Patent Publication Number: US-6988391-B2

Title: Fuel vapor leakage inspection apparatus

Description:
This is a Divisional of application Ser. No. 10/662,481, filed Sep. 16, 2003, now U.S. Pat. No. 6,945,093. 

   CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based upon, claims the benefit of priority of, and incorporates by reference, the contents of Japanese Patent Applications No. 2002-271205 filed Sep. 18, 2002, and No. 2003-28258 filed Feb. 5, 2003. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a fuel vapor leakage inspection apparatus. 
   2. Description of the Related Art 
   Generally, a system is known for processing fuel vapor using an adsorbent configured to adsorb fuel vapor generated in a fuel tank. For example, granular activated carbon can be housed in an adsorption container, and the container will exhaust the fuel vapor adsorbed by the adsorbent to an intake pipe by means of a negative pressure in the intake pipe. The fuel vapor exhausted into the intake pipe is combusted in a combustion chamber. If leakage occurs in the fuel vapor processing system, the fuel vapor flows out into the atmosphere. Therefore, in such a case, it is necessary to inspect for the occurrence of leakage in the fuel vapor processing system. As a leakage inspection apparatus for the fuel vapor processing system, an apparatus for pressurizing or depressurizing a sealed fuel vapor path with a pump so as to detect the occurrence of leakage depending on a change in pressure after pressurization or depressurization has been known (for example, see Japanese Patent Laid-Open Publication No. Hei 11-351078). 
   In addition, other apparatuses for detecting the leakage based on a change in pump characteristics while the pump is being driven are known (for example, Japanese Patent Laid-Open Publications No. Hei 10-90107 and No. 2002-4959). However, if the leakage inspection is executed by pressurizing or depressurizing the sealed fuel vapor path by using pressure means such as a pump when the adsorbability of the adsorbent is lowered, for example, in the case where the adsorbent housed within the adsorption container is deteriorated, in the case where the adsorbent adsorbs a large amount of fuel vapor, and the like, the following problems occur. 
   In the case where the fuel vapor path is pressurized to execute the leakage inspection, when the fuel vapor path is depressurized after the pressurization of the fuel vapor path so as to exhaust the air in the fuel vapor path into the atmosphere, the fuel vapor present in the fuel vapor path is sometimes not adsorbed by the adsorbent but flows out into the atmosphere. On the other hand, in the case where the fuel vapor path is depressurized to execute the leakage inspection, when the air in the fuel vapor path is exhausted into the atmosphere so as to depressurize the fuel vapor path, all the fuel vapor present in the fuel vapor path sometimes cannot be adsorbed by the adsorbent and flows out into the atmosphere. Therefore, even if the leakage does not occur in the fuel vapor path itself, when the adsorbability of the adsorbent is lowered, there is a possibility that the fuel vapor flows out into the atmosphere when the leakage inspection is executed. 
   In the case where the leakage from the fuel vapor path is determined based on a path pressure in the fuel vapor path measured by pressurizing or depressurizing the fuel vapor path, if the fuel vapor adsorbed in a canister flows out to the atmosphere by an air flow generated by the pressurization or the depressurization, the pressure in the fuel vapor path changes in accordance with a concentration of the fuel vapor that flows out. Therefore, the fuel vapor leakage inspection apparatus suffers from the problem that the occurrence of leakage from the fuel vapor path cannot be precisely determined. 
   SUMMARY OF THE INVENTION 
   In view of the above problems, the present invention has an object of providing a fuel vapor leakage inspection apparatus for stopping leakage inspection when the adsorbability of an adsorbent is lowered so as to prevent fuel vapor from flowing out into the atmosphere during the leakage inspection. The present invention has another object of providing a fuel vapor leakage inspection apparatus for preventing the fuel vapor from flowing out into the atmosphere during the leakage inspection, regardless of the adsorbability of the adsorbent. 
   The present invention has a further object of providing a fuel vapor leakage inspection apparatus for stopping the leakage determination when the adsorbability of the adsorbent is lowered. The present invention has yet another object of providing a fuel vapor leakage inspection apparatus for correcting the amount of leakage from the fuel vapor path in accordance with the amount of the fuel vapor flowing out to the atmosphere so as to determine the occurrence of leakage. 
   According to a fuel vapor leakage inspection apparatus — as set forth in a first aspect of the present invention, the amount of fuel vapor adsorbed by an adsorbent is calculated by a calculation means so as to determine whether or not to operate a pressure means. That is, whether or not to execute leakage inspection based on the calculated amount of the fuel vapor is determined. When a large amount of the fuel vapor is adsorbed by the adsorbent to lower the adsorbability of the adsorbent, the leakage inspection is stopped without pressurizing or depressurizing the sealed fuel vapor path by the pressure means. Thus, the fuel vapor can be prevented from flowing out into the atmosphere during the leakage inspection. 
   Generally, it is known that there is a correlation between the amount of the fuel vapor adsorbed by the adsorbent and a concentration of the fuel vapor exhausted from an adsorption container into an intake pipe by a negative pressure. As the amount of the fuel vapor adsorbed by the adsorbent increases, the concentration of the fuel vapor exhausted from the adsorption container into the intake pipe becomes higher. On the contrary, as the amount of the fuel vapor adsorbed by the adsorbent decreases, the concentration of the fuel vapor exhausted from the adsorption container into the intake pipe becomes lower. 
   In order to control the air-fuel ratio of an internal combustion engine, hereinafter referred to simply as an engine, when the fuel vapor is exhausted into the intake pipe, the amount of deviation between a theoretical air-fuel ratio and an actual air-fuel ratio, obtained by exhausting the fuel vapor into the intake pipe, is generally detected using an exhaust oxygen sensor or an A/F sensor for detecting the air-fuel ratio. The amount of the fuel vapor or the concentration of the fuel vapor exhausted into the exhaust pipe is calculated based on the amount of deviation between the theoretical air-fuel ratio and the actual air-fuel ratio so as to control the amount of a fuel to be injected. 
   According to the fuel vapor leakage inspection apparatus according to a second aspect of the present invention, the amount of fuel vapor adsorbed by the adsorbent is calculated based on the previous amount or concentration of the fuel vapor exhausted into the intake pipe or the amount of deviation in the air-fuel ratio generated by exhausting the fuel vapor. In the case where the amount of the fuel vapor adsorbed by the adsorbent is large enough to lower the adsorbability of the adsorbent, the operation of the pressure means is stopped to prevent the fuel vapor from flowing out into the atmosphere. 
   If a time period from the stopping of an engine to the execution of leakage inspection is long, the adsorbent adsorbs the fuel vapor generated in the fuel tank even when the engine is stopped. Therefore, the amount of the fuel vapor adsorbed by the adsorbent prior to execution of leakage inspection cannot be precisely calculated based on the amount of the fuel vapor exhausted into the intake pipe while the engine is in operation. 
   According to a fuel vapor leakage inspection apparatus according to a third aspect of the present invention, the amount of the fuel vapor adsorbed by the adsorbent is calculated based on at least one of the amount of fuel in the fuel tank, a fuel temperature, and the engine stop time. In this manner, even if an interval from the engine stop to the execution of the leakage inspection is long, the amount of the fuel vapor adsorbed by the adsorbent prior to execution of leakage inspection can be precisely calculated. In the case where the calculated amount of the fuel vapor is large and therefore the adsorbability of the adsorbent is lowered, the operation of the pressure means is stopped to prevent the fuel vapor from flowing out into the atmosphere. 
   When fuel is fed to the fuel tank, fuel vapor is generated. As a result, the adsorbent adsorbs a large amount of the fuel vapor. According to a fuel vapor leakage inspection apparatus according to a fourth aspect of the present invention, when fuel feeding the fuel tank is detected, it is determined that a large amount of the fuel vapor is adsorbed by the adsorbent to stop the leakage inspection. After the fuel vapor adsorbed by the adsorbent is exhausted into the intake pipe to decrease the amount of the fuel vapor adsorbed by the adsorbent while the leakage inspection is being stopped, the leakage inspection becomes executable. 
   According to a fuel vapor leakage inspection apparatus according to a fifth aspect of the present invention, after fuel is fed to the fuel tank, leakage inspection is stopped until a vehicle runs under predetermined conditions so as to be capable of exhausting the fuel vapor adsorbed by the adsorbent into the intake pipe. In this manner, the leakage inspection is prevented from being executed while the adsorbent is adsorbing a large amount of the fuel vapor. 
   According to a fuel vapor leakage inspection apparatus according to a sixth aspect of the present invention, when the adsorbability of the adsorbent is lowered so that the fuel vapor flows out to the atmosphere, the leakage inspection is stopped. Therefore, the fuel vapor is prevented from being further released to the atmosphere due to the leakage inspection. 
