Abstract:
An evaporative emission leak detection system provides for detecting a leakage of a fuel vapor evaporating in a fuel tank by using a pressure difference between an inside and outside of the fuel tank. The system includes a pump for providing the pressure difference between the inside and outside of the fuel tank, a brushless motor for operating the pump, a first passage connecting to the fuel tank, a second passage connecting to the outside of the fuel tank, and a switching device for switching connections between the pump and at least one of the first passage and the second passage. The first passage has an adsorbent for adsorbing the fuel vapor. This system ensures a long life time and high accuracy of the leak detection.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on Japanese Patent Application No. 2002-189578 filed on Jun. 28, 2002, the disclosure of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to an evaporative emission leak detection system for detecting leakage of fuel vapor leaking outside a fuel system. This leak detection system is suitably applied to a fuel system, which is mounted on an automotive vehicle. 
   BACKGROUND OF THE INVENTION 
   Recently, in addition to an automotive vehicle discharge emission regulation, it is required to regulate an evaporative fuel emission. For example, the California Air Resources Board (i.e., CARB) as well as the U.S. Environmental Protection Agency (i.e., EPA) require detection of evaporative emission leakage from a small opening of a fuel tank of an automotive vehicle. 
   In view of detecting an evaporative emission leakage, U.S. Pat. No. 5,146,902 (JP-A-5-272417) and U.S. Pat. No. 5,890,474 (JP-A-10-90107) disclose evaporative emission leak detection systems for detecting leakage of fuel vapor leaking outside a fuel tank. These prior arts utilize a pressure difference between an inside and outside of the fuel tank. The pressure difference is provided by increasing or decreasing the pressure of the fuel tank with a pump. When leakage exists, a pumping load of the pump changes in accordance with size of leakage opening. Therefore, the evaporative emission leakage can be estimated by measuring the pumping load change. 
   However, when the pump increases the pressure of the fuel tank, i.e., the pump pressurizes the fuel tank, the fuel vapor is released outside the fuel tank at every detection time. Further, when the pump decreases the pressure of the fuel tank, i.e., the pump depressurizes the fuel tank, the fuel vapor may be eliminated by a canister. However, the residual fuel vapor, which is not eliminated by the canister, penetrates into the pump. When the pump is driven by a brush motor, the residual fuel vapor adheres to a sliding portion of the pump, for example, a sliding portion of a brush. Therefore, the sliding portion will be abraded. Moreover, abraded powder of the sliding portion adheres to a commutator of the motor, so that the commutator will be abnormally abraded. Thus, the motor operation becomes unstable and a life time of the motor decreases. Further, operation characteristics of the motor deteriorate with age because of an abrasion of the brush and the commutator, so that the leak detection system does not detect leakage accurately. 
   SUMMARY OF THE INVENTION 
   In view of the above problems, it is an object of the present invention to provide an evaporative emission leak detection system, which ensures a long life time and high accuracy of the leak detection. 
   An evaporative emission leak detection system provides for detecting leakage of fuel vapor evaporating in a fuel tank by using a pressure difference between an inside and outside of the fuel tank. The system includes a pump for providing the pressure difference between the inside and outside of the fuel tank, a brushless motor for operating the pump, a first passage connecting to the fuel tank, a second passage connecting to the outside of the fuel tank, and a switching device for switching connections between the pump and at least one of the first passage and the second passage. The first passage has an adsorbent for adsorbing the fuel vapor. 
   The brushless motor has no mechanical contact portion so that the brushless motor does not have a sliding portion such as a commutator and a brush. Therefore, the brushless motor is not abraded by penetration of the fuel vapor into the brushless motor. Thus, the life time of the brushless motor is lengthened, and the brushless motor operates stably. Further, operation characteristics of the brushless motor do not deteriorate with age substantially, so that current supplied to the brushless motor is stabilized. Therefore, the operation of the pump can be stabilized. Moreover, the brushless motor does not generate a noise substantially. Therefore, the accuracy of the evaporative emission leak detection is improved. 
