Patent Publication Number: US-6983739-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 Ser. Nos. 11/134,524, 11/134,525 and 11/134,523, respectively. The disclosures 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 the evaporative fuel control system which determines failure of a switching valve based on pressure variation used for leakage diagnosis control (leak check), thereby eliminating the need for any additional system or parts for failure determination. 
     BACKGROUND OF THE INVENTION 
     Traditional designs of internal combustion engines permit for unwanted air pollution and loss of fuel due to evaporation of fuel, containing hydrocarbon (HC), from the tank, the carburetor, and other engine component. There are known prior art to obviate these problems. 
     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. See JP Laid-Open No. 2004-11561 and JP Laid-Open No. 2004-28060. 
     As shown in  FIG. 3 , the evaporative fuel control system  202  is associated with a conventional internal combustion engine. 
     This evaporative fuel control system  202  includes a canister  212 , an atmosphere open passage  214 , and a purge valve  216 . The canister  212  is disposed on an evaporative fuel control passage  210  connecting a fuel tank  208  with an intake passage  206  in an intake pipe  204  of the engine (not shown) mounted on a vehicle (not shown). The atmosphere open passage  214  connects the canister  212  with the atmospheric air. The purge valve  216  is disposed between the intake passage  206  and the canister  212 . 
     As shown in  FIG. 3 , the evaporative fuel control passage  210  connects the fuel tank  208  with the intake passage  206  on the downstream side of a throttle valve  218 . A controller  224  is connected to the purge valve  216 , a fuel level gauge  220  within the fuel tank  208 , and a leak check module  222  associated with the atmosphere open passage  214 . 
     As also shown in  FIG. 3 , the leak check module  222  is located on the atmosphere open passage  214  between the canister  212  and an air filter  226 . This leak check module  222  includes first, second and third atmosphere open passages  214 - 1 ,  214 - 2 , and  214 - 3 . More particularly, the first atmosphere open passage  214 - 1  connects the canister  212  and the air filter  226  through a solenoid switching valve  228 . The second atmosphere open passage  214 - 2  connects the canister  212  and the air filter  226  through the solenoid switching valve  228  and a pressure reducing pump  230 . The third atmosphere open passage  214 - 3  connects the canister  212  and the air filter  226  through a reference orifice  232  and the pressure reducing pump  230 . A pressure sensor  234  is disposed between the reference orifice  232  of the third atmosphere open passage  214 - 3  and the pressure reducing pump  230 . 
     Further, the evaporative fuel control system  202  permits the canister  212  to absorb the evaporative fuel generated in the fuel tank  208 , and supplies the evaporative fuel absorbed in the canister  212  to the intake passage  206  through the purge valve  216  for a purge control. 
     One method to examine leakage in the evaporative fuel control system  202  employs the pressure reducing pump  230  or the electric pump, the solenoid switching valve  228 , and the reference orifice  232 . 
     In this method, as shown in  FIGS. 4 and 5 , after activation of a leakage diagnosis system, the pressure reducing pump  230  or the electric pump is activated to vacuum or generate a negative pressure (pressure less than an ambient atmosphere), thereby causing the atmosphere through the reference orifice  232 , and a reference pressure is measured. 
     Then as shown in  FIGS. 4 and 6 , the switching valve  228  is activated to vacuum the fuel tank, and a pressure is measured after elapse of predetermined time D. Thereby, it is determined whether there is leakage (large leakage which is greater than the reference pressure generated by the flow of atmosphere through the orifice) by comparing the pressure measured after predetermined time D with the reference pressure. 
     However, there is a possibility that the above-mentioned leakage diagnosis method determines that the evaporative system is in a normal condition without leakage, even if one of the components, the switching valve, is in failure. 
     There is a method to diagnosis the closed switching valve (JP Laid-Open No. 2003-13810). This method cannot, however, diagnosis the failure of the opened switching valve. 
     Incidentally,  FIG. 3  shows an example of the existing leakage diagnosis system. Shown is the illustrated leakage check module  222  integrating thereinto the pressure reducing pump  230 , the orifice  232 , and the pressure sensor  234 , although these components may not be integrated. Also, the leak check module  222  is attached to an atmosphere side of the canister  212 . During the reduction of pressure in the evaporative system for the leakage diagnosis, the switching valve  228  is activated (placed in a shutoff state). Otherwise, the switching valve is deactivated (placed in an open state), thereby connecting the evaporative system  202  to the atmospheric air. 
