Fuel vapor purge system for internal combustion engine and method of diagnosis thereof

A fuel vapor purge system for an internal combustion engine, comprising:

• a fuel supply means having a fuel tank;
• conduit means for purging fuel vapor generated within said fuel tank into an intake passage of said engine;
• purge valve means installed in said conduit means;
• and
• control means for diagnosing said fuel vapor purge system as to occurrence of an abnormality;
• said control means comprising:
• pressure sensor means for detecting a pressure within said fuel tank;
• purge valve control means for opening said purge valve for a first predetermined period when said engine operates in a steady state;
• diagnosis means for making decision as to occurrence of an abnormality in said fuel vapor purge system on the basis of the magnitude of a change in the pressure within said fuel tank over a second predetermined period covering said first predetermined period;
• and
• wherein said magnitude of change is determined on the basis of a rate of change in the pressure within said purge system brought about by opening said purge valve means and a rate of change in the pressure within said system brought about by closing said purge valve means in succession to said opening of said valve means.

In a fuel vapor purge system for an internal combustion engine comprising fuel supply means including a fuel tank, conduit means for purging fuel vapor generated within said fuel tank into an intake passage of said engine, purge valve means installed in said conduit means, pressure sensor means for detecting a pressure within said fuel tank, and purge valve control means for opening said purge valve for a first predetermined period when said engine operates in a steady state,

• a method of diagnosing said fuel vapor purge system as to occurrence of an abnormality and activating an alarm means indicative of the abnormality, said method comprising the steps of:
• deciding, on the basis of sensor signals indicative of operation states of said engine, whether said engine operates in a steady state;
• fetching a pressure within said fuel tank from the output of said pressure sensor means when said engine is in the steady state and storing said pressure as an initial pressure value;
• opening said purge valve means for a first predetermined period to thereby allow the fuel vapor within the fuel tank to be purged into said intake passage of the engine and subsequently closing said purge valve means to thereby terminate said first predetermined period;
• determining differences between said initial pressure value and pressures within said fuel tank detected at a plurality of successive discrete time points, respectively, during a second predetermined period which starts simultaneously with the start of said first predetermined period and which extends longer than said first predetermined period;
• determining a cumulative value of said pressure differences;
• comparing said cumulative value with a preset minimum value indicating normality of said fuel vapor purge system;
• deciding that said fuel vapor purge system suffers an abnormality when said cumulative value is smaller than said preset minimum value;
• and
• activating said alarm means when said cumulative value is smaller than said preset minimum value.

A fuel vapor purge system for an internal combustion engine, comprising:

• a fuel supply means having a fuel tank;
• conduit means for purging fuel vapor generated within said fuel tank into an intake passage of said engine;
• purge valve means installed in said conduit means;
• and
• control means for diagnosing said fuel vapor purge system as to occurrence of an abnormality;
• said control means comprising:
• pressure sensor means for detecting a pressure within said fuel tank;
• purge valve control means for opening said purge valve for a first predetermined period when said engine operates in a steady state;
• integration means for calculating a cumulative change value defined by the cumulative value of the difference between the detected pressure before the start of said second predetermined period and the pressures detected during said second predetermined period;
• rate measuring means for calculating first rate change defined by the rate of change of said pressure brought about by opening said purge valve, and a second rate change defined by the rate of change of said pressure brought about by the closing of said purge valve;
• and
• comparing means for comparing the values of said cumulative change, said first rate change and said second rate change with respective predetermined values and using the results of the comparison to determined whether an abnormality exists.