Evaporative fuel-processing system for internal combustion engines

Abstract

An evaporative fuel processing system adapted to be capable of detecting abnormality of an evaporative emission control system for storing, in a canister, evaporative fuel from a fuel tank for holding fuel to be supplied to an internal combustion engine, and purging evaporative fuel into the intake system of the engine. A first control valve is arranged across a passage extending between the fuel tank and the canister. A second control valve is arranged across a passage extending between the canister and the intake system of the engine. A third control valve is provided for an air inlet part of the canister communicatable with the atmosphere. Through operating these control valves to open and close them, the evaporative emission control system is negatively pressurized, and abnormality of this system is detected based on the pressure detected in this negatively pressurized state thereof. Timing for carrying out abnormality determination is determined depending on conditions of the fuel tank. Before starting the whole process for abnormality diagnosis of the system evaporative fuel stored in the canister is allowed to be purged for a predetermined time period. When the temperature of fuel in the fuel tank exceeds a predetermined value, the abnormality determination is inhibited.

What is claimed is:  
     
       1. An evaporative fuel-processing system for an internal combustion engine having an intake system, including an evaporative emission control system having a fuel tank, a canister containing an adsorbent, said canister having an air inlet port communicatable with the atmosphere, an evaporative fuel-guiding passage extending between said canister and said fuel tank, a first control valve arranged across said evaporative fuel guiding passage, an evaporative fuel-purging passage extending between said canister and said intake system, and a second control valve arranged across said evaporative fuel-purging passage, 
       said evaporative fuel-processing system having an abnormality-determining system in which comprises:  
       pressure-detecting means for detecting pressure within said evaporative emission control system;  
       negatively-pressurizing means for negatively pressurizing said evaporative emission control system; and  
       abnormality-determining means for determining abnormality of said evaporative emission control system based on the pressure within said fuel tank detected after said evaporative emission control system has been negatively pressurized by said negatively-pressurizing means.  
     
     
       2. An evaporative fuel-processing system according to  claim 1 , wherein said abnormality-determining means determines the abnormality of said evaporative emission control system based on a rate of change in the pressure within said fuel tank occurring before said evaporative emission control system is set to a predetermined negatively-pressurized condition by said negatively-pressurizing means and a rate of change in the pressure within said fuel tank occurring after said predetermined negatively-pressurized condition of said evaporative emission control system has been established. 
     
     
       3. An evaporative fuel-processing system according to  claim 1 , including tank condition-detecting means for detecting conditions of said fuel tank, wherein said abnormality-determining means carries out abnormality determination when a predetermined time period has elapsed after said evaporative emission control system was negatively pressed said predetermined time period being corrected by a correcting time period set in response to said conditions of said fuel tank detected by said tank condition-detecting means. 
     
     
       4. An evaporative fuel-processing system according to  claim 2 , including tank condition-detecting means for detecting conditions of said fuel tank, wherein said abnormality-determining means carries out abnormality determination when a time period has elapsed after said evaporative emission control system was negatively pressurized, said predetermined time period being corrected by a correcting time period set in response to said conditions of said fuel tank detected by said tank conditioned-detecting means. 
     
     
       5. An evaporative fuel-processing system according to  claim 1 , wherein said abnormality-determining means determines abnormality of said evaporative emission control system by comparing a value of a parameter indicative a rate of change in the pressure within said fuel tank detected after said evaporative emission control system has been negatively pressurized by said negatively-pressurizing means with a predetermined reference value, said predetermined reference value being determined according to a time period required for setting said evaporative emission control system to said predetermined negatively-pressurized condition by said negatively-pressurizing means. 
     
     
       6. An evaporative fuel-processing system according to  claim 1 , including means for purging evaporative fuel stored in said canister for a predetermined time period before the abnormality-determining process is started by said abnormality-determining system. 
     
     
       7. An evaporative fuel-processing system according to  claim 1 , including fuel temperature-detecting means for detecting the temperature of fuel contained in said fuel tank and determination-inhibiting means for inhibiting execution of abnormality-determining process by said abnormality-determining system when said fuel temperature detected exceeds a predetermined value. 
     