     Referring to  FIG. 4  which illustrates control by the existing system, after the leak diagnosis begins when a certain diagnosis condition is satisfied, and after the pressure reducing pump is actuated, the switching valve  228  is switched from an opened state (deactivated) to closed state (activated) and the whole system is vacuumed by the pressure reducing pump  230  which pumps atmosphere out of the system, thereby generating a negative pressure within the system. It is determined that there is a leakage below a reference value if the pressure being reduced is below a pressure P 2 , and that there is a leakage above the reference value if the pressure is not reduced below the pressure P 2  after a certain elapsed time. Then, the pressure reducing pump  230  is deactivated and the switching valve  228  is opened (deactivated), and the leak diagnosis ends. 
     Further,  FIG. 5  shows airflow while the switching valve  228  is deactivated and the pressure reducing pump  230  is activated. Also,  FIG. 6  shows airflow while the switching valve  228  is activated and the pressure reducing pump  230  is deactivated. 
       FIGS. 8 and 9  illustrate transition of pressure when the switching valve  228  of the existing system is in failure and remains or becomes fixed in an opened or closed state. In both cases, there is a high possibility that a normal condition is determined when a leakage determination pressure variation ÄP 3  (ÄP 3 =P 4 −P 2 ) is less than LEAK (wherein LEAK is a certain value set around 0 [kPa]). 
     Now the operation of the control for the existing system is explained with reference to  FIG. 7 . 
     After a program for the control starts in step  302 , a determination is made in step  304  as to whether a monitoring condition is satisfied. If the determination in step  304  is “NO”, the program ends in step  306 . If the determination in step  304  is “YES”, then a process for measuring an initial pressure P 1  is performed in step  308 . 
     Then performed are a process for activation of the pressure reducing pump in step  310 , a process for measuring pressure P 2  after a certain time T 1  has elapsed in step  312 , and a process for calculation of a reference pressure variation ÄP 1  (ÄP 1 =P 1 −P 2 ) in step  314 . Then a determination is made in step  316  whether the reference pressure variation ÄP 1  is less than a first reference value for the reference pressure DP 11  (ÄP 1 &lt;DP 11 ). 
     If the determination in step  316  is “NO”, then another determination is made in step  318  whether the reference pressure variation ÄP 1  is greater than a second reference value for the reference pressure DP 12  (ÄP 1 &gt;DP 12 ). If the determination in step  316  is “YES”, then it is decided in step  320  that the reference pressure variation ÄP 1  is extremely low. Then a process to deactivate the pressure reducing pump is performed in step  322 , and the program returns in step  324 . 
     If the determination in step  318  is “NO”, then a process for activating (closing) the switching valve is performed in step  326 . If the determination in step  318  is “YES”, then it is decided in step  328  that the reference pressure variation ÄP 1  is extremely high. Then the process to deactivate the pressure reducing pump is performed in step  322 , and the program returns in step  324 . 
     After the process for activating (closing) the switching valve in step  326 , a process to measure a maximum pressure P 3  over a predetermined time T 2  is performed in step  330 . Then performed are a process to calculate a valve switching pressure variation ÄP 2  (pressure variation when the switching valve is shifted or switched; ÄP 2 =P 3 −P 2 ) in step  332 , a process to update a pressure P 4  being reduced in step  334 , and a process to calculate a leak determination pressure variation ÄP 3  (pressure variation for leak diagnosis; ÄP 3 =P 4 -P 2 ) in step  336 . A determination is made in step  338  whether a certain time T 3  has elapsed since activation (close) of the switching valve. 
     If the determination in step  338  is “NO”, then a determination is made in step  340  whether the leak determination pressure variation ÄP 3  is below a leak value LEAK (ÄP 3 &lt;LEAK). If the determination in step  338  is “YES”, a process to decide “failure for leakage” is performed in step  342 . 
     Further, if the determination in step  340  is “NO”, the program returns to the process for updating the reducing pressure P 4  in step  334 . If the determination in step  340  is “YES”, a process to decide a “normal condition” is performed in step  344 . 
     After the process to decide the “failure for leakage” in step  342  or the process to decide the “normal condition” in step  344 , a process to deactivate the pressure reducing pump and deactivate (open) the switching valve is performed in step  346 , and the program returns in step  348 . 
