Patent Publication Number: US-7585149-B2

Title: Fan variable immersion system

Description:
BACKGROUND 
   The present invention relates to a fan system including a rotating axial flow fan and a fan shroud. 
   Fan systems are known which include a rotating fan and a fan shroud. It is also known that the static pressure produced by a fan is a function of the immersion of the fan within the shroud, where immersion refers to how much, in the axial direction, of the outer periphery of the fan is surrounded by the fan shroud. It is also known that fan efficiency depends upon fan immersion. However, systems have not been provided for varying and controlling fan immersion. 
   SUMMARY 
   Accordingly, an object of this invention is to provide a system for reducing the level of emissions variability on engines. 
   A further object of the invention is to provide such a system which improves fan efficiency over a range of speeds. 
   These and other objects are achieved by the present invention, wherein a fan system includes a rotatable axial flow fan unit, a fan shroud unit adjacent to the fan unit and capable of surrounding at least a portion of an outer periphery of the fan unit; and an actuator coupled to one of the units and operable to move said one of the units with respect to the other of the units, thereby varying immersion of the fan unit within the shroud unit. The actuator may be coupled to the shroud unit and is operable to move the shroud unit with respect to the fan unit. A control unit controls the actuator to vary fan immersion as a function of sensed parameter signals, and thereby maximizes fan efficiency. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a fan assembly embodying the invention; 
       FIG. 2  is an end view of the fan assembly of  FIG. 1 ; 
       FIG. 3  is a side view of the fan assembly of  FIG. 1  with the actuator extended; and 
       FIG. 4  is a simplified schematic diagram of a control system the fan assembly of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1 and 2 , a fan and shroud assembly  10  includes a fan unit  12  which has fan blades  14  mounted on a shaft  16  which is rotated by a conventional fan driving mechanism (not shown). The assembly includes a shroud assembly  18  having a first fixed shroud  20  and a movable shroud  22  coupled thereto. Shroud  20  includes a hollow larger portion  24  and a hollow smaller diameter portion  26 . The larger portion  24  may be positioned to at least partially surround a heat exchange device (not shown), such as a vehicle radiator. Shroud portion  26  preferably has a set of helical threads  28  formed on its outer peripheral surface. Movable shroud  22  has a set of internal threads  30  for mating engagement with threads  28 . 
   An actuator  32 , such as an extendable piston or hydraulic cylinder has one end coupled to a bracket  34  on shroud  20  and another end coupled to a bracket  36  mounted on shroud  22 . As best seen in  FIG. 1 , when the actuator  32  is retracted, the shroud  22  only overlaps or surrounds a small end portion of the fan  12 . As best seen in  FIG. 3 , when the actuator  32  is extended, the shroud  22  overlaps or surrounds a larger portion of the fan  12 . Also, the hydraulic actuator  32  could be replaced with a linear electric or pneumatic actuator (not shown). 
   Referring now to  FIG. 4 , the control system  40  includes a fan immersion sensor  42  which senses how much of the fan blades  14  are immersed in or surrounded by the shroud  22 , a fan speed or rpm sensor  44 , and a coolant temperature sensor  46 . An electronic control unit (ECU)  48  receives signals from sensors  42 - 46  and generates an actuator control signal which is communicated to the actuator  32 . The ECU  48  is preferably programmed with an algorithm and look-up tables in accordance with desired static pressures at different fan speeds so that the immersion can be controlled so that the fan operates at maximum efficiency under different conditions. The immersion sensor  42  may e a cylinder position sensor installed in or on the cylinder  32 , or an ultrasonic position sensor installed between shroud  22  and shroud  20 . 
   While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. For example, the fan blades could be moved axially with respect to the shroud, instead of moving the shroud relative to the fan. The fan blades could be moved axially by with a sylphon type mechanism (a cylindrically symmetrical bellows), which could be heat actuated or hydraulically actuated. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.