Abstract:
A cooled fan motor may include a tankhead, an elongate housing attached to the tankhead and, having at least one longitudinally extending groove, a shaft rotatably attached to the housing, a hub attached to the shaft, the hub having at least one opening therethrough and shaped to form a gap with the tankhead, a rotor attached to the hub, and a stator mounted on the housing such that the groove in the housing forms an air passage between the housing and the stator connecting the gap and the opening; whereby air external to the motor is able to enter through the gap, flow along the air passage and exit the motor through the opening in the hub, thereby cooling an interior of the motor.

Description:
BACKGROUND 
     This disclosure relates to electric motors and more particularly, to cooled electric motors for operation in environments having elevated temperatures. 
     Electric motors often must be placed in service in harsh environments. For example, electric motors, typically three-phase alternating current (AC) induction motors, may be used to drive exhaust or cooling fans for the diesel engine enclosures of diesel-electric locomotives. Electric cooling fans may be mounted on the roof of the diesel locomotive to draw ambient air through the radiator, where it absorbs heat from engine and power generation components and exhausts it upwardly. Such fans are thus mounted on the “hot side” of the cooling air that flows through the diesel engine enclosure, so that the exhaust fans typically operate in a stream of heated air from the radiator. 
     Operating such fan motors in a stream of heated air results in heat build-up within the fan motor enclosures themselves, causing temperatures within fan motor enclosures to reach as high as 190° C. Such elevated motor temperatures may cause the bearing lubricants to degrade rapidly, resulting in increased shear forces, changes in viscosity and elevated lubricant bleed and evaporative rates. Rapid lubricant degradation may cause failure of the rotor bearings after approximately 18-24 months of motor service time, significantly less than the desired motor service time of 72 months. 
     A desired operating range of motors in such applications is approximately 150° C.-160° C. before failure of the bearing lubricating grease. For every 10° C.-15° C. increase in bearing grease temperature, there is typically a reduction of one half-life of the bearings due to lubricant failure. 
     SUMMARY 
     The disclosure is directed to a cooled fan motor in which air external to the motor may enter the motor enclosure and flow in an area adjacent the motor bearings in order to cool the motor bearings and lubricant and thereby extend bearing life, which extends the operating life of the motor. In one aspect, a cooled fan motor may include a housing adapted to be attached to a support structure, such as a tankhead, a shaft rotatably attached to the housing, a hub attached to the shaft, a rotor attached to the hub and a stator mounted on the housing. The housing may have at least one longitudinally extending groove, and preferably a plurality of grooves formed in and spaced about an outer periphery of the housing. The stator may be mounted on the housing such that the grooves form air passages between the housing and stator. 
     The hub may be shaped to form an annular gap with the support structure and may include an opening therethrough, preferably a plurality of openings therethrough. The openings may be positioned on the hub at a location opposite the gap. In one aspect, the hub may include a plurality of radially extending fan blades. The cooled fan motor thus may include a cooling air path so that air external to the motor and hub may enter through the gap between the hub and support structure, flow along the grooves formed in the housing and exit the hub through the hub openings. In one aspect, the blades may be positioned on the hub so that the gap between the hub and support structure is downstream of the blades and the hub openings are located upstream of the blades. 
     When the stator is energized, the rotor and hub rotate, causing the blades to move air around the hub. This air movement may cause ambient air to enter the gap between the hub and support structure, flow along the grooves between the housing and stator, and exit the openings in the hub. Thus, cooling air may flow through the motor in a direction opposite that of external air flow. 
     In one aspect, the housing may include bearings that support the shaft. The bearings may be positioned adjacent the grooves so that cooling air flow may cool the bearings and bearing lubricant, thus prolonging the operating life of the bearings and motor. 
     Other objects and advantages of the disclosed cooled fan motor and method of operation will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation in section of the disclosed cooled fan motor, shown incorporated in an exhaust fan of a diesel-electric locomotive; 
         FIG. 2  is a perspective view of a bearing housing of the cooled fan motor of  FIG. 1 ; and 
         FIG. 3  is a detail side elevation in section of the fan motor of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , the cooled fan motor, generally designated  10 , is shown incorporated in an exhaust fan, generally designated  12  of a type that may be suitable for use as an exhaust fan of a diesel-electric locomotive. The motor  10  is shown schematically as a three-phase, asynchronous, alternating current (AC) motor. However, it is within the scope of this invention to employ this design with other types of electric motors. 
     The fan  12  may include a tankhead  14  having an annular outer support rim  16 , adapted to be mounted on the roof of a locomotive engine enclosure (not shown) or other support structure, a plurality of vanes  18  attached to and extending radially inwardly from the support rim  16 , and an inner annular wall  20  supported by the vanes  18 . The inner annular wall  20  may be enclosed on its upper surface by an end plate  22  and may be strengthened by ribs  24  welded to the end plate  22  and wall  20 . The ribs  24  may support an annular mounting boss  26  having a stepped recess  28  (see also  FIG. 3 ). Power cables (not shown) for energizing the motor  10  are connected to a source of three-phase power and may extend through tubular conduit (not shown) that is be attached to a selected one of the vanes  18  and passes through the annular wall  20  to be connected to the motor. 
