System and method for exhaust gas sensor monitoring

Abstract

The present disclosure provides systems and methods for exhaust gas sensor monitoring. A method of monitoring an exhaust gas sensor coupled in an engine exhaust port in an engine is provided. The method includes entering a variable displacement engine (VDE) mode prior to a reduced traction fuel cut transition in which intake valves and exhaust valves of a first subset of cylinders of the engine are activated and intake valves and exhaust valves of a second subset of cylinders of the engine are deactivated; and performing a six-mode diagnosis to identify exhaust gas sensor degradation during fuel shut-off.

Description

Technical Field

[0001] This description generally relates to monitoring and diagnostics of exhaust gas sensors in motor vehicles. Background Art

[0002] An exhaust temperature sensor may be located in a vehicle's exhaust system to detect the air-fuel ratio of exhaust gas emitted from the vehicle's internal combustion engine. Exhaust gas sensor readings may be used to control operation of the internal combustion engine to propel the vehicle.

[0003] Degradation of exhaust gas sensors may result in degraded engine control, which may lead to increased emissions and / or reduced vehicle drivability. Additionally, on-board diagnostic requirements may require detection of six specific types of degradation. Therefore, it may be desirable to provide accurate determination of exhaust gas sensor degradation. The six behavior types, for which diagnostics are required in some parts of the world, can be categorized as: asymmetric degradation (e.g., rich-to-lean asymmetric delay, lean-to-rich asymmetric delay, rich-to-lean asymmetric slow response, lean-to-rich asymmetric slow response), which affects lean-to-rich or rich-to-lean exhaust gas sensor response rates differently; and symmetric degradation (e.g., symmetric delay, symmetric slow response), which affects lean-to-rich and rich-to-lean exhaust gas sensor response rates equally. Delayed-type degradation behavior may be associated with the exhaust gas sensor's initial reaction to changes in exhaust gas composition, and slow-response-type degradation behavior may be associated with the duration of time after the initial exhaust gas sensor response transitions from rich-to-lean exhaust output or lean-to-rich exhaust output.

[0004] Previous methods for monitoring exhaust gas sensor degradation (particularly identifying one or more of six degradation behaviors) have relied on direct data collection, such as via the Universal Exhaust Gas Oxygen (UEGO) six-mode diagnostic. That is, the engine may be intentionally operated in one or more rich-to-lean or lean-to-rich transitions to monitor exhaust gas sensor response. Attempts have also been made to monitor exhaust gas sensor degradation during reduced traction fuel shut-off transitions to perform unobtrusive diagnostic operations. The term reduced traction fuel shut-off refers to a feature in the engine management system that temporarily stops fuel injection during periods of reduced speed, such as when decelerating or coasting, which improves fuel efficiency and reduces emissions.

[0005] However, when the engine enters or exits a fuel cut, the engine's injectors may randomly ramp off or on, for example, based on torque scheduling. Random injector ramping may result in variability in the time stamp of six-mode monitoring entry. The spread of these ramps may be equivalent to the delay that six-mode diagnostics must detect, for example, approximately 600 to 800 milliseconds. Fuel cut entry or exit with high variability in injector ramping off / on may not be usable for six-mode monitoring, impacting monitoring completion time.

[0006] Furthermore, to date, V-8 or other eight-cylinder engines have been developed with a single exhaust gas sensor for every four cylinders. In such engines, ramping the four injectors into a fuel cut event can result in significant variability in the degradation behavior of the six-mode diagnostics. On the other hand, certain sensor configurations, such as the four-UEGO sensor configuration, reduce this variability by reducing the number of cylinders per exhaust gas sensor to two. However, the variability in the six-mode diagnostics, as outlined above, still persists due to random injector ramp variations. Summary of the Invention

[0007] The inventors herein have recognized the above-mentioned problems and have overcome at least some of them via a more robust fuel-cut-based six-mode diagnostic strategy for exhaust gas sensors. The strategy disclosed herein includes entering a variable displacement mode (VDE), such as a four-cylinder mode, prior to a fuel-cut transition. The strategy described herein can be implemented in an environment where one exhaust gas sensor corresponds to two cylinders of an engine (e.g., a four-UEGO sensor environment). When the fuel-cut transition is entered, entering the four-cylinder mode can include gradually closing the injectors to deactivate a first subset of the eight cylinders so that a second non-overlapping subset of the eight cylinders is active. The second subset can include one cylinder for each exhaust gas sensor, thereby allowing a 1:1 ratio of sensors to cylinders. When the fuel-cut transition is exited, entering the four-cylinder mode can include gradually opening the injectors to activate a second subset of cylinders.

[0008] By entering VDE mode before fuel cut entry or exit when the engine has a 1:1 sensor to cylinder ratio configuration, each exhaust gas sensor can only detect one cylinder. Allowing each sensor to detect only one cylinder mitigates injector ramp variability.

[0009] It should be understood that the above summary is provided to introduce a series of concepts that are further described in the detailed description in a simplified form. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined 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 illustrating an embodiment of a propulsion system for a vehicle including an exhaust gas sensor is shown;

[0011] Figure 2 shows a graph indicating symmetrical filter type degradation behavior of an exhaust gas sensor;

[0012] Figure 3 shows a graph indicating asymmetric rich-to-lean filter type degradation behavior of an exhaust gas sensor;

[0013] Figure 4 shows a graph indicating an asymmetric lean-to-rich filter type degradation behavior of an exhaust gas sensor;

[0014] Figure 5 shows a graph indicating symmetrical delayed type degradation behavior of an exhaust gas sensor;

[0015] Figure 6 shows a graph indicating asymmetric rich-to-lean delay type degradation behavior of an exhaust gas sensor;

[0016] Figure 7 shows a graph indicating asymmetric lean-to-rich delayed type degradation behavior of an exhaust gas sensor;

[0017] Figure 8 A number of graphs are shown indicating injector ramping into a traction-reducing fuel cutoff event.

[0018] Figure 9 A diagram showing an exhaust gas sensor setup for a V-8 engine;

[0019] Figure 10 Shown in V-4 mode Figure 9 Diagram of exhaust sensor setup;

[0020] Figure 11 A flow chart illustrating a first method for performing exhaust gas sensor diagnostics is shown; and

[0021] Figure 12 A flow chart illustrating a second method for performing exhaust gas sensor diagnostics is shown. DETAILED DESCRIPTION

[0022] The following description relates to a method for determining exhaust gas sensor degradation. More specifically, the system and method described below can be implemented to determine exhaust gas sensor degradation prior to a fuel cut transition (e.g., entering or exiting a fuel cut event) with reduced traction. In this way, a robust six-mode fuel cut-based diagnostic algorithm can be employed unobtrusively while reducing injector ramp variability. This method can be applied to Figure 1 Engine of the type shown. Figures 2 to 7 Expected λ and degraded λ are shown for each of six degradation behaviors of the exhaust gas sensor. Figure 8 An exemplary injector ramping into a fuel cutoff event is shown. Figure 9 An exemplary exhaust gas sensor arrangement for a V-8 engine is shown, and Figure 10 An exemplary exhaust gas sensor arrangement is shown for a V-4 mode of a V-8 engine. Figure 9 is an exemplary method for performing exhaust gas sensor diagnostics prior to fuel cut entry, and Figure 10 An exemplary method for performing exhaust gas sensor diagnostics prior to fuel cut exit is provided.

