Patent Publication Number: US-7216637-B2

Title: Evaporative fuel handling apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The following is based on and claims priority to Japanese Patent Application No. 2005-221086, filed Jul. 29, 2005, which is herein incorporated by reference in its entirety. 
   FIELD 
   The present invention relates to fuel handling and, more particularly, relates to an evaporative fuel handling apparatus for handling evaporative fuel produced in a fuel tank. 
   BACKGROUND 
   It is known to provide an evaporative fuel handling apparatus having a purge system. The purge system purges evaporative fuel produced in a fuel tank into an air intake system of an engine. Technology has been proposed for performing forcible purge of evaporative fuel into an air intake system by producing a pressure difference with a pump between the inside and outside of the purge system (see, e.g., U.S. Pat. No. 6,695,895, JP-2002-332921A). Technology has also been proposed for checking for leaks in the purge system by producing a pressure difference with a pump between the inside and outside of the purge system (see, e.g., U.S. Pat. No. 7,004,013, JP-2004-28060A). 
   The size and weight of the evaporative fuel handling apparatus could be reduced if the same components operate for both forcibly purging and checking for leaks. For instance, the size and weight could be reduced by using a pump common to both purging and leak checking operations. However, the requirements for pump for performing forcible purge are substantially different than those of a pump for leak checking. As such, incorporation of a common pump can be difficult. 
   More specifically, the pump for performing forcible purge (i.e., the purge pump) provides a relatively large flow rate for purge and sets a produced pressure at a specified value lower than a threshold value at which resistance to pressure exists. Hence, as shown by the solid line of  FIG. 7 , a characteristic curve relating pressure (P) and flow rate (Q) for the purge pump has a relatively large slope. Like the purge pump, the pump for leak checking sets a produced pressure at a specified value lower than a threshold value at which resistance to pressure exists; however, the pump for leak checking increases the change in produced pressure with respect to a change in flow rate. Hence, as shown by the broken line of  FIG. 7 , the slope of the characteristic curve relating pressure (P) and flow rate (Q) is lower. Thus, for example, if a pump set for performing forcible purge is used for leak checking, the slope of the P-Q characteristic curve is likely to be too large. Hence, a change in pressure with respect to a change in flow rate becomes too small, which causes reduced accuracy when leak checking. 
   SUMMARY OF THE INVENTION 
   An evaporative fuel handling apparatus for a vehicle with an air intake system of an engine and a fuel tank is disclosed. The evaporative fuel handling apparatus includes a purge system for purging evaporative fuel from the fuel tank into the air intake system. A first communication passage is fluidly coupled with the purge system. A second communication passage is fluidly coupled with the purge system and has a greater loss of pressure of flowing fluid than the first communication passage. A check device is coupled to the second communication passage for checking a leak of evaporative fuel from the purge system. A pump is included for producing a pressure difference between the inside and the outside of the purge system. A selector device is included for switching fluid communication of the pump between one of the first communication passage and the second communication passage. A controller controls the selector device to allow fluid communication between the first communication passage and the pump and then controls the pump to produce the pressure difference to thereby perform forcible purge of evaporative fuel. The controller further controls the selector device to allow fluid communication between the second communication passage and the pump, and then controls the pump to produce the pressure difference and controls the check device to check for a leak of evaporative fuel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing an evaporative fuel handling apparatus according to a first embodiment; 
       FIG. 2  is a block diagram of a check circuit of the embodiment of  FIG. 1 ; 
       FIG. 3  is a flow chart showing the operation of the evaporative fuel handling apparatus of  FIG. 1 ; 
       FIG. 4  is a flow chart showing the operation of the evaporative fuel handling apparatus of  FIG. 1 ; 
       FIG. 5  is a block diagram showing the operation of the evaporative fuel handling apparatus of  FIG. 1 ; 
