Abstract:
A fault diagnosing apparatus for evapopurge systems, including a device adapted to detect a pressure in the interior of an evapopassage including a fuel tank, a depressurization device adapted to close a first valve provided in an atmosphere-opened port of a canister and depressurize the interior of the evapopassage by a negative pressure occurring in a suction passage of an internal combustion engine, a repressurization device adapted to close a second valve after the operation of the depressurization device finishes, to repressurize the interior of the evapopassage, and a fault judgement device adapted to allow a judgement, which is based on an output from the pressure detecting device, that an evapopurge system is abnormal to be given on condition that the depressurization and repressurization devices are operated plural times.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a fault diagnosing apparatus for evapopurge systems, adapted to adsorb a transpiration gas in a fuel tank to a canister, and purge the canister of the adsorbed fuel and discharge the resultant fuel into a suction passage of an internal combustion engine. 
     2. Description of the Related Art 
     An internal combustion engine is usually provided with an evapopurge system for preventing a transpiration gas occurring in a fuel tank from being discharged to the atmosphere. The evapopurge system is adapted to adsorb a transpiration gas occurring in the fuel tank to the canister via a vapor passage communicating the fuel tank and canister with each other, and purge the canister of the adsorbed fuel and discharge the resultant fuel into a suction passage of an internal combustion engine via a purge passage communicating the canister and suction passage with each other. 
     When the vapor passage and purge passage are damaged from a certain cause in an internal combustion engine provided with such an evapopurge system, the transpiration gas is discharged from the damaged portion into the atmosphere. In order to eliminate such an inconvenience, a fault diagnosing apparatus for detecting damage to the vapor passage and purge passage is provided. 
     Such fault diagnosing apparatuses for evapopurge systems include, for example, the apparatus disclosed in Japanese Patent Laid-Open No. 159157/1994 (U.S. Pat. No. 5,425,344). In the fault diagnosing apparatus for evapopurge systems disclosed in this publication, an evapopassage including a fuel tank is depressurized by a negative pressure of a suction passage, and thereafter closed and repressurized, whereby the damage (leakage of a transpiration gas) to the evapopassage is detected on the basis of pressure variation occurring during this time. 
     However, in such a fault diagnosing apparatus for evapopurge systems, the hopping (which will hereinafter be referred to as sloshing) of a fuel in the fuel tank occurs due to the operating condition of a vehicle, and, during this time, an amount of a transpiration gas occurring from the fuel increases. In such a case, there is the possibility that the evapopurge system be diagnosed erroneously as being out of order. Namely, when the sloshing of the fuel causes the amount of the transpiration gas occurring therefrom to increase, the pressure in the fuel tank increases in accordance with the increase in the amount of transpiration gas when the depressurized evapopassage is closed and repressurized. Consequently, the regained pressure in the evapopassage becomes high in a short period of time. This causes the fault diagnosing system for evapopurge systems to judge that the evapopassage is damaged in spite of the fact that the evapopassage is not actually damaged (the leakage of the transpiration gas does not occur), and diagnose the evapopassage as being out of order. 
     The related art fault diagnosing apparatus for evapopurge systems disclosed in the above-mentioned publication is adapted to detect the occurrence of the sloshing of a fuel in the fuel tank, and interrupt a fault judgement operation when the sloshing of the fuel occurs. 
     A fault diagnosing apparatus for evapopurge systems which has been made with a view to solving similar problems is disclosed in U.S. Pat. No. 5,398,661 (EP0559854), the apparatus being adapted to interrupt a fault judgement operation when the fuel tank is in a filled-up condition since, in such a condition, there is the possibility that even a very low level of transpiration of the fuel causes the regaining of pressure to be attained in a short period of time; and carry out a fault judgement operation with the engine in an idling condition and at a vehicle speed of not higher than a predetermined threshold value. 
