Patent Publication Number: US-6990962-B2

Title: Evaporative fuel control system for internal combustion engine

Description:
This application is 1 of 3 related, concurrently filed applications, all entitled “Evaporative Fuel Control System for Internal Combustion Engine”, all having the same inventorship, and having application Ser. Nos. 11/134,524, 11/134,525, and 11/134,523, respectively. The disclosure of the related co-pending applications are herein incorporated by reference. 
   FIELD OF THE INVENTION 
   This invention relates to an evaporative fuel control system for an internal combustion engine, and more particularly to an evaporative fuel control system which examines leakage without reduction in a speed of an assembly line for checking the completed cars in factories. 
   BACKGROUND OF THE INVENTION 
   Traditional designs of internal combustion engines employ evaporative fuel control systems to control unwanted air pollution and loss of fuel due to evaporation of fuel from the tank, the carburetor, and other engine components. In particular, there is an evaporative fuel control system which employs a fuel vapor collection canister containing an adsorbent material, such as activated carbon, for adsorbing evaporative fuel, and a purge system for releasing the adsorbed fuel and supplying it to the engine during operation of the engine. 
   Conventional evaporative fuel control systems typically also include a leak check system employing different leak check methods to check for leakage of evaporative fuel (leak of vapor) to the atmosphere. 
   Conventional evaporative fuel control systems for an engine also exist wherein the systemchecks for evaporative fuel leaks after stop of the engine and refuel to a fuel tank. See JP No. 3412678. 
   Conventional evaporative fuel control systems for an engine also exist that provide a test mode which opens a purge passage between the fuel tank and an intake passage, and shuts an atmosphere open section, when the engine is in an idling state and a test signal is sent from a testing device to a control section. In this test mode, whether there is a failure in the evaporative fuel control system or not is determined based on a pressure variation of a purge passage toward the fuel tank over a predetermined time. See JP Laid-Open No. H10-89162. 
   One leak check method for an evaporative fuel control system for an engine utilizes an electric pressure reducing pump, a reference orifice, a pressure sensor, and a switching valve. In this leak check method, a reference pressure is primarily measured after the atmosphere is vacuumed by the pressure reducing pump through the reference orifice. A pressure is then measured after a certain time after the switching valve is switched such that the fuel tank is vacuumed. By comparing this pressure with the reference pressure, the occurrence of leakage (large leak greater than the reference orifice) is determined. 
   This leak check of the evaporative fuel control system is executed during normal operation of the vehicle (in fact during stop of the engine while stopping of the vehicle). It takes some time to conduct a leak check, since the pressure is measured while reducing the check passages of the system by the pressure reducing pump. 
   However, this increases the amount of time required to conduct a leak check in a checking process for completed cars in the factories, which may exceed an acceptable amount of process time required in assembly lines. 
   SUMMARY OF THE INVENTION 
   In order to obviate or at least minimize the above-described inconveniences, the present invention provides an evaporative fuel control system for an internal combustion engine. In this system, a canister is disposed on an evaporative fuel control passage connecting between an intake passage for the engine and a fuel tank to absorb the evaporative fuel generated in the fuel tank. Also, an atmosphere open passage connects the canister with the atmosphere. A purge valve is disposed between the intake passage and the canister. A purge controller controls the purge valve so that the evaporative fuel absorbed by the canister is purged and supplied to the intake passage. A leak check system examines leakage in the evaporative fuel control system by causing negative pressure in the evaporative fuel control system during stop of the engine. Such leak check system includes a factory test mode which is provided with a leak check time that is set shorter than the time required for a normal leak check when the evaporative fuel control system receives a factory test signal. 
   According to the present invention, the evaporative fuel control system is provided with the leak check system which examines leakage in the evaporative fuel control system by causing negative pressure in the evaporative fuel control system during stop of the engine. This leak check system includes the factory test mode which is provided with a leak check time that is less than the leak check time for a normal leak check when the evaporative fuel control system receives the factory test signal. Accordingly, in checking the completed cars in the factory, evaporative fuel leakage is tested without reduction in assembly line speed, and thus does not create a problem of exceeding the process time allowed for the assembly line. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a flow chart depicting the steps of a leak check for an evaporative fuel control system in a factory test mode according to an embodiment of the present invention. 