       FIG. 6  is a block diagram showing the operation of the check circuit of  FIG. 1 ; 
       FIG. 7  is a schematic diagram showing the characteristics of the evaporative fuel handling apparatus of  FIG. 1 ; 
       FIG. 8  is a flow chart showing the operation of an evaporative fuel handling apparatus according to a second embodiment; 
       FIG. 9  is a block diagram of the second embodiment of  FIG. 8 ; 
       FIG. 10  is a block diagram showing an evaporative fuel handling apparatus according to a third embodiment; 
       FIG. 11  is a flow chart showing the operation of the evaporative fuel handling apparatus of  FIG. 10 ; 
       FIG. 12  is a flow chart showing the operation of the evaporative fuel handling apparatus of  FIG. 10 ; 
       FIG. 13  is a block diagram showing the operation of the evaporative fuel handling apparatus of  FIG. 10 ; 
       FIG. 14  is a block diagram showing an evaporative fuel handling apparatus according to a fourth embodiment; 
       FIG. 15  is a block diagram showing an evaporative fuel handling apparatus according to a fifth embodiment; 
       FIG. 16  is a block diagram showing an evaporative fuel handling apparatus according to a sixth embodiment; 
       FIG. 17  is a block diagram showing an evaporative fuel handling apparatus according to a seventh embodiment; 
       FIG. 18  is a block diagram showing an evaporative fuel handling apparatus according to an eighth embodiment; 
       FIG. 19  is a flow chart showing the operation of the evaporative fuel handling apparatus of  FIG. 18 ; 
       FIG. 20  is a flow chart showing the operation of the evaporative fuel handling apparatus of  FIG. 18 ; and 
       FIG. 21  is a block diagram showing the operation of the evaporative fuel handling apparatus of  FIG. 18 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, a plurality of embodiments of the present invention will be described in reference to the drawings. The same reference numbers will be used to denote similar elements in the embodiments. 
   First Embodiment 
     FIG. 1  shows an evaporative fuel handling apparatus  2  according to a first embodiment of the present invention. The evaporative fuel handling apparatus  2  is mounted in a vehicle and handles evaporative fuel produced in a fuel tank  4  and purges the evaporative fuel into an intake passage  7  of an air intake system of an internal combustion engine  6 . The evaporative fuel handling apparatus  2  includes a purge system  10 , a first communication passage  20 , a second communication passage  22 , a selector valve  40 , a pump passage  42 , a pump  44 , an open passage  46 , and an electronic control unit  50  (hereinafter referred to as an “ECU”). 
   The purge system  10  includes a fuel tank  4 , a canister  12 , an introduction passage  13 , a purge passage  14 , and a purge control valve  15 . 
   The canister  12  includes a case  17  and adsorbent  16  within the case  17 . The adsorbent  16  can be of any suitable type such as activated charcoal. The canister  12  is fluidly coupled to the fuel tank  4  through the introduction passage  13 . Hence, evaporative fuel produced in the fuel tank  4  can flow through the introduction passage  13  into the canister  12  and be adsorbed by the adsorbent  16  in the canister  12  (i.e., the evaporative fuel is desorbed). 
   The canister  12  is fluidly coupled with the purge passage  14  such that the canister  12  is fluidly coupled to intake passage  7 . In the embodiment shown, the purge control valve  15  is included in the purge passage  14  such that fluid flowing away from the canister  12  flows through the purge control valve  15 . In one embodiment, the purge control valve  15  is an electromagnetically driven two-way valve. The purge control valve  15  is opened and closed to control the opening and closing of the purge passage  14 . Hence, in a state where the purge passage  14  is opened, evaporative fuel desorbed from the adsorbent  16  in the canister  12  can be purged into the intake passage  7 . More specifically, evaporative fuel purged into the intake passage  7  and fuel injected from a fuel injection valve (not shown) of the internal combustion engine  6  are combusted together in the internal combustion engine  6 . 
   The first and second communication passages  20 ,  22  are also fluidly coupled to the canister  12 . The canister  12  is provided between the first and second communication passages  20 ,  22  and the passages  13 ,  14 . In the embodiment shown, the first communication passage  20  is directly fluidly coupled to the canister  12 . Hence, this can shorten the first communication passage  20  and coincidentally reduce the size of the apparatus  2 . 
