Abstract:
The invention relates to a fan module, comprising a fan impeller having an axial inlet side and a radial outlet side, an electric motor for coaxially driving the fan impeller, and a cooling air guide that leads from the outlet side to the electric motor. From the electric motor, the cooling air guide further leads to the fan impeller, wherein the fan impeller has, in a region close to the axis, a cut-out for the passage of cooling air to the inlet side.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a fan module. In particular, the invention relates to a fan module having a cooling air ducting for an electric motor of the fan module. 
         [0002]    A fan module comprises a fan wheel and a coaxial electric motor for the purpose of driving the fan wheel. The fan wheel comprises an axial inlet side and a radial outlet side. The fan module is designed for the purpose of being installed in a ventilation system in order to convey air from the inlet side to the outlet side. In particular, the fan module can be installed in the region of a ventilation system of a motor vehicle. In particular, the ventilation system can be used to ventilate an interior of a motor vehicle. 
         [0003]    The fan module can be designed for the purpose of dissipating a high electrical power. Furthermore, a temperature of air that is conveyed by means of the fan module can extend over a large temperature range. In the above example of the interior lighting system of the motor vehicle, conveyed air can have temperatures between approx. −30 and approx +50 degrees Celsius. In order to cool the electric motor of the fan module, a cooling air ducting can be provided that leads from the outlet side of the fan module to the electric motor. In order to ensure a sufficient flow of cooling air past the electric motor, the cooling air is to be suitably guided past the electric motor. The efficiency of the cooling of the electric motor is to be high while simultaneously maintaining a low acoustic load by means of air that flows through the cooling air ducting. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the present invention is to provide a fan module that fulfills these requirements. 
         [0005]    A fan module in accordance with the invention comprises a fan wheel having an axial inlet side and a radial outlet side, an electric motor for the purpose of driving the fan wheel in a coaxial manner and a cooling air ducting that leads from the outlet side to the electric motor. After passing the electric motor, the cooling air ducting leads onwards to the fan wheel, wherein the fan wheel comprises a cut-out in a region near to the axis for the purpose of allowing cooling air to pass through to the inlet side. 
         [0006]    A drop in pressure between the outlet side and the inlet side of the fan module is advantageously used in order to convey the cooling air past the electric motor. The air that is flowing past the electric motor can absorb thermal energy and cool the electric motor. The heated cooling air is blended with the air that is flowing at the inlet side into the fan wheel and is conveyed together with said air in the direction of the outlet side. The flow of the cooling air is preferably considerably less than an entire flow of air through the fan wheel so that air that is tapped from the outlet side is only insignificantly warmed by means of the electric motor. 
         [0007]    It is possible to reduce the noise level by virtue of the fact that the cooling air is directed in opposite directions and by virtue of the air entering the inlet side while simultaneously the air flow that is flowing through the cooling air ducting is only insignificantly decelerated by the air that is taken in so that the efficiency of the cooling of the electric motor is ensured. 
         [0008]    The electric motor is preferably a commutated direct current motor having brushes and the cooling air ducting extends from the outlet side to the brushes and from there in the axial direction to the fan wheel. 
         [0009]    The brushes can be considered to be amongst the most thermally loaded elements of the electric motor. The brushes can be cooled with the still relatively cold air from the outlet side in the manner described above, prior to the air flowing onwards axially past the electric motor and where necessary absorbing further thermal energy. As a consequence, an admissible operating temperature of the brushes can also be maintained in the case of dissipation of a high electrical power. 
         [0010]    In a preferred embodiment, a diverting element is provided in the region of the brushes for the purpose of diverting the cooling air into the axial direction of the fan wheel. The cooling air can thus already flow past the brushes in the axial direction so that the cooling air within the cooling air ducting is not diverted and/or swirled any more than is necessary. 
         [0011]    In a particularly preferred embodiment, the cooling air ducting extends axially through the electric motor. In particular, the cooling air can be supplied through a region between a stator and a rotor of the electric motor. As a consequence, a particularly efficient cooling of the electric motor can be achieved in its interior. In an alternative embodiment, the cooling air can also be supplied externally axially past the electric motor. 
         [0012]    In a further preferred embodiment, the brushes are spaced from one another and the cooling air ducting comprises a diverting element for the purpose of guiding a part flow of cooling air to each of the brushes. As consequence, the individual brushes can be individually cooled in a purposeful manner and as a result it is possible to avoid a thermal overloading of each individual brush. Since a failure of the electric motor is likely in the case of damage to one of the brushes, reliability and where necessary service life of the electric motor can be increased in this manner. 
         [0013]    The cooling air ducting preferably extends between the outlet side and the electric motor along a plane that includes the axis of rotation of the electric motor. 