     In these related art fault diagnosing apparatuses for evapopurge systems described above, a fault judgement operation is interrupted when the sloshing of a fuel occurs or when the fuel tank is in a filled-up condition, so that a fault of an evapopurge system is not erroneously diagnosed. 
     However, since the fuel tank is vibrated during the travel of a vehicle, the sloshing of a fuel more or less occurs. Consequently, in the apparatus of Japanese Patent Laid-Open No. 159157/1994, in which a fault judgement operation is interrupted when the sloshing of a fuel occurs, the opportunity of practicing a fault diagnosing operation for the evapopurge system is limited, so that a sufficient fault diagnosing operation cannot be carried out. In the apparatus of U.S. Pat. No. 5,398,661, in which a fault judgement operation is also carried out when the fuel tank is not in a filled-up condition with the engine and a vehicle speed in an idling condition and at a level not higher than a predetermined level respectively. Even in such an operating condition, the fault judgement operation receives influence of the occurrence of the sloshing of the fuel, and an erroneous judgement cannot be prevented. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-mentioned circumstances, and provides a fault diagnosing apparatus for evapopurge systems, capable of solving these problems, preventing the sloshing of a fuel from causing an erroneous judgement that an evapopurge system is out of order to be given, and reliably determining a fault of the evapopurge system no matter what the operating condition of the engine is. 
     According to an aspect of the present invention, the fault diagnosing apparatus for evapopurge systems includes a device for detecting a pressure in an evapopassage inclusive of a fuel tank, a depressurization device adapted to close a first valve, which is provided in an atmosphere-opened port of a canister, and depressurize the interior of the evapopassage by a negative pressure occurring in the interior of a suction passage, a repressurization device adapted to close a second valve, which is provided in a purge passage, after the depressurization device is operated, to repressurize the interior of the evapopassage, and a fault judgement device adapted to permit a judgement, which is based on an output from the pressure detecting device, that the evapopurge system is abnormal to be given on condition that the depressurization device and repressurization device are operated plural times. 
     When the depressurization and repressurization of the interior of the evapopassage are carried out plural times, the air in the evapopassage is discharged, and the evapopassage is filled with a transpiration gas, i.e., put in a saturated state, so that pressure variation ascribed to the sloshing of the fuel does not substantially occur. When a fault diagnosing operation for the evapopurge system is carried out in this condition on the basis of an output from the pressure detecting device, a fault can be determined accurately. 
     According to another aspect of the present invention, the fault diagnosing apparatus includes a device for detecting an amount of a fuel remaining in a fuel tank, and a device for setting the number of times of execution of operations of a depressurization device and a repressurization device on the basis of an output from the amount of remaining fuel detecting device. A generation rate of the transpiration gas differs with the amount of the fuel remaining in the fuel tank. Accordingly, when the number of times of execution of the operations of the depressurization and repressurization devices is set on the basis of the amount of the remaining fuel, a fault of the evapopurge system can be determined accurately. 
     In the fault diagnosing apparatus for evapopurge systems, in which the number of times of execution of operations of depressurization and repressurization devices is set on the basis of an amount of a remaining fuel, the increasing of the number of times of execution of the depressurization and repressurization of the interior of an evapopassage in accordance with a decrease in the amount of the remaining fuel enables a fault to be determined more accurately. 
     Operating the fault judgement device when the amount of the remaining fuel determined by the amount of remaining fuel detecting device is larger than 40% of the capacity of the fuel tank reduces the fault diagnosis continuation time, and is therefore preferable. It is also preferable to provide a fuel temperature detecting device, and change the number, which is set by the number of operation setting device, of the execution of depressurization and repressurization operations on the basis of an output from the fuel temperature detecting device. This enables the numbers of the execution of the depressurization and repressurization operations to be set properly, and the fault diagnosis continuation time to be reduced. 