   Preferably, the system includes a throttle disposed between the second passage and the pump, and a detecting device for detecting a pressure. The pump depressurizes the fuel tank at least below the atmospheric pressure. The throttle throttles air flow to a predetermined amount so that the pressure in a passage between the pump and the switching device is decreased to a predetermined pressure and is regulated to the predetermined pressure when the first and second passages connect to the pump only through the throttle and the pump depressurizes the passage. The detecting device is disposed in the passage between the pump and the switching device, and detects the atmospheric pressure, the fuel vapor pressure, and the predetermined pressure. 
   In this case, the system detects the pressure of the fuel vapor evaporating from the fuel tank, so that the system can detect the evaporative emission leakage without influence of the atmospheric pressure, the altitude, the humidity, and other environmental conditions. Therefore, the detection accuracy of the leakage is improved. Moreover, the concentration of the fuel vapor in the fuel tank, the humidity, the atmospheric pressure, and other environmental conditions always change, as time passes. Therefore, the evaporative emission leakage changes, so that the detection accuracy of the leakage may change. However, the atmospheric pressure, the fuel vapor pressure, and the predetermined pressure are measured at every detection time so that the detection accuracy of the leakage preserves. 
   The detection device directly detects the pressure in the passage that connects to the fuel tank. Therefore, the detection accuracy of the evaporative emission leakage is higher than that in a case where the pressure of the fuel tank is calculated indirectly by measuring the current of the motor. 
   Further, the fuel tank is depressurized so as to detect the evaporative emission leakage. Therefore, the fuel vapor is not released outside the fuel tank, so that the environmental protection can be achieved. 
   Preferably, the system includes a microcomputer for controlling the switching device, the detecting device, the brushless motor, and the like. The pressure in the passage between the pump and the switching device is decreased to a leak detection pressure when the first passage connects to the pump and the pump depressurizes the passage between the pump and the switching device. The microcomputer determines that the leakage of the fuel vapor exceeds the predetermined amount of the air flow limited by the throttle when the leak detection pressure becomes larger than the predetermined pressure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIG. 1  is a schematic diagram showing an evaporative emission leak detection system according to the first embodiment of the present invention; 
       FIG. 2  is a cross-sectional view showing a detection module according to the first embodiment when a coil of the detection module is not energized; 
       FIG. 3  is a cross-sectional view showing the detection module according to the first embodiment when the coil of the detection module is energized; 
       FIG. 4  is a table showing steps for detecting an evaporative emission leakage, according to the first embodiment; 
       FIG. 5  is a timing chart showing pressure of a connection passage, according to the first embodiment; 
       FIG. 6  is a schematic diagram showing an evaporative emission leak detection system according to the second embodiment of the present invention; 
       FIG. 7  is a graph showing a relationship between pressure of a connection passage and current of a brushless motor, according to the second embodiment; 
       FIG. 8  is a graph showing a relationship between size of a leakage opening and current of the brushless motor, according to the second embodiment; and 
       FIG. 9  is a timing chart showing pressure of a connection passage, according to the third embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   (First Embodiment) 
   An evaporative emission leak detection system  1  according to the first embodiment of the present invention is applied to a fuel system of an automotive vehicle, as shown in  FIG. 1 . The detection system  1  includes a detection module  10 , a fuel tank  2 , a canister  3  as an adsorber, air intake equipment  80 , and ECU  4  (i.e., electric control unit). The detection module  10  has, as shown in  FIG. 2 , a housing  20 , a pump  11 , a brushless motor  12 , a switching device  30 , and a pressure sensor  13 . The detection module  10  is disposed at the higher position than the fuel tank  2  and the canister  3 , so that fuel and water leaking from the fuel tank  2  and the canister  3  do not penetrate into the detection module  10 . 
   The housing  20  includes a pump chamber  21  for accommodating the pump  11 , and a valve chamber  22  for accommodating the switching device  30 . The housing  20  also accommodates the brushless motor  12 . The housing  20  also includes a tank passage  41  as a first passage, an open passage  42  as a second passage, a connection passage  43 , and a discharge passage  44 . The open passage  42  has an opening  42   a,  which opens to the atmosphere outside the detection system  1 , as shown in  FIGS. 1 and 2 . The open passage  42  connects the opening  42   a  to the valve chamber  22  of the housing  20 . The connection passage  43  connects the valve chamber  22  to the pump  11 . The valve chamber  22  of the housing  20  connects to the fuel tank  2  through the tank passage  41  and the canister  3 . Therefore, the air including the fuel vapor flows from the fuel tank  2  to the pump  11  through the tank passage  41  and the connection passage  43 . Further the air flows from the opening  42   a  to the pump  11  through the open passage  42 , the valve chamber  22 , and the connection passage  43 . Here, the air flowing through the connection passage  43  is described as a mixed gas, infra. 
