Air/fuel mixture imbalance diagnostic systems and methods
View Patent ↗An air/fuel imbalance (AFIM) diagnostic system comprises a first module, an imbalance determination module, and an imbalance diagnostic module. The first module outputs imbalance data samples based on an oxygen signal provided by an oxygen sensor measuring oxygen in exhaust expelled from cylinders of a cylinder bank. The imbalance determination module determines an AFIM value based on the imbalance data samples. The imbalance diagnostic module selectively diagnoses an AFIM in the cylinder bank based on the AFIM value.
1. An air/fuel imbalance diagnostic system comprising:
a filtering module that receives an oxygen signal from an oxygen sensor, that selectively samples the oxygen signal, and that generates imbalance data samples using:
a Kalman filter;
estimates of the imbalance data samples generated based on a first matrix having elements that reflect a cyclical nature of imbalance data samples of an engine cycle;
oxygen signal data generated based on samples of the oxygen signal and samples of a reference oxygen signal determined based on an average of a predetermined number of oxygen signal samples; and
estimates of the oxygen signal data generated based on a second matrix having elements that reflect respective contributions of cylinders of a cylinder bank to the oxygen signal;
wherein the oxygen sensor measures oxygen in the exhaust from the cylinders of the cylinder bank;
an imbalance determination module that determines one air/fuel imbalance (AFIM) value for the entire cylinder bank based on a variance of a plurality of the imbalance data samples;
an imbalance diagnostic module that selectively indicates that an AFIM is present in the cylinder bank based on the AFIM value; and
a cylinder identification module that, in response to the imbalance diagnostic module indicating that the AFIM is present in the cylinder bank, attributes the AFIM to one of the cylinders of the cylinder bank.
2. The AFIM system of claim 1 wherein the imbalance diagnostic module indicates that the AFIM is present in the cylinder bank when the AFIM value is greater than a predetermined value.
3. The AFIM system of claim 1 wherein the imbalance determination module determines the AFIM value based on an average of a square of each of the imbalance data samples from a mean of the imbalance data samples.
4. The AFIM system of claim 1 wherein the imbalance determination module determines the AFIM value based on the equation:
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5. The AFIM system of claim 1 wherein the filtering module generates the imbalance data samples based on firing events of the cylinders.
6. The AFIM system of claim 1 wherein the filtering module outputs the imbalance data samples when each of the cylinders is fired and between when each of the cylinders is fired.
7. The AFIM system of claim 1 wherein the cylinder identification module commands a rich air/fuel mixture be supplied to a second one of the cylinders of the cylinder bank during a first engine cycle after the AFIM is indicated, that commands a lean air/fuel mixture be supplied to the second one of the cylinders during a second engine cycle after the AFIM is indicated, and that attributes the AFIM to the one of the cylinders of the cylinder bank based on imbalance data samples generated based on the first and second engine cycles.
8. An air/fuel imbalance (AFIM) diagnostic method comprising:
receiving an oxygen signal from an oxygen sensor, wherein the oxygen sensor measures oxygen in exhaust from cylinders of a cylinder bank;
selectively sampling the oxygen signal;
generating imbalance data samples using:
a Kalman filter;
estimates of the imbalance data samples generated based on a first matrix having elements that reflect a cyclical nature of imbalance data samples of an engine cycle;
oxygen signal data generated based on samples of the oxygen signal and samples of a reference oxygen signal determined based on an average of a predetermined number of oxygen signal samples; and
estimates of the oxygen signal data generated based on a second matrix having elements that reflect respective contributions of cylinders of a cylinder bank to the oxygen signal;
determining one air/fuel imbalance (AFIM) value for the entire cylinder bank based on a variance of a plurality of the imbalance data samples;
selectively indicating that an AFIM is present in the cylinder bank based on the AFIM value; and
attributing the AFIM to one of the cylinders of the cylinder bank in response to the indicating that the AFIM is present in the cylinder bank.
9. The AFIM diagnostic method of claim 8 further comprising indicating that the AFIM is present in the cylinder bank when the AFIM value is greater than a predetermined value.
10. The AFIM diagnostic method of claim 8 further comprising determining the AFIM value based on an average of a square of each of the imbalance data samples from a mean of the imbalance data samples.
11. The AFIM diagnostic method of claim 8 further comprising determining the AFIM value based on the equation:
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12. The AFIM diagnostic method of claim 8 further comprising generating the imbalance data samples based on firing events of the cylinders.
13. The AFIM diagnostic method of claim 8 further comprising generating the imbalance data samples when each of the cylinders is fired and between when each of the cylinders is fired.
14. The AFIM diagnostic method of claim 8 further comprising:
commanding a rich air/fuel mixture be supplied to a second one of the cylinders of the cylinder bank during a first engine cycle after the AFIM is indicated;
commanding a lean air/fuel mixture be supplied to the second one of the cylinders during a second engine cycle after the AFIM is indicated; and
attributing the AFIM to the one of the cylinders of the cylinder bank based on imbalance data samples generated based on the first and second engine cycles.