[0023] Figure 1 is a schematic diagram illustrating one cylinder of multi-cylinder engine 10. In some examples, multi-cylinder engine 10 may be a V-8 engine including eight cylinders. Multi-cylinder engine 10 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. The 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 operator 132 via input device 130. In this example, input device 130 is a driver demand pedal, and the position of the driver demand pedal may be sensed via pedal position sensor 134. Combustion chamber (e.g., 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. Further, a starter motor may be coupled to crankshaft 40 via a flywheel to enable a starting operation of engine 10 .

[0024] Combustion chamber 30 may receive intake air from intake manifold 44 via intake passage 42 and may exhaust combustion gases via exhaust passage 48. 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.

[0025] 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 utilize one or more cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems operable by controller 12 to vary valve operation. The position of intake valve 52 and exhaust valve 54 may be determined by position sensors 55 and 56, respectively. In an alternative embodiment, 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 a CPS system and / or a VCT system.

[0026] 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 a signal received from controller 12 via electronic driver 68. Fuel may be delivered to fuel injector 66 by a fuel injection 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 directly coupled to combustion chamber 30 for injecting fuel directly therein in a manner known as direct injection. It will be appreciated that while a single fuel injector is depicted in the figure, the system may include multiple fuel injectors. For example, in some cases, a fuel injector may be associated with each cylinder of the engine.

[0027] Ignition system 88 can provide an ignition spark to combustion chamber 30 via spark plug 92 in response to spark advance signals 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.

[0028] Exhaust gas sensor 126 is shown coupled to exhaust passage 48 of exhaust system 50 upstream of emission control device 70. Sensor 126 may be any suitable sensor for providing an indication of exhaust air-fuel ratio, such as a linear oxygen sensor or a universal or wide-range exhaust gas oxygen (UEGO) sensor, a two-state oxygen sensor or an EGO, HEGO (heated EGO), NOx, HC, or CO sensor. In some embodiments, exhaust gas sensor 126 may be the first of a plurality of exhaust gas sensors positioned in the exhaust system. For example, an additional exhaust gas sensor may be positioned downstream of emission control device 70. In other examples, the sensor may be positioned in a corresponding exhaust manifold. Sensor 126 may have a 1:4 configuration, wherein sensor 126 corresponds to four cylinders or chambers, such as in a standard UEGO sensor configuration (e.g., on a V8 engine); or a 1:2 sensor-to-cylinder ratio configuration, wherein sensor 126 corresponds to two cylinders or chambers, such as in a four-UEGO sensor configuration. As described below, the methods provided herein may be performed in a 1:2 sensor-to-cylinder configuration environment.

[0029] 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. Controller 12 may be configured to control the engine 10 to operate at a predetermined air-fuel ratio. Figure 110 is shown as a microcomputer, which includes: a microprocessor unit 102; input / output ports 104; an electronic storage medium for executable programs and calibration values (shown as read-only memory 106 in this particular example); random access memory 108; keep alive memory 110; and a data bus. In addition to those signals previously discussed, controller 12 may also receive various signals from sensors coupled to engine 10, including a measurement of intake mass air flow (MAF) from mass air flow sensor 120; engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; a surface ignition sense signal from sensor 118 (or other type of sensor) coupled to crankshaft 40; throttle position from a throttle position sensor; and an absolute manifold pressure signal from sensor 122. An engine speed signal may be generated by controller 12 based on the output of sensor 118. The manifold pressure signal from the manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold. It should be noted that various combinations of the above sensors may be used, such as using 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 charge (including air) inducted into the cylinder. In one example, sensor 118, which also serves as an engine speed sensor, may produce a predetermined number of equally spaced pulses every revolution of the crankshaft.

[0030] Furthermore, at least some of the above-described signals can be used in the exhaust gas sensor degradation determination method described in further detail below. For example, the inverse of engine speed can be used to determine the delay associated with the injection-intake-compression-expansion-exhaust cycle. As another example, the inverse of speed (or the inverse of the MAF signal) can be used to determine the delay associated with exhaust gas traveling from exhaust valve 54 to exhaust gas sensor 126. The above examples, as well as 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.

[0031] In some embodiments, exhaust gas sensor degradation determinations may be performed in a dedicated controller 140. Dedicated controller 140 may include processing resources 142 to handle the signal processing associated with generating, calibrating, and validating degradation determinations for exhaust gas sensor 126. Specifically, a sample buffer for recording the response rate of the exhaust gas sensor (e.g., generating 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, dedicated controller 140 may be operably coupled to controller 12 to perform exhaust gas sensor degradation determinations. Note that dedicated controller 140 may receive engine parameter signals from controller 12 to perform exhaust gas sensor degradation determinations. Note that dedicated controller 140 may receive engine parameter signals from controller 12 and may send engine control signals and degradation determination information, as well as other communications, to controller 12. Controller 12 and / or dedicated controller 140 may send and receive messages to a human / machine interface 143 (e.g., a touchscreen display, lights, display panel, etc.).

[0032] Note that storage medium read-only memory 106 and / or processing resource 142 may be programmed with computer readable data representing instructions executable by processor 102 and / or dedicated controller 140 for performing the methods described below as well as other variants.

[0033] As described herein, a fuel cutoff can be an operation in the vehicle's engine 10 in which the supply of fuel to the combustion chamber 30 is suspended, which can then be subsequently unsuspended. For example, entry into a fuel cutoff can be initiated when the throttle is substantially closed and the engine speed is above a threshold. Similarly, exiting a fuel cutoff can be initiated when the controller 12 receives a request to increase the speed (e.g., the throttle is open) and / or the engine speed drops below a threshold. In this way, fuel economy in the vehicle can be improved. Additionally or alternatively, a fuel cutoff can be triggered based on engine temperature. It should be understood that other fuel cutoff triggers and techniques are contemplated.

[0034] As discussed above, exhaust sensor degradation may be determined based on any or (in some examples) each of six discrete behaviors indicated by a delay in the response rate of air-fuel ratio readings generated by the exhaust sensor during rich-to-lean transitions and / or lean-to-rich transitions. Figures 2 to 7Each graph shows one of six discrete types of exhaust gas sensor degradation behavior. The graphs plot air-fuel ratio (λ) versus time (in seconds). In each graph, the dashed line indicates a λ signal that can be sent to engine components (e.g., fuel injectors, cylinder valves, throttle, spark plugs, etc.) to generate a commanded air-fuel ratio that steps through a cycle including one or more lean-to-rich transitions and one or more rich-to-lean transitions. In each graph, the dashed line indicates the expected λ response time of the exhaust gas sensor. In each graph, the solid line indicates the degradation λ signal that would be generated by a degraded exhaust gas sensor in response to the commanded λ signal. In each graph, a double-arrowed line indicates where a given degradation behavior type differs from the expected λ signal.

[0035] Figure 2 A graph is shown indicating a first type of degradation behavior that a degraded exhaust gas sensor may exhibit. The first type of degradation behavior is a symmetric filter type, which includes a slow exhaust gas sensor response to a commanded lambda signal for both rich-to-lean and lean-to-rich modulations. In other words, a degraded lambda signal may begin transitioning from rich-to-lean and lean-to-rich at expected times, but the response rate may be slower than expected, resulting in a reduction in lean peak time and rich peak time.

