Abstract:
A heat dissipation device for handy, effective, and cost saving heat dissipation for all kinds of motors utilizing a plurality of thermal conducting pipes filled with an easily evaporative liquid and a capillary material disposed uniformly in the surroundings of windings and in the core slots. These pipes are brought to be in contact with a heat dissipation plate and can be further communicated with a circulating refrigerant.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a motor with improved heat dissipation effect, and more particularly, to heat dissipation means for linear motor. 
     2. Description of the Prior Art 
     A stator and a rotor are two essential components of a motor. In general, the stator has armature windings for carrying load current, and the rotor is provided with a magnetic field formed of field windings on an iron core of laminated sheet steel. After the field windings are ready, the insulating material for example, epoxy resin, or other equivalents are enclosed over the windings and the core. With this structure, the motor converts electric energy to rotating torque according to the Fleming&#39;s left hand rule. 
     The energy of a motor is partially converted into heat which in turn gives rises to increase of winding resistance and I 2 R loss of the motor. As a result, the temperature rise of the motor is exacerbated to greatly lower the motor efficiency. It is well understood that both the stator and rotor is hard to cool down especially in the case the windings and the core are enclosed with thermal insulating epoxy resin. 
     The motor may be classified into rotating type and linear type. In the rotating type, the motor can be equipped with ventilation means such as cooling fans or providing ventilation holes through the laminated core so as to take away heat generated during operation of the motor. Unfortunately, such means are not applicable to a linear motor so that certain other heat dissipation mechanism must be added to it. 
     FIG. 6 shows conventional means for heat dissipation in a linear motor. In this case, the mover  25  of the linear motor includes an iron core  19  with field windings  20  wound on the iron core  19 , and a heat dissipation plate  18  attached on top of the core  19 , or attached to the front or the rear end, or to both sides. By heat exchange function performed by a refrigerant flowing in the cooling pipes contained in the heat dissipation plate  18 , heat is carried out of the motor. However, in this case, only the heat existing on the uppermost part or on both sides of the mover  25  can be dissipated, dissipation of heat loitering at the center portion of the core  19  and in the field windings is not easy and the heat dissipation efficiency for the entire motor is quite poor. 
     Another improvement made by U.S. Pat. No. 4,839,545 to upgrade the heat dissipation effect is shown in FIG.  7 . As shown in FIG. 7, a plurality of silicon sheet steels  21  for the mover  26  are formed into various configurations so as to facilitate burying refrigerant contained cooling pipes into a meandering groove  22  on the sheet steels  21 . Meanwhile, several sets of expensive dies have to be prepared for complicated fabricating process. Besides, the mover  26  becomes bulky for the resin containing cooling pipes therein. Moreover, refrigerants are generally corrosive so that the motor windings are apt to be damaged in case of leakage of refrigerant. 
     Another well-known heat dissipation means for a linear motor was provided by U.S. Pat. No. 5,751,077. In this disclosure, the principles of cooling an oil immersed transformer is employed wherein by filling a none electric and magnetic conducting liquid into a housing of the mover. Meanwhile, for perfectly carrying out the advantage of this design, a perfectly leak proof mover housing must be provided at first, which is not only difficult in manufacturing, but also expensive for production cost. Besides, weight of the mover will be inevitably increased, and an additional device for circulation of the cooling liquid in the mover with other external equipment for heat exchange. One thing more, the fear of damaging electrical circuit of the motor in case of leakage of refrigerant still remains unsolved! 
     Another solution for heat dissipation of a linear motor is shown in FIG. 8. A linear motor  27  is composed of a stator  28  and a mover  29 , pressurized air  23  is blown onto the surface of the mover  29 . Incidentally, in this method, the heat hidden in the inner part of the mover  29  enclosed by an epoxy resin layer or other equivalents  24  is hard to expel. Besides, additional cost for preparing an air compressor together with an air reservoir is considerably expensive. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in order to eliminate the inconvenience and disadvantages inherent to the conventional techniques as mentioned above. The essential object of the present invention is to provide heat dissipation means for a linear motor, with such means, the heat produced by the motor can be effectively carried away therefrom so as to perform heat dissipation with a high efficiency heat exchange procedure. 
