Patent Publication Number: US-11655824-B2

Title: Fan module including coaxial counter rotating fans

Description:
BACKGROUND 
     In some vehicles, a cooling fan is used to cool the vehicle engine during vehicle operation. For example, the cooling fan may be placed downstream of a heat exchanger used to cool engine coolant, and the cooling fan draws air through the heat exchanger. In some vehicles, the cooling fan is driven by the vehicle engine. However, fuel economy requirements are resulting in a shift from engine-driven cooling fans to electric motor-driven cooling fans. Use of electric motor-driven cooling fans in larger vehicles may be limited by the power of available electric motors. 
     SUMMARY 
     A first approach for overcoming the motor power limit includes dividing the power requirements between two motors. A second approach for overcoming the motor power limit includes improving fan efficiency, e.g., obtaining more air power for same electrical power. In some aspects, a counter rotating fan module is provided that combines dividing the power requirements between two motors and providing improved fan efficiency. Advantageously, the counter rotating fan module includes two axial flow fans and two motors in a single fan module. In the fan module, the two fans and corresponding motors are installed in a compact space (compared with side-by-side fans). 
     The action of a fan creates an inherent loss of kinetic energy by introducing rotation (swirl) in the air leaving the fan. In the case of a single fan, the energy in the swirl component of the flow is dissipated without doing useful work. In the fan module, a second axial flow fan is placed downstream from the first axial flow fan with respect to the direction of air flow through the fan module so that the fans rotate about a rotational axis that is approximately common to both fans, and so that the fans are counter-rotating (e.g., the first fan and the second fan rotate in opposite directions). It is understood that, in use, the rotational axes of the first and second fans may not be precisely co-linear. In some embodiments, the term “approximately common” is used to indicate that the fan rotational axes are co-linear within twelve degrees of rotation and/or an offset of up to twelve percent of the downstream fan diameter, as measured between the intersections of the two fan rotation axes with a plane that passes through the forward-most portion of the hub of the second fan. In other embodiments, the term “approximately common” is used to indicate that the fan rotational axes are co-linear within six degrees of rotation and/or an offset of up to six percent of the downstream fan diameter. In still other embodiments, the term “approximately common” is used to indicate that the fan rotational axes are co-linear within three degrees of rotation and/or an offset of up to three percent of the downstream fan diameter. The first fan generates air flow through the fan module that includes axial and tangential flow components. The second fan has substantially the same diameter as the first fan, and is configured to remove the tangential flow component from the air flow through the fan module. As a result, the second fan recovers the energy from the swirl of the air flow leaving the upstream fan. Additionally, the fan module is configured so that the flow leaving the second fan has little or no swirl, whereby, there is no resulting loss of kinetic energy due to the swirl. As a result, the combination of the two counter-rotating fans can operate more efficiently than a single fan. 
     In the fan module, each axial flow fan is driven by a separate motor. Each motor is supported within a shroud by a dedicated motor carrier, and each fan is supported on a corresponding motor such that the fan is disposed upstream of the respective motor carrier. 
     Each shroud includes a barrel, the motor carrier that supports the respective motor, and spoke-like vanes that support the motor carrier within the barrel. The vanes are disposed in the path of the air flowing through the shroud. Each vane has a profile, and includes a leading end and a trailing end that is opposed to the leading end. In most cases, it is advantageous to minimize the effect of the vanes on the air flowing through the shroud. To this end, the shroud of the first axial flow fan includes vanes that are configured so that a line extending between the leading end and the trailing end is angled relative to the fan rotational axis. In some embodiments, the line is angled so as to align with the swirl of the first fan. In the shroud of the second axial flow fan, the vanes are aligned axially (e.g., parallel to the fan rotational axis). 
