Abstract:
A solenoid for use in valves used in evaporative emission control systems, such as canister purge valves or vent solenoid valves. The solenoid includes a housing having an inlet port and an outlet port. The housing further includes a guide element having a bobbin section. A valve shaft is slidably mounted to the guide element, wherein the valve shaft includes a permanent magnet and a valve element. The valve element is movable between a closed position wherein the inlet port is closed and an open position wherein the inlet port is opened. A coil is formed on the bobbin adjacent the magnet. In use, the coil generates directional magnetic fields oriented to cause the magnet to be repelled to move the valve element to the open position and oriented to cause a magnetic attraction with the magnet to move the valve element to the closed position.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to evaporative emission control systems for internal combustion engines, and more particularly, to a valve having a bipolar coil for generating magnetic fields which interact with a permanent magnet to selectively open and close a valve element.  
       BACKGROUND OF THE INVENTION  
       [0002]     Motor vehicles having an internal combustion engine typically include an evaporative emission control system which serves to reduce fuel vapor emissions. Such systems include a vapor collection canister having carbon or other material which serves to absorb fuel vapors that are generated within a motor vehicle fuel system. A canister purge valve is located between the canister and an engine intake manifold. The canister purge valve may be opened or closed to either place the canister in fluid communication with the engine intake manifold or to isolate the canister from the engine intake manifold, respectively. The canister is also connected to a vent solenoid valve which serves to place the canister in fluid communication with atmospheric air and to isolate the canister from atmospheric air.  
         [0003]     Under the appropriate conditions, the canister is purged so that fuel vapors collected within the canister do not undesirably escape into the atmosphere. This is done by opening the canister purge valve and the vent solenoid valve, thus enabling 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. The fuel vapors are then used in the normal combustion process. 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.  
         [0004]     Conventional canister purge and vent solenoid valves include a solenoid and spring arrangement for moving a valve element between open and closed positions. During operation, the solenoid is energized so as to move the valve element to a desired position. The spring serves to return the valve element to its initial position when power to the solenoid is removed.  
         [0005]     However, the use of such valves increases the amount of components needed and thus increases manufacturing and other costs. Therefore, there is a need for valves having a reduced number of components and which cost less to manufacture and assemble.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention is directed to a solenoid for use in valves used in evaporative emission control systems, such as canister purge valves or vent solenoid valves. The solenoid includes a housing having an inlet port and an outlet port. The housing further includes a guide element having a bobbin section. A valve shaft is slidably mounted to the guide element, wherein the valve shaft includes a permanent magnet and a valve element. The valve element is movable between a closed position wherein the inlet port is closed and an open position wherein the inlet port is opened. A coil is formed on the bobbin adjacent the magnet. In use, the coil generates a first directional magnetic field that is oriented to cause the magnet to be repelled to thus move the valve element to the open position. The coil also generates a second directional magnetic field that is oriented to cause a magnetic attraction with the magnet to move the valve element to the closed position.  
         [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 accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a cross sectional view of a bipolar canister purge valve having a coil which is energized for opening an inlet port.  
         [0009]      FIG. 2  is a cross sectional view of the bipolar valve having wherein the coil is energized for closing the inlet port.  
         [0010]      FIG. 3  is an illustrative depiction of the canister purge valve in an evaporative emission control system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     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. 1-3 .  
         [0012]     The principles of the present invention may be applied to either canister purge valves or vent solenoid valves. For purposes of clarity, the invention will be described in relation to a canister purge valve configuration although it is understood that the principles of the present invention are also applicable to vent solenoid valves. Referring to  FIG. 1 , a cross sectional view of a bipolar canister purge valve  10  in accordance with the present invention is shown. The purge valve  10  includes a housing  12  having a lower wall  14  and an internal wall  16  for forming an internal passageway  18 . Inlet port walls  20  extend from the lower wall  14  to form an inlet port  22  having a first passageway  24  which is in fluid communication with a vapor collection canister  26  ( FIG. 3 ). A valve seat  28  for receiving a valve element  30  is formed at the intersection of the inlet port walls  20  and the lower wall  14 . Outlet port walls  32  extend from a side wall  34  of the housing  12  to form an outlet port  36  having a second passageway  38  which is in fluid communication with an engine intake manifold  97  ( FIG. 3 ).  
         [0013]     The housing  12  further includes a guide member  42  having a bobbin section  44  located between upper  46  and lower  48  flanges that extend outwardly to form a substantially C-shaped configuration. The upper flange  46  is fabricated from a non-magnetic material. Alternatively, an air gap may be formed between the upper flange  46  and remaining portions of the bobbin section  44  to isolate the upper flange  46 . The upper  46  and lower  48  flanges each include bearings  50  for enabling movement of a shaft  52  along an axial direction. It is noted that other devices and configurations for enabling movement may be used such as bushings. The shaft  52  includes a permanent magnet  54  that is located between the upper  46  and lower  48  flanges. A lower end  56  of the shaft  52  includes the valve element  30 . In  FIG. 1 , the valve element  30  is depicted in an open position wherein the valve element  30  is spaced apart from the valve seat  28  to enable fluid communication between the first passageway  24 , the internal passageway  18  and the second passageway  38 . The valve element  30  may also be moved to a closed position wherein the valve element  30  is in contact with the valve seat  28  to thus close the inlet port  22  as will be described in relation to  FIG. 2 .  