     
       8. An evaporative fuel-processing system for an internal combustion engine having an intake system, including an evaporative emission control system having a fuel tank a canister containing an adsorbent, said canister having an air inlet port communicatable with the atmosphere, an evaporative fuel-guiding passage extending between said canister and said fuel tank, a first control valve arranged across said evaporative fuel-guiding passage, an evaporative fuel-purging passage extending between said canister and said intake system and a second control valve arranged across said evaporative fuel-purging passage, 
       said evaporative fuel-processing system having an abnormality-determining system which comprises:  
       engine operating condition-detecting means for detecting operating conditions of said engine;  
       a third control valve for effecting and cutting off the communication of said air inlet port of said canister with the atmosphere;  
       tank internal pressure-detecting means for detecting pressure within said fuel tank;  
       negatively-pressurizing means for setting said evaporative emission control system to a predetermined negatively-pressurized condition by controlling said first to third control valves when it is detected by said said engine operating condition-detecting means that said engine is in operation;  
       a first rate of change-detecting means for detecting a rate of change in the pressure within said fuel tank caused by controlling opening and closing of said fast control valve;  
       a second rate of change-detecting means for detecting a rate of change in the pressure within said fuel tank caused by closing said second control valve after said negatively-pressurized condition of said evaporative emission control system has been established; and  
       abnormality-determining means for determining abnormality of said evaporative emission control system based on results of detection by said first and second rate of change-detecting means.  
     
     
       9. An evaporative fuel-processing system according to  claim 8 , including tank condition-detecting means for detecting conditions of said fuel tank wherein said abnormality-determining means carries out abnormality determination when a predetermined time period has elapsed after said evaporative emission control system was negatively pressurized said predetermined time period being corrected by a correcting time period set in response to said conditions of said fuel tank detected by said tank condition-detecting means. 
     
     
       10. An evaporative fuel-processing system according to  claim 8 , wherein said abnormality-determining means determines abnormality of said evaporative emission control system by comparing a value of a parameter indicative of a rate of change in the pressure within the said fuel tank detected after said evaporative emission control system has been negatively pressurized by said negatively-pressurizing means with a predetermined preference value during the negatively pressurizing, said predetermined reference value being determined according to a time period required for setting said evaporative emission control system to said predetermined negatively-pressurized condition by said negatively-pressurizing means. 
     
     
       11. An evaporative fuel-processing system according to  claim 9 , wherein said abnormality-determining means determines abnormality of said evaporative emission control system by comparing a value of a parameter indicative of a rate of change in the pressure within the aid fuel tank detected after said evaporative emission control system has been negatively pressurized by said negatively-pressurizing means with a predetermined reference value during the negatively pressurizing, said predetermined reference value being determined according to a time period required for setting said evaporative emission control system to said predetermined negatively-pressurized condition by said negatively-pressurizing means. 
     
     
       12. An evaporative fuel-processing system according to  claim 8 , wherein said abnormality-determining system includes fuel amount-detecting means for detecting an amount of fuel contained in said fuel tank, said abnormality-determining means determines the abnormality of said evaporative emission control system based on results of detection by said first and second rate of change-detecting means and said fuel amount-detecting means. 
     
     
       13. An evaporative fuel-processing system according to  claim 8 , including means for purging evaporative fuel stored in said canister for a predetermined time period before the abnormality-determining process is started by said abnormality-determining system. 
     
     
       14. An evaporative fuel-processing system according to  claim 8 , including fuel temperature-determining means for detecting the temperature of fuel contained in said fuel tank, and determination-inhibiting means for inhibiting execution of abnormality-determining process by said abnormality-determining system when said fuel temperature detected exceeds a predetermined value. 
     