     In some aspects, a fan module for an automotive cooling system includes a first fan that is configured to rotate about a fan rotational axis and a second fan that is configured to rotate about a second axis. The second fan is disposed downstream of the first fan with respect to the direction of airflow through the fan module, and the second axis is approximately common with the fan rotational axis. The fan module includes a first motor configured to drive the first fan to rotate about the fan rotational axis in a first direction and a second motor configured to chive the second fan to rotate about the second axis in a second direction. The second direction is opposed to the first direction. The fan module includes a first shroud that supports the first motor. The first shroud includes a first barrel that surrounds the fan rotational axis, a first motor carrier that is disposed inwardly with respect, to the first barrel, and first vanes that extend between the first barrel and the first motor carrier. The fan module also includes a second shroud that supports the second motor. The second shroud includes a second barrel that surrounds the fan rotational axis, a second motor carrier that is disposed inwardly with respect to the second barrel, and second vanes that extend between the second barrel and the second motor carrier. The first motor is supported by the first motor carrier, the second motor is supported by the second motor carrier, the first motor carrier is disposed downstream from the first fan with respect to the direction of air flow through the fan module, and the second motor carrier is disposed downstream from the second fan with respect to the direction of air flow through the fan module. Each first vane has a first nose that faces the direction of air flow through the fan module, and a first tail that is opposed to the first nose. A first line that extends between the first nose and the first tail is angled at a first angle relative to the fan rotational axis. Each second vane has a second nose that faces the direction of air flow through the fan module, and a second tail that is opposed to the second nose. A second line that extends between the second nose and the second tail is angled at a second angle relative to the second axis. The second angle is different than the first angle. 
     In some embodiments, the first angle is aligned with air flow discharged from the first fan. 
     In some embodiments, the first angle is a non-zero angle. 
     In some embodiments, the second angle is approximately zero. 
     In some embodiments, the second line is parallel to the second axis. 
     In some embodiments, the fan module includes an air guide that supports the first shroud and is configured to provide an air flow passage between the first fan and a heat exchanger, and the second shroud is supported on the first shroud. 
     In some embodiments, the first shroud is integral with the air guide. 
     In some embodiments, the first vane includes opposed first air flow surfaces that extend between the first nose and the first tail, and the distance between the respective first air flow surfaces is small relative to a distance between the first nose and the first tail. In addition, the second vane includes opposed second air flow surfaces that extend between the second nose and the second tail, and the distance between the respective second air flow surfaces is small relative to a distance between the second nose and second tail. 
     In some aspects, an automotive cooling system comprising a heat exchanger and a fan module configured to draw air through the heat exchanger. The fan module includes a first fan that is configured to rotate about a fan rotational axis and a second fan that is configured to rotate about a second axis. The second fan is disposed downstream of the first fan with respect to the direction of airflow through the fan module, and the second axis is approximately common with the fan rotational axis. The fan module includes a first motor configured to drive the first fan to rotate about the fan rotational axis in a first direction, and a second motor configured to drive the second fan to rotate about the second axis in a second direction, where the second direction is opposed to the first direction. The fan module includes a first shroud that supports the first motor. The first shroud includes a first barrel that surrounds the fan rotational axis, a first motor carrier that is disposed inwardly with respect to the first barrel, and a first vane that extends between the first barrel and the first motor carrier. The fan module includes a second shroud that supports the second motor. The second shroud includes a second barrel that surrounds the fan rotational axis, a second motor carrier that is disposed inwardly with respect to the second barrel, and a second vane that extends between the second barrel and the second motor carrier. The first motor is supported by the first motor carrier, the second motor is supported by the second motor carrier, the first motor carrier is disposed downstream from the first fan with respect to the direction of air flow through the fan module, and the second motor carrier is disposed downstream from the second fan with respect to the direction of air flow through the fan module. The first vane has a first nose that faces the direction of air flow the fan module, and a first tail that is opposed to the first nose. A first line that extends between the first nose and the first tail is angled at a first angle relative to the fan rotational axis. The second vane has a second nose that faces the direction of air flow through the fan module, and a second tail that is opposed to the second nose. A second line that extends between the second nose and the second tail is angled at a second angle relative to the second axis. The second angle is different than the first angle. 
     In some embodiments, the first angle is aligned with air flow discharged from the first fan. 
     In some embodiments, the first angle is a non-zero angle. 
     In some embodiments, the second angle is approximately zero. 
     In some embodiments, the second line is parallel to the second axis. 
     In some embodiments, an air guide that supports the first shroud and is configured to provide an air flow passage between the first fan and a heat exchanger, and the second shroud is supported on the first shroud. 