   The discharge passage  44  connects the pump chamber  21  to the open passage  42  through the valve chamber  22 . Thus, the mixed gas is discharged from the pump  11  to the outside of the fuel tank  2  through the discharge passage  44 . The connection passage  43  branches to an orifice passage  45  at the side of the valve chamber  22 . The orifice passage  45  connects the connection passage  43  to the valve chamber  22 , and includes an orifice  46  as a throttle. The orifice  46  flows the air at a predetermined amount that is equal to an amount of the air flowing from a permissible opening, which is a maximum leakage opening required by the governmental regulations. For example, the CARB as well as the EPA requires the detection of a leakage opening of φ0.5 mm. In this embodiment, the orifice  46  provides an air flow corresponding to the leakage opening at φ0.5 mm and less. 
   The pump  11  is accommodated in the pump chamber  21 , and includes a suction port  14  and a discharge port  15 . The suction port  14  is disposed in the connection passage  43 , and the discharge port  15  is disposed in the pump chamber  21 . The pump  11  is driven by the brushless motor  12 , so that the pump  11  sucks the mixed gas in the connection passage  43  through the suction port  14 . Then, the pressure of the mixed gas in the connection passage  43  is decreased, i.e., the connection passage is depressurized. The brushless motor  12  is a contact less direct current motor, which has no contact portion mechanically and rotates a moving portion (not show) by changing a position for energizing a coil of the motor  12 . The brushless motor  12  is controlled by the controller  5 . 
   The switching device  30  includes a valve body  31 , a valve member  50 , and an electromagnetic unit  60 . The valve body  31  is accommodated in the valve chamber  22  of the housing  20 . The valve body  31  has a first valve seat  32 , which is disposed on the side of the tank passage  41 . A washer  51  is mounted on the valve member  50 , and can be press-contacted to the first valve seat  32 . The valve member  50  is driven by the electromagnetic unit  60 . The electromagnetic unit  60  has a coil  61 , which electrically connects to the ECU  4 . 
   The valve member  50  includes a contact pad  52  for press-contacting a second valve seat  33 . The contact pad  52  is disposed on an end of the valve member  50 , which is opposite to the electromagnetic unit  60 . The second valve seat  33  is disposed on an end of the connection passage  43 , and is disposed in the valve chamber  22 . Normally, i.e., when the coil  61  is not energized, a force by a spring  63  is applied to the valve member  50  so that the valve member  50  moves toward the second valve seat  33 . When the valve member  50  moves toward the second valve seat  33 , the contact pad  52  contacts the second valve seat  33 . 
   Thus, the contact pad  52  is press-contacted to the second valve seat  33 , as shown in  FIG. 2 . Therefore, the tank passage  41  and the open passage  42  are connected together, and both the tank passage  41  and the open passage  42  are connected to the connection passage  43  only through the orifice passage  45 . 
   When the coil  61  is energized, a core  62  of the electromagnetic unit  60  is magnetized. The core  62  attracts the valve member  50  so that the valve member  50  moves toward the first valve seat  32 . When the valve member  50  moves toward the first valve seat  32 , the washer  51  contacts the first valve seat  32 . Thus, the washer  51  is press-contacted to the first valve seat  32 , as shown in  FIG. 3 . Therefore, the tank passage  41  and the open passage  42  are disconnected, and the tank passage  41  and the connection passage  43  are connected, as shown in  FIG. 3 . 
   When the washer  51  of the valve member  50  is press-contacted to the first valve seat  32  as shown in  FIG. 3 , electric power supplied to the coil  61  is smaller than that in a case where the valve member  50  is just moving toward the first valve seat  32 . In other words, a holding electric power for holding the press-contact between the washer  51  and the first valve seat  32  is comparatively small. Therefore, the holding electric power can be limited to be small to such an extent that the washer  51  is press-contacted to the first valve seat  32  and the valve member  50  does not move. For example, the holding electric power is supplied to the coil  61  intermittently by a pulse-modulated voltage or the like. Thus, the electric power supplied to the coil  61  can be reduced, so that heat generated by the coil  61  is also reduced. Therefore, the change of detection accuracy according to the heat can be reduced. 
