Abstract:
A method is provided for controlling a roof vent fan assembly having a fan motor operably coupled to a fan. The method comprises: monitoring an operating condition of the fan motor; detecting a jam condition of the fan based on the operating condition of the fan motor; and, upon detecting the jam condition, stopping operation of the fan motor and subsequently restarting operation of the fan motor.

Description:
FIELD  
       [0001]     The present invention relates to methods and systems for controlling a roof vent fan assembly.  
       BACKGROUND  
       [0002]     Conventional applications for roof vent fans include campers, trailers, motor homes and other recreational vehicles where the enclosed space is relatively small and proper ventilation is desired to provide fresh air to the occupants of the space. Roof vent fans function to ventilate harmful fumes, pollutants, and excess heat out of the enclosed space into the atmosphere.  
         [0003]     Conventional roof vent fans include a housing adapted to be mounted to a roof. A fan assembly within the housing is driven by a fan motor. The motor may be controlled by one or more switches indicating an on/off state and a speed of the motor. A cover opens during fan operation to allow the fan access to the atmosphere. The cover closes when the fan is not operating to protect fan components as well as the enclosed space. There remains an unfilled need to automatically control conventional roof vent fans to operate more efficiently.  
         [0004]     More specifically, it can be foreseen that when the cover is open, debris may fall into the roof vent fan assembly. The debris may be large enough in size to prevent the fan from rotating thereby jamming the fan assembly. Considerable damage can be done to the motor and the fan assembly when the fan assembly is jammed. It is desirable to automatically detect a jammed fan assembly and automatically control the roof vent fan appropriately, thereby eliminating overheating as well as other potential damage.  
         [0005]     Furthermore, it can be foreseen that a power outage may occur, depriving the RV or motor home of power. If the roof vent fan assembly is operating when the power outage occurs, upon restoration of the power, a motor that controls the position of the cover may attempt to close an already closed cover thereby providing a force sufficient to damage the motor and cover components. It is desirable to automatically detect such conditions and automatically control the roof vent fan cover appropriately.  
       SUMMARY  
       [0006]     A method is provided for controlling a roof vent fan assembly having a fan motor operably coupled to a fan. The method comprises: determining wattage associated with the fan motor; detecting a jam condition of the fan based on the wattage associated with the fan motor; and, upon detecting the jam condition, controlling operation of the fan motor.  
         [0007]     In another aspect of the disclosure, the method includes: monitoring an operating condition of the fan motor; detecting a jam condition of the fan based on the operating condition of the fan motor; and, upon detecting the jam condition, stopping operation of the fan motor and subsequently restarting operation of the fan motor.  
         [0008]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view of an exemplary roof vent fan assembly;  
         [0010]      FIGS. 2A and 2B  are functional block diagrams illustrating exemplary roof vent fan control systems;  
         [0011]      FIG. 3  is a flowchart illustrating a control method for detecting and controlling a fan assembly when a jam occurs; and  
         [0012]      FIG. 4  is a flowchart illustrating a second embodiment of a control method for detecting and controlling a fan assembly when a jam occurs; 
     
    
     DETAILED DESCRIPTION  
       [0013]     The following description of various embodiments is merely exemplary in nature and is in no way intended to limit the present teachings, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify the same elements.  
         [0014]      FIG. 1  is a perspective view of an exemplary roof vent fan assembly  10 . The roof vent fan assembly  10  is generally comprised of a housing  12 , a fan blade assembly  14 , a fan motor  16  and a cover  18 . The housing  12  is sized to fit over an opening in a roof and adapted to be mounted to the roof. For example, the housing  12  includes a flange which extends outwardly from a periphery of the housing, where the flange has a plurality of holes formed therein. The holes in the flange are receptive of fasteners which may be used to mount the housing to the roof. Although the roof vent fan assembly  10  is particularly suited for use in a camper, trailer, motor home, or other type of recreational vehicle, it is also suitable for ventilating other enclosures of a comparable size, including in either a vertical or horizontal application.  
         [0015]     In further detail, the housing  12  provides a cylindrical cavity for housing the fan blade assembly  14 . The fan blade assembly  14  and the fan motor  16  are coupled to a mounting bracket  22  which extends over the top of the housing cavity. To provide ventilation, the cover  18  moves between an open and closed position. One or more hinges are used to couple the cover  18  to the housing  12 . A cover lift mechanism  26  pivots the cover  18  up or down as well as holds the cover  18  in a desired position. The lift mechanism  26  may be manually actuated (e.g., by a handle) and/or electrically driven by a motor. Different types of lift mechanisms are contemplated by this disclosure. A screen may extend over an underside of the cavity to prevent access to the fan blade from within the enclosure. The cover  18  is configured to mechanically actuate a position switch  28  as will be further described below.  
         [0016]      FIGS. 2A and 2B  are diagrams of exemplary roof vent fan control systems. The roof vent fan control system  30  is comprised of a wall controller  32 , a fan controller  34 , a blade assembly  14 , a fan motor  16  and power source  36 . The fan controller  34  is integrated into the vent fan assembly  10  described above; whereas, the wall controller  32  is configured to be mounted onto an internal wall surface of the recreational vehicle. It is also envisioned that the wall controller  32  may be detachable from the wall. The fan and wall controllers can be any known microprocessor, controller, or combination thereof known in the art. In various embodiments, the controllers include a microprocessor having read only memory (ROM), random access memory (RAM) and a central processing unit (CPU). The microprocessor may include any number of software control modules that provide the functionality for controlling a feature of roof vent fan assemblies. In various other embodiments, the controllers can be application specific integrated circuits (ASIC), electronic circuits, combinational logic circuits and/or other suitable components that provide the described functionality.  