   A restrictor  23  for restricting an axial cross sectional area of the fluid flow passage is fluidly coupled to the second communication passage  22 . In other words, the axial cross sectional area of the restrictor  23  is less than the axial cross sectional area of the second communication passage  22 . Due to the restrictor  23 , pressure loss in the second communication passage  22  is larger than pressure loss in the first communication passage  20 . 
   A check circuit  24  is provided in the second communication passage  22  between the restrictor  23  and the canister  12 . As shown in  FIG. 2 , the check circuit  24  includes a first check passage  25 , a second check passage  26 , an atmosphere passage  27 , a communication control valve  28 , a restriction passage  29 , a pressure sensor  30 , a pressure introduction passage  31 , and the like. The first check passage  25  is fluidly coupled to a portion  22   a  of the second communication passage  22  that is directly coupled to the canister  12 . The second check passage  26  is fluidly coupled with a portion  22   b  of the second communication passage  22  that is directly coupled to restrictor  23 . The atmosphere passage  27  is open to the atmosphere at a terminal end. In one embodiment, the communication control valve  28  is made of an electromagnetically driven three-way valve connected to the passages  25 ,  26 ,  27 . The communication control valve  28  and switches to allow fluid communication (i.e., fluid flow) between the first check passage  25  and either the second check passage  26  or the atmosphere passage  27 . The restriction passage  29  bypasses the communication control valve  28  and fluidly couples the first check passage  25  and the second check passage  26 . A check restrictor  32  is included in the restriction passage  29  and restricts the axial cross sectional area of the restriction passage  29 . Here, the axial cross sectional area at the check restrictor  32  is smaller than the axial cross sectional area at the restrictor  23 . The pressure sensor  30  is fluidly coupled with the second check passage  26  through the pressure introduction passage  31  and detects pressure in the second check passage  26  supplied through the pressure introduction passage  31 . 
   Referring back to  FIG. 1 , the selector valve  40  is fluidly coupled to the passages  20 ,  22 , and  42 . The selector valve  40  switches to allow fluid communication (i.e., fluid flow) between the pump passage  42  and either the communication passage  20  or the second communication passage  22 . In one embodiment, the selector valve  40  is an electromagnetically driven three-way valve. 
   In one embodiment, the pump  44  is an electrically operated pump capable of changing the direction of discharge of fluid. The pump  44  has a first port  45  fluidly coupled to the pump passage  42  and a second port  47  fluidly coupled to the open passage  46 . Here, the open passage  46  is open to the atmosphere at one end. Hence, when the first port  45  becomes a discharge side and the second port  47  becomes a suction side, one of the passages  20 ,  22  is pressurized depending on the configuration of the selector valve  40 . In contrast, when the first port  45  becomes a suction side and the second port  47  becomes a discharge side, one of the passages  20 ,  22  is depressurized depending on the configuration of the selector valve  40 . 
   In one embodiment, the ECU  50  includes a microcomputer having a CPU and a memory. The ECU  50  is electrically connected to the valves  15 ,  28 ,  40 , the pressure sensor  30 , and the pump  44  for controlling the operation of the same. In one embodiment, the ECU  50  also controls the internal combustion engine  6 . 
   Next, the purge control flow of the evaporative fuel handling apparatus  2  will be described on the basis of the flow chart of  FIG. 3 . 
   The purge control flow starts when a purge start condition is established after the internal combustion engine  6  is started. In one embodiment, the purge start condition is established when a predetermined condition of the vehicle exists (e.g., the temperature of cooling water of the internal combustion engine  6 , the RPM of the internal combustion engine  6 , and/or the temperature of hydraulic oil is/are within predetermined ranges). Moreover, when the purge control flow starts, the selector valve  40  is configured to allow fluid communication (i.e., fluid flow) between the first communication passage  20  and the pump  44 , the pump  44  is stopped, and purge control valve  15  closes the purge passage  14 . 
