Patent Publication Number: US-9404445-B2

Title: Evaporated fuel treatment apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the foreign priority benefit under Title 35, United States Code, §119(a)-(d) of Japanese Patent Application No. 2013-107757, filed on May 22, 2013 in the Japan Patent Office and Japanese Patent Application No. 2013-107758, filed on May 22, 2013 in the Japan Patent Office, the disclosures of which are herein incorporated by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an evaporated fuel treatment apparatus for treating evaporated fuel. 
     2. Description of the Related Art 
     For example, on a vehicle provided with an internal combustion engine, when a fuel tank is filled with liquid fuel, the occupied volume of the liquid fuel reserved in the inner space of the fuel tank increases. As a result, the occupied volume of the gas phase region in the inner space relatively decreases so that the pressure of the gas phase region (hereinafter, referred to as ‘tank internal pressure’) becomes higher than the atmospheric pressure. Consequently, the evaporated fuel of the gas phase region remaining in the fuel tank urges to get out into the atmosphere. If the evaporated fuel is released out into the atmosphere, the atmosphere (global environment) comes to be contaminated. 
     In this situation, in order to prevent contamination of the atmosphere (global environment) caused by releasing evaporated fuel out into the atmosphere, a conventional evaporated fuel treatment apparatus is provided with a canister having an absorbing member at a communication passage between a fuel tank and the atmosphere to temporarily absorb the evaporation material, and the evaporated fuel is thereby absorbed by the absorbing member of the canister so that the tank internal pressure is prevented from increasing. 
     For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-77595 (Paragraphs 0028-0030)) discloses an evaporated fuel treatment apparatus that includes a fuel tank, a canister, a charge communication passage for communication and connection between the fuel tank and the canister, an air communication passage for communication and connection between the canister and the atmosphere, a vent shut valve for opening and closing the air communication passage, a purge communication passage for communication and connection between the canister and an internal combustion engine, and a purge control valve for opening and closing the purge communication passage. The vent shut valve is open during fuel feeding or purge execution. The purge control valve is open during purge execution. 
     On the evaporated fuel treatment apparatus disclosed by Patent Document 1, after an internal combustion engine is stopped, selectively used are a first determination method based on a parameter corresponding to the secondary differential value of the internal pressure of the fuel tank and a second determination method based on a stagnation time of the internal pressure of the fuel tank, and performed is leak diagnosis of the evaporated fuel tightly-sealed system including the fuel tank. Concretely, if the generation amount of the evaporated fuel in the fuel tank is comparatively large, a diagnosis result by the first determination method is selected while, if the generation amount of the evaporated fuel is comparatively small, a diagnosis result by the second determination method is selected. 
     The evaporated fuel treatment apparatus according to Patent Document 1 enables accurate leak diagnosis of the evaporated fuel treatment apparatus with a comparatively simple configuration during when an internal combustion engine is stopped. 
     SUMMARY OF THE INVENTION 
     The principles of leak diagnoses related to the first and second determination methods used for the evaporated fuel treatment apparatus according to Patent Document 1 are both based on that, assuming that the ambient temperature related to the fuel tank fluctuates, the transition characteristic of the tank internal pressure is highly correlated with the existence or non-existence of a leak of the evaporated fuel tightly-closed system including the fuel tank, wherein the transition characteristic fluctuates in time-series in the process in which liquid fuel sealed in the inner space of the fuel tank evaporates (or liquefies), accompanying change in the ambient temperature related to the fuel tank. 
     Accordingly, in order to perform leak diagnosis with high accuracy in a short time on the evaporated fuel treatment apparatus related to Patent Document 1, it is desirable that the ambient temperature related to the fuel tank dynamically fluctuates from second to second. 
     However, for example, in a case that the evaporated fuel treatment apparatus according to Patent Document 1 is applied to a hybrid vehicle, on which an internal combustion engine and an electric motor are mounted as power sources and the internal combustion engine being the primary heat source operates only intermittently, if the internal combustion engine is operated with a low frequency, the fluctuation range of the ambient temperature related to the fuel tank becomes relatively smaller than an existing vehicle on which only an internal combustion engine is mounted as a power source. As a result, it has been difficult to perform leak diagnosis, with high accuracy, of an evaporated fuel tightly-closed system. 
     The present invention has been developed to solve the above-described problems, and an object of the invention is to provide an evaporated fuel treatment apparatus capable of performing with high accuracy leak diagnosis of an evaporated fuel tightly-closed system even when, for example, the invention is applied to a hybrid vehicle. 
     In order to achieve the above-described object, in aspect (1) of the present invention, an evaporated fuel treatment apparatus includes: a fuel tank for reserving fuel, the tank being mounted on a vehicle having an internal combustion engine; a canister provided between communication passages connecting the fuel tank and atmosphere to collect evaporated fuel exhausted from the fuel tank through the communication passage; an on-off valve provided at the communication passage connecting the canister and the atmosphere to open or close the canister to/from the atmosphere; a tank internal pressure detection section for detecting a tank internal pressure of the fuel tank; a control section for issuing an instruction to open or close the on-off valve; and a diagnosis section for performing leak diagnosis of an evaporated fuel tightly-closed system including the fuel tank. 
     After an ignition switch of the vehicle is turned off, in a first diagnosis stage in which the on-off valve is in a close state, according to the instruction from the control section, the diagnosis section performs a first leak diagnosis, based on a relationship between the tank internal pressure detected by the tank internal pressure detection section and a predetermined first threshold value; and after the first leak diagnosis is completed, in a second leak diagnosis stage in which the on-off valve is in the close state, according to the instruction from the control section, the diagnosis section performs a second leak diagnosis, based on a relationship between the tank internal pressure detected by the tank internal pressure detection section and a predetermined second threshold value. The on-off valve is once opened, according to the instruction from the control section, after the first leak diagnosis is completed. Then, the first threshold value used in the first diagnosis stage is set with a larger deviation from an atmospheric pressure compared with the second threshold value used in the second diagnosis stage. 
     In aspect (1) of the invention, in performing leak diagnosis after the ignition switch of the vehicle is turned off, dividing the leak diagnosis into two stages, the residual heat of the internal combustion engine and the exhaustion system of the internal combustion engine after the turning off of the ignition switch has more significant effect in the first diagnosis stage than in the second diagnosis stage, and accordingly the first threshold value used in the first diagnosis stage is set with a larger deviation from the atmospheric pressure compared with the second threshold value used in the second diagnosis stage. 
     In aspect (1) of the invention, the first and second threshold values are appropriately set, taking into account the respective widths of fluctuation of the tank internal pressures detected by the tank internal detection section in the first and second diagnosis stages. Accordingly, it is possible to perform with high accuracy a leak diagnosis of an evaporated fuel tightly-closed system even when, for example, the invention is applied to a hybrid vehicle. 
     In aspect (2) of the present invention, the evaporated fuel treatment apparatus in aspect (1) is arranged such that a first diagnosis period of the first diagnosis stage is within a stabilizing time period that is supposed to be required for stabilization of the tank internal pressure in comparison with a state immediately after the ignition switch is turned off, and the first diagnosis period is set to a time length shorter than a second diagnosis period of the second diagnosis stage. 
     In aspect (2) of the invention, in performing leak diagnosis after the ignition switch of the vehicle is turned off, dividing the leak diagnosis into two stages, the residual heat of the internal combustion engine and the exhaustion system of the internal combustion engine after the turning off of the ignition switch has more significant effect in the first diagnosis stage than in the second diagnosis stage, and accordingly the first diagnosis period is set to a shorter time length compared with the second diagnosis period. 
     According to aspect (2) of the invention, the lengths of the first and second diagnosis periods are appropriately set, taking into account the respective temporal variation rates of the tank internal pressures detected by the tank internal detection section in the first and second diagnosis stages. Accordingly, the accuracy of leak diagnosis of an evaporated fuel tightly-closed system can be further improved, compared with that in aspect (1). 
     In aspect (3) of the present invention, the evaporated fuel treatment apparatus in aspect (1) is arranged such that the on-off valve is once opened, according to the instruction from the control section, within a stabilizing time period that is supposed to be required for stabilization of the tank internal pressure in comparison with a state immediately after the ignition switch is turned off; and the diagnosis section starts the second diagnosis immediately after the on-off valve is turned from an open state to the close state, according to the instruction from the control section. 
     In aspect (4) of the present invention, the evaporated fuel treatment apparatus in aspect (2) is arranged such that the on-off valve is once opened, according to the instruction from the control section, within a stabilizing time period that is supposed to be required for stabilization of the tank internal pressure in comparison with a state immediately after the ignition switch is turned off; and the diagnosis section starts the second diagnosis immediately after the on-off valve is turned from an open state to the close state, according to the instruction from the control section. 
     According to aspect (3) or (4) of the invention, according to the instruction from the control section, the on-off valve is once opened within a stabilizing time period that is supposed to be required for stabilization of the tank internal pressure in comparison with a state immediately after the ignition switch is turned off, and the diagnosis section starts the second diagnosis, omitting a wasteful time, immediately after the on-off valve is turned from an open state to a close state, according to the instruction from the control section. Accordingly, it is possible to perform leak diagnosis of an evaporated fuel tightly-closed system in a shorter time and with a further higher accuracy compared with aspect (1) or (2). 
     Similarly to aspect (1) of the invention, in aspect (5) of the invention, an evaporated fuel treatment apparatus includes: a fuel tank for reserving fuel, the tank being mounted on a vehicle having an internal combustion engine; a canister provided between communication passages connecting the fuel tank and atmosphere to collect evaporated fuel exhausted from the fuel tank through the communication passage; an on-off valve provided at the communication passage connecting the canister and the atmosphere to open or close the canister to/from the atmosphere; a tank internal pressure detection section for detecting a tank internal pressure of the fuel tank; a control section for issuing an instruction to open or close the on-off valve; and a diagnosis section for performing leak diagnosis of an evaporated fuel tightly-closed system including the fuel tank. 
