Patent Publication Number: US-2009220361-A1

Title: Cooling of stator for compressor

Description:
The present invention relates to a design for cooling an electric motor in a compressor according to the precharacterizing clause of Patent claim 1. 
     Technology within the field of fuel cells generating electrical energy as an alternative to fossil fuels, as a primary energy source for vehicles for example, is aiming at more compact and more efficient units. The principle of fuel cells can be described very generally as hydrogen gas and oxygen reacting with one another via electrodes, generating electrical energy. The “exhaust gas product” in the reaction between hydrogen and oxygen is water. The oxygen required in the process is supplied in the form of great quantities of air at positive pressure. 
     The present invention relates to cooling of an electric motor in a compressor for producing the process air required, where the compressor is supplied with energy via on the one hand an electric motor and on the other hand recovery of at least part of the energy remaining in the process air after it has passed through the fuel cells. The requirements for the unit are low weight and small volume, which is achieved in part by using an efficient and low-volume cooling method. This has been achieved by the invention having been provided with the features indicated in Patent claim 1. 
    
    
     The invention will be described in greater detail in the form of examples with reference to the drawing, in which  FIG. 1  shows an embodiment of the invention,  FIG. 2  shows another embodiment of the invention and  FIG. 3  shows a section along the line A-A in  FIG. 2 . 
     In  FIG. 1  and  FIG. 2 ,  1   a  and  1   b  designate an essentially cylindrical housing, which has centrally the stator  3  of an electric motor connected to the housing  1   a , and an impeller  4  and a turbine wheel  5  which are interconnected by means of a common shaft  6 . The common shaft  6 , bearing the impeller  4  and the turbine wheel  5 , can be mounted relative to the compressor housing by any bearing method, for example fluid bearings, magnetic bearings, ball bearings or roller bearings. 
     In the drawing,  9  designates the rotor of an electric motor, which rotor is fastened to the shaft  6 . The stator winding  2  of the electric motor is, together with its stator iron  3 , received in a space  12  in the housing  1   a ,  1   b . The parts  2 ,  3  of the electric motor, sleeves  7  and the housing  1   a ,  1   b  are cooled by a coolant which is introduced through an inlet  13 , flows through the stator winding  2  and the stator iron  3  via channels  10  (winding slots) and leaves the space  12  through an outlet  14 . The space  12  is sealed completely in relation to the rotating parts, the rotor  9 , the shaft  6 , with the aid of the cylindrical sealing sleeves  7  arranged between the stator winding  2  and the rotor  9  with the shaft  6 , which on the one hand seal in relation to the stator iron, the winding slots  10  of which are sealed  11  in the region between the stator winding and the rotor, and on the other hand are sealed by O rings for example in relation to the housing parts  1   a  and  1   b . The design of the cooling system as described contributes considerably to the compact design of the compressor.  17  indicates diagrammatically electric cables and other connections to the stator of the motor. 
     In  FIG. 3 ,  22  designates barriers which are arranged axially in the space  12  and bring about reduced direct communication between the volumes at the inlet  13  and the outlet  14  on the right side of the stator in the figure, which form inlet and outlet volumes in order to allow the bulk of the coolant to pass via the inlet  13  through the stator to its left side and back through the stator to the outlet  14 . Seen in  FIG. 2 , the barriers  22  extend from the inside of the right housing end wall to the right delimitation of the stator iron  3 , which thus separates the inlet  13  from the outlet  14  in fluid terms. The purpose of this design is that the coolant can be connected to the unit on only one side of the stator (the right side in  FIG. 2 ). 
     The compressor and turbine housings with inlets, guide vanes and outlets are not illustrated in the drawing, but it is understood that these function in a known manner. The arrow  18  thus indicates process air which is drawn in and fed out (indicated by arrow  19 ) at positive pressure to the fuel cell. In order to increase efficiency, residual process air is dealt with (indicated by arrows  20  and  21 ) by the turbine wheel  5 , which recovers energy, which is returned to the impeller  4  in order, together with the energy supplied via the electric motor, to drive the impeller  4 . 
     As mentioned, the space  12  is flowed through by a coolant (inlet  13 , outlet  14 ) which cools the stator iron, the stator winding and the compressor housing  1   a ,  1   b . In order to make cooling of the stator winding and the stator iron possible, these must be insulated against direct contact with the coolant as the coolant can be electrically conductive or corrosive. This can suitably be effected by means of a thin, heat-conducting protective film made of a material which is not electrically conductive and is not affected by the coolant. In order to make it possible to machine a close tolerance on the outside diameter of the stator without the stator iron being exposed, a machinable material  16 , which tolerates the coolant, has been applied firmly to the outside diameter of the stator iron before the protective film is applied, whereupon the outside diameter of the stator can be machined exactly. 
     In order to make it possible to machine a close tolerance on the outside diameter of the stator without the stator iron being exposed, a machinable material which tolerates the coolant has been applied firmly to the outside diameter of the stator iron before the protective film is applied, and the outside diameter of the stator can then be machined exactly.