Abstract:
A valve controlling a fuel tank pressure is disposed in a passage connecting the fuel tank and a canister that communicates with atmosphere. The control valve includes a first valve for introducing an atmospheric pressure into the fuel tank when the fuel tank pressure becomes negative and a second valve for releasing an excessively high pressure in the fuel tank. The first valve opens when the fuel tank pressure drops below a predetermined level and closes again when the fuel tank pressure is recovered. To prevent a vibrating operation of the first valve between its open and closed positions, the closing operation of the once opened valve is delayed by an orifice formed through a diaphragm of the valve. The orifice alleviates a quick change of the pressure applied to one surface of the valve. A magnet to restrict the quick movement of the valve may be used in place of the orifice. Preferably, an electromagnetic driver for forcibly opening the first valve, irrespective of the fuel tank pressure, is connected to the first valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims benefit of priority of Japanese Patent Application No. Hei-11-279064 filed on Sep. 30, 1999, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pressure control valve for controlling a pressure in a fuel tank, such as a fuel tank of an automotive vehicle. 
     2. Description of Related Art 
     A pressure control valve is disposed in a passage connecting a fuel tank of an automotive vehicle to an atmospheric pressure to prevent excessive negative pressure from being developed in the fuel tank. The atmospheric pressure is supplied, for example, from a drain port of a canister that temporarily holds fuel vapor generated in the fuel tank and suppresses fuel vapor exhaust from the fuel tank. 
     An example of such a pressure control valve is disclosed in JP-A-8-121619. The control valve includes a wall separating a valve chamber from a canister port and a valve body disposed in the valve chamber. A through-hole formed in the separating wall is opened or closed by the valve body according to a difference between the fuel tank pressure and an atmospheric pressure. The valve body is biased by a spring in a direction to close the through-hole. The valve chamber always communicates with a fuel tank port, and a canister inner pressure is applied to a front surface of the valve body while a fuel tank inner pressure is applied to a back surface of the valve body. When the fuel tank inner pressure decreases to a predetermined level, the valve body opens the through-hole to introduce atmospheric pressure into the fuel tank. The valve body is formed by connecting a dish-shaped metallic member to a rubber disc. A circular lip portion is formed on the rubber disc to tightly close the through-hole. 
     Another example of the valve device for preventing the fuel tank pressure from becoming excessively negative is disclosed in JP-A-6-50447. In this device, a hole communicating with atmosphere is formed in a top plate of a fuel tank cap, and the hole is usually closed by a valve body disposed inside the top plate. The valve body is biased by a spring in a direction to close the hole. When the fuel tank pressure decreases to a predetermined level, the valve body opens the hole against the biasing force of the spring to introduce the atmospheric pressure into the fuel tank. The valve body is composed of a cup-shaped rubber member having a circular sealing lip to tightly close the hole. 
     There is a problem in both of the conventional pressure control valves. When the atmospheric pressure is once introduced into the fuel tank through the open valve, the atmospheric pressure is immediately applied to the inner surface of the valve body. Accordingly, the open valve is instantly closed, and the negative pressure quickly develops in the fuel tank to open the valve again. This results in a vibrating operation of the valve between its closed and open positions with a short cyclic period. The vibrating operation of the valve generates vibrating noise. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved pressure control valve in which the valve vibration and the vibrating noise are prevented. 
     A pressure control valve having a first valve and a second valve is disposed in a passage connecting a fuel tank and a canister. The first valve opens to introduce an atmospheric pressure through the canister into the fuel tank when the fuel tank pressure becomes negative and lower than a predetermined level. The second valve opens to release the fuel tank pressure to the atmosphere through the canister when the fuel tank pressure becomes higher than a predetermined level. 
     The first valve is made of a rubber material partially reinforced by a metal disc, and includes a seal member and a diaphragm formed around the seal member. The atmospheric pressure is applied to a front surface of the first valve through the canister, while the fuel tank pressure is applied to a back surface through an orifice formed in the diaphragm. The first valve is normally biased to its closing position by a spring. When a vehicle stops and fuel temperature in the fuel tank drops, a negative pressure is developed in the fuel tank. At this time, the first valve opens to introduce the atmospheric pressure into the fuel tank, thereby alleviating the negative pressure in the fuel tank. Though the pressure in the fuel tank increases upon opening the first valve, the pressure applied to the back surface of the first valve does not immediately increase because that pressure is applied through the orifice having a small diameter. Accordingly, the first valve once opened does not close immediately. Thus, the first valve is prevented from being vibrated between its open and closed positions with a short cyclic time. The noise otherwise caused by such a vibration is prevented. 