       FIG. 2  is a time chart for a leak-check conducted in the factory test mode. 
       FIG. 3  is a flow chart depicting the steps of a leak-check in a normal condition of the evaporative fuel control system. 
       FIG. 4  is a time chart for a leak-check conducted in a normal condition of the evaporative fuel control system. 
       FIG. 5  is a diagram of evaporative fuel control system. 
       FIG. 6  depicts an operation of elements for measuring reference pressure in the leak check system. 
       FIG. 7  depicts an operation of elements during vacuuming of the leak check system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The evaporative fuel control system of the present invention includes the factory test mode which is provided with a leak check time that is set less than the leak check time for a normal leak check when the evaporative fuel control system receives the factory test signal. Accordingly, in checking the completed cars in the factory, leakage is tested without reduction in assembly line speed, and without creating a problem of exceeding the process time allowed for the assembly line. 
   Embodiments of the present invention will now be described in detail with reference to the drawings.  FIGS. 1–7  illustrate an embodiment of the present invention.  FIG. 7  shows an internal combustion engine  2  mounted on a vehicle (not shown), an intake pipe  4  of the engine  2 , an intake passage  6  defined by the intake pipe  4 , a throttle valve  8  disposed in the intake passage  6 , a fuel tank  10  to store fuel, and an evaporative fuel control system (evaporative system)  12 . 
   In the evaporative fuel control system  12 , an evaporative fuel control passage  14  connects an upper part of the fuel tank  10  with the intake passage  6  on a downstream side of the throttle valve  8 . On the evaporative fuel control passage  14 , a canister  16  is disposed to absorb the evaporative fuel generated in the fuel tank  10 . The evaporative fuel control passage  14  is formed by an evaporative passage  18  connecting the fuel tank  10  with the canister  16 , and a purge passage  20  connecting the canister  16  with the intake passage  6 . 
   In a boxy tank body  22 , the fuel tank  10  includes a fuel level sensor  24  to detect the quantity of fuel in the fuel tank  10 . This fuel level sensor  24  outputs electric signals based on the height of a float F which moves upwardly or downwardly in accordance with the fuel quantity. 
   The canister  16  contains an activated carbon  28  in a boxy canister body  26  to absorb the evaporative fuel, and connects, at a top section thereof, the evaporative passage  18  with the purge passage  20 . The evaporative passage  18  is directly connected to the activated carbon  28 , and the purge passage  20  is connected to an upper space  30  defined in the canister body  26 . 
   On the purge passage  20 , a purge valve  32  is disposed to control the quantity of the evaporative fuel (purge quantity) that is purged by the canister  16  and supplied to the intake passage  6 . Duty ratio of this purge valve  32  is controlled to be between 0–100%. That is, the purge valve  32  is closed at duty ratio 0% to fully shut the purge passage  20 , and is opened at duty ratio 100% to fully open the purge passage  20 . Opening degree of the purge passage  20  can be changed between duty ratio 0–100% for a purge control of the evaporative fuel absorbed in the canister  16  to supply to the intake passage  6 . 
   On a lower part of the canister  16 , an atmosphere open passage  34  is connected at a base end thereof to open the canister  16  to the atmosphere. On this atmosphere open passage  34 , a switching valve  42  as an atmosphere open/close valve (canister air valve) is disposed to connect/disconnect the air. The atmosphere open passage  34  has at one end thereof an air filter  36  to remove dust introduced from outside. 
   A purge controller  38  of the evaporative fuel control system  12  is connected to the fuel level sensor  24 , the purge valve  32 , and the switching valve  42 . The purge controller  38  controls the purge valve  32  and the switching valve  42  such that the evaporative fuel, absorbed in the canister  16 , is purged by the atmosphere through the atmosphere open passage  34  and is supplied to the intake passage  6  during normal operation of the engine  2 . 
   The evaporative fuel control system  12  includes a leak check system  40  which examines leakage in the evaporative fuel control system  12  by generating a negative pressure (pressure less than that of the ambient atmosphere) in the evaporative fuel control system  12  during stop of the engine  2 . 
   On the atmosphere open passage  34  in communication with the canister  16 , the leak check system  40  includes a switching valve  42  which can communicate/disconnect the atmosphere. The atmosphere open passage  34  is formed by a first open passage  34 - 1  toward the canister with respect to the switching valve  42 , and a second open passage  34 - 2  toward the air filter  36  with respect to the switching valve  42 . On this second open passage  34 - 2 , a pressure reducing pump  44  acting as a pressure reducing means is disposed to vacuum or generate a negative pressure in the evaporative fuel control system  12 . 
