Exhaust gas sensor control adaptation for asymmetric sensor degradation

Abstract

The present disclosure provides "Exhaust Gas Sensor Control Adaptation for Asymmetric Sensor Degradation." Methods and systems are provided for converting an asymmetric sensor response of an exhaust gas sensor to a symmetric response. In one example, a method includes adjusting fuel injection in response to a modified exhaust gas oxygen feedback signal from an exhaust gas sensor, wherein the modified exhaust gas oxygen feedback signal is modified by converting the asymmetric response of the exhaust gas sensor to a symmetric response. Additionally, the method may include adapting parameters of a look-ahead controller of the exhaust gas sensor based on the modified symmetric response.

Description

Technical Field

[0001] The present description generally relates to methods and systems for controlling the air-fuel ratio of an internal combustion engine based on a modified response from an exhaust gas sensor having asymmetric sensor degradation.

[0002] Background Art / Summary of the Invention

[0003] Exhaust gas sensors can be positioned in a vehicle's exhaust system to detect the air-fuel ratio of gases exhausted from an internal combustion engine. For example, exhaust gas sensor readings can be fed back to a controller to adjust the engine's air-fuel ratio by modifying the amount of fuel injected from the engine's fuel injectors.

[0004] Exhaust gas sensor degradation can lead to engine control degradation, resulting in increased emissions and / or reduced vehicle drivability. Specifically, exhaust gas sensors can exhibit a number of discrete degradation types. Sensor degradation types can be grouped into filter-type degradation and delay-type degradation. Furthermore, sensor degradation types can be symmetric or asymmetric. For example, a sensor with asymmetric sensor degradation can have different response dynamics (such as response time or response rate) when the sensor response increases compared to when the sensor output decreases.

[0005] Previous approaches to addressing sensor degradation include equipping exhaust gas sensors with look-ahead controllers to correct or compensate for degradation. For example, look-ahead controller parameters can be adjusted based on the type of sensor degradation. Additionally, to maintain look-ahead controller system stability, the gain of the controller's feedback control routine, such as a proportional / integral control routine, can be actively reduced to reduce system instability.

[0006] However, the present inventors have recognized potential issues with such systems. For example, adjusting the parameters of the look-ahead controller may not account for the asymmetric dynamics of the sensor response during rich-to-lean and lean-to-rich transitions. This can result in asymmetric engine operation when the commanded air-fuel ratio transitions in different directions (e.g., from rich to lean and from lean to rich). Consequently, more or less fuel may be delivered in the degraded direction, potentially increasing CO or NOx emissions.

[0007] In one example, the aforementioned issues can be addressed by a method comprising: sensing air-fuel ratio via an exhaust gas sensor; generating a modified air-fuel ratio having a symmetrical response based on the sensed air-fuel ratio in response to an asymmetric sensor response; and adjusting fuel injection based on the modified air-fuel ratio. In this manner, a look-ahead controller can similarly compensate for sensor degradation when the commanded air-fuel ratio transitions in both rich-to-lean and lean-to-rich directions, and asymmetric engine operation can be reduced.

[0008] As an example, a method may include: operating an engine at a commanded air-fuel ratio; and determining the type and magnitude of sensor degradation by comparing the sensed air-fuel ratio to the commanded air-fuel ratio. An exhaust gas sensor may be determined to exhibit asymmetric sensor degradation when a response rate and / or response time of the sensor response differ in response to transitions in different directions (e.g., from rich to lean or from lean to rich) in response to the commanded air-fuel ratio. While the response rate or response time differs from expected values, if the response rate and response time are the same in response to transitions in different directions of the commanded air-fuel ratio, the exhaust gas sensor may exhibit symmetric sensor degradation. In response to asymmetric sensor degradation, a modified sensor response may be formulated by introducing a lower response rate and an increased response time (e.g., modifying the sensor reading to be symmetric) compared to a non-faulty portion of the sensed air-fuel ratio. Thus, the modified sensor response may have the same response rate and / or response time when the commanded air-fuel ratio transitions in each of an increasing and decreasing direction. Thus, the modified sensor response is more symmetric relative to the sensed air-fuel ratio. The modified sensor response can then be fed into a look-ahead controller with parameters adapted based on sensor degradation. In this way, the look-ahead controller can operate more symmetrically and more efficiently to account for sensor degradation during rich-to-lean and lean-to-rich transitions. Additionally, controller calibration effort can be reduced, and engine NOx and CO emissions can be reduced.

[0009] It should be understood that the above Summary is provided to introduce a selection of some concepts further described in the Detailed Description in a simplified form. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims that follow the Detailed Description. Furthermore, the claimed subject matter is not limited to implementations that address any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A schematic diagram of an embodiment of an engine system of a vehicle including an exhaust gas sensor is shown.

[0011] Figure 2 A graph indicating symmetric filter-type sensor degradation of an exhaust gas sensor is shown.

[0012] Figure 3 A graph indicating asymmetric rich-to-lean filter type sensor degradation of an exhaust gas sensor is shown.

[0013] Figure 4 A graph indicating sensor degradation of an asymmetric lean-to-rich filter type of exhaust gas sensor is shown.

[0014] Figure 5A graph indicating symmetric delay type sensor degradation of an exhaust gas sensor is shown.

[0015] Figure 6 A graph indicating asymmetric rich-to-lean delay type sensor degradation of an exhaust gas sensor is shown.

[0016] Figure 7 A graph indicating asymmetric lean-to-rich delay type sensor degradation of an exhaust gas sensor is shown.

[0017] Figure 8 A graph showing an example response of a degraded exhaust gas sensor to a commanded air-fuel ratio is shown.

[0018] Figure 9 A high level flow chart of an example method of controlling the air / fuel ratio of an engine is shown.

[0019] Figure 10 An example method for converting a sensor response having an asymmetric type of degradation to a symmetric response is shown.

[0020] Figure 11 An example of a modified sensor response from an asymmetric rich to lean delayed sensor response transition is shown.

[0021] Figure 12 An example of a modified sensor response transitioning from an asymmetric rich to lean filtered sensor response is shown.

[0022] Figure 13 is a flow chart illustrating a method for adapting parameters of a PI controller and a look-ahead controller. DETAILED DESCRIPTION

[0023] The following description relates to a system and method for controlling the air-fuel ratio of an internal combustion engine cylinder based on feedback from an exhaust gas sensor. Specifically, the method includes adjusting fuel injection to compensate for an asymmetric response from a degraded exhaust gas sensor. Figure 1 An example embodiment of an engine system equipped with an exhaust gas sensor is shown. The sensor may present Figures 2 to 7 There are six types of degradation as shown in . Degradation can be classified into symmetrical sensor degradation ( Figure 2 and Figure 5 ) and asymmetric sensor degradation ( Figures 3 and 4 and Figures 6 and 7 Asymmetric sensor degradation may cause asymmetric engine operation in response to commanded air-fuel ratio transitions in different directions (e.g., from lean to rich and from rich to lean). Sensors with asymmetric degradation have different response dynamics when the sensed signal transitions in different directions. The dynamics of the sensor response can be quantified using parameters such as time delay, time constant, and line length, such as Figure 8 shown. Figure 9 An example method for air-fuel control is shown. The method includes modifying a sensor response and parameters of an exhaust gas sensor controller based on a type and magnitude of sensor degradation; and controlling fuel injection via the modified exhaust gas sensor controller based on the modified sensor response. Figure 10 A low-level flow chart for modifying an asymmetric sensor response to a symmetric response is shown. Figure 11 and Figure 12 Examples of the sensed air-fuel ratio and the modified air-fuel ratio in asymmetric delay type sensor degradation and asymmetric filter type sensor degradation, respectively. Figure 13 A process for adapting parameters of an exhaust gas sensor controller based on sensor degradation is shown.

[0024] Figure 1 1 is a schematic diagram illustrating one cylinder of multi-cylinder engine 10, which may be included in a propulsion system of a vehicle, wherein exhaust gas sensor 126 may be used to determine the air-fuel ratio of exhaust gas generated by engine 10. This air-fuel ratio (along with other operating parameters) may be used for feedback control of engine 10 in various operating modes. Engine 10 may be controlled at least partially by a control system including controller 12 and by input from a vehicle driver 132 via an input device 130. In this example, input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Combustion chamber (i.e., cylinder) 30 of engine 10 may include combustion chamber walls 32, with piston 36 positioned therein. Piston 36 may be coupled to crankshaft 40 such that reciprocating motion of the piston is converted into rotational motion of the crankshaft. Crankshaft 40 may be coupled to at least one drive wheel of the vehicle via an intermediate transmission system. Additionally, a starter motor may be coupled to crankshaft 40 via a flywheel to enable starting of engine 10.

[0025] Combustion chamber 30 can receive intake air from intake manifold 44 via intake passage 42 and can exhaust combustion gases via exhaust passage 48. A throttle valve 62, including a throttle plate 64, can be disposed between intake manifold 44 and intake passage 42 to vary the flow rate and / or pressure of intake air provided to the engine cylinders. Adjusting the position of throttle plate 64 can increase or decrease the opening of throttle valve 62, thereby varying the mass air flow rate, or the flow rate, of intake air entering the engine cylinders. For example, increasing the opening of throttle valve 62 can increase the mass air flow rate. Conversely, decreasing the opening of throttle valve 62 can decrease the mass air flow rate. In this manner, adjusting throttle valve 62 can adjust the amount of air entering combustion chamber 30 for combustion. For example, increasing the mass air flow rate can increase the torque output of the engine.