     Alternatively, a magnet is used in place of the orifice to delay the closing operation of the first valve. The magnet is placed to face a moving core connected to the first valve to magnetically attract the moving core and thereby to restrict a quick closing movement of the first valve. 
     Preferably, an electromagnetic driver is connected to the first valve to move the first valve to its open position, irrespective of the pressure in the fuel tank. Upon energization of the electromagnetic driver, the first valve is forcibly open to make a bypass passage between the fuel tank and the atmosphere. The bypass passage is readily formed, when needed, without providing a separate device. 
     According to the present invention, the closing operation of the first valve once opened is delayed, and thereby the vibration and the vibrating noise of the first valve are prevented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view showing a pressure control valve as a first embodiment of the present invention; 
     FIG. 2 is an enlarged cross-sectional view showing a first valve portion of the pressure control valve, a portion shown in a circle II in FIG. 1; and 
     FIG. 3 is a cross-sectional view showing a pressure control valve as a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. An entire structure of a pressure control valve is shown in FIG.  1 . The pressure control valve is disposed in a passage connecting a fuel tank to a canister that temporarily holds fuel vapor therein and supplies an atmospheric pressure to the fuel tank. The pressure control valve includes a first valve  11  for connecting the fuel tank and the canister to introduce an atmospheric pressure into the fuel tank when a pressure in the fuel tank becomes negative and a second valve  12  for connecting the fuel tank and the canister to release the fuel tank pressure when the fuel tank pressure increases to a predetermined level. The first valve  11  also includes an electromagnetic driver portion  7  that opens the first valve to establish a bypass passage between the fuel tank and the canister, irrespective of a pressure difference between the fuel tank and the atmosphere. 
     The first and the second valves  11 ,  12  are contained in a common housing  2  consisting of three portions  21 ,  22  and  23 . Upper and lower openings of a cylindrical side wall  22  are closed with a cap member  23  and a bottom member  21 , respectively, thereby forming the housing  2 . The cap member  23  includes a projected portion  204  in which the electromagnetic driver portion  7  is housed. The side wall  22  includes a canister port  202  connected to the canister and a fuel tank port  201  connected to the fuel tank. Both ports  201  and  202  stick out from the outer periphery of the side wall  22 . 
     An inside of the housing  2  is divided into two chambers, a fuel tank pressure chamber  31  and an atmospheric pressure chamber  32 , by a cylindrical separating wall  205 . The fuel tank pressure chamber  31  connected to the fuel tank port  201  is formed outside the atmospheric pressure chamber  32  connected to the canister port  202 . The fuel tank pressure chamber  31  includes a space  311  and a circular passage  312  formed at an inner periphery of the space  311  and communicating therewith. 
     The structure of the first valve  11  will be described with reference mainly to FIG. 2 that illustrates details of the first valve  11  in an enlarged scale. The projected portion  204  of the cap member  23  is positioned above both chambers  31 ,  32  and contains the electromagnetic driver portion  7  therein. A bobbin  71  is inserted into the projected portion  204 . A valve chamber  33  in which a valve body  4  is disposed is formed between a lower end of the bobbin  71  and an upper end of the separating wall  205 . The valve body  4  is disposed in the valve chamber  33 , so that it faces an opening  31   a  of the fuel tank pressure chamber  31  and an opening  32   a  of the atmospheric pressure chamber  32 . 
     The valve body  4  is formed by molding rubber  402  on a metal disc  401  that reinforces a center portion of the valve body  4 . The valve body  4  includes a seal member  41  formed at the center portion and a diaphragm  42  formed at the peripheral portion. A circular lip  4021  projecting downwardly from the rubber  402  is formed at outer periphery of the seal member  41 . The lip  4021  contacts an upper end surface  205   a  of the separating wall  205  to tightly close the opening  32   a  of the atmospheric pressure chamber  32 . The thin diaphragm  42  made of rubber encircles the seal member  41 . 
