Patent Publication Number: US-2004040547-A1

Title: Self latching canister vent solenoid valve

Description:
CROSS REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM  
     [0001] This application claims the benefit of U.S. Provisional Application No. 60/407,762 (Attorney Docket No. 2002 P 14197 US) filed on Aug. 30, 2002 in the name of Kirk Ivens and Russell Miles Modien and entitled SELF LATCHING CANISTER VENT SOLENOID USING PERMANENT MAGNETS, which is incorporated by reference herein in its entirety. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] This invention relates to evaporative emission control systems for internal combustion engines, and more particularly, to a canister vent solenoid valve which utilizes a permanent magnet for maintaining valve position.  
       BACKGROUND OF THE INVENTION  
       [0003] Motor vehicles having an internal combustion engine typically include an evaporative emission control system for reducing fuel vapor emissions. Such systems include a vapor collection canister which serves to absorb fuel vapors that are generated within a fuel system. The canister includes a vent solenoid valve which is opened under the appropriate conditions so as to place the canister in fluid communication with atmospheric air. This enables vacuum generated by the engine to draw in atmospheric air through the canister and then draw out the fuel vapors from the canister as part of a process for purging the canister.  
       [0004] Alternatively, the vent solenoid valve is closed to isolate the canister from atmospheric air. This enables the performance of a selected on board diagnostic procedure for detecting whether there is a fuel vapor leak in the system that is above a predetermined level. The vent solenoid valve includes a solenoid for moving a valve element between the open and closed positions. In a conventional vent solenoid valve, the solenoid is energized in order to move the valve element to the closed position. Further, the solenoid must continue to be energized for the valve element to remain in the closed position. A spring is utilized to return the valve to the open position when power to the solenoid is removed.  
       [0005] However, the use of such vent solenoid valves increases the amount of components needed and thus ultimately increases costs. Further, many engines are becoming smaller in capacity, resulting in smaller capacity alternators and thus less electrical power which is available for energizing such solenoids.  
       SUMMARY OF THE INVENTION  
       [0006] The invention is directed to a vent solenoid valve for use in an automotive emission system. The vent valve includes a housing having a canister port and an atmospheric port. The housing includes a bobbin having a coil for generating a magnetic field wherein the bobbin includes an internal channel. A stator is located in an upper portion of the channel and a stop element is located near a lower portion of the channel. The vent valve further includes an armature having a permanent magnet and a valve element, wherein the magnet is located in the channel and is moveable therein to enable movement of the valve element between a closed position wherein the canister port is isolated from the atmospheric port and an open position for enabling fluid communication between the canister port and the atmospheric port. When the coil is energized with a predetermined polarity, the valve element moves to the open position and is kept in the open position by a first magnetic attraction between the magnet and the stator. Further, when the coil is energized with a reverse polarity, the first magnetic attraction is overcome to move the valve element to the closed position wherein the valve element is kept in the closed position by a second magnetic attraction between the magnet and the stop.  
       [0007] The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, may be best understood by reference to the following description taken in conjunction with the accompanying figures. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008]FIG. 1 is a cross sectional view of vent solenoid valve in accordance with the present invention.  
     [0009]FIG. 2 is an illustrative depiction of an emission control system which includes the vent solenoid valve. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0010] While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of FIGS.  1 - 2 .  
     [0011] Referring to FIG. 1, a cross sectional view of a vent solenoid valve  10  in accordance with the present invention is shown. The vent valve  10  includes a generally cylindrically shaped housing  12  having upper  14  and lower  16  walls and left  18  and right  20  side walls. The housing  12  includes a bobbin  22  having a center member  24  positioned between upper  26  and lower  28  flanges that lie circumferentially about a center axis  30 . A coil  32  is positioned between the upper  26  and lower  28  flanges. The bobbin  22  resides within an enclosure  34  fabricated from a ferromagnetic material such as steel. A connector  36  extends from the housing  12  which serves to transmit electrical power from a power source to the coil  32  for forming a magnetic field.  
     [0012] The center member  24  includes a channel  38  that extends between the upper  26  and lower  28  flanges and through the enclosure  34 . In addition, the housing  12  includes a stator element  40  having a head portion  42  and a stator shaft  44  that extends into the channel  38  to form a substantially T-shaped configuration. The stator element  40  is affixed to the bobbin  22  and is also fabricated from a ferromagnetic material.  
     [0013] An armature  46  is positioned in a cooperative relationship with the stator element  40  to form a solenoid. The armature  46  includes a valve shaft  48  located between a valve element  50  and a magnet element  52 . The magnet element  52  includes a permanent magnet  54  and is located in the channel  38  between a lower end  56  of the stator shaft  44  and a lip or stop  58  that extends from the enclosure  34 . The magnet element  52  may be moved along the center axis  30  within the channel  38  so as to enable upward and downward movement of the armature  46  relative to the stator element  40 .  
     [0014] The housing  12  further includes an internal passageway  60  located between the enclosure  34  and the lower wall  16 . Canister port walls  62  extend from the lower wall  16  to form a canister port  64  having a first passageway  66  which is in fluid communication with a vapor collection canister  84  (FIG. 2). A valve seat  68  for receiving the valve element  50  is formed at the intersection of the canister port walls  62  and the lower wall  16 . Atmospheric port walls  70  extend from the right side wall  20  to form an atmospheric port  72  having a second passageway  74  which is in fluid communication with atmospheric air through a filter  88  (FIG. 2).  