[0036] Figure 3 A graph is shown indicating a second type of degradation behavior that a degraded exhaust gas sensor may exhibit. This second type of degradation behavior is an asymmetric rich-to-lean filter type, which includes a slow exhaust gas sensor response to a commanded lambda signal for a transition from a rich to lean air-fuel ratio. This type of behavior may initiate the rich-to-lean transition at the expected time, but the response rate may be slower than expected, which may result in a reduced lean peak time. This type of behavior is considered asymmetric because the exhaust gas sensor response is slow (or slower than expected) only during the rich-to-lean transition.

[0037] Figure 4 A graph is shown indicating a third type of degradation behavior that a degraded exhaust gas sensor may exhibit. This third type of degradation behavior is an asymmetric lean-to-rich filter type, which includes a slow exhaust gas sensor response to a commanded lambda signal for a transition from a lean to rich air-fuel ratio. This type of behavior may initiate the lean-to-rich transition at the expected time, but the response rate may be slower than expected, which may result in a reduced rich peak time. This type of behavior is considered asymmetric because the exhaust gas sensor response is slow (or slower than expected) only during the lean-to-rich transition.

[0038] Figure 5A graph is shown indicating a fourth type of degradation behavior that a degraded exhaust gas sensor may exhibit. This fourth type of degradation behavior is a symmetrical delay type, which includes a delayed response to the commanded lambda signal for both rich-to-lean and lean-to-rich modulations. In other words, the degraded lambda signal may begin transitioning from rich-to-lean and lean-to-rich at times that are delayed from the expected times, but the respective transitions may occur at the expected response rate, resulting in offsets in the lean and rich peak times.

[0039] Figure 6 A graph is shown indicating a fifth type of degradation behavior that a degraded exhaust gas sensor may exhibit. This fifth type of degradation behavior is an asymmetric rich-to-lean delay type, which includes a delayed response of the lambda signal to a rich-to-lean air-fuel ratio command. 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 an expected response rate, resulting in a shift and / or reduction in the lean peak time. This type of behavior is considered asymmetric because the exhaust gas sensor's response is delayed from the expected start time only during the rich-to-lean transition.

[0040] Figure 7 A graph is shown indicating a sixth type of degradation behavior that a degraded exhaust gas sensor may exhibit. This sixth type of degradation behavior is an asymmetric lean-to-rich delay type, which includes a delayed response of the lambda signal to a lean-to-rich air-fuel ratio command. 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 an expected response rate, resulting in a shift and / or reduction in the rich peak time. This type of behavior is considered asymmetric because the exhaust gas sensor's response is delayed from the expected start time only during the lean-to-rich transition.

[0041] It should be understood that a degraded EGT sensor may exhibit one or more degradation behaviors or a combination of two or more of the above degradation behaviors. For example, a degraded exhaust gas sensor may exhibit asymmetric rich to lean filter degradation behavior (e.g., Figure 3 ) and asymmetric rich-to-lean delay degradation behavior (e.g., Figure 6 ).

[0042] In some examples, determining whether fuel cutoff conditions are met may include determining, estimating, and / or measuring current engine operating parameters. Fuel cutoff conditions may include, but are not limited to, one or more of an accelerator pedal not being depressed, a constant or decreasing vehicle speed, and a wheel caliper pedal being depressed. An accelerator pedal position sensor may be used to determine the accelerator pedal position. When the accelerator pedal is not applied or depressed, the accelerator pedal position may occupy a base position, and as throttle application increases, the accelerator pedal may move away from the base position. Additionally or alternatively, in examples where the accelerator pedal is coupled to a throttle or where the throttle is operating in an accelerator pedal follow mode, the accelerator pedal position may be determined via a throttle position sensor. Since torque demand is constant or not increasing, a constant or decreasing vehicle speed may be preferable for a fuel cutoff to occur. Vehicle speed may be determined by a vehicle speed sensor. Depressing the brake caliper pedal may be determined via a brake caliper pedal sensor. In some examples, other suitable conditions for initiating a fuel cutoff may exist.

[0043] Now turn Figure 8 , a plurality of graphs 800 depicting typical injector ramping into a fuel cut event are shown. It will be appreciated that each graph may be drawn using a set of exhaust gas sensor response samples collected during a fuel cut transition (eg, into). Figure 8 The exhaust gas sensor response shown in can be from Figure 1 Response of exhaust gas sensor 126 or another suitable exhaust gas sensor of engine 10 is shown. In some examples, multiple graphs 800 may be aligned in time. Multiple graphs 800 include a first graph 802 plotting lambda versus time (in seconds), a second graph 808 plotting mass flow rate (e.g., pounds per minute) versus time for a first cylinder group, a third graph 818 plotting mass flow rate versus time for a second cylinder group, and a fourth graph 828 plotting a cylinder group timer for estimating exhaust gas sensor delay versus time. When the engine is an eight-cylinder (e.g., V-8) engine, the first cylinder group may include the first, second, third, and fourth cylinders, while the second cylinder group may include the fifth, sixth, seventh, and eighth cylinders.

[0044] First graph 802 includes a first curve 804 and a second curve 806. First curve 804 may correspond to the first cylinder group, and second curve 806 may correspond to the second cylinder group. The first cylinder group may lead the second cylinder group in the rich-to-lean reaction, as indicated by the lambda of first curve 804 rising earlier than the lambda of second curve 806. This is a result of the injectors of the first cylinder group ramping off earlier than the injectors of the second cylinder group, as illustrated in second graph 808 and third graph 818. Second graph 808 includes a first curve 810, a second curve 812, a third curve 814, and a fourth curve 816. First curve 810 may correspond to the first cylinder, second curve 812 may correspond to the second cylinder, third curve 814 may correspond to the third cylinder, and fourth curve 816 may correspond to the fourth cylinder. Similarly, third graph 818 includes a first curve 820, a second curve 822, a third curve 824, and a fourth curve 826. The first curve 820 may correspond to the fifth cylinder, the second curve 822 may correspond to the sixth cylinder, the third curve 824 may correspond to the seventh cylinder, and the fourth curve 826 may correspond to the eighth cylinder.

[0045] In second and third graphs 808 and 818, the first curves (e.g., first curve 810 and first curve 820) may have a decrease in mass flow rate to the corresponding cylinder, corresponding to the gradual closing of the corresponding injector. The second through fourth curves may then sequentially have decreases in mass flow rate corresponding to the gradual closing of the corresponding injector. In each of second and third graphs 808 and 818, there may be a delay of approximately 800 milliseconds between the first curve showing the decrease in mass flow rate and the fourth curve showing the decrease in mass flow rate. Although illustrated and described herein as the first cylinder injector being gradually closed first, followed by the second cylinder injector, and then the third and fourth cylinder injectors of the first cylinder bank, it should be understood that the order of the decreases may vary between different fuel cutoff events, and the delay between successive curve decreases may vary between different fuel cutoff events. In some examples, the delay between the first curve decrease and the fourth curve decrease may be approximately equal to the delay detected by the exhaust gas sensor when all injectors are closed.