   According to a fuel vapor leakage inspection apparatus according to a seventh aspect of the present invention, a second adsorbent for adsorbing the fuel vapor is provided upstream of a throttle device provided in the intake pipe. The intake pipe positioned between the second adsorbent and a combustion chamber of the engine and the atmosphere side of the pressure means are connected with each other through a connection pipe. Even in a case where the fuel vapor flows out into the atmosphere during the leakage inspection, the fuel vapor flows out through the connection pipe into the intake pipe so as to be adsorbed by the second adsorbent. Therefore, even when the engine is stopped, the pressure means can be operated to execute the leakage inspection. 
   According to a fuel vapor leakage inspection apparatus according to an eighth aspect of the present invention, the atmosphere side of the pressure means and a sealed container are connected with each other. In such a configuration, even if the fuel vapor flows out from the pressure means and toward the atmosphere during leakage inspection, the fuel vapor flowing out from the pressure means is stored in the sealed container. Therefore, even in a case where the fuel vapor begins flowing toward the atmosphere, the fuel vapor can be prevented from flowing out into the atmosphere so as to execute the leakage inspection. 
   According to a fuel vapor leakage inspection apparatus according to a ninth aspect of the present invention, pressure in the sealed container is made negative prior to pressurization or depressurization of the fuel vapor path by the pressure means. This pressurization or depressurization ensures that the fuel vapor can be stored in the sealed container. 
   According to a fuel vapor leakage inspection apparatus according to a tenth aspect of the present invention, since pressure in the sealed container is made negative by the pressure means used for the leakage inspection, it is not necessary to prepare additional or auxiliary means for making the pressure in the sealed container negative. 
   According to a fuel vapor leakage inspection apparatus according to an eleventh aspect of the present invention, since the pressure in the sealed container is made negative by a negative pressure of the intake pipe, means for making the pressure in the sealed container negative is not required. 
   According to a fuel vapor leakage inspection apparatus according to a twelfth aspect of the present invention, the sealed container increases or decreases its volume in accordance with the amount of the fuel vapor stored in the container. Even if means for delivering the fuel vapor to the sealed container is not provided, the fuel vapor can be stored as the result of increasing or decreasing the volume of the sealed container. 
   If a path pressure in the fuel vapor path is measured while the fuel vapor is flowing out to the atmosphere so as to execute the leakage inspection, for example, even leakage holes of the same size have different measured pressure values depending on the concentration of the fuel vapor. Thus, if the fuel vapor flows out to the atmosphere, the occurrence of leakage from the fuel vapor path cannot be precisely determined. 
   According to a fuel vapor leakage inspection apparatus according to a thirteenth aspect of the present invention, in the case where there is a possibility that leakage may occur from the fuel vapor path as a result of comparison between a first reference orifice pressure measured by pressurizing or depressurizing a reference orifice and a path pressure of the fuel vapor path measured by pressurizing or depressurizing the fuel vapor path after the measurement of the first reference orifice pressure, the reference orifice is pressurized or depressurized again to measure a second reference orifice pressure. Then, the first reference orifice pressure and the second reference orifice pressure are compared with each other. Fuel vapor is generated from the fuel tank when leakage inspection is executed by pressurizing or depressurizing the fuel vapor path. If the adsorbent is not capable of adsorbing all the fuel vapor, the fuel vapor flows out from the adsorption container to the atmosphere. When air containing the fuel vapor passes through the reference orifice, the reference orifice pressure in the reference orifice changes depending on the concentration of the fuel vapor. By comparing the first reference orifice pressure, which is measured prior to the pressurization or the depressurization of the fuel vapor path, and the second reference orifice pressure, which is measured when there is a possibility that the fuel vapor may be present in the vicinity of the reference orifice due to the pressurization or the depressurization, it is possible to determine whether the fuel vapor flows out from the adsorption container to the atmosphere when the leakage inspection is executed by pressurizing or depressurizing the fuel vapor path. 
   According to the fuel vapor leakage inspection apparatus according to a thirteenth aspect of the present invention, when a certain or larger amount of the fuel vapor flows out from the adsorption container to the atmosphere, it is determined that the measured path pressure in the fuel vapor path is imprecise. Therefore, the leakage determination is stopped. 
   According to a fuel vapor leakage inspection apparatus according to a fourteenth aspect of the present invention, in the case where there is a possibility that leakage may occur from the fuel vapor path as a result of comparison between the first reference orifice pressure obtained by pressurizing or depressurizing the reference orifice and the path pressure in the fuel vapor path, obtained by pressurizing or depressurizing the fuel vapor path after the measurement of the first reference orifice pressure, the second reference orifice pressure, which is obtained by pressurizing or depressurizing the reference orifice again, and the first reference orifice pressure are compared with each other. After the path pressure, which is measured by pressurizing or depressurizing the fuel vapor path, is corrected in accordance with the amount of a change in pressure between the first reference orifice pressure and the second reference orifice pressure, the occurrence of leakage from the fuel vapor path is determined. The occurrence of leakage can be precisely determined without stopping the leakage determination. 
   According to a fuel vapor leakage inspection apparatus according to a fifteenth aspect of the present invention, in the case where it is determined that there is a possibility that the leakage may occur from the fuel vapor path, based on the path pressure in the fuel vapor path, measured by pressurizing or depressurizing the fuel vapor path, the concentration of the fuel vapor on the atmosphere side of the adsorbent is measured. When the concentration of the fuel vapor is a predetermined value or larger, the leakage determination is stopped. 
   According to a fuel vapor leakage inspection apparatus according to a sixteenth aspect of the present invention, after the path pressure of the fuel vapor path obtained by pressurizing or depressurizing the fuel vapor path is corrected in accordance with the concentration of the fuel vapor on the atmosphere side of the adsorbent, the occurrence of leakage from the fuel vapor path is determined. Therefore, the occurrence of leakage can be precisely determined without stopping the leakage determination. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a partial configuration view and a partial cross-sectional view of a fuel vapor leakage inspection apparatus according to a first embodiment of the present invention; 
       FIG. 2  is a time chart showing a leakage inspection of the fuel vapor leakage inspection apparatus according to the first embodiment; 
       FIG. 3  is a graph showing the relationship between the amount of adsorption in a canister and the concentration of an exhausted fuel vapor; 
       FIG. 4  is a flowchart of a fuel vapor leakage inspection process according to the first embodiment; 
       FIG. 5  is a flowchart of a fuel vapor leakage inspection process according to the first embodiment; 
       FIG. 6  is a flowchart of the fuel vapor leakage inspection process according to the first embodiment; 
       FIG. 7  is a flowchart of a fuel vapor leakage inspection process according to a variation of the first embodiment; 
       FIG. 8  is a flowchart of the fuel vapor leakage inspection process according to the variation of the first embodiment; 
       FIG. 9  is a flowchart of a fuel vapor leakage inspection process according to a second embodiment of the present invention; 
       FIG. 10  is a flowchart of the fuel vapor leakage inspection process according to the second embodiment of the present invention; 
       FIG. 11  is a flowchart of a fuel vapor leakage inspection process according to a third embodiment of the present invention; 
       FIG. 12  is a flowchart of a fuel vapor leakage inspection process according to a fourth embodiment of the present invention; 
       FIG. 13  is a configuration view of a fuel vapor leakage inspection apparatus according to a fifth embodiment of the present invention; 
       FIG. 14  is a flowchart of a fuel vapor leakage inspection process according to the fifth embodiment; 
       FIG. 15  is a configuration view of a fuel vapor leakage inspection apparatus according to a sixth embodiment of the present invention; 
       FIG. 16  is a flowchart of a fuel vapor leakage inspection process according to the sixth embodiment; 
       FIG. 17  is a configuration view of a fuel vapor leakage inspection apparatus according to a seventh embodiment of the present invention; 
       FIG. 18  is a configuration view of a fuel vapor leakage inspection apparatus according to an eighth embodiment of the present invention; 
       FIG. 19  is a configuration view of a fuel vapor leakage inspection apparatus according to a ninth embodiment of the present invention; 
       FIG. 20  is a configuration view of a fuel vapor leakage inspection apparatus according to a tenth embodiment of the present invention; 
       FIG. 21  is a configuration view of a fuel vapor leakage inspection apparatus according to an eleventh embodiment of the present invention; 
       FIG. 22  is a time chart showing a leakage inspection with the fuel vapor leakage inspection apparatus in the eleventh embodiment; 
       FIG. 23  is a characteristic graph showing the relationship between a pump operation time period and a fuel vapor path pressure in accordance with a fuel vapor concentration in the eleventh embodiment; 
       FIG. 24  is a characteristic view showing the relationship between a pump operation time period and a reference orifice pressure in accordance with a fuel vapor concentration in the eleventh embodiment; 
       FIG. 25  is a flowchart of the fuel vapor leakage inspection process according to the eleventh embodiment; 
       FIG. 26  is a flowchart of the fuel vapor leakage inspection process according to the eleventh embodiment; 
       FIG. 27  is a view showing the configuration of a fuel vapor leakage inspection apparatus according to a twelfth embodiment of the present invention; 
       FIG. 28  is a flowchart of a fuel vapor leakage inspection process according to the twelfth embodiment; 
       FIG. 29  is a flowchart of the fuel vapor leakage inspection process according to the twelfth embodiment; 
       FIG. 30  is a view showing the configuration of a fuel vapor leakage inspection apparatus according to a thirteenth embodiment of the present invention; 
       FIG. 31  is a view showing the configuration of a fuel vapor leakage inspection apparatus according to a fourteenth embodiment of the present invention; 
       FIG. 32  is a view showing the configuration of a fuel vapor leakage inspection apparatus according to a fifteenth embodiment of the present invention; 
       FIG. 33  is a view showing the configuration of a fuel vapor leakage inspection apparatus according to a sixteenth embodiment of the present invention; and 
       FIG. 34  is a view showing the configuration of a fuel vapor leakage inspection apparatus according to a seventeenth embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiments with reference to the accompanying drawings is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   (First Embodiment) 
   A fuel vapor leakage inspection apparatus according to the first embodiment of the present invention is shown in  FIG. 1 . The fuel vapor leakage inspection apparatus serves to inspect if the leakage occurs in a fuel vapor processing system. The fuel vapor leakage processing system includes an intake pipe  12 , a fuel tank  40 , a canister  50 , and a purge valve  64 . A fuel vapor generated in the fuel tank  40  is adsorbed by an adsorbent  52  such as granular activated carbon housed within the canister  50 , which serves as an adsorption container. A fuel vapor path is constituted by spaces in the fuel tank  40 , in the canister  50  and in pipes  60 ,  62 . During engine operation, the purge valve  64 , serving as an exhaust device, and an open/close valve  72  are opened, the atmosphere passes through the pump  74  and the open/close valve  72  and is introduced into the canister  50 . The fuel vapor adsorbed by the adsorbent  52  is exhausted into the suction pipe  12  by a negative pressure in the suction pipe  12 , which is positioned downstream of a throttle device  14 . 