   As shown in  FIG. 1 , the canister  3  has an adsorbent  3   a.  The adsorbent  3   a  is, for example, an active carbon, and adsorbs the fuel vapor evaporating from the fuel tank  2 . The canister  3  is disposed in the tank passage  41  between the valve chamber  22  and the fuel tank  2 . A purge passage  82  connects to the canister  3 , and connects to an air intake duct  81  of the air intake equipment  80 . The fuel vapor is adsorbed by the adsorbent  3   a  in the canister  3 . After passing through the canister  3 , the mixed gas flowing from the canister  3  contains a small concentration of the fuel vapor, the concentration of which is smaller than a predetermined amount. Here, the air intake equipment  80  includes the air intake duct  81 , which connects to the air intake of the engine, and a throttle valve  83  for adjusting the intake air flowing through the air intake duct  81 . 
   The pressure sensor  13  is disposed in the connection passage  43 . The pressure sensor  13  detects pressure of the air in the connection passage  43 , and outputs a signal corresponding to the pressure. The ECU  4  receives the signal from the pressure sensor  13 . The ECU  4  includes a microcomputer that is composed of a central processing unit (i.e., CPU), a read only memory (i.e., ROM), and a random-access memory (i.e., RAM). The ECU  4  controls the whole engine system and the detection module  10 . For example, the ECU  4  controls the controller  5  and the switching device  30 . A plurality of signals is output from several sensors that are disposed on the vehicle, especially on the engine system such as the pressure sensor  13 , so that these signals are input into the ECU  4 . The ECU  4  receives these signals so that the ECU  4  controls the whole engine system according to a predetermined control program memorized in the ROM of the ECU  4 . 
   The detection module  10  in the evaporative emission leak detection system  1  operates as follows. 
   When a predetermined time has passed since the engine of the vehicle stopped, the evaporative emission leak detection system  1  begins to operate. This predetermined time is set to a period in which the temperature of the whole engine system is stabilized. 
   The evaporative emission leakage from the fuel tank  2  is detected on the basis of the pressure change. Therefore, an influence rising from a deviation of the atmospheric pressure PA at each altitude should be compensated. Therefore, at first, the atmospheric pressure PA is measured by the pressure sensor  13 , which is disposed in the connection passage  43 . When the coil  61  is not energized, as shown in  FIG. 2 , the open passage  42  connects to the connection passage  43  through the orifice passage  45 , so that the pressure in the connection passage  43  is almost equal to the atmospheric pressure PA. The pressure sensor  13  measures the pressure of the air in the connection passage  43 , i.e., the atmospheric pressure PA, and outputs a pressure signal corresponding to the measured pressure. 
   Here, the pressure signal is output as a voltage ratio signal, a duty ratio signal, or a bit output signal so that the pressure signal is not affected by an electromagnetic noise rising from the electrical driving portion such as the electromagnetic unit  60  and the like. Thus, the pressure sensor  13  preserves its accuracy of the detection. The pressure sensor  13  substantially measures the atmospheric pressure PA near the detection module  10 , so that the accuracy of the detection using the pressure sensor  13  is higher than that using another atmospheric sensor, for example, mounted on the fuel injection device, which is far from the detection module  10 . 
   During the above measurement, as shown by step A in  FIGS. 4 and 5 , only the pressure sensor  13  operates, and both the brushless motor  12  and the switching device  30  stop to operate. Here, step A is defined as an atmospheric pressure detection step. 
   Then, the altitude of the vehicle having the evaporative emission leak detection system  1  is calculated by using the measured atmospheric pressure PA. For example, the altitude is calculated by using a relationship between the atmospheric pressure PA and the altitude, which is memorized in the ROM of the ECU  4 . According to the calculated altitude, several parameters for detecting the evaporative emission leakage are compensated and corrected. These compensations and corrections are performed by the ECU  4 . 
