Abstract:
A fuel vapor purge system has a canister and a pump on a purge line arranged between the canister to the intake passage. The system further has a sub-canister on a branch passage of the purge line. The pump is driven when the engine is stopped, and reduces an inside pressure of the system. The vapor discharged from the pump is adsorbed in the sub-canister, therefore, no vapor is emitted to the atmosphere. The controller checks a leak by monitoring the inside pressure after the inside pressure is reduced. It is possible to improve an accuracy of the leak detection since a leak check is executed when the engine is stopped.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based on Japanese Patent Application No. 2001-104999 filed on Apr. 3, 2001 the contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a leak check apparatus for a fuel vapor purge system. The apparatus detects a leak on a fuel vapor purge system including a fuel tank.  
           [0004]    2. Description of Related Art  
           [0005]    In a Conventional fuel vapor purge system, a canister communicates with a fuel tank via a gas line that introduces an evaporated fuel vapor (referred to as a vapor) from the fuel tank to the canister. The vapor is adsorbed in the canister. The canister also communicates with the atmosphere via an intake line with a canister close valve (referred to as a canister valve). The canister also communicates with an intake passage via a purge-line with a purge control valve (referred to as a purge valve). Further, a controller is provided for operating the valves to adsorb the vapor in the canister and to desorb an adsorbed vapor into the intake passage. The controller also operates the valves to detect a leak on the system including the fuel tank and pipes providing the lines. The controller opens the purge-valve and closes the canister valve when an engine runs and an intake pressure is a negative pressure. Then, the controller closes the purge-valve when an inside pressure in the fuel tank reaches to a predetermined negative pressure. The controller monitors the inside pressure and detects the leak based on a variation of the inside pressure or an elapsed time until the inside pressure decreases to a specific pressure.  
           [0006]    However, in the conventional system, since the leak check procedure is executed during the engine is running, unstable fuel level that may wave due to a vibration of the engine or a vehicle affect a leak check accuracy. Further, since the negative pressure should be introduced into the system in a short period of time, the engine may supply an excessive amount of vapor that may make an exhaust emission worse.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the present invention to reduce an emission during a leak check procedure is executed.  
           [0008]    It is another object of the present invention to improve an accuracy of a leak check of a fuel vapor purge system.  
           [0009]    According to a first aspect of the present invention, an apparatus includes at least one valve which defines a closed space including a fuel tank, a main canister and at least a part of a purge passage. This closed space is subject to a leak check. A pump is disposed for discharging gaseous component in the closed space and for reducing an inside pressure of the closed space. A sub canister disposed in series to the pump which adsorb the vapor in the gaseous component discharged by the pump. Therefore, an emission of the vapor is reduced. A sensor is disposed for outputting a signal indicative of a leak on the closed space. Therefore, it is possible to detect the leak on the closed space with no significant increase of emission of the vapor.  
           [0010]    The leak check procedure executed by using the components of the apparatus may be executed when the engine is stopped. According to this arrangement, it is possible to improve accuracy of the leak check.  
           [0011]    According to another aspect of the present invention, an apparatus has at least one valve which defines a closed space including the fuel tank, the main canister and at least a part of the purge passage, and connects at least the remaining part of the purge passage to the intake passage of the engine. A pump is disposed on the system for pressurizing the closed space when the engine is stopped. A first sensor is disposed on the system for outputting a signal indicative of a leak on the closed space. Therefore, it is possible to detect the leak on the closed space while the engine is stopped. The apparatus further comprises a second sensor disposed on the engine which outputs a signal indicative of a leak on the remaining part of the purge passage when the engine is running. Since the remaining part of the purge passage is connected to the intake passage of the engine by the valve, a condition of the engine is influenced by the leak, and the sensor detects the condition. Therefore, it is possible to detect the leak on the remaining part. Further, a fluctuation caused by a wave on the fuel level does not affect on the leak check for the remaining part since the fuel tank is subject to the leak check while the engine is stopped.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Features and advantages of embodiments will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings:  
         [0013]    [0013]FIG. 1 is a block diagram showing a fuel vapor purge system according to a first embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is a block diagram of a controller according to the first embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is a block diagram of a fuel vapor purge system according to a second embodiment of the present invention;  
         [0016]    [0016]FIG. 4 is a block diagram of a controller according to the second embodiment of the present invention;  
         [0017]    [0017]FIG. 5 is a block diagram showing a part of a fuel vapor purge system according to a third embodiment of the present invention; and  
         [0018]    [0018]FIG. 6 is a block diagram showing a part of a fuel vapor purge system according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]    A first embodiment of the present invention is explained with reference to the drawings. In the embodiment, the present invention is applied to a fuel vapor purge system for a vehicle. FIGS. 1 and 2 show the fuel vapor purge system with a leak check apparatus for checking a leak on the fuel vapor purge system. FIG. 1 mainly shows an arrangement of the fuel vapor purge system. FIG. 2 mainly shows an arrangement of a controller that provides the fuel vapor purge system and the leak check apparatus.  
