Evaporative emission control in battery powered vehicle with gasoline engine powered generator
A plug-in hybrid vehicle is driven by one or more electric motors powered by a battery system with supplemental electric power provided by a gasoline engine powered generator. A canister, connected by a fuel vapor vent passage, is used to admit and temporarily adsorb fuel vapor from a vehicle fuel tank during refueling. The canister also has a first fuel vapor and air flow passage for venting the canister and introducing ambient air (in the reverse flow direction) for removing vapor stored in the canister during tank refueling. The canister has a second passage for conducting air and purged vapor from the canister to the operating engine. The first and second passages are opened only during engine operation for purging of stored fuel vapor. The first flow passage is selectively opened when the tank is being refueled. The sealed fuel system eliminates diurnal fuel tank vapor generation and canister bleed emissions.
1. A method of operating a fuel evaporative emission control system in a plug-in hybrid vehicle driven by a battery powered electric motor with a supplemental gasoline engine powered-electric generator operated on-demand for supplemental electric power for the vehicle, where the vehicle comprises a gasoline fuel tank, a fuel vapor vent passage from the fuel tank to a fuel vapor adsorption canister, a first air and fuel vapor flow passage from the canister for venting the canister and for introduction of purge air to the canister to purge fuel vapor from the canister, and a second air and fuel vapor flow passage from the canister for passage of purge air and purged fuel vapor from the canister to an air induction system of the engine, the method comprising:
opening the first and second air and fuel vapor passages during engine operation;
opening the first air and fuel vapor passage, but not the second air and fuel flow passage, when the vehicle is not operating and the gasoline is being added to the fuel tank; and
closing both of the first and second air and fuel vapor passages for preventing diurnal vapor generation and preventing bleeding of fuel vapor from the canister when the vehicle is not in operation and when the vehicle is in operation but the gasoline engine is not being operated.
2. A method of operating a fuel evaporative emission control system as recited in claim 1 in which the opening and the closure of the first and second air and fuel vapor passages is controlled by signal of a computer control module.
3. A method of operating a fuel evaporative emission control system as recited in claim 1 in which the opening and closure of the first and second air and fuel vapor passages is performed by an electric solenoid valve in each passage.
4. A method of operating a fuel evaporative emission control system as recited in claim 1 in which the passage of air and vapor in the first and second air and fuel vapor flow passages is controlled by an electric solenoid valve in each passage and the respective solenoid valves are operated by signal of a computer control module.
5. A method of operating a fuel evaporative emission control system as recited in claim 1 in which the vehicle comprises a computer control module for operation of the evaporative emission control system and the control module acquires temperature and pressure data of the fuel in the fuel tank at predetermined times during vehicle operation.
6. A method of operating a fuel evaporative emission control system as recited in claim 5 in which the control module compares fuel temperatures and fuel tank pressures taken at a first time and at a second later time to determine whether there is a fuel vapor leak from the fuel tank or canister.
7. A method of operating a fuel evaporative emission control system as recited in claim 6 in which in which the first time is at an occasion of vehicle shut down and the second time is the next occasion of vehicle start.
8. A method of operating a fuel evaporative emission control system as recited in claim 5 in which the control module compares fuel temperatures and fuel pressures taken at a first time and at a second later time to determine the Reid Vapor Pressure of the fuel then in the fuel tank.
9. A method of operating a fuel evaporative emission control system as recited in claim 6 in which a measured increase in temperature without a corresponding measured increase in pressure signals a fuel vapor leak from the fuel tank or canister.