Abstract:
A thermally efficient motor housing assembly including a plurality of transistors and a printed wire board (pwb) for controlling a stepper motor and also including a plunger array and a spring array along with a combined heat sink and pwb enclosure.

Description:
BACKGROUND OF THE INVENTION  
   Stepper motors such as described in U.S. Pat. No. 5,369,324 entitled “Electrical Stepper Motor” often contain power transistors within the motor control circuit. Since the power transistors generate heat upon operation of the associated stepper motor, heat sinks are required to prevent the stepper motor and motor control circuit from overheating. 
   In some electric circuits containing power transistors, a heat sink is attached to the power transistor by means of a spring clip arrangement to insure close contact between the power transistor and the heat sink for efficient heat transfer away from the power transistor, per se. One example of a spring clip arrangement is found in U.S. Pat. No. 5,671,118 entitled “Heat Sink and Retainer for Electronic Integrated Circuits” 
   When the power transistor is arranged within an electrical enclosure, a heat sink in the form of a metal support plate is arranged on the bottom of the enclosure to allow air flow access to the heat sink. One example of such an arrangement is found in U.S. Pat. No. 6,249,435 entitled “Thermally Efficient Motor Controller Assembly”. 
   The attachment of the power transistors to the heat sink within an electrical enclosure is complicated when the heat sink is part of the enclosure, per se. 
   One purpose of the instant invention is to provide an electrical stepper motor enclosure whereby the power transistors employed within the motor control circuit automatically become spring-loaded into contact with a heat sink, which serves as the power transistor enclosure, upon attachment of the enclosure to the stepper motor support housing. 
   BACKGROUND OF THE INVENTION  
   Stepper motors such as described in U.S. Pat. No. 5,369,324 entitled “Electrical Stepper Motor” often contain power transistors within the motor control circuit. Since the power transistors generate heat upon operation of the associated stepper motor, heat sinks are required to prevent the stepper motor and motor control circuit from overheating. 
   In some electric circuits containing power transistors, a heat sink is attached to the power transistor by means of a spring clip arrangement to insure close contact between the power transistor and the heat sink for efficient heat transfer away from the power transistor, per se. One example of a spring clip arrangement is found in U.S. Pat. No. 5,671,118 entitled “Heat Sink and Retainer for Electronic Integrated Circuits” 
   When the power transistor is arranged within an electrical enclosure, a heat sink in the form of a metal support plate is arranged on the bottom of the enclosure to allow air flow access to the heat sink. One example of such an arrangement is found in U.S. Pat. No. 6,249,435 entitled “Thermally Efficient Motor Controller Assembly”. 
   The attachment of the power transistors to the heat sink within an electrical enclosure is complicated when the heat sink is part of the enclosure, per se. 
   One purpose of the instant invention is to provide an electrical stepper motor enclosure whereby the power transistors employed within the motor control circuit automatically become spring-loaded into contact with a heat sink, which serves as the power transistor enclosure, upon attachment of the enclosure to the stepper motor support housing. 
   SUMMARY OF THE INVENTION  
   A thermally efficient motor housing assembly including a plurality of transistors and a printed wire board (pwb) for controlling a stepper motor and also including a plunger array and a spring array along with a combined heat sink and pwb enclosure. Attachment of the combined heat sink and pwb enclosure to the motor housing with the plunger and spring array intermediate the the pwb and the motor housing automatically positions the transistors in spring-loaded contact with the heat sink and pwb enclosure to insure thermal transfer between the transistors and the heat sink upon the occurrence of heating caused by the transistors and the environment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side view of the motor housing assembly of the invention with the combined heat sink-pwb enclosure, transistors, pwb, plunger array and spring array prior to attachment to the motor housing; and 
       FIG. 2  is side view of the motor housing assembly of  FIG. 1  after attachment of the combined heat sink-pwb enclosure, transistors, pwb, plunger array and spring array to the motor housing. 
   

   DESCRIPTION OF PREFERRED EMBODIMENT  
   The thermally efficient motor housing assembly  10  according to the invention is depicted in  FIG. 1  and includes a heat sink  11 , made from a metal having good thermal conductivity such as aluminum, in the shape of a hollow cylinder  8  with integral cooling fins  8 A, and a bottom plate  9 , having an inset  9 A, for attachment with a motor housing  16 . 
   The motor housing is a conventional housing of the type that includes a bottom surface  21  for attaching a stepper motor (not shown) along with an enclosure  22  for housing electrical components and connectors (not shown). 
   The motor housing is adapted to include spring retainer posts  17  extending from the top surface  18  thereof. 
   An array of transistors  12 , having depending connector pins  12 A, is positioned under the heat sink  11  and arranged for connection with the pwb  13  via first openings  13 A. 
   An array of plungers  14 , in the form of head caps  19 , which include recesses  19 A and tapered posts  20 , is positioned under the pwb  13  such that the tapered posts align with second openings  13 B in the pwb for contacting the transistors  12  in the manner to be described below in greater detail. 
   An array of compression springs  15  is positioned intermediate the plungers  14  and the motor housing  16  such that the springs  15  align with the recesses  19 A in the head caps  19  and the posts  17  extending upward from the top  18  of the motor housing  16 . 
   Once the transistors  12  are attached to the pwb  13 , the heat sink  11  is then moved in the down-ward indicated direction for connection with the motor housing  16 . 
   During the assembly of the heat sink to the motor housing; the inset  9 A within the bottom  9  of the heat sink  11  contacts the transistors  12  on the pwb  13  and moves the pwb into contact with the plungers  14  such that the tapered posts  20  pass thru the second openings  13 B and into contact with the transistors  12  to force the transistors into contact with the inset  9 A on the bottom plate  9  of the heat sink  11 . 
   The springs  15  become captured within the recesses  19 A formed in the ends of head caps  19 , and positioned over the posts  17  extending from the top  18  of the motor housing  16 . 
   The heat sink  11  is then fixedly attached to the motor housing  16  by means of metal fasteners (not shown). 
   The arrangement between the heat sink  11  and motor housing  16  within the completed thermally efficient motor housing assembly  10  of the invention is best seen by now referring to  FIG. 2 . 
   The positioning of the springs  15  over the posts  17 , extending from the top surface  18  of the motor housing  16 , and the capture of the springs within head caps  19  of plungers  14  fixedly holds the tapered posts  20  against the transistors  12  via second openings  13 B in the pwb  13  to force the transistors into good thermal contact with the inset  9 A on bottom plate  9  of the heat sink  11  under a wide range of operating temperatures. 
   A thermally efficient motor housing assembly wherein the power transistors on the motor control pwb are held in good thermal contact with the associated heat sink has herein been described. Although the invention has been described for use with electric motors, it is understood that other types of electrical equipment utilizing heat sinks, power transistors and pwbs can also be employed.