[0026] Intake manifold 44 and exhaust passage 48 can selectively communicate with combustion chamber 30 via respective intake valve 52 and exhaust valve 54. In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves. In this example, intake valve 52 and exhaust valve 54 may be controlled by cam actuation via respective cam actuation systems 51 and 53. Cam actuation systems 51 and 53 may each include one or more cams and may vary valve operation using one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems operable by controller 12. The position of intake valve 52 and exhaust valve 54 may be determined by position sensors 55 and 57, respectively. In alternative embodiments, intake valve 52 and / or exhaust valve 54 may be controlled by electric valve actuation. For example, cylinder 30 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and / or VCT systems.

[0027] Fuel injector 66 is shown arranged in intake manifold 44 in a configuration that provides what is known as port injection of fuel into the intake port upstream of combustion chamber 30. Fuel injector 66 may inject fuel in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 68. Fuel may be delivered to fuel injector 66 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber 30 may alternatively or additionally include a fuel injector coupled directly thereto to inject fuel directly therein, in a manner known as direct injection.

[0028] Ignition system 88 can provide an ignition spark to combustion chamber 30 via spark plug 92 in response to spark advance signal SA from controller 12, under select operating modes. Though spark ignition components are shown, in some embodiments, combustion chamber 30 or one or more other combustion chambers of engine 10 may be operated in a compression ignition mode, with or without an ignition spark.

[0029] Exhaust gas sensor 126 is shown coupled to exhaust passage 48 of exhaust system 50 upstream of emission control device 70. Exhaust gas sensor 126 may be any suitable sensor for providing an indication of exhaust air-fuel ratio, such as a linear oxygen sensor or UEGO (Universal or Wide Range Exhaust Gas Oxygen), a two-state oxygen sensor or EGO, HEGO (Heated EGO), a NOx, HC, or CO sensor. In some embodiments, exhaust gas sensor 126 may be the first of multiple exhaust gas sensors positioned in the exhaust system. For example, additional exhaust gas sensors may be positioned downstream of emission control device 70.

[0030] Emission control device 70 is shown arranged along exhaust passage 48 downstream of exhaust gas sensor 126. Emission control device 70 may be a three-way catalyst (TWC), a NOx trap, various other emission control devices, or combinations thereof. In some embodiments, emission control device 70 may be the first of multiple emission control devices positioned in the exhaust system. In some embodiments, during operation of engine 10, emission control device 70 may be periodically reset by operating at least one cylinder of the engine within a particular air-fuel ratio.

[0031] The controller 12 Figure 1 Controller 12 is shown as a microcomputer and includes a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values ​​(shown in this particular example as a read-only memory chip 106), random access memory 108, keep-alive memory 110, and a data bus. Controller 12 may also receive various signals from sensors coupled to engine 10, including, in addition to those previously discussed, a measurement of intake mass air flow (MAF) from a mass air flow sensor 120; engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling jacket 114; a surface ignition probe (PIP) signal from a Hall effect sensor 118 (or other type) coupled to crankshaft 40; a throttle position (TP) from a throttle position sensor; and an absolute manifold pressure signal (MAP) from sensor 122. Engine speed signal RPM may be generated by controller 12 from signal PIP. Manifold pressure signal MAP from the manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Note that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor can provide an indication of engine torque. Additionally, this sensor, along with the detected engine speed, can provide an estimate of the charge (including air) entering the cylinder. In one example, sensor 118, which also serves as an engine speed sensor, can produce a predetermined number of equally spaced pulses every revolution of the crankshaft.

[0032] Furthermore, some of the above signals can be used in various exhaust sensor degradation determination methods, which will be described in further detail below. For example, the reversal of engine speed can be used to determine the delay associated with the injection-intake-compression-expansion-exhaust cycle. As another example, the reversal of speed (or the reversal of the MAF signal) can be used to determine the delay associated with the travel of exhaust gas from exhaust valve 54 to exhaust gas sensor 126. The above examples, along with other uses of engine sensor signals, can be used to determine the time delay between a change in commanded air-fuel ratio and the response rate of the exhaust gas sensor.

[0033] The controller 12 receives the Figure 1 The signals of various sensors are used Figure 1 Controller 12 may control various actuators to adjust engine operation based on received signals and instructions stored in memory of controller 12. For example, adjusting the engine air intake may include adjusting an actuator of throttle plate 64 to adjust the amount of air flowing into the engine cylinders. Adjusting fuel injection may include adjusting a fuel injector by adjusting the FPW signal to control the amount of fuel entering the engine cylinders.

[0034] In some embodiments, exhaust sensor degradation determination and calibration may be performed in a dedicated controller 140. The dedicated controller 140 may include processing resources 142 to handle signal processing associated with the generation, calibration, and validation of degradation determinations of the exhaust sensor 126. Specifically, a sampling buffer for recording the response rate of the exhaust sensor (e.g., approximately 100 samples per second per engine bank) may be too large for the processing resources of the vehicle's powertrain control module (PCM). Therefore, the dedicated controller 140 may be operably coupled to the controller 12 to perform exhaust sensor degradation determinations. Note that the dedicated controller 140 may receive engine parameter signals from the controller 12 and may send engine control signals and degradation determination information therein to the controller 12. In another embodiment, the exhaust sensor degradation determination and calibration may be performed in the controller 12.

[0035] In one example, the air-fuel ratio can be controlled via an air-fuel controller that includes a look-ahead controller and a feedback control routine, such as a proportional / integral (PI) controller. The look-ahead controller can be used to compensate for sensor degradation. The look-ahead controller can include a Smith Predictor. The Smith Predictor can include a time constant T C-SP and time delay T D-SP The PI controller can include a proportional gain K P and integral gain K I. In response to degradation of the exhaust gas sensor, the controller parameters listed above may be adjusted to compensate for the degradation and improve the accuracy of the air-fuel ratio readings, thereby improving engine control and performance. The dedicated controller 140 may be communicatively coupled to the look-ahead controller. In this way, the dedicated controller 140 and / or the controller 12 may adjust the parameters of the look-ahead controller based on the type of degradation determined using any of the available diagnostic methods. In another embodiment, the look-ahead controller may be implemented in the dedicated controller 140. In yet another embodiment, the look-ahead controller may be implemented in the controller 12. A PI controller may be implemented in the controller 12. In one example, the exhaust gas sensor controller parameters may be adjusted based on the magnitude and type of sensor degradation. In another example, the dedicated controller 140 and / or the controller 12 may determine the degradation type, transform or modify the signal sensed from the exhaust gas sensor having asymmetric sensor degradation, and then feed or input the transformed or modified signal to the exhaust gas sensor controller having the adjusted controller parameters. Reference below Figures 2 to 7 Six types of degradation behavior are discussed. In addition, the following reference Figures 9 to 12 Details are presented regarding adjusting the gain, time constant, and time delay of an exhaust gas sensor controller and modifying the degraded response of the exhaust gas sensor.

[0036] Note that storage medium read-only memory chip 106 and / or processing resource 142 may be programmed with computer readable data representing instructions executable by processor 102 and / or dedicated controller 140 to perform the methods described below, as well as other variants.

[0037] In some examples, engine system 10 may be included in a hybrid vehicle having multiple torque sources available for one or more wheels 85. In other examples, the vehicle is a conventional vehicle having only an engine, or an electric vehicle having only an electric motor. In the illustrated example, the vehicle includes engine 10 and electric motor 82. Electric motor 82 may be a motor or a motor / generator. When one or more clutches 86 are engaged, crankshaft 140 of engine 10 and electric motor 82 are connected to wheels 85 via transmission 84. In the illustrated example, a first clutch 86 is provided between crankshaft 140 and electric motor 82, and a second clutch 86 is provided between electric motor 82 and transmission 84. Controller 12 may send signals to the actuator of each clutch 86 to engage or disengage the clutch, thereby connecting or disconnecting crankshaft 140 from electric motor 82 and its connected components, and / or connecting or disconnecting electric motor 82 from transmission 84 and its connected components. Transmission 84 may be a gearbox, a planetary gear system, or other type of transmission. The powertrain system may be configured in various ways, including parallel, series, or series-parallel hybrid vehicles.

[0038] The electric motor 82 receives power from the traction battery 89 to provide torque to the wheels 85. The electric motor 82 can also operate as a generator to provide power to charge the battery 89, such as during braking operations.