[0046] Fourth graph 828 includes a first graph 830 and a second graph 832. First graph 830 may correspond to a timer for the first cylinder group, and second graph 832 may correspond to a timer for the second cylinder group. The timer may be used to estimate exhaust gas sensor delay. The timer may be started after the first cylinder fuel mass flow rate decreases, as described with respect to third graph 818, and may be stopped when exhaust gas sensor lambda exceeds a predetermined threshold.

[0047] Figure 9An exemplary version of engine 10 is shown including a plurality of cylinders arranged in a V-configuration. In this example, engine 10 is configured as a variable displacement engine (VDE), wherein engine 10 can operate in a V-8 mode (e.g., an eight-cylinder mode in which all eight cylinders are activated) and a V-4 mode (e.g., a four-cylinder mode in which four of the eight cylinders are deactivated). Figure 9 The example shown in depicts V-8 mode.

[0048] Engine 10 includes a plurality of combustion chambers or cylinders 30, as previously described. The plurality of cylinders 30 of engine 10 are arranged as a plurality of groups of cylinders on different engine cylinder banks. In the depicted example, engine 10 includes two cylinder banks, a first cylinder bank 902 and a second cylinder bank 904. Thus, the cylinders are arranged as a first group of cylinders (four cylinders in the depicted example) arranged on first cylinder bank 902 and a second group of cylinders (four cylinders in the depicted example) arranged on second cylinder bank 904. The first group of cylinders may include a first cylinder 906, a second cylinder 908, a third cylinder 910, and a fourth cylinder 912, and the second group of cylinders may include a fifth cylinder 914, a sixth cylinder 916, a seventh cylinder 918, and an eighth cylinder 920. It should be understood that although Figure 9 The examples depicted in show a V-type engine with cylinders arranged on different banks, but this is not meant to be limiting, and in alternative embodiments the engine may be an in-line engine with all engine cylinders on a common engine bank.

[0049] Engine 10 may receive intake air via intake passage 42 which communicates with branched intake manifold 44. Figure 9 As depicted in FIG, branched intake manifold 44 may include multiple branches leading to each of first cylinder bank 902 and second cylinder bank 904. Although first cylinder bank 902 and second cylinder bank 904 are shown with a common intake manifold, it should be understood that in alternative examples, the engine may include two separate intake manifolds. The amount of air supplied to the cylinders of the engine can be controlled by adjusting the position of throttle valve 62 at throttle plate 64. Additionally, the amount of air supplied to each cylinder on a particular cylinder bank can be adjusted by varying the intake valve timing of one or more intake valves coupled to the cylinders.

[0050] As previously stated, engine 10 may include one or more exhaust gas sensors. Figure 9The example depicted in FIG includes four exhaust gas sensors, each having a 1:2 configuration, such as those used in a four-UEGO sensor configuration. For example, a first exhaust gas sensor 922 can sense the air-fuel ratio in a first exhaust manifold 930 communicating with first cylinder 906 and second cylinder 908 of first cylinder bank 902, and a second exhaust gas sensor 924 can sense the air-fuel ratio in a second exhaust manifold 932 communicating with third cylinder 910 and fourth cylinder 912 of first cylinder bank 902. A third exhaust gas sensor 926 can sense the air-fuel ratio in a third exhaust manifold 934 communicating with fifth cylinder 914 and seventh cylinder 918 of second cylinder bank 904, and a fourth exhaust gas sensor 928 can sense the air-fuel ratio in a fourth exhaust manifold 936 communicating with sixth cylinder 916 and eighth cylinder 920 of second cylinder bank 904.

[0051] On an eight-cylinder engine with a crossplane crankshaft, the firings of the four cylinders in the same bank are unevenly spaced at firing intervals of 90, 180, and 270 crank angle degrees. A 1:4 sensor-to-cylinder configuration can cause the exhaust streams from the cylinders to have different residence times at the exhaust gas sensor. For example, a cylinder that is preceded or followed by another cylinder firing at 90 crank angle degrees can have a short residence time and a particularly weak exhaust gas sensor reading. A 1:2 sensor-to-cylinder configuration (in which firings spaced at 90 crank angle degrees do not share the same UEGO sensor) can reduce the variation in residence time and reduce the chance of a weak UEGO sensor reading.

[0052] Figure 10 Shows about Figure 9 The engine 10 is described in V-4 mode (e.g., VDE mode) because similar part numbers are used and the parts will not be reintroduced. In V-4 mode, the engine 10 includes the same cylinders as in V-8 mode, where half of the cylinders (e.g., a first subset) have deactivated intake and exhaust valves and the other half (e.g., a second subset) have activated intake and exhaust valves. As an example, Figure 10As depicted, one of the two cylinders corresponding to a single exhaust gas sensor may have its intake and exhaust valves deactivated, while the other cylinder has its intake and exhaust valves activated, such that the exhaust gas sensor senses the air-fuel ratio of only one of the two cylinders. For example, in first cylinder bank 902, first cylinder 906 and fourth cylinder 912 have active intake and exhaust valves, while second cylinder 908 and third cylinder 910 have deactivated intake and exhaust valves. In this manner, exhaust gas from first cylinder 906 may be sensed by first exhaust gas sensor 922 while second cylinder 908 is deactivated, and exhaust gas from fourth cylinder 912 may be sensed by second exhaust gas sensor 924 while third cylinder 910 is deactivated. In second cylinder bank 904, sixth cylinder 916 and seventh cylinder 918 have active intake and exhaust valves, while fifth cylinder 914 and eighth cylinder 920 have inactive intake and exhaust valves. In this way, exhaust from seventh cylinder 918 may be sensed by third exhaust gas sensor 926 while fifth cylinder 914 is deactivated, and exhaust from sixth cylinder 916 may be sensed by fourth exhaust gas sensor 928 while eighth cylinder 920 is deactivated.

[0053] Entering VDE mode prior to fuel cut entry or exit may include disabling the intake and exhaust valves of one of a first subset of cylinders and a second subset of cylinders, and then, upon entering VDE, gradually closing or opening the injectors of the other of the first subset and the second subset to enter or exit the fuel cut. For example, entering VDE mode prior to fuel cut entry may include disabling the intake and exhaust valves of the deactivated first subset of cylinders to enter VDE mode from normal operation. The intake and exhaust valves of the second subset may remain enabled. Fueling to the second subset of cylinders may then be sequentially disabled to enter the fuel cut. Similarly, entering VDE mode prior to fuel cut exit may further include enabling the intake and exhaust valves of the second subset of cylinders. Fueling to the second subset of cylinders may then be enabled to exit the fuel cut. Without disabling the intake and exhaust valves of a given subset of cylinders, the sensor-to-cylinder ratio may be 1:2. Disabling the intake and exhaust valves of the corresponding subset of cylinders allows for a 1:1 sensor-to-cylinder ratio when in VDE mode.