   Next, the switching device  30  is operated, i.e., the coil  61  of the switching device  30  is energized, as shown by step B in  FIGS. 4 and 5 . Step B is defined as a fuel vapor detection step. When the coil  61  is energized, the valve member  50  is attracted to the core  62  so that the washer  51  is press-contacted to the first valve seat  31 . Thus, the open passage  42  and the connection passage  43  are disconnected, and the tank passage  41  and the connection passage  43  are connected. Therefore, the fuel tank  2  and the connection passage  43  are connected through the tank passage  41 . When the fuel in the fuel tank  2  evaporates so that the fuel vapor rises, the inner pressure of the fuel tank  2  becomes higher than the atmospheric pressure PA outside the fuel tank  2 . In this case, the pressure of the connection passage  43  increases. The pressure sensor  13  detects this increase of the pressure, so that the pressure of the fuel vapor can be detected. 
   After the pressure sensor  13  detects the pressure increase, the coil  61  stops to be energized, as shown by step C in  FIGS. 4 and 5 . Step C is defined as a reference pressure detection step. The valve member  50  moves toward the second valve seat  33 , so that the contact pad  52  is press-contacted to the second valve seat  33 . Thus, the tank passage  41  connects to the open passage  42 , and both the tank passage  41  and the open passage  42  are connected to the connection passage  43  only through the orifice passage  45 . 
   Then, the brushless motor  12  is energized so as to operate the pump  11  for depressurizing the mixed gas in the connection passage  43 . The air in the open passage  42  and the mixed gas in the tank passage  41  flow into the connection passage  43  through the orifice passage  45 , and are pumped by the pump  11  so that the pressure in the connection passage  43  is decreased as shown by step C in  FIG. 5 . However, the orifice  46  in the orifice passage  45  throttles a flow of the mixed gas flowing into the connection passage  43 , so that the pressure in the connection passage  43  is decreased to a predetermined pressure, i.e., a depressurizing reference pressure PR. Thus, the pressure in the connection passage  43  is stabilized at the depressurizing reference pressure PR, so that the pressure sensor  13  detects the depressurizing reference pressure PR, and outputs a pressure signal to the ECU  4 . 
   Then, the coil  61  of the switching device  30  is energized again, as shown by step D in  FIGS. 4 and 5 . In step D, the washer  51  is press-contacted to the first valve seat  32 , the tank passage  41  and the connection passage  43  are connected together, and the open passage  42  and the connection passage  43  are disconnected. Therefore, the fuel tank  2  connects to the connection passage  43  through the tank passage  41 , so that the pressure of the fuel tank  2  is equal to the pressure of the connection passage  43 . Thus, the pressure of the connection passage  43  increases rapidly and temporarily. 
   Then, the brushless motor  12  is energized to operate the pump  11  so that the pressure of the mixed gas in the fuel tank  2  is decreased through the tank passage and the connection passage, i.e., the fuel tank is depressurized. The controller  5  controls the brushless motor  12  so as to regulate a rotation speed of the brushless motor  12 . Therefore, even when a pressure difference between the inside and outside of the fuel tank  2  is comparatively small, the detection system  1  can detects the evaporative emission leakage. 
   Here, because the fuel tank  2  connects to the connection passage  43 , the pressure sensor  13  detects the pressure of the connection passage  43  that is equal to the pressure of the fuel tank  2 . When the detected pressure of the connection passage  43 , i.e., the pressure of the fuel tank  2 , is decreased below the depressurizing reference pressure PR, it is determined that the evaporative emission leakage from the fuel tank  2  is below the allowable amount, as shown by D 1  in  FIG. 5 . This means that the outside air outside the fuel tank  2  does not penetrate into the fuel tank  2 , so that the fuel tank  2  is airtight sufficiently. Reversely, the fuel vapor rising in the fuel tank  2  does not leak outside the fuel tank  2  substantially, and the evaporative emission leakage is below the allowable amount. 
   When the detected pressure of the connection passage  43  is almost equal to the depressurizing reference pressure PR, the evaporative emission leakage leaking from the fuel tank  2  corresponds to a leakage from the orifice  46 , as shown by D 2  in  FIG. 5 . 