     In the present invention, thermal conducting pipes and a heat dissipation gel instead of conventional cooling circulation pipes buried in the iron or windings. With this structure, the small sized light weighted, and non-ferrite heat conducting pipes are able to be buried deeply into the core or windings of the motor beneath the epoxy resin so as to perform highly efficient heat dissipation. 
     In the present invention a thermal conducting pipe is used, comprising a closed, vacuum-tight envelope, a porous lining called a “wick structure”, and a moving fluid. The thermal conducing pipe, also known as a heat pipe, is an efficient heat transfer device recently used in the electronics industry, especially in laptop computers. The thermal conducting metallic tubes are almost completely evacuated, filled with a small amount of special liquid materials, for example, methane or acetone having a low boiling point, and a material with capillary characteristics. As the pipes are heated, pressure variation in the pipes causes evaporation of the liquid with the result that vaporized liquid flows with a very high velocity from a high temperature region to a low temperature region. As soon as the vaporized liquid comes in contact with the wall surface of the metallic pipes at the low temperature region, heat is conducted to the wall surface of the low temperature metallic pipes. After having released the heat energy, vaporized liquid restores its liquid state and flows back to the high temperature region with the aid of gravity or by capillary action of the capillary material. By such repeated circulation, the heat produced by copper loss and iron loss during operation of the motor is carried away from the iron core and the windings directly outside through the metallic pipes without detention by the epoxy resin layer. 
     In the present invention, for further enhancing heat dissipation effect, a metallic heat dissipation plate is attached to the outer surface of the mover, the heat dissipation plate is in contact with the metallic pipes so as to assist the heat dissipation thereof. During operation, the heat is dissipated to the air from the heat dissipation plate without providing any additional means for forced cooling. Fins can be provided for the heat dissipation plate to increase contact area with air thereby improving heat dissipation effect. 
     In the present invention, a recirculating circuit for refrigerant can be formed in the heat dissipation plate which is in contact with the thermal conducting metallic pipes for assisting to dissipate heat to the air in the case of a large motor producing great amount of heat. However, the metallic heat dissipation plate is located far away from the core and windings so that there is no fear of leakage of refrigerant which might cause a short circuit of the motor. 
     In the present invention, a thermal conducting gel can be filled between the metallic thermal conducting pipes and the heat dissipation plate thereof for further improving the thermal conducting effect. 
     Besides, the technique of the present invention is all applicable to a rotating motor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings in which 
     FIG.  1 ( a ) is a three dimensional exploded view in an embodiment of the present invention; 
     FIG.  1 ( b ) is a side view of FIG.  1 ( a ); 
     FIG.  1 ( c ) is a top view of FIG.  1 ( a ); 
     FIG.  1 ( d ) is a front view of FIG.  1 ( a ); 
     FIG. 2 is view of a second embodiment of the present invention which is applied to a coreless linear servo motor; 
     FIG. 3 is a side cross sectional view of FIG. 2; 
     FIG. 4 is a view of a third embodiment of the present invention which is applied to a general linear pulse motor; 
     FIG. 5 is a cross sectional view cut along line B—B in FIG. 4; 
     FIG. 6 is a view showing conventional means for heat dissipation in a linear motor; 
     FIG. 7 is a view showing means for heat dissipation in a linear motor disclosed by U.S. Pat. No. 4,839,545; and 
     FIG. 8 is view showing means for heat dissipation in a linear motor disclosed by U.S. Pat. No. 5,703,418. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 consists of four sub-drawings (a), (b), (c) and (d) respectively expressing a three dimensional exploded view, a side view, a top view, and a front view. The mover of a linear motor includes an iron core and field windings, the iron core is formed of a stack of laminated sheet steels  1 , and the windings are wound around the core. The highly thermal conducting pipes  2  are disposed in slots  3  of the laminated sheet steel core  1 . Since the clearances between the thermal conducting pipes  2  and the steel core  1  might increase thermal reluctance so as to degrade thermal conductivity, the clearances there between are filled with thermal conducting gel  4  for lowering thermal reluctance, on the other hand, it has an effect of fastening the thermal conducting pipes  2  thereat. 
