Method to diagnose SCR catalyst
First Claim
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1. A method for an engine including a SCR catalyst, the method comprising:
- for a vehicle in motion;
in response to SCR temperature below a first threshold;
monitoring SCR conversion efficiency in a first mode based on NOx-in and NOx-out concentrations, but without adjusting engine operation to artificially increase feedgas NOx;
in response to SCR temperature above the first threshold, artificially increasing feedgas NOx by adjusting an EGR valve to reduce EGR flow, and monitoring SCR conversion efficiency in a second mode based on NOx-in and NOx-out concentrations; and
indicating SCR degradation based on the monitored conversion efficiency from each of the first and second modes.
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Abstract
Methods and systems are described for an engine with a SCR system including NOx sensors upstream and downstream of catalyst. One method includes monitoring SCR performance via calculating SCR conversion efficiency at different catalyst temperatures. Further, feedgas NOx levels are artificially increased when SCR device temperature is above a threshold to obtain more reliable readings from NOx sensors.
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Citations
20 Claims
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1. A method for an engine including a SCR catalyst, the method comprising:
for a vehicle in motion; in response to SCR temperature below a first threshold;
monitoring SCR conversion efficiency in a first mode based on NOx-in and NOx-out concentrations, but without adjusting engine operation to artificially increase feedgas NOx;in response to SCR temperature above the first threshold, artificially increasing feedgas NOx by adjusting an EGR valve to reduce EGR flow, and monitoring SCR conversion efficiency in a second mode based on NOx-in and NOx-out concentrations; and indicating SCR degradation based on the monitored conversion efficiency from each of the first and second modes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for monitoring performance of a SCR catalyst in an engine with NOx sensors, the method comprising:
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operating the engine in a first mode when SCR temperature is below a first threshold and monitoring SCR conversion efficiency; operating the engine in a second mode when SCR temperature is above the first threshold and feedgas NOx concentration is above a threshold, by artificially increasing feedgas NOx by a first amount and monitoring SCR conversion efficiency; operating the engine in the second mode when SCR temperature is above the first threshold and feedgas NOx concentration is below the threshold, by increasing feedgas NOx by a second amount, the second amount greater than the first amount, and monitoring SCR conversion efficiency; and indicating SCR degradation based on cumulative monitored efficiency of the two modes. - View Dependent Claims (10, 11, 12)
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13. A system for an engine in a vehicle comprising:
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a SCR catalyst; one or more NOx sensors; and a controller with computer readable instructions stored in non-transitory memory for; when the vehicle is travelling; during a first condition, when SCR catalyst temperature is below a first threshold, evaluating SCR conversion efficiency in a first mode based on NOx-in and NOx-out concentrations; and during a second condition, when SCR catalyst temperature is above the first threshold, artificially raising feedgas NOx levels, the artificial NOx increase being smaller when feedgas NOx concentration is greater than a threshold, and being larger when feedgas NOx concentration is smaller than the threshold; and monitoring SCR conversion efficiency in a second mode based on NOx-in and NOx-out concentrations. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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Specification