   On the other hand, when the detected pressure of the connection passage  43  is not decreased below the depressurizing reference pressure PR, it is determined that the evaporative emission leakage exceeds the allowable amount, as shown by D 3  in  FIG. 5 . In this case, the outside air outside the fuel tank  2  penetrates into the fuel tank  2 , as the fuel tank  2  is depressurized. Reversely, it is considered that the fuel vapor evaporating in the fuel tank  2  leaks outside the fuel tank  2 . 
   When the evaporative emission leakage is determined to exceed the allowable amount, a warning lamp (not shown) mounted on the instrument panel turns on when the engine starts at next time. A driver of the vehicle recognizes the warning lamp and is informed about the evaporative emission leakage. 
   After that, both the brushless motor  12  and the switching device  30  stop to be energized, as shown by step E in  FIGS. 4 and 5 . Step E is defined as a detection completion step. The pressure of the connection passage  43  recovers to the atmospheric pressure PA. The pressure sensor  13  detects the atmospheric pressure PA and outputs the pressure signal to the ECU  4 . Then, the ECU  4  controls the pressure sensor  13  to stop its operation. Then, the evaporation emission leak detection is completed. 
   In the detection module  10 , the brushless motor  12  is used for operating the pump  11 . The brushless motor  12  has no mechanical contact portion so that the brushless motor  12  does not have a sliding portion such as a commutator and a brush. Therefore, even when the mixed gas rising from the fuel tank  2  penetrates into the pump  11  or the brushless motor  12 , the brushless motor  12  is not abraded, and has no abraded powder. Thus, the life time of the brushless motor  12  is lengthened, and the brushless motor  12  operates stably. Further, operation characteristics of the brushless motor  12  do not deteriorate with age substantially, so that current supplied to the brushless motor  12  is stabilized. Therefore, the operation of the pump  11  can be stabilized. 
   Moreover, the brushless motor  12  does not generate a noise substantially, because the brushless motor  12  has no contact portion. Further, the brushless motor  12  is controlled by the controller  5  with a constant voltage control. Therefore, the operation of the brushless motor  12  is stable, and also the operation of the pump  11  driven by the brushless motor  12  can be stabilized. Thus, the accuracy of the evaporative emission leak detection by the pressure sensor  13  is improved. 
   Further, the brushless motor  12  and the pump  11  are disposed in space, which is filled with the fuel vapor. Therefore, the brushless motor  12  needs no rotation shaft sealing so that the structure of the brushless motor  12  is simplified. If the brushless motor  12  is disposed outside the space, which filled with the fuel vapor, the brushless motor  12  necessitates a rotation shaft sealing for preventing the fuel vapor from leaking. 
   In this embodiment, the pressure of the mixed gas, which flows through the orifice  46  of the orifice passage  45 , is measured, before the fuel tank  2  is depressurized. Therefore, the evaporative emission leak detection system  1  detects the pressure of the fuel vapor evaporating from the fuel tank  2 , so that the detection system  1  can detect the evaporative emission leakage without influence of the atmospheric pressure PA, the altitude of the vehicle, the humidity, and other environmental conditions. Therefore, the detection accuracy of the leakage is improved. 
   In general, the concentration of the fuel vapor in the fuel tank  2 , the humidity, the atmospheric pressure PA, and other environmental conditions always change, as time passes. Therefore, the evaporative emission leakage changes, so that the detection accuracy of the leakage may change. However, in this embodiment, the reference pressure is measured at every detection time so that the detection accuracy of the leakage preserves. 
   The pressure sensor  13  directly detects the pressure of the connection passage  43  that connects to the fuel tank  2 . Therefore, the detection accuracy of the evaporative emission leakage is higher than that in a case where the pressure of the fuel tank  2  is calculated indirectly by measuring the current of the motor. 
   In steps C and D, the fuel tank  2  is depressurized so as to detect the evaporative emission leakage. Therefore, the mixed gas including the fuel vapor is not released outside the fuel tank  2 , so that the environmental protection can be achieved. 
