Abstract:
An electric machine for a vehicle comprises a housing, a rotor shaft, a first fan member, and a second fan member. The housing includes a first end portion having at least one air inlet opening and an opposite second end portion having at least one air outlet opening. The rotor shaft extends through at least one of the first end portion and the second end portion and is configured to rotate relative to the housing. The first fan member is located within the housing and is mounted on the rotor shaft. The second fan member is located outside of the housing and is mounted on the rotor shaft. Rotation of the rotor shaft causes each of the first and second fan members to generate an airflow from the at least one air inlet opening to the at least one air outlet opening.

Description:
FIELD 
       [0001]    This disclosure relates to the field of electric machines and in particular to airflow systems for electric machines. 
       BACKGROUND 
       [0002]    A vehicle electrical system includes a battery, an engine, and an alternator among other components. The battery is typically used to supply a starter motor with electrical energy for starting the engine. The engine includes a rotating output that is used to drive a transmission of the vehicle for moving the vehicle. The alternator is connected to the rotating output of the engine and operates as an electrical energy generator. In particular, the alternator converts mechanical energy from the operating engine into electrical energy for consumption by the vehicle. In a common configuration, the electrical energy from the alternator charges the battery so that the battery is maintained at a state of charge sufficient for starting the engine. 
         [0003]    The typical alternator includes a stator and a rotor shaft supporting a field coil. The field coil is located in proximity to the stator, and a belt connects the rotor shaft and field coil to the rotating output of the engine. Operation of the engine results in rotation of the rotor shaft and the field coil relative to the stator. Current flowing through the rotating field coil induces a corresponding current in the stator. The corresponding current of the stator is rectified and conditioned to provide electrical energy for consumption by the vehicle. 
         [0004]    In addition to generating electrical energy, the alternator also generates heat. Specifically, the electrical interaction between the field coil and the stator heats the field coil and the stator. This heat radiates to each other component of the alternator and increases the overall temperature of the alternator. Typically, it is desirable to maintain the alternator within a particular range of operating temperatures; thus, most alternators include at least one fan that is configured to expel heat from the alternator. However, as customers require more output out of smaller machines, improved cooling methods become desirable, because prior art cooling methods are not optimized for cooling modern alternators. For example, a prior art alternator may include an internal fan and an external fan. In response to being rotated, the internal fan generates a first airflow and the external fan generates a second airflow. Instead of working together to optimally cool the alternator, portions of the airflows generated by the fans interfere and conflict with each other, thereby resulting in a non-optimized configuration that does not cool the alternator in the most effective manner. In the worst case, exhaust air from one fan tries to exit an outlet opening that also acts as an inlet opening for the other fan, resulting in interference of the airflows, such that efficient cooling of the alternator is diminished. In another example, a prior art alternator may include internal fans which are too small to effectively cool a high power alternator, or an external fan which is unable to provide desired cooling to all components simultaneously. 
         [0005]    Based on the above, further developments in the area of cooling fans for alternators are desirable. 
       SUMMARY 
       [0006]    According to an exemplary embodiment of the disclosure, an electric machine for a vehicle comprises a housing, a rotor shaft, a first fan member, and a second fan member. The housing including a first end portion having at least one air inlet opening and an opposite second end portion having at least one air outlet opening. The rotor shaft extends through at least one of the first end portion and the second end portion and is configured to rotate relative to the housing. The first fan member is located within the housing and is mounted on the rotor shaft. The second fan member is located outside of the housing and is mounted on the rotor shaft. Rotation of the rotor shaft causes each of the first and second fan members to generate an airflow from the at least one air inlet opening to the at least one air outlet opening. 
         [0007]    According to another exemplary embodiment of the disclosure, an electric machine for a vehicle comprises a housing, a stator, a field coil, a first fan member, and a second fan member. The stator is located within the housing. The field coil is located in proximity to the stator and is configured to rotate relative to the stator about an axis of rotation. The first fan member is located within the housing at a first end of the field coil and is configured to rotate with the field coil and to generate a first airflow primarily in an axial direction defined by the axis of rotation. The second fan member is located at a second opposite end of the field coil and is configured to rotate with the field coil and to generate a second airflow in the axial direction. The axial direction extends from the first fan member to the second fan member. 