     A thicker periphery  4022  is formed to encircle the diaphragm  42  and is held between the bobbin  71  and the side wall  22 . The valve chamber  33  is divided into two chambers, a first valve chamber  331  and a second valve chamber  332 , by the valve body  4 . The fuel tank pressure chamber  31  communicates with the first valve chamber  331 , and the opening  31   a  of the fuel tank pressure chamber  31  is closed by the diaphragm  42  having the lip  4021  and the thicker periphery  4022 . A hole having a diameter of about 0.4 mm is formed through the diaphragm  42 , so that it serves as an orifice  4023 . The second valve chamber  332  communicates with the first valve chamber  331  through the orifice  4023 . Projections  4024  are formed on the seal member  41  so that they stick out upward. The projections  4024  abut against a lower surface of a stopper piece  52  fixed in the bobbin  71  when the valve body  4  moves upward to open the valve. The upward movement of the valve body  4  is limited by the stopper piece  52 , and the abutting shock is alleviated by the projections  4024  made of rubber. 
     A hole  711  is formed in the bobbin  71 , and a moving core  6  fixedly connected to the metal disc  401  is slidably supported in the hole  711 . The cylinder-shaped moving core  6  made of iron has a flange portion at its bottom end, and the flange portion is welded to the metal disc  401 . A stator core  73  is fixedly supported in the hole  711  above the moving core  6 . The stopper piece  52  is fixedly inserted into a center hole of the stator core  73 , and a lower portion of the stopper piece  52  sticks out from the stator core  73 . A ring-shaped spring stopper  521  is formed on the lower portion of the stopper piece  52 . A spring  51  is disposed between the spring stopper  521  and the seal member  41  in the compressed state, so that the valve body  4  is downwardly biased to close both openings  31   a ,  32   a.    
     The electromagnetic driver portion  7  contained in the projected portion  204  is structured as follows. As better seen in FIG. 1, a coil  72  is wound around the bobbin  71 , to which electric current is supplied from a terminal  76 . A yoke  74  connected to a top portion of the stator core  73  is held in the projected portion  204 . A magnetic plate  75  held in a bottom flange of the bobbin  71  is disposed surrounding the moving core  6 . The coil  72 , stator core  73 , the yoke  74  and the magnetic plate  75  constitute a magnetic circuit. When the coil  72  is energized, the moving core  6  is electromagnetically pulled upward to lift the valve body  4  against the biasing force of the spring  51 . Though the first valve  11  is designed to automatically open the openings  31   a ,  32   a  when the excessive negative pressure is developed in the fuel tank pressure chamber  31 , the first valve  11  can be opened by operation of the electromagnetic driver  7 , irrespective of the pressure in the fuel tank, thereby to establish communication between the fuel tank and the atmosphere. A pressure sensor port  203  communicating with the fuel tank pressure chamber  31  sticks out upwardly from the cap member  23 . A pressure sensor (not shown) is connected to the pressure sensor port  203  for monitoring hermetical quality of a fuel tank system. 
     Referring to FIG. 1, the second valve  12  will be described. The second valve  12  is substantially the same as a known diaphragm valve. An inner cavity  206  is formed in the bottom member  21  that closes the bottom opening of the side wall  22 . A second valve body  8  is disposed in the cavity  206 . The second valve body  8  is composed of a seal member  81  formed at its center portion and a diaphragm  82  formed around the seal member  81 . The seal member  81  made of rubber  802  is reinforced by attaching a resin disc  801  underneath the seal member  81 . The seal member  81  includes a flat portion  8021  having a diameter larger than that of a bottom surface  205   b  of the separating wall  205 . A bottom opening  32   b  of the atmospheric pressure chamber  32  is closed by the flat portion  8021 . 
     The thin diaphragm  82  made of rubber is formed around the seal member  81 , and a thick periphery  8022  is formed around the diaphragm  82 . The thick periphery  8022  is firmly held between the side wall  22  and the bottom member  21 , and thereby the second valve body  8  defines a bottom end of the fuel tank pressure chamber  31 . A spring  9  biasing the seal member  81  upward is disposed between the resin disc  801  and the bottom member  21  in a compressed state. 