   (Second Embodiment) 
   According to a second embodiment, as shown in  FIG. 6 , the detection module  10  has no pressure sensor. Therefore, the ECU  4  gets the information about operation characteristics of the brushless motor  12  from the controller  5 . Here, the operation characteristics are, for example, voltage and current supplied to the brushless motor  12 , and rotation speed of the brushless motor  12 . Here, the brushless motor  12  is controlled with constant voltage control, and the brushless motor  12  operates stably in each current supplied to the brushless motor  12 . Therefore, the operation characteristics of the brushless motor  12  can be detected accurately by measuring the current. 
   For example, the current supplied to the brushless motor  12  relates to the inner pressure of the fuel tank  2 , as shown in FIG.  7 . Also as shown in  FIG. 8 , the current supplied to the brushless motor  12  relates to a leakage opening, i.e., a size of leakage opening. The fuel vapor leaks through this leakage opening. 
   Thus, the ECU  4  gets the information about the operation characteristics of the brushless motor  12  from the controller  5 , so that the inner pressure of the fuel tank  2  as well as the size of the leakage opening can be calculated. Further, the pressure of the connection passage  43  can be obtained indirectly by measuring the operation characteristics of the brushless motor  12  without the pressure sensor. 
   In general, the controller  5  includes the detection means of the operation characteristics of the brushless motor  12 . In other words, the controller  5  can be used as a load detection device for measuring the operation characteristics, so that no additional circuit is necessitated. 
   In this embodiment, because the evaporative emission leak detection system  1  has no pressure sensor, the atmospheric pressure PA is obtained by another pressure sensor mounted on other equipment of the vehicle such as fuel injection equipment and air intake equipment. 
   (Third Embodiment) 
   Evaporative emission leak detection system according to the third embodiment is a modification of the first embodiment. 
   At first, the pressure sensor  13  detects the atmospheric pressure PA in step A as shown in  FIG. 9 , i.e., in the atmospheric pressure detection step. Then, the altitude of the vehicle having the detection system  1  is calculated by using the detected atmospheric pressure PA. 
   Then, the coil  61  of the switching device  30  is energized, in step B in  FIG. 9 , i.e., in the fuel vapor detection step. When the fuel in the fuel tank  2  evaporates so that the fuel vapor rises, the inner pressure of the fuel tank  2  becomes higher than the atmospheric pressure PA outside the fuel tank  2 . In this case, the pressure of the air in the connection passage  43  increases, as shown by step B in  FIG. 9 . 
   After the pressure sensor  13  detects the pressure rising, the coil  61  stops to be energized, as shown by step F in  FIG. 9 , i.e., in the reference pressure detection step. The valve member  50  moves toward the second valve seat  33 , so that the contact pad  52  is press-contacted to the second valve seat  33 , as shown in  FIG. 2 . Thus, the tank passage  41  connects to the open passage  42 , and both the tank passage  41  and the open passage  42  are connected to the connection passage  43  only through the orifice passage  45 . 
   Then, the brushless motor  12  is energized so as to operate the pump  11  for pressurizing the connection passage  43 . The mixed gas in the connection passage  43  flows into the valve chamber  22  through the orifice passage  45 , and then the mixed gas flowing into the valve chamber  22  is released to the outside of the fuel tank  2  through the opening  42   a  of the open passage  42 . However, the orifice  46  in the orifice passage  45  throttles flow of the mixed gas flowing into the valve chamber  22 , so that the pressure in the connection passage  43  is increased to a predetermined pressure, i.e., a pressurizing reference pressure PP. Then, the pressure in the connection passage  43  is stabilized at the pressurizing reference pressure PP. Thus, the pressure sensor  13  detects the pressurizing reference pressure PP, and outputs a pressure signal to the ECU  4 . 
   Then, the coil  61  of the switching device  30  is energized again, as shown by step G in  FIG. 9 . In step G, the washer  51  is press-contacted to the first valve seat  32 , the tank passage  41  and the connection passage  43  are connected together, and the open passage  42  and the connection passage  43  are disconnected, as shown in  FIG. 3 . Thus, the fuel tank  2  connects to the connection passage  43  through the tank passage  41 , so that the pressure of the fuel tank  2  becomes equal to that of the connection passage  43 . Therefore, the pressure of the connection passage  43  decreases rapidly and temporarily. Then, the brushless motor  12  is energized to operate the pump  11  so that the inside air of the fuel tank  2  is pressurized. The controller  5  controls the brushless motor  12  so as to regulate a rotation speed of the brushless motor  12 . Therefore, even when a pressure difference between the inside and outside of the fuel tank  2  is comparatively small, the detection system  1  can detect the evaporative emission leakage. 