     In some embodiments, the first shroud is integral with the air guide. 
     In some embodiments, the first vane includes opposed first air flow surfaces that extend between the first nose and the first tail, and the distance between the respective first air flow surfaces is small relative to a distance between the first nose and the first tail. In addition, the second vane includes opposed second air flow surfaces that extend between the second nose and the second tail, and the distance between the respective second air flow surfaces is small relative to a distance between the second nose and second tail. 
     In some aspects, a method of manufacturing a fan module for a vehicle is provided. The fan module includes a first fan, a first motor configured to drive the first fan to rotate about a fan rotational axis in a first direction, and a first shroud that supports the first motor relative to the first fan via a first motor carrier that is disposed downstream of the first fan with respect to the direction of air flow through the fan module. The fan module includes a second fan that is disposed downstream of the first fan with respect to the direction of airflow through the fan module, and a second motor configured to drive the second fan to rotate about a second axis in a second direction, where the second direction is opposed to the first direction and the second axis is approximately common with the fan rotational axis. The fan module includes a second shroud that supports the second motor relative to the second fan via a second motor carrier that is disposed downstream of the second fan with respect to the direction of air flow through the fan module. The method includes assembling a first subassembly that includes the first fan, the first shroud, the first motor carrier and the first motor, assembling a second subassembly that includes the second fan, the second shroud, the second motor carrier and the second motor, and assembling the first sub assembly with the second subassembly to provide a third subassembly in which the second fan is disposed downstream relative to the first fan with respect to a direction of air flow through the first fan. 
     In some embodiments, the fan module comprises an air guide, and the method includes assembling the third subassembly with the air guide. 
     In some embodiments, the hi some embodiments, the first shroud is integrally formed with an air guide, and the method step of assembling the first sub assembly with the second subassembly to provide a third subassembly includes securing the second subassembly to an end of the first shroud. 
     In some embodiments, the first shroud includes a first barrel that surrounds the fan rotational axis the first motor carrier that is disposed inwardly with respect to the first barrel, and first vanes that extend between the first barrel and the first motor carrier. In addition, the second Shroud includes a second barrel that surrounds the fan rotational axis, the second motor carrier that is disposed inwardly with respect to the second barrel, and second vanes that extend between the second barrel and the second motor carrier. Each first vane has a first nose that faces the direction of air flow exiting the first fan, and a first tail that is opposed to the first nose, and a first line that extends between the first nose and the first tail is angled at a first angle relative to the fan rotational axis. Each second vane has a second nose that faces the direction of air flow exiting the second fan, and a second tail that is opposed to the second nose, and a second line that extends between the second nose and the second tail is angled at a second angle relative to the second axis. The second angle is different than the first angle. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a perspective view of a fan module that includes two, co-axial, counter-rotating axial flow fans. 
         FIG.  2    is a side cross-sectional view of the fan module of  FIG.  1    as seen along line  2 - 2  of  FIG.  1   . 
         FIG.  3    is an enlarged view of a portion of  FIG.  2    as indicated by the reference label “ FIG.  3   ” in  FIG.  2   . 
         FIG.  4    is an exploded view of the fan module of  FIG.  1   . 
         FIG.  5    is a side cross-sectional view of a portion of the fan module of  FIG.  1    as seen along line  5 - 5  of  FIG.  1   . 
         FIG.  6    is an enlarged view of a portion of  FIG.  5    as indicated by the reference label “ FIG.  6   .” 
         FIG.  7    is an enlarged view of a portion of  FIG.  5    as indicated by the reference label “ FIG.  7   .” 
