Patent Publication Number: US-6992411-B2

Title: Liquid cooling arrangement for electric machines

Description:
This is a division of Application No. 10/198,186, filed Jul. 18, 2002, now U.S. Pat. No. 6,819,016. 

   FIELD OF THE INVENTION 
   The present invention relates to electric machines. More specifically, the present invention is concerned with a liquid cooling arrangement for electric machines. 
   BACKGROUND OF THE INVENTION 
   Electric machines, whether they are motors or generators, are well known in the art. It is also widely known that electric machines generate heat as a by-product and that this heat must be somehow extracted from the machine to improve the performances of the machine and prevent early degradation of the machine. 
   Conventionally, electric machines are often air-cooled. This is easily done by providing apertures in the body of the machine to let air be forced therein. The efficiency of such a cooling arrangement is poor since air is a generally non-efficient cooling fluid. Furthermore, some electric machines operate in environment that are such that it is not possible to provide an electric machine with apertures. 
   Electric machines using cooling fluid have also been designed. For example, European Patent Number 0,503,093 entitled “Liquid Cooling Device of Motor” and naming Nakamura as inventor discloses an electric motor where the laminations are provided with apertures allowing an axial flow of cooling liquid when the laminations are assembled. A drawback of Nakamura&#39;s system is the risk of failure of the motor caused by leaks. Indeed, a failure-causing link could spring should the seal between adjacent laminations fail. 
   OBJECTS OF THE INVENTION 
   An object of the present invention is therefore to provide an improved liquid cooling arrangement for electric machines. 
   SUMMARY OF THE INVENTION 
   More specifically, there is provided a cooling arrangement for electric machines comprising a heat storing element provided with generally C-shaped channels; a cooling tube so configured and sized as to be insertable in the C-shaped channels of the heat storing element; the cooling tube, once inserted in the channels, being deformed to conform to the C-shaped channels; and heat stored in the heat storing element being extractable by the cooling tube, wherein the heat storing element is formed of laminations of a stator of the electric machine. 
   It is further provided an electric machine comprising a generally hollow cylindrical stator; a rotor rotatably mounted to the stator; a cooling arrangement including a heat storing element provided with generally C-shaped channels; the heat storing element being associated with the stator to extract heat therefrom; a cooling tube so configured and sized as to be insertable in the C-shaped channels of the heat storing element; wherein the cooling tube, once inserted in the channels is deformed to conform to the C-shaped channels; heat stored in the heat storing element is extractable by the cooling tube; the heat storing element is formed of laminations of the stator; and the C-shaped channels are provided on an inner surface of the stator. 
   It is to be noted that the expression “electric machine” is to be construed herein as encompassing both electric motors and electric generators disregarding the technology used in these machines. 
   Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the appended drawings: 
       FIG. 1  is a perspective, partly exploded view, of the stator of an electric machine provided with a cooling arrangement according to a first embodiment of the present invention; 
       FIG. 2  is a perspective view of the stator of  FIG. 1  where the cooling tube is inserted in channels provided therein; 
       FIG. 3  is a perspective view illustrating the completed stator of  FIG. 1 ; 
       FIG. 4  is a sectional view illustrating the insertion of sections of the cooling tube in the channels provided in the stator; 
       FIG. 5   a  is a sectional view illustrating the cooling tubes inserted in the channels and deformed according to a first pattern to permanently mount them in the channels; 
       FIG. 5   b  is a sectional view illustrating the cooling tubes inserted in the channels and deformed according to a second pattern to permanently mount them in the channels; 
       FIG. 6  is an exploded view of a cooling arrangement according to a second embodiment of the present invention; 
       FIG. 7  is a side elevational view of the cooling arrangement of  FIG. 6  illustrating the deformation of the cooling tube in the channels of the heat storing element; 
       FIG. 8  is a perspective, partly exploded view, of the cooling arrangement of  FIG. 6  and the stator of an electric machine; and 
       FIG. 9  is a side elevational view of the assembled stator including the cooling arrangement of  FIG. 6 . 