[0039] As discussed above, exhaust gas sensor degradation may be determined based on any, or in some examples, each, of six discrete behaviors characterized by time delays and response rates of air-fuel ratio readings generated by the exhaust gas sensor in response to a commanded air-fuel ratio signal during a rich-to-lean transition and / or a lean-to-rich transition. Figures 2 to 7 Each shows a graph indicating one of six discrete types of exhaust gas sensor degradation. That is, symmetrical filter type sensor degradation ( Figure 2 ), Rich to Lean Filter Sensor Degradation ( Figure 3 ), Lean to Rich Filter Sensor Degradation ( Figure 4 ), Symmetrical delay type sensor degradation ( Figure 5 ), Rich to Lean Delay Sensor Degradation ( Figure 6 ) and lean-to-rich delayed sensor degradation ( Figure 7 ). Among them, rich to lean filtered sensor degradation, lean to rich filtered sensor degradation, rich to lean delayed sensor degradation and lean to rich delayed sensor degradation are asymmetric sensor degradation. The graph shows air-fuel ratio (λ) versus time (in seconds). As indicated by the arrows, the air-fuel ratio increases. In each graph, the dashed line indicates a commanded λ signal that can be sent from a controller (such as controller 12) to an engine component (e.g., a fuel injector, a cylinder valve, a throttle, a spark plug, etc.) to generate an air-fuel ratio that undergoes a cycle including one or more lean to rich transitions and one or more rich to lean transitions. The dashed line indicates the expected λ response of the exhaust gas sensor. In addition, in each graph, the solid line indicates the λ signal sensed by the degraded exhaust gas sensor in response to the commanded λ signal. In each graph, the double-arrowed line indicates that a given degradation behavior type is different from the expected λ signal.

[0040] Figure 2 A graph is shown indicating a first type of sensor degradation that may be exhibited by a degraded exhaust gas sensor. This first type of sensor degradation is of the symmetrically filtered type, which includes a slow response rate of the sensed signal to the commanded lambda signal in response to transitions of the commanded lambda signal in both the rich-to-lean and lean-to-rich directions. The time delay of the sensed signal relative to the commanded lambda signal is the same as the expected lambda response. In other words, the degraded lambda signal may begin transitioning from rich to lean and back again at the expected time, but the response rate may be slower than expected, resulting in reduced lean and rich peak times. Herein, the response rate can be calculated by taking the derivative of the sensor output over time.

[0041] Figure 3 A graph is shown that indicates a second type of sensor degradation that may be exhibited by a degraded exhaust gas sensor. The second type of sensor degradation is an asymmetric rich-to-lean filtering type that includes a low response rate of the sensed signal to the commanded lambda signal in response to the commanded lambda signal transitioning in the rich-to-lean direction rather than the lean-to-rich direction. This type of behavior may initiate a rich-to-lean transition at an expected time, but the response rate may be lower than the expected response rate, which may result in a reduced lean peak time. This type of sensor degradation may be considered asymmetric because the response rate of the exhaust gas sensor is slower (or lower than expected) during a rich-to-lean transition than during a lean-to-rich transition. In response to this type of degradation behavior, the controller may deliver less fuel during the rich-to-lean transition. As a result, NOx emissions may increase.

[0042] Figure 4 A graph is shown that indicates a third type of sensor degradation that may be exhibited by a degraded exhaust gas sensor. The third type of sensor degradation is an asymmetric lean-to-rich filtering type that includes a slow response rate of the sensed signal in response to a commanded lambda signal transitioning in the lean-to-rich direction rather than the rich-to-lean direction. This type of behavior may initiate a lean-to-rich transition at the expected time, but the response rate may be lower than the expected response rate, which may result in a reduced rich peak time. This type of sensor degradation may be considered asymmetric because the response rate of the exhaust gas sensor is only slow (or lower than expected) in response to the commanded lambda signal transitioning from lean to rich. In response to this type of sensor degradation, the controller may deliver more fuel during the lean-to-rich transition. As a result, CO emissions may increase.

[0043] Figure 5 A graph is shown indicating a fourth type of sensor degradation that may be exhibited by a degraded exhaust gas sensor. The fourth type of sensor degradation is a symmetrical delayed type, which includes a delayed response of the commanded lambda signal to transitions in both the rich-to-lean and lean-to-rich directions. In other words, the degraded lambda signal may begin transitioning from rich-to-lean and lean-to-rich at a time that is delayed from the expected time, but the transitions in response may occur at the expected response rate, resulting in offset lean and rich peak times.

[0044] Figure 6A graph is shown indicating a fifth type of sensor degradation that may be exhibited by a degraded exhaust gas sensor. This fifth type of sensor degradation is an asymmetric rich-to-lean delay type, which includes a delayed response to a commanded lambda signal in response to the commanded lambda signal transitioning in the rich-to-lean direction rather than the lean-to-rich direction. In other words, a degraded lambda signal may begin transitioning from rich to lean at a time that is delayed from the expected time, but the transition may occur at the expected response rate, resulting in a shifted and / or reduced lean peak time. This type of behavior can be considered asymmetric because the exhaust gas sensor's response time is only delayed from the expected start time during the rich-to-lean transition.

[0045] Figure 7 A graph is shown indicating a sixth type of sensor degradation that may be exhibited by a degraded exhaust gas sensor. This sixth type of sensor degradation is an asymmetric lean-to-rich delay type, which includes a delayed response to a commanded lambda signal in response to the commanded lambda signal transitioning in the lean-to-rich direction rather than the rich-to-lean direction. In other words, a degraded lambda signal may begin transitioning from lean to rich at a time that is delayed from the expected time, but the transition may occur at the expected response rate, resulting in a shifted and / or reduced rich peak time. This type of degradation can be considered asymmetric because the exhaust gas sensor's response time is only delayed from the expected start time during the lean-to-rich transition.

[0046] The six sensor degradation types described above can be divided into two groups. The first group includes filter-type degradation, where the response rate of the sensed air-fuel ratio is slower than the expected response rate (e.g., the response lag increases). The response rate can be quantified in terms of line length or time constant. The second group includes delay-type degradation, where the response time of the air-fuel ratio reading is delayed. The delayed response time can be quantified in terms of time delay. The line length and time delay of the sensed air-fuel ratio in response to the commanded air-fuel ratio are defined in Figure 8 Further details are given in .

[0047] Filter-type degradation and delay-type degradation can affect the dynamics of an exhaust gas sensor controller differently. In response to exhaust gas sensor degradation, look-ahead controller control compensation may be required to maintain control system stability. Therefore, in response to exhaust gas sensor degradation, look-ahead controller parameters can be adjusted to compensate for the degradation and improve the accuracy of air-fuel ratio readings, thereby improving engine control and performance. For example, if delay-type degradation is detected, new controller time delays and gains can be determined based on the time delay of the degraded sensor response. If filter-type degradation is detected, new controller time constants, time delays, and gains can be determined based on the time constant of the degraded sensor response.

[0048] The six sensor degradation types can also be divided into symmetric degradation and asymmetric degradation. In asymmetric degradation, the sensor response has different (or asymmetric) dynamics (e.g., response rate or response time) in response to the commanded air-fuel ratio transitioning in different directions. If the sensor degradation is asymmetric, then adjusting the look-ahead controller gains and delay compensation parameters in the direction of the degradation may only maintain stability in the closed-loop fuel control system operation. This may not be sufficient to allow the engine control system to operate around stoichiometry, requiring further calibration of the look-ahead controller based on the severity (e.g., magnitude) of the asymmetric filter degradation. However, by transforming the asymmetric sensor response into a symmetric sensor response, the operation of the closed-loop system can be maintained around stoichiometry, and the lean and / or rich bias caused by the asymmetric operation can be compensated. Refer below Figures 9 to 13 Additional details regarding compensating for and correcting for asymmetric sensor responses and adjusting controller parameters for exhaust gas sensors are further described.

[0049] Figure 8 An example of determining the time delay, time constant, and line length based on the exhaust gas sensor response and its corresponding commanded air-fuel ratio is shown. In particular, Figure 8 shows a diagram similar to that of Figures 2 to 7 A graph 210 of commanded lambda, desired lambda, and degraded lambda is shown. Figure 8 Rich to lean delayed degradation is shown, where the response time of the degraded lambda to the commanded air-fuel ratio transition is delayed. Arrow 202 shows the time delay, which is the duration from the change in commanded lambda to the time when a threshold change in measured lambda is observed (τ0). The threshold change in lambda can be a small change, e.g., 5%, 10%, 20%, etc., indicating that the response to the commanded change has begun. Arrow 204 shows the time constant (τ 63 ), which is the time from τ0 to when 63% of the steady-state response is achieved in a first-order system. Arrow 206 indicates the duration from τ0 to when 95% of the desired response is achieved, or the threshold response time (τ 95 ). In a first-order system, the threshold response time (τ 95 ) is approximately equal to three times the time constant (3*τ 63 ).

[0050] From these parameters, the dynamics of the sensor response can be quantified. In addition, the type and magnitude of sensor degradation can be determined. For example, the time delay indicated by arrow 202 can be compared with the expected time delay to determine whether the sensor exhibits delay degradation behavior. The time constant indicated by arrow 204 can be used to predict τ 95Finally, the line length can be determined based on the change in λ over the response duration starting from τ0. The line length is the sensor signal length and can be used to determine whether there is response degradation (e.g., filtering type degradation). The line length can be determined based on the following equation:

[0051]

[0052] Where Δt indicates the time increment and Δλ indicates the normalized measured λ increment from UEGO. If the determined line length is greater than the expected line length, then the exhaust gas sensor may exhibit filter-type degradation. The time constant and / or time delay of the degraded exhaust gas sensor response may be used to adjust the parameters of the exhaust gas sensor controller for air-fuel ratio control. Figure 13 A method for adjusting controller parameters based on degradation behavior is presented.