         [0020]    Referring to FIG. 1, the system  100  is disposed between an intake system and a fuel system of an engine  3 . The engine  3  has an intake passage  31 . The intake passage has an air cleaner  32  and a throttle valve  33 . The throttle valve  33  is operated in accordance with an operating degree of an accelerator (not shown).  
         [0021]    The system  100  has a fuel tank  1  that has a filler tube  12  with filler cap  11 . The fuel tank  1  contains fuel  14  therein. A pressure sensor  13  is disposed on an upper portion of the fuel tank  1  to detect an inside pressure in the fuel tank  1 .  
         [0022]    The system  100  has a main canister  2 , a sub-canister  4 , a purge pump  24 , valves  22 ,  25 ,  41 ,  43  and  45 , and connecting pipes for providing a plurality of communicating lines. A main canister  2  has an adsorbent housed in a housing. The housing has a first end  2   a  and a second end  2   b  separated by the adsorbent. The first end  2   a  communicates with the fuel tank  1  via a gas line  21 . The first end  2   a  is also communicates with the intake passage at a downstream side of the throttle valve  33  via purge line  26 . A purge pump  24  and a purge valve  25  are disposed on the purge line  26  in this order from the main canister  2 . The second end  2   b  communicates to the atmosphere through an intake-line  23  in which a canister valve  22  is disposed.  
         [0023]    The sub-canister  4  which has a smaller capacity than the main canister  2  is disposed so as to bypass the purge valve  25  and to be connected in series to the pump  4  when the purge valve  25  is closed. The sub-canister  4  has an adsorbent housed in a housing that has a first end  4   a  and a second end  4   b . The first end  4   a  communicates with the intake passage  31  via a sub-purge line  42  in which a sub-purge valve  41  is disposed. The second end  4   b  communicates with a line between the purge pump  24  and the purge valve  25  via a leak check line  46  in which a leak check valve  45  is disposed. The second end  4   b  also communicates with the atmosphere via a sub-intake line  44  in which a sub-canister valve  43  is disposed. The lines  42  and  46 , and the sub-canister  4  provides a branch path to the intake passage  31 . In this embodiment, the valves are open-close type electromagnetic valve. The sub canister  4  may be disposed on the suction side of the pump  4  for adsorbing the vapor in gaseous component discharged by the pump  4 . It is also effective to dispose the sub canister  4  even if a leak check procedure is executed when the engine is running.  
         [0024]    Referring to FIG. 2, a controller  5  is provided to control the valves  22 ,  25 ,  41 ,  43 , and  45 , the pump  24 , and a LED  7  as a warning device. The controller  5  inputs sensor signals indicative of operating condition of the engine and the vehicle detected by a plurality of sensors  6  including the pressure sensor  13 . The controller  5  provides a purge control that includes an adsorbing control  5   d  for adsorbing the vapor into at least one of the canisters  2  and  4 , and a desorbing control  5   e  for desorbing an adsorbed vapor into the intake passage  31 . The controller  5  further provides a leak check control procedure including for checking and detecting a leak on the system. The controller  5  activates the LED  7  if the leak is detected. A separated controller may provide the purge control. In this embodiment, the valves  22 ,  25 , and  41  are provided for defining a closed space that includes at least the fuel tank  1 , the main canister  2  and a part of a purge passage provided by the lines  21 ,  23 ,  26 ,  46 , and  43 . The pump  24  is provided for discharging gaseous component in the system and for reducing an inside pressure of the closed space.  
         [0025]    In the adsorbing control  5   d , the controller  5  outputs control signals to the valves and the pump so as to introduce the vapor from the fuel tank  1  to the canister  2 .  