   While bypassing the switching valve  42 , the atmosphere open passage  34  includes a first bypass passage  46  of which one end is connected to the first open passage  34 - 1  toward the canister  16  with respect to the switching valve  42 , and the other end is connected to the second open passage  34 - 2  between the switching valve  42  and the pressure reducing pump  44 . On the first bypass passage  46 , a pressure sensor  48  is disposed toward the second open passage  34 - 2  as a pressure detector to detect the pressure in the evaporative fuel control system  12 . A reference orifice  50  is also disposed toward the first open passage  34 - 1  as a reference pressure regulator to adjust the pressure applied to the pressure sensor  48  to the reference pressure. 
   In addition, the atmosphere open passage  34  includes a second bypass passage  52  of which one end is connected to the second open passage  34 - 2  between the pressure reducing pump  44  and the air filter  36  and other end is connected to the switching valve  42 , while bypassing the pressure reducing pump  44 . 
   The switching valve  42  has a solenoid  54  and a valve element  56  that is operated by energizing of the solenoid  54 . The valve element  56  includes a straight port  58  and a diagonal port  60 . As shown in  FIG. 5 , when the solenoid  54  is not energized (deactivated), the switching valve  42  shuts the atmosphere open passage  34  and the diagonal port  60  is positioned to communicate the first open passage  34 - 1  with the second bypass passage  52 . Also as shown in  FIG. 6 , the switching valve  42  communicates the atmosphere open passage  34  when the solenoid  54  is energized (activated) and the straight port  58  is positioned to communicate the first and second main passages  34 - 1 ,  34 - 2 . 
   The purge controller  38  of the evaporative fuel control system  12  is connected to the pressure reducing pump  44 , the pressure sensor  48 , and the solenoid  54  of the switching valve  42 . Also, the purge controller  38  includes a leak determination means  62  to determine whether there is a leakage in the evaporative fuel control system  12 . 
   Thus, the leak check system  40  includes, on the atmosphere open passage  34 , the switching valve  42  to communicate/disconnect to the atmosphere, the pressure reducing pump  44  to vacuum or generate a negative pressure inside of the evaporative fuel control system  12 , the pressure sensor  48  as a pressure detecting means to detect the pressure within the evaporative fuel control system  12 , the reference orifice  50  as a reference pressure regulator to adjust the pressure applied to the pressure sensor  48  to the reference pressure, and the leak determination means  62  to determine whether there is leakage in the evaporative fuel control system  12  by using the reference pressure adjusted by the reference orifice  50  and a reduced pressure in which the switching valve  42  is switched to an atmosphere shut side and the pressure reducing pump  44  vacuums the evaporative fuel control system  12  during stop of the engine  2 . 
   The evaporative fuel control system  12  includes a system-side connector  64  through which the factory test signal is input to the purge controller  38 . Device-side connector  68  of a testing device  66  is detachably fitted to the system-side connector  64 . This testing device  66  outputs the factory test signal to the purge controller  38  when the system-side connector  64  is engaged with the device-side connector  68  in testing of the completed cars in the factories. 
   The leak check system  40  is provided with a factory test mode in which a leak check time is set to be less than the leak check time for the normal operation of the engine  2  when the evaporative fuel control system  12  receives the factory test signal. The leak check in the factory test mode is performed independently from the operation of the engine  2 . 
   Operation of one embodiment of the present invention is explained as follows. 
   Referring to  FIG. 3 , a program for the leak check of the evaporative fuel control system  12  starts in step  102  during a normal operation of the engine  2  (in fact, during stop of the engine  2  while the vehicle stops). A determination is made in step  104  whether a start condition is satisfied. 
   If the determination in step  104  is “NO”, the program ends in step  106 . If the determination in step  104  is “YES”, the leak check system  40  is actuated after a certain amount of time has elapsed in step  108 . Then a determination is made in step  110  whether a leak check condition is satisfied. At this time, in the leak check system  40 , the switching valve  42  is deactivated (opened), and the pressure reducing pump  44  is deactivated. 