     
       15. An evaporative fuel-processing system for an internal combustion engine having an intake system, including an evaporative emission control system having a fuel tank, a canister containing an adsorbent, said canister having an air inlet port communicatable with the atmosphere, an evaporative fuel-guiding passage extending between said canister and said fuel tank, a first control valve arranged across said evaporative fuel-guiding passage, an evaporative fuel-purging passage extending between said canister and said intake system, and a second control valve arranged across said evaporative fuel-purging passage, 
       said evaporative fuel-processing system having an abnormality-determining system which comprises:  
       engine operating condition-detecting means for detecting operating conditions of said engine,  
       a third control valve for effecting and cutting off the communication of said air inlet port of said canister with the atmosphere,  
       tank internal pressure-detecting means for detecting pressure within said fuel tank;  
       negatively-pressurizing means for setting said evaporative emission control system to a predetermined negatively-pressurized condition by controlling said first to third control valves when it is detected by said said engine operating condition-detecting means that said engine is in operation; and  
       abnormality-determining means for effecting a determination as to whether or not said evaporative emission control system is abnormally functioning, when a predetermined time period has elapsed during the negatively-pressurizing by said negatively-pressurizing means.  
     
     
       16. An evaporative fuel-processing system according to  claim 15 , wherein said abnormality-determining system includes evaporative fuel generation rate-detecting means for detecting a parameter of an amount of evaporative fuel generated per unit time within said fuel tank, said abnormality-determining means determining that said evaporative emission control system is abnormal on condition that said parameter indicative of said amount of evaporative fuel generated per unit time within said fuel tank is smaller than a predetermined value. 
     
     
       17. An evaporative fuel-pressing system according to  claim 15 , including means for purging evaporative fuel stored in said canister for a predetermined time period before the abnormality-determining process is started by said abnormality-determining system. 
     
     
       18. An evaporative fuel-processing system according to  claim 15 , including fuel temperature-detecting means for detecting the temperature of fuel contained in said fuel tank, and determination-inhibiting means for inhibiting execution of abnormality-determining process by said abnormality-determining system when said fuel temperature detected exceeds a predetermined value. 
     
     
       19. An evaporative fuel-processing system for an internal combustion engine having an intake system, including an evaporative emission control system having a fuel tank, a canister containing an adsorbent, said canister having an air inlet port communicatable with the atmosphere, an evaporative fuel-guiding passage extending between said canister and said fuel tank, an evaporative fuel-purging passage extending between said canister and said intake system, and a purge control valve arranged across said evaporative fuel-purging passage, 
       said evaporative emission control system comprising:  
       a drain shut valve disposed to establish and shut off communication between said air inlet port of said canister and the atmosphere;  
       pressure-detecting means for detecting pressure within said evaporative emission control system;  
       negatively-pressurizing means for negatively pressurizing said evaporative emission control system; and  
       abnormality-determining means for determining abnormality of said evaporative emission control system based on an extent to which the pressure is maintained within said evaporative emission control system, said extent being detected based on the pressure within said evaporative emission control system detected by said pressure-detecting means, after said evaporative emission control system has been negatively pressured by sad negatively-pressurizing means.  
     
     
       20. An evaporative fuel processing system according to  claim 19 , wherein said abnormality-determining means includes pressure-holding means for holding the pressure within said evaporative emission control system after said evaporative emission control system has been negatively pressurized by said negatively-pressurizing means, said abnormality-determining means detecting the extent to which the pressure is maintained within said evaporative emission control system based on the pressure within said evaporative emission control system detected by said pressure-detecting means, while the pressure within said evaporative emission control system is held by said pressure-holding means. 
     
     
       21. An evaporative fuel-processing system according to  claim 20 , wherein said negatively-pressurizing means opens said purge control valve and at the same time closes said drain shut valve to negatively pressurize said evaporative emission control system, and said pressure-holding means closes said purge control valve and at the same time closes said drain shut valve to hold the pressure within said evaporative emission control valve. 
     
     
       22. An evaporative fuel-processing system according to  claim 20 , wherein said abnormality-determining means determines the extent to which the pressure is maintained within said evaporative emission control means, by detecting a change in the pressure within said evaporative emission control system detected by said pressure-detecting means over a predetermined time period, and determines that there is an abnormality in said evaporative emission control system, when the detected change exceeds a predetermined value. 
     