     In a state that the on-off valve is closed according to the instruction from the control section after an ignition switch of the vehicle is turned off, the diagnosis section: performs a leak diagnosis of the evaporated fuel tightly-closed system, using a double differentiation method based on a correlation parameter related to a secondary differentiation value of the tank internal pressure detected by the tank internal pressure detection section; performs a leak diagnosis of the evaporated fuel tightly-closed system, using a stagnation time method based on a relationship between a tank internal pressure detected by the tank internal pressure detection section and a stagnation time of the tank internal pressure; and uses a result of the leak diagnosis using the stagnation time method, giving priority over a result of the leak diagnosis using the double differentiation method. 
     The evaporated fuel treatment apparatus in aspect (5) of the invention uses a result of a leak diagnosis using the stagnation time method with a higher accuracy compared with the double differentiation method, giving priority over a result of a leak diagnosis using the double differentiation method. Concretely, for example, in a case that the result of the leak diagnosis using the stagnation time method is a normal state without leak, the diagnosis section determines a normal state without leak, regardless of the result of the leak diagnosis using the double differentiation method. 
     According to aspect (5) of the invention, a result of a leak diagnosis using a stagnation time method with a higher diagnosis accuracy compared with a double differentiation method is used, being given priority over a result of leak diagnosis using the double differentiation method. Accordingly, it is possible to perform a leak diagnosis of an evaporated fuel tightly-closed system even when the invention is applied, for example, to a hybrid vehicle. 
     In aspect (6) of the present invention, the evaporated fuel treatment apparatus in aspect (5) is arranged such that a diagnosis time for obtaining a result of a leak diagnosis using the stagnation time method is set to a time length longer than a diagnosis time for obtaining a result of a leak diagnosis using the double differentiation method. 
     According to aspect (6) of the invention, the diagnosis time for obtaining a result of a leak diagnosis using the stagnation time method is set to a time length longer than the diagnosis time for obtaining a result of a leak diagnosis using the double differentiation method. Accordingly, it is possible to perform a leak diagnosis of an evaporated fuel tightly-closed system with a further higher accuracy. 
     In aspect (7) of the present invention, the evaporated fuel treatment apparatus in aspect (5) is arranged such that, in a first diagnosis stage in which the on-off valve is in a close state according to the instruction from the control section after the ignition switch of the vehicle is turned off, the diagnosis section performs a first leak diagnosis based on a relationship between the tank internal pressure detected by the tank internal pressure detection section and a predetermined first threshold value; and in a second diagnosis stage in which the on-off valve is in the close state according to the instruction from the control section after completion of the first leak diagnosis, the diagnosis section performs a second leak diagnosis, using a pressure fluctuation detection method based on a relationship between the tank internal pressure detected by the tank internal pressure detection section and a predetermined second threshold value, the double differentiation method, and the stagnation time method. 
     After the first leak diagnosis is completed, the on-off valve is once opened according to the instruction from the control section, and if a result of the second leak diagnosis using the pressure fluctuation detection method is an abnormal state with leak, the diagnosis section determines an abnormal state with leak, regardless of a result of the second leak diagnosis using the double differentiation method or the stagnation time method. 
     According to aspect (7) of the invention, in a case that a result of the second leak diagnosis using the pressure fluctuation detection method is an abnormal state with leak, the diagnosis section determines an abnormal state with leak, regardless of a result of the second leak diagnosis using the double differentiation method or the stagnation time method. Accordingly, a leak diagnosis of an evaporated fuel tightly-closed system can be performed in a shorter time, compared with aspect (5) of the invention. 
     In aspect (8) of the present invention, the evaporated fuel treatment apparatus in aspect (6) is arranged such that, in a first diagnosis stage in which the on-off valve is in a close state according to the instruction from the control section after the ignition switch of the vehicle is turned off, the diagnosis section performs a first leak diagnosis based on a relationship between the tank internal pressure detected by the tank internal pressure detection section and a predetermined first threshold value; and in a second diagnosis stage in which the on-off valve is in the close state according to the instruction from the control section after completion of the first leak diagnosis, the diagnosis section performs a second leak diagnosis, using a pressure fluctuation detection method based on a relationship between the tank internal pressure detected by the tank internal pressure detection section and a predetermined second threshold value, the double differentiation method, and the stagnation time method. 
     After the first leak diagnosis is completed, the on-off valve is once opened according to the instruction from the control section. If a result of the second leak diagnosis using the pressure fluctuation detection method is an abnormal state with leak, the diagnosis section determines an abnormal state with leak, regardless of a result of the second leak diagnosis using the double differentiation method or the stagnation time method. 
     According to aspect (8) of the invention, in a case that a result of the second leak diagnosis using the pressure fluctuation detection method is an abnormal state with leak, the diagnosis section determines an abnormal state with leak, regardless of a result of the second leak diagnosis using the double differentiation method or the stagnation time method. Accordingly, a leak diagnosis of an evaporated fuel tightly-closed system can be performed in a shorter time, compared with aspect (6) of the invention. 
     An evaporated fuel treatment apparatus according to the invention enables performing leakage diagnosis, with high accuracy, of an evaporated fuel tightly-closed system, for example, even in a case of applying the invention to a hybrid vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an entire configuration diagram showing the overview of an evaporated fuel treatment in an embodiment according to the present invention; 
         FIG. 2A  is a flowchart diagram showing the flow of a leak diagnosis process performed by the evaporated fuel treatment apparatus in an embodiment according to the invention; 
         FIG. 2B  is a flowchart diagram showing the flow of integrated leak diagnosis performed by an evaporated fuel treatment apparatus in an embodiment according to the invention; 
         FIG. 3A  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in a normal state without leak) of a comparative example after switching the ignition switch from ON to OFF; 
         FIG. 3B  is a time chart diagram for illustrating the operation of the evaporated fuel treatment apparatus (in the normal state without leak) of the comparative example after switching the ignition switch from ON to OFF; 
         FIG. 3C  is a time chart diagram for illustrating the operation of the evaporated fuel treatment apparatus (in the normal state without leak) of the comparative example after switching the ignition switch from ON to OFF; 
         FIG. 3D  is a time chart diagram for illustrating the operation of the evaporated fuel treatment apparatus (in the normal state without leak) of the comparative example after switching the ignition switch from ON to OFF; 
         FIG. 3E  is a time chart diagram for illustrating the operation of the evaporated fuel treatment apparatus (in an abnormal state with leak) of the comparative example after switching the ignition switch from ON to OFF; 
         FIG. 3F  is a time chart diagram for illustrating the operation of the evaporated fuel treatment apparatus (in the abnormal state with leak) of the comparative example after switching the ignition switch from ON to OFF; 
         FIG. 3G  is a time chart diagram for illustrating the operation of the evaporated fuel treatment apparatus (in the abnormal state with leak) of the comparative example after switching the ignition switch from ON to OFF; 
         FIG. 3H  is a time chart diagram for illustrating the operation of the evaporated fuel treatment apparatus (in the abnormal state with leak) of the comparative example after switching the ignition switch from ON to OFF; 
         FIG. 4A  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in a normal state without leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4B  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the normal state without leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4C  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the normal state without leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4D  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the normal state without leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4E  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the normal state without leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4F  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the normal state without leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4G  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the normal state without leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4H  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the normal state without leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4I  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in an abnormal state with leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4J  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the abnormal state with leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; 
         FIG. 4K  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in the abnormal state with leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention; and 
         FIG. 4L  is a time chart diagram for illustrating the operation of an evaporated fuel treatment apparatus (in an abnormal state with leak) after switching the ignition switch from ON to OFF, in an embodiment according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Evaporated fuel treatment apparatuses in embodiments according to the present invention will be described below, referring to the drawings. 
     Overview of an Evaporation Fuel Treatment apparatus  11  in an Embodiment of the Invention 
     First, overview of an evaporated fuel treatment apparatus  11  in an embodiment according to the invention will be described with reference to  FIG. 1 , taking an example applied to a hybrid vehicle provided with an internal combustion engine  13  and an electric motor (not shown) as driving sources.  FIG. 1  is an entire configuration diagram showing the overview of an evaporated fuel treatment apparatus  11  in an embodiment according to the present invention. 
     Incidentally, the same reference symbol will be assigned to the same member or corresponding members in the drawings described below. The size and the shape of a member may be schematically represented with deformation or exaggeration for the convenience of illustration. 
     As shown in  FIG. 1 , the evaporated fuel treatment apparatus  11  taking the role of treating evaporated fuel is provided with a fuel tank  15  for reserving fuel such as gasoline, the fuel tank  15  being mounted on a vehicle having an internal combustion engine  13 , a canister  17  having a function to absorb evaporated fuel generated in the fuel tank  15 , and an ECU (Electronic Control unit)  19  performing integrated control of the evaporated fuel treatment apparatus  11 . 
     The fuel tank  15  is provided with a fuel inlet pipe  21 . A fuel fill opening  21   a , into which the nozzle of a fuel fill gun (neither not shown) is inserted, is provided on the side of the fuel inlet pipe  21  opposite to the fuel tank  15  side. A screw type filler cap  23  is fitted to the fuel fill opening  21   a.    
     The fuel tank  15  is provided with an evaporated fuel exhaust passage  25  for communication and connection between the fuel tank  15  and the canister  17 . The evaporated fuel exhaust passage  25  has a function as a flow passage of the evaporated fuel. The canister  17  is provided with an atmospheric air flow passage  26  for communication and connection between the canister  17  and the atmosphere. The atmospheric air flow passage  26  has a function as a flow passage of atmospheric air. The evaporated fuel exhaust passage  25  and the atmospheric air flow passage  26  are corresponding to ‘communication passage’ according to the invention. 
     The evaporated fuel exhaust passage  25  is provided with a tank internal pressure sensor  27 . The tank internal pressure sensor  27  corresponds to ‘tank internal pressure detection section’ according to the invention. The tank internal pressure sensor  27  has a function to detect tank internal pressure Ptank that is a pressure in the gas phase region in the fuel tank  15 . Alternately, arrangement may be made such that the tank internal pressure sensor  27  is provided directly to the fuel tank  15 . As the pressure detection section of the tank internal pressure sensor  27 , for example, a piezoelectric element can be used. Information regarding the tank internal pressure Ptank detected by the tank internal pressure sensor  27  is sent to the ECU  19 . 