   The fuel vapor leakage inspection device includes an air-fuel ratio sensor  22 , an electronic control unit (hereinafter, abbreviated as ECU)  30 , a pressure sensor  54 , a pump  74 , a reference orifice  76 , and an orifice valve  78 . A flow meter  16  measures the amount of drawn air flowing through the intake pipe  12 . The air-fuel ratio sensor  22  provided in an exhaust pipe  20  measures an air-fuel ratio in an exhaust gas. An ignition signal, the number of engine revolutions, an engine cooling water temperature, the opening position of the accelerator, the amount of drawn air, and an air-fuel ratio are input from the flowmeter  16 , the air-fuel ratio sensor  22 , and the like into the ECU  30 , which functions as a control means so as to control the opening position of the throttle device  14 , the amount of fuel injection from the injector  18 , and the like. 
   The air-fuel ratio sensor  22  and the ECU  30  constitute a calculation means. An exhaust oxygen sensor may be-used instead of the air-fuel ratio sensor  22 . The pressure sensor  54  serving as a leakage detection means for measuring pressure in the fuel vapor path is provided for the canister  50 . Instead of providing the pressure sensor  54  for the canister  50 , the pressure sensor  54  may be provided for the fuel tank  40 , the pipe  60 ,  62 , or a pipe  70  positioned between the pump  74  and the canister  50  as long as the above-described pressure in the fuel vapor path can be measured. 
   The canister  50  is connected to the fuel tank  40  through the pipe  60  and to the intake pipe  12  through the pipe  62 . The purge valve  64  serving as an exhaust device is placed in the pipe  62 . The open/close valve  72  is opened so that the canister  50  can be opened to the atmosphere through the pipe  70 . In the pipe  70 , the open/close valve  72  and the pump  74 , serving as the pressure means, are provided. The open/close valve  72  is opened so that the canister  50  is opened through the pump  74  and the pipe  70  to the atmosphere. In a pipe branching from the pipe  70 , the reference orifice  76  and the orifice valve  78  are provided. The pump  74  is used to depressurize a fuel vapor path. The reference orifice  76  is for determining the size of a leakage hole formed in the fuel vapor path. 
   Next, operation of the fuel vapor leakage inspection apparatus will be described with reference to a time chart shown in  FIG. 2  and a flowchart shown in  FIG. 4 . The flowchart shown in  FIG. 4  is a main routine of a leakage inspection, which is therefore regularly executed. 
   At step  100 , the ECU  30  determines whether or not leakage inspection conditions are established. For the leakage inspection conditions, it is determined whether or not operating conditions, temperature conditions, and the like satisfy predetermined conditions. In the case where the leakage inspection conditions are not established, the ECU  30  does not execute leakage inspection. 
   If the leakage inspection conditions are established, a concentration of an exhausted fuel vapor, which is precalculated in the ECU  30  based on a measured signal from the air-fuel ratio sensor  22 , is read at step  101 . The ECU  30  calculates in advance a concentration of the fuel vapor exhausted from the canister  50  into the intake pipe  12  from the amount of a deviation between an air-fuel ratio in the exhaust gas, detected by the air-fuel ratio sensor  22 , and a theoretical air-fuel ratio. Instead of the concentration of the exhausted fuel vapor, the amount of the exhausted fuel vapor may be calculated. The concentration of the exhausted fuel vapor and the amount of the adsorbed fuel vapor in the canister  50  have the relationship shown in  FIG. 3 . If a map of the concentration of the exhausted fuel vapor and the amount of the adsorbed fuel vapor in the canister  50  is produced based on the relationship shown in  FIG. 3 , the amount of adsorption M 1  of the fuel vapor adsorbed in the canister  50  can be calculated from the concentration of the exhausted fuel vapor (step  102 ). The amount of adsorption M 1  stored in memory is updated to the calculated amount of adsorption M 1  of the fuel vapor at step  103 . 
   At step  104 , it is determined whether an ignition key is turned OFF or not. Steps  101 ,  102 , and  103  are repeated until the ignition key is turned OFF. When the ignition key is turned OFF, the processing proceeds to step  105 . Since the condition in the fuel tank is not stabilized immediately after the ignition key is turned OFF, a timer t is initialized at step  105  so as to be in a waiting state while repeating steps  106  and  107  until a predetermined time period is elapsed. 
   When the predetermined time period elapses after the ignition key is turned OFF, it is determined whether or not the amount of adsorption M 1  is larger than a predetermined amount M 0 . If the amount of adsorption M 1  is larger than the predetermined amount M 0 , the leakage inspection is not executed. If the amount of adsorption M 1  is the predetermined amount M 0  or smaller, the leakage inspection is executed at step  109 . The predetermined amount M 0  is a threshold value of the amount of adsorption M 1 , which is allowable when the fuel vapor flows out to the atmosphere during the execution of the leakage inspection. 
   The details of the leakage inspection execution routine at step  109  will be described with reference to the flowcharts shown in  FIGS. 5 and 6 . When execution of leakage inspection is permitted, the purge valve  64  and the orifice valve  78  are closed, whereas the open/close valve  72  is opened at step  110  shown in  FIG. 5 . Next, at step  111 , the pump  74  is turned ON so as to reduce pressure in the fuel vapor path within an interval a–b as shown in  FIG. 2 . The purge valve  64  and the orifice valve  78  may be closed simultaneously with the turning-ON of the pump  74 . In this first embodiment, in order to prevent the pressure from being released from each of the valves due to a difference in timing of the opening or closing the valves, it is after each of the valves is opened or closed at step  110  that the pump  74  is turned ON at step  111 . Even if the fuel vapor path has a leakage hole of a similar size to that of the reference orifice  76 , the pump  74  is set to have the ability of reducing the pressure in the fuel vapor path to the predetermined pressure P 0  or lower while the purge valve  64  and the orifice valve  78  are being closed to seal the fuel vapor path. 
   At step  112 , the pressure P in the fuel vapor path is measured by the pressure sensor  54 . Then, at step  113 , it is determined whether or not the pressure P in the fuel vapor path becomes smaller than the predetermined pressure P 0 . 
   In the case where the pressure P does not become smaller than the predetermined pressure P 0  even if a time period ta, during which the pump  74  is driven, exceeds a predetermined time period ta 1  (step  114 ), the processing proceeds to step  136  shown in  FIG. 6  where it is determined that the abnormality occurs. Subsequently, at step  137 , a warning lamp serving as a warning means is lit so as to inform an operator of the occurrence of an abnormality. In this manner, the leakage inspection is terminated. Alternatively, warning sounds may be produced as the warning means. The predetermined time period ta 1  is long enough to make the pressure P smaller than the predetermined pressure even if the leakage hole having a similar size to that of the reference orifice  76  is formed in the leakage inspection apparatus. 