[0053] Go to Figure 9 , an example method 900 for air-fuel ratio control is shown. A sensed air-fuel ratio from an exhaust gas sensor is fed to an exhaust gas sensor controller comprising a look-ahead controller and a PI controller. The look-ahead controller may be adapted to compensate for sensor degradation. Method 900 may determine the type and magnitude of sensor degradation. In response to asymmetric sensor degradation, the sensed air-fuel ratio may be modified to a symmetric response before being input to the look-ahead controller of the exhaust gas sensor controller. The method may also include adjusting one or more parameters of the exhaust gas sensor controller based on the type and magnitude of sensor degradation.

[0054] Instructions for executing method 900 and the remainder of the methods included herein may be provided by a controller such as Figure 1 The controller 12) is based on instructions stored in the memory of the controller and in combination with sensors from the engine system (such as those referenced above). Figure 1 According to the following method, the controller can use the engine actuator of the engine system to adjust the engine operation.

[0055] At 902 , method 900 determines engine operating conditions. Engine operating conditions may be determined based on feedback from various engine sensors and may include engine speed and load, air / fuel ratio, temperature, and the like.

[0056] At 904, method 900 determines whether exhaust gas sensor monitoring conditions are met based on engine operating conditions. For example, exhaust gas sensor monitoring conditions may include the engine being running and input parameters being operational and / or the exhaust gas sensor being at a certain temperature such that it outputs a functional reading. Furthermore, exhaust gas sensor monitoring conditions may include combustion occurring in the cylinders of the engine, e.g., the engine is not in a shutdown mode such as deceleration fuel shutoff (DFSO). Exhaust gas sensor monitoring conditions may also include the engine operating under steady-state conditions.

[0057] If it is determined that the engine is not running and / or the selected conditions are not met, method 900 continues to monitor engine operating conditions at 906. However, if the exhaust gas sensor conditions are met at 904, the method proceeds to 908 to collect the commanded air-fuel ratio output from controller 12 and corresponding data from the exhaust gas sensor. This may include collecting and storing air-fuel ratio (e.g., lambda) data detected by the sensor. Data collection may continue until the necessary number of samples (e.g., air-fuel ratio data) are collected.

[0058] At 910 , method 900 includes determining whether the exhaust gas sensor is degraded based on the commanded air-fuel ratio and the corresponding sensed air-fuel ratio from the exhaust gas sensor. The method at 910 may also include determining a type and magnitude of sensor degradation.

[0059] Various methods can be used to determine the type of exhaust gas sensor degradation. In one example, degradation can be determined based on a time delay and line length of the sensed air-fuel ratio relative to the commanded air-fuel ratio. For example, in response to a transition of the commanded air-fuel ratio in the rich-to-lean or lean-to-rich direction, the time delay and line length of the sensed air-fuel ratio relative to the commanded air-fuel ratio may be determined based on the time delay and line length of the sensed air-fuel ratio relative to the commanded air-fuel ratio. Figure 8Determine. If the time delay is greater than the expected time delay, then delay-type sensor degradation can be determined. If the line length is greater than the expected line length, then filter-type sensor degradation can be determined. If the time delay or line length is different in response to the commanded air-fuel ratio transitioning in the rich-to-lean and lean-to-rich directions, then asymmetric sensor degradation can be determined. If the time delay is the same in response to the commanded air-fuel ratio transitioning in both directions, and the time delay is greater than the expected time delay, then symmetric delay-type sensor degradation can be determined. If the line length is the same in response to the commanded air-fuel ratio transitioning in both directions, and the line length is greater than the expected line length, then symmetric filter-type sensor degradation can be determined. The magnitude of sensor degradation can be measured by the degraded time delay (a time delay greater than the expected time delay) and the degraded line length (a line length greater than the expected line length) of the degraded sensor signal. In another example, the magnitude of sensor degradation can be measured by the time constant of the degradation (a time constant greater than the expected time constant). If the time delay or line length during a transition of the sensed air-fuel ratio in either direction is greater than the expected time delay or expected line length, the sensor's degraded time delay or degraded line length may be set to the greater time delay or greater line length. For example, method 900 may determine a first time delay for the sensed air-fuel ratio from the commanded air-fuel ratio in response to the commanded air-fuel ratio transitioning in a first direction, and a second time delay for the sensed air-fuel ratio from the commanded air-fuel ratio in response to the commanded air-fuel ratio transitioning in a second direction. Method 900 may determine asymmetric sensor degradation when the first delay differs from the second delay. If both the first and second time delays are greater than the expected delay, and the first time delay is less than the second time delay, the sensor's degraded time delay is set to the second time delay. The expected time delay and expected line length may be predetermined thresholds for a non-degraded sensor.

[0060] In another example, the type and magnitude of sensor degradation may be determined based on a time constant rather than line length.

[0061] In another example, exhaust gas sensor degradation can be detected by monitoring characteristics of the extreme value distribution from multiple sets of consecutive sensed air-fuel ratio samples during steady-state operating conditions. In one example, the characteristics can be the mode and central peak of the generalized extreme value (GEV) distribution of limiting lambda differences collected during steady-state operating conditions. Asymmetric sensor degradation can be determined based on the magnitude of the central peak and / or the magnitude of the mode. Another classification, such as symmetric sensor degradation, can be determined based on the time delay or time constant of the sensed air-fuel ratio relative to the commanded air-fuel ratio. In particular, if the time delay is greater than a nominal time delay, then sensor symmetric delay is indicated (e.g., indicating delay-type degradation). The nominal sensor time delay is the expected delay of the sensor in responding to a commanded air-fuel ratio change based on the delay from fuel injection, combustion, and exhaust gas traveling from the combustion chamber to the exhaust gas sensor. The sensor time delay can be when the sensor actually outputs a signal indicative of the changed air-fuel ratio. Similarly, if the sensor time constant is greater than the nominal time constant, then sensor symmetric response degradation behavior is indicated (e.g., indicating filter-type degradation). The nominal time constant may be a time constant that indicates how quickly the sensor responds to a commanded lambda change and may be determined offline with a non-degraded sensor. As discussed above, the controller may use the determined time constant and / or time delay of the degraded exhaust gas sensor response to adapt controller parameters.

[0062] In yet another example, exhaust gas sensor degradation can be indicated by parameters estimated from two operating models, a rich burn model and a lean burn model. The commanded air-fuel ratio can be compared to the sensed air-fuel ratio obtained from the sensor under the assumption that the combustion event produced the air-fuel ratio was rich (e.g., inputting the commanded lambda into the rich model), and also under the assumption that the combustion event was lean (e.g., inputting the commanded lambda into the lean model). For each model, a set of parameters can be estimated that best fits the commanded lambda value to the measured lambda value. The model parameters can include the model's time constant, time delay, and static gain. The estimated parameters from each model can be compared to each other, and the type of sensor degradation (e.g., filtering versus delay) can be indicated based on the difference between the estimated parameters.

[0063] At 912, method 900 determines whether sensor degradation was detected at 910. If sensor degradation was not detected, method 900 moves to 914 and adjusts the engine's air-fuel ratio based on the current exhaust gas sensor controller parameters. If sensor degradation was detected, method 900 moves to 916.

[0064] At 916, method 900 determines whether asymmetric sensor degradation was detected at 910. In response to asymmetric sensor degradation, method 900 moves to 918 and modifies the degraded asymmetric sensor response to a symmetric response. The modification is described in detail in Figure 10 If the sensor degradation is not asymmetric sensor degradation, then the method 900 moves to step 920 .

[0065] At 920 , method 900 adapts or adjusts parameters of the exhaust gas sensor controller based on the type and magnitude of sensor degradation. The magnitude of sensor degradation may include Figure 8 In one example, method 900 may determine the magnitude of sensor degradation based on the modified symmetric response at 918. The exhaust gas sensor controller parameters may include one or more parameters of a PI controller and a look-ahead controller. The detailed process of controller parameter adaptation is described in Figure 13 Shown in.

[0066] At 922, the engine is operated using an adapted exhaust gas sensor controller based on feedback of the sensed air-fuel ratio. If the sensor has asymmetric sensor degradation, the air-fuel ratio is controlled using the adapted controller based on feedback of a modified symmetric air-fuel ratio. As an example, the filtered symmetric response may be fed back to the adapted look-ahead controller and subsequently used to adjust fuel injection to the engine cylinders.

[0067] In this way, only symmetric responses are processed by the adapted exhaust gas sensor controller to generate a commanded air-fuel ratio for air-fuel ratio control. The symmetric response can be a sensor response with a symmetric fault or a modified sensor response from 918. Asymmetric engine operation caused by asymmetric sensor responses to air-fuel ratio transition directions can be avoided.