         [0008]    According to yet another exemplary embodiment of the disclosure, an electric machine for a vehicle includes a housing, a rotor shaft, a first fan member, and a second fan member. The housing includes a first end portion, an opposite second end portion, and an axial portion extending from the first end portion to the second end portion. The first end portion includes at least one air inlet opening, and the second end portion includes at least one air outlet opening. The axial portion is void of the at least one air outlet opening. The rotor shaft extends through at least one of the first end portion and the second end portion, and is configured to rotate relative to the housing. The first fan member is located within the housing and is mounted on the rotor shaft. The second fan member is located outside of the housing and is mounted on the rotor shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]    The above-described features and advantages, as well as others, should become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying figures in which: 
           [0010]      FIG. 1  is a cross sectional view of an alternator assembly, as disclosed herein, including a front end fan member and a rear end fan member that are configured to generate complementary airflows; 
           [0011]      FIG. 2  is a perspective view of the rear end fan member of the alternator assembly of  FIG. 1 ; 
           [0012]      FIG. 3  is a plan view of the rear end fan member of the alternator assembly of  FIG. 1 ; 
           [0013]      FIG. 4  is a cross sectional view of the rear end fan member taken along line V-V of  FIG. 1 ; 
           [0014]      FIG. 5  is a perspective cross sectional view of a blade of the rear end fan member of the alternator assembly of  FIG. 1 ; 
           [0015]      FIG. 6  is an elevational view of a blade portion of the rear end fan member of the alternator assembly of  FIG. 1 ; 
           [0016]      FIG. 7  is a perspective view of the front end fan member of the alternator assembly of  FIG. 1 ; 
           [0017]      FIG. 8  is a cross sectional view of the alternator assembly of  FIG. 1 , showing airflows generated by the rear end fan member and the front end fan member; and 
           [0018]      FIG. 9  is a cutaway view of another embodiment of an alternator assembly including a rear end fan member and a front end fan member that are configured to generate complementary airflows. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that this disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one skilled in the art to which this disclosure pertains. 
         [0020]    As shown in  FIG. 1 , an alternator assembly  100  includes a housing  104 , a stator  108  located within the housing  104 , a rotor shaft  112 , a field coil  116 , a rear end fan member  120 , and a front end fan member  124 . The housing  104  includes a rear end portion  128 , an opposite front end portion  132 , and an axial portion  136  extending from the rear end portion  128  to the front end portion  132 . The rear end portion  128  is substantially circular and includes at least one air inlet  140  opening that extends completely through the rear end portion  128 . In  FIG. 1 , two of the air inlet openings  140  are partially shown. The air inlet openings  140  are formed as circular passages through the rear end portion  128 . In another embodiment, the rear end portion  128  includes from one to fifty of the air inlet openings  140 , and the openings  140  have any desired shape. 
         [0021]    The front end portion  132  is substantially circular and includes at least one air outlet opening  144  that extends completely through the front end portion  132 . In  FIG. 1 , two of the air outlet openings  144  are partially shown. The air outlet openings  144  are formed as circular passages through the front end portion  132 . In the illustrated embodiment, the air outlet openings  144  are aligned with the air inlet openings  140  in an axial direction  148 , which extends from the rear end portion  128  toward the front end portion  132 . In another embodiment, the front end portion  132  includes from one to fifty of the air outlet openings  144 , and the openings  144  have any desired shape. 
         [0022]    The axial portion  136  is substantially cylindrical and is terminated by the rear end portion  128  and the front end portion  132 . The axial portion  136  includes at least one air inlet opening  152 . In the illustrated embodiment, two of the inlet openings  152  are partially shown. The air inlet openings  152  are formed as circular passages through the axial portion  136 . In the exemplary embodiment of  FIG. 1 , the air inlet openings  152  are located between the front end portion  132  of the housing  104  and a plane  158  defined by the rear end fan member  120 . The air inlet openings  152  are located at any point on the axial portion  136  between the plane  158  and the front end portion  132 , such that no portion of the air inlet openings  152  overlaps with the rear end fan member in the axial direction  148 . Accordingly, there are no openings formed in the axial portion  136  between the plane  158  and the rear end portion  128  of the housing  104 . In another embodiment, the axial portion  136  includes from one to fifty of the air inlet openings  152 , and the openings  152  have any desired shape. Moreover, in at least one embodiment, the axial portion  136  is substantially imperforate except for the air inlet openings  152 , such that the axial portion  136  is completely void of all air outlets. 
         [0023]    With continued reference to  FIG. 1 , the rotor shaft  112  extends through shaft openings  156  defined in the rear end portion  128  and the front end portion  132  of the housing  104 . The rotor shaft  112  is configured for rotation relative to the housing  104  about an axis of rotation  160  that is parallel to the axial direction  148 . Bearings  164  are configured to rotatably support the rotor shaft  112 , and to prevent airflow through the openings  156 . A pulley  168  is fixedly mounted on the rotor shaft  112  and is configured to support an endless belt (not shown) for operably connecting the alternator assembly  100  to a motor (not shown). 
         [0024]    The field coil  116  is fixedly mounted on the rotor shaft  112  in proximity to the stator  108 , such that the field coil  116  is configured for rotation relative to the stator  108  about the axis of rotation  160 . The field coil  116  is operably connected to the stator  108 , in a manner known to those of ordinary skill in the art. 