   When the pressure P is dropped to the predetermined pressure P 0  or lower within the predetermined time period ta 1 , the open/close valve  72  is closed at step  115 . Then, after the pump  74  is turned OFF at step  116 , the orifice valve  78  is opened at step  117 . The operations of the open/close valve  72 , the pump  74 , and the orifice valve  78  may be simultaneously performed. In this first embodiment, however, the open/close valve  72  is closed first so as to prevent the negative pressure in the fuel vapor path from being released from the open/close valve  72  due to a difference in timing of operations. 
   The purge valve  64  and the open/close valve  72  are closed. Therefore, when the orifice valve  78  is opened, the atmospheric gases flow from the orifice valve  78  through the reference orifice  76  into the fuel vapor path. Thus, as shown in  FIG. 2 , the pressure in the fuel vapor path gradually increases within an interval b–c. In the case where leakage occurs from the fuel vapor path, the atmosphere flows into the fuel vapor path from both the portion where the leakage occurs and the reference orifice  76 . 
   After the orifice valve  78  is opened, the timer t 1  is initialized at step  118 , followed by step  119  where the pressure P in the fuel vapor path is measured. At steps  120  and  121 , the amount of time required to make the pressure P higher than the predetermined pressure P 1  is measured. When the pressure P becomes higher than the predetermined pressure P 1 , a required time period, that is, a value indicated by the timer t 1 , is stored in the memory at step  122 . 
   At step  123 , the orifice valve  78  is closed again, whereas the open/close valve  72  is opened. Next, the pump  74  is turned ON at step  124  so as to reduce the pressure in the fuel vapor path in an interval c–d shown in  FIG. 2 . The processing is in a waiting state until the pressure P becomes lower than the predetermined pressure P 0  at steps  125  and  126 . 
   When the pressure P becomes lower than the predetermined pressure P 0 , the open/close valve  72  is closed at step  127 . Then, the pump  74  is turned OFF at step  128 . Since the orifice valve  78  remains closed, the atmosphere flows into the fuel vapor path from the leakage hole formed in the fuel vapor path. After the pump  74  is turned OFF, a timer t 2  is initialized at step  129 . At steps  130 ,  131  and  132 , the timer t 2  is counted up until the pressure P becomes higher than the predetermined pressure P 1  in an interval d–e in  FIG. 2 . 
   When the pressure P becomes higher than the predetermined pressure P 1 , a value indicated by the timer t 2  at this time is stored in the memory at step  133 . In the case where the atmosphere flows into the sealed fuel vapor path from the leakage hole, the velocity of the atmosphere flowing from the leakage hole is the same as long as the pressure is constant according to Bernoulli&#39;s theorem (see the following Formula 1).
 
( v   2 /2)+( P /ρ)+ gz =Constant  [Formula 1]
 
where v: flow velocity, ρ: density, P: pressure, g: gravitational constant, z: position
 
   Thus, the flow volume of leakage is proportional to a leakage cross-sectional area A (volume of flow Q=flow velocity v×leakage cross-sectional area A) as long as the pressure P is constant. When the cross-sectional area of the leakage hole is doubled, the amount of leakage is also doubled. Accordingly, when the cross-sectional area of the leakage hole is doubled, a pressure increase rate in the sealed space is also doubled. Specifically, in the case where the leakage occurs in the sealed space whose pressure is reduced to the same pressure, the amount of time required to increase the pressure to the same pressure P is halved with the double cross-sectional area of the leakage hole. 
   With the application of this principal to the first embodiment, in the case where a leakage hole having the same cross-sectional area as that of the reference orifice  76  is present in the leakage inspection apparatus, the cross-sectional area of the leakage hole is halved at the second pressure increase as compared with that at the first pressure increase because the orifice valve  78  remains closed for the second pressure increase. Therefore, the amount of time required to increase the pressure to the predetermined pressure P 1 , that is, the value indicated by the timer t 2 , is twice the value indicated by the timer t 1  (t 2 =t 1 ×2). In the case where a leakage hole having a cross-sectional area larger than that of the reference orifice  76  is present in the leakage inspection apparatus, a ratio of the cross-sectional area of the leakage hole at the first pressure increase to that at the second pressure increase becomes larger than ½. Thus, the value indicated by the timer t 2 , that is, the amount of time required to increase the pressure to the predetermined pressure P 1 , is smaller than twice the value indicated by the timer t 1  (t 2 &lt;t 1 ×2), as indicated with a dotted line between d and e in  FIG. 2 . 
   As described above, at step  134 , a value indicated by t 2  and a value of t 1 ×2 are compared with each other. In the case where the value of the timer t 2  is not larger than t 1 ×2, it is determined that the rate of pressure increase is high, that is, the cross-sectional area of the leakage hole is larger than that of the reference orifice  76 . Therefore, it is determined at step  136  that the abnormality occurs, followed by step  137  where the warning lamp is lit. In the case where the value indicated by the timer t 2  is larger than t 1 ×2, after it is determined that the state is normal, the leakage inspection is terminated. 
   In the first embodiment, since the depressurization of the fuel vapor path having the same volume is performed twice, that is, at the first depressurization (in the interval a–b in  FIG. 2 ) and at the second depressurization (in the interval c–d in FIG.  2 ), it is unnecessary to correct the measured value in accordance with a difference in the amount of the fuel remaining in the fuel tank  40 . Moreover, since the temperature condition remains the same, it is also unnecessary to correct the measured value in accordance with the temperature. 
   Since the pump  74  is stopped after the pressure is reduced to the predetermined pressure P 0  in the first embodiment, the amount of time required to reduce the pressure is shortened if the pump  74  still has the ability of reducing the pressure. Therefore, the lifetime of the pump  74  is prolonged to allow the reduction of power consumption. In the case where the leakage inspection is executed while the engine is stopped, the reduction in power consumption is effective. 
   Although the leakage inspection is executed by depressurizing the fuel vapor path with the pump  74  in the above-described embodiment, the leakage inspection may also be executed by pressurizing the fuel vapor path.  FIGS. 7 and 8  are flowcharts in such a case. The processing is the same as that described above except that the magnitude relations between the pressure P in the fuel vapor path and the predetermined pressure P 0  or P 1  at steps  143 ,  150 ,  156 , and  161  are opposite to those at steps  113 ,  120 ,  126 , and  131  in the flowcharts shown in  FIGS. 5 and 6 . 
   In the first embodiment, it is determined if the amount of adsorption M 1  of the canister  50  is larger than the predetermined amount M 0  prior to the execution of the leakage inspection execution routine (step  109 ) in the main routine. If the amount of adsorption M 1  is larger than the predetermined amount M 0 , the leakage inspection execution routine is not executed. Therefore, the fuel vapor is prevented from flowing out into the atmosphere during execution of the leakage inspection. 
   The same effects can be obtained even if any leakage inspection method (for example, a leakage inspection method employing a leakage inspection execution routine shown in  FIGS. 25 and 26  in a configuration shown in  FIG. 21  as described below in an eleventh embodiment) is used as the leakage inspection execution routine at step  109  in  FIG. 4  as long as the main routine shown in  FIG. 4  is employed. 
   (Second Embodiment) 
     FIGS. 9 and 10  show flowcharts of a liquid inspection execution routine according to a second embodiment of the present invention. The configuration of a fuel vapor leakage inspection apparatus is substantially the same as that in the first embodiment. The main routine of the leakage inspection is the same as that in the first embodiment shown in  FIG. 4 . Moreover, in the leakage inspection execution routine, steps  170  to  184  shown in  FIG. 9  and steps  185  to  189  shown in  FIG. 10  are the same as steps  110  to  124  shown in  FIG. 5  and steps  125  to  129  shown in  FIG. 6 , respectively. 
   In the first embodiment, the processing is in a waiting state while counting up the timer t 2  until the pressure P in the fuel vapor path becomes the predetermined pressure P 1  after depressurization. However, in the case where leakage scarcely occurs from the fuel vapor path, a pressure increase after the second depressurization (represented by an interval d–e shown in  FIG. 2 ) becomes extremely gradual. Therefore, it takes a long time for the pressure to reach the predetermined pressure P 1 . 
   In the second embodiment, in order to overcome this disadvantage, at step  190  after depressurization, it is first determined which of t 1 ×2 and t 2  is larger. Then, at step  192 , the pressure P and the predetermined pressure P 1  are compared with each other. Therefore, when t 2  becomes larger than t 1 ×2 before the pressure P becomes higher than the predetermined pressure P 1 , it is determined that the state is normal at step  194  to terminate the leakage inspection. 