   If the determination in step  110  is “NO”, then program ends in step  112 . If the determination in step  110  is “YES”, then initial pressure P 1  in the evaporative fuel control system  12  is measured in step  114 . The pressure reducing pump  44  is actuated in step  116 . Then a pressure P 2  in the evaporative fuel control system  12  is measured in step  118  after a first predetermined amount of time T 1  has elapsed since the activation of the pressure reducing pump  44 . In step  120 , a reference pressure variation P 1  is calculated (P 1 =P 1 −P 2 ). 
   As shown in  FIG. 5 , the atmosphere open passage  34  is suitable to measure the reference pressure when the switching valve  42  is deactivated (open) and the pressure reducing pump  44  is activated. The switching valve  42  shuts the atmosphere open passage  34  and the diagonal port  60  of the switching valve  42  places the first and second bypass passages  46  and  52 , respectively, in communication with one another. 
   In step  122 , a determination is made whether the reference pressure variation P 1  calculated in step  120  is below DP 11  (first reference pressure determination value). If the determination in step  122  is “YES”, it is determined that the reference pressure variation P 1  is extremely low in step  124 , followed by deactivation of the pressure pump  44  in step  126 . Then the program ends in step  128 . 
   If the determination in step  122  is “NO”, then another determination is made in step  130  whether the reference pressure variation P 1  exceeds DP 12  (second reference pressure determination value). If this determination in step  130  is “YES”, it is determined that the reference pressure variation P 1  is extremely high in step  132 , then the program goes to step  126 . 
   If this determination in step  130  is “NO”, the switching valve  42  is actuated (closed) in step  134 . In step  136 , maximum pressure P 3  in the evaporative fuel control system  12  is measured over a second predetermined amount of time T 2  after the activation of the switching valve  42 . Then pressure variation P 2  at switching of the switching valve is calculated in step  138  (P 2 =P 3 −P 2 ). In step  140 , a determination is made whether the reference pressure variation P 1  is below DP 13  (third reference pressure determination value). 
   As shown in  FIG. 6 , when the pressure reducing pump  44  is deactivated and the switching valve  42  is actuated (closed), the atmosphere open passage  34  is opened and is under decreased pressure while the straight port  58  of the switching valve  42  places the first and second open passages  34 - 1  and  34 - 2 , respectively, in communication with one another. 
   If the determination in step  140  is “YES”, another determination is made in step  142  whether the valve switching pressure variation P 2  is below DP 21  (determination pressure value at switching of valve). 
   If the determination in step  142  is “NO”, then it is determined in step  144  that the pressure reducing pump  44  is in failure at a low flow rate. The pressure reducing pump  44  is deactivated and the switching valve  42  is deactivated (opened) in step  146 , and the program ends in step  148 . 
   If the determination in step  140  is “NO” or the determination in step  142  is “YES”, then a reducing pressure P 4  in the evaporative fuel control system  12  is updated in step  150 . Then a leak determination pressure variation P 3  is calculated in step  152  (P 3 =P 4 −P 2 ). In step  154 , a determination is made whether the valve switching pressure variation P 2  is below DP 21  (determination pressure value at switching of valve). 
   If the determination in step  154  is “YES”, then another determination is made in step  156  whether a fourth predetermined time T 4  has elapsed from activation (close) of the switching valve  42 . If the determination in step  156  is “NO”, the program returns to step  150  to update the reducing pressure P 4  in the evaporative fuel control system  12 . 
   If the determination in step  156  is “YES”, then a further determination is made in step  158  whether leak determination pressure variation P 3  is below DP 31  (pressure determination value). 
   If the determination in step  158  is “YES”, then it is determined in step  160  that the switching valve  42  is in failure, remaining opened. The pressure reducing pump  44  is deactivated and the switching valve  42  is deactivated (opened) in step  162 , and the program ends in step  164 . If the determination in step  158  is “NO”, then it is determined in step  166  that the switching valve  42  is in failure, remaining closed. The pressure reducing pump  44  is deactivated and the switching valve  42  is deactivated (opened) in step  162 , and the program ends in step  164 . 
   If the determination in step  154  is “NO”, then another determination is made in step  168  whether a third predetermined time T 3  has elapsed from activation (close) of the switching valve  42 . If the determination in step  168  is “YES”, then it is determined in step  170  that the evaporative fuel control system  12  is in failure for leak, and the program goes to step  162 . If the determination in step  168  is “NO”, then a further determination is made in step  172  whether the leak determination pressure variation P 3  is below LEAK (leak determination value). 
