Abstract:
A novel explosion-proof motor, which includes an integrated explosion-proof housing. In some embodiments, the integrated explosion-proof housing contains various electronic components that support the operation of the explosion-proof motor. To this end, embodiments of the explosion-proof motor may include a stator having an end ring, a plurality of stator coils extending from a core, and an end bracket fitted to the stator end ring to form a generally circumferential flame path. The end bracket may include an inner volume on one side thereof for receiving the stator coils, and an integrated explosion-proof housing on the other side. To reduce the number of explosion-proof seals, the inner volume and integrated explosion-proof housing may share the circumferential flame path to enclose their respective volumes.

Description:
BACKGROUND  
       [0001]     The invention relates generally to electric motors. More specifically, the invention relates to a housing for an explosion-proof electric motor.  
         [0002]     Often, electric motors operate in an explosive environment. For example, electric motors power machinery in and near coal mines, where coal dust and methane are often concentrated. Similarly, electric motors operate in explosive environments in grain silos with explosive grain dust and in chemical plants processing volatile chemicals.  
         [0003]     Typically, industrial standard “explosion-proof” motors are employed in such explosive environments. Generally, an explosion-proof motor includes a housing constructed to withstand a discharge or ignition within the housing and, should such an event occur, prevents the ignition of materials surrounding the housing. The explosion-proof motor housing often includes sealed joints that serve two functions. First, the sealed joints may prevent hot exhaust gas or flame produced by the internal ignition from escaping the housing. Second, the sealed joints channel those hot gases or flame that do escape over a distance to lower the temperature of the gas or flame before it reaches the surrounding environment. By cooling and containing hot gases within the motor, the housing may prevent an internal spark or ignition from spreading to the surrounding environment.  
         [0004]     While various electronic and electrical components are increasingly added to other motors, it is unfortunately expensive and complicated to add electronic components to explosion-proof motors. Generally, a separate explosion-proof housing contains electronic components added to such motors. The separate explosion-proof housing reduces the risk of one of the electronic components igniting surrounding combustible materials. However, a separate explosion-proof housing consumes scarce space near the electric motor, and the sealed joints associated with such explosion-proof housings often include tight tolerances that may be expensive to manufacture.  
         [0005]     Accordingly, there is a need for an explosion-proof motor that accommodates supporting electronic components within an integrated explosion-proof housing.  
       BRIEF DESCRIPTION  
       [0006]     The present invention provides, in certain embodiments, a novel explosion-proof motor. The explosion-proof motor may include an integrated explosion-proof housing. In some embodiments, the integrated explosion-proof housing contains various electronic components that support the operation of the explosion-proof motor. To this end, embodiments of the explosion-proof motor may include a stator having an end ring, a plurality of stator coils extending from a core, and an end bracket fitted to the stator end ring to form a generally circumferential flame path. The end bracket may include an inner volume on one side thereof for receiving the stator coils, and an integrated explosion-proof housing on the other side. To reduce the number of explosion-proof seals, the inner volume and integrated explosion-proof housing may share the circumferential flame path to enclose their respective volumes. 
     
    
     DRAWINGS  
       [0007]     These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:  
         [0008]      FIG. 1  is a side profile view of an exemplary explosion-proof motor in accordance with embodiments of the present techniques;  
         [0009]      FIG. 2  is a cross-sectioned side view of the explosion-proof motor of  FIG. 1 ;  
         [0010]      FIG. 3  is a cross-sectioned side view of an end bracket for the explosion-proof motor of  FIGS. 1 and 2 ;  
         [0011]      FIG. 4  is an enlarged view of a portion of the cross-section of  FIG. 2 , illustrating a flame path in accordance with embodiments of the present techniques;  
         [0012]      FIG. 5  is a front perspective view of an end bracket of the type shown in  FIG. 2 ; and  
         [0013]      FIG. 6  is a rear perspective view of an end bracket of the type shown in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0014]     The following discussion describes an explosion-proof motor that, in certain embodiments, includes various electronic components and electrical connections within a single integrated explosion-proof housing. Advantageously, as is described in greater detail below, certain embodiments house a motor, electronic component, and various electrical connections within a relatively compact volume. Moreover, certain embodiments include two volumes within a single integrated housing: one volume housing a motor and the other volume housing electronic components and electrical connections.  