         [0026]    In the desorbing control  5   e , the controller  5  outputs control signals to the valves and the pump so as to introduce fresh air into the canisters and purge the adsorbed vapor in the canisters. In this embodiment, the desorbing control  5   e  is executed when the engine is running. Preferably, the desorbing control  5   e  is executed when a downstream side of the throttle valve  33  is maintained in a negative pressure. The negative pressure is usually obtained when the throttle valve  33  is almost closed.  
         [0027]    In this embodiment, the controller provides two desorbing controls  5   f  and  5   g . In a desorbing control  5   f  for the sub-canister  4 , the controller  5  closes the purge valve  25 , opens the sub-purge valve  41 , closes the leak check valve  45 , and opens the sub-canister valve  43 . As a result, the adsorbed vapor in the sub-canister  4  is desorbed and purged into the intake passage  31  by fresh air introduced into the sub-canister  4  via the sub-intake line  44 . In a desorbing control  5   g  for the canister  2 , the controller  5  opens the purge valve  25 , closes the sub-purge valve  41 , opens the leak check valve  45 , closes the sub-canister valve  43  and opens the canister valve  22 . As a result, the adsorbed vapor in the canister  2  is desorbed and purged into the intake passage  31  by fresh air introduced into the system via the intake line  23 . In this embodiment, the pump  24  communicates its suction and discharge side when the pump  24  is not driven, therefore the pump  24  allows airflow therethrough. The controller  5  additionally drives the pump  24  to introduce fresh air when a sufficient negative pressure is not obtained in the intake passage due to a widely opened throttle valve  33  or the like.  
         [0028]    The controller  5  executes the leak check procedure when the engine is stopped. First, the controller  5  executes a pressure control  5   a  for reducing an inside pressure of the system. In the pressure control, the controller  5  outputs control signals to the valves and the pump to control a pressure in the system. The controller  5  closes the purge valve  25 , opens the sub-purge valve  41 , opens the leak check valve  45 , closes the sub-canister valve  43 , closes the canister valve  22  and drives the pump  24 . As a result, air and the vapor in the fuel tank  1 , the gas line  21 , the canister  2 , and the purge line  26  from the canister  2  to the pump  24  is discharged to the intake passage  31  through the sub-canister  4 . During the pressure control  5   a , the pump  24  discharges a certain volume of gas into the intake passage  31  while the engine  3  is stopped. However, the vapor is adsorbed in the sub-canister  4 , and is not emitted to the atmosphere. The controller  5  monitors the inside pressure detected by the pressure sensor  13 , and determined whether or not the inside pressure is decreased to a predetermined negative pressure. If the inside pressure is decreased to the predetermined negative pressure, the controller  5  executes a holding control  5   b  by closing the sub-purge valve  41  and stopping the pump  24 . Then, the controller  5  executes a leak check control  5   c  by monitoring the inside pressure detected by the pressure sensor  13 . In the leak check control  5   c , the controller  5  detects a variation of the inside pressure within a predetermined time period, and determined that whether or not the detected variation indicates the leak on system components. The controller  5  may detects a time indicative of the leak, e.g. duration until the inside pressure increases to the predetermined pressure, instead.  
         [0029]    According to the embodiment described above, it is possible to detect the leak accurately, since the embodiment executes the leak check procedure while the engine is stopped.  
         [0030]    [0030]FIGS. 3 and 4 show a second embodiment of the present invention. In this embodiment the same reference numbers are used for the same or equivalent components as the first embodiment to eliminate repeated descriptions. The system  200  has lines  51 , and  52 , and three-port valves  27  and  28  instead of the components  4 ,  41 ,  42 ,  43 ,  44 ,  45 ,  46  utilized in the first embodiment. A first three-port valve  27  is disposed on a suction side of the pump  24 . The first three-port valve has three ports  271 ,  272 , and  273 , and selectively connects the port  272  to the port  271  or the port  273 . A second three-port valve  28  is disposed between the pump  24  and the purge valve  25 . The three-port valve  28  has three ports  281 ,  282 , and  283 , and selectively connects the port  283  to the port  281  or the port  282 . The second end  2   b  of the canister  2  communicates with the port  281  of the second three-port valve  28  via a pressurizing line  52 . The port  271  of the first three-port valve  27  communicates with the intake passage  31  via a suction line  51 . The controller  5  inputs a signal from an oxygen sensor  15  disposed in an exhaust passage for detecting an oxygen amount in the exhaust passage.  
