Method and system for fuel vapor control
First Claim
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1. A method of monitoring a fuel vapor recovery system, comprising,modulating a fuel tank isolation valve (FTIV) coupled between a fuel tank and a canister of the fuel vapor recovery system;
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Abstract
Methods and systems are provided for monitoring a fuel vapor recovery system including a fuel tank isolation valve coupled between a fuel tank and a canister. During selected conditions, the valve is modulated and pressure pulsations in the fuel vapor recovery system are monitored. Valve degradation is identified based on correlations between the valve modulation and the resultant pressure pulsations.
11 Citations
16 Claims
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1. A method of monitoring a fuel vapor recovery system, comprising,
modulating a fuel tank isolation valve (FTIV) coupled between a fuel tank and a canister of the fuel vapor recovery system; - and
indicating FTIV degradation based on pressure pulsations upstream and/or downstream of the FTIV responsive to the modulation, wherein the modulation is performed during an engine-off condition in response to obtaining a threshold pressure difference across the FTIV, and wherein the modulation includes intermittently opening the FTIV with a duty cycle based on a bandwidth of the valve, wherein an increased modulation duty cycle is applied during higher pressure differential conditions relative to the threshold pressure difference, and a decreased modulation duty cycle is applied during lower pressure differential conditions relative to the threshold pressure difference. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of monitoring a fuel vapor recovery system, comprising,
modulating a fuel tank isolation valve (FTIV) coupled between a fuel tank and a canister of the fuel vapor recovery system; - and
indicating FTIV degradation based on pressure pulsations upstream and downstream of the FTIV responsive to the modulation, wherein the modulation is a periodic modulation at a selected frequency, and the indication is based on an amplitude of the pressure pulsations at the selected frequency. - View Dependent Claims (8, 9, 10, 11)
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12. A method of operating a fuel vapor recovery system including a fuel tank coupled to a canister through a fuel tank isolation valve, comprising,
during a first engine-off diurnal cycle, with a pressure difference across the valve being higher than a threshold, modulating the valve with a duty cycle based on a bandwidth of the valve, the modulating including intermittently opening the valve with the duty cycle; - and
indicating valve degradation based on pressure pulsations upstream and/or downstream of the valve responsive to the modulation; and during a second engine-off diurnal cycle, immediately following the first diurnal cycle, performing a leak detection operation if no valve degradation is indicated in the first diurnal cycle. - View Dependent Claims (13, 14, 15, 16)
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Specification