     Incidentally, when the canister  17  is communicating with the atmosphere by opening an atmosphere on-off valve  29 , the tank internal pressure sensor  27  can detect the atmospheric pressure. On the other hand, when a later-described ‘evaporated fuel tightly-closed system’ is formed by closing the atmosphere on-off valve  29  and a purge control valve  35 , the tank internal pressure sensor  27  can detect the fluctuation of the tank internal pressure Ptank of the fuel tank  15 . The atmospheric air flow passage  26  is provided with the atmosphere on-off valve  29 . The atmosphere on-off valve  29  corresponds to ‘on-off valve’ according to the invention. The atmosphere on-off valve  29  has a function to open or close the inner space of the canister  17  to/from the atmosphere. Concretely, the atmosphere on-off valve  29  is a normally-closed electromagnetic valve that operates according to a control signal transmitted from the ECU  19 . When current is not applied, the atmosphere on-off valve  29  is closed so that the canister  17  and the atmosphere are shielded from each other, and when the atmosphere on-off valve  29  is opened, according to an open control signal from the ECU  19 , the canister  17  and the atmosphere communicate with each other. 
     The canister  17  contains an absorbing member (not shown) of activated carbon for absorbing evaporated fuel. The absorbing member of the canister  17  absorbs evaporated fuel transferred from the fuel tank  15  side through the evaporated fuel exhaust passage  25 . The canister  17  is communicated and connected with, in addition to the atmospheric air flow passage  26 , a purge communication passage  31  used in performing purge processing. The canister  17  is communicated and connected with an intake pipe (intake manifold)  33  through the purge communication passage  31 . 
     In the purge processing, by opening a purge control valve  35  described below, the evaporated fuel absorbed by the absorbing member of the canister  17  is transferred to the intake pipe  33  through the purge communication passage  31 , together with air taken in through the atmospheric air flow passage  26 . 
     The purge communication passage  31  is provided with the purge control valve  35 . The purge control valve  35  has a function to open or close the purge communication passage  31  for communication and connection between the canister  17  and the intake pipe  33 . Concretely, the purge control valve  35  is a normally-open electromagnetic valve that operates, according to a control signal transmitted from the ECU  19 . The purge control valve  35  shields the canister  17  and the intake pipe  33  from each other by being closed when current is not applied, and on the other hand, operates to make the canister  17  and the intake pipe  33  communicate with each other by being opened, according to an open control signal from the ECU  19 . 
     Herein, ‘evaporated fuel tightly-closed system’ according to the invention refers to a closed space partitioned by the fuel tank  15 , the evaporated fuel exhaust passage  25 , the canister  17 , the atmospheric air flow passage  26  and the atmosphere on-off valve  29 , and the purge communication passage  31  and the purge control valve  35 . 
     The fuel tank  15  and the intake pipe  33  are communicated and connected with each other through a fuel supply passage  37 . The fuel supply passage  37  is provided with a fuel pump module  39  for pumping up fuel reserved in the fuel tank  15  and supplying out the fuel to a fuel injection nozzle  41 . The fuel injected from the fuel injection nozzle  41  is supplied to the internal combustion engine  13  in a state of mixture with air supplied from the intake pipe  33 . 
     As shown in  FIG. 1 , the ECU  19  is connected with, as an input system, the above-described tank internal pressure sensor  27 , an ignition switch  43 , an atmospheric pressure sensor  45 , and a vehicle speed sensor  47 . The vehicle speed sensor  47  has a function to detect the speed of the own vehicle (not shown). Information related to the speed of the own vehicle detected by the vehicle speed sensor  47  is transmitted to the ECU  19 . 
     Further, as shown in  FIG. 1 , the ECU  19  is connected with, as an output system, the above-described atmosphere on-off valve  29 , the purge control valve  35 , the fuel pump module  39 , and the fuel injection nozzle  41 . 
     As shown in  FIG. 1 , the ECU  19  is provided with a storage section  51 , a diagnosis section  53 , and a control section  55 . The ECU  19  is configured by a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. This microcomputer reads out and executes programs and data stored in the ROM, and operates such as to perform integrated control of the entire of the leak diagnosis function of the ECU  19  and the evaporated fuel treatment apparatus  11 . 
     The storage section  51  has a function to store a first threshold value P_th 1 , a second threshold value P_th 2 , a first diagnosis period dt 1  related to a first diagnoses stage, a second diagnosis period dt 2  related to a second leak diagnosis, a preset open time period ot of the atmosphere on-off valve  29 , and the like. The preset open time period ot of the atmosphere on-off valve  29  can be set, as appropriate, to a time length that is long enough for the pressure (tank internal pressure Ptank) of the evaporated fuel tightly-closed system to be reset to the atmospheric pressure. 
     The first and second threshold values P_th 1  and P_th 2 , the first and second diagnosis periods dt 1  and dt 2 , and the preset open time period ot of the atmosphere on-off valve  29  are referred to, as appropriate, in performing, for example, leak diagnosis by the diagnosis section  53  in the first and second diagnosis stages described later. 
     The diagnosis section  53  has a function to perform leak diagnosis of the evaporated fuel tightly-closed system. This function will be described below in more details. That is, after the ignition switch  43  of the own vehicle is turned off, in the first diagnosis stage where the atmosphere on-off valve  29  is closed according to a closing instruction from the control section  55 , the diagnosis section  53  performs the first leak diagnosis, based on the relationship between a tank internal pressure Ptank by the tank internal pressure sensor  27  and the first threshold value P_th 1 , and after performing the first leak diagnosis, in the second diagnosis stage where the atmosphere on-off valve  29  is closed according to a closing instruction from the control section  55 , the diagnosis section  53  performs the second leak diagnosis, based on the relationship between a tank internal pressure Ptank detected by the tank internal pressure sensor  27  and the second threshold value P_th 2 . 
     Herein, in an embodiment according to the invention, for a method of leak diagnosis of the evaporated fuel tightly-closed system, a pressure fluctuation detection method (hereinafter, referred to as ‘PFD method’), a double differentiation method (hereinafter, referred to as ‘DDP method’), and a stagnation time method (hereinafter, referred to as ‘DTM method’) will be used. In performing leak diagnosis using PFD method, DDP method, and DTM method, it is assumed that an evaporated fuel tightly-closed system is formed (The atmosphere on-off valve  29  and the purge control valve  35  are in a closed state). 
     Incidentally, a leak diagnosis method by DDP method and DTM method are described in detail, for example, in Japanese Patent Application Laid-Open No. 2006-77595. This patent application publication is incorporated by reference in the specification of present application. Accordingly, only overview of the leak diagnosis method by DDP method and DTM method will be described here. 
     First, a principle common to leak diagnosis methods related to PFD method, DDP method, and DTM method will be described below. In general, assuming that an evaporated fuel tightly-closed system is formed in a normal state (without leak), when a certain time has elapsed from a time when the internal combustion engine  13  was stopped (turning off the ignition switch  43 ), the tank internal pressure Ptank deviates from the vicinity of the atmospheric pressure (a certain allowable range including the atmospheric pressure) in most cases. This is because inside the fuel tank  15  of a parked vehicle, in general, evaporated fuel is generated from the effect of residual heat of the internal combustion engine  13  or the ambient temperature. 
     However, if the evaporated fuel tightly-closed system including the fuel tank  15  has a leak, the temporal characteristic of the tank internal pressure Ptank shows a special tendency, such as convergence to the vicinity of the atmospheric pressure. Accordingly, based on whether or not the temporal characteristic of the tank internal pressure Ptank shows the above-described special tendency, it is possible to make a diagnosis as to whether or not an evaporated fuel tightly-closed system has a leak. 
     The overview of PFD method will be described below. When the evaporated fuel tightly-closed system is in a normal state (without leak), the temporal characteristic of the tank internal pressure Ptank detected by the tank internal pressure sensor  27  tends to increase substantially linearly with a relatively large gradient. On the other hand, when the evaporated fuel tightly-closed system is in an abnormal state (with leak), it tends to that, in most cases, the temporal characteristic of the tank internal pressure Ptank at first increases with a relatively large variation rate (the gradient of the temporal characteristic graph of the tank internal pressure Ptank), however, the tank internal pressure Ptank plateaus at a certain pressure level corresponding to the diameter of a hole, and then the variation rate (the gradient of the temporal characteristic graph) gradually decreases. 
     Accordingly, it is possible to make a diagnosis as to whether or not the evaporated fuel tightly-closed system has a leak by evaluating the tendency of the temporal characteristic of the tank internal pressure Ptank. Concretely, a leak diagnosis is made, based on the relationship between a tank internal pressure Ptank and predetermined threshold values (for example, the first threshold value P_th 1  and the second threshold value P_th 2 ). If the tank internal pressure Ptank detected by the tank internal pressure sensor  27  has exceeded the threshold value/values (for example, the first threshold value P_th 1  and the second threshold value P_th 2 ), the diagnosis determines that the evaporated fuel tightly-closed system is in a normal state (without a leak). 
     Therefore, according to PFD method, a leak diagnosis of the evaporated fuel tightly-closed system can be made by determining as to whether or not the tank internal pressure Ptank, which is detected after stopping the internal combustion engine  13  (turning off the ignition switch  43 ), has exceeded a threshold (for example, the first threshold value P_th 1  and the second threshold value P_th 2 ). 
     The overview of DDP method will be described below. If the evaporated fuel tightly-closed system is in a normal state (without a leak), the temporal characteristic of the tank internal pressure Ptank detected by the tank internal pressure sensor  27  tends to increase substantially linearly with a relatively large gradient. On the other hand, if the evaporated fuel tightly-closed system is in an abnormal state (with a leak), it tends to that, in most cases, the temporal characteristic of the tank internal pressure Ptank at first increases with a relatively large variation rate (the gradient of the temporal characteristic graph of the tank internal pressure Ptank), however, the tank internal pressure Ptank plateaus at a certain pressure level corresponding to the diameter of the hole, and then the variation rate (the gradient of the temporal characteristic graph) gradually decreases. 
     Therefore, it is possible to make a diagnosis as to whether or not an evaporated fuel tightly-closed system has a leak by evaluating the tendency of the temporal characteristic of the above-described tank internal pressure Ptank. Concretely, in order to make a leak diagnosis with high accuracy even if the generation amount of the evaporated fuel fluctuates with time, the double differential value (can also be the correlation value of the double differential value) obtained by twice differentiating the tank internal pressure Ptank is used as a determination parameter. Then, the determination parameter becomes approximately ‘0’ when the evaporated fuel tightly-closed system is in a normal state, and the determination parameter becomes a negative value when the evaporated fuel tightly-closed system is in an abnormal state. 