         FIG.  8    is an exploded view of an alternative embodiment fan module. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS.  1 - 4   , a fan module  1  of the type used to cool the engine of a motor vehicle includes an air guide  2 , a first motor  30  coupled to the air guide  2  via a first shroud  40 , and a first axial flow fan  20  coupled to, and driven by, the first motor  30 . In addition, the fan module  1  includes a second motor  60  coupled to the air guide  2  via, a second shroud  80 , and a second axial flow fan  50  coupled to, and driven by, the second motor  60 . In the illustrated embodiment, the first and second motors  30 ,  60  may be, for example, brushless DC motors. The first and second motors  30 ,  60  each drive a respective fan  20 ,  50  about a fan rotational axis  12  that is approximately common to both fans  20 ,  50 . In the fan module  1 , the second fan  50  is disposed downstream from the first fan  20  with respect to the direction of airflow through the fan module  1 , where the direction of airflow through the fan module  1  is represented by an arrow having reference number  10 . The first and second fans  20 ,  50  are counter-rotating such that the first fan  20  and the second fan  50  rotate in opposite directions. The first and second shrouds  40 ,  80  include features that improve the efficiency of the fan module  1 , as discussed below. 
     The air guide  2  is configured to be coupled to a heat exchanger (not shown) in a “draw-through” configuration, such that the first and second fans  20 ,  50  draw an airflow through the heat exchanger. Alternatively, the fan module  1  may be coupled to the heat exchanger in a “push-through” configuration (not shown), such that the first and second fans discharge an airflow through the heat exchanger. 
     In the illustrated embodiment, the air guide  2  is a molded, one-piece tube that provides an airflow passage between the heat exchanger and the first and second fans  20 ,  50 . The air guide  2  includes a frame portion  4  and a conical portion  6  that protrudes from the frame portion  4 . The frame portion  4  has a rectangular profile and is configured to be secured to the heat exchanger via known connection techniques and/or using any of a number of different connectors. The conical portion  6  is generally conical in shape, and includes a first end  8  that is joined to the frame portion  4 , and a second end  9  that is spaced apart from the first end  8 . The conical portion second end  9  has a smaller diameter than the conical portion first end  8  whereby the conical portion  6  is angled relative to the direction  10  of airflow through the air guide  2 . In the illustrated draw-through configuration, the conical portion second end  9  is downstream from the conical portion first end  8  with respect to the direction  10  of airflow through the fan module  1 . 
     The first fan  20  is an axial flow fan that includes a first central hub  22  and first blades  24  that extend radially outwardly from the hub  22 . In some embodiments, the first central hub  22  and the first blades  24  are formed as a single piece, for example in an injection molding process. Each first blade  24  includes a first root  26  coupled to the first central hub  22  and a first tip  28  that is spaced apart front the first root  26 . The surfaces of each first blade  24  have a complex, three-dimensional curvature that is determined by the requirements of the specific application. The direction of the air flow that is discharged from the first fan  20  is dependent at least in part on the blade curvature, and includes an axial flow component and a tangential flow component. As used herein, the term “axial flow component” refers to a component of air flow that flows in parallel to the direction  10  of air flow through the fan module  1 . In the illustrated embodiment, the axial flow component is also parallel to the fan rotational axis  12 . As used herein, the term. “tangential flow component” refers to a component of air flow that flows in a direction that is tangential to a circle defined by the rotating first tips  28 , and may also be referred to as “swirl.” 
     The first central hub  22  is mechanically connected to the first motor  30  in such a way that the first fan  20  is driven for rotation about the fan rotational axis  12  by the first motor  30 , and is supported relative to the air guide  2  by the first motor  30 . The first fan  20  rotates about the fan rotational axis  12  in a first direction (represented by an arrow having a reference number  14 ), for example in a clockwise direction when viewed in a direction  10  parallel to the direction of air flow through the fan module  1 . 
     Similarly, the second fan  50  is an axial flow fan that includes a second central hub  52  and second blades  54  that extend radially outwardly from the second central hub  52 . In some embodiments, the second central hub  52  and the second blades  54  are formed as a single piece, for example in an injection molding process. Each second blade  54  includes a second root  56  coupled to the second central hub  52  and a second tip  58  that is spaced apart from the second root  56 . The surfaces of each second blade  54  have a complex, three-dimensional curvature that is determined by the requirements of the specific application. The direction of the air flow that is discharged from the second fan  50  is dependent at least in part on the blade curvature. In this counter-rotating arrangement, the second blades  54  are shaped to remove the tangential flow component or swirl imparted to the air flow through the fan module  1  by the first fan  20 . 
