Abstract: A method for determining the efficiency of a three-way catalyst is presented. It is shown that more accurate results are achieved if the efficiency estimates are performed when the engine is at idle or during low load operating conditions. The efficiency is inferred from the amount of fuel required to purge the device after it has been fully saturated with oxidants due to lean operation. Due to improved accuracy and reduced reductant waste, this method allows for improved emission control and fuel efficiency.

Abstract: A method for monitoring efficiency of an exhaust gas aftertreatment device is presented. The efficiency is inferred from the amount of fuel required to perform purge of the device after it has been saturated with exhaust gas components such as NOx and oxygen to a predetermined level. The level of saturation is determined from the amount of tailpipe emissions as indicated by the tailpipe exhaust gas sensor. This method improves precision in determining device efficiency and therefore eliminates unnecessary sulfur purges and improves fuel economy. Also, better emission control is achieved since the tailpipe exhaust gas sensor allows closed loop monitoring of NOx emissions and prevents the device from overfilling.

Abstract: An improved method for monitoring an efficiency of a three-way catalyst coupled in an exhaust passage of an internal combustion engine is presented. First, a reference efficiency estimate (shortly after a SOx purge) is generated based on several data points obtained during normal vehicle driving conditions over varying device temperatures. Next, a current efficiency estimate is obtained from several data points. The two estimates are compared to obtain a measure of reduction in the catalyst efficiency due to device sulfation.

Abstract: A method and system are provided for adjusting an amount of fuel provided to an internal combustion engine based on an output signal from an exhaust gas oxygen sensor positioned downstream of an emission control device. The output signal from the exhaust gas oxygen sensor is compared to a set point reference value. The set point reference value is varied as a function of time, preferably according to a set point waveform that oscillates around an average set point. The average set point may either be a pre-determined constant or it may be determined based on at least one engine operating parameter. An electronic engine controller adjusts the amount of fuel provided to the engine based on the result of the comparison between the output signal of the exhaust gas oxygen sensor and the set point reference value.

Abstract: An engine air/fuel controller is responsive to an exhaust gas oxygen sensor positioned upstream of a catalytic converter and a proportional exhaust gas oxygen sensor positioned downstream of the catalytic converter. An air/fuel ratio signal provided by the downstream exhaust gas oxygen sensor is adjusted by a correction bias value. A first preferred method of deriving the correction bias value includes calculating the difference between the average of the upstream and downstream air/fuel ratios when the upstream sensor indicates lean operation of the engine. The second preferred method includes deriving the correction bias according a pre-determined and pre-programmed correction bias function, which provides correction bias values as a function of the of the air/fuel ratio measured by the downstream sensor.

Abstract: A method for improving a purge conversion efficiency of a Lean NOx Trap coupled downstream of a lean-burn internal combustion engine is presented. This method recognizes that during a purge of the LNT, its temperature increases due to the exothermic reactions in the LNT. Once the LNT temperature exceeds a certain threshold, further increases lead to a reduction in the NOx storage capacity, and therefore an increase in NOx emissions during the purge of the LNT. Therefore, it is proposed to cool the LNT temperature once the threshold is exceeded. This method improves emission control and fuel economy during purge.

Abstract: A method for obtaining an accurate cylinder air-charge estimate is presented. First, a sensor-based powertrain torque estimate is obtained. Next, a torque converter-based powertrain torque estimate is obtained when the torque converter clutch is unlocked. The two estimates are compared, and if they differ by more than a predetermined amount, sensor drift is diagnosed, and corrected.

Abstract: A method for improving a purge conversion efficiency of a Lean NOx Trap coupled downstream of a lean-burn internal combustion engine is presented. This method proposes adjusting the purge air-fuel ratio of the device based on its temperature. According to the proposed method, a less rich air-fuel ratio is provided at lower operating temperatures to reduce hydrocarbon emissions since within this temperature range air-fuel ratio does not have a significant affect on NOx emissions. At mid-range operating temperatures, the air-fuel ratio is gradually decreased (made more rich) to reduce NOx emissions. And, finally, at high operating temperatures, HC and NOx emissions are reduced, and therefore, the purge air-fuel is kept at a constant more rich value. This method improves emission control and fuel economy during purge.

Abstract: A method of optimizing vehicle emissions during lean engine operation is disclosed wherein an emission control device receiving engine exhaust gases is filled with one or more constituent gases of the exhaust gas to a predetermined fraction of the device storage capacity, and is then completely emptied during a subsequent purge. As the device storage capacity is substantially reduced, as indicated by an actual fill time becoming equal to or less than a predetermined minimum fill time, a device regeneration cycle is performed to attempt to restore device capacity. A programmed computer controls the fill and purge times based on the amplitude of the voltage of a switching-type oxygen sensor and the time response of the sensor. The frequency of the purge, which ideally is directly related to the device capacity depletion rate, is controlled so that the device is not filled beyond its storage capacity limit.

Abstract: A system and method is provided for controlling a lean-burn engine whose exhaust gas is directed through an exhaust treatment system which includes an emission control device that alternately stores and releases a selected constituent of the exhaust gas, such as NOx, based on engine operating conditions, and a downstream NOx sensor. The system estimates the concentration of NOx flowing into the device based on engine operating conditions while determining a value for the concentration of NOx flowing out of the device based upon the output signal generated by NOx sensor. A device purge event is scheduled when the device efficiency, calculated based on the NOx concentrations flowing into and out of the device, falls below a predetermined minimum efficiency value. The length of a purge event is determined as a function of an accumulated measure based on the difference between the NOx concentrations into and out of the device.