[0054] While sensor degradation diagnostics during fuel cuts provide an indirect method of degradation monitoring, injectors can randomly ramp off or on as the engine enters or exits a fuel cut. This random ramping off or on can result in variability in the timestamps of when the monitoring is entered. In some cases, the spread of the ramp can be equal to or nearly equal to the delay that the diagnostic is intended to detect. This delay can be approximately 800ms, as discussed above with respect to Figure 8As described above, fuel cut entry or exit with high variability in injector ramp times may not be available for six-mode diagnostics, thereby increasing monitoring completion time and reducing monitoring efficiency. This variability in injector ramping during fuel cut entry / exit may be more pronounced in a 1:4 exhaust gas sensor configuration. The system disclosed herein may be configured with a 1:2 exhaust gas sensor to cylinder ratio as previously described, which can help reduce some injector ramp variability since each exhaust gas sensor is only responsible for two cylinders.

[0055] Additionally, when the engine is VDE, entering V-4 mode before fuel cut entry / exit can also reduce injector ramp variability because in V-4 mode, each exhaust gas sensor is responsible for sensing the air to fuel ratio in only one cylinder.

[0056] Figure 11 and Figure 12 A flow chart illustrating a method for performing exhaust gas sensor diagnostics is shown. The method as described herein includes entering a four-cylinder mode (eg, VDE mode) prior to a fuel cut transition, which may be a fuel cut entry or a fuel cut exit. Figure 11 Specifically shown is a flow chart illustrating a method 1100 for performing exhaust gas sensor diagnostics during fuel cut entry, and Figure 12 Specifically, a flow chart illustrating a method 1200 for performing exhaust gas sensor diagnostics during a fuel cut exit is shown. Both methods 1100 and 1200 may be implemented as described above with respect to Figure 1 The vehicle, engine, system, component, etc. described herein may be implemented or may be implemented by another suitable vehicle, engine, system, and component. Specifically, one or more of the steps disclosed in method 1100 and / or 1200 may be implemented via Figure 1 The controller 12 and / or the controller 140 are shown as implementations.

[0057] Starting with method 1100, at 1102, method 1100 includes determining, estimating, and / or measuring current engine operating parameters. Current engine operating parameters may include, but are not limited to, vehicle speed, throttle position, and / or air-fuel ratio. Determining operating conditions may also include determining one or more fuel cutoff conditions. Fuel cutoff entry conditions may include, but are not limited to, one or more of an accelerator pedal not depressed, a constant or decreasing vehicle speed, and a wheel caliper pedal depressed. An accelerator pedal position sensor may be used to determine the accelerator pedal position. When the accelerator pedal is not applied or depressed, the accelerator pedal position may occupy a base position, and as throttle application increases, the accelerator pedal may move away from the base position. Additionally or alternatively, in examples where the accelerator pedal is coupled to the throttle or where the throttle is operating in accelerator pedal follow mode, the accelerator pedal position may be determined via a throttle position sensor. Since torque demand is constant or not increasing, a constant or decreasing vehicle speed may be preferable for a fuel cutoff to occur. Vehicle speed may be determined by a vehicle speed sensor. It may be determined via a brake caliper pedal sensor that the brake caliper pedal is depressed.In some examples, other suitable conditions for entering a fuel cut may exist.

[0058] At 1104, method 1100 includes determining whether one or more fuel cut entry conditions are met. As outlined above, one or more fuel cut entry conditions may be met such that the vehicle and engine enter a fuel cut. If one or more fuel cut entry conditions are met (yes at 1104), method 1100 proceeds to 1106. If the fuel cut entry conditions are not met (no at 1104), method 1100 returns to 1102.

[0059] At 1106, method 1100 includes determining whether four-cylinder (e.g., V-4) mode is available. In the event of a VDE system error, for example, if there is an error in the actuators for deactivating the intake and / or exhaust valves, four-cylinder mode may not be available. Four-cylinder mode may also not be available if one or more entry conditions for four-cylinder mode are not met, such as oil pressure below a threshold in the case of a hydraulic valve deactivation actuator. Four-cylinder mode may be available when the VDE system is operating normally and entry conditions are met. Furthermore, in some examples, although four-cylinder mode may be available based on the VDE system and entry conditions, factors such as fuel consumption or noise, vibration, and harshness may make four-cylinder mode less desirable than maintaining eight-cylinder mode in certain circumstances, and therefore four-cylinder mode may not be available. If four-cylinder mode is available (yes at 1106), method 1100 proceeds to 1108. If four-cylinder mode is not available (no at 1106), method 1100 ends. In the event that four-cylinder mode is not available, method 1100 may be repeated at a later time to again determine whether V4 mode is available in order to proceed to perform a six-mode diagnostic.

[0060] At 1108, method 1100 includes entering a four-cylinder mode (e.g., VDE mode). Entering the four-cylinder mode includes gradually closing the injectors for a first subset of the engine's eight cylinders and disabling the intake and exhaust valves of the first subset of cylinders. Thus, in VDE mode, deactivated cylinders may have disabled intake and exhaust valves, while activated cylinders may have enabled intake and exhaust valves. For example, in the above description of Figure 9 and Figure 10 An engine is described in which the injectors corresponding to the second, third, fifth, and eighth cylinders may be ramped closed, thereby deactivating each of those cylinders.

[0061] At 1110, method 1100 includes ramping down the injectors of the active cylinders in four-cylinder mode to enter fuel cutoff. The active cylinders may be those cylinders having active intake and exhaust valves and active injectors. Figure 9 and Figure 10 In the depicted example, the active cylinders may be the first, fourth, sixth, and seventh cylinders. Gradually deactivating the active cylinders may include sequentially disabling injectors for the active cylinders to deactivate those cylinders. Gradually deactivating the active cylinders may cause the engine to enter a fuel cutoff. The cylinders deactivated at 1110 may continue to have active intake and exhaust valves.

[0062] At 1112, method 1100 determines whether the injector for the first exhaust gas sensor has been ramped closed. The first exhaust gas sensor may be a selected sensor to be diagnosed for potential degradation. The injector may correspond to one of the injectors ramped closed at 1110. If the injector for the first exhaust gas sensor has not been ramped closed (NO at 1112), method 1100 returns to 1110 to continue ramping the injector closed. If the injector for the first exhaust gas sensor has been ramped closed (YES at 1112), method 1100 proceeds to 1114.

[0063] At 1114, method 1100 includes initiating a rich-to-lean six-mode diagnostic for the first exhaust gas sensor. Once the corresponding injector is disabled, the six-mode diagnostic for the rich-to-lean transition may be initiated. In some examples, this may include incrementing a separate timer to measure the duration from when the injector is disabled until lambda exceeds a predetermined threshold. If the duration is greater than a threshold duration (e.g., the duration is longer than expected), the exhaust gas sensor has rich-to-lean delay or filter-type degradation.

[0064] Method 1100 may include repeatedly determining whether the injector corresponding to the exhaust gas sensor is gradually closing for each of the four active cylinders in the four-cylinder mode (as at 1112). For example, method 1100 may determine whether the injector corresponding to the second exhaust gas sensor has been gradually closed. In addition, method 1100 may include independently performing a six-mode diagnostic for each exhaust gas sensor (as at 1114). For example, when the injector of the first active cylinder is disabled, a first timer may be started to measure a first duration until the lambda measured by the first exhaust gas sensor exceeds a threshold. Then, when the injector of the second active cylinder is disabled, a second timer may be started to measure a second duration until the lambda measured by the second exhaust gas sensor exceeds a second threshold. Thus, the steps described at 1112 and 1114 may be repeated for each of the four exhaust gas sensors to determine its degradation mode.