     Accordingly, by DDP method, a leak diagnosis of an evaporated fuel tightly-closed system can be made by evaluating the value of a determination parameter. 
     However, by the above-described DDP method, it is difficult to detect a leak abnormality in case that a comparatively small hole is made through the evaporated fuel tightly-closed system and the gradient of a temporal characteristic graph of the tank internal pressure Ptank is gradual. The following DTM method is effective in a case that leak abnormality is caused by a small hole (hereinafter, referred to as ‘small hole leak’) as described above. 
     In DTM method, first, the time period of (continuous) convergence of the tank internal pressure Ptank detected by the tank internal pressure sensor  27  in a certain pressure range is defined as stagnation time TSTY. Then, making x-axis represent the tank internal pressure Ptank and y-axis represent the stagnation time TSTY, a correlation characteristic graph representing the transition of the stagnation time TSTY accompanying change in the tank internal pressure Ptank is created, and a regression graph of the correlation characteristic graph is drawn. If attention is focused on the gradient of the regression graph of the correlation characteristic graph representing the transition of the stagnation time TSTY accompanying change in the tank internal pressure Ptank, in case that the evaporated fuel tightly-closed system is in a normal state (without a leak), the gradient of the regression graph is of a relatively small positive value, and on the other hand, in case that the evaporated fuel tightly-closed system is in an abnormal state (with a leak), the gradient of the regression graph is of a negative value with a large absolute value. 
     Thus, by DTM method, depending on whether the gradient of the regression graph of the correlation characteristic graph is of a positive value or a negative value, and by evaluation of the magnitude relationship, the existence or non-existence of leak of the evaporated fuel tightly-closed system can be diagnosed, including small hole leak. 
     The control section  55  has a function to perform integrated control of the entire evaporated fuel treatment apparatus  11 . Further, the control section  55  also has a function to issue an instruction to close the atmosphere on-off valve  29  and the purge control valve  35 , for example, after the ignition switch  43  is turned off (The internal combustion engine  13  is stopped). Incidentally, if an arrangement is adopted such that current supply to the purge control valve  35  is stopped when the ignition switch  43  is turned off, it is possible to configure the control section  55 , omitting the function to issue an instruction to close the purge control valve  35 . 
     Operation of the Evaporation Fuel Treatment apparatus  11  in an Embodiment According to the Invention 
     The operation of an evaporated fuel treatment apparatus  11  in an embodiment according to the invention will be described below, referring to  FIG. 2A . 
       FIG. 2A  is a flowchart diagram showing the flow of a leak diagnosis process performed by an evaporated fuel treatment apparatus in an embodiment according to the invention. 
     In step S 11  shown in  FIG. 2A , the ECU  19  checks whether or not the ignition switch  43  has been turned off. The ECU  19  repeats the determination processing in step S 11  until it is determined that the ignition switch  43  has been turned off. 
     As a result of the determination in step S 11 , if it is determined that the ignition switch  43  has been turned off (‘Yes’ in step S 11 ), then the ECU  19  makes the flow of the process proceed to the next step S 12 . 
     In step S 12 , the control section  55  of the ECU  19  performs control to make the atmosphere on-off valve  29  into a close state. When the atmosphere on-off valve  29  is thus closed, and the purge control valve  35  is closed (by stopping current supply), an evaporated fuel tightly-closed system is formed, and preparation for a leak diagnosis is thereby complete. 
     In step S 13 , the diagnosis section  53  performs the first leak diagnosis. The first leak diagnosis is the procedure of a leak diagnosis, of the evaporated fuel tightly-closed system, that is performed by the diagnosis section  53  in the first diagnosis stage beginning immediately after the turning off of the ignition switch  43  and uses PFD method (pressure fluctuation detection method). The first diagnosis period dt 1  of the first diagnosis stage is within a stabilizing time period that is started at the turning off time of the ignition switch  43  and is supposed to be required for stabilization of the tank internal pressure Ptank detected by the tank internal pressure sensor  27 , in comparison with the state immediately after the ignition switch  43  is turned off. The first diagnosis period dt 1  is set to a time length shorter than the second diagnosis period d of the second diagnosis stage described later. The first leak diagnosis will be described in detail later. 
     In step S 14 , the ECU  19  refers to the first diagnosis period dt 1  stored in the storage section  51 , and checks whether or not the elapsed time from the turning off of the ignition switch  43  has reached the first diagnosis period dt 1  (whether or not the first leak diagnosis is complete.) The ECU  19  repeats the determination processing of step S 14  until it is determined that the elapsed time from the turning off of the ignition switch  43  has reached the first diagnosis period dt 1  (The first leak diagnosis is complete.) 
     As a result of the determination in step S 14 , if it is determined that the elapsed time from the time of turning off the ignition switch  43  has reached the first diagnosis period dt 1  (The first leak diagnosis is complete.) (‘Yes’ in step S 14 ), the ECU  19  makes the flow of the process proceed to the next step S 15 . 
     In step S 15 , the control section  55  of the ECU  19  performs control to make the atmosphere on-off valve  29  into an open state. When the atmosphere on-off valve  29  is thus opened, the tank internal pressure Ptank detected by the tank internal pressure sensor  27  converges to the atmospheric pressure. 
     In step S 16 , the ECU  19  refers to the preset open time period ot of the atmosphere on-off valve  29  stored in the storage section  51 , and thereby checks whether or not the open time period of the atmosphere on-off valve  29  has reached the preset open time period ot. The ECU  19  repeats the determination processing of step S 16  until it is determined that the open time period of the atmosphere on-off valve  29  has reached the preset open time period ot of the atmosphere on-off valve  29 . 
     As a result of the determination in step S 16 , if it is determined that the open time period of the atmosphere on-off valve  29  has reached the preset open time period ot of the atmosphere on-off valve  29  (‘Yes’ in step S 16 ), then the ECU  19  makes the flow of the process proceed to the next step S 17 . 
     In step S 17 , the ECU  19  performs control to switch the atmosphere on-off valve  29  from the open state to the close state. When the atmosphere on-off valve  29  is thus closed (the close state of the purge control valve  35  being maintained by stopping current supply), an evaporated fuel tightly-closed system is formed, and preparation for a leak diagnosis is thereby complete. 
     In step S 18 , the diagnosis section  53  performs the second leak diagnosis. The second leak diagnosis is the procedure of a leak diagnosis, of the evaporated fuel tightly-closed system, that is performed by the diagnosis section  53  in the second diagnosis stage in which the atmosphere on-off valve  29  is in the close state. Herein, prior to the second leak diagnosis stage in which the atmosphere on-off valve  29  is in the close state, the first leak diagnosis is completed and then the atmosphere on-off valve  29  is once opened, according to a closing instruction from the control section  55 . The second leak diagnosis uses a combination of PFD method (pressure fluctuation detection method), DDP method (double differentiation method), and DTM (stagnation time method). The second diagnosis period dt 2  of the second leak diagnosis is set sufficiently longer than the first diagnosis period dt 2  . The second leak diagnosis will be described later in detail. 
     In step S 19 , the ECU  19  refers to the second diagnosis period dt 2  stored in the storage section  51 , and thereby checks whether or not the elapsed time, from when the atmosphere on-off valve  29  has been switched from the open state to the close state, has reached the second diagnosis period dt 2  (whether or not the second leak diagnosis is completed.) The ECU  19  repeats the determination processing of step S 19  until it is determined that the elapsed time, from when the atmosphere on-off valve  29  has been switched from the open state to the close state, has reached the second diagnosis period dt 2  (The second leak diagnosis is completed.) 
     As a result of step S 19 , when it is determined that the elapsed time, from when the atmosphere on-off valve  29  has been switched from the open state to the close state, has reached the second diagnosis period dt 2  (The second leak diagnosis is completed.)(‘Yes’ in step S 19 ), then the ECU  19  makes the flow of the process proceed to step S 20 . 
     In a subroutine of step S 20 , the diagnosis section  53  of the ECU  19  performs an integrated leak diagnosis. The integrated leak diagnosis is the procedure of leak diagnosis of the evaporated fuel tightly-closed system performed by the diagnosis section  53  after completion of the first and second leak diagnoses, to obtain a result of an integrated leak diagnosis that is the integration of the results of the first and second leak diagnoses. The integrated leak diagnosis will be described below in detail. 
     Integrated Leakage Diagnosis Performed by the Evaporation Fuel Treatment Apparatus  11  in an Embodiment According to the Invention 
     In the following, an integrated leak diagnosis performed by an evaporated fuel treatment apparatus  11  in an embodiment according to the invention will be described, referring to  FIG. 2B . 
       FIG. 2B  is a flowchart diagram showing the flow of the integrated leak diagnosis performed by an evaporated fuel treatment apparatus  11  in an embodiment according to the invention. 
     The integrated leak diagnosis according to the subroutine of step S 20  shown in  FIG. 2B  is performed by the diagnosis section  53  after results of the first and second leak diagnoses are obtained. 
     Incidentally, as described above, in the first leak diagnosis, a leak diagnosis of the evaporated fuel tightly-closed system is performed, using PFD method (pressure fluctuation detection method). In the second leak diagnosis, a leak diagnosis of the evaporated fuel tightly-closed system is performed, using PFD method (pressure fluctuation detection method), DDP method (double differentiation method), and DTM method (stagnation time method). 
     In step S 31  shown in  FIG. 2B , based on the result of the second leak diagnosis using PFD method (pressure fluctuation detection method), the diagnosis section  53  checks whether or not the tank internal pressure Ptank detected by the tank internal pressure sensor  27  is stagnating in the vicinity of the atmospheric pressure. Concretely, for example, in the second diagnosis period dt 2  of the second diagnosis stage, if the tank internal pressure Ptank detected by the tank internal pressure sensor  27  is converging in the vicinity of the atmospheric pressure (in a certain allowed range including the atmospheric pressure), the diagnosis section  53  determines as a result of the diagnosis that the tank internal pressure Ptank is stagnating in the vicinity of the atmospheric pressure. 