         [0025]    The rear end fan member  120  is located adjacent to the rear end portion  128  of the housing  104  and is shown as an axial-flow fan. The rear end fan member  120  is fixedly mounted on the rotor shaft  112  for rotation with the rotor shaft  112 . In the illustrated embodiment, the rear end fan member  120  is located within the housing  104  between the air inlet openings  140  of the first end portion  128  and the air inlet openings  152  of the axial portion  136  along the axis of rotation  160 . The rear end fan member  120  is also located between the rear end portion  128  and the field coil  116  along the axis of rotation  160 . In another embodiment, the rear end fan member  120  is located outside of the housing  104  on the opposite side of the rear end portion  128 . 
         [0026]    An exemplary embodiment of the rear end fan member  120  is shown in  FIGS. 2-6 . The rear end fan member  120  includes a hub  172  and a plurality of blades  176 . The hub  172  defines a circular opening  180 , the center of which is aligned with the axis of rotation  160 . The diameter of the circular opening  180  is approximately the same as the diameter of the rotor shaft  112 . In one embodiment, the hub  172  is press fit onto the rotor shaft  112 . 
         [0027]    As shown in  FIG. 4 , the blades  176  extend radially away from the hub  172  for a radial distance  184  and axially away from the hub  172  for an axial distance  188 . Each blade  176  defines a generally radial portion  192 , a generally axial portion  196 , and flat plateau portion  198 . The axial portion  196  is angled with respect to the radial portion  192 , such that a plane defined by the axial portion  196  intersects a plane defined by the radial portion  192 . The plateau portion  198  is a substantially flat portion of the blade  176  that is bordered by a chamfered portion  200  ( FIG. 5 ). In the illustrated embodiment, the rear end fan member  120  defines twelve of the blades  176 ; however, in other embodiments, the rear end fan member  120  defines any desired number of the blades  176 . Moreover, in the illustrated embodiment, each blade  176  is imperforate. 
         [0028]    As shown in  FIG. 7 , an exemplary embodiment of the front end fan member  124  includes a hub  220 , a plurality of blades  222 , and a backplate  224 . The hub  220  is configured, in at least one embodiment, to be slip fit onto the rotor shaft  112  and clamped in place by a shaft nut (not shown). The blades  222  extend radially away from the hub  220 , and each blade  222  defines a radially inner portion  226  and a radially outer portion  228 . The radially inner portions  226  are configured to pull air in the axial direction  148  ( FIG. 1 ) when the front end fan member  124  is rotated. The radially outer portions  228  are configured to push air in a radially outward direction (radially away from the axis of rotation  160 ) when the front end fan member  124  is rotated. The backplate  224  is connected to at least the radially outer portions  228  and is substantially imperforate. The backplate  224  is configured at least partially to prevent airflow through the front end fan member  124  in the axial direction  148  ( FIG. 1 ). In another embodiment, the front end fan member  124  is provided as any desired type of fan member, including a fan member without a distinct radially inner portion  226  and a radially outer portion  228 . 
         [0029]    With reference again to  FIG. 1 , the front end fan member  124  is fixedly mounted on the rotor shaft  112  for rotation with the rotor shaft  112 . In the illustrated embodiment shown in  FIG. 1 , the front end fan member  124  is located outside of the housing  104  between the air outlet openings  144  and the pulley  168  along the axis of rotation  160 . In another embodiment, the front end fan member  124  is located inside of the housing  104  on the opposite side of the front end portion  132 , between the front end portion  132  and the field coil  116 . 
         [0030]    In operation, the alternator assembly  100  generates airflow through the housing  104  that efficiently cools the stator  108 , the field coil  116 , and any electronic components (such as a voltage regulator) located within or in proximity to the housing  104 . As shown in  FIG. 8 , during rotation of the rotor shaft  112 , the rear end fan member  120  generates an airflow  232  that extends through the housing  104  in primarily the axial direction  148 . In particular, the rear end fan member  120  pulls air into the housing  104  through air inlet openings  140  and pushes air out of the housing  104  through the air outlet openings  144 . The airflow  232  is described as being “primarily” in the axial direction  148 , because the rear end fan member  120  may generate smaller airflows (not shown) in a direction other than the axial direction  148 . For example, the smaller airflows generated by the rear end fan member  120  may flow somewhat in a radial direction, may circulate within the housing  104 , or may flow in any other direction. However, the rotation of the rear end fan member  120  predominately generates airflow  232 , which moves primarily in the axial direction  148  (e.g. the airflow  232  moves from left to right on the page as shown in  FIG. 1 , but not necessarily in a straight line). The rear end fan member  120  is distinguished from a radial fan member, which generates airflow primarily in a radial direction. 