[0065] At 1116, method 1100 includes determining whether all injectors have been ramped closed. If not all injectors have been ramped closed, method 1100 returns to 1110 to continue ramping closed injectors for active cylinders. If all injectors have been ramped closed, all cylinders of the engine may be deactivated, the system may be placed in a fuel cutoff state, and method 1100 may end.

[0066] The six-mode diagnostic may generate results for determining whether exhaust gas sensor degradation has occurred or is functioning as expected. If exhaust gas sensor degradation has occurred, adjusting engine operation based on the exhaust gas sensor may be temporarily disabled.

[0067] Except exiting fuel cutoff instead of entering it, Figure 12 Method 1200 follows a flow path of steps similar to method 1100. Thus, at 1202, method 1200 includes determining vehicle operating conditions, including but not limited to vehicle speed, throttle position and / or air-fuel ratio, and one or more fuel cutoff conditions, such as accelerator pedal position, wheel brake caliper pedal position, etc., as previously discussed.

[0068] At 1204, method 1200 includes determining whether fuel cutoff exit conditions are met. Fuel cutoff exit conditions may include, but are not limited to, one or more of an accelerator pedal being depressed, increasing vehicle speed, and a wheel caliper pedal being in a base position. If one or more fuel cutoff exit conditions are met (yes at 1204), method 1200 proceeds to 1206. If the fuel cutoff exit conditions are not met (no at 1204), method 1200 returns to 1202.

[0069] At 1206, method 1200 includes determining whether four-cylinder mode is available. If four-cylinder mode is available, method 1200 proceeds to 1208. If four-cylinder mode is not available due to one or more of the reasons discussed above, method 1200 ends.

[0070] At 1208, method 1200 includes entering a four-cylinder mode (e.g., VDE mode). Entering four-cylinder mode from a fuel cut includes activating the intake and exhaust valves of a first subset of cylinders and disabling the intake and exhaust valves of a second subset of cylinders. As described above, at the time of the fuel cut, all injectors have been ramped closed such that all cylinders are deactivated. In some examples, the intake and exhaust valves may all be disabled when in a fuel cut, in which case entering VDE mode may involve activating the intake and exhaust valves of a first subset of cylinders. In other examples, the intake and exhaust valves may all be enabled when in a fuel cut, in which case entering VDE mode may involve disabling the intake and exhaust valves of a second subset of cylinders. In either case, in VDE mode, fueling of the cylinders may remain deactivated. As an example, corresponding to Figure 9 and Figure 10 The intake and exhaust valves of the first, fourth, sixth, and seventh cylinders of the described engine may be enabled, and the intake and exhaust valves of the second, third, fifth, and eighth cylinders may be disabled.

[0071] At 1210, method 1200 includes ramping open injectors for a first subset of cylinders (eg, cylinders with activated intake and exhaust valves). Figure 9 and Figure 10 In the example presented, the first, fourth, sixth, and seventh cylinders can be sequentially activated by ramping open their corresponding injectors. Ramping open the injectors of cylinders with active intake and exhaust valves while another subset of cylinders has their intake and exhaust valves disabled can maintain a 1:1 sensor-to-cylinder ratio.

[0072] At 1212, method 1200 determines whether the injector for the first exhaust gas sensor has been ramped open. The first exhaust gas sensor may be the selected sensor to be diagnosed for potential degradation. If the injector for the first exhaust gas sensor has not been ramped open (NO at 1212), method 1200 returns to 1210 to continue ramping the injector open. If the injector for the first exhaust gas sensor has been ramped open (YES at 1212), method 1200 proceeds to 1214.

[0073] At 1214, method 1200 includes initiating a lean-to-rich six-mode diagnostic for the first exhaust gas sensor. Once the corresponding injector is ramped on, the six-mode diagnostic for the lean-to-rich transition may be initiated. In some examples, this may include incrementing a separate timer to measure the duration from when the injector is activated until lambda drops below a predetermined threshold. If the duration is greater than the threshold duration, the exhaust gas sensor has a lean-to-rich delay. Similar to method 1100, method 1200 includes sequentially repeating the above-described determination and execution of the six-mode diagnostic for each of the exhaust gas sensors as the remaining deactivated cylinders are activated by ramping on the corresponding injectors. For example, when the injector for the first active cylinder is activated, a first timer may be initiated to measure a first duration until lambda measured by the first exhaust gas sensor drops below a threshold. Then, when the injector for the second active cylinder is activated, a second timer may be initiated to measure a second duration until lambda measured by the second exhaust gas sensor drops below a second threshold. Thus, the steps described at 1212 and 1214 may be repeated for each of the four exhaust gas sensors to determine their degradation mode.

[0074] At 1216, method 1200 includes determining whether all injectors for four-cylinder mode have been ramped open. If not all injectors have been ramped open, method 1200 returns to 1210 to continue ramping open the injectors to exit fuel cut. If all injectors have been ramped open, the engine may have exited fuel cut, and method 1200 may end.

[0075] The six-mode diagnostic may generate results for determining whether exhaust gas sensor degradation has occurred or is functioning as expected. If exhaust gas sensor degradation has occurred, adjusting engine operation based on the exhaust gas sensor may be temporarily disabled.

[0076] Entering four-cylinder mode when the engine includes exhaust gas sensors with a 1:2 configuration allows each exhaust gas sensor to detect only one active cylinder. Having a 1:1 ratio between sensor and cylinder during monitoring and diagnosis can reduce injector ramp variability and therefore improve the efficiency and usability of six-mode diagnostic entry based on fuel cutoff.

[0077] The present disclosure also provides support for a method for monitoring an exhaust gas sensor coupled to an engine exhaust port in an engine, the method comprising: entering a variable displacement engine (VDE) mode prior to a fuel cut transition for reduced traction, wherein intake and exhaust valves of a first subset of cylinders of the engine are activated and intake and exhaust valves of a second subset of cylinders are deactivated; and performing a six-mode diagnostic during the fuel cut to identify exhaust gas sensor degradation. In a first example of the method, the engine is an eight-cylinder engine, and the first subset of cylinders having activated intake and exhaust valves in VDE mode includes four cylinders. In a second example of the method (optionally including the first example), the engine includes four exhaust gas sensors, each having a sensor-to-cylinder ratio of 1:2. In a third example of the method (optionally including one or both of the first and second examples), in VDE mode, each exhaust gas sensor senses the air-fuel ratio in one of the first subset of cylinders. In a fourth example of the method (optionally including one or more or each of the first through third examples), the method further includes adjusting engine operation in response to identifying exhaust gas sensor degradation, the degradation being identified during a fuel cut. In a fifth example of the method (optionally including one or more or each of the first through fourth examples), the fuel cut transition is one of a fuel cut entry and a fuel cut exit. In a sixth example of the method (optionally including one or more or each of the first through fifth examples), when the fuel cut transition is a fuel cut entry, entering VDE mode includes gradually closing injectors corresponding to the second subset of cylinders, the second subset of cylinders not including any of the first subset of cylinders. In a seventh example of the method (optionally including one or more or each of the first through sixth examples), when the fuel cut transition is a fuel cut exit, the tractive effort-reducing fuel cut transition includes gradually opening injectors corresponding to the first subset of cylinders.