   When the pressure P becomes larger than the predetermined pressure P 1  before t 2  becomes larger than t 1 ×2, it is determined that the cross-sectional area of the leakage hole is larger than that of the reference orifice  76 . It is determined at step  195  that the abnormality occurs, followed by step  196  where the warning lamp is lit. 
   Since the elapsed time periods are compared before the comparison between the pressures, the amount of time required for the inspection becomes shorter than in the first embodiment, in the case where the cross-sectional area of the leakage hole is small. 
   Since the main routine of the leakage inspection in the second embodiment is the same as that in the first embodiment, the leakage inspection execution routine is not executed if the amount of adsorption M 1  in the canister  50  is larger than the predetermined amount M 0 . Thus, the fuel vapor is prevented from flowing out into the atmosphere during execution of the leakage inspection. 
   (Third Embodiment) 
     FIG. 11  shows a flowchart of a main routine of a leakage inspection according to a third embodiment of the present invention. The configuration of a fuel vapor leakage inspection apparatus is substantially the same as that in the first embodiment. 
   For example, in the case where the temperature is high or the temperature fluctuates greatly, if the leakage inspection is executed while a vehicle is stopping, the amount of the fuel vapor adsorbed in the canister  50  increases within a time period from the vehicle stop to the execution of the leakage inspection. Therefore, the amount of adsorption in the canister  50 , which is calculated based on the amount of the exhausted fuel vapor when the fuel vapor adsorbed by the adsorbent  52  is exhausted into the intake pipe  12  while the car is running, may differ from that in the canister  50  when the leakage inspection is executed. 
   In view of this problem, in the third embodiment, the amount of the fuel vapor, which is adsorbed in the canister  50  in a time period from the vehicle stop to the execution of the leakage inspection, is calculated. In accordance with the calculated amount of the fuel vapor, it is determined whether or not to execute the leakage inspection execution routine (step  214 ). 
   First, at steps  200  to  204 , in the case where the leakage inspection conditions are established, the amount of the fuel vapor M 1  adsorbed in the canister  50  is updated. After the ignition key is turned OFF, the amount of remaining fuel is measured by a sensor such as a level gauge of the fuel tank  40  at step  205 . Next, at step  206 , an ambient temperature T 1  measured immediately after the vehicle stops is measured by a temperature sensor such as an intake-air temperature sensor or a vehicle compartment temperature sensor. 
   Since the state in the fuel tank  40  immediately after the turning-OFF of the ignition key is not stabilized, the fuel vapor processing system is in a waiting state at steps  207 ,  208 , and  209  until a predetermined time period elapses after the ignition key is turned OFF. 
   After elapse of the predetermined time period, an ambient temperature T 2  is measured again at step  210 . Then, at step  211 , the amount of the fuel vapor M 2 , which is generated in the fuel tank  40  while the vehicle is stopping is calculated based on the amount of remaining fuel and a change in temperature after the vehicle stops (T 2 −T 1 ). At step  212 , the amount of adsorption M 1  updated at step  203  is added to the amount of the fuel vapor M 2  generated after the vehicle stops so as to update the amount of adsorption M 1  again. If it is determined that the updated amount of adsorption M 1  is equal to or smaller than the predetermined amount M 0  at step  213 , the leakage inspection execution routine (step  214 ) is executed. On the other hand, if it is determined that the updated amount of adsorption M 1  is larger than the predetermined amount M 0  at step  213 , the leakage inspection execution routine (step  214 ) is not executed. Thus, the fuel vapor is prevented from flowing out into the atmosphere during the execution of the leakage inspection. The leakage inspection execution routine is the same as that in the first embodiment or that in the second embodiment. 
   The same effects can be obtained even if any leakage inspection method is used for the leakage inspection execution routine (step  214 ) as long as the main routine shown in  FIG. 11  is employed. 
   (Fourth Embodiment) 
     FIG. 12  shows a flowchart of a main routine of a leakage inspection according to a fourth embodiment of the present invention. The configuration of a fuel vapor leakage inspection apparatus is substantially the same as that in the first embodiment. In addition to the case where the temperature is high or the temperature fluctuates greatly, the amount of the fuel vapor generated in the fuel tank  40  increases if fuel is fed to the fuel tank  40 . Correspondingly, the amount of the fuel vapor adsorbed in the canister  50  increases. Therefore, the amount of adsorption in the canister  50 , calculated based on the amount of the exhausted fuel vapor when purging is executed while the vehicle is running may sometimes differ from that in the canister  50  when the leakage inspection is executed during fuel feeding. 
   In view of this problem, in the fourth embodiment, it is determined whether or not the fuel is fed after the vehicle stops. Steps  220  to  224  and  226  to  235  shown in  FIG. 12  are the same as steps  200  to  214  shown in  FIG. 11  in the third embodiment. In the fourth embodiment, after it is determined that the ignition key is turned OFF at step  224  in the main routine, it is determined whether or not the fuel is fed at step  225 . The determination whether or not the fuel is fed is made by detecting, for example, if a fuel cap is opened, with a sensor serving as a fuel-feeding detection means. If the fuel is fed, the leakage inspection execution routine (step  235 ) is not executed. If the fuel is not fed, the same processing as that in the third embodiment is performed after step  225 . 
   The same effects can be obtained even if any leakage inspection method is used for the leakage inspection execution routine (step  235 ) as long as the main routine shown in  FIG. 12  is employed. 
   (Fifth Embodiment) 
     FIG. 13  shows a fuel vapor leakage inspection apparatus according to a fifth embodiment of the present invention. The components in the fifth embodiment, which are substantially the same as those in the first embodiment, are denoted by the same reference numerals. A concentration sensor  56  serving as a concentration measurement means for measuring a concentration of the fuel vapor is provided for the canister  50  on its atmosphere side. The concentration sensor  56  may be provided at any position as long as it is situated for the canister  50  on its atmosphere side. 
     FIG. 14  shows a flowchart of a main routine of a leakage inspection. Since steps  240  to  244  are the same as steps  100  and  104  to  107  in the first embodiment, their descriptions are omitted here. A fuel vapor concentration C 1  on the atmosphere side of the canister  50  is measured by the concentration sensor  56  immediately before the execution of the leakage inspection (step  245 ). At step  246 , it is determined if the fuel vapor concentration C 1  is larger than a predetermined value C 0 . If the fuel vapor concentration C 1  is larger than the predetermined value C 0 , leakage inspection is not executed. If the fuel vapor concentration C 1  is equal to or smaller than the predetermined value C 0 , the leakage inspection is executed at step  247 . The predetermined value C 0  is a threshold value of the fuel vapor concentration C 1  that is allowed when the fuel vapor flows out to the atmosphere during the execution of the leakage inspection. The leakage inspection execution routine is the same as that in the first embodiment or that in the second embodiment. 
   In the above-described first to fifth embodiments, it is determined whether or not the leakage inspection execution routine is to be executed by determining the amount of adsorption in the canister  50 , the fuel vapor concentration, or if the fuel is fed after the vehicle stops, in the main routine. Therefore, the fuel vapor can be prevented from flowing out into the atmosphere during the execution of the leakage inspection. 
   Moreover, the main routine shown in  FIG. 4 ,  11 ,  12 , or  14  is regularly executed. Therefore, in the case where the leakage inspection is stopped because of a large amount of adsorption in the canister  50 , when the fuel vapor adsorbed in the canister  50  is exhausted into the intake pipe  12  so that the amount of adsorption M 1  becomes equal to or smaller than the predetermined amount M 0 , the leakage inspection is started again. Furthermore, the running conditions of the vehicle, which allow the amount of adsorption M 1  to be equal to or smaller than the predetermined amount M 0 , may be preset. When the running conditions are satisfied, the leakage inspection may be executed. 
   (Sixth Embodiment) 
     FIG. 15  shows a fuel vapor leakage inspection apparatus according to a sixth embodiment of the present invention. The components of the fuel vapor leakage inspection apparatus, which are substantially the same as those of the first embodiment, are denoted by the same reference numerals. 
   The pipe  70  serving as a connection pipe, which is connected to the pump  74 , is connected to the suction pipe  12  between the throttle device  14  and an air cleaner  80  upstream of the throttle device  14 . The pipe  70  may be connected to the intake pipe  12  at any position as long as it is positioned between an adsorbent  82  and the combustion chamber of the engine  10 . 