[0068] Figure 10 An example method 1000 for modifying an asymmetric sensor response to a symmetric response is shown. As one example, degradation can be introduced into a non-faulty portion of the sensed air-fuel ratio so that the dynamics of the sensor response (e.g., response rate and response time) are the same (or symmetric) with respect to the commanded air-fuel ratio transition direction or the sensed air-fuel ratio transition direction. As another example, a portion of the sensor response with a lower degradation magnitude (e.g., lower response rate or less response time) can be modified so that the dynamics of the sensor response are the same (or symmetric) with respect to the commanded air-fuel ratio transition direction or the sensed air-fuel ratio transition direction.

[0069] At 1002 , method 1000 determines whether asymmetric delay type sensor degradation is detected. If the answer is yes, method 1000 proceeds to 1004 or 1008 based on the specific type of delay degradation. If asymmetric delay type sensor degradation is not detected, method 1000 proceeds to 1018 .

[0070] In response to rich to lean delay type sensor degradation at 1004 (e.g. Figure 6 ), method 1000 selects a portion of the sensed air-fuel ratio having a lean-to-rich transition at 1006 and introduces a delay to the selected portion at 1016, but does not introduce a delay to the portion of the sensed air-fuel ratio having a rich-to-lean transition at 1012. In response to the lean-to-rich delay type sensor degradation at 1008 (e.g., Figure 7 ), method 1000 selects a portion of the sensed air-fuel ratio having a rich-to-lean transition at 1010 and introduces a delay to the selected portion at 1016, but does not introduce a delay to the portion of the sensed air-fuel ratio having a lean-to-rich transition at 1014. Thus, the delay is introduced only to the non-faulty portion of the asymmetric sensor response. The faulty portion of the asymmetric sensor response is not modified. The modified sensor response resembles a symmetric delay-type sensor degradation, i.e., having the same amount of time delay in both the lean-to-rich and rich-to-lean transitions.

[0071] At 1016, the unfaulted portion of the sensed air-fuel ratio is delayed to produce a symmetrical response. For example, for a sensor with a lean-to-rich delayed degradation, a time delay is introduced during the transition of the sensed air-fuel ratio from lean to rich. As another example, for a sensor with a lean-to-rich delayed degradation, a time delay is introduced during the transition of the sensed air-fuel ratio from rich to lean. The introduced time delay can be the difference between the time delays of the faulty and unfaulted portions of the sensed air-fuel ratio, or the difference between the time delays of the sensed air-fuel ratio transitioning in opposite directions. In this way, the modified air-fuel ratio has the same average air-fuel ratio as the commanded air-fuel ratio over time.

[0072] As an example, a delay can be introduced by filtering the unfaulted portion of the sensed air-fuel ratio through a filter. The filter can be constructed as follows:

[0073]

[0074] Among them S 过滤 (k) indicates the kth filtered air-fuel ratio, S is the sensed air-fuel ratio with delayed degradation, TD is the time delay of degradation, and DT is the sampling time of the sensed air-fuel ratio.

[0075] In an alternative example, an exhaust gas sensor may experience asymmetric delay-type sensor degradation, where degradation occurs in both transition directions. For example, a lean-to-rich transition may degrade by a first amount (e.g., with a first time delay) and a rich-to-lean transition may degrade by a second amount (e.g., with a second time delay), the first amount and the second amount being different. In one example, the first time delay may be greater than the second time delay, resulting in a slower response time in the lean-to-rich direction than in the rich-to-lean direction. In this example, an additional time delay may be introduced in the rich-to-lean transition direction so that it has the same time delay as the first time delay. In this way, an asymmetric sensor response may be made symmetric.

[0076] As an example, Figure 11 A graphical example of an exhaust gas sensor output with rich-to-lean delay degradation and a corresponding filtered response is shown. Specifically, graph 1102 shows a commanded air-fuel ratio at curve 1106, an expected air-fuel ratio at curve 1108, and a sensed air-fuel ratio at curve 1110. As shown at curve 1108, the expected air-fuel ratio is symmetric about stoichiometry (e.g., λ=1). In other words, the lean peak amplitude 1112 and the rich peak amplitude 1114 of the expected air-fuel ratio (e.g., the expected sensor response) are substantially equal.

[0077] The degraded lambda shown at curve 1110 has a response time greater than the expected air-fuel ratio 1108 in the lean-to-rich direction or transition (e.g., during the duration indicated by 1122). However, the response time of the sensed air-fuel ratio 1110 has the same response time as the expected air-fuel ratio 1108 in the rich-to-lean transition (as indicated by 1120). Therefore, the dynamics of the sensor response differ with respect to the direction of transition (e.g., rich-to-lean or lean-to-rich) of the sensor output or commanded air-fuel ratio. Consequently, the sensor response is asymmetric. Lean peak amplitude 1116 and rich peak amplitude 1112 are not equal. Because the asymmetric delayed degradation occurs only in the lean-to-rich direction, the lean peak amplitude of the expected response (curve 1108) and the lean peak amplitude of the degraded response (curve 1110) are substantially the same. However, the rich peak amplitude 1116 of the degraded response (curve 1110) is smaller than the lean peak amplitude 1114 of the expected response (curve 1108). Furthermore, the region of the sensed air-fuel ratio during lean combustion (region 1140) is greater than the region during rich combustion (region 1141). Consequently, the average of the sensed air-fuel ratio (line 1118) over time (i.e., the air-fuel ratio averaged over time) deviates from the average of the commanded air-fuel ratio. Consequently, asymmetric, delayed degradation causes the engine system to operate away from stoichiometry.

[0078] The asymmetrically degraded sensor response (curve 1110) includes a faulty portion 1122 (the sensed air-fuel ratio moves in the rich-to-lean direction) in which the time delay of the degraded sensed air-fuel ratio relative to the commanded air-fuel ratio is greater than the time delay of the expected air-fuel ratio. In the non-faulty portion 1120 (the sensed air-fuel ratio moves in the lean-to-rich direction), the time delay of the sensed air-fuel ratio is the same as the expected air-fuel ratio.

[0079] In response to an asymmetric filtered sensor response (such as the asymmetric delay-degraded response shown at curve 1102), a controller (such as Figure 1 A dedicated controller 140 or controller 12 (shown in FIG. 1 ) can filter or modify the asymmetric response to a more symmetric response by introducing a delay to the sensed air-fuel ratio in the non-faulty portion (e.g., portion 1120). The modified symmetric response can have the same degradation magnitude (e.g., time delay) when transitioning in both the rich-to-lean and lean-to-rich directions. Graph 1104 shows an example of a modified symmetric response (shown at curve 1128) obtained by modifying the asymmetric sensor response (curve 1110) shown in graph 1102.

[0080] In particular, graph 1104 shows the same commanded air-fuel ratio and expected air-fuel ratio as shown in graph 1102 at curves 1124 and 1126, respectively. Additionally, graph 1104 shows a modified response at curve 1128. The modified response can be achieved by selectively modifying the non-faulty portion 1120 (e.g., non-degraded portion) of the asymmetric sensor response (curve 1110) based on a time delay of the faulty portion 1122 (e.g., degraded portion) of the asymmetric sensor response. As a result of the modification, the region below the filtered air-fuel ratio during the rich air-fuel ratio period (1151) and the region below the filtered air-fuel ratio during the lean air-fuel ratio period (1150) are the same. Thus, the modified air-fuel ratio has an average air-fuel ratio that is the same as the average air-fuel ratio of the commanded air-fuel ratio. In another example, the region of the filtered air-fuel ratio during both the rich and lean burn periods is within a stoichiometric threshold. The threshold may be less than the difference in area between regions 1140 and 1141 of the sensed air / fuel ratio in curve 1102. Thus, the modified air / fuel ratio has a response that is more symmetrical about stoichiometry than the sensed air / fuel ratio.

[0081] Note that in Figure 11 In the example of , the average value of the commanded air / fuel ratio is approximately 1. In other examples, the average value of the commanded air / fuel ratio may be different than 1. The asymmetric sensor response may be filtered to have the same average value as the average value of the commanded air / fuel ratio.

[0082] Transfer back Figure 10At 1018, method 1000 determines whether asymmetric filter type sensor degradation is detected. If the answer is yes, method 1000 proceeds to 1020 or 1024 based on the specific type of filter degradation. If asymmetric filter type sensor degradation is not detected, method 1000 returns to 918 of method 900 and proceeds to 920 to adjust the parameters of the exhaust gas sensor controller.

[0083] In response to the rich to lean filter sensor degradation at 1020 ( Figure 3 ), method 1000 selects a portion of the sensed air-fuel ratio having a lean-to-rich transition at 1022 and filters the selected portion at 1032, but does not filter the portion of the sensed air-fuel ratio having a rich-to-lean transition at 1028. In response to the lean-to-rich filtered sensor degradation ( Figure 4 ), method 1000 selects the portion of the sensed air / fuel ratio having a rich-to-lean transition at 1026 and filters the selected portion at 1032, but does not filter the portion of the sensed air / fuel ratio having a rich-to-lean transition at 1030. In this way, only the non-faulty portion of the asymmetric sensor response is filtered. The faulty portion of the asymmetric sensor response is not modified.

[0084] At 1032, filtering is applied to the unfaulted portion of the sensed air-fuel ratio to produce a symmetrical response. For example, for a sensor with rich-to-lean filtering-type degradation, filtering is applied during transitions of the sensed air-fuel ratio from lean to rich. As another example, for a sensor with lean-to-rich filtering-type degradation, filtering is applied during transitions of the sensed air-fuel ratio from rich to lean. The filtered air-fuel ratio has an average air-fuel ratio that is the same as the commanded air-fuel ratio over time.