     The second central hub  52  is mechanically connected to the second motor  60  in such a way that the second fan  50  is driven for rotation about the fin rotational axis  12  by the second motor  60 , and is supported relative to the air guide  2  by the second motor  60 . The second fan  50  rotates about the fan rotational axis  12  in a second direction (represented by an arrow having a reference number  16 ), for example in a counter-clockwise direction when viewed in a direction parallel to the direction  10  of air flow through the fan module  1 . 
     Referring to  FIGS.  4 - 7   , the first shroud  40  supports the first motor  30  relative to the air guide  2 . The first shroud  40  includes a first barrel  41 , a first motor carrier  42  that is spaced apart from, and disposed inwardly relative to, the first barrel  41 , and first vanes  43  that extend radially between the first barrel  41  and the first motor carrier  42 . 
     The first barrel  41  is a ring-shaped band, and is configured to be joined to the air guide  2 . For example, in some embodiments, an outer surface of the first barrel  41  may include mounting features  49  having through holes (pot shown) that are axially aligned with corresponding openings (not shown) in the conical portion second end  9 . Fasteners (not shown) may extend through the through holes of the mounting features  49  and engage with the openings in the conical portion  6 , whereby the barrel  41  is secured to the conical portion second end  9 . The first barrel  41  may have a double-wall structure that includes an inner wall  32  and an outer wall  33 . In some embodiments, the downstream end  34  of the first barrel outer wall  33  may be scalloped. The scallops  35  are formed due to removal of material between the first vanes  43  for the purpose of fan module weight reduction. 
     The first motor carrier  42  is a generally ring-shaped structure having an outer diameter that is less than a diameter of the first barrel  41  The first motor carrier  42  is concentric with the first barrel  41 , and supports the first motor  30 . Although the first motor carrier  42  is surrounded by the first barrel  41  in the illustrated embodiment, it is not limited to this configuration. For example, in some embodiments, the first motor carrier  42  may be disposed slightly upstream or downstream from the first barrel  41  with respect to the direction  10  of airflow through the fan module  1 . The first motor  30  is supported by the first motor carrier  42  in such a way that the first fan  20  is disposed upstream of the first motor carrier  42  with respect to the direction  10  of air flow through the fan module  1 . 
     The first vanes  43  support the first motor carrier  42  relative to the first barrel  41 . To this end, each first vane  43  includes a rounded leading end or nose  44  that faces into, or upstream with respect to, the direction  10  of air flow through the fan module  1 , and a rounded trailing end or tail  45  that is opposed to the nose  44  (e.g., faces away front or is downstream with respect to, the direction  10  of air flow through the fan module  1 . Each first vane  43  includes opposed air flow surfaces  47 ,  48  that extend between the nose  44  and the tail  45 . When viewed in a cross-section that is obtained by taking a cylindrical section of the first shroud  40  in which the cylinder used to form the section is concentric with the rotation axis of the first fan  20  and passes through the first vanes  43  (see, for example,  FIG.  6   ), the air flow surfaces  47 ,  48  are linear and parallel to each other. Each first vane is a thin beam in that the distance between the air flow surfaces  47 ,  48  is small relative to a distance between the nose  44  and the tail  45 . 
     Each first vane  43  is at an angle θ 1  (e.g., is at a non-zero angle) relative to the fan rotational axis  12 . In particular, a first line  46  that extends between the nose  44  and the tail  45 , and is parallel to the air flow surfaces  47 ,  48 , is at an angle θ 1  (e.g., at a non-zero angle) relative to the fan rotational axis  12 . More specifically, the first line  46  corresponds to the longest straight line that can be drawn through the cylindrical cross section of the first vane  43 . 
     The specific angle θ 1  that is used is determined by the requirements of the specific application. In the some embodiments, each first vane  43  is designed to be aligned with the air flow leaving the first fan  20  at all radii. In other words, the angle θ 1  is set so that the first line  46  is aligned with the an flow exiting the first fan  20 . By aligning the first line  46  with the tangential component of the air flow exiting the first fan  20 , the disruptive effect of the presence of the first vanes  43  in the path of the air flow is minimized (e.g., air flow losses are minimized). Since the air flow leaves the first fan  20  at an angle that varies from blade root  26  to blade tip  28 , for each vane  43 , the angle θ 1  varies from the first vane inner end  37  to the first vane outer end  39 . In the illustrated embodiment, for a given radius, the first vane  46  is at an acute angle, such as a 45 degree angle, relative to the fan rotational axis  12 . 