   The air cleaner  80  houses a filter  81  and a second adsorbent or the adsorbent  82  serving as an intake adsorbent downstream of the filter  81  in its case. In the canister  50 , the adsorbent  52 , which serves as a first adsorbent, is housed. If the fuel vapor is contained in the air exhausted from the pump  74  when the fuel vapor path is depressurized, the fuel vapor passes through the pipe  70  and the intake pipe  12  so as to be adsorbed by the adsorbent  82 . The air, from which the fuel vapor is removed through the adsorbent  82 , passes through the filter  81  so as to flow out into the atmosphere. Even if the fuel vapor is exhausted from the pump  74  during the execution of the leakage inspection, the fuel vapor is prevented from flowing out into the atmosphere. The leakage inspection can be executed regardless of the amount of the adsorbed fuel vapor in the canister  50 . Therefore, in contrast with the main routine shown in  FIG. 4  in the first embodiment, the amount of the adsorbed fuel vapor in the canister  50  is not calculated in the main routine shown in  FIG. 16  in the sixth embodiment. 
   The same effects can be obtained even if the configuration of the evaporation system is altered. For example, as shown in  FIG. 30  described below, as long as the atmosphere side of the pump  74  and the intake pipe  12  are connected with each other through the pipe  70  and the adsorbent  82  is provided in the vicinity of a suction port of the intake pipe  12 , the same effects can be obtained. 
   (Seventh Embodiment) 
     FIG. 17  shows a fuel vapor leakage inspection apparatus according to the seventh embodiment of the present invention. The components of the fuel vapor leakage inspection apparatus according to the seventh embodiment, which are substantially the same as those of the first embodiment, are denoted by the same reference numerals. 
   A sealed container  84  is connected to an end of the pipe  70  connected to the pump  74 . The air exhausted from the pump  74  is stored in the sealed container  84  by a discharge pressure of the pump  74 . Therefore, even if the fuel vapor is exhausted from the pump  74  during the execution of the leakage inspection, the fuel vapor is prevented from flowing out into the atmosphere. Since the leakage inspection can be executed regardless of the amount of the adsorbed fuel vapor in the canister  50 , the amount of the adsorbed fuel vapor in the canister  50  is not calculated in the main routine of the leakage inspection in the seventh embodiment as in the sixth embodiment. The same effects can be obtained even if the configuration of the evaporation system is altered, for example, as in  FIG. 31  described below as long as the sealed container  84  is connected to the atmosphere side of the pump  74  through the pipe  70 . 
   (Eighth Embodiment) 
     FIG. 18  shows a fuel vapor leakage inspection apparatus according to an eighth embodiment of the present invention. The components of the fuel vapor leakage inspection apparatus of the eighth embodiment that are substantially the same as those of the seventh embodiment are denoted by the same reference numerals. 
   A switching valve  86  is connected to the pump  74  on its canister  50  side, whereas another switching valve  87  is connected to the pump  74  on its atmosphere side. The sealed container  84  is provided in a negative-pressure introduction pipe  88  connecting the switching valves  86 ,  87  with each other. The switching valve  86  switches between a first state where the canister  50  and the pump  74  are connected with each other and a second state where the pump  74  and the sealed container  84  are connected with each other. The switching valve  87  switches between a first state where the pump  74  and the sealed container  84  are connected with each other and a second state where the pump  74  and the atmosphere side are connected with each other. 
   The switching valves  86 ,  87  are set to be in their second states, respectively, prior to the execution of the leakage inspection. Then, the pump  74 , which serves as a negative pressure means, is operated. As a result, the air in the sealed container  84  is drawn by the pump  74  and passes through the switching valve  87  to be exhausted to the atmosphere. Therefore, the pressure in the sealed container  84  becomes negative. By switching the switching valve  86  to the first state when the pressure in the sealed container  84  becomes negative, the pressure in the sealed container  84  can be kept negative. 
   By setting the switching valves  86 ,  87  to their first states when the leakage inspection is executed, the fuel vapor, which cannot be adsorbed by the adsorbent  52  in the canister  50 , passes through the switching valve  86 , the pump  74 , and the switching valve  87  so as to be drawn into the sealed container  84 . Since the fuel vapor is drawn into the sealed container  84  by the negative pressure, it is not necessary to deliver the fuel vapor into the sealed container  84  by the pump  74 . Thus, a discharge pressure of the pump  74  can be lowered as compared with the seventh embodiment. 
   Even if the fuel vapor is contained in the air exhausted from the pump  74 , the fuel vapor is stored in the sealed container  84 . When the pump  74  is stopped after the completion of the leakage inspection, the fuel vapor in the sealed container  84  is drawn into the canister  50  whose pressure is reduced by the pump  74 . Therefore, the fuel vapor is prevented from flowing out into the atmosphere. Since the leakage inspection can be executed regardless of the amount of the adsorbed fuel vapor in the canister  50 , the amount of the adsorbed fuel vapor in the canister  50  is not calculated in the main routine of the leakage inspection in the eighth embodiment as it is in the sixth embodiment. 
   The same effects can be obtained even if the configuration of the evaporation system is altered, for example, as shown in  FIG. 32  described below as long as the sealed container  84  is connected to the pump  74  on its atmosphere side in a similar configuration. 
   (Ninth Embodiment) 
     FIG. 19  shows a fuel vapor leakage inspection apparatus according to a ninth embodiment of the present invention. The components of the fuel vapor leakage inspection apparatus according to the ninth embodiment, which are substantially the same as those of the seventh embodiment, are denoted by the same reference numerals. 
   The pipe  70  connected to the pump  74  is connected to the intake pipe  12  downstream of the throttle device  14 . The sealed container  84  is provided in the pipe  70  between the pump  74  and the intake pipe  12 . An open/close valve  90  is provided in the sealed container  84  on its intake pipe  12  side. 
   The open/close valve  90  is opened prior to the execution of the leakage inspection. As a result, the air in the sealed container  84  is drawn into the intake pipe  12  by the negative pressure in the intake pipe  12 . Therefore, the pressure in the sealed container  84  becomes negative. When the pressure in the sealed container  84  becomes negative, the open/close valve  90  is closed so as to allow the pressure in the sealed container  84  to be kept negative. 
   Since the fuel vapor exhausted from the pump  74  is drawn into the sealed container  84  by the negative pressure during the execution of the leakage inspection, it is not necessary to deliver the fuel vapor into the sealed container  84  by the pump  74 . Thus, a discharge pressure of the pump  74  can be lowered as compared with the seventh embodiment. 
   Even if the fuel vapor is contained in the air exhausted from the pump  74 , the fuel vapor is stored in the sealed container  84 . When the pump  74  is stopped after the completion of the leakage inspection, the fuel vapor in the sealed container  84  is drawn into the canister  50  whose pressure is reduced by the pump  74 . Therefore, the fuel vapor is prevented from flowing out to the atmosphere. Since the leakage inspection can be executed regardless of the amount of the adsorbed fuel vapor in the canister  50 , the amount of the adsorbed fuel vapor in the canister  50  is not calculated in the main routine of the leakage inspection in the ninth embodiment as in the sixth embodiment. The same effects can be obtained even if the configuration of the evaporation system is altered, for example, as shown in  FIG. 33  described below as long as the sealed container  84  is connected to the pump  74  on its atmosphere side in a similar configuration. 
   (Tenth Embodiment) 
     FIG. 20  shows a fuel vapor leakage inspection apparatus according to the tenth embodiment of the present invention. The components of the fuel vapor leakage inspection apparatus according to the tenth embodiment, which are substantially the same as those of the first embodiment, are denoted by the same reference numerals. A bellows-type variable volume container  92  serving as a sealed container is connected to an end of the pipe  70  connected to the pump  74 . The variable volume container  92  is capable of increasing and reducing its volume. Instead of the bellows-type container, it is also possible to form a sealed container having a variable volume by using a diaphragm. 
   Since the volume of the variable container  92  is increased by a discharge pressure of the pump  74  for reducing the pressure in the fuel vapor path during execution of the leakage inspection, the variable container  92  stores the fuel vapor exhausted from the pump  74 . The pump  74  can deliver the fuel vapor to the variable container  92  with a small discharge pressure as long as the variable container  92  is formed so that its volume is increased even with a small discharge pressure of the pump  74 . Therefore, the discharge pressure of the pump  74  can be reduced as compared with the seventh embodiment. 
   Even if the fuel vapor is contained in the air exhausted from the pump  74 , the fuel vapor is stored in the variable container  92 . When the pump  74  is stopped after completion of the leakage inspection, the fuel vapor in the variable container  92  is drawn into the canister  50  whose pressure is reduced by the pump  74 . Therefore, the fuel vapor is prevented from flowing out into the atmosphere. Since the leakage inspection can be executed regardless of the amount of the adsorbed fuel vapor in the canister  50 , the amount of the adsorbed fuel vapor in the canister  50  is not calculated in the main routine of the leakage inspection in the tenth embodiment as in the sixth embodiment. 
