Patent ID: 6216674
Filing Date: 2001-04-17
Classification: F02M

Abstract:
A vehicle fuel system with on-board diagnostics for leak testing comprising:a) a fuel tank for containing fuel for delivery to an internal combustion engine;b) a purge canister connected to the space in the tank above the fuel;c) a canister vent valve (CVV) for connecting the purge canister to the atmosphere;d) a purge valve for connecting the purge canister to the engine; ande) an electronic control unit (ECU) arranged for monitoring pressure and fuel level in the tank and other engine, vehicle and ambient conditions and for controlling opening and closing of the valves;f) the CVV and the purge valve being controlled by the ECU for venting the tank to atmosphere via the purge canister (purge valve closed, CVW open), and for purging vapor from the canister by allowing air to be drawn through the canister by manifold vacuum (both valves open);g) the ECU being arranged to carry out a periodic vapor integrity test, when the engine is running;h) the vapor integrity test including:i) evacuation of the tank with the purge valve open and the CVV closed (evacuation phase);ii) monitoring pressure rise in the tank with both valves closed (bleedup phase); andiii) developing an indication of loss of vapor integrity from time and pressure values measured during the bleedup;in which:pressure in the tank is measured at intervals during the evacuation phase and a correction is made to the loss of vapor integrity indication based on the values and timing of the pressure measurements made during the evacuation phase, the correction being effective to reduce errors in the loss of vapor integrity indication due to temperature variations in the air/vapor in the tank at the commencement of bleedup due to variations in the evacuation phase.