     SUMMARY OF THE INVENTION 
     In order to obviate or at least minimize the above inconvenience, 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 that connects an intake passage of the engine with a fuel tank to absorb the evaporative fuel. An atmosphere open passage connects the canister with the atmospheric air. A purge valve is located between the intake passage and the canister for a purge control of the evaporative fuel generated in the fuel tank and absorbed by the canister. This system includes a switching valve, a reference pressure detecting means, a pressure reducing means, a leak diagnosis means, and a failure determination means. The switching valve communicates/shuts the atmosphere open passage with/to the atmosphere. The pressure reducing means vacuums or generates a negative pressure inside of the evaporative fuel control system. The leak diagnosis means diagnoses leakage within the evaporative fuel control system by using a reduced pressure in the evaporative fuel control system which is reduced by the pressure reducing means when the switching valve is shifted to shut the atmospheric air, and a reference pressure detected by the reference pressure detecting means. The failure determination means determines whether the switching valve is in failure by using a pressure variation when shifting of the switching valve for the leak diagnosis. 
     According to the present invention having such configuration, the diagnosis of the failure of the switching valve can be achieved by using the pressure variation used for the leak diagnosis, which eliminates the need for additional system or parts for failure diagnosis. 
     Accordingly, the diagnosis of the failure of the switching valve can be achieved by using the pressure variation used for the leak diagnosis, which eliminates the need for an additional system or parts for failure diagnosis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a control flowchart for an evaporative fuel control system of an internal combustion engine according to an embodiment of the present invention. 
         FIG. 2  is a schematic block diagram of the evaporative fuel control system. 
         FIG. 3  is a block diagram of a conventional evaporative fuel control system of the engine. 
         FIG. 4  is a time chart depicting the occurrence of certain events in the conventional evaporative fuel control system of the engine. 
         FIG. 5  is a flowchart of airflow when the switching valve is deactivated and the pump is activated. 
         FIG. 6  is a flowchart of airflow when the switching valve is activated and the pump is deactivated. 
         FIG. 7  is a control flowchart for the evaporative fuel control system of the engine. 
         FIG. 8  is a time chart depicting the occurrence of certain events when the switching valve remains in an opened state (failure). 
         FIG. 9  is a time chart depicting the occurrence of certain events when the switching valve remains in a closed state (failure). 
     
    
    
     DETAILED DISCLOSURE OF THE INVENTION 
     The present invention will now be described in specific detail with reference to the accompanying drawings. 
       FIGS. 1 and 2  illustrate an embodiment of the present invention.  FIG. 2  show an evaporative fuel control system  2  for an internal combustion engine. 
     See the above-mentioned explanation of the prior art for an explanation of this general configuration of the evaporative fuel control system  2 . 
     Incidentally, in the evaporative fuel control system  2 , a canister is disposed on an evaporative fuel control passage (not shown) connecting a fuel tank (not shown) with an intake passage (not shown) in an intake pipe of the engine (not shown) mounted a vehicle (not shown). An atmosphere open passage (not shown) connects the atmosphere with the canister. A purge valve (not shown) is disposed between the intake passage and the canister to supply the evaporative fuel which is generated in the fuel tank and is absorbed by the canister to the intake passage for a purge control. 
     Also the evaporative fuel control system  2  includes a switching valve  4 , a reference pressure detecting means  6 , a pressure reducing means  8 , a leak diagnosis means  10 , and a failure determination means  12 . The switching valve  4  communicates the atmosphere open air passage with the atmosphere or shuts the atmosphere open air passage to the atmosphere. The pressure reducing means  8  vacuums or reduces the pressure inside of the evaporative fuel control system. The leak diagnosis means  10  diagnosis the presence or absence of leakage within the evaporative fuel control system  2  by using a reduced pressure in the evaporative fuel control system  2  which is reduced by the pressure reducing means  8  when the switching valve is shifted so as to shut the system off from the atmospheric air, and a reference pressure detected by the reference pressure detecting means  6 . The failure determination means  12  determines that the switching valve  4  is in failure by using a pressure variation when switching of the shifting valve for the leak diagnosis. 
     In particular, the reference pressure detecting means  6  corresponds to, e.g., the pressure sensor  234  of the prior art associated with the leak check module  222  disclosed herein. 
     Also, the pressure reducing means  8  corresponds to, e.g., the pressure reducing pump  230  of the prior art associated with the leak check module  222  disclosed herein. 
     As shown in  FIG. 2 , a control means  14  is connected to the switching valve  4 , the reference pressure detecting means  6 , and the pressure reducing means  8 . 