         [0015]      FIG. 1  illustrates an exemplary explosion-proof motor  10  that is manufactured in accordance with embodiments of the present techniques. As is described in greater detail below, the explosion-proof motor  10  includes a front end bracket  12  that integrally houses both a portion of the motor  10  and various electronic components. The illustrated explosion-proof motor  10  includes an alternating current induction motor. However, in other embodiments within the scope of the present technique, the explosion-proof motor  10  may include a direct current motor, a brushless direct current motor, a servo motor, a brushless direct current servo motor, a brushless alternating current servo motor, a stepper motor, or a linear motor, for example.  
         [0016]     The illustrated explosion-proof motor  10  includes the front end bracket  12 , a stator  14 , a rotor and shaft assembly  16 , and a flame path  18 . The illustrated front end bracket  12  encloses one end of the stator  14  and rotationally supports the shaft  16 . When energized, the stator  14  cooperates with the rotor  16  to convert electrical energy into mechanical energy. The junction of the front end bracket  12  and the stator  14  forms the flame path  18 , which is described in greater detail below.  
         [0017]     As used herein, the term “flame path” refers to a joint between two components of a motor housing that satisfy certain standards pertaining to explosion-proof motors. For example, the joint may satisfy the requirements promulgated by the Underwriters Laboratories for class I explosion-proof motors or class II explosion-proof motors. In other words, the term “flame path” refers to a junction between two components in a motor housing that is sufficiently tight and sufficiently long that an ignition event within the motor housing is unlikely to propagate to the surrounding environment.  
         [0018]     The exemplary front end bracket  12  includes various features that support the operation of the explosion-proof motor  10 . For example, the present front end bracket  12  partially encloses an outer volume  20  that contains an encoder  22 . Alternatively, or additionally, the outer volume  20  or other portions of the front end bracket  12  may contain a drive, a contactor, a terminal board, a control device, and/or a brake, for example. A cover  24  coupled to the front end bracket  12  encloses the outer volume  20 . Cover fasteners  26  secure the cover  24  to the front end bracket  12 . The illustrated cover fasteners  26  include bolts fitted into threaded apertures, but other embodiments in accordance with the present techniques may include other types of fasteners  26 , such as a welded joint, rivets, or snap rings, for example. The illustrated front end bracket  12  also includes a cable outlet  28 . Various leads or cables that support the operation of the motor may pass through the cable outlet  28 , for instance power leads and communication cables. Front supports  30  extending from the front end bracket  12  may secure the explosion-proof motor  10  to a larger chassis or piece of equipment. The illustrated front end bracket  12  couples to the stator  14  through an array of bracket fasteners  32 . The illustrated bracket fasteners  32  include circumferentially disposed bolts fitted within threaded apertures. However, in other embodiments, other forms of fasteners, such as those listed above, may be employed.  
         [0019]     The exemplary stator  14  features a front end ring  34 , an eye bolt  36 , a core  38 , a back end ring  40 , and an eye bolt  42 . As is described in greater detail below, the front end ring  34  and the back end ring  40  may cooperate to compress the core  38 . Eye bolts  36  and  42  couple to the front end ring  34  and the back end ring  40  respectively and may facilitate movement of the explosion-proof motor  10 . The illustrated front end ring  34  affixes to the front end bracket  12 , and the junction between these two components  12  and  34  forms the flame path  18 .  
         [0020]     A back end bracket  44  encloses one end of the stator  14  and supports various functions of the explosion-proof motor  10 . The back end bracket  44  couples to the back end ring  40 . Back supports  46  extending from the bottom of the back end bracket  44  may cooperate with the front supports  30  to secure the explosion-proof motor  10  to a machine frame. The back end bracket  44  and the front end bracket  12  enclose opposing ends of the stator  14  and rotatably support the rotor and shaft assembly  16 .  
         [0021]     The illustrated rotor and shaft assembly  16  rotates within the stator  14  and transfers mechanical energy out of the explosion-proof motor  10 . To this end, the assembly shaft includes a keyway  48  to secure the shaft to other rotating members. Of course, other techniques to secure the shaft  16  to rotating members may be employed in accordance with the present techniques, such as a spline, a force fit bushing or a direct drive, for example.  
         [0022]      FIG. 2  illustrates the interior of the explosion-proof motor  10  in a cross-sectional view. Returning to the front end bracket  12 , an interior wall  50  separates the outer volume  20  from an inner volume  52 . As is described in greater detail below, the inner volume  52  partially houses various moving parts within the explosion-proof motor  10 .  
