Abstract:
A motor includes a protector electrically connected to the windings and positioned on the coil. A rigid bracket is sized and shaped to receive the protector. A fastening system extends over the coil, bracket and the protector and compresses the bracket against the coil. The bracket inhibits transmission of the compressive force of the fastening system to the protector and thereby shields the protector from damaging force. In another configuration, a sleeve receives the protector, and the fastening system extends only over the sleeve rather than over the protector.

Description:
[0001]     This invention relates to a motor having a thermal and/or current sensing protector for protecting the motor from damage, and more particularly to apparatus for attaching such a protector on the windings of the motor.  
       BACKGROUND OF THE INVENTION  
       [0002]     An electric motor often includes a protector capable of shutting down the motor before it is damaged due to an abnormality such as excessive heat. A typical protector is electrically connected to the winding and is adapted to break the current through the winding when the protector senses excessive temperature and/or current in the winding.  
         [0003]     Protectors may be “on-winding” protectors, which are mounted directly on the windings, or “off-winding” protectors, which are mounted in a position remote from the windings. It is often beneficial to use on-winding protectors so that the thermal sensor is more responsive to changes in temperature in the windings. By measuring the temperature at the windings, e.g., without a significant gap between the windings and the sensor, the protector can respond more quickly to break current when the windings overheat.  
         [0004]     A major disadvantage of many on-winding protectors is simply the added cost. For example, the on-winding protectors are more expensive because they must be more robust to withstand the stress of being mounted on the windings. On-winding protectors are typically formed with housings that are rigid enough to allow the protector to be “strapped” to the windings, e.g., the protector is fastened to the windings by lacing or straps. The robust housing of the on-winding protector is designed to prevent the lacing from bending or otherwise damaging the sensor or sensors inside the housing. In contrast, off-winding protectors are not as robust, and can therefore be made significantly cheaper than on-winding protectors.  
         [0005]     Accordingly, it is known in the prior art to mount on-winding protectors directly on the windings using lacing or straps over the protector. It is also known to alter the pattern of lacing or straps (referred to in the lacing art as “controlling the dwell of the lacing”) so that they do not extend directly over the on-winding protector. However, the prior art solutions fail to create an economical apparatus for mounting a cheaper, off-winding protector directly on the windings.  
       SUMMARY OF THE INVENTION  
       [0006]     In one aspect, a motor comprises a stator including slots and windings extending through the slots on the stator. The windings include end turns that extend from the slots and form a coil. A protector is electrically connected to the windings and is positioned on the coil. A rigid bracket is sized and shaped to receive the protector. A fastening system extends over the coil, bracket and the protector and compresses the bracket against the coil. The bracket inhibits transmission of the compressive force of the fastening system to the protector and thereby shields the protector from damaging force.  
         [0007]     In another aspect, the motor comprises windings that include wire extending from the slots on the stator. The fastening system extends over the coil so as to compress the coil. The protector is disposed in a gap in the fastening system so that the fastening system does not extend over the top of the protector. The protector includes a housing that is incapable of withstanding compression by the fastening system. A sleeve receives the protector, and at least a portion of the sleeve is disposed between the protector and the coil. The sleeve has sufficient length so that the fastening system extends over the sleeve but not over the protector to thereby inhibit transmission of the compressive force of the system to the protector. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a perspective of a portion of a motor of one embodiment.  
         [0009]      FIG. 2  is a perspective of a bracket and protector used with the motor of  FIG. 1 .  
         [0010]      FIG. 3  is an exploded view of the bracket and protector.  
         [0011]      FIGS. 4 and 5  section views taken along lines  4 - 4  and  5 - 5 , respectively, in  FIG. 2 .  
         [0012]      FIG. 6  is an end view of the bracket.  
         [0013]      FIG. 7  is a perspective of a portion of a motor of another embodiment.  
         [0014]      FIG. 8  is a perspective of only the protector and a sleeve around the protector. 
     
    
       [0015]     Corresponding reference characters indicate corresponding parts throughout the drawings.  
       DETAILED DESCRIPTION  
       [0016]     Referring to  FIG. 1 , a motor of one embodiment of the invention is generally designated  11 . The motor generally includes a stator  13  including slots  15 , and windings  17  comprising wire  19  extending through the slots. The windings  17  include end turns  21  extending from the slots  15 . The end turns  21  form a coil  23  on each side of the stator  13 . Each coil  23  has a top or axial end  25  and a radially facing side  27 . It is understood that orientation terms such as “top” and the like used herein refer only to the orientation as depicted in the drawings and are not meant to be limiting in any way. A fastening system  29 , which may include lacing, cable ties, straps, or any combination thereof, is used to hold the coil together. The fastening system  29  of this embodiment includes lacing extending over each coil  23  and between the winding wire  19  extending from the slots  15 . For clarity, the rotor and housing are omitted; many different types of rotors and housings are suitable for use with this invention. More generally, it should be understood that a variety of motor configurations can be used within the scope of this invention.  