     As a result of the determination in step S 31 , if it is determined that the tank internal pressure Ptank is not stagnating in the vicinity of the atmospheric pressure (‘No’ in step S 31 ), then the diagnosis section  53  makes the flow of the process to the next step S 32 . 
     On the other hand, as a result of the determination in step S 31 , if it is determined that the tank internal pressure Ptank is stagnating in the vicinity of the atmospheric pressure (‘Yes’ in step S 31 ), then diagnosis section  53  makes the flow of the process jump to ‘integration NG’ in step S 35 . 
     Incidentally, ‘integration NG’ means that the result of the integrated leak diagnosis by integration of the first and second leak diagnoses is ‘NG (abnormality with leak)’. 
     In step S 32 , the diagnosis section  53  determines if the result of the second leak diagnosis using DTM method (stagnation time method) is abnormality with leak, normality without leak, or holding due to impossibility of diagnosis. 
     As a result of determination by the second leak diagnosis using DTM method in step S 32 , if holding due to impossibility of diagnosis is determined (‘holding’ in step S 32 ), then the diagnosis section  53  makes the flow of the process proceed to the next step S 33 . 
     As a result of determination by the second leak diagnosis using DTM method in step S 32 , if abnormality with leak is determined (‘Yes’ in step S 32 ), then the diagnosis section  53  makes the flow of the process jump to ‘integration ‘NG’ in step S 35 . 
     Further, as a result of determination by the second leak diagnosis using DTM method in step S 32 , if normality without leak is determined (‘No’ in step S 32 ), then the diagnosis section  53  makes the flow of the process jump to ‘integration OK’ in step S 37 . 
     Incidentally, ‘integration OK’ means that the result of integrated leak diagnosis is ‘OK (normality without leak)’. 
     In short, arrangement is made such that if either abnormality with leak or normality without leak is determined as a result of the second leak diagnosis using DTM method in step S 32 , a result of integrated leak diagnosis is determined using, giving priority to, the result of the second leak diagnosis using DTM method (stagnation time method), regardless of a result of the second leak diagnosis using DDP method (double differentiation method) in step S 34 . This is because, in general, a result of leak diagnosis with a higher accuracy can be obtained by DTM method, compared with DDP method. 
     In step S 33 , the diagnosis section  53  determines, in the second diagnosis stage, whether or not the maximum value Pmax of the tank internal pressure Ptank detected by the tank internal pressure sensor  27  is exceeding the minimum value DDPmin of the tank internal pressure Ptank that enables leak diagnosis using DDP method. 
     In DDP method, in case that the maximum value Pmax of the tank internal pressure Ptank detected by the tank internal pressure sensor  27  is lower than the minimum value DDPmin, of the tank internal pressure Ptank, that is the lower limit for application of DDP method, it is difficult to appropriately perform leak diagnosis of the evaporated fuel tightly-closed system. 
     Step S 33  enables simple and quick judgment as to whether or not a leak diagnosis using DDP method in the second diagnosis stage is effective. 
     Incidentally, the minimum value DDPmin, of the tank internal pressure Ptank, that enables leak diagnosis using DDP method may be a predetermined fixed value and may be a variable value corresponding to a parameter related to DDP method. 
     As a result of the determination in step S 33 , if determination is made such that the maximum value Pmax of the tank internal pressure Ptank is exceeding the minimum value DDPmin of the tank internal pressure Ptank, the minimum value DDPmin enabling leak diagnosis using DDP method, (‘Yes’ in step S 33 ), the diagnosis section  53  makes the flow of the process jump to the next step S 34 . 
     On the other hand, as a result of the determination in step S 33 , if determination is made that the maximum value Pmax of the tank internal pressure Ptank is not exceeding the minimum value DDPmin of the tank internal pressure Ptank, the minimum value DDPmin enabling leak diagnosis using DDP method, (‘No’ in step S 33 ), the diagnosis section  53  makes the flow of the process jump to ‘integration holding’ in step S 36 . 
     Herein, ‘integration holding’ means that the result of the integrated leak diagnosis is ‘holding (including cases that diagnosis for determination of normality or abnormality is impossible). 
     In step S 34 , the diagnosis section  53  determines as to whether the result of the second leak diagnosis using DDP method is abnormality with leak, normality without leak, or holding due to impossibility of diagnosis. 
     As a result of the determination in step S 34 , if the result of the second leak diagnosis using DDP method is determined to be holding (‘holding’ in step S 32 ), the diagnosis section  53  makes the flow of the process proceed to ‘integration holding determined’ in step S 36 . 
     As a result of determination in step S 34 , if the result of the second leak diagnosis using DDP method is determined to be abnormality with leak (‘Yes’ in S 34 ), the diagnosis section  53  makes the flow of the process jump to ‘integration NG’ in step S 35 . 
     As a result of determination in step S 34 , if the result of second leak diagnosis using DDP method is determined to be normality without leak (‘No’ in S 34 ), the diagnosis section  53  makes the flow of the process jump to ‘integration OK’ in step S 37 . 
     In short, in determining a result of the second leak diagnosis using DDP method in step S 34 , if it is determined that the tank internal pressure Ptank is not stagnating in the vicinity of the atmospheric pressure as a result of the second leak diagnosis using PFD method in step S 31  and if a result of the second leak diagnosis using DTM method in step S 32  is holding, then a result of integrated leak diagnosis is determined, using a result, as it is, of the second leak diagnosis using DDP method, wherein DDP method has a lower leak diagnosis accuracy compared with DTM method. 
     Time Series Operation of the Evaporated Fuel Treatment Apparatus in a Comparative Example 
     In the following, the time series operation of an evaporated fuel treatment apparatus in a comparative example will be described, referring to  FIGS. 3A-3D  and  FIGS. 3E-3H . 
       FIGS. 3A-3D  are time chart diagrams for illustrating the operation of the evaporated fuel treatment apparatus (in a normal state without leak) of a comparative example after switching the ignition switch  43  from ON to OFF.  FIGS. 3E-3H  are time chart diagrams for illustrating the operation of the evaporated fuel treatment apparatus (in an abnormal state with leak) of the comparative example after switching the ignition switch  43  from ON to OFF. 
     Incidentally, an evaporated fuel treatment apparatus  11  in an embodiment according to the invention and the evaporated fuel treatment apparatus of the comparative example are mainly different in the following two points. 
     The first difference is that an evaporated fuel treatment apparatus  11  in an embodiment according to the invention performs leak diagnosis (in a close state of the atmosphere on-off valve  29 ) in the first diagnosis stage (within a stabilizing time period supposed to be required for stabilization in comparison with the state immediately after the ignition switch  43  is turned off), and on the other hand, the evaporated fuel treatment apparatus of the comparative example does not perform leak diagnosis within a time period corresponding to the first diagnosis stage (The open state of the atmosphere on-off valve  29  is maintained). 
     The second difference is as follows. On an evaporated fuel treatment apparatus  11  in an embodiment according to the invention, in the second diagnosis stage (after elapse of the stabilizing time period supposed to be required for stabilization compared with the state immediately after the ignition switch  43  is turned off), a result of leak diagnosis by DTM method is adopted being given priority as a result of integrated leak diagnosis, and a result of leak analysis by DDP method is secondarily adopted as a result of integrated leak diagnosis in a case that the result of leak diagnosis by DDM method is holding (including impossibility of diagnosis). On the other hand, on the evaporated fuel treatment apparatus in the comparative example, a result of the leak diagnosis using DDP method is adopted being given priority as a result of integrated leak diagnosis, and a result of leak diagnosis by DTM method is adopted as backup. 
     First, operation of the evaporated fuel treatment apparatus of the comparative example in a normal state without leak will be described below. It will be assumed that the season is spring, and the ambient temperature is for example approximately 20 degrees centigrade. 
     At time t 1  shown in  FIG. 3A , when the ignition switch  43  is turned from ON to OFF, a timer for leak diagnosis (not shown) starts counting. 
     At the time t 1  shown in  FIGS. 3B-3D , operation of respective sections belonging to the evaporated fuel treatment apparatus of the comparative example other than an ignition switch  43  is as follows. That is, an atmosphere on-off valve  29  maintains an open state (see  FIG. 3B ). The tank internal pressure Ptank detected by a tank internal pressure sensor  27  indicates the atmospheric pressure (see  FIG. 3C ). A leak diagnosis flag representing a result of leak diagnosis is in a holding state because it is before leak diagnosis (see  FIG. 3D ). 
     During time t 1 -t 2  shown in  FIG. 3A , the ignition switch  43  continues to maintain the OFF state. 
     During time t 1 -t 2  shown in  FIGS. 3B-3D , operation of the respective sections belonging to the evaporated fuel treatment apparatus of the comparative example other than the ignition switch  43  is the same as that at time t 1  . That is, the atmosphere on-off valve  29  maintains the open state (see  FIG. 3B ). The tank internal pressure Ptank detected by the tank internal pressure sensor  27  indicates the atmospheric pressure (see  FIG. 3C ). The leak diagnosis flag is in the holding state because it is before leak diagnosis (see  FIG. 3D ). 
     At time t shown in  FIG. 3B , the atmosphere on-off valve  29  is turned from the open state to a close state. 
     Time t 2  is a timing when the count value of the timer for leak diagnosis has reached a stabilizing time supposed to be required for stabilization compared with the state immediately after the ignition switch  43  is turned off. That is, the period from time t 1  to t 2  shown in  FIGS. 3A-3D  corresponds to the first diagnosis period dt 1  of the first leak diagnosis stage in an embodiment according to the invention. The evaporated fuel treatment apparatus of the comparative example does not perform leak diagnosis during the period from time t 1  to t 2 . 
     During time the time t 2  to t 4  shown in  FIG. 3C , the tank internal pressure Ptank detected by the tank internal pressure sensor  27  shows a tendency to deviate, at time t 3  , from the atmospheric pressure stagnating region (A.P.S.R.)(the pressure region that has equal margins on the positive pressure side and the negative pressure side with respect to the atmospheric pressure and can be considered the vicinity of the atmospheric pressure) to the positive pressure side and thereafter converges again into the atmospheric pressure stagnating region. 