         [0023]     In addition to the encoder  22 , the outer volume  20  houses several components that deliver power to the explosion-proof motor  10 . Stator leads  54  pass from the inner volume  52 , through the interior wall  50 , and into the outer volume  20 . The stator leads  54  conduct electrical power to various subsequently discussed windings within the explosion-proof motor  10 . For example, the stator leads  54  may deliver three-phase alternating current power. The illustrated stator leads  54  pass through an inner wall aperture  58  in the interior wall  50 . Thus, the inner volume  52  is in communication with the outer volume  20  through the inner wall aperture  58 . In the illustrated embodiment, power leads  56  conduct electricity from a power source  57  into the outer volume  20  by connection to the stator leads  54  in the outer volume  20 . Advantageously, the stator leads  54  connect to the power leads  56  within the front end bracket  12 , thereby avoiding the need for a separate explosion-proof housing to contain these connections. However, in other embodiments, the power leads  56  may connect to the stator leads  54  elsewhere within the explosion-proof motor  10 , such as within the inner volume  52 , or outside the explosion-proof motor  10 . In the present embodiment, a packing gland  60  seals the cable outlet  28  while permitting the power leads  56  to exit the front end bracket  12 . The illustrated cover  24  includes an alternate cable outlet  64  that may be sealed when not in use.  
         [0024]     Additionally, the front end bracket  12  includes an encoder support  62  on the interior wall  50 . The illustrated encoder support  62  resides on the side of the interior wall  50  adjacent the outer volume  20 , but, in other embodiments in accordance with the present techniques, the encoder support  62  may be disposed elsewhere within the outer volume  20 , in the inner volume  52 , or external to the explosion-proof motor  10 , for example.  
         [0025]     The exemplary interior wall  50  includes a bearing support  66  on the side of the interior wall  50  adjacent the inner volume  52 . The illustrated bearing support  66  supports bearing  68 , which, in turn, rotatably supports the rotor and shaft assembly  16 . Of course, in other embodiments, the bearing support  66  may be disposed on the opposing side of the interior wall  50  or the cover  24 , for example.  
         [0026]     The illustrated stator  14  features a stator coil  70  with a front head  72  and a rear head  74 . The stator coil  70  includes a plurality of windings in any suitable winding pattern, defining poles and groups in a manner generally known in the art. When these windings conduct an electric current, they generate an electromagnetic field that drives the rotation of the shaft  16 . The front head  72  of the illustrated stator coil  70  reaches into the inner volume  52  of the front end bracket  12 , and the rear head  74  reaches into a volume enclosed by the back end bracket  44 .  
         [0027]     In the present embodiment, the core  38  is pre-compressed by tensile members. A number of rod apertures  76  in the core  38 , and a number of weld access apertures  78  in the front end ring  34  and the back end ring  40  house the tensile members that tie the stator  14  together. The rod apertures  76  extend through the core  38 , from the front end ring  34  to the back end ring  40 . The rod apertures  76  align with the weld access apertures  78 , so that a tensile member threaded through the rod apertures  76  extends into the weld access apertures  78 . To tie the stator  14  together, tensile members are welded to the front end ring  34  and to the back end ring  40  within the weld apertures  78 . However, before the tensile members are welded, the core  38  is externally pre-compressed, thereby placing the tensile members in tension and leaving the core  38  compressed when the external pressure is removed. It should be noted that other techniques may be used for maintaining the stator or frame elements as a tight unit, such as threaded tie rods, external welds, and so forth.  
         [0028]     The stator  14  encircles a generally cylindrical interior volume  79  that holds a rotor  80 . The rotor  80  may include permanent magnets or electromagnets that cooperate with electromagnetic fields generated by the stator coil  70  to rotate the shaft  16 . A bearing  82  supported by the back end bracket  44  cooperates with the bearing  68  to rotatably support the rotor and shaft assembly  16 .  
         [0029]      FIG. 3  illustrates additional features of the front end bracket  12  with a cross-sectional view. The present front end bracket  12  includes ribs  84  and an end bracket extension  86 . The ribs  84 , which stabilize the bearing support  66 , are circumferentially disposed about the bearing support  66 . The illustrated end bracket extension  86  is an annular member extending from the front end bracket  12  around the interior volume  52 .  