[0085] As an example, a filter can be constructed as follows:

[0086]

[0087] Where S indicates the current sensor air-fuel ratio with filtering fault, TC is the time constant, DT is the sampling rate of the sensed air-fuel ratio, and S 过滤 is the filtered air-fuel ratio.

[0088] In an alternative example, an exhaust gas sensor may undergo asymmetric filtered sensor degradation, where degradation occurs in both transition directions. For example, the lean-to-rich transition may degrade by a first amount (e.g., having a first time constant) and the rich-to-lean transition may degrade by a second amount (e.g., having a second time constant), the first amount and the second amount being different. In one example, the first time constant may be greater than the second time constant, resulting in a slower response in the lean-to-rich direction than in the rich-to-lean direction. In this example, the lean-to-rich transition direction may be filtered so that it has a time constant similar to the second time constant. In this way, the asymmetric response may become more symmetric around stoichiometry.

[0089] Figure 12 A graphical example of exhaust gas sensor output with rich-to-lean filter degradation and the corresponding filtered response is shown. Specifically, graph 1202 shows a commanded air-fuel ratio at curve 1206, an expected air-fuel ratio at curve 1208, and a sensed air-fuel ratio at curve 1210. As shown at curve 1208, the expected air-fuel ratio is symmetric about stoichiometry (e.g., λ=1). In other words, the lean peak amplitude 1212 and the rich peak amplitude 1214 of the expected air-fuel ratio (e.g., the expected sensor response) are substantially equal.

[0090] The degraded lambda shown at curve 1210 has a response rate lower than the expected air-fuel ratio 1208 in the rich-to-lean direction or transition (e.g., during the duration indicated by 1222). However, the response rate of the degraded lambda 1210 is the same as the expected lambda 1208 in the lean-to-rich transition (as indicated by 1220). Therefore, the dynamics of the sensor response differ with respect to the direction of transition (e.g., rich-to-lean or lean-to-rich) of the sensor output or commanded air-fuel ratio. Therefore, the sensor response is asymmetric. The lean peak amplitude 1216 and the rich peak amplitude 1214 are not equal. Because the asymmetric filter degradation occurs only in the rich-to-lean direction, the expected rich peak amplitude of the response (curve 1208) and the degraded rich peak amplitude of the response (curve 1210) are substantially the same. However, the degraded lean peak amplitude 1216 (curve 1210) is smaller than the expected lean peak amplitude 1212 (curve 1208). Thus, as shown by the accumulated air / fuel ratio of the sensed air / fuel ratio (line 1218 ), asymmetric filtering type degradation causes the engine system to operate away from stoichiometry.

[0091] The asymmetrically degraded response (curve 1210) includes a faulty portion 1222 (where the degraded response shifts in the rich-to-lean direction) where the slope of the degraded lambda is less steep than the expected lambda slope. In the fault-free portion 1220 (where the degraded response shifts in the lean-to-rich direction), the slope of the degraded lambda is the same as the expected lambda slope.

[0092] In response to an asymmetric filtered sensor response (such as the asymmetric filtered degradation response shown at curve 1202), a controller (such as Figure 1 The dedicated controller 140 or controller 12 shown in FIG. 12 can filter or modify the asymmetric response to a more symmetric response by filtering the sensed air-fuel ratio in the non-faulty portion (e.g., portion 1222). The filtered symmetric response can have the same degradation magnitude (e.g., time constant or line length) when transitioning in the rich-to-lean and lean-to-rich directions. Graph 1204 shows an example of a filtered symmetric response (shown at curve 1228) obtained by filtering the asymmetric sensor response (curve 1210) shown in graph 1202.

[0093] In particular, graph 1204 illustrates the same commanded air-fuel ratio and desired air-fuel ratio as shown in graph 1202 at curves 1224 and 1226, respectively. Additionally, graph 1204 illustrates a filtered or modified response at curve 1228. The filtered response can be achieved by selectively filtering the unfaulty portion 1220 (e.g., non-degraded portion) of the asymmetric sensor response (curve 1210) based on the time constant of the faulty portion 1222 (e.g., degraded portion) of the asymmetric sensor response. As a result of the filtering, the modified response (curve 1228) is more symmetric about stoichiometry than the degraded response shown at curve 1210. As shown at curve 1228, the lean peak amplitude 1230 and the rich peak amplitude 1232 are substantially the same. In other examples, the lean peak amplitude 1230 and the rich peak amplitude 1232 of the modified response may be within a threshold range of each other. The threshold may be less than the difference between the rich peak amplitude 1214 and the lean peak amplitude 1216 of the asymmetric degraded response (curve 1210). Thus, the average filtered air-fuel ratio is the same as the average commanded air-fuel ratio.

[0094] Note that in Figure 12 In the example of , the average value of the commanded air / fuel ratio is approximately 1. In other examples, the average value of the commanded air / fuel ratio may be different than 1. The asymmetric sensor response may be filtered to have the same average value as the average value of the commanded air / fuel ratio.

[0095] Figure 13 A method 1300 is shown for adapting parameters of an exhaust gas sensor controller based on the type and magnitude of sensor degradation. The exhaust gas sensor controller may include a PI controller and a look-ahead controller (such as a SP delay compensator). The method 1300 may be performed by the controller 12 and / or the dedicated controller 140 and may be used in Figure 9The method 900 is executed during 920. As an example, the time constant and / or time delay of the degraded sensor response relative to the commanded air-fuel ratio is determined. These parameters may be referred to herein as the degraded (e.g., faulty) time constant T C-F , and the degenerate time delay T D-f The degenerate time constant and time delay can then be used together with the nominal time constant T C-nom and the nominal time delay T D-nom Together we determine the parameters of the look-ahead controller and the PI controller. As discussed above, the controller parameters that can be tuned may include the proportional gain K P , integral gain K I , controller time constant T C-SP and controller time delay T D-SP The adapted controller parameters may further be based on nominal system parameters (eg, parameters preset in a look-ahead controller).

[0096] At 1302, the method determines whether the sensor exhibits filter-type sensor degradation. If the answer is yes, method 1300 moves to step 1310, where the engine system is approximated by a first-order model and the parameters of the exhaust gas sensor controller are adapted based on the time constant. If the answer at 1302 is no, method 1300 moves to 1304 to determine whether the degradation is delay-type degradation. If the sensor exhibits delay-type degradation, the method continues to 1324, where the parameters of the exhaust gas sensor controller are determined based on the time delay. If the answer at 1304 is no, method 1300 determines that the sensor does not exhibit degradation, and the controller parameters remain the same.

[0097] At 1310 , method 1300 includes estimating a degradation time constant T C-F and the nominal time constant T C-nom The nominal time constant may be a time constant that indicates how quickly the sensor responds to a change in the commanded air-fuel ratio and may be determined offline based on non-degraded sensor functionality. The degraded time constant may be estimated using any of the methods used to determine degradation at 910 in method 900. Alternatively, the time constant of time degradation may be estimated based on the filtered air-fuel ratio and the commanded air-fuel ratio. In determining the degraded time constant T C-F and the nominal time constant T C-nom Thereafter, the method 1300 proceeds to 1312 to approximate the second-order system by a first-order model (e.g., FOPD). The method at 1312 may include applying a semi-regular approximation to the degraded system. The semi-regular approximation includes uniformly distributing smaller time constants (between the nominal time constant and the degraded time constant) between the larger time constant and the nominal time delay. This can be accomplished using the following equation:

[0098]

[0099]

[0100] If the degenerate time constant T C-F Less than the nominal time constant T C-nom , then the equation becomes:

[0101]

[0102]

[0103] At 1314, the controller may use the determined equivalent time constant T C-Equiv and the equivalent time delay T D-Equiv Instead of the controller time constant T used in the SP delay compensator (in the look-ahead controller) C-SP and controller time delay T D-SP .

[0104] At 1316, the controller determines an intermediate multiplier α. The intermediate multiplier is defined by the following equation:

[0105]

[0106] At 1318, the integral gain K of the PI controller may be determined using the intermediate multiplier α. I Integral gain K I is determined from the following equation:

[0107] K I＝ α*K I-nom

[0108] where K I-nom is the nominal integral gain of the PI controller. Since α = 1 for filter degradation, K I Maintain at nominal value.

[0109] At 1320 , method 1300 calculates the integral gain K based on the integral gain K. I and the equivalent time constant T C-Equiv And determine the proportional gain K of the PI controller P Proportional gain K P is determined from the following equation:

[0110] K P =T C-Equiv *K I

[0111] As the magnitude of the filter degradation increases (e.g., such as the time constant of the degradation increases), the equivalent time constant TC-Equiv Increase, thereby increasing K P After determining the new controller parameters, the method returns to 920 of method 900 and continues to 922 to apply the new controller parameters in engine air-fuel ratio control.