         [0031]    Due at least in part to the gaps  240  between the blades  176 , the airflow  232  flows through the rear fan member  120  in the axial direction  148 . The airflow  232  is pushed toward the front end fan member  124  past the stator  108  and the field coil  116 , such that the airflow  232  carries heat away from the stator  108 , the field coil  116 , and the voltage regulator; thereby maintaining the stator  108 , the field coil  116 , and the voltage regulator at an optimized operating temperature. The number of the gaps  240  and the total area of the gaps  240  contributes to the volume of air that the airflow  232  carries through the rear end fan member  120 . 
         [0032]    During rotation of the rotor shaft  112 , the front end fan member  124  generates a primary airflow  236  that extends through the housing  104  in primarily the axial direction  148 . Specifically, the front end fan member  124  pulls air into the housing  104  through air inlet openings  140  and pulls air out of the housing  104  through the air outlet openings  144 . The front end fan member  124  directs the airflow  236  radially away from the rotor shaft  112  (relative to the axis of rotation  160 ) after the airflow  236  is pulled through the air outlet openings  144 . Also, the front end fan member  124  pulls air through gaps  240  ( FIG. 3 ) between the blades  176  of the rear end fan member  120 . In the illustrated embodiment, the airflow  236  is prevented from passing through the backplate  224 ; however, in other embodiments the backplate  224  may define openings (not shown) through which the airflow  236  may pass. 
         [0033]    The airflows  232 ,  236  generated by the fan members  120 ,  124  generate a low pressure space  244  within the housing  104  near the air inlet openings  152  in the axial portion  136  of the housing  104 . The air pressure in the low pressure space  244  is lower than an air pressure outside of the housing  104  near the air inlets  152 . Accordingly, the pressure differential created by the airflows  232 ,  236  induces another airflow  248  that is pulled into the housing  104  through the air inlet openings  152 , is pushed out of the housing  104  through the air outlets  144  by the rear end fan member  120 , and is pulled out of the housing  104  through the air outlets  144  by the front end fan member  124 . Accordingly, as shown in  FIG. 8 , no portion of the airflows  232 ,  236 ,  248  exit the housing through the axial portion  136 , which, as stated above, is void of all air outlets. 
         [0034]    The rear end fan member  120  and the front end fan member  124  are arranged in series, such that the fans  120 ,  124  work together to create the airflows  232 ,  236 ,  248 , which are primarily in the axial direction  148 . The fans  120 ,  124  are also described as being arranged in a serial configuration with respect to the axis of rotation  160  ( FIG. 1 ). Fan members arranged in a serial configuration have the same axis of rotation and generate airflows primarily in the same direction. Thus, in the embodiment of  FIG. 8 , the airflow  232  generated by the rear end fan member  120  and the airflow  236  generated by the front end fan member  124  combine serially to form a combined airflow  232 ,  236 ,  248  that extends from the air inlet openings  140 ,  152  to the air outlet openings  144 . 
         [0035]    In  FIG. 8 , the airflows  232 ,  236 ,  248  are shown as taking a particular path through the housing  104 . The actual paths of the airflows  232 ,  236 ,  248  may deviate from that shown in  FIG. 8 , due at least to turbulent air within the housing  104  generated by the rotating field coil  116 , for example. The turbulent air, among other factors, results in commingling of the airflows  232 ,  236 ,  248  within the housing  104 . Nonetheless, the airflows  232 ,  236 ,  248  each primarily flow in the axial direction  148 . 
         [0036]    As shown in  FIG. 9 , another embodiment of the alternator assembly  300  includes a housing  304 , a stator  308  located within the housing  304 , a rotor shaft  312 , a field coil  316 , a rear end fan member  320 , and a front end fan member  324 . Slip rings  326  are operably connected to the field coil  316  through the rotor shaft  312 , which rotates about an axis of rotation  360 . The housing  104  includes at least one air inlet  340  opening, at least one air inlet opening  352 , and at least one air outlet opening  344 . 
         [0037]    In operation, the alternator assembly  300  generates airflows  332 ,  336 ,  348  through the housing  304  that efficiently cool the stator  308 , the field coil  316 , and any electronic components (such as a voltage regulator) located within or in proximity to the housing  304 . In particular, rotation of the rear end fan member  320  generates the airflow  332 , which is pulled into the housing  304  through the air inlets  340  and pushed out of the housing  304  through the air outlets  344 . Rotation of the front end fan member  324  generates the airflow  336 , which is pulled into the housing  304  through the air inlets  340  and pulled out of the housing  304  through the air outlets  344 . The airflows  332 ,  336  induce the airflow  348 , which is pulled into the housing  304  through the air inlets  352 , pushed out of the housing  304  through the air outlets  344  by the rear end fan member  320 , and pulled out of the housing  304  through air outlets  344  by the front end fan member  324 . The rear end fan member  320  and the front end fan member  324  are arranged in a serial configuration with respect to the axis of rotation  360 . 
         [0038]    While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.