     In a conventional moving core linear servo motor, when the windings  6  are carrying current, windings  6  get a poor thermal conducting effect because the heat dissipation is detained by an epoxy resin layer  7  having a very poor thermal conductivity and enclosing the windings  6 . In the present invention, the heat loitering or accumulating in the epoxy resin layer  7  is conducted therefrom by the thermal conducting pipes  2  with one end being inserted into the epoxy resin layer  7 , and the other end being stretched out of the epoxy resin layer  7  thereby providing a passage for releasing heat outside. For further enhancing the above-mentioned heat releasing effect, the other end of the pipe  2  is buried in a metallic heat dissipation plate  5 , whose surface has a plurality of fins. Furthermore, a thermal conducting gel  4  can be filled into the clearances between the pipes  2  and plate  5  for lowering thermal reluctance there between and assisting to tightly fastening the pipes  2  in the plate  5 . Besides, the heat exchange effect of the plate  5  with external air may be improved by means of additional refrigerant circulation pipes provided in the plate  5 . 
     FIG. 2 is a view of a second embodiment of the present invention which is applied to a coreless linear servo motor, and FIG. 3 shows its side cross sectional view. The heat of this type of linear motor is generated by the mutual reaction of an electromagnetic field built-up by current in windings  9  of the mover  10  and a permanent magnet  11  in a stator  12 . In this embodiment, the stator  12  is divided into upper and lower layers, whereas mover  10  is interposed between the two stators with a definite gap  17  and movable in accordance with a guide mechanism. The mover  10  is enclosed with an epoxy resin layer  8  having a poor thermal conductivity so that the heat accumulated in the inner part of the mover  10  is hard to be dissipated. In the present invention, the heat loitering or accumulating in the epoxy resin layer  8  is conducted therefrom by the thermal conducting pipes  13  with one end being inserted into the epoxy resin layer  8  near the winding  9  and the other end being stretched out of the epoxy resin layer  8  thereby providing a passage for releasing heat outside. With this structure, the heat accumulated in the windings  9  can be more directly and promptly carried out than cooling the mover with cooling air blown from outside as that employed by the conventional technique. 
     FIG. 4 is a view of a third embodiment of the present invention which is applied to a general linear pulse motor, and FIG. 5 is a cross sectional view cut along line B—B in FIG. 4. A mover  30  of the linear pulse motor includes a plurality of electromagnet units  31  with thermal conducting pipes  15 , laminated sheet steels  16  and windings  32  wound around the laminated sheet steels  16 . The pipes  15  are in contact with the laminated sheet steels  16  so that the heat produced by the sheet steels  16  and the windings  32  may be carried out of the mover  30 . In this embodiment, when fabricating the electromagnet units  31 , the thermal conducting pipes  15  are at first inlaid into the electromagnet units  31  so as to be in contact with nearby laminated sheet steel  16 , and then by filling the clearances between the pipes  15  and the laminated sheet steels  16  with a thermal conducting gel so as to improve thermal conductivity of the pipes  15  and stabilize the pipes in the position. Although the pipes  15  can be enclosed in the laminated sheet steels  16 , yet the configuration of the laminated sheet steel  16  shall be formed to match the contour of the pipes  15  resulting in increasing production cost. 
     Many changes and modifications in the above described embodiments of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, to promote the progress in science and the useful arts, the invention is disclosed and is intended to be limited only by the scope of the appended claims.