[0112] In this way, the controller gains, time constants, and time delays can be adjusted based on the magnitude and type of degradation behavior. In particular, for filter-type degradation (e.g., time constant degradation), the proportional gain, integral gain, controller time constant, and time delay (T C-SP and T D-SP ) can be adjusted based on the time constant of degradation.

[0113] At 1324 , method 1300 includes estimating the degraded time delay T D-F and the nominal time delay T D-nom The nominal time delay is the expected delay of the exhaust gas sensor in responding to a commanded air-fuel ratio change based on the delay from fuel injection, combustion, and exhaust gas traveling from the combustion chamber to the exhaust gas sensor. The degraded time delay T may be estimated at 910 of method 900. D-F Alternatively, a time delay of temporal degradation may be estimated based on the filtered air-fuel ratio and the commanded air-fuel ratio.

[0114] In determining the degradation time delay T D-F and the nominal time delay T D-nom Thereafter, method 1300 proceeds to 1326 to delay the degradation based on the time T D-F and the nominal time delay T D-nom And determine the equivalent time delay T D-Equiv . Equivalent time delay T D-Equiv It can be estimated by the following equation:

[0115] T D-Equiv =T D-nom +T D-F

[0116] In this manner, the equivalent time delay is an additional time delay (eg, a degraded time delay) after the expected time delay (eg, the nominal time delay).

[0117] For delay degradation, the time constant may not change. Therefore, at 1328, the equal value time constant T C-Equiv Set to the nominal time constant T C-nom .

[0118] At 1330, method 1300 may use the determined equivalent time constant T C-Equiv and the equivalent time delay T D-EquivInstead of the controller time constant T used in the SP delay compensator (in the look-ahead controller) C-SP and controller time delay T D-SP For delay degradation, the controller time constant T C-SP Can remain unchanged.

[0119] At 1332, the controller determines an intermediate multiplier α. The intermediate multiplier may be based on the degraded time delay and the nominal time delay. The intermediate multiplier is defined by the following equation:

[0120]

[0121] Then, at 1334, the integral gain K of the PI controller may be determined using the intermediate multiplier α I Integral gain K I is determined from the following equation:

[0122] K I＝ α*K I-nom

[0123] where K I-nom is the nominal integral gain of the PI controller. As the magnitude of the delay degradation (such as the time constant of the degradation) increases, α can be reduced. This in turn leads to the integral gain K I Therefore, as the degradation time delay T D-F As the magnitude of delay degradation increases, the integral gain can be reduced by a larger amount.

[0124] At 1336 , method 1300 calculates the integral gain K based on the integral gain K. I and the equivalent time constant T C-Equiv And determine the proportional gain K P Proportional gain K P is determined from the following equation:

[0125] K P =T C-Equiv *K I

[0126] Since the equivalent time constant T C-Equiv For delayed degradation, the proportional gain K P Can be based on the integral gain K I Therefore, in K I With the time delay T of degradation D-F When the proportional gain K P After determining the new look-ahead controller parameters, the method returns to 920 of method 900 and continues to 922 to apply the new controller parameters for engine air-fuel ratio control.

[0127] In this way, the controller gains, time constants, and time delays can be adjusted based on the magnitude and type of degradation behavior. In particular, for delay-type degradation (e.g., time-delay degradation), the proportional gain, integral gain, and controller time delay (T D-SP ) can be adjusted based on the degraded time delay, while the controller time constant (T C-SP ) is maintained.

[0128] As described above, an engine method may include adjusting fuel injection in response to exhaust oxygen feedback from an exhaust gas sensor, and converting an asymmetric, degraded sensor response of the exhaust gas sensor to a symmetric, degraded response based on the type and magnitude of the asymmetric sensor response. For example, the asymmetric, degraded response may be an asymmetric, delayed degradation response having a time delay in only one transition direction. Converting the asymmetric, delayed response to a more symmetric response may include filtering healthy transitions of the asymmetric sensor response, but not filtering faulty transitions of the asymmetric sensor response. In one example, filtering healthy transitions of the asymmetric sensor response may include filtering rich-to-lean transitions of the sensor response when sensor degradation is lean-to-rich. In another example, filtering healthy transitions of the asymmetric sensor response may include filtering lean-to-rich transitions of the sensor response when sensor degradation is rich-to-lean. Additionally, healthy transitions of the asymmetric sensor response may be filtered by an amount based on the dynamics of the faulty transition of the asymmetric sensor response. In one example, the magnitude of the degraded delayed transition may be quantified by a time delay, and healthy transitions of the asymmetric, delayed sensor response may be filtered based on the time delay. The method may further include adjusting one or more parameters of an exhaust gas sensor controller of the exhaust gas sensor in response to the filtered symmetric response. In one example, adjusting the one or more parameters of the exhaust gas sensor controller may include adjusting the one or more parameters based on a time delay and a time constant of the filtered symmetric response. The engine is then operated with the adapted air / fuel controller in response to feedback of the filtered symmetric response.

[0129] The technical effect of modifying an asymmetric sensor response to a symmetric response is that asymmetric engine operation can be avoided. The technical effect of filtering the non-faulty portion of the sensor response is that the filtered response can have the same dynamics as the commanded air-fuel ratio increases and decreases, and the average air-fuel ratio of the filtered sensor response can be the same as the commanded air-fuel ratio. The technical effect of adjusting controller parameters based on sensor degradation is that the accuracy of air-fuel ratio command tracking can be improved and the stability of the controller can be improved.

[0130] As an embodiment, a method includes: sensing an air-fuel ratio via an exhaust gas sensor; generating a modified air-fuel ratio having a symmetric response based on the sensed air-fuel ratio in response to an asymmetric sensor response; and adjusting fuel injection based on the modified air-fuel ratio. In a first example of the method, the asymmetric sensor response includes a sensor response having different dynamics when a commanded air-fuel ratio transitions in different directions. A second example of the method optionally includes the first example and further includes: determining a first time delay for the sensed air-fuel ratio from a commanded air-fuel ratio when the sensed air-fuel ratio transitions in a first direction; determining a second time delay for the sensed air-fuel ratio from the commanded air-fuel ratio when the sensed air-fuel ratio transitions in a second, different direction; and determining the asymmetric sensor response in response to the first time delay being different from the second time delay. A third example of the method optionally includes one or more of the first and second examples and further includes: wherein the first time delay is less than the second time delay, and the time delay of the modified air-fuel ratio in response to the commanded air-fuel ratio transitioning in the different direction is the same as the second time delay. A fourth example of the method optionally includes one or more of the first through third examples and further includes: wherein the average air-fuel ratio of the modified air-fuel ratio over time is the same as the average air-fuel ratio of the commanded air-fuel ratio over time. A fifth example of the method optionally includes one or more of the first through fourth examples and further includes: determining a type of sensor degradation and a magnitude of sensor degradation based on the sensed air-fuel ratio and the commanded air-fuel ratio, and generating the modified air-fuel ratio based on the type and magnitude of sensor degradation. A sixth example of the method optionally includes one or more of the first through fifth examples and further includes: adjusting the fuel injection via an exhaust gas sensor controller, and adapting one or more parameters of the controller in response to the type of sensor degradation and the magnitude of sensor degradation. A seventh example of the method optionally includes one or more of the first through sixth examples and further includes: wherein the exhaust gas sensor controller includes a feedback control routine and a Smith predictor. An eighth example of the method optionally includes one or more of the first through seventh examples and further includes: adjusting the fuel injection via the adapted exhaust gas controller based on the modified air-fuel ratio.

[0131] As another embodiment, a method includes: operating an engine component at a commanded air-fuel ratio; sensing the air-fuel ratio via an exhaust gas sensor; determining sensor degradation based on the sensed air-fuel ratio; modifying the sensed air-fuel ratio in response to asymmetric sensor degradation, wherein the modified air-fuel ratio has a symmetric response; and adjusting fuel injection based on the modified air-fuel ratio. In a first example of the method, determining sensor degradation includes determining a time constant and a time delay of the sensed air-fuel ratio relative to the commanded air-fuel ratio. A second example of the method optionally includes the first example and further includes: modifying the sensed air-fuel ratio includes delaying a non-faulty portion of the sensed air-fuel ratio in response to asymmetric delayed sensor degradation. A third example of the method optionally includes one or more of the first and second examples and further includes: modifying the sensed air-fuel ratio includes filtering the non-faulty portion of the sensed air-fuel ratio based on the time constant in response to asymmetric filtered sensor degradation. A fourth example of the method optionally includes one or more of the first to third examples and further includes adjusting the fuel injection based on feedback of the filtered air-fuel ratio modified by an exhaust gas sensor controller, wherein parameters of the exhaust gas sensor controller are adjusted based on sensor degradation. A fifth example of the method optionally includes one or more of the first to fourth examples and further includes adapting the parameters of the exhaust gas sensor controller based on the time delay or the time constant.