     As shown in  FIGS. 1 and 3 , the motor  10  may include an annular bearing housing  30  having an upper end  31  shaped to fit within the stepped recess  28  and may be bolted to the mounting boss  26  by bolts (not shown). The bearing housing  30  may be generally cylindrical in shape, having an inner cylindrical surface  32 . The bearing housing  30  may include an upper bearing  34 , mounted within the interior of the bearing housing adjacent an upper end thereof, and lower or drive end bearings  36 , also mounted within the interior of the bearing housing  30  adjacent a slightly enlarged lower end  37  thereof. Preferably, the bearings  34  and  36  are heat shrunk and slip fitted into the interior of the bearing housing. Upper and lower bearings  34 ,  36  are shown as sets of lubricated ball bearings. However, it is within the scope of the invention to employ other types of rolling element bearings, such as roller bearings or tapered roller bearings, as well as journal bearings or fluid bearings. 
     A central, generally cylindrical shaft  38  may be mounted within the bearing housing  30  and may be rotatably connected thereto at upper and lower drive end bearings  34 ,  36 , respectively. The central shaft  38  may be concentric with the bearing housing  30 . The central shaft  38  may protrude from a lower end of the bearing housing  30  and terminate in a disc-shaped head  40 . 
     A hub, generally designated  42 , may be attached to the central shaft  38  by bolts  44  that may be threaded into the head  40 . The hub  42  may include a cup-shaped body  46  and a plurality of radially extending fan blades  48  attached to the body by bolts  50 . As best shown in  FIG. 3 , the hub body  46  may terminate in an annular upper edge  52  that forms an annular gap  54  with the inner annular wall  20  of the tankhead  12 . In the embodiment shown, the gap is about ⅜ inches. However, gaps of greater or lesser size may be employed without departing from the scope of the invention. 
     The lower end of the hub body  46  opposite the gap  54  may include a plurality of openings  56  and drain holes  57  that connect an interior portion  58  of the hub body  46  to the ambient. Although  FIGS. 1 and 3  show the hub body  46  having two openings  56  on opposite sides of the hub body  46 , the hub body may have a single opening  56 , or as many as six or more openings spaced generally evenly about the periphery of the hub, without departing from the scope of the invention. Similarly, while  FIGS. 1 and 3  show the hub body  46  as having a single drain hole  57 , the hub body may have several drain holes spaced evenly about the hub periphery without departing from the scope of the invention. The drain holes  57  preferably are round in cross section, but may be any shape in cross section, or a variety of shapes, without departing from the scope of the invention. 
     The openings  56  preferably are elongate in shape, approximately 1.00″×4.00″ in a circumferential direction. However, the openings  56  may be any shape or size, or a variety of shapes and sizes, such as generally circular or polygonal, without departing from the scope of the invention. 
     The hub body  46  includes an inner, cylindrical wall  60 . A rotor  62 , generally cylindrical in shape and part of the AC motor, is mounted on the inner wall  60 , preferably by press fitting. The AC motor  10  may include a complementary stator  64 , mounted on the bearing housing  30  and concentric with the rotor  62 . The stator  64  includes a stator core having a cylindrical inner wall  66 . There preferably is minimal clearance between the outer diameter of the stator  64  and the inner diameter of the rotor  62  in order to maximize the torque generated by the motor. However, such minimal clearance does not permit air to circulate between the stator  64  and rotor  62  within the interior  58  of the motor  10 . 
     As best shown in  FIG. 2 , the bearing housing  30  may include an outer surface  68  having a plurality of longitudinally extending grooves  70  formed thereon. The grooves  70  preferably extend the entire length of the bearing housing  30 , including the enlarged lower end  37 . The bearing housing  30  shown in the figures includes eight grooves  70 , each approximately 1.25 inches wide and 0.340 inches deep. However, it is within the scope of the invention to provide a greater or fewer number of grooves  70 , or to vary the width or depth of the grooves, or to provide grooves of varied widths and depths. 
     As best shown in  FIG. 3 , when the stator  64  is mounted on the bearing housing  30 , the inner cylindrical surface  66  of the stator engages the outer surface  68  of the bearing housing, and the grooves  70  may form air passages  72  with the inner surface  66 . 
     In operation, the windings of the stator  64  may be energized by a source of three-phase electrical power (not shown), causing the rotor  62  and hub  42  to rotate relative to the stator. The rotation of the hub  42  causes the blades  48  to displace ambient air upwardly, as shown in  FIGS. 1 and 3 . The movement of air causes ambient air to enter through the annular gap  54  between the wall  20  and end of the hub body  52 , as shown by arrow A. Ambient air entering the interior  58  of the hub may then flow downwardly, as indicated by arrows B and C, along the air passages  72  formed by the cooperation of the grooves  70  and inner wall  66  of the stator  64 . Then, as indicated by arrows D, the air flows past the drive end bearing  36  and end turns of the stator  64 , and outwardly through openings  56  and drain holes  57  in the hub body  46 , as indicated by arrows E. 
     Continued operation of the fan  10  causes ambient air to continue to flow in the direction of arrows, A, B, C, D, E, thus cooling the interior  58  of the hub body  46 , and in particular, cooling drive end bearing  36  and in addition, upper bearing  34  and upper and lower end turns of the stator  64 . Thus, by cooling the bearings  34 ,  36 , the temperature of the lubricants in the bearings is lowered, thereby extending the useful life of the lubricant and bearings. Further, the overall service life of the motor  10  is extended relative to a motor not having the interior ventilation capabilities of the disclosed motor. 
     While the forms of apparatus and methods disclosed herein may constitute preferred embodiments of the invention, it is to be understood that other forms of apparatus and components may be employed without departing from the scope of the invention.