   If the determination in step  172  is “NO”, the program returns to step  150  to update the reducing pressure P 4  in the evaporative fuel control system  12 . If the determination in step  172  is “YES”, it is determined in step  174  that the evaporative fuel control system  12  is in a normal condition. The pressure reducing pump  44  is deactivated and the switching valve  42  is deactivated (opened) in step  162 , and the program ends in step  164 . 
   Leak check during normal operation of the engine  2  is next explained with reference to a time chart of  FIG. 4 . 
   As shown in  FIG. 4 , the leak check starts at time t 1 . After the pressure reducing pump  44  is switched from a deactivate state to an actuation state at time t 2 , the pressure in the evaporative fuel control system  12  drops toward the negative pressure side (−) from pressure P 1  (substantially zero) until the pressure in the evaporative fuel control system  12  reaches the reference pressure or pressure P 2 . 
   After the first predetermined time T 1  has elapsed from the activation of the pressure reducing pump  44  (from time t 2 ), the switching valve  42  is switched for actuation (close) at time t 3 . Over the first predetermined time T 1  between time t 2  and time t 3 , the reference pressure in the evaporative fuel control system  12  has been measured. 
   After time t 3  at which the switching valve  42  is activated (closed), the negative pressure in the evaporative fuel control system  12  rapidly increases toward a positive pressure (+) reaching the pressure P 3  (substantially zero). The pressure P 3  is a maximum pressure over a second predetermined time T 2  after the activation (close) of the switching valve  42 . 
   While the switching valve  42  is activated (closed) at time t 3  and remains actuated (closed), the pressure in the evaporative fuel control system  12  begins to drop toward a negative pressure (+). 
   If the evaporative fuel control system  12  is in a normal condition (without leak, shown by a solid line), the pressure in the evaporative fuel control system  12  suddenly begins to drop toward a negative pressure (−). At time t 4 , the pressure reducing pump  44  is deactivated when the pressure in the evaporative fuel control system  12  reaches the determination reference pressure, or pressure P 4 . The third predetermined time T 3  between time t 3  and time t 4  is a pressure reducing time for the evaporative fuel control system in the normal condition. 
   After time T 3  has elapsed and after time t 5  at which the switching valve  32  is deactivated, the pressure in the evaporative fuel control system  12  increases toward a positive pressure (+). Then the leak check is stopped at time t 6  and the pressure in the evaporative fuel control system  12  is maintained at zero. 
   In contrast, in the event the evaporative fuel control system is failing (leaking) while actuation of the switching valve  42  is maintained after time t 3 , the pressure in the evaporative fuel control system  12  remains closer to zero as compared to that of normal condition, which is associated with a relatively lower negative pressure as shown by a dashed-line. Even at time t 4  at which the third predetermined time T 3  has elapsed, the pressure in the evaporative fuel control system  12  does not reach the determination reference pressure. 
   As a result, in the event the evaporative fuel control system is failing (leaking), the pressure reducing pump  44  is deactivated at time t 7  with long delay as compared to the normal condition. The third predetermined time T 3  is extended as shown in dashed lines. After time t 8  when the switching valve  32  is deactivated (closed), the pressure in the evaporative fuel control system  12  increases toward a positive pressure (+). Then the leak check is stopped at time t 9  and the pressure in the evaporative fuel control system  12  is maintained at zero. 
   As thus described, the leak check system  40  includes, on the atmosphere open passage  34 , the switching valve  42  to communicate/disconnect to the atmosphere, the pressure reducing pump  44  to vacuum or generate negative pressure inside of the evaporative fuel control system  12 , the pressure sensor  48  as a pressure detecting means to detect the pressure within the evaporative fuel control system  12 , the reference orifice  50  as a reference pressure regulator to adjust the pressure applied to the pressure sensor  48  to the reference pressure, and the leak determination means  62  to determine whether there is a leakage in the evaporative fuel control system  12  by using the reference pressure adjusted by the reference orifice  50  and a reduced pressure in which the switching valve  42  is switched to an atmosphere shut side and the pressure reducing pump  44  vacuums the evaporative fuel control system  12  during stop of the engine  2 . 