     The second shroud  80  supports the second motor  60  relative to the air guide  2 . The second shroud  80  includes a second barrel  81 , a second motor carrier  82  that is spaced apart from, and disposed inwardly relative to, the second barrel  81 , and second vanes  83  that extend radially between the second barrel  81  and the second motor carrier  82 . 
     The second barrel  81  is a ring-shaped band, and is configured to be joined to the downstream end of the first barrel  41 . For example, in some embodiments, an outer surface of the second barrel  81  may include mounting features  89  that align with corresponding mounting features  49  provided on the outer surface of the first barrel  41 . The mounting features  89  of the second barrel  81  include through holes, and the fasteners may extend through the through holes of the mounting features  49 ,  89  of both the first and second barrels  41 ,  81  and engage with the openings in the conical portion  6 , whereby the barrel  41  is secured to the conical portion second end  9 . 
     The second barrel  81  may have a double-wall structure that includes an inner wall  62  and an outer wall  63 . In some embodiments, the downstream ends  64  of the second barrel inner wall  62  and outer wall  63  may be scalloped. The scallops  65  are formed due to removal of material between the second vanes  83  for the purpose of fan module weight reduction. 
     The upstream end  66  of the second barrel  81  may include a collar  68  that protrudes axially toward the first barrel  41 . The collar  68  is dimensioned to correspond to an outer diameter of the first barrel inner wall  32 , and is received within space between the first barrel inner and outer walls  32 ,  33  when the second barrel  81  is assembled with the inner barrel  41 . The collar  68  serves to locate the second barrel  81  with respect to the first barrel  41 , and also facilitates an air-tight joint between the first and second barrels  41 ,  81 . 
     The second motor carrier  82  is a generally ring-shaped structure having an outer diameter that is less than a diameter of the second barrel  81  The second motor carrier  82  is concentric with the second barrel  81 , and supports the second motor  60 . In the illustrated embodiment, the second motor carrier  82  is surrounded by the second barrel  81 , but is not limited to this configuration. For example, in some embodiments, the second motor carrier  82  may be disposed slightly upstream or downstream from the second barrel  81  with respect to the direction  10  of airflow through the fan module  1 . The second motor  60  is supported by the second motor carrier  82  in such a way that the second fan  50  is disposed upstream of the second motor carrier  82  with respect to the direction  10  of air flow through the fan module  1 . 
     The second vanes  83  support the second motor carrier  82  relative to the second barrel  81 . To this end, each second vane  83  includes a rounded leading end or nose  84  that faces into, or upstream with respect to, the direction  10  of air flow through the fan module  1 , and a rounded trailing end or tail  85  that is opposed to the nose  84  (e.g., faces away from, or downstream with respect to, the direction  10  of air flow through the fan module  1 . Each second vane  83  includes opposed air flow surfaces  87 ,  88  that extend between the nose  84  and the tail  85 . When viewed in a cross-section obtained by taking a cylindrical section of the second shroud  80  in which the cylinder used to form the section is concentric with the rotation axis of the second fan  50  and passes through the second vanes  83  (see, for example,  FIG.  7   ), the air flow surfaces  87 ,  88  are linear and parallel to each other. Each second vane  83  is a thin beam in that the distance between the air flow surfaces  87 ,  88  is small relative to a distance between the nose  84  and the tail  85 . 
