allow the jumpers to avoid contact with surrounding jumpers.  
         [0032]    FIGS.  9 A- 9 C provide an exemplary jumper arrangement, as positioned within the end cap  40  of FIG. 5, for connecting the three coil phases  108 A,  108 B and  108 C. FIG. 9A is a top view of the exemplary jumper arrangement. From the top view of FIG. 9A, only some of the bridge portions  32  and side extensions  33  can be seen. Additional bridge portions and side extensions exist directly below the bridge portions and side extensions shown in FIG. 9A. Although the connection channels  34  can not be physically seen from this top view of FIG. 9A, the connection channels  34  extend perpendicular to the side extensions  33  and bridge portions  32 , and are indicated by the dotted circles in FIG. 9A.  
         [0033]    [0033]FIG. 9B is a side view of the exemplary jumper arrangement along lines B-B of FIG. 9A. From the view of FIG. 9B, the connection channels  34  can be seen. The connection channels are of several differing heights. This allows each jumper to avoid interference with other jumpers. Other connection channels exist behind those shown in FIG. 9B. In addition, bridge portions  34  which connect the connection channels can be seen extending behind the connection channels shown in FIG. 9B.  
         [0034]    [0034]FIG. 9C is a side view of the exemplary jumper arrangement along lines C-C of FIG. 9A. FIG. 9C shows a number of the connection channels  34  of the jumper arrangement along with their associated side extensions  33  and bridge portions  32  (the cross section of the bridge portions are shown in cross-hatching). Additional connection channels exist behind those shown in FIG. 9C. Again, the connection channels  34  are of several differing heights, and the side extensions  33  are of several differing lengths, and this allows the jumpers to avoid contact with each other.  
         [0035]    One advantage of the present invention is that the end turns may be arranged in any number of different ways to provide various winding configurations for a single stator. This is possible because the working lengths of the coils are place in the stator slots in a generic fashion and the end turns in the end caps actually connect the pins to each other in a specific winding arrangement. Thus, the pins in one slot may be connected to pins in any other slot to form the desired winding configuration. For example, the end turns  30  in the end cap  40  of FIG. 5 may be arranged to provide either a delta winding configuration or a wye winding configuration when jumpers are attached to the pins. On both delta and wye winding configurations, both concentrated and distributed configurations maybe used. In addition, the number of turns in any given winding may be decreased by shorting pins  16  together within the stator.  
         [0036]    Two end caps  40  with embedded jumpers  30  are provided for connecting the tapered ends of the pins on both the top and bottom sides of the stator  20 . This arrangement is shown by the profile view of FIG. 6 in which the end caps  40  sandwich the stator  20 . With all of the pins  12  properly positioned within the slots  22  of the stator  20 , the end caps  40  are simply positioned upon the top and bottom sides of the stator to complete the stator windings. When an end cap  40  is placed on the stator  20 , jumpers  30  within the end cap mate with the tapered ends  16  of the pins  12 , thereby providing complete electrical paths for the stator windings. The stator windings typically include three coils carrying different current phases, including phase A, phase B and phase C. The pins act as the working lengths of each coil and the jumpers act as the end turns, with the end turns of the coils positioned at right angles to the working lengths.  
         [0037]    The jumpers  30  within each end cap  40  are designed to physically connect to the pins  12  in more than one way when an end cap  40  is place on the stator  20 . In one embodiment, the mouths  36  of the jumpers  30  may be friction fit over the tapered ends  16  of the pins  12 . According to this embodiment, the mouths  36  of the pins  12  are slightly flared and the connection channels  34  are dimensioned slightly smaller than the tapered ends  16  of the pins  12 . Thus, when the tapered ends  16  of the pins  12  are forced into the connection channels  34 , the slits  44  allow the connection channels to slightly expand such that the connection channels fit snugly against the pins.  
         [0038]    Another embodiment for connecting the jumpers  30  to the pins  12  is shown with reference to FIG. 7, which shows a cross section of the tapered end  16  of a pin  12  inserted through the mouth  36  of a connection channel  34 . In this embodiment, each connection channel  34  is surrounded by a heat shrink material  46 . In order to position the heat shrink material  46  around the connection channel  34 , a cavity must be left open between the connection channel  34  and the end cap  40  when the end cap is molded. After the end cap is molded, the connection channels are in place, and the heat shrink material may be slid into the cavity around the connection channel  34 . With the heat shrink material  46  positioned around each connection channel  34  in the end cap, the end cap may be joined to the stator by inserting the tapered ends  16  of the pins  12  into the connection channels  34 . Heat is typically provided to the heat shrink material by placing the end cap in an oven. Application of heat to the heat shrink material  46  causes the heat shrink material to shrink and apply inward force to the connection channel  34 . As inward force is applied to the connection channel  34 , the slit  44  in the connection channel allows the connection channel to shrink in diameter and close around the tapered end  16  of the pin  12 , thus securing the jumper  30  to the pin  12 .  
         [0039]    To further assist in securing the jumpers to the pins, solder paste may be inserted through the mouths  36  and into the connection channels  34  before the pins  16  are inserted into the connection channels. When solder paste is used, placement of the end cap into the oven causes the solder paste to flow within the connection channel  34  and around the pin  16 . Then, when the end cap reaches a critical temperature sufficient to collapse the heat shrink material, the heat shrink material forces the connection channel to close around the pin and secure the connection channel against the pin. Once removed from the oven, the solder paste hardens and provides a solid bond between the connection channel and the pin.  
         [0040]    Another alternative embodiment of the invention involves the use of L-shaped pins. This embodiment is described with reference to FIGS. 8A and 8B. In this embodiment of the invention, each pin  12  includes a main body  14 , a tapered end  12 , and a foot  18  extending from the main body at a right angle. The main body  14  of the pin  12  and the foot  18  form an L shape structure. The tapered end of the pin is exposed copper while the main body  14  is coated with an insulating epoxy material along with most of the foot  18 . However, a tip  19  of the foot is exposed copper. When two L-shaped pins are joined at their copper tips  19  and welded together, a U-shaped conductor is formed. This U-shaped conductor may then be inserted into the stator with the main body  14  of each L-shaped pin in different stator slots  22 . With the U-shaped conductor inserted into the stator in this fashion, the two feet  18  of the L shaped pins act as a coil end turn along one side of the stator. Many U-shaped conductors may be formed and placed into the stator such that the coils are partially complete with end turns formed along the one side of the stator. An end cap having jumpers as described above may then be place on the other side of the stator to complete the stator coils.  
         [0041]    Accordingly, the pin and end cap structure of the present invention provides for reduced profile end turns. When the electric motor is used, electric current flows through one pin and into the jumper attached to the pin. The jumper conducts the current to another pin attached to the same jumper. With all jumpers and pins properly attached, coils are formed having reduced profile end turns. The reduced profile end turns minimize the heat generated by the electric motor and also allow the electric motor to be reduced in size. Furthermore, the pin and end cap structure of the present invention provides for easily assembled electric motor coils.  
         [0042]    Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, other alternative methods for connecting the end turns to the pins include welding or soldering the end turns to the pins. Furthermore, in another alternative embodiment of the invention, the jumpers may be used without an end cap. In this embodiment, the jumpers would be placed on the pins one at a time instead of collective placement of the jumpers on the pins with the end cap. Of course, many other alternative embodiments of the invention are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.