         [0014]    A gap between the outlet side and the electric motor along the cooling air ducting can thus be minimized. Furthermore, the cooling air can flow in this region in sections in a direction that extends in an inclined manner with respect to the axis of rotation as a result of which noises in particular whistling and howling sounds can be avoided and/or suppressed. 
         [0015]    A base plate having a cut-out for the purpose of allowing cooling air to flow axially through from the outlet side into the cooling air ducting can be provided in a plane of rotation between the electric motor and the fan wheel. 
         [0016]    Air that is exiting at the outlet side is predominantly accelerated in the tangential and radial direction. However, air that is entering from the outlet side into the cooling air ducting moves predominantly in the axial direction. As a consequence, a relatively constant cooling air flow from the outlet side can be drawn off, which can suffice in order to cool the electric motor even under unfavorable circumstances such as in the case of high air temperature and dissipation of a high electrical power. 
         [0017]    In a particularly preferred embodiment, a vane is provided on a border of the cut-out and said vane extends in an axial direction. The flow characteristics through a cooling air ducting can be defined by means of the cross section of the cooling air ducting, in particular in the region of the cut-out, and a corresponding dimensioning of the vane in such a manner that the flow rate of cooling air past the electric motor suffices for the cooling process without leading to an acoustic load. 
         [0018]    In a further preferred embodiment, the fan wheel comprises a multiplicity of axial cut-outs for the purpose of allowing cooling air to pass through to the inlet side. It is preferred that the axial cut-outs are distributed in relation to an axis of rotation in such a manner that an imbalance of the fan wheel is avoided. 
         [0019]    In one embodiment, the fan wheel comprises a dome-like base plate that is facing the electric motor in an axial manner. In a radial region near to the axis, the base plate accordingly extends as far as possible in the opposite direction to that of the axially entering air. Since the fan wheel radially accelerates the incoming air, the incoming air in the region of axis of the dome is relatively slow so that a noise load can be low by means of the air currents of the cooling air and the incoming air that counter one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The invention is described in detail with reference to the attached figures, in which: 
           [0021]      FIG. 1  illustrates a longitudinal sectional view of a fan module; 
           [0022]      FIG. 2  illustrates flows of cooling and conveying air through the fan module in  FIG. 1 ; 
           [0023]      FIG. 3  illustrates a cross sectional view of the fan module in  FIG. 1 ; 
           [0024]      FIG. 4  illustrates a plan view of a part of the fan module in  FIG. 1 ; and 
           [0025]      FIG. 5  illustrates a plan view of a further part of the fan module in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  illustrates a longitudinal sectional view of a fan module  100 . The fan module  100  comprises a fan wheel  105  and an electric motor  110  that are mutually connected in an axial manner such that the electric motor  110  can rotate the fan wheel  105  about an axis of rotation  115 . 
         [0027]    The fan wheel  105  comprises several fan blades that extend in an axial direction and are arranged on a periphery around the axis of rotation  115 . The fan blades  120  are held together at the top by means of a circumferential outer edge  125  and terminate at the bottom at a dome-like curved base plate  130 . Several cut-outs  135  are integrated near to the axis of rotation  115  into the curved base plate  130  of the fan wheel  105 . 
         [0028]    The electric motor  110  comprises a stator (field magnet)  140  and a rotor (lamella)  145 . The rotor  145  is mounted in the stator  140  in such a manner as to be able to rotate about the axis of rotation  115  and is connected to the fan wheel  105  in such a torqued manner. In different embodiments, the stator  140  can be arranged radially outside or radially inside the rotor  145 . In the illustrated embodiment, the stator  140  lies outside and the rotor  145  lies inside. Two brushes  150  are attached to the stator  140  and lie opposite one another preferably in relation to the axis of rotation  115 . The brushes  150  render possible an electrical current flow between the stator  140  and the rotor  145 , wherein different coils of the rotor  145  are connected to the connectors of the brushes  150  in dependence upon a relative angle of rotation. 
         [0029]    In the illustrated embodiment, the fan module  100  further comprises a module housing  155  and a housing cover  160 . The module housing  155  is fastened to the stator  140  of the electric motor  110  and is designed for the purpose of fastening the fan module  100  to a ventilation system. The module housing  155  comprises a base plate  165  that lies in a plane of rotation about the axis of rotation  115 . A cut-out  170  is provided through the base plate  165  in a region radially outside a contour of the fan wheel  105 , wherein a diverting element  175  protrudes axially upwards on a border of the cut-out  170 . The cut-out  170  represents the beginning of a cooling air ducting  180  that is initially formed by means of the module housing  155  and the housing cover  160  and leads from the cut-out  170  to an axially lower end of the electric motor  110 . From there, the cooling air ducting  180  extends past the brushes  150  of the electric motor  110  and axially upwards through the electric motor  110  to the fan wheel  105  where the cooling air ducting  180  terminates at the cut-outs  135 . 