   The evaporative fuel control system  12  executes the leak check after reducing the pressure in the check passage in the evaporative fuel control system  12  by the pressure reducing pump  44 , thereby providing a leak check result with high accuracy. 
   Next, the leak check for the factory test mode is explained with reference to a flowchart of  FIG. 1 . 
   The factory test mode is configured to have predetermined times for test modes T 1 S, T 2 S, T 3 S, T 4 S which are shorter in duration than predetermined times for normal modes T 1 , T 2 , T 3 , T 4 , respectively (T 1 S&lt;T 1 , T 2 S&lt;T 2 , T 3 S&lt;T 3 , T 4 S&lt;T 4 ). In this factory test mode, the determination reference pressure is changed with respect to that for normal mode. Also, the leak check for the factory test mode is performed during running of the vehicle or purging, as shown in  FIG. 2 . 
   For the factory test mode, a program for the leak check of the evaporative fuel control system  12  starts in step  202  during the process of checking the completed cars in the factories. A determination is made in step  204  whether a factory test mode condition is satisfied. This factory test mode condition is satisfied if the purge controller  38  receives the factory test mode signal which is output when the system-side connector  64  is engaged with the device-side connector  68 , as shown in  FIG. 7 . At this time, in the leak check system  40 , the switching valve  42  is deactivated (opened), and the pressure reducing pump  44  is deactivated. 
   If the determination in step  204  is “NO”, then the program ends in step  206 . If the determination in step  204  is “YES”, then initial pressure P 1  in the evaporative fuel control system  12  is measured in step  208 . The pressure reducing pump  44  is actuated in step  210 . Then a pressure P 2  in the evaporative fuel control system  12  is measured in step  212  after a first predetermined time TIS has elapsed since activation of the pressure reducing pump  44 . In step  214 , a reference pressure variation P 1  is calculated (P 1 =P 1 −P 2 ). 
   As shown in  FIG. 5 , the atmosphere open passage  34  is suitable for measuring the reference pressure when the switching valve  42  is deactivated (open) and the pressure reducing pump  44  is activated. The switching valve  42  shuts the atmosphere open passage  34  and the diagonal port  60  of the switching valve  42  communicates the first bypass passage  46  with the second bypass passages  52 . 
   In step  216 , a determination is made as to whether the reference pressure variation P 1  calculated in step  214  is below DP 11  (first reference pressure determination value). If the determination in step  216  is “YES”, it is determined that the reference pressure variation P 1  is extremely low in step  218 , followed by deactivation of the pressure pump  44  in step  220 . Then the program ends in step  222 . 
   If the determination in step  216  is “NO”, then another determination is made in step  224  whether the reference pressure variation P 1  exceeds DP 12  (second reference pressure determination value). If this determination in step  224  is “YES”, it is determined that the reference pressure variation P 1  is extremely high in step  226 , then the program goes to step  220 . 
   If this determination in step  224  is “NO”, the switching valve  42  is actuated (closed) in step  228 . In step  230 , a maximum pressure P 3  in the evaporative fuel control system  12  is measured over a second predetermined time T 2 S after the activation of the switching valve  42 . Then pressure variation P 2  at switching of the switching valve is calculated in step  232  (P 2 =P 3 −P 2 ). In step  234 , a determination is made whether the reference pressure variation P 1  is below DP 13  (third reference pressure determination value). 
   As shown in  FIG. 6 , when the pressure reducing pump  44  is deactivated and the switching valve  42  is actuated (closed), the atmosphere open passage  34  is opened and is under decreased pressure while the straight port  58  of the switching valve  42  communicates the first open passage  34 - 1  with the second open passage  34 - 2 . 
   If the determination in step  234  is “YES”, another determination is made in step  236  whether the valve switching pressure variation P 2  is below DP 21  (determination pressure value at switching of valve). 
   If the determination in step  236  is “NO”, then it is determined in step  238  that the pressure reducing pump  44  is failing at a low flow rate. The pressure reducing pump  44  is deactivated and the switching valve  42  is deactivated (opened) in step  240 , and the program ends in step  242 . 