   In step S 11  of the purge control flow, the ECU  50  controls the selector valve  40  to maintain fluid communication between the first communication passage  20  and the pump  44  as shown in  FIG. 1 . Here, this state is maintained at least until the purge control flow is finished. Next, in step S 12 , the ECU  50  controls the purge control valve  15  to open the purge passage  14  and controls the pump  44  to pressurize the first communication passage  20 . This action of pressurizing extends to the canister  12  and the purge passage  14 , such that evaporative fuel is desorbed from the adsorbent  16  in the canister  12  and is forcibly purged into the intake passage  7 . Hence, the amount of purged fuel can be adjusted by controlling of flow rate of the pump  44 . 
   Then, a purge stop condition is established during the forcible purge. In one embodiment, the purge stop condition is established when a predetermined condition of the vehicle exists (e.g., the RPM of the internal combustion engine  6  and/or the accelerator position of the vehicle is/are within predetermined ranges different from those of the above-mentioned purge start conditions). Once the purge stop condition is established, the method of operation moves to step S 13  in which the ECU  50  controls the purge control valve  15  to close the purge passage  14  and stops the pump  44 . As such, the forcible purge is stopped and the purge control flow is completed. 
   Next, the leak check flow of the evaporative fuel handling apparatus  2  will be described on the basis of a flow chart in  FIG. 4 . 
   The leak check flow is started after the internal combustion engine  6  is stopped. When the leak check flow is started, the first communication passage  20  is made to communicate with the pump  44  by the selector valve  40 , the atmosphere passage  27  is made to communicate with the first check passage  25  by the communication control valve  28 , the purge passage  14  is brought into a closed state by the purge control valve  15 , and the pump  44  is stopped. 
   In step S 21  of the leak check flow, the ECU  50  controls the pressure sensor  30  to detect the pressure of the second check passage  26 . The second check passage  26  is in communication with the atmosphere passage  27  through the restriction passage  29 . Therefore, the pressure detected at this time is substantially equal to the atmospheric pressure of the atmosphere passage  27 . 
   When the atmospheric pressure is detected, in step S 22 , the ECU  50  controls the communication control valve  28  to make the second check passage  26  communicate with the first check passage  25  as shown in  FIG. 6 . Then, in step S 23 , the ECU  50  controls the pressure sensor  30  to again detect the pressure in the second check passage  26 . The second check passage  26  is fluidly coupled to the fuel tank  4  through the first check passage  25 , and as such, the pressure detected is more than the atmospheric pressure if evaporative fuel is present in the fuel tank  4 . Hence, in step S 23 , the ECU  50  determines whether evaporative fuel is present in the fuel tank  4  on the basis of the detected pressure. If the detected pressure is higher than a threshold value, the ECU  50  determines that the production of evaporative fuel is excessive and finishes the leak check flow. In contrast, when the detected pressure is lower than the threshold valve, the ECU  50  determines that the production of evaporative fuel is stable and advances the leak check flow to step S 24 . 
   In step S 24 , the ECU  50  controls the selector valve  40  to make the second communication passage  22  communicate with the pump  44  as shown in  FIG. 5 . This state of communication is maintained until the leak check flow is completed. 
   Next, in step S 25 , the ECU  50  controls the communication control valve  28  to make the atmosphere passage  27  communicate with the first check passage  25  as shown in  FIG. 2 . Then, in step S 26 , the ECU  50  controls the pump  44  to depressurize the second communication passage  22  and controls the pressure sensor  30  to detect the pressure in the second check passage  26 . Depressurization of the second communication passage  22  coincidentally causes depressurization of the passages  26 ,  29 ,  25 , and  27  because these passages communicate with each other. Thus, in step S 26 , the detected pressure corresponds to the pressure of gas passing through the check restrictor  32  and is determined by the axial cross sectional area of the check restrictor  32 . Hence, the ECU  50  stores the detected pressure as a reference pressure in memory. 
   After the reference pressure is detected and stored, step S 27  commences, in which the ECU  50  makes the second check passage  26  again communicate with the first check passage  25 . Then, in step S 28 , the ECU  50  controls the pump  44  to thereby depressurize the second communication passage  22  and controls the pressure sensor  30  to detect the pressure of the second check passage  26 . Depressurization of the second communication passage  22  coincidentally causes depressurization of the passages  26 ,  25 , and  22   a  and to the purge system  10  because they are each in communication. By detecting the pressure in the second check passage  26  in step S 28 , the leak check is performed. More specifically, the ECU  50  compares the pressure detected in step S 28  to the above-mentioned reference pressure to determine whether leak occurs or not. In other words, if a leak exists the pressure detected in step S 28  will change (i.e., increase or decrease) according to the size of the leak opening of the purge system  10 . 