     According to still another aspect of the present invention, the fault diagnosing apparatus includes a device for detecting an amount of a fuel remaining in a fuel tank, and a fault judgement device, the fault judgement device including a member for setting reference number of times of execution of operations of depressurization and repressurization devices on the basis of an output from the amount of remaining fuel detecting device, and a reference value setting member for setting a reference repressurization value on the basis of an output from the amount of remaining fuel detecting device, the fault judgement device being preferably adapted to judge that an evapopurge system is normal when the number of times of execution of the operations of the depressurization and repressurization devices is not smaller than one and not larger than the reference number set by the number of times of operations setting member with a regained pressure in an evapopassage detected by a pressure detecting device becoming not higher than a reference regained pressure value set by the reference value setting member; and judge that the evapopurge system is abnormal when the number of times of execution of the operations of the depressurization and repressurization devices exceeds the reference number of times set by the number of times of operations setting member with regained pressure in the evapopassage detected by the pressure detecting device every time the depressurization and repressurization operations are executed exceeding a reference regained pressure value set by the reference value setting member. Since the normality of the evapopurge system can be determined speedily, and since the determination of the abnormality thereof can be done accurately, the reduction of total fault diagnosis continuation time can be attained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention will be described in detail on the basis of the following figures, wherein: 
     FIG. 1 is a schematic construction diagram of a mode of embodiment of the fault diagnosing apparatus for evapopurge systems according to the present invention; 
     FIG. 2 is a flow chart of an operation of the fault diagnosing apparatus for evapopurge systems; 
     FIG. 3 is a time chart showing the operation of the fault diagnosing apparatus for evapopurge systems; 
     FIG. 4 is a graph showing pressure variation and the number of times of execution of depressurization and repressurization operations with respect to an amount of a remaining fuel; and 
     FIG. 5 is a graph showing the processing time and the number of times of execution of the above-mentioned operations with respect to the amount of the remaining fuel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A mode of embodiment of the present invention will now be described in detail with reference to FIGS. 1-5. 
     In an evapopurge system, an air cleaner (not shown) is connected to a suction port of an engine  13  via a suction pipe  11  and a surge tank  12  as shown in FIG.  1 . The suction pipe  11  is provided with a throttle valve  14 . A canister  17  is connected to a fuel tank  15  via a discharge pipe (vapor passage)  16 . The canister  17  is also connected to the suction pipe  11  via a supply pipe (purge passage)  19  having a purge control valve (second valve)  18 , while a discharge pipe  21  having a vent control valve (first valve)  20  is connected to the canister  17 . A filter  22  is fixed to a free end portion of this discharge pipe  21 . The canister  17  temporarily stores a transpiration gas (noxious substances, such as HC) occurring in the fuel tank  15 , and has the transpiration gas sucked into the suction pipe  11  by a negative pressure during an operation (at the starting) of the engine  13 . Therefore, the fuel tank  15 , discharge pipe  16 , canister  17 , supply pipe  19  and discharge pipe  21  form an evapopassage. 
     The fuel tank  15  is provided with a level sensor  23  as a device for detecting an amount of a remaining fuel, a temperature sensor  24  as a device for detecting a temperature of the fuel, and a pressure sensor  25  as a device for detecting a pressure in the interior of the evapopassage. These sensors  23 ,  24 ,  25  are connected to an electronic control unit (which will hereinafter be referred to as ECU)  26 , and the results of detection are outputted therefrom. The ECU  26  is capable of controlling the opening and closing of the purge control valve  18  and vent control valve  20  in accordance with the operating condition of the engine  13 . 
     In this mode of embodiment of the fault diagnosing apparatus for evapopurge systems, the vent control valve  20  is closed to depressurize (depressurization device) the interior of the evapopassage by a negative pressure occurring in the interior of the suction pipe  11 , and the purge control valve  18  is thereafter closed with the vent control valve  20  kept closed, to repressurize (repressurization device) the interior of the evapopassage, damage (leakage of a transpiration gas) to the evapopassage being detected (fault judgement device) on the basis of variation of a pressure therein. In this mode of embodiment of the fault diagnosing apparatus for evapopurge systems, the making of a fault diagnosis (judgement of the abnormality of an evapopurge system) is allowed on condition that the depressurization and repressurization operations are carried out plural times. 