     Herein, the phenomenon, during when an evaporated fuel tightly-closed system is formed, that the tank internal pressure Ptank detected by the tank internal pressure sensor  27  deviates from the atmospheric pressure stagnating region (see time t 3  in  FIG. 3C ) is a phenomenon which occurs in a case that the evaporated fuel tightly-closed system is in a normal state without leak. Thus, based on a result of leak diagnosis using PFD method and results of leak diagnoses using DDP method and DTM method, the evaporated fuel treatment apparatus of the comparative example determines that the evaporated fuel tightly-closed system is in a normal state without leak (OK state) from a view point of adopting the result of leak diagnosis by DDP method as a result of integrated leak diagnosis, giving priority to this result, and adopting the result of leak diagnosis by DTM method as backup. 
     The leak diagnosis period during time t 2  to t 4  shown in  FIGS. 3A to 3D  corresponds to the second leak diagnosis stage in an embodiment according to the invention. In the comparative example, similarly to an embodiment according to the invention, leak diagnoses (not shown) using DDP method and DTM method are performed in the period from time t 2  to t 4  , in addition to a leak diagnosis using PFD method (see elapsed time characteristic diagram of the tank internal pressure Ptank in  FIG. 3C ). However, as described above as the second difference, in the comparative example, arrangement is made such that the result of leak diagnosis by DDP method is adopted, being given priority, as a result of integrated leak diagnosis, and the result of leak diagnosis by DTM method is adopted as backup. 
     During time t 2  to t 4  shown in  FIG. 3A , the ignition switch  43  maintains OFF state. During time t 2  to t 4  shown in  FIG. 3B , the atmosphere on-off valve  29  maintains a close state. At time t 3  shown in  FIG. 3D , the leak diagnosis flag transits from a holding state to OK state, and thereafter maintains OK state until and after time t 4 . 
     The operation of the evaporated fuel treatment apparatus of the comparative example in an abnormal state with leak will be described below. Herein, as the operation during time t 1  to t 2  shown in  FIGS. 3E-3H  is the same as that in the normal state without leak described above, overlapping description will be omitted, and operation from time t 2  will be described. 
     During the leak diagnosis period from t 2  to t 4  shown in  FIG. 3G , the tank internal pressure Ptank detected by the tank internal pressure sensor  27  maintains a state converging in the atmospheric pressure stagnating region (A.P.S.R.). 
     Herein, the phenomenon that, while an evaporated fuel tightly-closed system is formed, the tank internal pressure Ptank detected by the tank internal pressure sensor  27  maintains the convergence state in the atmospheric pressure stagnating region is a phenomenon that occurs in a case that the evaporated fuel tightly-closed system is in an abnormal state with leak. Thus, at time t 4  when the leak diagnosis period terminates, based on a result of leak diagnosis using PDF method and results of leak diagnoses using DDP method and DTM method, the evaporated fuel treatment apparatus of the comparative example determines that the evaporated fuel tightly-closed system is in an abnormal state (NG state) from a view point of adopting a result of leak diagnosis by DDP method as a result of integrated leak diagnosis, giving priority to this result, and adopting a result of leak diagnosis by DTM method as backup. 
     During the period from time t 2  to t 4  shown in  FIG. 3E , the ignition switch  43  maintains OFF state. During the same period from time t 2  to t 4  shown in  FIG. 3F , the atmosphere on-off valve  29  maintains a close state. The leak diagnosis flag transits from a holding state to NG state at time t 4  shown in  FIG. 3H . 
     Time Series Operation of Evaporation Fuel Treatment Apparatus  11  in an Embodiment According to the Invention 
     In the following, the time series operation of an evaporated fuel treatment apparatus  11  in an embodiment according to the invention will be described, referring to  FIGS. 4A-4D, 4E-4H, and 4I-4L . 
       FIGS. 4A-4D and 4E-4H  are time chart diagrams for illustration of the operation of an evaporated fuel treatment apparatus  11  (in a normal state without leak) in an embodiment according to the invention after turning the ignition switch from ON to OFF.  FIGS. 4I-4L  are time chart diagrams for illustration of the operation of an evaporated fuel treatment apparatus  11  (in an abnormal state with leak) in an embodiment according to the invention after turning the ignition switch from ON to OFF. 
     First, the operation of an evaporated fuel treatment apparatus  11  in an embodiment according to the invention in the normal state without leak will be described, referring to  FIGS. 4A-4D . It will be assumed that the season is spring and the ambient temperature is for example approximately 20 degrees centigrade. 
     When the ignition switch  43  is turned from ON to OFF at time t 11  shown in  FIG. 4A , the timer for leak diagnosis starts counting. 
     At time t 11  shown in  FIGS. 4B-4D , the operation of the respective sections other than the ignition switch  43  belonging to an evaporated fuel treatment apparatus  11  in an embodiment according to the invention is as follows. That is, the atmosphere on-off valve  29  is turned from open state to close state (see  FIG. 4B ). The tank internal pressure Ptank detected by the tank internal pressure sensor  27  indicates the atmospheric pressure (see  FIG. 4C ). The leak diagnosis flag representing a result of leak diagnosis is in a holding state because it is before the leak diagnosis (see  FIG. 4D ). 
     Incidentally, although description has been made above, taking an example of turning the atmosphere on-off valve  29  from open state to close state in synchronization with the timing t 11  when the ignition switch  43  is turned from ON to OFF, the invention is not limited to this example. Arrangement may be adopted such that the atmosphere on-off valve  29  is turned from open state to close state after a predetermined time (earlier than time t 12  ) delayed from time t 11 . 
     With such an arrangement, after the ignition switch  43  is turned from ON to OFF at time t 11 , the tank internal pressure Ptank can be stabilized before the first diagnosis period dt 1  of the first diagnosis stage starts (in this case of example, the first diagnosis period dt 1  is started at the time when a predetermined delay time has elapsed from time t 11 ). 
     During the period from time t 11  to t 13  shown in  FIG. 4A , the ignition switch  43  maintains OFF state. The atmosphere on-off valve  29  maintains the close state (see  FIG. 4B ). The tank internal pressure Ptank detected by the tank internal pressure sensor  27  tens to deviate at time t 12  shown in  FIG. 4C  from an expanded atmospheric pressure stagnating region to the positive pressure side, and thereafter continue to gradually increase. 
     Herein, the expanded atmospheric pressure stagnating region (E.A.P.S.R.) is a region partitioned by the first threshold value P_th 1  used in the first diagnosis stage (see  FIG. 4C ) to judge whether the tank internal pressure Ptank detected by the tank internal pressure sensor  27  is stagnating in the vicinity of the atmospheric pressure. 
     Based on that, as described above, the first diagnosis period dt 1  of the first diagnosis stage is set to a shorter time length compared with the second diagnosis period dt 2  of the second leak diagnosis described later, the expanded atmospheric pressure stagnating region is expanded by (P_th 1 -P_th 2 ) compared with the reference atmospheric pressure stagnating region (R.A.P.S.R., see  FIG. 4C ) partitioned by the second threshold value P_th 2  used in the second diagnosis stage. This is based on a requirement for performing leak diagnosis with high accuracy in a short time length. 
     The period from time t 11  to time t 13  shown in  FIGS. 4A-4D  (the period in which the count value of the timer for leak diagnosis is within a stabilizing time period supposed to be required for stabilization compared with the state immediately after the ignition switch  43  is turned off (time t 11 )) corresponds to the first diagnosis period dt 1  of the first diagnosis stage. On the evaporated fuel treatment apparatus  11  in an embodiment according to the invention, the first leak diagnosis using PFD method (pressure fluctuation detection method) is performed in the first diagnosis period dt 1  from time t 11  to time t 13 . It is appropriate to perform leak diagnosis of the evaporated fuel tightly-closed system in the first diagnosis period dt 1  , because residual heat caused by the internal combustion engine  13  itself and the exhaust system of the internal combustion engine  13  is high immediately after the ignition switch  43  is turned off. 
     Incidentally, on the evaporated fuel treatment apparatus of the comparative example, leak diagnosis is not performed during the period from time t 1  to t 2  (the period corresponding to the stabilizing time) shown in  FIGS. 3A-3D . 
     The phenomenon that, during when an evaporated fuel tightly-closed system is formed, the tank internal pressure Ptank detected by the tank internal pressure sensor  27  deviates from the expanded atmospheric pressure stagnating region (see time t 12  in  FIG. 4C ) is a phenomenon which occurs in a case that the evaporated fuel tightly-closed system is in a normal state without leak in the first diagnosis stage. Thus, an evaporated fuel treatment apparatus  11  in an embodiment according to the invention determines at time t 12  by leak diagnosis using PFD method that the evaporated fuel tightly-closed system is in a normal state without leak (OK state). Accordingly, the leak diagnosis flag representing a result of leak diagnosis transits from the holding state to OK state, and thereafter maintains OK state until time t 16  and after (see  FIG. 4D ). 
     At time t 13  shown in  FIG. 4B , the atmosphere on-off valve  29  is turned from the close state to the open state to reset the history of the tank internal pressure Ptank related to the first leak diagnosis, and thereafter maintains the open state until time t 14  . During the same period from t 13  to t 14  shown in  FIG. 4C , the tank internal pressure Ptank detected by the tank internal pressure sensor  27  indicates the atmospheric pressure. The leak diagnosis flag representing a result of leak diagnosis maintains OK state (see  FIG. 4D ). 
     Time t 14  is a timing when the count value of the timer for leak diagnosis has reached a value corresponding to the stabilizing time period supposed to be required for stabilization compared with the state immediately the ignition switch  43  is turned off (time t 11 ). 
     When the atmosphere on-off valve  29  is turned from the open state to the close state at time t 14  shown in  FIG. 4B , during the second diagnosis period dt 2  of the second diagnosis stage (see time from t 14  to time t 16 ), in addition to leak diagnosis using PFD method (see the temporal characteristic graph of the tank internal pressure Ptank in  FIG. 4C ), the second leak diagnoses (not shown) using DTM method and DDP method are performed. 
     Incidentally, the second leak diagnosis performed during the period from time t 14  to time t 16  on an evaporated fuel treatment apparatus  11 , in an embodiment according to the invention, corresponds to the leak diagnosis performed during the period from time t 2  to t 4  on the evaporated fuel treatment apparatus of the comparative example. 
