Apparatus for detecting malfunction in evaporated fuel purge system

Abstract

A malfunction detection apparatus for detecting a malfunction in an evaporated fuel purge system for use in an internal combustion engine. The apparatus includes a vapor passage connecting a fuel tank to a canister for feeding fuel vapor from the fuel tank into the canister, a purge passage connecting the canister to an intake passage of the engine for feeding the fuel vapor adsorbed in an adsorbent in the canister into the intake passage, a purge control valve provided for controlling a flow of the adsorbed fuel vapor in the canister being fed into the intake passage, a pressure sensor provided for outputting a signal indicative of pressure in the vapor passage, and a malfunction detection part responsive to the signal outputted by the pressure sensor for detecting a malfunction in the evaporated fuel purge system.

What is claimed is:  
     
       1. An apparatus for detecting a malfunction in an evaporated fuel purge system for use  used in an internal combustion engine, said apparatus comprising: 
       a fuel tank in which fuel is evaporated into a fuel vapor;  
       a canister including an adsorbent for adsorbing the fuel vapor from the fuel tank;  
       a vapor passage connecting said fuel tank to said canister for feeding the fuel vapor from said fuel tank into said canister;  
       a purge passage connecting said canister to an intake passage of the internal combustion engine for feeding the adsorbed fuel vapor in said adsorbent in said canister into said intake passage;  
       purge control  valve means provided at an intermediate portion infor closing said purge passage for controlling a flowto prohibit the feeding of the adsorbed  fuel vapor being fed by a vacuumfrom said canister to said intake passage due to a negative pressure in said intake passage from said canister to said intake passage;  
       a pressure sensor provided at an intermediate portion  in said vapor passage for outputting a signal indicative of a pressure in said vapor passage  fuel purge system, wherein the purge system includes said fuel tank, said purge passage, said vapor passage and said canister; and  
       malfunction detection means responsive to said signal outputted by said pressure sensor  for detecting whether a malfunction has occurred in said evaporated fuel purge system in response to a pressure change corresponding to a difference between a first output signal of said pressure sensor at a first time while the purge passage is closed by said valve means and a second output signal of said pressure sensor a predetermined time after the first time,  
         wherein said malfunction detection means determines that a malfunction has occurred in said evaporated fuel purge system when the pressure change is less than a predetermined reference value .  
     
     
       2. The system as claimed in  An apparatus according to claim  1 , further comprising warning lamp means for giving a warning of the malfunction to  informing a vehicle driver of the malfunction when said malfunction is detected in said evaporated fuel pure system by said malfunction detection means. 
     
     
       3. The system as claimed in  apparatus according to claim  1 , wherein said purge control  valve means includes a vacuum switching valve which is operated by a microcomputer and switched ON when the pressure in the vapor passage indicated by the signal outputted by said pressure sensor has reached a predetermined high pressure. 
     
     
       4. The system as claimed in  apparatus according to claim  1 , wherein said purge control  valve means includes a vacuum switching valve operated by a microcomputer and a bimetal vacuum switching valve operated in response to a temperature of engine cooling water in the internal combustion engine. 
     
     
       5. The system as claimed in  An apparatus according to claim  1 , wherein said malfunction detection means determines that there is  a malfunction has occurred in said evaporated fuel purge  system when the pressure in the vapor passage  indicated by the output signal outputted by said  of the pressure sensor when the malfunction detection procedure is performed has not reached a predetermined low pressure for more than a  reference value greater than atmospheric pressure after said predetermined first time period has elapsed. 
     
     
       6. The system as claimed in claim  1 , wherein said malfunction detection means determines that there is a malfunction in said evaporated fuel purge system when a change in the pressure in the vapor passage, indicated by the signal outputted by said pressure sensor, from an OFF state of said purge control valve to an ON state of said purge control valve means does not become greater than a predetermined reference value  An apparatus for detecting a malfunction in an evaporated fuel purge system used in an internal combustion engine, said apparatus comprising: 
       
         a fuel tank in which fuel is evaporated into a fuel vapor;  
       
       
         a canister including an adsorbent for adsorbing the fuel vapor from the fuel tank;  
       
       
         a vapor passage connecting said fuel tank to said canister for feeding the fuel vapor from said fuel tank into said canister;  
       
       
         a purge passage connecting said canister to an intake passage of the internal combustion engine for feeding the adsorbed fuel vapor in said adsorbent in said canister into said intake passage;  
       
       
         valve means provided at an intermediate portion in said purge passage for controlling the flow of the adsorbed fuel vapor fed due to a negative pressure in said intake passage from said canister to said intake passage;  
       
       
         a pressure sensor for outputting a signal indicative of a pressure in said fuel purge system, wherein the purge system includes said fuel tank, said purge passage, said vapor passage and said canister; and  
       
         malfunction detection means for detecting whether or not a malfunction has occurred in said evaporated fuel purge system by detecting a pressure difference between a first output signal of said pressure sensor before the valve means is switched from a closed state to an open state and a second output signal of said pressure sensor a predetermined time after the valve means has been switched from the closed state to the open state .  
     
     
       7. The system as claimed in  An apparatus according to claim  6 , wherein said determination is made by  said malfunction detection means determines that a malfunction has occurred in said system when the value of the pressure difference indicated by the output signal of the pressure sensor has not reached a predetermined reference value after said purge control means is switch ON and a  the predetermined second  time period elapses  has elapsed. 
     
     
       8. The system as claimed in  apparatus according to claim  1 , wherein said canister includes a check valve means which is actuated by a spring so as to close an inlet port of said canister communicating with the vapor passage leading to the fuel tank, said inlet port being opened against the actuating force produced by said spring when the pressure in the vapor passage is lower than a predetermined pressure, thus allowing external air to be fed into the vapor passage from an air inlet port provided at a bottom portion of said canister. 
     
     
       9. An apparatus according to claim  7 , wherein the value of the pressure difference is indicated as a difference between pressures respectively indicated by the output signal of the pressure sensor when the valve means is switched ON and when the valve means is switched OFF after the predetermined time period has elapsed.  
     
     
       10. An apparatus according to claim  6 , further comprising warning lamp means for informing a vehicle driver of the malfunction when said malfunction is detected in said evaporated fuel purge system by said malfunction detection means.