   Thereafter, in step S 29 , the ECU  50  makes the atmosphere passage  27  again communicate with the first check passage  25  to detect the atmospheric pressure. Then, the leak check is finished. 
   According to the first embodiment described above, a loss of pressure of flowing fluid is larger in the second communication passage  22  than in the first communication passage  20 . Hence, as shown in  FIG. 7 , the inclination of the P-Q characteristic curve of the pump  44  becomes smaller at the time of executing step S 26  and step S 28  (i.e., performing the leak check by depressurization of the second communication passage  22 ) than at the time of executing step S 12  (i.e., performing the forcible purge by pressurizing the first communication passage  20 ). Accordingly, the pump  44  is able to produce a characteristic in which the flow rate is large and in which pressure is lower than a value of resistance to pressure of the apparatus  2  for performing the forcible purge, and the same pump  44  is able to produce a characteristic in which a change in pressure with respect to a change in flow rate is small while performing the leak check. Hence, it is possible to perform the forcible purge and the leak check using a common pump  44 , so that it is possible to reduce the size and weight of the apparatus  2 . As a result, the apparatus  2  is less expensive, more compact, and the apparatus  2  can be constructed and mounted more easily. 
   Further, according to the first embodiment, in step S 12  (where the forcible purge is performed) the pump  44  pressurizes the canister  12  and purge passage  14  of the purge system  10  through the first communication passage  20 . As such, it is possible to reduce evaporative fuel desorbed from the canister  12  from extending to and being sucked by the pump  44 . Hence, it is possible to lower the levels of hermeticity, reduce the likelihood of explosion, and reduce the resistance to evaporation. 
   Still further, according to the first embodiment, the first and second communication passages  20 ,  22  are pressurized and depressurized, respectively. Hence, the direction of discharge of the pump  44  during the forcible purge in step S 12  is opposite to the direction of discharge of the pump  44  at the time of leak checking in step S 26  and S 28 . Hence, construction can be simplified by employing a mode of reversing the direction of discharge of the pump  44  in this manner. 
   In addition, according to the first embodiment, the magnitude of loss of pressure in the second communication passage  22  and the pump characteristic during leak checking of steps S 26  and S 28  vary according to the amount of axial cross sectional area restriction provided by the restrictor  23 . Hence, for example, a pump  44  having a characteristic appropriate for the forcible purge can be easily incorporated for leak checking by adjusting the amount of restriction by the restrictor  23  until the pump characteristic is appropriate for leak checking. 
   Second Embodiment 
   As shown in  FIGS. 8 and 9 , a second embodiment of the present disclosure is illustrated. Specifically, in the leak check flow of the second embodiment, steps S 46  and S 48  in which the second communication passage  22  is pressurized is executed in place of S 26  and S 28  in which the second communication passage  22  is depressurized. 
   As such, the direction of discharge of the pump  44  is the same during the forcible purge in step S 12  as the direction of discharge of the pump  44  during the leak check of steps S 46  and S 48 . Hence, it is possible to use an inexpensive pump  44  that does not change the direction of discharge. 
   It will be appreciated that in the second embodiment, a pump  44  that can change the direction of discharge may be employed. It will be appreciated that steps S 41  through S 45 , S 47 , and S 49  in the leak check flow of the second embodiment are substantially the same as steps S 21  through S 25 , S 27 , and S 29 , respectively, of the first embodiment. 
   Third Embodiment 
   Referring now to  FIG. 10 , a third embodiment of the present invention is illustrated. The third embodiment is a modified embodiment of the first embodiment. Specifically, in the third embodiment, the selector valve  40  and the first and second communication passages  20 ,  22  are not arranged on one side of the pump  44  similar to the first embodiment. Instead, a combination of a first selector valve  100  and first communication passage  110  and another combination of a second selector valve  102  and a second communication passage  112  are arranged on opposite sides of the pump  44 . 