     During the period from time t 14  to t 16  shown in  FIG. 4A , the ignition switch  43  continues to maintain OFF state. During the same period from time t to time t 16  shown in  FIG. 4B , the atmosphere on-off valve  29  maintains the close state. The tank internal pressure Ptank detected by the tank internal pressure sensor  27  tends to deviate at the time t 15  shown in  FIG. 4C  from the reference atmospheric pressure stagnating region partitioned by the second threshold value P_th 2  used in the second diagnosis stage, and thereafter again converse into the referential atmospheric pressure stagnating region. 
     Herein, the phenomenon that, during when an evaporated fuel tightly-closed system is formed, the tank internal pressure Ptank detected by the tank internal pressure sensor  27  deviates from the reference atmospheric pressure stagnating region (see time t 15  in  FIG. 4C ) is a phenomenon which occurs in a case that the evaporated fuel tightly-closed system is in a normal state without leak during the second diagnosis stage. Thus, an evaporated fuel treatment apparatus  11  in an embodiment according to the invention determines at time t 15  by leak diagnosis using PFD method that the evaporated fuel tightly-closed system is in a normal state without leak (OK state). In the case shown in  FIGS. 4A-4D , the leak diagnosis flag was already transited at time t 12  from the holding state to OK state. In this case, an evaporated fuel treatment apparatus  11  in an embodiment according to the invention makes the leak diagnosis flag maintain OK state as it is (see  FIG. 4D ). 
     Incidentally, an evaporated fuel treatment apparatus  11  in an embodiment according to the invention performs an integrated leak diagnosis according to the procedure based on  FIG. 2B . Concretely, in this integrated leak diagnosis, starting at time t 14  in the second diagnosis stage, in addition to a leak diagnosis using PFD method, leak diagnoses using DTM method and DDP method are respectively performed. When results of the leak diagnoses by PFD method, DTM method, and DDP method are obtained, the result of leak diagnosis by DTM method is in principle adopted being given priority as a result of integrated leak diagnosis, and on the other hand, the result of the leak diagnosis by DDP method is secondarily adopted as a result of an integrated leak diagnosis in a case that the result of the leak diagnosis by DTM method is held (including impossibility of diagnosis.) 
     However, in a case that the result of the leak diagnosis using PFD method is normal (OK state), as shown in  FIG. 4D , the result of the leak diagnosis by PFD method may be used being given priority over the results of the leak diagnoses by DDM method and DDP method. 
     In the following, the operation of an evaporated fuel treatment apparatus  11  in an embodiment according to the invention in a normal state without leak will be described, referring  FIGS. 4E-4H . Partial operation is common to the case shown in  FIGS. 4A-4D  in a normal state without leak and the case shown in  FIGS. 4E-4H  in a normal state without leak. Therefore, on the case of  FIGS. 4E-4H , description overlapping with the case of  FIGS. 4A-4D  will be omitted, and description will be made, focusing on the difference between the two cases. 
     The difference between the two cases is that while determination is made in the case of  FIGS. 4A-4D  by diagnosis that both the first diagnosis stage and the second diagnosis stage are free from leak, determination is made in the case of  FIGS. 4E-4H  by diagnosis that only the second diagnosis stage is free from leak (Determination is not made through the first leak diagnosis such that there is no leak.) 
     Concretely, in the case of  FIGS. 4E-4H , an evaporated fuel treatment apparatus  11  in an embodiment according to the invention determines at time t 15  shown in  FIG. 4H  that the evaporated fuel tightly-closed system is in a normal state (OK state) without leak by a leak diagnosis using PFD method. Then, at the same time t 15 , the leak diagnosis flag representing a result of the leak diagnosis transits from a holding state to OK state, and then maintains OK state until time t 16  and after (see  FIG. 4H ). 
     An evaporated fuel treatment apparatus  11  in an embodiment according to the invention performs an integrated leak diagnosis according to the procedure based on  FIG. 2B , similarly to the case of  FIGS. 4A-4D . Concretely, in this integrated leak diagnosis, starting at time t 14  of the second diagnosis stage, in addition to a leak diagnosis using PFD method, leak diagnoses using DTM method and DDP method are respectively performed. When results of the leak diagnoses by PFD method, DTM method, and DDP method are obtained, while the result of leak diagnosis by DTM method is in principle adopted being given priority as a result of integrated leak diagnosis, the result of the leak diagnosis by DDP method is secondarily adopted as a result of an integrated leak diagnosis in a case that the result of the leak diagnosis by DTM method is held (including impossibility of diagnosis.) 
     In the following, the operation of an evaporated fuel treatment apparatus  11  in an embodiment according to the invention in an abnormal state with leak will be described, referring  FIGS. 4I-4L . Partial operation is common to the case shown in  FIGS. 4A-4D  in a normal state without leak and the case shown in  FIGS. 4I-4L  in an abnormal state with leak. Therefore, on the case of  FIGS. 4I-4L , description overlapping with the case of  FIGS. 4A-4D  will be omitted, and description will be made, focusing on the difference between the two cases. 
     The difference between the two cases is that while determination is made through diagnosis in the case of  FIGS. 4A-4D  that both the first diagnosis stage and the second diagnosis stage are free from leak, determination is made through diagnosis in the case of  FIGS. 4I-4L  that leak occurs at least in the second diagnosis stage. 
     Concretely, in the case of  FIGS. 4I-4L , an evaporated fuel treatment apparatus  11  in an embodiment according to the invention determines at time t 16  shown in  FIG. 4L  that the evaporated fuel tightly-closed system has leak (NG state) if a diagnosis result that the second diagnosis stage is free from leak is not obtained. Then, at the same time t 16 , the leak diagnosis flag representing a result of the leak diagnosis transits from a holding state to NG state, and thereafter maintains NG state (see  FIG. 4L ). 
     An evaporated fuel treatment apparatus  11  in an embodiment according to the invention performs an integrated leak diagnosis according to the procedure based on  FIG. 2B , similarly to the case of  FIGS. 4A-4D . Concretely, in this integrated leak diagnosis, starting at time t 14  of the second diagnosis stage, in addition to a leak diagnosis using PFD method, leak diagnoses using DTM method and DDP method are respectively performed. When results of the leak diagnoses by PFD method, DTM method, and DDP method are obtained, while the result of leak diagnosis by DTM method is in principle adopted being given priority as a result of integrated leak diagnosis, the result of the leak diagnosis by DDP method is secondarily adopted as a result of an integrated leak diagnosis in a case that the result of the leak diagnosis by DTM method is held (including impossibility of diagnosis.) 
     The case of  FIGS. 4I-4L  assumes that an evaporated fuel treatment apparatus  11  (the diagnosis section  53 ) in an embodiment according to the invention has determined, by leak diagnosis related to DTM method, that the evaporated fuel tightly-closed system has leak (NG state). As a result, according to the principle of adopting a result of leak diagnosis by DTM method, giving priority, as a result of integrated leak diagnosis, the evaporated fuel treatment apparatus  11  (the diagnosis section  53 ) determines that the evaporated fuel tightly-closed system has leak and is in an abnormal state (NG state). 
     Operation and Advantages of an Evaporation Fuel Treatment Apparatus  11  in an Embodiment According to the Invention 
     The operation and the advantages of an evaporated fuel treatment apparatus  11  in an embodiment according to the invention will be described below. 
     An evaporated fuel treatment apparatus  11  based on the first point of view in the present embodiment according to the invention includes the fuel tank  15 , which is mounted on the vehicle having the internal combustion engine  13  to reserve fuel, the canister  17 , which is provided between the communication passages (the evaporated fuel exhaust passage  25  and the atmospheric air flow passage  26 ) connecting the fuel tank  15  and the atmosphere to collect evaporated fuel exhausted from the fuel tank  15  through the communication passages  25  and  26 , the atmosphere on-off valve  29 , which is provided at the communication passage  26  connecting the canister  17  and the atmosphere to open/close the canister  17  to/and from the atmosphere, the tank internal pressure sensor (tank internal pressure detection section)  27  for detecting the tank internal pressure Ptank of the fuel tank  15 , the control section  55  for instructing the atmosphere on-off valve  29  to open and close, and the diagnosis section  53  for performing leak diagnosis of the evaporated fuel tightly-closed system including the fuel tank  15 . 
     In the evaporated fuel treatment apparatus  11  based on the first point of view, after the ignition switch  43  of the vehicle is turned off, in the first diagnosis stage in which the atmosphere on-off valve  29  is in a close state, according to a closing instruction from the control section  55 , the diagnosis section  53  performs the first leak diagnosis using PFD method (pressure fluctuation detection method), based on the relationship between the tank internal pressure Ptank detected by the tank internal pressure sensor (the tank internal pressure detection section)  27  and the predetermined first threshold value P_th 1 ; and after the first leak diagnosis is completed, in the second leak diagnosis stage in which the atmosphere on-off valve  29  is in the close state, according to a closing instruction from the control section  55 , the diagnosis section  53  performs the second leak diagnosis using PFD method (pressure fluctuation detection method), based on the relationship between a tank internal pressure Ptank detected by the tank internal pressure sensor (the tank internal pressure detection section)  27  and the predetermined second threshold value P_th 2 . Herein, after completion of the first leak diagnosis, the atmosphere on-off valve  29  is once opened, according to an opening instruction from the control section  55 . The first threshold value P_th 1  used in the first diagnosis stage is set with a larger deviation from the atmospheric pressure compared with the second threshold value P_th 2  used in the second diagnosis stage. 
     In the evaporated fuel treatment apparatus  11  based on the first point of view, in performing leak diagnosis using PFD method (pressure fluctuation detection method) in divided two stages after the ignition switch  43  of the vehicle is turned off, the residual heat of the internal combustion engine  13  and the exhaustion system of the internal combustion engine  13  after the turning off of the ignition switch  43  has more significant effect in the first diagnosis stage than in the second diagnosis stage, and accordingly the first threshold value P_th 1  used in the first diagnosis stage is set with a larger deviation from the atmospheric pressure compared with the second threshold value P_th 2  used in the second diagnosis stage. 