         [0017]     Referring now to  FIGS. 1-6 , the motor includes a protector  31  ( FIG. 3 ) mounted on the windings  17 . As shown, the protector  31  is mounted on the top, or the axial end  25 , of one of the coils  23  but may be mounted elsewhere on the coil or windings. In one embodiment, the protector  31  is of the type that senses both current and temperature and is adapted to cut power to the motor  11  in response to excessive heat or a current abnormality. However, it is contemplated that the protector  31  only senses either temperature or current. As shown in  FIG. 3 , an insulating sleeve  33  is disposed around the protector  31  for electrical insulation. The sleeve of this embodiment is made of a material, e.g., mylar, that minimizes any thermal insulation so that the protector can better sense heat from the coil.  
         [0018]     The protector  31  is, in general, not capable of withstanding the compressive force of the fastening system  29 . Such protectors are sometimes referred to as “off-winding protectors” and are generally not designed by the manufacture for mounting on the windings. Examples of such protectors include those designated “3MP” and sold by Texas Instruments, though there are many other protectors contemplated for use with this invention. A housing  35  of the protector  31  is not rigid enough to prevent damage to the sensor(s) under the compressive force of the fastening system  29 .  
         [0019]     In one embodiment, the protector  31  is mounted within a rigid bracket  37  on the coil  23  of the windings  17 . Generally, the bracket  37  is sized and shaped to retain the protector  31  therein and to shield the protector from damage. As best shown in  FIG. 4 , the bracket  37  of this embodiment includes an elongate rib  39  that extends over the protector  31 . The rib  39  includes a downwardly projecting detent  41  adapted to hold the protector  31  against the coil  23 . The detent  41  applies a sufficiently light force to hold the protector  31  against the coil  23 , while preventing damage to the sensors inside the protector.  
         [0020]     Sidewalls  43  extend downward from both sides of the rib  39  in this embodiment, and lower edges  45  of the sidewalls contact the coil  23 . The sidewalls  43  include retention features, and to avoid thermally shielding the protector  31  from the heat of the coil  23 , the features do not extend a significant distance under the protector. As best shown in  FIGS. 5 and 6 , the retention features include shoulders  47  projecting from the sidewalls  43 , the shoulders tapering inwardly to correspond to the tapered shape of the protector  31 . The retention features also include inwardly extending tabs  49  disposed at one end of the bracket  37 . The tabs  49  extend from the lower edges  45  at the one end, but additional tabs or similar features may extend from other portions of the bracket  37 . A socket  51  ( FIGS. 2 and 3 ) is formed at the opposite end of the bracket  37  for receiving one of two lead wires  53  that extend from the protector  31 . In this embodiment, there is no socket for the other lead wire in case such wire has a large terminal at its end.  
         [0021]     As can be seen from the above discussion, the bracket  37  inhibits transmission of the compressive force of the fastening system  29  to the protector  31 . The bracket  37  thereby shields the protector  31  so as to prevent damage due to mechanical stress on the protector.  
         [0022]     Referring now to  FIGS. 7-8 , a protector  131  of a second embodiment is like the protector  31  described above in that it is not built to be placed on the windings, but in this embodiment it is not enclosed in a bracket. Rather, the protector  131  is disposed in a gap in the fastening system  129  (e.g., the lacing shown in this embodiment) so that the lacing does not extend over the top of the protector. Note that the length of the gap or “dwell” is designed into the lacing pattern and may vary with the size of the protector and sleeve. A modified sleeve  133  is received over the protector  131 . The sleeve  133  has sufficient length so that the lacing or other fastener extends over the ends of the sleeve but not over the protector  131 , or over terminals extending therefrom. The sleeve  133  thereby inhibits transmission of the compressive force of the fastening system  129  to the protector  131 . A standard insulator sleeve provided with the off-the-shelf protector is not of suitable length. Accordingly, the modified sleeve  133  of this embodiment has an extended length so that the lacing can be wound over the ends of the sleeve. As one example, the sleeve may be at least 20% larger than the standard sleeve. In another example, a mylar sleeve provided by a manufacturer for a protector was 37.5 mm, and the modified sleeve was 48 mm or 28% longer than the standard. In this way, the protector  131  is retained on the windings  17  by the fastening system without lacing over the protector itself, or over the terminals extending from the protector.  
         [0023]     As can be seen, the fastening system  129  extends between the wire extending from the slots  15  and thus between the slots of the stator. The slots  15  of this embodiment are evenly spaced apart a predetermined length, and the protector is generally disposed above the slots. The sleeve of the protector may extend a distance equivalent to at least one-half the length between slots, or at least one-half to 4 slot lengths, or even 1 to 3 slot lengths beyond each end of the protector so that the lacing can be disposed over each end of the sleeve.  
         [0024]     The embodiments of the invention described above reduce the cost of the motor without sacrificing performance. These embodiments enable one to use a less expensive, non-robust protector directly on the windings. The prior art has been significantly limited because such protectors have only been applied to areas remote from the windings, e.g., on the endshield. Indeed, vendors have taught against using these protectors directly on the windings. Thus, the invention is surprisingly effective and significantly reduces the overall cost of the motor.  
         [0025]     When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.  
         [0026]     As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.