Evaporative purge monitoring strategy and system

Claim 1

A method of monitoring an evaporative purge flow path of a fuel system for a vehicle including sealing the evaporative flow path with respect to the atmosphere by the step of: closing a vapor management valve positioned between an engine manifold vacuum and an evaporative purge flow path of a fuel tank; waiting a predetermined period of time; obtaining an indication of the extent to which pressure is increasing in the fuel tank due to vapor generation; stopping further testing if the increase in pressure is above a predetermined maximum pressure value; continuing with the test if the pressure increase is below the predetermined maximum pressure value, so that any pressure change by vapor generation is within an acceptable amount; applying a vacuum to the evaporative purge flow path; isolating the evaporative purge flow path from the atmosphere and the vacuum source and monitoring any change in vacuum; and returning the evaporative purge flow path to a normal purge operation.

Claim 2

A method of monitoring an evaporative purge flow path of a fuel system for a vehicle including sealing the evaporative flow path with respect to the atmosphere by the step of: closing a vapor management valve positioned between an engine manifold vacuum and an evaporative purge flow path of a fuel tank; waiting a predetermined period of time; obtaining an indication of the extent to which pressure is increasing in the fuel tank due to vapor generation; stopping further testing if the increase in pressure is above a predetermined maximum pressure value; continuing with the test if the pressure increase is below the predetermined maximum pressure value, so that any pressure change by vapor generation is within an acceptable amount; applying a vacuum to the evaporative purge flow path; isolating the evaporative purge flow path from the atmosphere and the vacuum source and monitoring any change in vacuum; and returning the evaporative purge flow path to a normal purge operation.

Claim 5

A method of monitoring an evaporative purge flow path including the steps of: closing a vapor management valve positioned between an engine manifold vacuum and an evaporative purge flow path of a fuel tank, in order to obtain an indication of the extent to which pressure is increasing in the fuel tank due to vapor generation; stopping further testing if the increase in pressure is above a calibrated maximum value; continuing with the test if the pressure increase is below a calibrated maximum value, so that pressure during a vacuum bleed up period is not altered by vapor generation beyond a desired amount; closing a canister vent valve to the atmosphere and opening the vapor management valve; adjusting engine operation to accommodate consumption of fuel vapor from the evaporative purge flow path; stopping further testing if a predetermined target vacuum is not reached within a calibrated amount of time and storing an error code indicating test failures; if a target vacuum is reached within the calibrated amount of time, closing the vapor management valve; closing the vapor management valve and the canister vent valve in order to hold the vacuum in the evaporative purge flow path; waiting a predetermined period of time; detecting a change in fuel tank vacuum; comparing the change to a calibrated maximum acceptable pressure change; passing the test if the pressure change is less than the maximum acceptable change; failing the test if the pressures change is more than the maximum allowable pressure change; and opening the canister vent valve at a calibrated ramp rate to the open flow position.

Claim 6

A method of monitoring an evaporative purge flow path including the steps of: closing a vapor management valve positioned between an engine manifold vacuum and an evaporative purge flow path of a fuel tank, in order to obtain an indication of the extent to which pressure is increasing in the fuel tank due to vapor generation; stopping further testing if the increase in pressure is above a calibrated maximum value; continuing with the test if the pressure increase is below a calibrated maximum value, so that pressure during a vacuum bleed up period is not altered by vapor generation beyond a desired amount; closing a canister vent valve to the atmosphere and opening the vapor management valve; adjusting engine operation to accommodate consumption of fuel vapor from the evaporative purge flow path; stopping further testing if a predetermined target vacuum is not reached within a calibrated amount of time and storing an error code indicating test failures; if a target vacuum is reached within the calibrated amount of time, closing the vapor management valve; closing the vapor management valve and the canister vent valve in order to hold the vacuum in the evaporative purge flow path; waiting a predetermined period of time; detecting a change in fuel tank vacuum; comparing the change to a calibrated maximum acceptable pressure change; passing the test if the pressure change is less than the maximum acceptable change; failing the test if the pressures change is more than the maximum allowable pressure change; and opening the canister vent valve at a calibrated ramp rate to the open flow position.