   If the determination in step  234  is “NO” or the determination in step  236  is “YES”, a reducing pressure P 4  in the evaporative fuel control system  12  is updated in step  244 . Then a leak determination pressure variation P 3  is measured in step  246  (P 3 =P 4 −P 2 ). Also, a leak determination pressure variation P 4  is measured in step  248  (P 4 =P 1 −P 4 ). In step  250 , a determination is made whether the valve switching pressure variation P 2  is below DP 21  (switching valve pressure determination value). 
   If the determination in step  250  is “YES”, then another determination is made in step  252  whether a fourth predetermined time T 4 S has elapsed from activation (close) of the switching valve  42 . If the determination in step  252  is “NO”, the program returns to step  244  to update the reducing pressure P 4  in the evaporative fuel control system  12 . 
   If the determination in step  252  is “YES”, then a further determination is made in step  254  as to whether leak determination pressure variation P 3  is below DP 31  (pressure determination value). 
   If the determination in step  254  is “YES”, then it is determined in step  256  that the switching valve  42  has failed, remaining opened. The pressure reducing pump  44  is deactivated and the switching valve  42  is deactivated (opened) in step  258 , and the program ends in step  260 . If the determination in step  254  is “NO”, then it is determined in step  262  that the switching valve  42  has failed, remaining closed. Then the program goes to process in step  258 . 
   If the determination in step  250  is “NO”, then another determination is made in step  264  whether a third predetermined time T 3 S has elapsed from activation (closing) of the switching valve  42 . If the determination in step  264  is “YES”, then a further determination is made in step  266  whether the leak determination pressure variation P 4  is below LEAK 2 S (second leak determination value). 
   If the determination in step  266  is “YES”, then it is determined in step  268  that the evaporative fuel control system  12  is in failure for leak, and the program goes to step  258 . If the determination in step  266  is “NO”, it is determined in step  270  that the evaporative fuel control system  12  is in a normal condition, and the program goes to step  258 . 
   If the determination in step  264  is “NO”, then a further determination is made in step  272  whether the leak determination pressure variation P 3  is below LEAK (leak determination value). If the determination in step  272  is “NO”, the program returns to step  244  to update the reducing pressure P 4  in the evaporative fuel control system  12 . If the determination in step  272  is “YES”, it is determined in step  270  that the evaporative fuel control system  12  is in a normal condition. The pressure reducing pump  44  is deactivated and the switching valve  42  is deactivated (opened) in step  258 , and the program ends in step  260 . 
   Next, the leak check for the factory test mode is explained with reference to a time chart of  FIG. 2 . 
   As shown in  FIG. 2 , the vehicle speed and the purge duty ratio increase from zero, and the factory test mode condition is satisfied at time t 1 . At time t 2  when the pressure reducing pump  44  is actuated, the pressure in the evaporative fuel control system  12  decreases toward a the negative pressure (−) from pressure P 1  (substantially zero) until the pressure in the evaporative fuel control system  12  reaches pressure P 2  beyond the reference pressure. 
   After the first predetermined time T 1 S has elapsed from the activation of the pressure reducing pump  44  (from time t 2 ), the switching valve  42  is actuated (closed) at time t 3 . Over the first predetermined time T 1 S between time t 2  and time t 3 , the reference pressure in the evaporative fuel control system  12  has been measured. 
   After time t 3  at which the switching valve  42  is activated (closed), the (negative) pressure in the evaporative fuel control system  12  rapidly increases toward a more positive pressure, reaching the pressure P 3  (substantially zero). The pressure P 3  is a maximum pressure over a second predetermined time T 2 S after the activation (close) of the switching valve  42 . 
   While the switching valve  42  is activated (closed) at time t 3  and remains actuated (closed), the pressure in the evaporative fuel control system  12  begins to decrease, or move toward a more negative pressure, from the pressure P 3 . 
   If the evaporative fuel control system  12  is in a normal condition (without a leak, shown by a solid line), the pressure in the evaporative fuel control system  12  suddenly decreases or drops toward a more negative pressure. At time t 4 , the pressure reducing pump  44  is deactivated when the pressure in the evaporative fuel control system  12  reaches the pressure P 4  beyond the determination reference pressure. The third predetermined time T 3 S between time t 3  and time t 4  is a pressure reducing time for the evaporative fuel control system in the normal condition. 