   

   DESCRIPTION OF THE EMBODIMENTS 
   In a nutshell, a first embodiment of the present invention, illustrated in  FIGS. 1 to 5   b , uses the laminations of the stator as a heat storing element provided with generally C-shaped channels in which a cooling tube is mounted. In operation, cooling fluid is circulated in the cooling tube to extract heat stored in the laminations. 
   A second embodiment of the present invention, illustrated in  FIGS. 6 to 9 , uses a separate heat storing element also provided with generally C-shaped channels in which a cooling tube is mounted. The heat storing element is then inserted in the stator of an electric machine with the cooling tube in contact with both the heat storing element and the stator. In operation, cooling fluid is circulated in the cooling tube to extract heat accumulated in the heat storing element and in the stator. 
   Turning now to  FIGS. 1 to 5   b  a cooling arrangement  10  according to the first embodiment of the present invention will now be described. 
     FIG. 1  shows a stator  12  of an electric machine (not shown). The stator  12  is made of a plurality of identical laminations stacked together. The stator  12  is generally cylindrical and includes rectangular external channels  14  in which coils  16  are mounted. It is to be noted that the stator  12  is a so-called internal stator, i.e. that the rotor (not shown) is so mounted to the stator as to be coaxial and external to the stator  12 . 
   The laminations of the stator  12  are used as a heat storing element, as will be described hereinbelow. 
   The inside surface  18  of the stator  12  is provided with a plurality of generally C-shaped channels  20 . 
   The cooling arrangement  10  also includes a cooling tube  22  having a generally circular cross-section and provided with an inlet  24  and an outlet  26 . As can be clearly seen in  FIG. 1 , the cooling tube  22  is so folded as to form a serpentine. 
   As will be explained hereinbelow, the cooling tube is so configured and sized to be inserted in the C-shaped channels  20  of the stator  12 . 
     FIG. 2  illustrates the cooling tube  22  inserted in the generally C-shaped channels of the stator  12 . As can be seen in this Figure, the serpentine folding of the cooling tube  22  is optionally configured so that the rounded portions thereof extend outside of the stator  12 . This arrangement may be interesting since is allows the rounded portions of the cooling tube to be folded outwardly as illustrated in  FIG. 3  to increase the contact surface between the cooling tube  22  and the stator  12 . 
   Turning now to  FIGS. 4 and 5   a , it can be better seen that each C-shaped channel  20  has a generally closed C-shape configuration, i.e. that the opening of the channel is smaller than the widest portion of the channel. It is also to be noted that the circular cross section of the cooling tube  22  is at most equals to the opening of the channel to allow its insertion therein. 
   To insert the cooling tube  22  in the channels  20 , a first step is to generally align the straight portions of the cooling tube  22  with a corresponding channel  20  of the stator  12 , as can be seen in  FIG. 4 . This operation is facilitated by the possibility to significantly deform the serpentine configuration of the tube  22  to allow its insertion into the central opening of the stator  12 . 
   The next insertion step is to deform the serpentine configuration of the cooling tube  22  so that each straight section is inserted in a corresponding channel (see arrows  28  in  FIG. 4 ). The result of this step is illustrated in dashed lines in  FIG. 4 . 
   To maintain the straight portions of the cooling tube  22  into the channels  20 , these straight portions are deformed to conform to the generally closed C-shaped configuration of the channels  20 . To achieve this, a pressure is radially applied (see arrows  30   a  in  FIG. 5   a ) onto the cooling tube  22 . This radial pressure causes the widening of the tube as can be seen from arrows  32 . It is to be noted that according to this first type of deformation of the cooing tube  22 , the cooling tube  22 , once deformed, presents a slightly convex surface with respect to the inner surface of the stator  12 . 