     The first valve  11  structured as described above operates as follows. The atmospheric pressure in the atmospheric pressure chamber  32  is applied to a front surface (lower surface)  4   a  of the valve body  4  facing the opening  32   a , while the pressure in the fuel tank pressure chamber  31  is applied to a back surface (upper surface)  4   b  of the valve body  4  through the orifice  4023  formed in the diaphragm  42 . When a vehicle stops, the temperature of fuel in the fuel tank decreases, and thereby the pressure in the fuel tank becomes negative. At this time, because the negative pressure is applied to the back surface  4   b  of the valve body  4 , the valve body  4  moves upward against the biasing force of the spring  51 . Accordingly, the opening  32   a  of the atmospheric pressure chamber  32  opens to communicate with the opening  31   a  of the fuel tank pressure chamber  31 . The atmospheric pressure is introduced into the fuel tank pressure chamber  31  from the atmospheric pressure chamber  32 . 
     Upon introduction of the atmospheric pressure into the fuel tank pressure chamber  31 , the negative pressure therein starts to be alleviated. The negative pressure alleviation starts from an immediate downstream of the lifted lip  4021 , i.e. from an outside periphery of the lip  4021  in the first valve chamber  331 . The negative pressure in the second valve chamber  332  is also alleviated because the second valve chamber  332  communicates with the first valve chamber  331  through the orifice  4023 . 
     However, speed of the negative pressure alleviation in the second valve chamber  332  is slower than that in the first valve chamber  331 , because both chambers communicate with each other only through the orifice  4023  having a small opening. Therefore, the negative pressure in the second valve chamber  332  is kept for a certain period of time after the atmospheric pressure is introduced into the first valve chamber  331 . If the atmospheric pressure were applied to the back surface  4   b  of the valve body  4  immediately after the valve is opened as in the conventional valve device, the valve would be closed again before the negative pressure in the fuel tank is sufficiently alleviated. This would cause vibration of the valve between open and closed positions. Since the negative pressure alleviation in the second valve chamber  332  is delayed according to the present invention, repetition of opening and closing of the valve with a short cycle time is surely avoided and noises due to the vibration are prevented. 
     The second valve  12  opens to establish communication between the fuel tank pressure chamber  31  and the atmospheric pressure chamber  32  when the pressure in the chamber  31  exceeds a level determined by the biasing force of the spring  9 . In other words, when the fuel tank pressure becomes excessively high, the high pressure is released to the atmosphere through the second valve  12 . 
     To establish communication between the canister port  202  and the fuel tank port  201 , irrespective of the pressure in the fuel tank, the first valve  11  is forcibly opened by energizing the electromagnetic driver  7 . 
     Though the second valve chamber  332  communicates with the fuel tank pressure chamber  31  through the orifice  4023  in the embodiment described above, it is possible to form a passage having an orifice, in place of the orifice  4023 , in the housing to establish communication between the second valve chamber  332  and the fuel tank pressure chamber  31 . 
     A second embodiment of the present invention will be described with reference to FIG.  3 . In the second embodiment, the first valve  11  of the first embodiment is replaced with a first valve  11 A, and the second valve  12  remains unchanged. Since most structures and operation are the same as those of the first embodiment, only the differences from the first embodiment will be described below. 
     The housing  2 A is composed of three members,  21 ,  22 A and  23 A. Both open ends of a cylindrical side wall  22 A having an oval cross-section are closed with a cap member  23 A and the bottom member  21  in the same manner as in the first embodiment. The cap member  23 A includes a cylindrical portion  208  in which the electromagnetic driver portion  7  is contained. The inner space of the housing  2 A is divided into two chambers, a fuel tank pressure chamber  31 A communicating with the fuel tank port  201  and an atmospheric pressure chamber  32 A communicating with the canister port  202 . 
     The structure of the first valve  11 A will be described. The cap member  23 A includes a flange  207  and a cylindrical portion  208  extending upwardly from the flange  207 . The cylindrical portion  208  is formed coaxially with the separating wall  205 A and contains the electromagnetic driver portion  7  therein. The diameter of the cylindrical portion  208  is larger than that of the separating wall  205 A. The bobbin  71  is inserted in the cylindrical portion  208 , and a valve chamber  33 A is formed between the lower surface of the cylindrical portion  208  and the upper surface  205   c  of the separating wall  205 A. A valve body  4 A is disposed in the valve chamber  33 A to face an opening  32   c  of the atmospheric pressure chamber  32 A. The valve body  4 A is composed of a rubber member  402 A having a diameter a little larger than that of the opening  32   c  and a metal disc  401 A reinforcing the rubber member  402 A. A circular lip  4021  is formed on the lower surface of the rubber member  402 A to contact the upper surface  205   c  and thereby to close the opening  32   c.    