Abstract: A system and a method of controlling an engine during and after a temporary fueling shut-off during idling, deceleration or a switch to auxiliary power generating device is presented. According to this method, maintaining power to the heater of an exhaust gas sensor during the temporary shut-off, and thus keeping the sensor operational shortly following resumption of fueling can eliminate a delay in closed loop air-fuel ratio control. This method provides improvements to fuel economy and emission control.

Abstract: An exhaust gas treatment system for an internal combustion engine includes a three-way catalyst and a NOx device located downstream of the three-way catalyst. The device is preconditioned for emissions reduction at engine operating conditions about stoichiometry by substantially filling the device with oxygen and NOx; and purging stored oxygen and stored NOx from only an upstream portion of the device, whereupon the upstream portion of the device operates to store oxygen and NOx during subsequent lean transients while the downstream portion of the device operates to reduce excess HC and CO during subsequent rich transients.

Abstract: The invention relates to the performance evaluation of an oxygen gas sensor in a motor vehicle, where the oxygen gas sensor is used to measure the oxygen content of the combusted air fuel mixture of a motor vehicle exhaust. The method involves measuring the fall time for the detected oxygen level to fall to a pre-determined lower threshold after the fuel supply to the engine has been cut off, and if the measured fall time exceeds a pre-set time, producing an oxygen sensor degradation signal.

Abstract: A method for air/fuel operation of an engine. The engine is supplied fuel from both a fuel purging system to purge fuel in a fuel supply and feed such purged fuel to an intake manifold of the engine and a fuel injection system to inject fuel from such fuel supply into a cylinder of such engine. The method includes producing a first air/fuel ratio control signal in accordance with measured exhaust gas oxygen emission from the engine; producing a second air/fuel ratio control signal in accordance with fuel transport delay through the fuel purging system; combining the first and second air/fuel ratio control signals into a composite control signal; and feeding such composite control signal to the fuel injection system. Producing the first air/fuel ratio control signal comprises determining fuel flow rate through the purge system.

Abstract: A carbon monoxide sensor placed downstream of the catalytic converter and a temperature sensor placed upstream of the converter in a diesel engine provide information to build a real time CO conversion efficiency versus catalyst temperature curve to determine whether a catalyst has deteriorated beyond a predetermined point with respect to On-Board Diagnostic (OBD) requirements. Pre catalyst CO concentration is inferred from the engine operating conditions, and catalyst temperature is determined using the temperature sensor output and the engine exhaust flow heat transfer model. The real time curve is compared to a reference curve to determine catalyst performance. Catalyst performance with respect to CO conversions can then be correlated to that for HC and NOx to meet OBD requirements.

Abstract: A method and system are provided for adaptive control of a purge time and a fill time for an emission control device used to reduce emission of a selected constituent gas, such NOx, of an engine's generated exhaust gas, with optimization and adapting of stored values to reflect changes in device operating conditions. The invention determines a present value representative of the quantity of oxygen stored in the device, as well as a present value for the maximum device NOx-storage capacity to provide real-time adjustment of purge and fill time to achieve optimum overall operation of the device. The invention also periodically determines actual fill times which corresponding to optimal fill times to generate adaptive values for use during normal open-loop control.

Abstract: A method and system for controlling the operation of an internal combustion engine, wherein exhaust gas generated by the engine is directed through an emission control device, includes determining instantaneous rates of storage for a constituent of the exhaust gas, such as NOx, as well as the capacity reduction of the device to store the exhaust gas constituent as a function of a calculated value representing an amount of SOx which has accumulated in the device since a prior device-regeneration (desulfation) event. The calculated accumulated SOx value is also preferably used to schedule a device-regeneration event, as when the calculated accumulated SOx value exceeds a predetermined threshold value.

Abstract: A method and system for controlling the operation of a lean-burn engine whose exhaust gas is directed through an emission control device and a downstream reductant-concentration sensor, wherein a stored value for the device's instantaneous capacity to store a selected exhaust gas constituent, such as NOx, is periodically adaptively updated when the sensor's output signal falls outside a predetermined range during a device purge event. A device purge event is scheduled when an accumulated measure of instantaneous feedgas NOx concentration during lean engine operation exceeds the stored NOx-storage capacity value. The purge event is discontinued when the sensor's output signal exceeds the upper limit of the predetermined range, or when a determined value representing a cumulative amount of excess fuel supplied to the engine during the purge event exceeds a threshold value calculated based upon previous values for stored NOx and stored oxygen.

Abstract: An exhaust gas treatment system for an internal combustion engine includes a pair of upstream emission control devices which respectively receive the exhaust gas generated by a respective group of cylinders, and a single, shared downstream emission control device receiving catalyzed exhaust gas from each of the upstream emission control devices. After the downstream device stores a selected constituent gas generated when each cylinder group is operating “lean,” the downstream device is purged by operating the first cylinder group with a stoichiometric air-fuel mixture while operating the second cylinder group with a rich air-fuel mixture, such that the combined catalyzed exhaust gas flowing through the downstream device during the purge event has an air-fuel ratio slightly rich of stoichiometry. As a result, the invention improves overall vehicle fuel economy because only one of the upstream devices is purged of stored oxygen when purging the downstream device of previously-stored constituent gas.

Abstract: A method for diagnosing engine thermostat is presented. Indicated engine coolant temperature is estimated based on engine operating conditions, such as engine speed, net engine torque, air flow, fuel-air ratio, net engine torque, etc. This estimate is compared to the reading of the engine coolant temperature sensor in areas below the temperature at which the thermostat starts to open and above in order to detect degradation in the performance of the sensor or the engine thermostat. If the estimate and the reading agree in one area and disagree in the other, then the thermostat performance is degraded. If the estimate and the reading disagree in both temperature ranges, then the coolant sensor performance may be degraded.