   It is to be noted that, optionally, a heat conducting and/or adhesive substance may be placed between the channel and the tube to provide improved heat transfer between these elements. 
   It is also to be noted that while many materials can be used for the cooling tube  22 , good results have been obtained by using copper tubing. 
   Turning now briefly o  FIG. 5   b  of the appended drawings a second type of deformation of the cooling tube  22  inside the channels  20  will be briefly described. As can be seen from this figure, the second type of deformation of the cooing tube  22  presents a slightly concave surface with respect to the inner surface of the stator  12 . Again, to achieve this, a pressure is radially applied (see arrows  30   b  in  FIG. 5   b ) onto the cooling tube  22 . 
   This second type of deformation is believed interesting since, it would prevent unwanted loosening of the cooling tube inside the channels. 
   Turning now to  FIGS. 6 to 9 , a cooling arrangement  100  according to a second embodiment of the present invention will now be described. 
   As mentioned hereinabove, the cooling arrangement  100  uses a separate heat storing element  102 . This heat storing element  102  includes an external and generally circumferential channel  104  into which a cooling tube  106  having a serpentine configuration may be inserted as will be described hereinbelow. It is to be noted that while it is not expressly illustrated in the appended figures, the channel  104  has a serpentine configuration generally corresponding to the serpentine configuration of the cooling tube  106 . 
   The cooling tube  106  has a generally serpentine configuration and includes an inlet  110  and an outlet  112 . 
   As can be better seen from  FIGS. 7 and 9 , the C-shaped channel  104  has a generally open C-shape configuration, i.e. that the opening of the channel is the same width as the widest portion of the channel. 
   Again, the insertion of the cooling tube  106  into the channel  106  is generally straightforward. The cooling tube  106  is first positioned so that is adequately faces the channel  104 . The tube is then inserted in the channel (see the tube  106  in full lines in  FIG. 7 ). The final step is to deform the cooling tube so that it does not protrudes from the external surface of the heat storing element  102  (see the tube  106  in dashed lines in  FIG. 7 ). This is done by applying an inwardly radial pressure (see arrows  114 ), which forces the tube  106  to conform to the channel  104  (see arrows  116 ). 
   As mentioned hereinabove, a heat conducting and/or adhesive substance may optionally be placed between the channel and the tube to provide improved heat transfer between these elements. 
   Turning now briefly to  FIG. 8  of the appended drawings, once the cooling tube  106  is properly inserted in the heat storing element  102 , the cooling arrangement  100  may be inserted in the stator  118  of an electric machine (not shown). 
     FIG. 9  is a sectional view of the cooling arrangement  100  mounted in the stator  118 . One skilled in the art will appreciate that since the cooling tube  106  contacts both the heat storing element  102  and the stator  118 , heat from these two elements will be extracted by the cooling fluid circulating in the cooling tube  106 . 
   It is to be noted that even though the two embodiments of the present invention have been illustrated as being part of an electric machine provided with an internal stator and an external rotor (not shown), one skilled in the art could easily adapt the present invention to be used in an electric machine having an external stator and an internal rotor. 
   It is also to be noted that while the embodiments of the present invention have been described hereinabove as using an open cooling tube where a flow of fluid is used to extract the heat from the heat storing element, other cooling technologies, such as, for example, the heat pipe technology could be used. Indeed, one skilled in the art would have no problem designing or modifying conventionally known heat pipes so that they can be mounted in the C-shaped channels. For example, in the first embodiment illustrated in  FIGS. 1–5   b , separate straight heat pipes (not shown) could be inserted in each longitudinal channel  20 , and in the second embodiment illustrated in  FIGS. 6–9 , a continuous heat pipes (not shown) could be inserted in the channel  114 . 
   It is also to be noted that the two embodiments illustrated respectively in  FIGS. 1 to 5   b  and  6  to  9  could be combined to increase the cooling possibilities. 
   Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.