Evaporative emission leak detection method with vapor generation compensation

A method of detecting leaks in an automotive evaporative emission system, including leak tests to detect a first-sized leak and a second-sized leak, with the second-sized leak being smaller than the first-sized leak, the method including the steps of:

• repeatedly measuring a pressure in the system;
• conducting a first vapor generation test substantially at the beginning of a driving cycle by closing all venting of the system and monitoring a first change in the measured pressure;
• comparing the first pressure change to upper and lower thresholds;
• disabling the leak tests for both first-sized and second-sized leaks if the first pressure change exceeds the upper threshold;
• bringing the measured pressure to a reference value below atmospheric pressure, and then determining a rate of change of the measured pressure;
• conducting a second vapor generation test after completion of the leak test by closing all venting of the system and monitoring a second change in the measured pressure;
• compensating the determined rate of change based upon the greater of the first and second pressure changes;
• and
• detecting the existence of both first-sized leaks and second-sized leaks based on the compensated rate of change if the first pressure change is less than the lower threshold;
• and
• detecting the existence of a first-sized leak but not a second-sized leak based on the compensated rate of change if the first pressure change exceeds the lower threshold but not the upper threshold.

A method of detecting leaks in an automotive evaporative emission system, including leak tests to detect a first-sized leak and a second-sized leak, with the second-sized leak being smaller than the first-sized leak, the method including the steps of:

• repeatedly measuring a pressure in the system;
• conducting a first vapor generation test substantially at the beginning of a driving cycle by closing all venting of the system and monitoring a first change in the measured pressure;
• bringing the measured pressure to a reference value below atmospheric pressure, and then determining a rate of change of the measured pressure;
• conducting a second vapor generation test after completion of the leak test by closing all venting of the system and monitoring a second change in the measured pressure;
• compensating the determined rate of change based upon the greater of the first and second pressure changes;
• comparing the second pressure change to upper and lower thresholds;
• disabling the leak tests for both first-sized and second-sized leaks if the second pressure change exceeds the upper threshold;
• detecting the existence of both first-sized leaks and second-sized leaks based on the compensated rate of change if the second pressure change is less than the lower threshold;
• and
• detecting the existence of a first-sized leak but not a second-sized leak based on the compensated rate of change if the second pressure change exceeds the lower threshold but not the upper threshold.

A method of detecting a leak in an automotive evaporative emission system by repeatedly measuring a pressure in the system, and conducting a leak test by bringing the measured pressure to a reference value below atmospheric pressure, and then determining a rate of change of the measured pressure, the improvement comprising the steps of:

• conducting a first vapor generation test substantially at the beginning of a driving cycle, and prior to conducting the leak test, by closing all venting of the system and monitoring a first change in the measured pressure;
• and
• conducting a second vapor generation test after completion of the leak test by closing all venting of the system and monitoring a second change in the measured pressure;
• compensating the determined rate of change based upon the greater of the first and second pressure changes;
• and
• detecting the existence of a system leak when the compensated rate of change exceeds a threshold.

A method of leak testing an automotive evaporative emission system by repeatedly measuring a pressure in the system, and conducting a leak test by bringing the measured pressure to a reference value below atmospheric pressure, and then determining a rate of change of the measured pressure, wherein the leak test includes tests to detect a first-sized leak and a second-sized leak, with the second-sized leak being smaller than the first-sized leak, the improvement comprising the steps of:

• conducting a first vapor generation test substantially at the beginning of a driving cycle, and prior to conducting the leak test, by closing all venting of the system and monitoring a first change in the measured pressure;
• and
• conducting a second vapor generation test after completion of the leak test by closing all venting of the system and monitoring a second change in the measured pressure;
• compensating the determined rate of change based upon the greater of the first and second pressure changes;
• comparing the first pressure change to upper and lower thresholds;
• disabling the detecting of both first-sized and second-sized leaks if the first pressure change exceeds the upper threshold;
• detecting the existence of both first-sized leaks and second-sized leaks based on the compensated rate of change if the first pressure change is less than the lower threshold;
• and
• detecting the existence of a first-sized leak but not a second-sized leak based on the compensated rate of change if the first pressure change exceeds the lower threshold but not the upper threshold.

A method of leak testing an automotive evaporative emission system by repeatedly measuring a pressure in the system, and conducting a leak test by bringing the measured pressure to a reference value below atmospheric pressure, and then determining a rate of change of the measured pressure, wherein the leak test includes tests to detect a first-sized leak and a second-sized leak, with the second-sized leak being smaller than the first-sized leak, the improvement comprising the steps of:

• conducting a first vapor generation test substantially at the beginning of a driving cycle, and prior to conducting the leak test, by closing all venting of the system and monitoring a first change in the measured pressure;
• and
• conducting a second vapor generation test after completion of the leak test by closing all venting of the system and monitoring a second change in the measured pressure;
• compensating the determined rate of change based upon the greater of the first and second pressure changes;
• comparing the second pressure change to upper and lower thresholds;
• disabling the detecting of both first-sized and second-sized leaks if the second pressure change exceeds the upper threshold;
• detecting the existence of both first-sized leaks and second-sized leaks based on the compensated rate of change if the second pressure change is less than the lower threshold;
• and
• detecting the existence of a first-sized leak but not a second-sized leak based on the compensated rate of change if the second pressure change exceeds the lower threshold but not the upper threshold.