     By the evaporated fuel treatment apparatus  11  based on the first point of view, the first and second threshold values P_th 1  and P_th 2  are appropriately set, taking into account the widths of fluctuation of the respective tank internal pressures Ptank detected by the tank internal pressure sensor (the tank internal pressure detection section)  27  in the first and second diagnosis stages. Consequently, for example, even in a case of applying the invention to a hybrid vehicle, leak diagnosis of the evaporated fuel tightly-closed system can be carried out with high accuracy. 
     An evaporated fuel treatment apparatus  11  based on the second point of view in an embodiment according to the invention is the evaporated fuel treatment apparatus  11  based on the first point of view, wherein arrangement may be adopted such that the first diagnosis period of the first diagnosis stage is a stabilizing time period supposed to be required for stabilization of the tank internal pressure Ptank, the stabilization being made compared with the tank internal pressure Ptank that is immediately after the ignition switch  43  is turned off, and the first diagnosis period of the first diagnosis stage may be set to a shorter time length compared with the second diagnosis period of the second diagnosis stage. 
     In the evaporated fuel treatment apparatus  11  based on the second point of view, in performing leak diagnosis in divided two stages after the ignition switch  43  of the vehicle is turned off, the residual heat of the internal combustion engine  13  and the exhaustion system of the internal combustion engine  13  after the turning off of the ignition switch  43  has more significant effect in the first diagnosis stage than in the second diagnosis stage, and accordingly the first diagnosis period dt 1  of the first diagnosis stage is set to a shorter time length than the second diagnosis period dt 2  of the second diagnosis stage. 
     By the evaporated fuel treatment apparatus  11  based on the second point of view, the lengths of the first diagnosis period dt 1  and the second diagnosis period dt 2  are set to appropriate lengths, taking into account the temporal variation rates of the respective tank internal pressures Ptank detected by the tank internal pressure sensor (tank internal pressure detection section)  27  in the respective diagnosis stages, namely the first and second diagnosis stages. Consequently, compared with the evaporated fuel treatment apparatus  11  based on the first point of view, the accuracy of leak diagnosis of the evaporated fuel tightly-closed system can be further improved. 
     Further, an evaporated fuel treatment apparatus  11  based on the third (fourth) point of view in an embodiment according to the invention is the evaporated fuel treatment apparatus  11  based on the first point of view, wherein arrangement may be adopted such that the atmosphere on-off valve  29  is once opened immediately after completion of the first leak diagnosis, according to an opening instruction from the control section  55 , and the diagnosis section  53  starts the second diagnosis immediately after the atmosphere on-off valve  29  is switched from the open state to a close state, according to a closing instruction from the control section  55 . 
     By the evaporated fuel treatment apparatus  11  based on the third (fourth) point of view, the atmosphere on-off valve  29  is once opened immediately after completion of the first leak diagnosis, according to an opening instruction from the control section  55 , and the diagnosis section  53  starts the second diagnosis, omitting a wasteful time, immediately after the atmosphere on-off valve  29  is switched from the open state to a close state, according to a closing instruction from the control section  55 . Consequently, it is possible to carry out leak diagnosis of the evaporated fuel tightly-closed system in a shorter time and with a further higher accuracy, compared with the evaporated fuel treatment apparatus  11  based on the first (second) point of view. 
     On the other hand, the evaporated fuel treatment apparatus  11  based on the fifth point of view may be arranged such that, after the ignition switch  43  of the vehicle is turned off, in a state that the atmosphere on-off valve  29  is closed, according to a closing instruction from the control section  55 , the diagnosis section  53  performs a leak diagnosis of the evaporated fuel tightly-closed system using the double differentiation method based on a correlation parameter related to the secondary differentiation value of the tank internal pressure Ptank detected by the tank internal pressure sensor  27 ; performs a leak diagnosis of the evaporated fuel tightly-closed system using the stagnation time method based on the relationship between the tank internal pressure Ptank detected by the tank internal pressure sensor (the tank internal pressure detection section)  27  and the stagnation time of the tank internal pressure Ptank; and uses a result of the leak diagnosis using the stagnation time method (DTM method), giving priority over a result of the leak diagnosis using the double differentiation method (DDP method). 
     The evaporated fuel treatment apparatus  11  based on the fifth point of view uses a result of a leak diagnosis using the stagnation time method (DTM method) with a higher accuracy compared with the double differentiation method (DDP method), giving priority over a result of a leak diagnosis using the double differentiation method (DDP method). For example, in a case that the result of the leak diagnosis using the stagnation time method (DTM method) is a normal state without leak, the diagnosis section  53  determines a normal state without leak, regardless of the result of the leak diagnosis using the double differentiation method (DDP method). 
     In this way, as the evaporated fuel treatment apparatus  11  uses a result of a leak diagnosis using the stagnation time method (DTM method) with a higher accuracy compared with the double differentiation method (DDP method), giving priority over a result of a leak diagnosis using the double differentiation method (DDP method), it is possible by the evaporated fuel treatment apparatus  11  based on the fifth point of view to carry out leak diagnosis of the evaporated fuel tightly-closed system with high accuracy even in a case of applying the invention to a hybrid vehicle. 
     Further, the evaporated fuel treatment apparatus  11  based on the sixth point of view is the evaporated fuel treatment apparatus  11  based on the fifth point of view, and arrangement may be adopted such that the diagnosis time for obtaining a result of a leak diagnosis using the stagnation time method (DTM method) is set to a time length longer than the diagnosis time for obtaining a result of a leak diagnosis using the double differentiation method (DDP method). 
     By the evaporated fuel treatment apparatus  11  based on the sixth point of view, as it is possible to appropriately perform a leak diagnosis using the stagnation time method (DTM method), which requires a longer diagnosis time compared with the double differentiation method (DDP method), it is possible to carry out a leak diagnosis of the evaporated fuel tightly-closed system with a further higher accuracy. 
     Still further, the evaporated fuel treatment apparatus  11  based on the seventh (eighth) point of view is the evaporated fuel treatment apparatus  11  based on the fifth (sixth) point of view, wherein in the first diagnosis stage in which the atmosphere on-off valve  29  is in a close state according to a closing instruction from the control section  55  after the turning off of the ignition switch  43  of the vehicle, the diagnosis section  53  performs the first leak diagnosis using PFD method (pressure fluctuation detection method) based on the relationship between a tank internal pressure Ptank by the tank internal pressure sensor (tank internal pressure detection section)  27  and the predetermined first threshold value P_th 1 ; and after completion of the first leak diagnosis, in the second diagnosis stage in which the atmosphere on-off valve  29  is in a close state according to a closing instruction from the control section  55 , the diagnosis section  53  performs the second leak diagnosis, using the pressure fluctuation detection method (PFD method) based on the relationship between the tank internal pressure Ptank by the tank internal pressure sensor (tank internal pressure detection section)  27  and the predetermined second threshold value P_th 2 , using the above-described double differentiation method (DDP method), and using the above-described stagnation time method (DTM method). 
     After the first leak diagnosis is completed, the atmosphere on-off valve  29  is once opened according to an opening instruction from the control section  55 . If a result of the second leak diagnosis using the pressure fluctuation detection method (PFD method) is an abnormal state with leak, the diagnosis section  53  determines an abnormal state with leak, regardless of a result of the second leak diagnosis using the double differentiation method (DDP method) or the stagnation time method (DTM method). 
     Herein, the pressure fluctuation detection method (PFD method) is suitably used in detecting a leak hole with a comparatively large diameter, while the double differentiation method (DDP method) is suitably used in detecting a leak hole with a comparatively small diameter. Accordingly, even in a case that a result of the second leak diagnosis using the pressure fluctuation detection method (PFD method) is a normal state without leak, it is still possible that there is a leak hole with a comparatively small diameter. 
     In this situation, even in a case that a result of the second leak diagnosis using the pressure fluctuation detection method (PFD method) is a normal state without leak, leak diagnosis using the double differentiation method (DDP method) or the stagnation time method (DTM method) is definitely performed. On the other hand, in case that a result of the second leak diagnosis using the pressure fluctuation detection method (PFD method) is an abnormal state with leak, it is not always necessary to perform the second leak diagnosis using the double differentiation method (DDP method) or the stagnation time method (DTM method). 
     In the evaporated fuel treatment apparatus  11  based on the seventh (eighth) point of view, in a case that a result of the second leak diagnosis using the pressure fluctuation detection method (PFD method) is an abnormal state with leak, the diagnosis section  53  determines an abnormal state with leak, regardless of a result of the second leak diagnosis using the double differentiation method (DDP method) or the stagnation time method (DTM method). Consequently, a leak diagnosis of the evaporated fuel tightly-closed system can be performed in a shorter time compared with the evaporated fuel treatment apparatus  11  based on the fifth (sixth) view point. 
     Other Embodiments 
     In the foregoing plural embodiments, examples of embodying the invention have been described. Accordingly, the technical scope of the invention should not be understood, being limited by these embodiments. This is because the invention can be carried out in various embodiments, without departing from the spirit and the primary features thereof. 
     For example, the forgoing embodiments of the invention have been described, taking examples where the temperature in an evaporated fuel tightly-closed system after an ignition switch  43  is turned off transits to the higher temperature side, however, the invention is not limited to these examples. The invention can also be applied to a case that the temperature in an evaporated fuel tightly-closed system after an ignition switch  43  is turned off transits to the lower temperature side (for example, a case with a temperature of zero degree centigrade or lower). In a case that the temperature in an evaporated fuel tightly-closed system after an ignition switch  43  is turned off transits to the lower temperature side, the tank internal pressure in a tightly closed state becomes a negative pressure through liquefaction (condensation) of evaporated fuel reserved in a fuel tank  15 . In such a case, the invention can be carried out similarly to an embodiment in which the tank internal pressure in a tightly closed state becomes a positive pressure, by making appropriate modification. 
     Further, the foregoing embodiments according to the invention have been described, taking an example where an evaporated fuel treatment apparatus  11  in an embodiment according to the invention is applied to a hybrid vehicle provided with an internal combustion engine  13  and an electric motor as drive sources, however, the invention is not limited thereto. It is needless to say that the invention may be applied to a vehicle provided with only an internal combustion engine  13  as a drive source.