     This control means  14  corresponds to, e.g., the above-mentioned control means  224  of the prior art. 
     The leak diagnosis means  10  and the failure determination means  12  can be integrated into or separated from the control means  14 . In the embodiment of the present invention, the leak diagnosis means  10  and the failure determination means  12  are integrated into the control means  14 . 
     As shown in  FIG. 2 , the leak diagnosis means  10  and the failure diagnosis means  12  are provided within the control means  14 . The leak diagnosis means  10  diagnoses leakage in the evaporative fuel control system  2  by using a pressure value P 2  which is a pressure reduced by the pressure reducing means  8  in the evaporative fuel control system  8  after a certain time T 1  has elapsed, and an initial pressure P 1  detected by the reference pressure detecting means  6 . The failure determination means  12  determines the failure of the switching valve  4  by using a valve switching pressure variation ÄP 2  which is a difference of the pressure at which the switching valve  4  is shifted or switched during diagnosing of the leakage. 
     In addition, a failure state determination means  16  is provided within the control means  14  as shown in  FIG. 2  to determine a failure state of the switching valve  4  by using the pressure variation in the evaporative fuel control system  2  at the leak diagnosis, after failure is determined by the failure diagnosis means  12 . 
     More particularly, according to the embodiment of the present invention, after the measurement of the initial pressure P 1 , the pressure reducing pump as the pressure reducing means  8  is activated. After a certain time T 1  has elapsed, pressure P 2  is measured. It is decided that the switching valve  4  is in failure if the valve switching pressure variation ÄP 2  (ÄP 2 =P 3 -P 2 ) is not more than or equal to a first reference value DP 21  for the switching valve pressure. Further, depending on a leak diagnosis pressure variation ÄP 3  after a certain time has elapsed, it is determined that the switching valve  4  is in failure either in an opened or closed state. 
     The relationship between the first, second, third determination values DP 11 , DP 12 , DP 13  for the reference pressure which is used for determination of the reference pressure variation ÄPI is as follows: DP 11 &lt;DP 13 &lt;DP 12 . 
     Next, the operation of the embodiment of the present invention is explained with reference to  FIG. 1 , which illustrates a control flowchart for the evaporative fuel control system  2 . 
     After a program for the control starts in step  102 , a determination is made in step  104  as to whether a monitoring 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”, then a process for measuring the initial pressure P 1  is performed in step  108 . 
     Then performed are a process for activation of the pressure reducing pump in step  110 , a process for measuring the pressure P 2  after the certain time T 1  has elapsed in step  112 , and a process for calculation of the reference pressure variation ÄP 1  (ÄP 1 =P 1 −P 2 ) in step  114 . Then a determination is made in step  116  whether the reference pressure variation ÄP 1  is less than a first reference value for the reference pressure DP 11  (ÄP 1 &lt;DP 11 ). 
     If the determination in step  116  is “NO”, then another determination is made in step  118  as to whether the reference pressure variation ÄP 1  is greater than a second reference value for the reference pressure DP 12  (ÄP 1 &gt;DP 12 ). If the determination in step  116  is “YES”, then it is decided in step  120  that the reference pressure variation ÄP 1  is extremely low. Then a process to deactivate the pressure reducing pump is performed in step  122 , and the program returns in step  124 . 
     If the determination in step  118  is “NO”, then a process for activating (closing) the switching valve is performed in step  126 . If the determination in step  118  is “YES”, then it is decided in step  128  that the reference pressure variation ÄP 1  is extremely high. Then the process to deactivate the pressure reducing pump is performed in step  122 , and the program returns in step  124 . 
     After the process for activating (closing) the switching valve in step  126 , a process to measure a maximum pressure P 3  over a predetermined time T 2  is performed in step  130 . Then a process to calculate the valve switching pressure variation ÄP 2  (pressure variation when the switching valve is shifted or switched; ÄP 2 =P 3 −P 2 ) is performed in step  132 . A determination is made in step  134  whether the reference pressure variation ÄP 1  is below the third determination value DP 13  for the reference pressure (ÄP 1 &lt;DP 13 ). 
     If the determination in step  134  is “NO”, then a process for updating the pressure P 4  being reduced is performed in step  136 . If the determination in step  134  is “YES”, then a determination is made in step  138  whether the valve switching pressure variation ÄP 2  is below the first determination value DP 21  for the switching valve pressure (ÄP 2 &lt;DP 21 ). 