     The fuel tank pressure is applied to the back surface (upper surface)  4   d  of the valve body  4 A through a circular space between the separating wall  205 A and the cylindrical portion  208 . The atmospheric pressure is applied to the front surface (lower surface)  4   c  of the valve body  4 A. 
     The valve body  4 A is downwardly biased by the spring  51  to close the opening  32   c.    
     The moving core  6  fixed to the valve body  4 A is slidably supported in an inner bore  711  of the bobbin  71 . The valve body  4 A can be electromagnetically driven by the electromagnetic driver  7  in the same manner as in the first embodiment. 
     A circular magnet  53  is disposed outside the moving core  6  with the bobbin  71  interposed therebetween. The circular magnet  53  is magnetized to form poles on its upper and lower surfaces. 
     The first valve  11 A of the second embodiment operates as follows. As described above, the atmospheric pressure is applied to the front surface  4   c  of the valve body  4 A, while the fuel tank pressure is applied to the back surface  4   d  of the valve body  4 A. When the vehicle stops and the fuel temperature drops, the fuel tank pressure becomes negative, applying negative pressure to the back surface  4   d  of the valve body  4 A. This generates a pressure difference between both surfaces  4   c  and  4   d  of the valve body  4 A. The valve body  4 A moves upward against the biasing force of the spring  51 , and thereby the opening  32   c  opens. Thus, the atmospheric pressure chamber  32 A communicates with the fuel tank pressure chamber  31 A, and thereby the atmospheric pressure is introduced into the fuel tank. 
     Upon introduction of the atmospheric pressure into the fuel tank pressure chamber  31 A, the negative pressure therein is alleviated first from the immediate downstream of the valve body  4 A. As the negative pressure is alleviated, the valve tends to close again. However, since the circular magnet  53  disposed outside the moving core  6  attracts the moving core  6 , the frictional force between the moving core  6  and the inner bore  711  of the bobbin  71  is generated. This frictional force is generated, because there are some unevenness of the magnetic field of the circular magnet  53  and a certain dimensional deviation in the clearance between the moving core  6  and the inner bore  711 , and therefore the attractive force of the circular magnet  53  is not perfectly uniform around the entire periphery of the moving core  6 . Because of the frictional force, the downward movement of the valve to close the opening  32   c  is delayed, and the valve vibration between the open and closed positions with a short cyclic period is avoided. Thus, the noise due to the valve vibration is also avoided. 
     The structure and operation of the second valve  12  of the second embodiment are the same as those of the first embodiment. That is, the fuel tank pressure becomes higher than a predetermined level, the second valve  12  opens to release the fuel tank pressure to the atmosphere. Also, the operation of the electromagnetic driver portion  7  in the second embodiment is the same as that in the first embodiment. That is, the communication between the fuel tank port  201  and the canister port  202  is forcibly established, irrespective of the pressure difference between two chambers  31 A and  32 A, by operation of the electromagnetic driver  7 . 
     The circular magnet  53  may be replaced with a rod magnet placed at a side of the moving core  6 . The magnetic field of the rod magnet and the distance between the rod magnet and the moving core  6  may be adjusted, so that a proper control force is given to the movement of the valve body  4 A. 
     Though the first valve  11  operative in response to the fuel tank pressure is also forcibly operated by the electromagnetic driver  7  to make a bypass passage in both embodiments described above, the bypass passage may be formed by a valve device disposed separately from the first valve  11 . Further, though the first valve  11  and the second valve  12  are housed in a common housing in the above embodiments, it is possible to separately dispose both valves. Though the pressure control valve having two valves  11  and  12  is disposed in the passage connecting the fuel tank to the canister in the above embodiments, it is possible to dispose the valve to relieve the negative pressure in a fuel tank cap. 
     While the present invention has been shown and described with reference to the foregoing preferred embodiments, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.