     A fault diagnosing method carried out by this fault diagnosing apparatus for evapopurge systems will now be described with reference to a flow chart of FIG. 2 and a time chart of FIG.  3 . 
     As shown in FIG. 2, an amount of remaining fuel detected by the level sensor  23  and a fuel temperature detected by the temperature sensor  24  are read in a step S 1 . In a step S 2 , the fault diagnosing conditions are judged as to whether they are satisfied with a permitted operational condition, i.e., a fuel temperature and an amount of the remaining fuel are judged as to whether they are not at an extremely high level, and not higher than a predetermined level, for example, 40% respectively. When the fuel temperature is not at an extremely high level with the amount of the remaining fuel over 40%, a fault diagnosing process is started. 
     In a step S 3 , a reference regained pressure value Pt and a reference number of times (reference number of times of operations) of execution Nt of depressurization and repressurization operations in the interior of the evapopassage are set. This reference regained pressure value Pt is set (reference value setting device) on the basis of a map set in advance by experiment, for example, a map of FIG. 4 showing variation of pressure (repressurization) with respect to the amount of the remaining fuel. The parenthesized numerals in the graph of FIG. 4 show that the pressure in the interior of the evapopassage does not vary greatly due to the transpiration of the fuel in the fuel tank  15 , i.e., it shows the number of times of execution of operations at which a substantial saturated condition can be attained. The reference number of times Nt is also set (number of times of operation setting device) on the basis of a map set in advance by experiment, for example, a map of FIG. 5 showing the number of times of execution of operations (processing time) with respect to the amount of the remaining fuel. 
     Thus, the reference regained pressure value Pt and reference number of times of execution Nt of operations are changed in accordance with the amount of the remaining fuel, and also in accordance with the fuel temperature. 
     In a step S 4 , the purge control valve  18  is closed, and, in a step S 5 , the vent control valve  20  is closed, whereby the interior of the evapopassage is changed from an atmospheric condition into a tightly closed condition (zones A-B in FIG.  3 ). Then, in a step S 6 , the number of times of execution N of operations is reset, and one is thereafter added to the number of times of execution N of operations in a step S 7 , i.e., N is set to N=1, the purge control valve  18  being opened in a step S 8 . Consequently, the evapopassage (supply pipe  19 ) is communicated with the suction pipe  11  in a step S 9  to cause the evapopassage to be depressurized (zone C 1  in FIG. 3) due to a negative pressure occurring in the suction pipe  11 . When the purge control valve  18  is closed in a step S 10 , the interior of the evapopassage is put in a tightly closed state again, and gradually repressurized (zone D 1  in FIG. 3) due to the occurrence of a transpiration gas, or due to the leakage of the same gas when there is damage to an inner portion of the evapopassage. In a step S 11 , the pressure in the evapopassage is detected by the pressure sensor  25  after the purge control valve is closed, and after a predetermined period of time elapses, respectively. In a step S 12 , a regained pressure ΔP representative of pressure variation in the evapopassage occurring after the lapse of a predetermined period of time and the reference regained pressure value Pt are compared with each other. 
     When there is not damage (atmosphere-opened portion) to the inner portion of the evapopassage, the actual regained pressure ΔP is not higher than the reference regained pressure value Pt (solid line shown in a zone D 1  of FIG. 3) but, when there is damage to the inner portion of the evapopassage, the actual regained pressure ΔP becomes higher (one-dot chain line shown in the zone D 1  of FIG. 3) owing to the inflow of the air than the reference regained pressure value Pt, whereby the pressure in the evapopassage returns gradually to an atmospheric pressure. 
     Therefore, when the regained pressure ΔP is not higher than the reference regained pressure value Pt in the step S 12 , a judgement that the evapopassage is free from damage and normal is given in a step S 13 , and the vent control valve  20  is opened in a step S 16  to finish the fault diagnosing process. 