     
       23. In an abnormality- determining system of an evaporative fuel - processing system of a vehicle for supplying and controlling an evaporative fuel adsorbed and held in a canister to an internal combustion engine in accordance with an operating condition of the internal combustion engine, comprising an improvement wherein said abnormality determining system includes:    
         first engine coolant temperature determining means for determining whether engine coolant temperature is lower than a first predetermined value at an initial start - up of said internal combustion engine;    
       
         second engine coolant temperature determining means for determining when said engine coolant temperature is above a second predetermined value only if said first engine coolant temperature determining means initially determines said engine coolant temperature is lower than said first predetermined value;  
       
         engine - operating condition - detecting means for detecting one or more predetermined engine operating conditions and/or vehicle running conditions when said second engine coolant temperature determining means determines said engine coolant temperature is above said second predetermined value; and    
         abnormality - determining means for determining an abnormality of said evaporative fuel - processing system when said engine operating condition detecting means determines one or more predetermined engine operating conditions and/or vehicle running conditions are satisfied.   
     
     
       24. In an abnormality- determining system of an evaporative fuel - processing system of a vehicle for supplying and controlling an evaporative fuel adsorbed and held in a canister to an internal combustion engine in accordance with operating conditions of said internal combustion engine, comprising an improvement wherein said abnormality determining system includes:    
         abnormality determining means for determining an abnormality of said evaporative fuel - processing system only when engine coolant temperature is greater than a first predetermined value; and    
         means for activating said abnormality - determining means at engine start - up only when said engine coolant temperature is less than a second predetermined value which is less than said first predetermined value.   
     
     
       25. An abnormality- determining system for an evaporative fuel - processing system of a vehicle, the evaporative fuel - processing system including a fuel tank coupled to an intake passage of an internal combustion engine via an evaporative fuel - purging passage, a canister disposed in line with said evaporative fuel - purging passage for adsorbing and holding evaporative fuel from said fuel tank, said canister having an air inlet port for introducing outside air into said evaporative fuel - processing system, and check valve means disposed between said fuel tank and said canister for maintaining a predetermined pressure in said fuel tank, said abnormality - determining system comprising:    
         pressure - determining means for determining pressure within said evaporative fuel processing system;    
       
         first control valve means, arranged across an evaporative fuel guiding passage which is between said fuel tank and said canister, for opening and closing said evaporative fuel passage in response to a first control signal;  
       
         second control valve means, arranged across said evaporative fuel - purging passage between said canister and said intake passage, for opening and closing the evaporative fuel - purging passage in response to a second control signal;    
       
         a third control valve means for effecting and cutting off communication with said air inlet port of said canister with the atmosphere in response to a third control signal; and  
       
         an abnormality - determining means for determining presence or absence of evaporative fuel leakage in said evaporative fuel - processing system when one or more predetermined engine operating conditions and/or vehicle running conditions are satisfied, said abnormality determining means selectively generating said first, second and third control signals to determined presence or absence of evaporative fuel leakage.   
     
     
       26. An abnormality determining system according to  claim 23 , wherein said second predetermined value is greater than said first predetermined value. 
     
     
       27. An abnormality determining system according to  claim 23 , wherein said one or more conditions comprise a vehicle velocity state or an engine rotational speed state. 
     
     
       28. An abnormality determining system according to  claim 27 , wherein said one or more conditions further comprise one of a vehicle velocity fluctuation over time, intake pipe pressure, and throttle opening degree. 
     
     
       29. An abnormality determining system according to  claim 25 , wherein said one or more conditions include an engine coolant temperature being greater than a predetermined value. 
     
     
       30. An abnormality determining system according to  claim 29 , wherein said one or more conditions comprise a vehicle velocity state or an engine rotational speed state. 
     
     
       31. An abnormality determining system according to  claim 30 , wherein said one or more conditions further comprise one of vehicle velocity fluctuation over time, intake pipe pressure, and throttle opening degree. 
     