   The same effects can be obtained even if the configuration of the evaporation system is altered, for example, as shown in  FIG. 34  described below as long as the variable container  92  is connected to the pump  74  on its atmosphere side in a similar configuration. 
   (Eleventh Embodiment) 
     FIG. 21  shows a fuel vapor leakage inspection apparatus according to an eleventh embodiment of the present invention. The components of the fuel vapor leakage inspection apparatus according to the eleventh embodiment, which are substantially the same as those of the first embodiment, are denoted by the same reference numerals. The pressure sensor  54  serving as a pressure measurement means is provided between the switching valve  73  and the pump  74 . The switching valve  73 , which is provided in the pipe  66  for connecting the canister  50  and the pump  74  with each other, performs ON and OFF operations by an instruction from the ECU  30  serving as the control means. The switching valve  73  enters a first state where the pipe  66  and the pipe  70  are in communication with each other when it is in an OFF state, whereas the switching valve  73  enters a second state where the pipe  66  and the pump  74  are in communication with each other when it is in an ON state. The reference orifice  76  is provided in the pipe  77  for connecting the pipe  66  and the pump  74  with each other over the switching valve  73  being interposed therebetween. 
   If the pump  74  is operated while the switching valve  73  is in an OFF state, that is, in the state where the pipe  66  and the pipe  70  are in communication with each other, the air passes through the atmosphere side of the pump  74 , the pipe  70 , the switching valve  73 , the pipe  66 , and the reference orifice  76  to be exhausted from the pump  74  to the atmosphere. Therefore, a pressure between the pump  74  and the reference orifice  76  is reduced. 
   If the pump  74  is operated while the switching valve  73  is in an ON state, that is, in the state where the pipe  66  and the pipe  74  are in communication with each other, the air passes through the fuel tank  40 , the pipe  60 , the canister  50 , the pipe  66 , and the switching valve  73  to be exhausted from the pump  74  to the atmosphere. Therefore, the pressure in the fuel vapor path is reduced. 
   Next, operation of the fuel vapor leakage inspection apparatus will be described with reference to  FIGS. 22 to 26 . The leakage inspection execution routines shown in  FIGS. 25 and 26  are executed in the ECU  30 . Since the main routine of the leakage inspection is the same as that in the first embodiment, the description thereof is herein omitted. 
   When execution of the leakage inspection is allowed in the main routine, the purge valve  64  is closed at step  300  in  FIG. 25 . Since the switching valve  73  is in an OFF state, the pipe  66  and the pipe  70  are in communication with each other. Next, the pump  74  is turned ON at step  301  to reduce the pressure between the reference orifice  76  and the pump  74  as indicated with interval a–b in  FIG. 22 . In this time period, the fuel vapor path is not reduced. The pressure sensor  54  measures the pressure of the reference orifice  76 . 
   In a loop formed by steps  303  to  305 , when a pressure between the reference orifice  76  and the pump  74  satisfies: P(i− 1 )−P(i)&lt;Pa to reach a constant pressure, the processing exits the loop so as to set the pressure P(i) at this time as a first reference orifice pressure P 1  at step  306 . 
   At step  307 , the switching valve  73  is turned ON so that the pipe  66  and the pump  74  are brought into communication with each other. As a result, the pressure in the fuel vapor path that is formed by the fuel tank  40 , the pipe  60 , the pipe  62 , the canister  50 , and the pipe  66  is reduced (an interval b–c in  FIG. 22 ). The pressure measured by the pressure sensor  54  is a path pressure in the fuel vapor path. 
   If the path pressure in the fuel vapor path becomes smaller than the first reference orifice pressure P 1  in a loop formed by steps  309  to  312 , the switching valve  73  is turned OFF at step  313 . Then, at step  314 , it is determined that the leakage from the fuel vapor path is small and therefore the state is normal. Subsequently, the pump  74  is turned OFF at step  322  to terminate the leakage inspection execution routine. 
   If the path pressure in the fuel vapor path does not become smaller than the first reference orifice pressure P 1  to reach a constant pressure in the loop formed by steps  309  to  312 , the processing exits from the loop to proceed to step  315 . The fact that the path pressure in the fuel vapor path reaches a constant pressure without becoming smaller than the first reference orifice pressure P 1  means that the leakage from the fuel vapor path is equal to or larger than that from the reference orifice  76 . 
   However, when the pressure in the fuel vapor path is reduced, the pressure in the fuel tank  40  is also reduced so that the fuel vapor may be further generated from the fuel in the fuel tank  40 . In the main routine of the leakage inspection shown in  FIG. 4 , it is determined that the amount of adsorption M 1  in the canister  50 , which is allowed when the fuel vapor flows out to the atmosphere prior to the execution of the leakage inspection, is equal to or smaller than the predetermined amount M 0 , thereby confirming that the adsorbent in the canister  50  has predetermined adsorbability. However, when the pressure in the fuel vapor path is reduced so that the fuel vapor generated from the fuel tank  40  flows out into the canister  50 , the adsorbability of the canister  50  is lowered. As a result, the fuel vapor is not adsorbed in the canister  50  so as to be exhausted to the atmosphere in some cases. As shown in  FIG. 23 , the path pressure in the fuel vapor path, which is measured by the pressure sensor  54 , increases as the fuel vapor concentration becomes higher. 
   The pressure P(i) at step  309 , which is measured while the fuel vapor is flowing out from the canister  50  due to lowered adsorbability of the canister  50 , includes a factor of the fuel vapor concentration in addition to a factor of the leakage from the fuel vapor path. Therefore, if the measured pressure P(i) in the fuel vapor path is smaller than the first reference orifice pressure P 1  at step  310 , the leakage from the fuel vapor path is surely smaller than that from the reference orifice  76 . 
   On the other hand, when the measured pressure P(i) in the fuel vapor path reaches a constant pressure without becoming smaller than the first reference orifice pressure P 1 , two possibilities are considered as a reason. The first possibility is that the leakage from the fuel vapor path is larger than that from the reference orifice  76 . The second possibility is that the fuel vapor is flowing out from the canister  50 . Therefore, when the measured pressure P(i) in the fuel vapor path reaches a constant pressure without becoming smaller than the first reference orifice pressure P 1 , the switching valve  73  is turned OFF at step  315  (at c in  FIG. 22 ). Then, the pressure between the pump  74  and the reference orifice  76  is reduced again (interval c–d in  FIG. 22 ). 
   The quantity of flow Q of a gas passing through the reference orifice  76  is expressed by the following Formula 2.
 
 Q=A ×α×(2 ×ΔP /ρ) 1/2   [Formula 2]
 
where A: area of a flow path of the reference orifice  76 , α: flow quantity coefficient, ΔP: a difference in pressure between both ends of the reference orifice, and ρ: gas density. When the fuel vapor flows out from the canister  50 , the gas density ρ, that is, the fuel vapor concentration, is increased to decrease the quantity of flow Q. When the fuel vapor concentration is increased to decrease the quantity of flow, the pressure in the reference orifice  76 , measured by the pressure sensor  54 , in the interval c–d in  FIG. 22 , is lower than that measured when the fuel vapor path is low, as shown in  FIG. 24 .
 
   In the leakage inspection execution routine shown in  FIGS. 25 and 26 , when the reference orifice pressure becomes a constant value in a loop formed by steps  317  to  319 , the pressure P(i) at that time is set as a second reference orifice pressure P 2  at step  321 . At step  321 , the second reference orifice pressure P 2  and the first reference orifice pressure P 1  are compared with each other. If P 2 &lt;P 1  is established, it is determined that the second reference orifice pressure P 2  becomes lower than the first reference orifice pressure P 1  because the fuel vapor flows out from the canister  50  to increase the fuel vapor concentration. Since the path pressure in the fuel vapor path, which is measured in the interval b–c in  FIG. 22 , is also increased at a high fuel vapor concentration, the occurrence of leakage cannot be precisely determined by comparing the first reference orifice pressure P 1  to the path pressure in the fuel vapor path. Therefore, if P 2 &lt;P 1  is established at step  321 , the pump  74  is turned OFF at step  322  to stop the leakage determination, thereby completing the leakage inspection execution routine. 
   At step  321 , if the second reference orifice pressure P 2  becomes equal to or larger than the first reference orifice pressure P 1 , it is determined that the fuel vapor does not flow out from the canister  50 . The fact that the path pressure in the fuel vapor path does not become smaller than the first reference orifice pressure P 1  although the fuel vapor does not flow from the canister  50  means that the leakage larger than that from the reference orifice  76  occurs from the fuel vapor path. Thus, at step  323 , it is determined that the leakage occurs from the fuel vapor path and therefore the state is abnormal. The warning lamp  34  is lit at step  324 , and then, the pump  74  is turned OFF at step  322  to terminate the leakage inspection execution routine. 