   After the third predetermined time T 3 S has elapsed and after time t 4  at which the pressure reducing pump  44  is deactivated, switching valve  32  is deactivated (opened) simultaneously. Consequently, the pressure in the evaporative fuel control system  12  rapidly builds up toward a positive pressure, and is maintained at zero. At time t 6 , the leak check ends. 
   In the event the evaporative fuel control system  12  is in failure for leakage while the switching valve  42  is actuated (closed) at time t 3 , the pressure in the evaporative fuel control system  12  remains closer to zero, as shown by the dashed line, compared to that in a normal condition. Even at time t 4  when the third predetermined time T 3 S has elapsed, the pressure in the evaporative fuel control system  12  does not reach the determination reference pressure. 
   Accordingly, in the event the evaporative fuel control system  12  is in failure for leakage, the pressure reducing pump  44  is deactivated at time t 5  with a delay as compared to the normal condition, which results in extension of the third predetermined time (T 3 S) as shown by the dashed-line. At time t 5  when the switching valve  32  is deactivated (closed), the pressure in the evaporative fuel control system  12  is maintained at zero and thus is now closer to being a positive pressure (+) is maintained at zero. At time t 6 , the leak check ends. 
   The evaporative fuel control system  12  reduces the amount of time required to check the completed cars in the factories, while maintaining the precision required in the assembly process as well as reducing costs. The testing device  66  and the purge controller  38 , which are placed at a side of the factory lines, are connected through communication cables, so that the testing device  66  issues an order to change to the factory test mode for the leak check of the completed cars by the leak detecting means  62  of the leak check system  40 . 
   The factory test mode includes additional or changed control with respect to the normal mode as described below. (1) The leak check starts even during running of the vehicle on the check lines, and is not interrupted or stopped by a vehicle speed condition. (2) In order to minimize the vacuum time to check the leak in the evaporative fuel control system  12 , the pressure reducing pump  44  and purge from the canister  16  to the intake passage  6  is utilized. (3) Time for each section is reduced as much as possible. (4) For determination of failure, the determination reference pressure is changed from that used in the normal mode, with a comparison being made not to the determination reference pressure but to the atmospheric pressure. 
   As shown in  FIG. 7 , the leak check system  40  of the evaporative fuel control system  12  has the switching valve  42 , the pressure reducing pump  44 , the pressure sensor  48 , and the reference orifice  50  integrated thereinto as an integral leak check module, although it is possible that these elements are not integrated. The modularized leak check system  40  is positioned toward an air-side with respect to the canister  16 . 
   If the leak check starts when the leak check condition is satisfied during operation of the vehicle (in fact during stop of the engine while the vehicle is stopped), the pressure pump  44  is actuated while the switching valve  42  is opened and the reference pressure P 2  is measured after a certain time has elapsed. Then while the pressure pump  44  remains actuated, the switching valve  42  is switched to an opened state from a closed state, and the entire evaporative fuel control system  12  is vacuumed or subject to a negative pressure. If the reducing pressure is below P 2 , then leakage below the reference is determined, and if the reducing pressure is not below P 2  after a certain time, then the leakage over the reference is determined. The pressure reducing pump  44  is deactivated and the switching valve  42  is deactivated to finish the leak check. 
   In contrast to this normal operation, the factory test mode for the completed cars includes the shortened predetermined times T 1 S, T 2 S, T 3 S, T 4 S, and includes the changed reference pressure for determination of failure. The leak check is performed even during running of the vehicle, and the purge from the canister  16  is utilized to reduce pressure. 
   As thus described, the leak check system  40  includes the factory test mode which is provided with the leak check time set to a lower amount than that for ordinary operation of the engine  2  when the evaporative fuel control system  12  receives the factory test signal. 
   Accordingly, in checking the completed cars in the factory, the leakage is tested without reduction in assembly line speed. This in turn reduces the chance that the process time may exceed the allowed time for the assembly line. 
   In addition, the leak check in the factory test mode is performed independently from the operation of the engine  2 , which is an easier condition in which to perform the leak check for the completed cars. This subsequently maximizes the chance that the leak check is conducted and quickly finished. 
   The evaporative fuel control system of the present invention includes the factory test mode which is provided with a decreased leak check time than that of a normal leak check when the evaporative fuel control system receives the factory test signal. Accordingly, in checking the completed cars in the factory, the leakage is tested without reduction in assembly line speed, or increase in processing time beyond that allowed for the assembly line.