   The first selector valve  100  is fluidly coupled to the first communication passage  110 , a first open passage  120  that is open to the atmosphere at one end, and a first pump passage  130  fluidly coupled to the first port  45  of the pump  44 . As such, the first selector valve  100  switches to allow fluid communication between the pump passage  130  (i.e., the pump  44 ) and either the first communication passage  110  or the first open passage  120 . In one embodiment, the first selector valve  100  is an electromagnetically driven three-way valve. 
   Moreover, the second selector valve  102  is connected to the second communication passage  112 , a second open passage  122  that is open to the atmosphere at one end, and a second pump passage  132  that is fluidly coupled to the second port  47  of the pump  44 . As such, the second selector valve  102  switches to allow fluid communication between the second pump passage  132  and either the second communication passage  112  or the second open passage  122 . In one embodiment, the second selector valve  102  is made of an electromagnetically driven three-way valve. Also, in the embodiment shown, the first and second selector valves  100 ,  102  are electrically connected to the ECU  50  and are controlled and operated by the ECU  50 . 
   Next, a purge control flow of the third embodiment will be described on the basis of the flow chart in  FIG. 11 . Here, when the purge control flow is started, the first communication passage  110  is made to communicate with the pump  44  by the first selector valve  100 , and the second open passage  122  is made to communicate with the pump  44  by the second selector valve  102 . 
   In step S 61  of the purge control flow, as shown in  FIG. 10 , the ECU  50  controls the first and second selector valves  100 ,  102  to maintain a state in which the first communication passage  110  is in fluid communication with the pump  44  and the second open passage  122  is in fluid communication with the pump  44 . This state is continuously held at least until the present purge control flow is finished. Then, in step S 62 , the ECU  50  opens the purge passage  14  and controls the pump  44  to pressurize the first communication passage  110 . Pressurization of the first communication passage  110  pressurizes the canister  12  and the purge passage  14 , such that fuel desorbed from the canister  12  is forcibly purged into the intake passage  7 . Thereafter, step S 63  is executed in a substantially similar manner to step S 13  of the first embodiment, and the purge control flow is completed. 
   Next, the leak check flow of the third embodiment will be described on the basis of the flow chart the  FIG. 12 . In one embodiment, when the leak check flow is started, the first communication passage  110  is made to communicate with the pump  44  by the first selector valve  100  and the second open passage  122  is made to communicate with the pump  44  by the second selector valve  102 . 
   First, steps S 71  through S 73  of the leak check flow are substantially similar to steps S 21  through S 27 , respectively, of the first embodiment. Next, in step S 74 , as shown in  FIG. 13 , the ECU  50  controls the first selector valve  100  to make the first open passage  120  communicate with the pump  44  and controls the second selector valve  102  to make the second communication passage  112  communicate with the pump  44 . This mode of communication is maintained at least until this leak check flow is finished. Next, steps S 75  through S 79  are substantially similar to steps S 25  through S 29 , respectively, of the first embodiment. 
   Thus, according to the third embodiment, the direction of discharge of the pump  44  remains the same for performing the forcible purge in step S 62  and for the leak checking of steps S 76  and S 78 . Hence, it is possible to use an inexpensive pump  44  that does not change the direction of discharge. It will be appreciated, however, that a pump  44  capable of changing the direction of discharge may be used. 
   Fourth Embodiment 
   As shown in  FIG. 14 , a fourth embodiment of the present invention is a modification example of the first embodiment. Specifically, a first communication passage  200  is included that is fluidly coupled to the introduction passage  13 . As such, the first connection passage  200  communicates with the canister  12  through the introduction passage  13 . Hence, in step S 12  of the purge control flow, the action of pressurizing the first communication passage  200  by the pump  44  causes pressurization of the canister  12  and the purge passage  14  through the introduction passage  13 , and fuel desorbed from the canister  12  is forcibly purged into the intake passage  7 . In other words, the introduction passage  13  is purged of gas by the action of pressurizing the first communication passage  200  by the pump  44 , so that evaporative fuel flowing into the introduction passage  13  is surely introduced into the canister  12 , and the amount of fuel adsorbed by the canister  12  is increased and the amount of fuel desorbed from the canister  12  is increased. Hence, the fourth embodiment can be especially effective for supplying a relatively large amount of purge. 