[0078] The present disclosure also provides support for a system for a vehicle, the system comprising: an engine including a fuel injection system and eight cylinders; a plurality of exhaust gas sensors coupled to an exhaust system of the engine; and a controller including instructions stored in a memory, the instructions operable by a processor to: enter a four-cylinder mode prior to a fuel cut transition with reduced traction; and perform a fuel cut-based six-mode diagnostic on one or more of the plurality of exhaust gas sensors to identify one or more degradation behaviors thereof. In a first example of the system, when the fuel cut transition is a fuel cut entry, entering the four-cylinder mode comprises: gradually closing injectors of the fuel injection system corresponding to a first subset of the eight cylinders and disabling intake and exhaust valves of the first subset of the eight cylinders. In the first example (optionally including the first example) of the system, when the fuel cut transition is a fuel cut exit, entering the four-cylinder mode comprises: enabling intake and exhaust valves of the fuel injection system corresponding to a second subset of the eight cylinders and disabling intake and exhaust valves of the first subset of the eight cylinders. In a third example of the system (optionally including one or both of the first and second examples), each of the plurality of exhaust gas sensors is configured to sense the air-fuel ratio in two corresponding cylinders. In a fourth example of the system (optionally including one or more or each of the first to third examples), the engine includes a first cylinder group and a second cylinder group, the first cylinder group including a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder, and the second cylinder group including a fifth cylinder, a sixth cylinder, a seventh cylinder, and an eighth cylinder, wherein a first exhaust gas sensor is positioned in a first exhaust manifold communicating with the first cylinder and the second cylinder, a second exhaust gas sensor is positioned in a second exhaust manifold communicating with the third cylinder and the fourth cylinder, a third exhaust gas sensor is positioned in a third exhaust manifold communicating with the fifth cylinder and the seventh cylinder, and a fourth exhaust gas sensor is positioned in a fourth exhaust manifold communicating with the sixth cylinder and the eighth cylinder. In a fifth example of the system (optionally including one or more or each of the first to fourth examples), in four-cylinder mode, the first cylinder, the fourth cylinder, the sixth cylinder and the seventh cylinder are activated, and the second cylinder, the third cylinder, the fifth cylinder and the eighth cylinder are deactivated.

[0079] The present disclosure also provides support for a method for monitoring an exhaust gas sensor coupled to an engine exhaust port of an engine, the method comprising: prior to a traction-reducing fuel cutoff transition, placing the engine into a four-cylinder mode; entering the traction-reducing fuel cutoff transition in response to determining that an injector corresponding to a first exhaust gas sensor has been ramped closed upon entry or ramped open upon exit; incrementing a separate timer for the exhaust gas sensor to initiate a sensor delay timer of a six-mode diagnostic; and performing the six-mode diagnostic to identify one or more degradation behaviors in the first exhaust gas sensor. In a first example of the method, the method further comprises: adjusting engine operation in response to identifying degradation of the exhaust gas sensor. In a second example of the method (optionally including the first example), the engine is a variable displacement engine including eight cylinders and four exhaust gas sensors, and wherein each of the four exhaust gas sensors is configured with a 1:2 sensor-to-cylinder ratio. In a third example of the method (optionally including one or both of the first and second examples), when the fuel cut transition is the entry, entering four-cylinder mode includes gradually closing injectors corresponding to a first subset of cylinders of the engine and disabling intake and exhaust valves of the first subset of cylinders, and wherein entering the traction-reducing fuel cut transition includes sequentially gradually closing injectors corresponding to a second subset of cylinders, the second subset of cylinders not including any cylinders in the first subset. In a fourth example of the method (optionally including one or more or each of the first to third examples), when the fuel cut transition is the exit, entering four-cylinder mode includes enabling intake and exhaust valves corresponding to a first subset of cylinders of the engine and disabling intake and exhaust valves of a second subset of cylinders, and wherein entering the traction-reducing fuel cut transition includes sequentially gradually opening injectors corresponding to the first subset of cylinders, the second subset of cylinders not including any cylinders in the first subset. In a fifth example of the method (optionally including one or more or each of the first to fourth examples), the exhaust gas sensor is a Universal Exhaust Gas Oxygen (UEGO) sensor, and the engine has a four UEGO sensor configuration.

[0080] It should be noted that the exemplary 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-threading, etc.). Therefore, the various actions, operations, and / or functions shown can be performed in the sequence shown, in parallel, or omitted in some cases. 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 actions, operations, and / or functions shown 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 implemented by executing instructions in a system including various engine hardware components in combination with an electronic controller.

[0081] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments should not be considered limiting, as many variations are possible. Furthermore, unless expressly indicated to the contrary, the terms "first," "second," "third," etc. are not intended to denote any order, position, quantity, or importance, but are merely used as labels to distinguish one element from another. 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.

[0082] As used herein, unless otherwise specified, the term "about" is interpreted to mean a range of ±5%.

[0083] The appended 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. Such 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 also deemed included within the subject matter of the present disclosure.

[0084] According to the present invention, a method of monitoring an exhaust gas sensor coupled in an engine exhaust port in an engine includes: entering a variable displacement engine (VDE) mode prior to a fuel cut transition for reduced traction, wherein intake and exhaust valves of a first subset of cylinders of the engine are activated and intake and exhaust valves of a second subset of cylinders are deactivated; and performing a six-mode diagnostic during the fuel cut to identify exhaust gas sensor degradation.

[0085] In one aspect of the present invention, the engine is an eight-cylinder engine and the first subset of cylinders having activated intake and exhaust valves in VDE mode comprises four cylinders.

[0086] In one aspect of the present invention, the engine includes four exhaust gas sensors, each sensor having a sensor to cylinder ratio of 1:2.

[0087] In one aspect of the present invention, in the VDE mode, each exhaust gas sensor senses the air-fuel ratio in one of the first subset of cylinders.

[0088] In one aspect of the present invention, the method includes adjusting engine operation in response to identifying exhaust gas sensor degradation, the degradation being identified during a fuel cut.

[0089] In one aspect of the present invention, the fuel cut transition is one of a fuel cut entry and a fuel cut exit.

[0090] In one aspect of the present invention, when the fuel cut transition is a fuel cut entry, entering the VDE mode includes ramping down injectors corresponding to the second subset of cylinders that do not include any of the first subset of cylinders.

[0091] In one aspect of the present invention, the tractive effort reducing fuel cut transition comprises ramping open injectors corresponding to the first subset of cylinders when the fuel cut transition is a fuel cut exit.

[0092] According to the present invention, a system for a vehicle is provided, comprising: an engine including a fuel injection system and eight cylinders; a plurality of exhaust gas sensors coupled to an exhaust system of the engine; and a controller including instructions stored in a memory, the instructions being operable by a processor to: enter a four-cylinder mode prior to a fuel-cut transition for reduced traction; and perform a fuel-cut-based six-mode diagnostic on one or more of the plurality of exhaust gas sensors to identify one or more degradation behaviors thereof.

[0093] According to an embodiment, when the fuel cut transition is a fuel cut entry, entering the four-cylinder mode includes ramping closing injectors of the fuel injection system corresponding to a first subset of the eight cylinders and disabling intake and exhaust valves of the first subset of the eight cylinders.