     [0015] In FIG. 1, the valve element  50  is shown in a closed position. In this position, the valve element  50  is in contact with the valve seat  68  to thus close the canister port  64  and isolate the canister port  64  from the atmospheric port  72 . In addition, the magnet element  52  is located adjacent the stop  58  to enable magnetic attraction between the magnet element  52  and the stop  58 . In accordance with the present invention, the magnetic attraction keeps the valve element  50  in the closed position. As such, electrical power is not needed to maintain the valve element  50  in the closed position.  
     [0016] The valve element  50  is also moveable to an open position. In the open position, the valve element  50  is located above the valve seat  68  to enable fluid communication between the canister port  64 , the internal passageway  60  and the atmospheric port  72 . The valve element  50  is moved to the open position by first energizing the coil  32  with electrical power having a predetermined polarity sufficient to overcome the magnetic attraction between the magnet element  52  and the stop  58 . The valve element  50  continues to move upward from the closed position until the magnet element  52  is adjacent the lower end  56 . This results in magnetic attraction between the magnet element  52  and the lower end  56  which serves to keep the valve element  50  in the open position. As such, electrical power is not needed to maintain the valve element  50  in the open position and may be turned off.  
     [0017] In order to move the valve element  50  back to the closed position, the coil  32  is again energized with electrical power, but with a reversed polarity, which is sufficient to overcome the magnetic attraction between the magnet element  52  and lower end  56 . The valve element  50  continues to move downward until contact is made between the valve element  50  and the valve seat  68  and the magnet element  52  is located adjacent the stop  58 . This enables magnetic attraction between the magnet element  52  and the stop  58  which serves to keep the valve element  50  in the closed position as previously described. As such, electrical power is not needed to maintain the valve element  50  in the closed position and may again be turned off.  
     [0018] Accordingly, the coil  32  is only energized to overcome the magnetic attraction between the magnet element  52  and either the stop  58  or lower end  56  and to move the valve element  50  to either the open or closed position. Further, the magnet element  52  serves to keep the valve element  50  in either the open or closed position. Once the valve element  50  is in either position, power to the coil  32  may be removed, resulting in less power usage than in conventional vent valves. In addition, the present invention also eliminates the need for a return spring to move the valve element  50  to its original position as in a conventional vent valve.  
     [0019] A switch may be used to provide feedback information regarding the position of the valve element to an engine electronic control unit (ECU)  80 . By way of example, a mechanical switch may be used that is actuated through contact with the armature  46  when the valve element  50  is in either the open or closed position, as desired. Actuation of the switch then enables the ECU  80  to determine the position of the valve element  50 .  
     [0020] Alternatively, a switch that does not require actual contact for actuation may be used such as a magnetic reed switch. Referring to FIG. 1, an illustrative depiction of a magnetic reed switch  76  is shown. The switch  76  includes two magnetizable contacts  78  located in a glass tube or other container  81  filled with a protective gas. The switch  76  is located adjacent the housing  12  such that when the valve element  50  is in the open position, the magnet element  52  is sufficiently close to the contacts  78  to cause the contacts  78  to become magnetized and attracted to each other. This closes the switch  76  and enables the ECU  80  to determine the position of the valve element  50 . When the magnet element  52  is moved away from the contacts  78 , the contacts  78  demagnetize and separate, thus opening the switch  76 . It is noted that the location of the switch  76  shown in FIG. 1 is for illustrative purposes only and that the switch  76  may be located such that the switch  76  is closed when the valve element  50  is in the closed position.  
     [0021] Referring to FIG. 2, the vent valve  10  in accordance with the present invention is shown in an emission control system  82 . The system  82  includes a leak detection monitor  85  which is used as part of a selected on board diagnostic procedure for determining whether there is a fuel vapor leak in the system  82  that is above a predetermined level.  
     [0022] The canister  84  is in fluid communication with a fuel tank  86  and includes carbon or other similar material which serves to absorb fuel vapors that are generated within the fuel tank  86  and in the emission control system  82 . The canister  84  includes the vent valve  10  which is opened under the appropriate conditions so as to place the canister  84  in fluid communication with atmospheric air through the filter  88  as described in relation to FIG. 1. Alternatively, the vent valve  10  is closed as previously described to isolate the canister  84  from atmospheric air so as to enable performance of the on board diagnostic procedure.  
     [0023] A canister purge valve  90  is located between the canister  84  and an engine intake manifold  92  of an internal combustion engine  94 . The canister purge valve  90  may be opened to place the canister  84  in fluid communication with the intake manifold  92 . Alternatively, the canister purge valve  90  may be closed to isolate the canister  84  from the intake manifold  92 . The opening and closing of both the canister purge valve  90  and the vent valve  10  is controlled by the ECU  80 .  
     [0024] Under the appropriate conditions, the canister  84  is purged so that fuel vapors collected within the canister  84  do not undesirably escape into the atmosphere. This is done by opening the canister purge valve  90  and the vent valve  10 , thus enabling vacuum which is present at the intake manifold  92  to draw in atmospheric air through the canister  84  and then draw out the fuel vapors from the canister  84 . The purged fuel vapors are then used in the normal combustion process. The ECU  80  determines when purging is to occur based on received signals indicative of various engine parameters. Further, the ECU  80  may be programmed to allow purging of the canister  84  at differential rates depending upon the prevailing engine operating conditions. As such, greater amounts of purging may be permitted at certain times while at other times lesser amounts may be allowed.  
     [0025] While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those skilled in the art in light of the foregoing description. In particular, it noted that more than one magnet may be used. Further, the entire enclosure  34  may be substituted with a separate stop element located near the bottom of the channel  38 . In addition, the vent valve  10  may be configured such that the magnet element  52  magnetically attracts a top portion of the enclosure  34  rather than the lower end  56  to move the valve element  50  to the open position. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.