         [0030]     The end bracket extension  86  may include a several surfaces that interface with the front end ring  34  to form flame path  18 . For instance, the illustrated end bracket extension  86  includes a forward surface  88 , an outer diameter surface  90 , and a rear surface  92 . In the current embodiment, the forward surface  88  and rear surface  92  generally fall within parallel planes. The illustrated outer diameter surface  90  extends orthogonally between these planes. In other words, the intersection of the outer diameter surface  90  with the forward surface  88  and the rear surface  92  generally forms right angles. The outer diameter surface  90  extends through a tubular width  94  between the front surface  88  and the rear surface  92 , and the outer diameter surface  90  generally traces the perimeter of a circle with an outer diameter  96 . In certain embodiments, the tubular width  94  may range from 1.24 to 1.26 inches, 1.23 to 1.27 inches, 1.22 to 1.28 inches, 1.21 to 1.29 inches, 1.20 to 1.30 inches, 1.15 to 1.35 inches, 1.10 to 1.40 inches, 1.05 to 1.45 inches, 1.00 to 1.50 inches, 0.50 to 2.00 inches, or 0.25 to 2.25 inches, for example. Similarly, in various embodiment, the outer diameter  96  may range from 14.00 to 16.00 inches and have a tolerance of less than 0.001 inches, 0.002 inches, 0.003 inches, 0.004 inches, 0.005 inches, 0.01 inches, 0.05 inches, or 0.10 inches, for instance.  
         [0031]     The exemplary front end bracket  12  includes a cap contact surface  98  with a cap contact width  100 . The present cap contact surface  98  contacts the cover  24  and seals the outer volume  20 . The cap contact width  100  may range, in various embodiments, from 1.37 to 1.39 inches, 1.36 to 1.40 inches, 1.35 to 1.41 inches, 1.34 to 1.42 inches, 1.33 to 1.43 inches, 1.00 to 2.00 inches, or 0.50 to 2.50 inches, for example. The illustrated cap contact surface  98  generally lies within a plane. However, in other embodiments, the cap contact surface  98  may be non-planar (e.g., curved or undulating).  
         [0032]      FIG. 4  depicts view of a flame path  18 , which, in the present embodiment, is the gap between the adjacent portions of the front end bracket  12  and the front end ring  34 . The exemplary front end ring  34  includes an inner diameter surface  106  that mates with the outer diameter surface  90  of the end bracket extension  86 . That is, the front end ring  34  forms a bushing around the end bracket extension  86 . The flame path  18  has a flame path width  108 , which is the distance between the inner diameter surface  106  of the front end ring  34  and the outer diameter surface  90  of the end bracket extension  86 . In certain embodiments, the flame path width  108  may range from 0.003-0.005 inches, 0.002-0.006 inches, 0.001-0.007 inches, 0.000-0.008 inches, or 0.000-0.050 inches, for example. Alternatively, the front end bracket  12  and the front end ring  34  may be joined by an interference or a transition fit. The illustrated flame path  18  includes a tubular portion  110  and an annular portion  112 . The tubular portion  110  is generally orthogonal to the annular portion  112 . As will be appreciated, other embodiments in accordance with the present technique may include a flame path  18  without an annular portion  112 , a tubular portion  110 , or both. Additionally, some embodiments may include multiple concentric tubular portions  110  and/or multiple annular portions  112 . Advantageously, in the event of an internal discharge, hot exhaust gases or flames escaping from the explosion-proof motor  10  change direction when passing from the annular portion  112  to the tubular portion  110 , thereby potentially further cooling the hot gases or flames.  
         [0033]     Also illustrated by  FIG. 4 , the front end ring  34  includes an annular notch  102  that houses a seal  104 . The notch  102  and seal  104  cooperate with the flame path  18  to contain and cool hot gases or flames resulting from a discharge within the explosion-proof motor  10 . Of course, other embodiments in accordance with the present techniques may employ multiple seals  104  or no seals  104 .  
         [0034]     A plurality of stacked laminations  114  form the core  38 . These laminations  114  may include various features to prevent hot gases or flames from escaping between the laminations  114 , such as a cold worked or peened finish. In general, a flame path is also defined between each pair of adjacent laminations  114 . However, these flame paths are longer than flame path  16  described above, making the latter the favored path for the escape of gases or flames in the event of a discharge within the motor.  
         [0035]      FIGS. 5 and 6  respectively illustrate front and rear perspective views of a front end bracket  12  in accordance with embodiments of the present techniques. The illustrated front end bracket  12  includes two cable outlets  28  and two inner wall apertures  58 .  FIG. 5  illustrates an open side  116  of the front end bracket  12 . In operation, the cover  24  seals the open side  116  of the front end bracket  12 . Advantageously, the cover  24  may be removed and connections or components within the outer volume  20  may be easily accessed.  
         [0036]     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.