   Fifth Embodiment 
   Referring now to  FIG. 15 , a fifth embodiment of the present invention is shown, which is a modification of the first embodiment. Specifically, a first communication passage  250  is included that is fluidly coupled to the fuel tank  4 . The introduction passage  13  is separately coupled to the top of the fuel tank  4 . As such, the first connection passage  250  is fluidly coupled to the canister  12  through the fuel tank  4  and the introduction passage  13 . Hence, in step S 12  of the purge control flow, pressurization of the first communication passage  250  by the pump  44  causes pressurization of the canister  12  and the purge passage  14  through the fuel tank  4  and the introduction passage  13 , such that fuel desorbed from the canister  12  is forcibly purged into the intake passage  7 . Thus, atmosphere can pass over the liquid fuel in the fuel tank  4 , so that the amount of evaporative fuel in the fuel tank  4  is made stable. In other words, when performing the forcible purge, the space  260  in the upper portion of the fuel tank  4  and the introduction passage  13  are purged of gas due to the pressurization of the first communication passage  250 , so that a stable amount of evaporative fuel is introduced into the canister  12 . The concentration of fuel desorbed from the canister  12  is unlikely to fluctuate, and thus, the fifth embodiment provides a stable concentration of purged fuel. 
   Sixth Embodiment 
   Referring now to  FIG. 16 , a sixth embodiment of the present invention is shown, which is a combination of the third embodiment and the fourth embodiment. Specifically, the sixth embodiment has substantially the same construction as the third embodiment except that a first communication passage  200  is included that is fluidly coupled to the introduction passage  13 . Hence, the sixth embodiment can produce the same effect as the third and fourth embodiments. 
   Seventh Embodiment 
   Referring now to  FIG. 17 , a seventh embodiment of the present invention is shown, which is a combination of the third embodiment and the fifth embodiment. Specifically, the seventh embodiment has substantially the same construction as the third embodiment except that a first communication passage  250  is included that is fluidly coupled to the fuel tank  4 . Hence, the seventh embodiment can produce the same effect as the third and fifth embodiments. 
   Eighth Embodiment 
   Referring now to  FIG. 18 , an eighth embodiment of the present invention is illustrated that is a modification of the third embodiment. Specifically, in the eighth embodiment, a first open passage  304  is fluidly coupled to the canister  300  on a side opposite to the introduction passage  13  (i.e., across the adsorbent  16 ), and a first communication passage  310  is fluidly connected to the canister  300  on a side opposite to a second communication passage  312  (i.e., across the adsorbent  16 ). While the purge control valve  15  is not arranged in the purge passage  302 , an opening/closing valve  306  made of an electromagnetically driven two-way valve is arranged in the middle of the first open passage  304 . Here, the valve  306  is opened and closed to control the opening/closing of the first open passage  304 . 
   A first pump passage  130  is fluidly coupled to the pump  44  and the first selector valve  320 . The first selector valve  320  is also fluidly coupled to the second communication passage  312 . The first selector valve  320  can switch to allow fluid communication between the pump  44  and either the first communication passage  310  or the second communication passage  312 . 
   A second pump passage  132  is fluidly coupled to the pump  44  and a second selector valve  322 . The second selector valve  322  has a purge passage  302  fluidly coupled thereto. As such, the second selector valve  322  can switch to allow fluid communication between the pump  44  and either the purge passage  302  or the second open passage  122 . In one embodiment, the opening/closing valve  306  and the first and second selector valves  320 ,  322  are electrically connected to the ECU  50  and are controlled and operated by the ECU  50 . 
