Patent Application
20150361913
This disclosure is related to controlling internal combustion engines using wide-range air/fuel ratio sensors.
The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Compression-ignition internal combustion engines operate at lean air/fuel ratios to achieve desirable fuel efficiencies. Lean engine operation may produce oxides of nitrogen (NOx) when nitrogen and oxygen molecules present in engine intake air disassociate in the high temperatures of combustion. Rates of NOx production follow known relationships in the combustion process, for example, with higher rates of NOx production being associated with higher combustion temperatures and longer exposure of air molecules to the higher temperatures. NOx molecules may be reduced to elemental nitrogen and oxygen in aftertreatment devices. Efficiency and efficacy of known aftertreatment devices is dependent upon operating conditions including operating temperature, which is associated with exhaust gas flow temperatures and engine air/fuel ratio.
Aftertreatment systems include catalytic devices to carry out chemical reactions to purify and otherwise treat exhaust gas constituents. Lean NOx trap catalysts store NOx when an engine is operating at a lean air/fuel ratio, and subsequently purge and reduce the stored NOx to nitrogen and water during rich engine operating conditions. Diesel particulate filters (DPF) are able to trap particulate matter in the exhaust gas feedstream, which may then be periodically purged, e.g., during high temperature regeneration events.
A selective catalytic reaction device (SCR) includes catalytic material that promotes the reaction of NOx with a reductant such as ammonia (NH3) or urea to produce nitrogen and water. Reductants, e.g., urea, may be injected into an exhaust gas feedstream upstream of the SCR device. Reductants, e.g., NH3, may be generated in an exhaust gas feedstream upstream of the SCR device during specific engine operating conditions. An engine operating at a rich air/fuel ratio to purge and reduce stored NOx or operating to generate reductants can negatively affect engine fuel efficiency.
A method for controlling an internal combustion engine includes commanding operation of the engine at a selected air/fuel ratio and adjusting a signal output from a lambda sensor corresponding to the selected air/fuel ratio. A controller executes control of the engine based upon the adjusted signal output from the lambda sensor corresponding to the selected air/fuel ratio.
One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,
The exhaust system 20 is illustrative, and includes a first aftertreatment device 30 fluidly coupled to a downstream second aftertreatment device 40. When the internal combustion engine 10 is a compression-ignition engine, the first aftertreatment device 30 can be a lean NOx adsorber or trap (LNT) and the second aftertreatment device 40 can be a particulate filter in one embodiment. Alternatively, the first aftertreatment device 30 can be a lean NOx adsorber or trap (LNT) and the second aftertreatment device 40 can be a particulate filter coupled with a selective catalytic reactor (SCR) device. When the internal combustion engine 10 is a spark-ignition engine, the first aftertreatment device 30 can be an oxidation catalyst and the second aftertreatment device 40 can be a selective catalytic reactor (SCR) device in one embodiment. These exhaust configurations are illustrative. Other exhaust aftertreatment devices can be employed as substitutes for or in addition to the described aftertreatment devices. The catalyst element in the form of a lean NOx adsorber or trap (LNT) includes a substrate element coated with a washcoat that is capable of adsorbing and desorbing and reducing NOx molecules. The substrate element is coated with a washcoat including platinum-group metal catalysts, barium, and ceria in one embodiment.
The exhaust system 20 also includes one or a plurality of sensors that monitor the exhaust gas feedstream at various locations in the exhaust system 20. As shown, the sensors include a first sensor 51 configured to monitor the exhaust gas feedstream at an engine-out location, a second sensor 52 configured to monitor the exhaust gas feedstream downstream of the first aftertreatment device 30, and a third sensor 53 configured to monitor the exhaust gas feedstream downstream of the second aftertreatment device 40. Each of the sensors 51, 52, 53 signally connects to controller 60, and the signals are employed to control the engine 10 and monitor operation of the engine 10 and the various elements of the exhaust system 20 for purposes related to control under various operating conditions and related to fault detection and root-cause diagnosis.
One or more of the sensors 51, 52, 53 is a wide-range air/fuel ratio (lambda) sensor that generates a signal output that is monitored by a signal processor, with the signal processor generating an output signal that is responsive to air/fuel ratio of the sensed feedstream. The signal processor for a lambda sensor may be a stand-alone controller that signally connects to the controller 60, or may be incorporated into the controller 60. A change in air/fuel ratio generates a corresponding change in the output signal from the sensor that can be employed in engine control and monitoring routines. Construction and configuration of lambda sensors and accompanying signal processors is known and not described in further detail herein.
A lambda sensor generates a signal output under lean air/fuel ratio conditions (i.e., λ≧1.05) that has high correlation with measurement by a bench analyzer. Thus, a signal output from a lambda sensor measuring air/fuel ratio based upon measured oxygen (O2) correlates with an air/fuel ratio calculated from measured exhaust gas constituents from a bench analyzer with minimal error. At stoichiometry and rich air/fuel ratios (λ≦1.0) there can be a significant difference between O2 measured by a lambda sensor and O2 measured by a bench analyzer. As shown with reference to
The general lambda sensor calculation can be represented in accordance with the following relationship:
λ=[O2]*α+[CO]*β+[HC]*γ+[PM]*δ+[H2]*ε [1]
During lean engine operation, contributions of CO, HC, PM and H2 are almost negligible, but when λ<1.05, their contributions increase due to increased concentrations in the exhaust gas feedstream. H2 and CO molecules are relatively small, with rapid diffusion through a lambda test cell, whereas HC and PM molecules are relatively large, with corresponding slower diffusion through the lambda test cell. When there are high concentrations of HC, CO and PM, available O2 is used for oxidation. Thus, the lambda sensor may not be capable of sensing all the oxygen in the gas mixture. During LNT DeNOx regeneration, high amounts of NH3, H2 and HCs downstream of the catalyst have been measured. Thus, knowledge of cross-sensitivity between measured lambda value downstream of a LNT and the concentration of H2, HCs and NH3 is useful for adjusting signal measurement of a lambda sensor in rich conditions.