         [0014]     A wire  58  having first  60  and second  62  ends is wound around a section of the bobbin  44  to form a coil  65 . The first  60  and second  62  ends are connected to first  76  and second  72  terminals, respectively. The coil  65  is located adjacent the magnet  54 . In one embodiment, the magnet  54  is oriented such that the south and north magnetic poles are located adjacent first  82  and second  84  portions, respectively of the coil  65 . In operation, the coil  65  is energized by maintaining the second terminal  72  at 0 volts and the first terminal  76  at a positive voltage such as approximately +12 volts, for example. The coil  65  is wound such that a magnetic field is generated having south and north magnetic poles oriented near top  82  and bottom  84  portions, respectively, of the coil  65 . As a result, the polarity of the magnetic field along the bobbin  44  is oriented to repel the magnet  54 , thus causing the valve element  30  to move upward to the open position as shown in  FIG. 1 .  
         [0015]     Referring to  FIG. 2 , the valve element  30  is shown in the closed position. In order to move the valve element  30  to the closed position, the voltage applied to the first  76  and second  72  terminals is reversed. In particular, coil  65  is energized by maintaining the first terminal  76  at 0 volts and the second terminal  72  at a positive voltage such as approximately +12 volts, for example. As a result, the orientation of the magnetic poles along the bobbin  44  is reversed from that which occurs when the valve element  30  is moved to the first position so as to form a bipolar coil. Thus, a magnetic field is generated having north and south magnetic poles oriented near the top  82  and bottom  84  portions, respectively, of the coil  65 . As a result, the polarity of the magnetic field along the bobbin  44  is oriented to magnetically attract the magnet  54 . This causes the valve element  30  to move downward to the closed position as shown in  FIG. 2 .  
         [0016]     In the second position, the magnet  54  is located so as to form a magnetic latch between the magnet  54  and the lower flange  48 . This serves to maintain the valve element  30  in the closed position when the coil  65  is not energized, thus reducing the amount of power required for operating the purge valve  10 . In  FIG. 2 , the magnet  54  is shown in contact with the lower flange  48 . Alternatively, the magnet  54  may be spaced apart and located in sufficient proximity to the lower flange  48  to form the magnetic latch.  
         [0017]     In order to move the valve element  30  back to the open position, the voltage applied to the first  76  and second  72  terminals is again reversed such that a magnetic field is generated having south and north magnetic poles oriented near top  82  and bottom  84  portions, respectively, of the coil  65  as previously described in relation to  FIG. 1 . The magnetic field is of sufficient strength to overcome the magnetic latch between the magnet  54  and the lower flange  48 . As such, the polarity of the coil  65  may be selectively reversed to cause movement of the valve element  30  between the open and closed positions. In addition, movement of the valve element  30  between the open and closed positions is achieved without the use of a spring. It is noted that other suitable voltages may be used to energize coil  65 . Further, it is noted that the polarity of the magnet  54  and that of the magnetic field generated by coil  65  may be correspondingly reversed as desired to enable movement of the valve element  30  between the open and closed positions. In one embodiment, pulse width modulation techniques may be used to control movement of the valve element  30 . In another embodiment, the coil  56  may be wound around the magnet  54  to form a coaxial configuration.  
         [0018]     Referring to  FIG. 3 , the purge valve  10  in accordance with the present invention is shown in an emission control system  90 . The system  90  includes a leak detection monitor  92  which is used as part of a selected on board diagnostic procedure for determining whether there is an unacceptable fuel vapor leak in the system  90 .  
         [0019]     The canister  26  is in fluid communication with a fuel tank  94  and includes carbon or other similar material which serves to absorb fuel vapors that are generated within the fuel tank  94  and in the emission control system  90 . The canister  26  also includes a vent solenoid valve  96  which is opened under the appropriate conditions so as to place the canister  26  in fluid communication with atmospheric air through a filter  40 . Alternatively, the vent valve  96  is closed to isolate the canister  26  from atmospheric air so as to enable performance of an on board diagnostic procedure. As previously described, the principles of the present invention regarding the use of a bipolar coil may be applied to either canister purge valves or vent solenoid valves. In addition, for vent valve applications, the coil  65  may be energized to a higher level when the valve element  30  is in the closed position than in purge valve applications so as to achieve an improved seal between the valve element  30  and the valve seat  28 .  
         [0020]     The purge valve  10  is located between the canister  26  and the engine intake manifold  97  of an internal combustion engine  98 . The purge valve  10  may be opened as previously described in relation to  FIG. 1  to place the canister  26  in fluid communication with the intake manifold  97 . Alternatively, the purge valve  10  may be closed as previously described in relation to  FIG. 2  to isolate the canister  26  and the fuel tank  94  from the intake manifold  97 . The opening and closing of both the purge valve  10  and the vent valve  96  is controlled by an engine electronic control unit (ECU)  99 .  
         [0021]     Under the appropriate conditions, the canister  26  is purged so that fuel vapors collected within the canister  26  do not undesirably escape into the atmosphere. This is done by opening both the purge valve  10  and the vent valve  96 , thus enabling vacuum which is present at the intake manifold  97  to draw in atmospheric air through the canister  26  and then draw out the fuel vapors from the canister  26 . The purged fuel vapors are then used in the normal combustion process. The ECU  99  determines when purging is to occur based on received signals indicative of various engine parameters. Further, the ECU  99  may be programmed to allow purging of the canister  26  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.  
         [0022]     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. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.