         [0030]    During operation of the fan module  100 , air enters axially from above at an inlet side  185  of the fan wheel  105  and is accelerated radially outwards to an outlet side  190 . A part of the air that is accelerated enters from the outlet side  190  through the cut-out  170  axially into the cooling air ducting  180  and then, after the circulation, exits axially through the cut-outs  135  of the fan wheel  105 . The exiting cooling air blends there with the incoming air and can be conveyed afresh through the fan wheel  105 . 
         [0031]      FIG. 2  illustrates flows of cool and conveying air through the fan module  100  in  FIG. 1 .  FIGS. 2   a  and  2   b  illustrate longitudinal sectional views through the fan module  100 , wherein the section that is illustrated in  FIG. 2   b  is rotated 180° and the section that is illustrated in  FIG. 2   a  is rotated 90° about the axis of rotation  115  in relation to the direction of the sectional view of the illustration in  FIG. 1 . 
         [0032]    It is evident in the two  FIGS. 2   a  and  2   b  how conveying air at the inlet side  185  of the fan wheel  105  enters axially downwards from above and is conveyed radially outwards to the outlet side  190 . A part of the conveyed air is conveyed in an inclined manner downwards to the lower axial end of the electric motor  110  from the outlet side  190  through the cooling air ducting  180  between the module housing  155  and the housing cover  160 . The air flows axially upwards at this site past the brushes  150 , flows through the electric motor  110  between its stator  145  and its rotor  140  and flows onwards axially upwards in the direction of the fan wheel  105 . The cooling air ducting  180  terminates at the cut-out  135  in the base plate  130  of the fan wheel  105 . The cooling air exits upwards in a region near to the axis of rotation  115  and flows essentially in the opposite direction to the air that enters from above at the inlet side  185 . 
         [0033]      FIG. 3  illustrates a plan view of the module housing  155  of the fan module  100  in  FIG. 1 . The viewing direction is downward from above in relation to the illustration in  FIG. 1 . 
         [0034]    The cut-out  170  through the base plate  130  of the module housing  155  is clearly evident. The fan wheel  105  (not illustrated) rotates anticlockwise in the illustrated exemplary embodiment so that the diverting element  175  closes off the cut-out  170  in the movement direction of the air towards the rear. The diverting element  175  is designed for the purpose of diverting a part of the air, which is flowing past said diverting element, axially downwards into the cooling air ducting  180 . 
         [0035]    A first aperture  305  through the base plate  165  is provided in the region of the axis of rotation  115 . In the illustrated embodiment, the aperture  305  is subsequently filled by means of an axial end of the electric motor  110 . In addition, a second aperture  310  is optionally provided through the base plate  165  and said second aperture is designed for the purpose of receiving an electronic control circuit for the purpose of controlling the electric motor  110 . The electronic control circuit can be cooled in this manner by means of the air that flows past said electronic control unit. 
         [0036]      FIG. 4  illustrates the housing cover  160  of the fan module  100  in  FIG. 1 . The housing cover  160  is illustrated in the correct position with respect to the illustration in  FIG. 3 , however without the module housing  155 . It is evident how the housing cover  160  closes the cooling air ducting  180  on the section between the cut-out  170  and the lower axial end of the electric motor  110  in  FIG. 1 . 
         [0037]    The cooling air ducting  180  extends radially from left to right in the direction of the axis of rotation  115 . A diverting element  410  is embodied on the housing cover  160  in the path of the cooling air and said diverting element divides the flow of cooling air into two flows that are preferably of equal magnitude. As the two currents flow onwards they are subsequently diverted in an inclined manner downwards and/or upwards, in that they are guided in inclined sections of the cooling air ducting  180 , are bordered by the housing cover  160 . In order to divert the two flows of cooling air axially to the brushes  150 , axially diverting elements  405  are embodied on the housing cover in regions that lie axially above the brushes  150  after mounting the housing cover  160  on the fan module  100 . It is preferred that the axial diverting elements  405  comprise in each case a pre-defined curvature along which the respective flow is guided in order to effect a low-loss deflection of approx. 90°. 
         [0038]      FIG. 5  illustrates a cross sectional view of the fan module  100  in  FIG. 1 . The illustration is in part transparent so that the elements can be seen in different axial positions along the axis of rotation  115 . 
         [0039]    The fan module  100  is arranged in an air duct  505  having a spiral shaped border. The air duct  505  is used for the purpose of collecting the air that is being accelerated radially by the fan wheel  105  in order to release the air through a tangential exhaust duct  510 .