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In a system and a method for purging a vapor storage canister having adsorbed fuel vapor (or hydrocarbon vapor) by drawing air through the storage canister the storage canister being coupled with an engine having a system for controlling the amount of fuel provided to the engine, the amount of fuel

In a system and a method for purging a vapor storage canister having adsorbed fuel vapor (or hydrocarbon vapor) by drawing air through the storage canister the storage canister being coupled with an engine having a system for controlling the amount of fuel provided to the engine, the amount of fuel vapor in the purge is estimated using a model that predicts fuel vapor concentration in the purge vapor. The engine controller uses the estimated amount of fuel vapor and air brought into the engine from the evaporative vapor storage canister for better control of engine air and fuel during purging.

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What is claimed is: 1. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor, comprising the steps of: providing an initial value, CHC0, for the concentration of hydrocarbon vapor in the canis

What is claimed is: 1. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor, comprising the steps of: providing an initial value, CHC0, for the concentration of hydrocarbon vapor in the canister containing adsorbed hydrocarbon vapor; drawing air into the canister containing adsorbed hydrocarbon vapor and withdrawing from the canister a volume of purge vapor containing desorbed hydrocarbon vapor; calculating a concentration of desorbed hydrocarbon vapor in the purge vapor; and using purge vapor volume and concentration of desorbed hydrocarbon vapor in the purge vapor to calculate the amounts of purge hydrocarbon vapor and purge air and adjusting an amount of fuel to be taken from the fuel tank and an amount of intake air based on the amounts of purge hydrocarbon vapor and purge air. 2. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor according to claim 1, wherein CHC0 is measured by monitoring the fuel injection rate with and without canister purge at steady state engine operation. 3. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor according to claim 1, wherein CHC0 is estimated from purge canister and/or vehicle conditions. 4. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor according to claim 1, wherein the concentration of desorbed hydrocarbon vapor in the purge vapor is calculated using a curve fitted to experimentally measured values for hydrocarbon concentration in the purge vapor as a function of commanded purge vapor volume for a specific vehicle, purge canister, absorbent, and purge conditions. 5. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor according to claim 1, wherein the concentration of desorbed hydrocarbon vapor in the purge vapor is calculated using a model that predicts exponential decrease for hydrocarbon concentration in the purge vapor from the initial hydrocarbon concentration with continuing purge. 6. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor according to claim 1, wherein the concentration of hydrocarbon in the purge vapor, CHC, is calculated from an equation: description="In-line Formulae" end="lead"CHC=CHC0EXP(-(αCHC0+β) V), in whichdescription="In-line Formulae" end="tail" V is the cubic feet of commanded purge volume; CHC0 is the initial concentration of hydrocarbon vapor in the purge; CHC is the concentration of hydrocarbon vapor in the purge after V cubic feet of commanded purge volume; and α and β are constants, the values of which depend on the particular-engine and make of vehicle. 7. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor according to claim 1, wherein the concentration of hydrocarbon in the purge vapor, CHC, is calculated using a model combining material balance and isotherm equations. 8. A method for controlling amounts of air and fuel introduced to an engine during purge of hydrocarbon vapor from a canister containing adsorbed hydrocarbon vapor according to claim 1, wherein the concentration fraction of hydrocarbon CHC in the purge vapor is determined from a ratio of its partial pressure P to the atmospheric pressure Patm, using the equation description="In-line Formulae" end="lead"CHC=P/Patm,description="In-line Formulae" end="tail" wherein wherein a =KBb, b=K-QBb+QmBb, and c=-Q, and K =ΔV/(KcKf(1-ε)VcRT) where ΔV is the volume of purge vapor, kc is a correction factor for carbon utilization, kf is a correction factor for partial fill, (1-ε)Vc is the volume of the carbon in the evap canister, ε is the porosity of the adsorbent in the evap canister, and Vc is the evap canister volume, R is the gas law constant, and T is the air temperature in Kelvin, Q is the initial adsorbed amount of hydrocarbon per unit volume of carbon, Q1 is the final adsorbed amount of hydrocarbon per unit volume of carbon after ΔV volume of purge vapor wherein Q1=QmBbP첨(1+QmBbP), and Qm and Bb are isotherm constants in which Qm=A+B/T and Bb=EXP(C+D/T), with A, B, C, and D being characteristic constants of the adsorbent in the evap canister. 9. A method of operating a vehicle having an internal combustion engine with an air induction system, a fuel tank connected to the engine to supply fuel to the engine, an electronic engine control module comprising a programmed microprocessor controlling fuel delivery to the engine and intake air to the engine, and a canister to adsorb vapor from the fuel tank comprising a vapor inlet coupled to the fuel tank and a purge outlet coupled to the air induction system, comprising steps of: adsorbing fuel vapor from the fuel tank into the canister through the vapor inlet; desorbing fuel vapor from the canister through the purge outlet by opening the purge valve through a signal from the electronic engine control module and drawing air through the canister into the air induction system; calculating the concentration of desorbed hydrocarbon vapor in the purge vapor; using the concentration of desorbed hydrocarbon vapor and purge vapor volume to calculate the amounts of purge hydrocarbon vapor and purge air and using the electronic engine control module to adjust fuel delivery from the fuel tank to the engine and/or the amount of intake air in response to the calculated amounts of purge hydrocarbon vapor and purge air. 10. An engine controller having an algorithm for determining the concentration of hydrocarbon vapor in purge vapor drawn from a canister containing adsorbed hydrocarbon vapor, said algorithm including steps for providing an initial concentration of hydrocarbon in purge vapor; steps for determining commanded purge volume and purge vapor composition; and steps for calculating purge air correction and purge hydrocarbon correction and applying the corrections in engine air and fuel intake calculations; wherein the controller is adapted to apply the corrections in engine air and fuel intake calculations to adjust the amount of air and fuel taken into an engine. 11. A controller according to claim 10, wherein the purge vapor composition is determined using a curve fitted to experimentally measured values for hydrocarbon concentration in the purge vapor as a function of commanded purge vapor volume for a specific vehicle, purge canister, absorbent, and purge conditions. 12. A controller according to claim 10, wherein the purge vapor composition is determined using a model that predicts exponential decrease for hydrocarbon concentration in the purge vapor from the initial hydrocarbon concentration with continuing purge. 13. A controller according to claim 10, wherein the purge vapor composition is determined using a model combining material balance and isotherm equations. 14. A vehicle having an internal combustion engine with an air induction system, a fuel tank connected to the engine to supply fuel to the engine, an electronic engine control module comprising a programmed microprocessor controlling fuel and air delivery to the engine, and a canister to adsorb vapor from the fuel tank comprising a vapor inlet coupled to the fuel tank, a purge outlet coupled to the air induction system, and an air inlet, wherein the microprocessor is programmed to estimate concentration of hydrocarbon vapor in purge air drawn through the air inlet, through the canister, and through the purge outlet from the canister from an equation that predicts a decrease of fuel vapor concentration in the purge air from an initial fuel vapor concentration in the purge air and further wherein the electronic engine control module adjusts fuel and air delivery to the engine in response to the estimated concentration of hydrocarbon vapor in the purge air. 15. A vehicle according to claim 14, wherein the equation predicts exponential decrease for hydrocarbon concentration in the purge vapor from the initial hydrocarbon concentration with continuing purge. 16. A vehicle according to claim 14, wherein the equation combines material balance and isotherm equations.