Method and system for fuel vapor control
First Claim
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1. A vehicle system, comprising,a battery;
- an engine including an engine intake, the engine selectively started in response to a battery state of charge falling below a threshold;
a fuel tank coupled to a canister through a fuel tank isolation valve;
a canister, configured to store fuel vapors, coupled to an engine intake through a canister purge valve, the canister further coupled to a vacuum accumulator through a vacuum accumulator valve;
a first pressure sensor coupled to the fuel tank to estimate a fuel tank pressure;
a second pressure sensor coupled to the canister to estimate a canister pressure; and
a control system with computer readable instructions for,during an engine-off mode of operation, with the fuel tank isolation valve opened and the canister purge valve closed,applying a pressure on the fuel tank first and then the canister, when an absolute value of the fuel tank pressure is above a threshold;
applying a pressure on the canister first and then the fuel tank, when the absolute value of the fuel tank pressure is below a threshold;
indicating fuel tank isolation valve and/or canister purge valve degradation based on a change in the fuel tank pressure and the canister pressure following pressure application.
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Abstract
A method and system for fuel vapor control in a hybrid vehicle (HEV). The HEV fuel vapor recovery system includes a fuel tank isolation valve, which is normally closed to isolate storage of refueling from storage of diurnal vapors. The method for fuel vapor control includes selectively actuating the fuel tank isolation valve during interrelated routines for refueling, fuel vapor purging, and emission system leak detection diagnostics to improve regulation of pressure and vacuum the HEV fuel vapor recovery system.
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Citations
20 Claims
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1. A vehicle system, comprising,
a battery; -
an engine including an engine intake, the engine selectively started in response to a battery state of charge falling below a threshold; a fuel tank coupled to a canister through a fuel tank isolation valve; a canister, configured to store fuel vapors, coupled to an engine intake through a canister purge valve, the canister further coupled to a vacuum accumulator through a vacuum accumulator valve; a first pressure sensor coupled to the fuel tank to estimate a fuel tank pressure; a second pressure sensor coupled to the canister to estimate a canister pressure; and a control system with computer readable instructions for, during an engine-off mode of operation, with the fuel tank isolation valve opened and the canister purge valve closed, applying a pressure on the fuel tank first and then the canister, when an absolute value of the fuel tank pressure is above a threshold; applying a pressure on the canister first and then the fuel tank, when the absolute value of the fuel tank pressure is below a threshold; indicating fuel tank isolation valve and/or canister purge valve degradation based on a change in the fuel tank pressure and the canister pressure following pressure application. - View Dependent Claims (2)
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3. A method of monitoring a vehicle fuel vapor recovery system including a fuel tank coupled to a canister, comprising,
under a first condition, applying a pressure in the fuel tank before applying the pressure on the canister; -
under a second condition, applying a vacuum on the canister before applying the vacuum on the fuel tank; and under either condition, indicating degradation based on a change in a fuel vapor recovery system pressure value upon application. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of monitoring flow of fuel vapors and/or air through a vehicle fuel vapor recovery system including a fuel tank with a refueling valve on an outer body of a vehicle, the fuel tank coupled to a canister and an engine, the canister coupled to an engine intake, and further coupled to a vacuum accumulator, the engine coupled to a battery and selectively operated in response to a battery state of charge falling below a threshold, the method comprising,
during a first engine-off condition, when a fuel tank absolute pressure is greater than a threshold, applying a pressure on the fuel tank before applying a pressure on the canister; -
during a second engine-off condition, when a fuel tank absolute pressure is lower than the threshold, monitoring a change in fuel tank and canister pressure upon applying a pressure on the canister before applying a pressure on the fuel tank; and during the first engine-off condition or the second engine-off condition, indicating degradation based on a monitored change in fuel tank and canister pressure. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification