Patent ID: 6164123
Filing Date: 2000-12-26
Classification: F02M

Abstract:
A vehicle fuel system with on-board diagnostics for leak testing comprises: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 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, CVV 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 leak test, when the engine is running,h) the leak test including:i) evacuation of the tank with the purge valve open and the CVV closed;ii) monitoring pressure rise in the tank with both valves closed;iii) recording the pressure rise dP.sub.-- A over a period.sub.-- A following increase of tank pressure to a predetermined value p2; andiv) calculating using dP.sub.-- A to determine whether or not unacceptable leakage is occurring; andv) venting the tank to atmospheric pressure via the CVV then sealing the tank by closing the CVV; andvi) measuring the amount dP.sub.-- B by which the pressure in the tank rises above atmospheric due to vapor generation over a period.sub.-- B following closure of the CVV;the ECU being arranged to calculate a value X representative of leakage from the difference between dP.sub.-- A and dP.sub.-- B using a scaling factor K and to compare X with a threshold level R indicative of leakage below acceptable levels;i) period A being adjusted in accordance with fuel level/vapor volume, a shorter period A being used for higher fuel level (lower vapor volume) and a longer period A being used for lower fuel level (higher vapor volume).