[0094] According to an embodiment, when the fuel cut transition is a fuel cut exit, entering the four-cylinder mode includes enabling intake and exhaust valves of the fuel injection system corresponding to a second subset of the eight cylinders and disabling intake and exhaust valves of a first subset of the eight cylinders.

[0095] According to an embodiment, each of the plurality of exhaust gas sensors is configured to sense the air-fuel ratio in two corresponding cylinders.

[0096] According to an embodiment, the engine includes a first cylinder group and a second cylinder group, the first cylinder group includes a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder, and the second cylinder group includes a fifth cylinder, a sixth cylinder, a seventh cylinder, and an eighth cylinder, wherein a first exhaust gas sensor is positioned in a first exhaust manifold communicating with the first cylinder and the second cylinder, a second exhaust gas sensor is positioned in a second exhaust manifold communicating with the third cylinder and the fourth cylinder, a third exhaust gas sensor is positioned in a third exhaust manifold communicating with the fifth cylinder and the seventh cylinder, and a fourth exhaust gas sensor is positioned in a fourth exhaust manifold communicating with the sixth cylinder and the eighth cylinder.

[0097] According to an embodiment, in the four-cylinder mode, the first cylinder, the fourth cylinder, the sixth cylinder, and the seventh cylinder are activated, and the second cylinder, the third cylinder, the fifth cylinder, and the eighth cylinder are deactivated.

[0098] A method for monitoring an exhaust gas sensor coupled to an engine exhaust port of an engine includes: prior to a traction-reducing fuel cutoff transition, placing the engine into a four-cylinder mode; entering the traction-reducing fuel cutoff transition in response to determining that an injector corresponding to a first exhaust gas sensor has been ramped closed when the fuel cutoff transition is entered or that the injector has been ramped open when the fuel cutoff transition is exited; incrementing a separate timer for the exhaust gas sensor to initiate a sensor delay timer of a six-mode diagnostic; and performing the six-mode diagnostic to identify one or more degradation behaviors in the first exhaust gas sensor.

[0099] In one aspect of the present invention, the method includes adjusting engine operation in response to identifying degradation of the exhaust gas sensor.

[0100] In one aspect of the present invention, the engine is a variable displacement engine including eight cylinders and four exhaust gas sensors, and wherein each of the four exhaust gas sensors is configured with a sensor to cylinder ratio of 1:2.

[0101] In one aspect of the present invention, when the fuel cut transition is the entry, entering the four-cylinder mode includes gradually closing injectors corresponding to a first subset of cylinders of the engine and disabling intake and exhaust valves of the first subset of cylinders, and wherein entering the traction-reducing fuel cut transition includes sequentially gradually closing injectors corresponding to a second subset of cylinders, the second subset of cylinders not including any cylinders in the first subset.

[0102] In one aspect of the present invention, when the fuel cut transition is the exit, entering the four-cylinder mode includes enabling intake and exhaust valves corresponding to a first subset of cylinders of the engine and disabling intake and exhaust valves of a second subset of cylinders, and wherein entering the traction-reduced fuel cut transition includes sequentially ramping open injectors corresponding to the first subset of cylinders, the second subset of cylinders not including any of the first subset.

[0103] In one aspect of the present invention, the exhaust gas sensor is a Universal Exhaust Gas Oxygen (UEGO) sensor and the engine has a four UEGO sensor configuration.

Claims

1. A method for monitoring an exhaust gas sensor coupled to an engine exhaust port in an engine, comprising: entering a variable displacement engine (VDE) mode prior to a traction-reducing fuel cutoff transition, wherein intake and exhaust valves of a first subset of cylinders of the engine are activated and intake and exhaust valves of a second subset of cylinders are deactivated; as well as A six-mode diagnostic is performed during a fuel cut to identify exhaust gas sensor degradation. 2 . The method of claim 1 , wherein the engine is an eight-cylinder engine and the first subset of cylinders having activated intake and exhaust valves in VDE mode includes four cylinders. 3 . The method of claim 1 , wherein the engine includes four exhaust gas sensors, each sensor having a sensor to cylinder ratio of 1:

2. 4 . The method of claim 3 , wherein in the VDE mode, each exhaust gas sensor senses the air-fuel ratio in one of the first subset of cylinders. 5 . The method of claim 1 , further comprising adjusting engine operation in response to identifying exhaust gas sensor degradation, the degradation being identified during a fuel cut. The method of claim 1 , wherein the fuel cut transition is one of a fuel cut entry and a fuel cut exit. 7 . The method of claim 6 , wherein when the fuel cut transition is a fuel cut entry, entering the VDE mode includes ramping down injectors corresponding to the second subset of cylinders that does not include any of the first subset of cylinders. 8 . The method of claim 6 , wherein when the fuel cut transition is a fuel cut exit, the tractive effort reducing fuel cut transition comprises ramping open injectors corresponding to the first subset of cylinders.

9. A system for a vehicle, comprising: an engine comprising a fuel injection system and eight cylinders; a plurality of exhaust gas sensors coupled to an exhaust system of the engine; as well as A controller comprising instructions stored in a memory, the instructions operable by a processor to: Entering four-cylinder mode before the traction-reducing fuel cutoff transition; and A fuel cut-based six-mode diagnostic is performed on one or more of the plurality of exhaust gas sensors to identify one or more degradation behaviors thereof.

10. The system of claim 9, wherein when the fuel cut transition is a fuel cut entry, entering the four-cylinder mode comprises: Injectors of the fuel injection system corresponding to a first subset of the eight cylinders are ramped closed and intake and exhaust valves of the first subset of the eight cylinders are disabled.

11. The system of claim 9, wherein when the fuel cut transition is a fuel cut exit, entering the four-cylinder mode comprises: Intake valves and exhaust valves of the fuel injection system corresponding to a second subset of the eight cylinders are enabled and intake valves and exhaust valves of a first subset of the eight cylinders are disabled. 12 . The system of claim 9 , wherein each of the plurality of exhaust gas sensors is configured to sense an air-fuel ratio in two corresponding cylinders.

13. The system of claim 9, wherein the engine includes a first cylinder group and a second cylinder group, the first cylinder group including a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder, and the second cylinder group including a fifth cylinder, a sixth cylinder, a seventh cylinder, and an eighth cylinder, wherein a first exhaust gas sensor is positioned in a first exhaust manifold communicating with the first cylinder and the second cylinder, a second exhaust gas sensor is positioned in a second exhaust manifold communicating with the third cylinder and the fourth cylinder, a third exhaust gas sensor is positioned in a third exhaust manifold communicating with the fifth cylinder and the seventh cylinder, and a fourth exhaust gas sensor is positioned in a fourth exhaust manifold communicating with the sixth cylinder and the eighth cylinder. 14 . The system of claim 13 , wherein in the four-cylinder mode, the first cylinder, the fourth cylinder, the sixth cylinder, and the seventh cylinder are activated, and the second cylinder, the third cylinder, the fifth cylinder, and the eighth cylinder are deactivated.

15. The system of claim 9, wherein each of the plurality of exhaust gas sensors is a Universal Exhaust Gas Oxygen (UEGO) sensor and the engine has a four UEGO sensor configuration.

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