Correlation based fuel tank leak detection
First Claim
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1. A method for an engine, comprising:
- sealing a fuel tank by closing a fuel tank isolation valve; and
while the fuel tank is sealed and the engine is off,indicating fuel system degradation based on a comparison of a first correlation coefficient, determined based on a change in fuel tank pressure and a change in fuel tank temperature, to a second correlation coefficient determined based on a change in ambient pressure and a change in ambient temperature;
the fuel tank pressure and the fuel tank temperature measured from a fuel tank pressure sensor and a fuel tank temperature sensor, respectively; and
the ambient pressure and ambient temperature measured from an ambient pressure sensor and an ambient temperature sensor, respectively,wherein determining the first correlation coefficient includes determining if a fuel tank temperature entropy is greater than an entropy threshold;
wherein determining the first correlation coefficient further includes determining a first covariance between fuel tank temperature and fuel tank pressure based on recursive estimates of mean fuel tank temperature and mean fuel tank pressure over a duration, and determining recursive estimates of standard deviation of fuel tank temperature and standard deviation of fuel tank pressure over the duration; and
wherein determining the second correlation coefficient includes determining a second covariance between ambient temperature and ambient pressure based on recursive estimates of mean ambient temperature and mean ambient pressure over the duration, and determining recursive estimates of standard deviation of ambient temperature and standard deviation of ambient pressure over the duration.
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Abstract
A method for an engine, comprising: sealing a fuel tank; and indicating fuel system degradation based on a comparison of a first correlation coefficient, determined based on a change in fuel tank pressure and a change in fuel tank temperature, to a second correlation coefficient determined based on a change in ambient pressure and a change in ambient temperature. In this way, leak tests, such as engine-off natural vacuum tests, may be performed without knowledge of the properties of the fuel stored in the fuel tank.
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Citations
20 Claims
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1. A method for an engine, comprising:
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sealing a fuel tank by closing a fuel tank isolation valve; and while the fuel tank is sealed and the engine is off, indicating fuel system degradation based on a comparison of a first correlation coefficient, determined based on a change in fuel tank pressure and a change in fuel tank temperature, to a second correlation coefficient determined based on a change in ambient pressure and a change in ambient temperature; the fuel tank pressure and the fuel tank temperature measured from a fuel tank pressure sensor and a fuel tank temperature sensor, respectively; and the ambient pressure and ambient temperature measured from an ambient pressure sensor and an ambient temperature sensor, respectively, wherein determining the first correlation coefficient includes determining if a fuel tank temperature entropy is greater than an entropy threshold; wherein determining the first correlation coefficient further includes determining a first covariance between fuel tank temperature and fuel tank pressure based on recursive estimates of mean fuel tank temperature and mean fuel tank pressure over a duration, and determining recursive estimates of standard deviation of fuel tank temperature and standard deviation of fuel tank pressure over the duration; and wherein determining the second correlation coefficient includes determining a second covariance between ambient temperature and ambient pressure based on recursive estimates of mean ambient temperature and mean ambient pressure over the duration, and determining recursive estimates of standard deviation of ambient temperature and standard deviation of ambient pressure over the duration. - View Dependent Claims (2, 3, 4, 5, 6, 7, 20)
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8. A method for testing a vehicle fuel tank for leaks, comprising:
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sealing the vehicle fuel tank by closing a canister vent valve and a canister purge valve; while the fuel tank is sealed and an engine coupled to the fuel tank is off, determining whether a fuel tank fill level is between a first fill level limit and a second fill level limit; monitoring fuel tank temperature, fuel tank pressure, ambient temperature, and ambient pressure for a duration based on indications from a fuel tank temperature sensor, a fuel tank pressure sensor, an ambient temperature sensor, and an ambient pressure sensor, respectively; determining entropy levels for fuel tank temperature, fuel tank pressure, ambient temperature, and ambient pressure over the duration; determining recursive means and standard deviations for fuel tank temperature, fuel tank pressure, ambient temperature, and ambient pressure over the duration; determining a first correlation coefficient based on the recursive means and standard deviations for fuel tank pressure and fuel tank temperature over the duration; determining a second correlation coefficient based on the recursive means and standard deviations for ambient pressure and ambient temperature over the duration; and indicating a fuel tank leak if the first correlation coefficient is less than the second correlation coefficient. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A system for a vehicle, comprising:
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a fuel tank temperature sensor coupled to a fuel tank; a fuel tank pressure sensor coupled to the fuel tank; a fuel level sensor coupled within the fuel tank; an ambient temperature sensor; an ambient pressure sensor; one or more valves configured to seal the fuel tank when closed; and a controller configured with instructions stored in non-transitory memory, that when executed cause the controller to; seal the fuel tank; while the fuel tank is sealed and the engine is off, determine whether a fuel tank fill level is between a first fill level limit and a second fill level limit based on indications from the fuel level sensor; monitor fuel tank temperature, fuel tank pressure, ambient temperature, and ambient pressure for a duration based on indications from the fuel tank temperature sensor, the fuel tank pressure sensor, the ambient temperature sensor, and the ambient pressure sensor, respectively; determine entropy levels for fuel tank temperature, fuel tank pressure, ambient temperature, and ambient pressure over the duration; determine recursive means and standard deviations for fuel tank temperature, fuel tank pressure, ambient temperature, and ambient pressure over the duration; determine a first correlation coefficient based on the recursive means and standard deviations for fuel tank pressure and fuel tank temperature over the duration; determine a second correlation coefficient based on the recursive means and standard deviations for ambient pressure and ambient temperature over the duration; and indicate a fuel tank leak if the first correlation coefficient is less than the second correlation coefficient. - View Dependent Claims (16, 17, 18, 19)
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Specification