     Each second vane  83  is parallel to the fan rotational axis  12 . In particular, a second line  86  that extends between the nose  84  and the tail  85 , and is parallel to the air flow surfaces  87 ,  88 , is set at an angle θ 2  relative to the fan rotational axis  12 . More specifically, the second line  86  corresponds to the longest straight line that can be drawn through the cylindrical cross section of the second vane  83 . The angle θ 2  of the second line  86  is oriented so as to match the direction of air flow exiting the second fan  50  at all radii. Since the tangential component of air flow is removed from the overall air flow by the shape of the blades  54  of the second fan  50 , the second line  86  is set as parallel to the fan rotational axis  12  (e.g., angle θ 2  is approximately zero) for all radii. It is understood that, in use, the second line  86  and the fan rotational axis  12  may not be precisely parallel. In some embodiments, the term “approximately zero” is used to indicate that the second line  86  is parallel to the fan rotational axis  12  within twelve degrees. In other embodiments, the term “approximately zero” is used to indicate that the second line  86  is parallel to the fan rotational axis  12  within six degrees. In still other embodiments, the term “approximately zero” is used herein to indicate that the second line  86  is parallel to the fan rotational axis  12  within three degrees. 
     When the fan module  1  is in use, air enters the first fan  20  in a direction that is parallel with the fan rotational axis  12 . The first fan  20  introduces swirl within the air guide  2 . That is, the air flow leaving the first fan  20  includes a component of flow that travels in a tangential direction relative to the fan rotational axis  12 . The swirl has the same direction as the rotation of the first fan  20 . 
     The air leaving the first fan  20  passes through the first vanes  43 , which are downstream with respect to the first fan  20 . The first vanes  43  are set at an angle substantially aligned with the swirl of the air passing through, so as to present minimum resistance to the air flow at this location. 
     After exiting the first fan  20  and the first shroud  40 , the flow of air, including the swirl imparted by the first fan  20 , enters the second fan  50 . The second fan  50  applies a swirl (e.g., a “counter-swirl”) to the flow in the opposite direction. The counter swirl imparted by the second fan  50  substantially counteracts the swirl introduced by the first fan  20 . As a result, the air flow leaving the second fan  50  is substantially parallel with the fan rotational axis. 
     The air leaving the second fan  50  passes through the second vanes  83 . The second vanes  83  are set at an angle substantially aligned with the rotational axis of the second fan  50 , so as to present minimum resistance to the air flow. 
     Referring to  FIG.  8   , an alternative embodiment fan module  100  is similar to the fan module  1  described above with respect to  FIGS.  1 - 4   , and common reference numbers are used to refer to common elements. The fan module  100  shown in  FIG.  8    differs from the fan module  1  described above with respect to  FIGS.  1 - 7    in that the fan module  100  includes a modified air guide  102 . Like the air guide  2  of the previous embodiment, the modified air guide  102  includes the frame portion  4  and the conical portion  6  that extends from the frame portion  4 . In addition, the modified air guide  102  includes the first shroud  140  formed integrally with the conical portion  6  so as to protrude from the conical portion second end  9 . By forming the first shroud  140  and the air guide  102  as a single piece, the number of parts and assembly costs are reduced. In the fan module  100 , the second shroud  80  is secured to the downstream end  34  of the first barrel  41 . 
     Although the first and second shrouds include the motor carriers  42 ,  82  and the barrels  41 ,  81  that are generally circular in profile, the motor carriers  42 ,  82  and the bands  41 ,  81  are not limited to having a generally circular profile. For example, the motor carriers  42 ,  82  may be shaped and dimensioned to accommodate the respective motors  30 ,  60 , and the barrels  41 ,  81  may be shaped and dimensioned to accommodate the shape and dimensions of a portion of the inner surface of the air guide  2 . Moreover, in some embodiments, the motor carriers  42 ,  82  may not have the same shape as the barrels  41 ,  81 , and/or the motor carriers  42 ,  82  may not be concentric with the barrels  41 ,  81 . 
     Although in the illustrated embodiment, the air flow surfaces  47 ,  48 ,  87 ,  88  of the vanes  43 ,  83 , when viewed in cross-section, are linear and parallel to each other, the vanes  43 ,  83  are not limited to this configuration. The cross-sectional shape of the vanes  43 ,  83  is determined by the requirements of the specific application. 
     Selective illustrative embodiments of the fan module are described above in some detail. It should be understood that only structures considered necessary for clarifying the fan module have been described herein. Other conventional structures, and those of ancillary and auxiliary components of the fan module, are assumed to be known and understood by those skilled in the art. Moreover, while a working example of the fan module has been described above, the fan module is not limited to the working example described above, but various design alterations may be carried out without departing from the fan module as set forth in the claims.