[0132] As yet another embodiment, an engine system includes an engine including a fuel injection system; an exhaust gas sensor coupled to an exhaust passage of the engine, wherein the exhaust gas sensor has asymmetric sensor degradation; and a controller having computer-readable instructions stored on a non-transitory memory, the controller configured to: generate a modified air-fuel ratio having a symmetric response based on the sensed air-fuel ratio; and adjust the fuel injection system based on the modified air-fuel ratio. In a first example of the engine system, the controller is further configured to compensate for the sensor degradation using a look-ahead controller. A second example of the engine system optionally includes the first example and further includes: wherein the modified air-fuel ratio is fed into the look-ahead controller. A third example of the engine system optionally includes one or more of the first and second examples and further includes: wherein the controller is further configured to determine a time delay and a time constant by comparing the modified air-fuel ratio to a commanded air-fuel ratio. A fourth example of the engine system optionally includes one or more of the first to third examples and further includes: wherein the controller is further configured to: adapt the parameters of the look-ahead controller based on the time delay in response to delay-type degradation, and adapt the parameters of the look-ahead controller based on the time constant in response to filter-type degradation.

[0133] It should be noted that the example control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in a non-transitory memory and can be executed by a control system including a controller in combination with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies (such as event-driven, interrupt-driven, multi-tasking, multi-threaded, etc.). Therefore, the various actions, operations, and / or functions described can be performed in the described sequence, in parallel, or in some cases omitted. Similarly, the processing order is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the described actions, operations, and / or functions can be repeatedly performed depending on the specific strategy used. In addition, the described actions, operations, and / or functions can graphically represent code to be programmed into the non-transitory memory of a computer-readable storage medium in the engine control system, wherein the described actions are performed by executing instructions in a system including various engine hardware components in combination with an electronic controller.

[0134] It will be understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments should not be construed in a limiting sense, as many variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or properties disclosed herein.

[0135] The following claims particularly point out certain combinations and subcombinations regarded as novel and non-obvious. These claims may refer to "an" element or a "first" element or the equivalent thereof. These claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amendment of the present claims or by presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, are deemed included within the subject matter of the present disclosure.

[0136] According to the present invention, a method includes sensing air-fuel ratio via an exhaust gas sensor; generating a modified air-fuel ratio having a symmetric response based on the sensed air-fuel ratio in response to an asymmetric sensor response; and adjusting fuel injection based on the modified air-fuel ratio.

[0137] According to one embodiment, the asymmetric sensor response includes a sensor response having different dynamics when the commanded air / fuel ratio transitions in different directions.

[0138] According to one embodiment, the above invention is further characterized by determining a first time delay of the sensed air-fuel ratio from the commanded air-fuel ratio when the sensed air-fuel ratio transitions in a first direction; determining a second time delay of the sensed air-fuel ratio from the commanded air-fuel ratio when the sensed air-fuel ratio transitions in a second, different direction; and determining the asymmetric sensor response in response to the first time delay being different from the second time delay.

[0139] According to one embodiment, the first time delay is less than the second time delay, and the time delay for the modified air / fuel ratio to transition in a different direction in response to the commanded air / fuel ratio is the same as the second time delay.

[0140] According to one embodiment, the average air-fuel ratio of the modified air-fuel ratio over time is the same as the average air-fuel ratio of the commanded air-fuel ratio over time.

[0141] According to one embodiment, the above invention is further characterized by determining a type of sensor degradation and a magnitude of sensor degradation based on the sensed air-fuel ratio and the commanded air-fuel ratio, and generating the modified air-fuel ratio based on the type and the magnitude of the sensor degradation.

[0142] According to one embodiment, the above invention is further characterized by regulating the fuel injection via an exhaust gas sensor controller, and adapting one or more parameters of the controller in response to a type of sensor degradation and a magnitude of the sensor degradation.

[0143] According to one embodiment, the exhaust gas sensor controller includes a feedback control routine and a Smith predictor.

[0144] According to one embodiment, the above invention is further characterized by adjusting said fuel injection via said adapted exhaust gas controller based on said modified air-fuel ratio.

[0145] According to the present invention, a method includes operating an engine component at a commanded air-fuel ratio; sensing the air-fuel ratio via an exhaust gas sensor; determining sensor degradation based on the sensed air-fuel ratio; modifying the sensed air-fuel ratio in response to asymmetric sensor degradation, wherein the modified air-fuel ratio has a symmetric response; and adjusting fuel injection based on the modified air-fuel ratio.

[0146] According to one embodiment, determining the sensor degradation includes determining a time constant and a time delay of the sensed air / fuel ratio relative to a commanded air / fuel ratio.

[0147] According to one embodiment, modifying the sensed air / fuel ratio includes delaying a non-faulty portion of the sensed air / fuel ratio in response to asymmetric delayed sensor degradation.

[0148] According to one embodiment, modifying the sensed air / fuel ratio includes filtering a non-faulty portion of the sensed air / fuel ratio based on the time constant in response to asymmetric filtered sensor degradation.

[0149] According to one embodiment, the above invention is further characterized by adjusting the fuel injection based on feedback of the filtered air-fuel ratio modified by an exhaust gas sensor controller, wherein parameters of the exhaust gas sensor controller are adjusted based on the sensor degradation.

[0150] According to one embodiment, the parameters of the exhaust gas sensor controller are adapted based on the time delay or the time constant.

[0151] According to the present invention, an engine system is provided, comprising: an engine including a fuel injection system; an exhaust gas sensor coupled to an exhaust passage of the engine, wherein the exhaust gas sensor has asymmetric sensor degradation; a controller having computer-readable instructions stored on a non-transitory memory, the controller being configured to: generate a modified air-fuel ratio having a symmetric response based on the sensed air-fuel ratio; and adjust the fuel injection system based on the modified air-fuel ratio.

[0152] According to one embodiment, the controller is further configured to compensate for the sensor degradation using a look-ahead controller.

[0153] According to one embodiment, the modified air-fuel ratio is fed into the look-ahead controller.

[0154] According to one embodiment, the controller is further configured to determine a time delay and a time constant by comparing the modified air / fuel ratio to a commanded air / fuel ratio.

[0155] According to one embodiment, the controller is further configured to adapt parameters of the look-ahead controller based on the time delay in response to delay-type degradation, and to adapt parameters of the look-ahead controller based on the time constant in response to filter-type degradation.

Claims

1. A method for an exhaust gas sensor, the method comprising: sensing an air-fuel ratio via the exhaust gas sensor; determining a first time delay of the sensed air-fuel ratio from a commanded air-fuel ratio when the sensed air-fuel ratio transitions in a first direction; determining a second time delay for the sensed air / fuel ratio from the commanded air / fuel ratio when the sensed air / fuel ratio transitions in a second different direction; determining an asymmetric sensor response in response to the first time delay being different from the second time delay; generating a modified air / fuel ratio having a symmetric response based on the sensed air / fuel ratio in response to the asymmetric sensor response; as well as Fuel injection is adjusted based on the modified air-fuel ratio. 2 . The method of claim 1 , wherein the asymmetric sensor response comprises a sensor response having different dynamics when the commanded air / fuel ratio transitions in different directions. 3 . The method of claim 1 , wherein the first time delay is less than the second time delay, and the time delay for the modified air / fuel ratio to transition in a different direction in response to the commanded air / fuel ratio is the same as the second time delay. 4 . The method of claim 1 , wherein the average air-fuel ratio of the modified air-fuel ratio over time is the same as the average air-fuel ratio of the commanded air-fuel ratio over time.

5. The method of claim 1, further comprising: The fuel injection is adjusted via an exhaust gas sensor controller, and one or more parameters of the exhaust gas sensor controller are adapted in response to the type of sensor degradation and the magnitude of the sensor degradation. 6 . The method of claim 5 , wherein the exhaust gas sensor controller includes a feedback control program and a Smith predictor. 7 . The method of claim 5 , further comprising adjusting said fuel injection via said adapted exhaust gas sensor controller based on said modified air / fuel ratio. 8 . The method of claim 5 , wherein the parameters of the exhaust gas sensor controller are adapted based on a time delay of the sensed air / fuel ratio from a commanded air / fuel ratio.

9. An engine system, comprising: an engine, the engine comprising a fuel injection system; an exhaust gas sensor coupled to an exhaust passage of the engine, wherein the exhaust gas sensor has asymmetric sensor degradation; a controller having computer-readable instructions stored on a non-transitory memory, the controller configured to: sensing an air-fuel ratio via the sensor; determining a first time delay of the sensed air-fuel ratio from a commanded air-fuel ratio when the sensed air-fuel ratio transitions in a first direction; determining a second time delay for the sensed air / fuel ratio from the commanded air / fuel ratio when the sensed air / fuel ratio transitions in a second different direction; determining the asymmetric sensor degradation in response to the first time delay being different from the second time delay; generating a modified air / fuel ratio having a symmetrical response based on the sensed air / fuel ratio; as well as The fuel injection system is adjusted based on the modified air / fuel ratio. 10 . The engine system of claim 9 , wherein the controller is further configured to compensate for the asymmetric sensor degradation with a look-ahead controller.

11. The engine system of claim 10, wherein the modified air-fuel ratio is fed into the look-ahead controller. 12 . The engine system of claim 10 , wherein the controller is further configured to determine a time delay by comparing the modified air / fuel ratio to the commanded air / fuel ratio.

13. The engine system of claim 12, wherein the controller is further configured to adapt parameters of the look-ahead controller based on the time delay in response to delayed-type degradation and to adapt parameters of the look-ahead controller based on a time constant in response to filtered-type degradation.

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