   Next, the purge control flow of the eighth embodiment will be described on the basis of a flow chart in  FIG. 19 . In one embodiment, when the purge control flow is started, the first communication passage  310  is made to communicate with the pump  44  by the first selector valve  320 , the second open passage  122  is made to communicate with the pump  44  by the second selector valve  322 , and the first open passage  304  is brought into a closed state by the opening/closing valve  306 . 
   In step S 101  of the purge control flow, the ECU  50  controls the opening/closing valve  306  to open the first open passage  304 . In this embodiment, the opening/closing valve  306  remains open until the purge control flow is finished. Next, in step S 102 , the ECU  50  controls the first selector valve  320  to maintain fluid communication between the first communication passage  310  and the pump  44 , and the ECU  50  controls the second selector valve  322  to make the purge passage  302  fluidly communicate with the pump  44 . 
   Next, in step S 103 , the ECU  50  controls the pump  44  to depressurize the first communication passage  310  and to pressurize the purge passage  302 . Depressurization of the first communication passage  310  causes depressurization of the canister  300 , thereby causing evaporative fuel to be desorbed from the canister  300  and sucked through the first port  45  by the pump  44 . The evaporative fuel sucked by the pump  44  is discharged from the pump  44  through the second port  47  and then is forcibly purged into the intake passage  7  due to pressurization of the purge passage  302 . 
   Thereafter, in step S 104 , when the purge stop conditions are established, the ECU  50  controls the second selector valve  322  to make the second open passage  122  fluidly communicate with the pump  44  and stops the pump  44 . As such, the forcible purge is completed, and the purge control flow is finished. 
   Next, the leak check flow of the eighth embodiment will be described on the basis of the flow chart of  FIG. 20 . Here, when the leak check flow is started, the first communication passage  310  is made to communicate with the pump  44  by the first selector valve  320 , the second open passage  122  is made to communicate with the pump  44  by the second selector valve  322 , and the first open passage  304  is brought into an opened state by the opening/closing valve  306 . 
   In S 111  of the leak check flow, the ECU  50  controls the opening/closing valve  306  to close the first open passage  304 . In this embodiment, this closed state is maintained until the leak check flow is completed. The contents of successive steps S 112  through S 114  are substantially similar as those of steps S 71  through S 73 , respectively, of the third embodiment (i.e., steps S 21  through S 23 , respectively of the first embodiment). Further, in step S 115 , as shown in  FIG. 21 , the ECU  50  controls the second selector valve  322  to maintain a state where the second open passage  122  is made to communicate with the pump  44 , and the ECU  50  controls the first selector valve  320  to make the second communication passage  312  communicate with the pump  44 . In this embodiment, the second open passage  122  remains in communication with the pump  44  until this leak check flow is completed. Also, in this embodiment, the second communication passage  312  remains in communication with the pump  44  until finishing the check. 
   Steps S 116  through S 120  executed after S 115  are substantially the same as those of steps S 75  through S 79  of the third embodiment (i.e., steps S 25  through S 29  of the first embodiment). 
   Thus, according to the eighth embodiment, the pump  44  is fluidly coupled to the purge passage  302  and can be arranged close to the intake passage  7 . As such, flow rate responsivity in purge can be increased. Hence, by controlling the pump  44 , the amount of purged fuel can be adjusted with high accuracy. Further, similar to the third embodiment, the direction of discharge of the pump  44  need not be reversed for performing the forcible purge (i.e., step S 103 ) and the leak check (i.e., steps S 117  and S 119 ). Hence, it is possible to use an inexpensive pump  44  that does not change the direction of discharge. It will be appreciated, however, that a pump  44  capable of changing the direction of discharge may be used. 
   While the first to eighth embodiments have been described up to this point, it should not be understood that the present invention is limited to these embodiments but the present invention can be applied to various embodiments without departing from the scope of the present invention. 
   For example, the third through eighth embodiments, respectively, can be varied such that in steps S 26 , S 28 , S 76 , S 78 , S 117 , and S 119 , the second communication passages  22 ,  112 ,  312  are pressurized instead of depressurized similar to the second embodiment. Furthermore, in a variation of the third and sixth through eighth embodiments, the first open passages  120 ,  304  are made to communicate with the second open passage  122  at least on the end open to the atmosphere.