Control module, module, control, controller, control unit, processor and similar terms mean any one or various combinations of one or more of Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s) (preferably microprocessor(s)) and associated memory and storage (read only, programmable read only, random access, hard drive, etc.) executing one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, appropriate signal conditioning and buffer circuitry, and other components to provide the described functionality. Software, firmware, programs, instructions, routines, code, algorithms and similar terms mean any instruction sets including calibrations and look-up tables. The controller has a set of control routines executed to provide the desired functions. Routines are executed, such as by a central processing unit, and are operable to monitor inputs from sensing devices and other networked control modules, and execute control and diagnostic routines to control operation of actuators. Routines may be executed at regular intervals, for example each 100 microseconds, 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, routines may be executed in response to occurrence of an event.
The results shown with reference to
The engine control routine 600 executes by selecting an air/fuel ratio for engine operation, i.e., selecting λ (602) and determining if the selected air/fuel ratio is rich, i.e., is λ<1.0 (604). Engine operating conditions in which a rich air/fuel ratio may be selected include, by way of example, conditions associated with regenerating an exhaust aftertreatment device such as a lean NOx adsorber. By way of example only, a selected air/fuel ratio for engine operation may include commanding operation of the engine at a rich air/fuel ratio to effect regeneration of an exhaust aftertreatment device such as a lean NOx adsorber fluidly coupled to an exhaust outlet of the internal combustion engine, with the selected rich air/fuel ratio having a magnitude of λ=0.95 in one embodiment. When the selected air/fuel ratio is not rich, i.e., when λ≧1.0 (604)(0), engine operation is controlled to the selected air/fuel ratio employing a non-adjusted signal output from the lambda sensor. Engine control has been shown to be unaffected by cross-sensitivity between the measured air/fuel ratio and exhaust gases produced as a byproduct of combustion under lean air/fuel ratio operating conditions. Thus, no adjustment to the signal output from the lambda sensor is necessary (620).
When the selected air/fuel ratio is rich, i.e., when λ<1.0 (604)(1), engine operation is controlled to the selected air/fuel ratio employing an adjusted signal output from the lambda sensor. Adjusting the signal output from the lambda sensor corresponding to the selected air/fuel ratio under rich operation includes determining an expected exhaust gas hydrogen concentration at the selected air/fuel ratio, and determining a shift in an expected signal output from the lambda sensor at the selected air/fuel ratio based upon the expected exhaust gas hydrogen concentration (606). The shift in the expected signal output from the lambda sensor at the selected air/fuel ratio based upon the expected exhaust gas hydrogen concentration can be determined from data collected on a representative system that includes lambda sensor signal variation (%) in relation to hydrogen concentration (%). By way of illustration,
Alternatively, or in addition, adjusting the signal output from the lambda sensor corresponding to the selected air/fuel ratio under rich operation can include determining an expected concentration of a selected exhaust gas constituent, e.g., ammonia or a hydrocarbon, at the selected air/fuel ratio, and determining a shift in an expected signal output from the lambda sensor at the selected air/fuel ratio based upon the expected concentration of the selected exhaust gas constituent. Alternatively, or in addition, adjusting the signal output from the lambda sensor corresponding to the selected air/fuel ratio under rich operation can include determining expected concentrations of a plurality of selected exhaust gas constituents, e.g., hydrogen, ammonia and hydrocarbons, at the selected air/fuel ratio, and determining a shift in an expected signal output from the lambda sensor at the selected air/fuel ratio based upon the expected concentrations of the plurality of selected exhaust gas constituents.
The signal output from the lambda sensor is adjusted based upon the shift in the expected signal output from the lambda sensor (608). Engine operation is controlled to the selected air/fuel ratio employing the adjusted signal output from the lambda sensor to accommodate the cross-sensitivity between the measured air/fuel ratio and exhaust gases produced as a byproduct of combustion under rich air/fuel ratio operating conditions (610). This may include executing a closed-loop control of the engine employing the adjusted signal output from the lambda sensor as a feedback signal corresponding to the selected air/fuel ratio, thus causing the engine to adjust engine fueling in response to the adjusted signal output from the lambda sensor. Thus, engine operation can be controlled to the selected air/fuel ratio employing the adjusted signal output from the lambda sensor
By way of example, control, monitoring and diagnostics of an LNT are based on the information coming from lambda sensors located both upstream and downstream of the LNT. The lambda sensor output voltage is influenced by the reducing species concentration, such as carbon monoxide (CO), HCs and hydrogen whereas ammonia does not significantly influence the lambda sensor outputs. The adjusted signal output from the lambda sensor is used to ensure that the air/fuel ratio control through the lambda sensor in a rich environment works as intended to achieve a target lambda value within known accuracy. The adjusted signal output from the lambda sensor can be in the form of a correction factor that is determined based upon cross-sensitivity with respect to H2 for lambda sensor reading adjustment during LNT regeneration events under rich air/fuel ratio operating conditions.
The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