     If the determination in step  138  is “YES”, the program returns to step  136 . If the determination in step  138  is “NO”, then performed are a process to decide the reducing pump in an abnormal condition at a low flow rate in step  140 , a process for deactivating the pressure reducing pump and deactivating (closing) the switching valve in step  142 . Then the program returns in step  144 . 
     After the step  136  for updating the reducing pressure P 4 , a process for calculating the leak determination pressure variation ÄP 3  (pressure variation for leak diagnosis; ÄP 3 =P 4 −P 2 ) is performed in step  146 . Then a determination is made in step  148  whether the valve switching pressure variation ÄP 2  is below the first determination value DP 21  for the switching valve pressure (ÄP 2 &lt;DP 21 ). If the determination in step  148  is “NO”, then another determination is made in step  150  whether a certain time T 3  has elapsed from the activation (closing) of the valve. If the determination in step  148  is “YES”, then another determination is made in step  152  whether a certain time T 4  has elapsed from the activation (closing) of the valve. 
     If the determination in step  152  is “NO”, then the program returns to the process for updating the reducing pressure P 4  in step  136 . If the determination in step  152  is “YES”, then a further determination is made in step  154  whether the leak determination pressure variation ÄP 3  is below the first determination value DP 31  for the leak diagnosis pressure (ÄP 3 &lt;DP 31 ). If the determination in step  154  is “YES”, a process to decide whether the switching valve is in failure in the opened state is performed in step  156 . If the determination in step  154  is “NO”, then a process to decide whether the switching valve is in failure in the closed state is performed in step  158 . After the process in step  156  or  158 , a process for deactivating the pressure reducing pump and deactivating (closing) the switching valve is performed in step  160 , and then the program returns in step  162 . 
     Further, if the determination at step  150  as to whether a certain time T 3  has elapsed from the activation (closing) of the valve is “NO”, a further determination is made in step  164  as to whether the leak diagnosis pressure variation ÄP 3  is below a leak value LEAK (predetermined value) (ÄP 3 &lt;LEAK). If the determination in step  150  is “YES”, then a process to decide for “failure for leakage” is performed in step  166 . After this step  166 , a process to deactivate the pressure reducing pump and also deactivate (open) the switching valve is performed in step  160 , then the program returns in step  162 . 
     Still further, if the determination in step  164  is “NO”, the program returns to step  136 . If the determination in step  164  is “YES”, a process to decide a “normal condition” is performed in step  168 . After this step  168 , a process to deactivate the pressure reducing pump and also deactivate (open) the switching valve is performed in step  170 . The program then returns in step  172 . 
     With this configuration, the diagnosis of the failure of the switching valve  4  can be achieved by using the pressure variation used for the leak diagnosis, which eliminates the need for an additional system or parts for failure diagnosis. This keeps the system simple and reduces costs, which is advantageous from an economical viewpoint. 
     The failure diagnosis can also be achieved by using the pressure variation at which the switching valve  4  is activated and deactivated, which improves the precision of the diagnosis. 
     Also, detailed diagnosis for the switching valve is provided, i.e., the information of the switching valve failure is provided in more detail, which is advantageous in repairing. 
     The present invention is not limited to the above-mentioned embodiment, but is adaptable for various applications and variations or modifications. 
     For example, in the embodiment of the present invention, as shown in  FIG. 4 , the leak diagnosis is performed during vacuuming or pressure reduction in the fuel tank by comparing the reference pressure to the pressure measured when the predetermined time D has elapsed from activation of the switching valve for the fuel tank vacuuming. However, the leak diagnosis can be performed at an earlier stage as a special configuration. 
     More particularly, as shown in  FIG. 4 , a normal pressure (without leak; shown in a solid line) and the pressure with leakage (shown in a dashed line) present the different pressure just after activation of the switching valve. It is therefore possible to diagnosis the leakage without waiting for predetermined time D to elapse, which is between the time at which the switching valve is activated and the time the pressure reducing pump is deactivated. 
     Just after the switching valve is activated, the pressure variation is checked for leakage more than once (e.g., one to three times) at a certain short time interval. 
     This short time interval can be set at a time shorter in duration than the time D, e.g., time divided into one-fifth or one-tenth of the time D. 
     As a result, the diagnosis for the leakage is achieved without waiting for predetermined time D to elapse, which is between the time at which the switching valve is activated and the time the pressure reducing pump is deactivated, thereby permitting quick diagnosis control.