     
       32. An abnormality determining system according to  claim 24 , wherein said abnormality- determining means includes engine - operating condition - detecting means for detecting one or more predetermined engine operating conditions and/or vehicle running conditions before executing said abnormality - determining means, said one or more predetermined engine operating conditions and/or vehicle running conditions being from a group including a vehicle velocity state, an engine rotational speed state, a vehicle velocity fluctuation over time, an engine rotational speed, and a throttle opening degree.   
     
     
       33. An abnormality determining system for detecting an abnormality in an evaporative fuel processing system having a fuel tank storing an amount of fuel, an evaporative fuel- guiding passage extending between said fuel tank and a canister, an evaporative fuel - purging passage through which fuel vapor stored in said canister is purged into an intake passage of an internal combustion engine and a purge control valve arranged across said evaporative fuel - purging passage to allow a purge operation by opening of said purge control valve, said abnormality - determining system comprising:    
         negatively - pressurizing means for introducing a negative pressure from said intake passage of said internal combustion engine into said evaporative fuel processing system;    
         pressure - detecting means for detecting pressure within said evaporative fuel processing system when negative pressure is introduce therein by said negatively - pressurizing means;    
         abnormality - determining means for determining an abnormality in said evaporative fuel processing system based upon pressure in said evaporative fuel processing system, said determination using values supplied by said pressure - detecting means; and    
         negative pressure controlling means for controlling said negatively - pressurizing means so as to prohibit negatively - pressurizing of said negatively - pressurizing means while said abnormality - determining means is determining the abnormality, when said negative pressure is introduced into said evaporative fuel processing system by said negatively - pressurizing means wherein suctioning of said fuel vapor collected in the fuel tank with air into the engine results in fluctuation of an air - fuel ratio.   
     
     
       34. An abnormality- determining system according to    claim 33   , further comprising a control valve for effecting and cutting off communication of an air inlet port of said canister with the atmosphere wherein;    
         said negatively - pressurizing means comprises controlling means for controlling said purge control valve and control valve, negative pressure inside said intake passage being introduced into said evaporative fuel processing system by closing said control valve and opening said purge control valve.   
     
     
       35. An abnormality determining system for detecting an abnormality in an evaporative fuel processing system having a fuel tank storing an amount of fuel, an evaporative fuel- guiding passage extending between said fuel tank and a canister, an evaporative fuel - purging passage through which fuel vapor stored in said canister is purged into an intake passage of an internal combustion engine and a purge control valve arranged across said evaporative fuel - purging passage to allow a purge operation by opening of said purge control valve, said abnormality - determining system comprising:    
         negatively - pressurizing means for introducing a negative pressure from said intake passage of said internal combustion engine into said evaporative fuel processing system;    
         pressure - detecting means for detecting pressure within said evaporative fuel processing system when negative pressure is introduce therein by said negatively - pressurizing means;    
         negative pressure controlling means for controlling said negatively - pressurizing when said negative pressure is introduced into said evaporative fuel processing system by said negatively - pressurizing means wherein suctioning of said fuel vapor collected in the fuel tank with air into the engine results in fluctuation of an air - fuel ratio; and    
         abnormality - determining means for determining an abnormality in said evaporative fuel processing system based upon pressure in said evaporative fuel processing system, said determination using values supplied by said pressure - detecting means, said system further comprising    
         means for determining a fuel amount stored in said canister and said negatively - pressurizing means is activated based upon said fuel amount stored in said canister.   
     
     
       36. An abnormality determining system according to  claim 35 , said fuel amount stored in said canister is determined by time elapsed since said purge control valve was opened. 
     
     
       37. An abnormality determining system according to  claim 36 , wherein said opening and closing of said purge control valve is controlled to be linearly changed. 
     
     
       38. An abnormality determining system according to  claim 35 , wherein said abnormality determining means determines the existence or non- existence of a malfunction of said evaporative fuel processing system by comparing a rate of pressure change inside said evaporative fuel processing system over a predetermined period of time with a predetermined value, said rate of pressure change being obtained by using pressure values detected and supplied by said pressure detecting means.