         [0017]     In operation, a wall controller  32  receives user input  40  indicating desired fan parameters. At a minimum, the fan parameters include an on/off state of the fan and a desired fan speed. The wall controller  32  converts the user input  40  to corresponding signals and sends the signals to the fan controller  34 . The fan controller  34  regulates power to the fan motor  16  from a power source  36  based on signals received from a wall controller  38 . The fan motor  16  in turn drives the fan assembly  14 . The fan controller  34  may send notification signals to the wall controller  32  indicating a status of the fan assembly. In an exemplary embodiment, there is a wired connection between the wall controller  32  and the fan controller  34 . In an alternative embodiment, the wall controller  32  and fan controller  34  communicate via a wireless communication link using a communication protocol such Bluetooth, USB, IEEE 1394, or Wi-Fi.  
         [0018]     In  FIG. 2B , the roof vent fan control system  30 ′ further includes a motor  38  for actuating the cover  18 . The fan controller  34  also controls the operation of the cover motor  38  and thus the position of the cover  18 . In the event of a malfunction or loss of power, a knob  39  is preferably provided to manually adjust the position of the cover. The position switch  28  is electrically interposed between the fan controller  34  and the fan motor  16 . When the cover  18  is opened, the cover position switch  28  is in a closed state, thereby allowing current to flow to the fan motor  16 . When the cover  18  is in a closed position, the cover position switch is in an open state, thereby preventing current from flowing to the fan motor  16 .  
         [0019]     When power is restored following a power outage, conventional control schemes will try to close the cover  18  of the roof vent fan assembly  10 . In the control system  30  of the present disclosure, the fan controller  34  determines the cover position before closing the cover. If the fan controller  34  detects that the position switch  28  is in a closed state, it will drive the cover motor  38  to actuate the cover to a closed position. However, if the fan controller  34  detects that the position switch  28  is in an open state, no further action is taken, thereby preventing over tightening of the cover assembly.  
         [0020]     In one aspect of this disclosure, the roof vent fan control system  30  is operable to detect a jam condition of the fan assembly. When there is a jam condition, the fan blades as well as the drive shaft of the fan motor will stop rotating. This in turn causes a spike in the motor current which can be sensed by the fan controller. In addition, there will be an increase in the amount of power drawn by the fan motor, thereby leading to a decrease in voltage output by the power source. This change in the power source may also be monitored by the fan controller. Based on changes in these parameters, the fan controller can detect a jam condition of the fan blade and control the operation of the same accordingly.  
         [0021]      FIGS. 3 and 4  illustrate exemplary control schemes for a roof vent fan assembly  10 . Referring to  FIG. 3 , the fan controller monitors the wattage associated with the fan motor as indicated at  100 . When the wattage falls outside of a predetermined range, a jam condition is inferred. In an exemplary embodiment, the wattage is determined by multiplying the fan motor current by the voltage output of the power source. It is readily understood that other techniques may be employed to determine the wattage associated with the fan motor. Moreover, it is envisioned that the motor current or power source voltage individually as well as other parameters individually or in combination may be used to infer a jam condition.  
         [0022]     Upon detecting a jam condition, control increments a jam detection counter and stores a current fan speed at  120 . Control commands the fan motor to stop at  130  for a selectable period of time. The length of the delay period is based on the number of times a jam has been detected as indicated by the jam detection counter. For each time a jam condition is detected, the length of delay period is increased. Once the delay period has elapsed at  140 , control commands the fan motor to start at  150 . To facilitate jarring loose any obstruction in the fan, the fan motor is preferably started at the next highest fan speed. Control loops back and again processes the fan wattage at  100 . If the wattage is still outside of the predetermined range at  110 , then processing repeats in a manner as described above. When the wattage falls in the predetermined range, control resets the jam detection counter at  160 . Thus, control continues starting and stopping the fan motor until the jam occurrence is resolved.  
         [0023]     In an alternative approach, the fan motor will be cycled off and on a predetermined number of times as shown in  FIG. 4 . A single iteration of the jam detection method as described above in relation to  FIG. 3  is performed at  200 . If the jam detection counter is greater than a threshold X at  210 , the fan is commanded OFF at  220 . Otherwise control loops back and performs another iteration of the jam detection method. Control will continually perform iterations of the jam detection method until the jam detection counter is greater than the threshold X at  210 . If the jam detection threshold is greater than the threshold X at  210 , control will continue to command the fan OFF at  220  until a fan unit OFF command is received from the wall controller. If a fan unit OFF command is received from the wall controller at  230 , control resets the jam detection counter at  240 . The fan motor remains off until an ON command is received from the wall controller.  
         [0024]     It is to be understood that only the relevant steps of the methodology are discussed in relation to  FIGS. 3 and 4 , but that other software-implemented instructions may be needed to control and manage the overall operation of the system. Furthermore, the disclosure is merely exemplary in nature and, thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.