Method and system for control of an EGR valve during lean operation in a boosted engine system
First Claim
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1. A method, comprising:
- while operating an engine with an air-fuel ratio adjusted to be leaner than stoichiometry, in response to exhaust air-fuel ratio being leaner than a threshold, closing an EGR valve, the threshold increased as an engine speed and load increases.
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Abstract
Methods and systems are provided for reducing EGR estimation errors during lean engine operating conditions. During lean engine operation, EGR is disabled if the estimated exhaust air-fuel ratio becomes leaner than a lean threshold. The lean threshold is adjusted based on an upper limit of EGR errors that may be tolerated by the engine at a given engine speed and load.
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Citations
19 Claims
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1. A method, comprising:
while operating an engine with an air-fuel ratio adjusted to be leaner than stoichiometry, in response to exhaust air-fuel ratio being leaner than a threshold, closing an EGR valve, the threshold increased as an engine speed and load increases. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for an engine, comprising:
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flowing low pressure EGR; and in response to an exhaust air-fuel ratio becoming leaner than a threshold based on engine speed and load, disabling the EGR; and while disabling the EGR, suspending a counter of an EGR monitor. - View Dependent Claims (14, 15, 16)
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17. An engine system, comprising:
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an engine with an intake and an exhaust; an EGR system including an EGR passage for recirculating exhaust residuals from the exhaust to the intake via an EGR valve; an EGR monitor including a counter; an intake oxygen sensor coupled to the intake, upstream of an intake throttle and downstream of an outlet of the EGR passage, the intake oxygen sensor configured to estimate one or more of a combustion air-fuel ratio and EGR; an exhaust oxygen sensor coupled to the exhaust, upstream of an emission control device, the exhaust oxygen sensor configured to estimate an exhaust air-fuel ratio; and a controller with computer readable instructions for; flowing EGR based on engine speed and load; during the flowing, incrementing the counter in response to an indication of EGR system error; and in response to the exhaust air-fuel ratio rising above a lean threshold, closing the EGR valve; and suspending the counter. - View Dependent Claims (18, 19)
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Specification