     When the regained pressure ΔP is higher than the reference regained pressure value Pt in the step S 12 , it indicates that there is damage to the evapopassage, or that the sloshing of the fuel occurs. Namely, when the answer to the question in the step S 12  is affirmative, a judgement as to whether the number of times of execution N of the depressurization and repressurization operations in the evaporation passage is larger than the reference number of times of execution Nt of the same operations or not is given in the step S 14 . Namely, the step S 14  is a method of ascertaining that an increase in the regained pressure ΔP is caused by damage to the evapopassage or the sloshing of the fuel. When the depressurization and repressurization operations in the evapopassage are executed plural times, it can be rendered possible to prevent variation from occurring in the amount of regained pressure even through the sloshing of the fuel occurs. 
     When the depressurization and repressurization operations are thus carried out plural times in the evapopassage, the air therein is discharged, and a saturated condition in which the evapopassage is filled with a transpiration gas is formed, and pressure variation due to the sloshing of the fuel does not substantially occur. When the regained pressure ΔP increases even in this condition, a judgement that there is damage to the evapopassage can be given. 
     Therefore, when a judgement that the regained pressure ΔP is not higher than the reference regained pressure value Pt is not given in the step S 12 , the operation is returned from the step S 14  to the step S 7  to repeat the process of the steps S 7 -S 14  (except S 13 ) until the number of times of execution N of depressurization and repressurization operations exceeds the reference number of times of execution Nt of the same operations. The reference number of times of execution Nt of these operations is set on the basis of the fuel temperature and the amount of the remaining fuel. 
     When the process of the steps S 7 -S 14  is thus repeated with damage to the evapopassage not existing, the interior of the evapopassage is saturated with a transpiration gas, so that the regained pressure ΔP due to the transpiration gas is held down. Consequently, the regained pressure ΔP becomes not higher than the reference regained pressure value Pt in the step S 12 , and the operation advances to the step S 13 , in which a judgement that the evapopassage is free from damage and normal is given. 
     When there is damage to the evapopassage, the regained pressure ΔP exceeds the reference regained pressure Pt due to the inflow of the air from the damaged portion (atmosphere-opened portion) even though the process of the steps S 7 -S 14  is repeated, so that the number of times of execution N of the depressurization and repressurization operations exceeds the reference number of times of execution Nt of the same operations. 
     Accordingly, in the step S 14 , giving a judgement that the evapopurge system is abnormal is allowed on condition that the number of times of execution N of the depressurization and repressurization operations exceeds the reference number of times of execution Nt. In a step S 15 , a judgement that the evapopurge system is abnormal due to the existence of damage to the evapopassage is given, and an alarm lamp is lit or an alarm sound is made against the driver. In a step S 16 , the vent control valve  20  is opened to finish the fault diagnosing process. 
     Thus, in this mode of embodiment of the fault diagnosing apparatus for evaposystems, depressurization and repressurization operations are executed plural times in the evapopassage to put the interior of the evapopassage in a transpiration gas-filled saturated state in which pressure variation ascribed to the sloshing of a fuel does not substantially occur, and the magnitude of the regained pressure ΔP is then determined, whereby the damage (leakage of the transpiration gas) to the evapopassage can be detected properly. 
     In this mode of embodiment, a judgement that the evapopurge system has a fault is allowed to be given in the step S 2  on condition that the amount of the remaining fuel is not smaller than 40% but the amount of the remaining fuel is not limited to this numerical value. When the reduction of the diagnosis processing time is desired, the amount of the remaining fuel, which constitutes the conditions for allowing a judgement that the evapopurge system has a fault to be given, may be set, for example, larger than 40%. Although the reference number of times of execution Nt of depressurization and repressurization operations in this embodiment is set on the basis of the amount of the remaining fuel and fuel temperature, it may be set on the basis of only the amount of the remaining fuel so as to simplify the maps to be used.