   Here, because the fuel tank  2  connects to the connection passage  43 , the pressure sensor  13  detects the pressure of the connection passage  43  that is equal to the pressure of the fuel tank  2 . When the detected pressure of the connection passage  43 , i.e., the pressure of the fuel tank  2 , is increased above the pressurizing reference pressure PP, it is determined that the evaporative emission leakage from the fuel tank  2  is below the allowable amount, as shown by G 1  in  FIG. 9 . This means that the inside air inside the fuel tank  2  is not released outside the fuel tank  2 , so that the fuel tank  2  is airtight sufficiently. Therefore, the fuel vapor rising in the fuel tank  2  does not leak outside the fuel tank  2 , and the evaporative emission leakage is below the allowable amount. 
   When the detected pressure of the connection passage  43  is almost equal to the pressurizing reference pressure PP, the evaporative emission leakage leaking from the fuel tank  2  corresponds to a leakage from the orifice  46 , as shown by G 2  in  FIG. 9 . 
   On the other hand, when the detected pressure of the connection passage  43  is not increased above the pressurizing reference pressure PP, it is determined that the evaporative fuel emission leakage exceeds the allowable amount, as shown by G 3  in  FIG. 9 . In this case, the inside air inside the fuel tank  2  is released outside the fuel tank  2 , as the fuel tank  2  is pressurized. Therefore, the fuel vapor rising in the fuel tank  2  leaks outside the fuel tank  2 . 
   When the evaporative emission leakage is determined to exceed the allowable amount, the warning lamp (not shown) mounted on the instrument panel turns on when the engine starts at next time. A driver of the vehicle recognizes the warning lamp and is informed about the evaporative emission leakage. 
   After that, both the brushless motor  12  and the switching device  30  stop to be energized, as shown by step E in  FIG. 9 , i.e., in the detection completion step. The pressure of the connection passage  43  recovers to the atmospheric pressure PA. The pressure sensor  13  detects the atmospheric pressure PA and outputs the pressure signal to the ECU  4 . Then, the ECU  4  controls the pressure sensor  13  to stop its operation. Then, the evaporation emission leak detection is completed. 
   In this embodiment, even when the mixed gas rising from the fuel tank  2  penetrates into the pump and the brushless motor  12 , the brushless motor  12  is not abraded. Therefore, the life time of the brushless motor  12  will be lengthened. Moreover, the accuracy of the evaporative emission leak detection by the pressure sensor  13  is improved because of the stable operation of the pump  11 . Further, the detection accuracy of the leakage can be improved because of direct detection of the pressure of the fuel vapor. 
   Although the evaporative emission leak detection system  1  has the pressure sensor  13 , the pressure sensor  13  can be eliminated. In this case, the ECU  4  gets the information about the operation characteristics of the brushless motor  12  from the controller  5 , so that the inner pressure of the fuel tank  2  as well as the size of the leakage opnening can be calculated. Thus, the pressure of the connection passage  43  can be obtained indirectly by measuring the operation characteristics of the brushless motor  12  without the pressure sensor. Here, because the detection system  1  has no pressure sensor, the atmospheric pressure PA is obtained by another pressure sensor mounted on other equipment of the vehicle such as fuel injection equipment and air intake equipment. 
   (Modifications) 
   Although the evaporative emission leak detection system  1  has the orifice  46  for throttling the air flow, the orifice  46  can be eliminated. In this case, the absolute change of the pressure of the connection passage  43  or the absolute change of the operation characteristics of the brushless motor  12  is detected by the detection system  1  so that the evaporative emission leakage can be detected. 
   Although the brushless motor  12  is operated with constant voltage control, the brushless motor  12  can be operated with constant rotation speed control. In this case, the pressure difference between the inside and outside of the fuel tank  2  can be controlled at a predetermined difference that can be detected by the detection system  1 . Moreover, the operation characteristics of the brushless motor  12  can be detected by measuring the rotation speed of the brushless motor  12 . Besides, the brushless motor  12  can be operated with constant current control. 
   Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.