   In the eleventh embodiment, if it is determined that the fuel vapor flows out from the canister  50  during the execution of the leakage inspection, it is determined that the leakage inspection is not executable to stop the leakage inspection. As a result, it is possible to prevent imprecise leakage determination. 
   Moreover, in the eleventh embodiment, a concentration of the fuel vapor flowing out from the canister  50  may be calculated based on the amount of a change in pressure between the first reference orifice pressure P 1  and the second reference orifice pressure P 2 . Based on this calculated fuel vapor concentration, the path pressure in the fuel vapor path, which is measured in the interval b–c in  FIG. 22 , may be corrected. As a result of comparison between the corrected path pressure in the fuel vapor path to the first reference orifice pressure, precise leakage determination can be performed. 
   (Twelfth Embodiment) 
     FIG. 27  shows a fuel vapor leakage inspection apparatus according to a twelfth embodiment of the present invention. The components of the fuel vapor leakage inspection apparatus according to the twelfth embodiment, which are substantially the same as those of the eleventh embodiment, are denoted by the same reference numerals. In the twelfth embodiment, in addition to the configuration of the leakage inspection apparatus in the eleventh embodiment shown in  FIG. 21 , the concentration sensor  56  is provided on the atmosphere side of the pump  74 . 
   Next, an operation of the fuel vapor leakage inspection apparatus will be described with reference to flowcharts of a leakage inspection execution routine shown in  FIGS. 28 and 29 . Since the main routine of the leakage inspection is the same as that in the first embodiment, repetitious descriptions are not included here. The flowcharts shown in  FIGS. 28 and 29  correspond to those shown in  FIGS. 25 and 26  in the eleventh embodiment in the following parts: steps  330  to  336  to steps  300  to  306 ; steps  338  to  343  to steps  307  to  312 ; and steps  344  and  345  to steps  313  and  314 . 
   In the twelfth embodiment, after the first reference orifice pressure P 1  is kept at step  336 , the first fuel vapor concentration C 1  of the fuel vapor exhausted to the atmosphere is measured by the concentration sensor  56  at step  337 . Then, when it is determined that a constant pressure obtained by reducing the pressure in the fuel vapor path is equal to or larger than the first reference orifice pressure P 1  in a loop formed by steps  340  to  343 , a second fuel vapor concentration C 2  of the fuel vapor exhausted to the atmosphere is measured by the concentration sensor  56  at step  346 . Then, at step  347 , the switching valve  73  is turned OFF. 
   In the case where it is determined that the second fuel vapor concentration C 2  is larger than the first fuel vapor concentration C 1  as a result of a comparison therebetween at step  348 , it is determined that a precise leakage determination is not executable because the fuel vapor flows out from the canister  50  during the depressurization of the fuel vapor path. Thus, the leakage determination is stopped. Then, at step  349 , the pump  74  is turned OFF to terminate the leakage inspection execution routine. 
   In the case where it is determined that the second fuel vapor concentration C 2  is equal to or smaller than the first fuel vapor concentration C 1 , the fuel vapor does not flow out from the canister  50  during the depressurization of the fuel vapor path. The fact that the pressure in the fuel vapor path does not become smaller than the first reference orifice pressure P 1 , even when the fuel vapor does not flow out from the canister  50 , means that leakage larger than that from the reference orifice  76  occurs from the fuel vapor path. Therefore, it is determined that leakage occurs from the fuel vapor path and therefore the state is abnormal at step  350 . The warning light is lit at step  351 . Then, the pump  74  is turned OFF at step  349  to terminate the leakage inspection execution routine. 
   In the twelfth embodiment, if it is determined that the fuel vapor flows out from the canister  50  during the execution of the leakage inspection, the leakage inspection is not executable to stop the leakage inspection. As a result, imprecise leakage determination can be prevented. 
   Although the concentration sensor  56  is provided on the atmosphere side of the pump  74  in the twelfth embodiment, the concentration sensor  56  can be provided at any position as long as it is positioned on the atmosphere side of the canister  50 . 
   A concentration of the fuel vapor flowing out from the canister  50  is calculated based on the amount of a change in concentration between the first fuel concentration C 1  and the second fuel concentration C 2  in the twelfth embodiment. Based on the calculated fuel vapor concentration, the pressure in the fuel vapor path, measured at step  340 , may be corrected. As a result of comparison between the corrected path pressure in the fuel vapor path and the first reference orifice pressure, precise leakage determination can be performed. 
   In the above-described eleventh and twelfth embodiments, even during the execution of the leakage inspection execution routine after the ignition key is turned OFF, or even in the case where the fuel vapor flows out from the canister  50  because of lowered adsorbability of the canister during the execution of the leakage inspection so that the leakage cannot be determined, imprecise leakage determination can be prevented. Alternatively, the pressure in the fuel vapor path is corrected based on the fuel vapor flowing out from the canister  50  so as to perform precise leakage determination. Furthermore, the main routines in the third embodiment and the fourth embodiment may be used as the main routines of the leakage inspection execution routines in the eleventh embodiment and the twelfth embodiment. 
   In the eleventh and twelfth embodiments, the amount of adsorption in the canister  50  is calculated prior to the execution of the leakage inspection during the vehicle stop as in the first embodiment. If the amount of adsorption is equal to or larger than a predetermined amount of adsorption, the leakage inspection is stopped. However, the leakage inspection execution routines described in the eleventh and twelfth embodiments may be executed without calculating the amount of adsorption in the canister  50 . Furthermore, the execution of the leakage inspection routine described in the eleventh and twelfth embodiments is not limited to only the vehicle stop; the leakage inspection routine may also be executed while the vehicle is running. 
   In the eleventh and twelfth embodiments, even when the determination of the leakage from the fuel vapor path is stopped because of lowered adsorbability of the canister  50 , the leakage can be precisely determined through the inspection execution routines described in the eleventh and twelfth embodiments if the adsorbability of the canister  50  is restored by purging while the vehicle is running. Although the leakage from the fuel vapor path is inspected based on a change in pressure at the depressurization with the pump  74  in the eleventh and twelfth embodiments, the leakage from the fuel vapor path may be inspected based on a change in pressure when the atmosphere is exhausted from the fuel vapor path after pressurization with the pump  74 . 
   (Thirteenth to Seventeenth Embodiments) 
     FIGS. 30 to 34  show fuel vapor leakage inspection apparatuses according to thirteenth to seventeenth embodiments of the present invention, respectively. The components of the fuel vapor leakage inspection apparatus, which are substantially the same as those of the first to the twelfth embodiments, are denoted by the same reference numerals.  FIG. 30  shows the thirteenth embodiment. The atmosphere side of the pump  74  is opened in the eleventh and twelfth embodiments. In the thirteenth embodiment, however, as in the sixth embodiment, a second adsorbent or the adsorbent  82  serving as an intake adsorbent for adsorbing the fuel vapor is provided upstream of the throttle device  14  provided in the intake pipe  12 , independently of the adsorbent serving as the first adsorbent housed within the canister  50 . The intake pipe  12 , which is positioned between the adsorbent  82  and a combustion chamber of the engine, and the atmosphere side of the pump  74  are connected through the pipe  70  serving as a connection pipe. 
   In the fourteenth embodiment shown in  FIG. 31 , the sealed container  84  is connected to the pipe  70  on the atmosphere side of the pump  74  as in the seventh embodiment in configurations of the eleventh and twelfth embodiments. With such a configuration, the fuel vapor is prevented from flowing out into the atmosphere even if the fuel vapor is exhausted from the pump  74  during the execution of the leakage inspection. 
   In the fifteenth embodiment shown in  FIG. 32 , as in the eighth embodiment, the switching valve  86  is connected to the canister  50  side of the pump  74 , the switching valve  87  is connected to the atmosphere side of the pump  74 , and the sealed container  84  for housing the fuel vapor therein is provided in the negative introduction pipe  88  for connecting the switching valves  86 ,  87  with each other in configurations of the eleventh and twelfth embodiments. 
   In the sixteenth embodiment shown in  FIG. 33 , the pipe  70  connected to the atmosphere side of the pump  74  is connected to the suction pipe  12  downstream of the throttle device  14 , and the sealed container  84  is provided between the pump  74  of the pipe  70  and the intake pipe  12 , as in the ninth embodiment, in the configurations of the eleventh and twelfth embodiments. The open/close valve  90  for stopping or starting communication between the sealed container  84  and the intake pipe  12  is provided for the sealed container  84  on its intake pipe  12  side. 
   In the seventeenth embodiment shown in  FIG. 34 , the sealed, bellows-type variable container  92  is connected to the end of the pipe  70  connected to the pump  74  on its atmosphere side so as to store the fuel vapor exhausted from the pump  74  therein as in the tenth embodiment, in configurations of the eleventh and twelfth embodiments. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.