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.
7 Citations
17 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, the modulation being a periodic modulation at a selected frequency and the indication based on an amplitude of the pressure pulsations at the selected frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An emission control system, comprising,
a fuel tank; -
a canister configured to store fuel vapors, a fuel tank isolation valve coupled between the fuel tank and the canister; 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 a first engine-off diurnal cycle, when a pressure difference across the valve is greater than a pressure threshold, modulating the valve (FTIV) with a duty cycle; indicating valve degradation based on pressure pulsations estimated by the first and/or second pressure sensor responsive to the modulation; disabling leak detection of the emission control system during a second, subsequent engine-off diurnal cycle in response to an indication of valve degradation; and enabling leak detection of the emission control system during the second diurnal cycle in response to an indication of no valve degradation, wherein a frequency of the modulation is based on a bandwidth of the valve, and the duty cycle of the modulation is based on the pressure difference across the valve. - View Dependent Claims (10, 11, 12, 13)
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14. 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; - 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 (15, 16, 17)
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Specification