         [0031]    The controller  5  provides two leak check procedures. The controller  5  executes a first leak check procedure when the engine is stopped. First, the controller  5  executes a pressure control  5   h . In the pressure control  5   h , the controller  5  closes the canister valve  22 , drives the first three-port valve  27  so as to connect the first port  271  and the second port  272 , drives the second three-port valve  28  so as to connect the first port  281  and the third port  283 , and drives the pump  24 . As a result, the pump  24  introduces air from the intake passage  31  into the system through the canister  2 . The controller  5  monitors the inside pressure detected by the pressure sensor  13 , and determines whether or not the inside pressure is increased to a predetermined positive pressure. If the inside pressure is increased to the predetermined pressure, the controller  5  executes a holding control  5   i  by stopping the pump  24 , and driving the first three-port valve  27  so as to connect the second port  272  and the third port  273 . Therefore, the fuel tank  1 , the canister  2 , the line  52  and the line  26  from the canister  2  to the second three-port valve  28  form a closed space. Then, the controller  5  executes a first leak check control  5   j  by monitoring the inside pressure and determines whether or not a variation of the inside pressure indicates the leak on the components. For instance, the controller  5  detects a decreased amount of the inside pressure in a predetermined time, and detects the leak if the detected decreased amount is greater than a predetermined mount. Alternatively, the controller  5  may detects duration until the inside pressure decreases to a predetermined pressure, and detects the leak if the detected duration is shorter than a predetermined duration. The controller  5  opens the canister valve  22  to release the pressurized inside pressure to the atmosphere through the canister  2  when the first leak check procedure is completed. Therefore the vapor in the closed space is adsorbed in the canister  2  at the end of the first leak check procedure.  
         [0032]    The controller  5  executes a second leak check procedure when the engine is running and the throttle valve is almost closed. First, the controller  5  executes a holding control  5   k . In the holding control  5   k , the controller  5  opens the purge valve  25 , drives the first three-port valve  27  so as to connect the first port  271  and the second port  272 , drives the second three-port valve  28  so as to connect the second port  282  and the third port  283 , and drives the pump  24 . Therefore, the line  51  and a part of the line  26  from the first three-port valve  27  to the intake passage  31  are connected to the intake passage  31 . The line  51  and a part of the line  26  from the first three-port valve  27  to the intake passage  31  are the remaining part of the passage of the system that is not inspected by the above described first leak check procedure. The controller  5  monitors the signal from the oxygen sensor  15 , and determines that whether or not the signal indicates the leak. For instance, if the leak exists on the components  51 ,  27 ,  24 ,  28 ,  25  and  26 , the signal from the oxygen sensor  15  indicates an excessive oxygen amount.  
         [0033]    The controller  5  executes an adsorbing control  5   m  by controlling the valves and the pump so as to introduce the vapor into the canister  2 .  
         [0034]    The controller executes a desorbing control  5   n  when the engine is running. The controller  5  opens the canister valve  22 , drives the first three-port valve  27  so as to connect the second port  272  and the third port  273 , and drives the second three-port valve  28  so as to connect the second port  282  and the third port  283 . As a result, the adsorbed vapor in the canister  2  is desorbed and purged into the intake passage  31 . The controller  5  additionally drives the pump  24  if the negative pressure is insufficient due to an operating condition of the engine.  
         [0035]    According to the second embodiment, main components of the system  200  are subject to the leak check while the engine  3  is stopped. Therefore, it is possible to detect the leak accurately without an influence of waving fuel level. Further, the remaining components including at least a part of the purge line is subject to the leak check while the engine  3  is running.  
         [0036]    [0036]FIG. 5 shows a third embodiment of the present invention. FIG. 5 shows a partial arrangement of the system. In the third embodiment, a three-port valve  47  is used instead of the valves  43  and  45  in the first embodiment.  
         [0037]    [0037]FIG. 6 shows a fourth embodiment of the present invention. In this embodiment, the pump  24  doesn&#39;t communicate a suction side and a discharge side when the pump is stopped. A bypass line  62  and a valve  61  are added in a bypassing manner to communicate the suction side and the discharge side of the pump  24 . The controller  5  controls the valve  61  so that the bypass line  62  communicates the suction side and the discharge side when the pump  24  is stopped. This arrangement may apply to either the first and second embodiment.  
         [0038]    Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the present invention as defined in the appended claims.